The hypothalamo-pituitary-adrenal axis across the normal menstrual cycle and in polycystic ovary syndrome

OBJECTIVE We explored the hypothesis that activation of the hypothalamo-pituitary-adrenal axis is involved in the pathogenesis of hyperandrogenism in the polycystic ovary syndrome. PATIENTS Seven women with polycystic ovary syndrome (mean age 27.6 ± 1.6 (SEM) years) (hirsutism, oligo/ amenorrhoea and elevated serum testosterone and dehydroepiandrosterone sulphate) and nine normal female controls (mean age 24.6 ± 15 years) were studied. To exclude anovulation as a confounding factor, four of these normal women were studied in both the follicular and luteal phase of the menstrual cycle. DESIGN AND MEASUREMENTS Plasma ACTH and Cortisol levels were measured at 15-minute intervals between 0600 h and 1800 h. ACTH and Cortisol mean levels, pulse number and amplitude were calculated using established computer software, programmed to identify ACTH and Cortisol peaks. RESULTS With the exception of mean plasma levels of ACTH over the 12-hour period, which were reduced in the luteal phase of the menstrual cycle (1.8 ± 0.3 pmol/l) compared to the follicular phase (2.3 ± 0.2 pmol/l, P < 005), there were no differences in the pattern of ACTH or Cortisol secretion across the normal cycle. In polycystic ovary syndrome, 12-hour ACTH pulse frequency was reduced (3.6 ± 0 7) compared with controls (5.9 ± 0.6, P<0.05), but Cortisol pulsatility and ACTH and Cortisol mean levels were similar in both groups. CONCLUSION The hyperandrogenism of polycystic ovary syndrome cannot be explained by enhanced ACTH secretion. Normal circulating Cortisol levels, yet elevated dehydroepiandrosterone sulphate levels, suggests that polycystic ovary syndrome is yet another example of discrepant adrenal glucocorticoid and androgen secretion, and provides further evidence for a putative adrenal androgen stimulating factor.     

The plasma ACTH, AVP, CRH and catecholamine responses to conventional and laparoscopic cholecystectomy

OBJECTIVES We compared the responses of the stress hormones, Cortisol, ACTH, vasopressin (AVP), corticotrophin releasing hormone (CRH) and catecholamines to elective conventional and laparoscopic cholecystectomy. DESIGN A right upper quadrant transverse incision was used for conventional cholecystectomy, and four 1–2-cm incisions for the laparoscopic procedure (for insertion of surgical instruments, diathermy, fibreoptic telescope and light source, and carbon dioxide insufflation). Blood was sampled immediately prior to premedication (temazepam), after induction of anaesthesia (fentanyl and thiopentone) and at 10-minute intervals until the end of the procedure (N₂O maintenance, vecuronium relaxation). A blood sample was taken after reversal, and then at 10-minute intervals for 50 minutes. Plasma sodium and blood pressure were measured at similar intervals. Results are expressed as mean ± standard error. PATIENTS Twelve patients were studied (six in each group). MEASUREMENTS Peptide hormones were measured by radioimmunoassay, Cortisol by ELISA and catecholamines by HPLC. RESULTS The mean premedication hormone values for the conventional and laparoscopic procedures did not increase significantly after induction of anaesthesia. Within 10 minutes of the first incision, however, there was a marked concordant rise in mean plasma ACTH and AVP levels for both procedures (conventional: ACTH, from a premedication value of 10 2 ± 1 7 to 80 1 ± 14 3 pmol/l, AVP from 1 2 ± 0 4 to 117 ± 4 24 pmol/l, P<0 01 for both hormones; laparoscopic: ACTH from 5 8 ± 26 to 551 ± 260 pmol/l, AVP from 1 6 ± 0 11 to 49 2 ± 27 09 pmol/l). At the end of both types of operation mean levels of ACTH and AVP were still elevated, although the ACTH: AVP ratio had increased. Greater variability in ACTH and AVP responses was seen in the laparoscopic than in the conventional procedure, three patients showing a relatively small response to surgery. Total secretion of ACTH during both types of surgery was not significantly different but the total secretion of AVP was significantly less both during (P<0 05), and after (P<0 01) laparoscopic surgery. For both procedures, the timing of AVP and ACTH peaks was significantly related (P< 0 002). A small but significant rise in CRH was observed 30 minutes after the start of surgery for both procedures P <005). The timing of CRH and ACTH peaks was unrelated. The maximum mean plasma Cortisol level for the conventional procedure (1268 ± 147 nmol/l) was reached 20 minutes after reversal of anaesthesia and remained at this level until the end of sampling. The Cortisol response was comparable during the laparoscopic procedure but was beginning to fall at 60 minutes post-operatively. Plasma adrenaline responses to the two types of surgery were not significantly different, but the plasma total noradrenaline response to laparoscopic surgery as indicated by the response area during the first 20 minutes was significantly increased (P<0 02). Plasma sodium, renin activity and initial systolic blood pressure fall were not significantly different during the two procedures. CONCLUSIONS For both procedures, the peak of ACTH secretion after incision is likely to be AVP dependent, and the timing of peak levels of these two hormones was significantly related. Subsequent ACTH secretion may be the result of an interaction between AVP and CRH. Laparoscopic cholecystectomy results in a smaller AVP rise than does the conventional procedure, and plasma AVP falls more rapidly post-operatively. During the period of observation, ACTH, CRH, Cortisol and adrenaline responses were not significantly lessened by the laparoscopic approach, but there was a significant increase in the noradrenaline response. Stress hormone monitoring may assist further improvements in surgical technique.     

Effect of hyperinsulinaemia on the function of the pituitary-adrenal axis in healthy man

OBJECTIVE Circulating insulin levels in themselves have been reported to influence the counter-regulatory hormone response to hypoglycaemia in man. The effect of insulin on a specific aspect of this response was examined during euglycaemia by stimulating the pituitary-adrenal axis with human corticotrophin-releasing hormone (CRH). SUBJECTS Eight healthy males. DESIGN Following an overnight fast, insulin was infused at 15 (low) and 60 (high) mU/kg/h from 0900 h for 180 minutes on separate occasions in random order. On each occasion, blood glucose was clamped at euglycaemia, and 1 μ/kg/kg (i.v. bolus) human CRH was administered at 120 minutes. MEASUREMENTS Circulating hormone concentrations were determined by radioimmunoassay. Peak Cortisol and ACTH responses were compared for the two study conditions. RESULTS Mean serum insulin levels were threefold higher during the high compared with the low insulin infusion (mean difference 320 pmol/l, 95% confidence interval (CI) 150-490, P<0001). Blood glucose levels during the clamps were comparable (mean difference 0 15 mmol/l, 95% CI 0-0.63). Plasma Cortisol levels increased following CRH, although the peak concentration was significantly lower during the high insulin infusion (mean difference 36 nmol/l, CI 0-110, P< 0.02). However, peak ACTH levels were comparable for the two insulin levels (mean difference 8 ng/l (1.8 pmol/l), CI 0-50). CONCLUSIONS The peak Cortisol response to CRH was diminished at the higher circulating insulin levels. This was not dependent upon concurrent hypoglycaemia and did not appear to be mediated at the level of the pituitary gland.     

The effect of β-endorphin on basal and insulin-hypoglycaemia stimulated levels of hypothalamic-pituitary-adrenal axis hormones in normal human subjects

OBJECTIVE It has been demonstrated that β-endorphin reduces CRH production and hypoglycaemia-induced ACTH secretion in the rat. We aimed to determine whether supraphysiological levels of β-endorphin inhibit the ACTH and CRH response to insulin-induced hypoglycaemia in human subjects. DESIGN Plasma glucose, prolactin, cortisol, ACTH, CRH and AVP were measured at intervals over a 3-hour period. Intravenous β-endorphin 5 mg/50 ml or an equal volume of normal saline was infused between 30 and 90 minutes, with soluble insulin 0.15 units/kg administered i.v. at 60 minutes in a cross-over design. SUBJECTS Six healthy male volunteers aged 20–35 years. MEASUREMENTS Prolactin was measured by a fluoroimmunometric assay, ACTH, CRH and AVP by radioimmunoassay, and cortisol was measured by enzyme-linked immunosorbent assay. Haemodynamic measurements were recorded prior to each blood sample. Results are expressed as mean ± standard error of the mean. RESULTS β-Endorphin resulted in a significant decrease in baseline cortisol (P < 0.05) but not ACTH. Plasma glucose (P < 0.001) and CRH (P < 0.05) and PRL (P < 0.05) increased significantly during β-endorphin compared to normal saline. After insulin administration, glucose reached a similar nadir during β-endorphin and normal saline (2.1 ± 0.1 and 1.9 ± 0.15 mmol/l, respectively) but the fall in plasma glucose was delayed during β-endorphin (P < 0.01 by ANOVA). This resulted in a significantly altered time-course for the ACTH and cortisol responses (P < 0.05 for each), but no difference overall in the magnitude of the response. In contrast, neither the timing nor the magnitude of the CRH and AVP responses were affected. Prolactin also reached a similar peak value after the administration of insulin, while the haemodynamic responses to hypoglycaemia were not significantly altered during β-endorphin. CONCLUSIONS While β-endorphin has been shown to be inhibitory to basal ACTH and cortisol secretion in humans, we note a significant increase in plasma CRH in response to β-endorphin, which may be arising from a peripheral source. Intravenous β-endorphin increases plasma glucose and delays the onset of hypoglycaemia following insulin but does not result in significant inhibition of the ACTH and cortisol response. This may reflect the poor penetration of β-endorphin into the central nervous system, although a hypothalamic effect of β-endorphin is implied by the increased PRL. The significantly delayed time course in ACTH and cortisol secretion noted during β-endorphin is not explained by a later response of either CRH or AVP. Although peripheral levels of these hormones may be a relatively insensitive measure of hypothalamic function, an additional factor may influence ACTH release during hypoglycaemia.     

An association between hypothalamic-pituitary dysfunction and peripheral endocrine function in extreme obesity

OBJECTIVE: The aim was to investigate a possible relationship between measures of insulin secretion and glucose disposal and hypothalamic-pituitary function in extreme obesity. DESIGN: A cross-sectional analysis of obese subjects attending the Obesity Clinic at the Royal London Hospital and normal weight volunteers was undertaken. Investigations were performed on separate occasions and in random order. PATIENTS: The subjects were 34 extremely obese women, menstruating and with normal glucose tolerance (mean Body Mass Index, BMI = 42) and 15 normal weight female controls (mean BMI = 22). MEASUREMENTS: The following were measured: fasting insulin, relative insulin resistance calculated using fasting insulin and plasma glucose by the homeostatic model of assessment, insulin release during a 75-g oral glucose tolerance test (insulin area under the curve), steady-state plasma glucose level achieved during a simultaneous intravenous infusion of dextrose, insulin and somatostatin, and the prolactin and growth hormone (GH) responses to insulin-induced hypoglycaemia. RESULTS: In the obese group an impaired prolactin response to hypoglycaemia (mean area under the curve obese 54 U/l min, controls 155 U/l min; P = 0.0001) was inversely correlated to fasting insulin, r2 = 0.142, P = 0.03; relative insulin resistance, r2 = 0.134, P = 0.03 and steady-state plasma glucose level, r2 = 0.345, P = 0.0004 whereas the impaired GH response (mean GH area under the curve obese 1.9 U/l min, controls 65.7 U/l min; P = 0.0001) was inversely correlated to steady-state plasma glucose level, r2 = 0.196, P = 0.01. Backward procedure for stepwise regression analysis confirmed the steady-state plasma glucose level to be the most important variable associated with the prolactin and growth hormone response among the remaining indices of insulin secretion/resistance. CONCLUSION: We conclude from these findings that hyperinsulinaemia in obesity is an important association with altered hypothalamic-pituitary function indicated by impaired prolactin and growth hormone secretion to insulin-induced hypoglycaemia.     

EFFECT OF OBESITY AND WEIGHT LOSS ON THE ARGININE VASOPRESSIN RESPONSE TO INSULIN-INDUCED HYPOGLYCAEMIA

Arginine vasopressin (AVP) response to insulin-induced hypoglycaemia was evaluated in 16 men with normal weight and in 9 obese men. Obese subjects were restudied following substantial weight loss. The decrease in blood glucose concentrations after insulin injection (0.15 U/kg i.v. bolus) had a similar pattern and magnitude in the normal controls and in the obese subjects both before and after weight loss. Basal plasma insulin concentrations in the obese patients were significantly higher than in the normal weight subjects, but were back to normal after weight reduction. During all tests, blood osmolality, haematocrit and blood pressure remained constant. The AVP rise during the insulin tolerance test (ITT) was significantly lower in the obese patients than in the normal controls. The mean peak plasma AVP level was 2.3 times higher than the basal value in the normal controls, but only 1.6 times in the obese patients. After weight loss, the obese men regained normal AVP responses during the ITT. These data indicate that a hypothalamic pituitary disorder affects the AVP response to insulin-induced hypoglycaemia in obese men.     

Plasma corticotrophin releasing hormone, vasopressin, ACTH and Cortisol responses to acute myocardial infarction

OBJECTIVES We assessed the magnitude and duration of the response of hypothalamic-pituitary-adrenal hormones to the stress of myocardial infarction, in the presence and absence of angiotensin converting enzyme inhibitors. In particular, we wished to analyse the interrelationships between peripheral plasma levels of corticotrophin releasing hormone (CRH), vasopressin (AVP) and adrenocorticotrophin (ACTH), and also between ACTH and Cortisol, during a prolonged medical stress. DESIGN All hormones were measured within 6 hours of the onset of an acute myocardial infarction. Patients were randomly allocated to three different study groups according to a double blind procedure. PATIENTS Group 1 (10 patients) received placebo treatment, Group 2 (13 patients) received a maintenance dose of captopril 25 mg three times daily, Group 3 (11 patients) received enalapril 5 mg three times daily. MEASUREMENTS Peptide hormones were measured by radioimmunoassay, and Cortisol by ELISA. Reference ranges for all hormones were obtained from 40 or more volunteers from the electoral roll. RESULTS At the start of the study, mean±SEM plasma AVP (27.9 ± 4.6 pmol/l) was significantly (P<0 001) raised above the mean for the reference range (1.82 ± 0.09 pmol/ I), and 12 patients had values >50 pmol/l. Mean plasma Cortisol (960 ± 89.6 nmol/l) was also raised above the reference range mean (554±28 nmol/l, P<0.001), as was mean plasma CRH (4.97 ± 0.5 pmol/l, reference mean 1.52± 0.09 pmol/l, P<0001). By contrast, mean ACTH (3.88 ± 0.66 pmol/l) was significantly less than the reference mean (10.7 ± 0.7 pmol/l, P<0.001). During the 72-hour observation period there was a highly significant fall (P<0.001) in plasma CRH, AVP and Cortisol. By contrast, plasma ACTH rose, and the change with time of ACTH was significantly different from the fall in plasma CRH, AVP or Cortisol (P<0.001 for each comparison). No significant differences in plasma CRH, AVP, ACTH or Cortisol responses to placebo, captopril or enalapril were observed. CONCLUSIONS Within 6 hours of a myocardial infarction, mean plasma CRH, AVP and Cortisol values were very significantly raised above mean control values, while ACTH was very significantly reduced. During the 3 days following an acute myocardial infarction, plasma CRH, AVP and Cortisol fell substantially, and this pattern was not influenced by angiotensin converting enzyme inhibitors. By contrast, plasma ACTH showed a significant increase with time. This suggests that the usual relationships between CRH, AVP and ACTH, and between ACTH and Cortisol are disturbed in patients admitted to hospital with myocardial infarction. Maximum levels of AVP observed in 12 patients exceeded 50 pmol/l, which may be sufficiently high to interfere with tissue perfusion. It is postulated that V₁, AVP receptor antagonists may have a therapeutic application in limiting infarct size.     

ACTH and cortisol response to combined corticotropin releasing hormone-arginine vasopressin stimulation in obese males and its relationship to body weight, fat distribution and parameters of the metabolic syndrome.

OBJECTIVES: To investigate the activity of the hypothalamic-pituitary-adrenal (HPA) axis in male obesity and its relationship with several prominent parameters of the metabolic syndrome. DESIGN: A cross-sectional clinical study of the activity of the HPA axis in groups of obese males and normal-weight controls. SUBJECTS: Seventeen obese non-diabetic males with a body mass index (BMI) >28 and eight normal-weight controls were examined. MEASUREMENTS: Fat free mass (FFM) and fat mass (FM) were measured by bioelectrical impedance, and the waist-to-hip circumference ratio (WHR) was calculated in all subjects. Baseline samples were taken for sex hormone and lipid determination, and an oral glucose tolerance test (OGTT) was performed for glucose and insulin determination. The activity of the HPA axis was determined by the combined administration of human corticotropin releasing hormone (CRH) (100 microg) and arginine vasopressin (AVP) (0.3 IU). RESULTS: As expected, FFM and FM and the WHR were higher in obese men than in controls, as were fasting insulin and stimulated (as area under the curve (AUC)) glucose and insulin concentrations. Baseline adrenocorticotropin (ACTH) and cortisol concentrations were similar in both groups, but stimulated (as AUC), ACTH was higher (P < 0.05) in obese subjects than in controls, whereas no significant difference in cortisolAUC was present. Since the main differences between obese subjects and controls were present during the early 30 min of the test, the correlation coefficients between total and incremental ACTH(AUC 0-30 min) and CortisolAUC 0-30 min and all other variables were analyzed. A significant correlation coefficient was present between them and all anthropometric parameters, fasting insulin and insulinAUC, but not with androgens and gonadotrophins. In addition, a significant correlation was present between total and incremental ACTH(AUC 0-30 min) and triglyceride concentrations. However, after adjusting for BMI or FM values, all correlation coefficients became non-significant, except the one between incremental ACTH(AUC 0-30 min) and insulinAUC (P < 0.05). CONCLUSION: These findings indicate that obese men may also have an altered pituitary response to combined CRH/AVP stimulation, which appears to be predominantly related to body size and total body fat. ACTH hyperresponsiveness after CRH/AVP stimulation also appears to be related to hyperinsulinaemia, but underlying mechanisms of this relationship remain to be elucidated.     

A comparison of the naloxone test with ovine CRH and insulin hypoglycaemia in the evaluation of the hypothalamic-pituitary-adrenal axis in normal man

OBJECTIVE It has been suggested that naloxone might be useful in clinical testing of the hypothaiamic-pituitary-adrenal (HPA) axis. We have therefore evaluated this non-selective oploid receptor antagonist, as a test of HPA axis function, and compared the results to ovine cortlcotro-phin-releasing hormone (oCRH) and the Insulin tolerance test (ITT). DESIGN Following i.v. administration at the zero of naloxone 20mg (n= 12) on day 1, and either oCRH 1 μg/kg (n= 6) or soluble insulin 0.15 U/kg (n= 6) on day 2, venous blood was sampled at times -20, 0, 15, 30, 45,60,90 and 120 minutes for cortisol, ACTH and AVP. Peripheral CRH was also measured following naloxone and insulin hypoglycaemia. SUBJECTS Twelve normal males (age 20–57 years) with no history of hypothalamic-pituitary-adrenal axis disease. MEASUREMENTS Peptide hormones in plasma samples were measured by radioimmunoassay and cortisol by ELISA. Results are expressed as mean ± SEM. RESULTS Following naloxone, there was a highly significant overall rise in ACTH (P < 0.0005) and cortisol (P < 0.0001), but 1 out of the 12 subjects failed to respond. This subject had a normal ACTH and cortisol response to oCRH, indicating normal pituitary-adrenal function. Peripheral levels of CRH also increased significantly following naloxone (P < 0.002), while AVP did not alter significantly (P= 0.38). Maximal levels of CRH were seen following the ACTH peak however, at a time when ACTH was returning to baseline. All six subjects who received oCRH had an increase in ACTH and cortisol, and the ACTH response to oCRH was greater than that to naloxone (P < 0–05). One subject who developed nausea and hypotension following oCRH had a large rise In AVP and very high levels of ACTH and cortisol. Following Insulin each subject had symptomatic hypoglycaemla and significant rises in cortisol (P < 0.0001), ACTH (P < 0.0001), AVP (P < 0.0005) and CRH (P < 0.01) were seen. Both cortisol and ACTH responses to ITT were significantly greater than those to naloxone (P < 0.05 for each). CONCLUSION The HPA axis response to naloxone Is smaller In magnitude overall compared to oCRH or insulin hypoglycaemia and Is variable in normal subjects. This variability probably reflects changes In central opiold tone rather than alterations in pituitary responsiveness to CRH. It Is unlikely that the naloxone test will replace currently used clinical tests of HPA axis function, particularly in the setting of possible ACTH deficiency, because some subjects with a normal HPA axis appear not to respond to naloxone. As the mechanism involved in the ACTH response to naloxone has not yet been defined with certainty, the naloxone test should not be regarded simply as a test of endogenous CRH release.     

THE CORTISOL RESPONSE TO CORTICOTROPHIN-RELEASING FACTOR IS BLUNTED IN OBESITY

Abnormalities of the adrenal cortex may be associated with extreme obesity but there is little information about hypothalamic-pituitary function. We have investigated this by measuring plasma ACTH and cortisol responses to ovine corticotrophin releasing factor (CRF-41), 0.5 microgram/kg/body weight, in 10 obese women and seven age-matched normal weight women. The cortisol response to insulin-induced hypoglycaemia and intravenous synacthen (2.5 ng/kg/body weight) were also measured on different occasions in some of the subjects. The peak ACTH response to CRF was less in the obese but this was not significant (obese ACTH +/- SEM, 31 +/- 4 ng/l, controls 39 +/- 4 ng/l) whereas the peak cortisol was significantly reduced in the obese (obese cortisol, 456 +/- 21 nmol/l, controls 638 +/- 50 nmol/l). Doubling the dose of CRF did not significantly alter either ACTH or cortisol responses in six of the obese patients. The peak cortisol response to symptomatic hypoglycaemia and following i.v. low dose synacthen stimulation was similar in the obese and normal weight women. We conclude that obese women have a normal cortisol response to hypothalamic-pituitary stimulation by hypoglycaemia and direct adrenal stimulation by synacthen but an impaired adrenal response to pituitary stimulation with CRF. Although the explanation for these findings is uncertain, our study underlines the importance of considering an individual's body weight when assessing the cortisol response to CRF stimulation.     

Alteration of ghrelin-neuropeptide Y network in obese patients with polycystic ovary syndrome: role of hyperinsulinism

Objective Insulin, ghrelin, neuropeptide Y (NPY) and leptin interact in the regulation of energy homeostasis. Most of these signals are altered in polycystic ovary syndrome (PCOS), which is characterized by a high prevalence of obesity. The present study was conducted to evaluate ghrelin–NPY and ghrelin–leptin interplays in relation to insulin secretion in obese PCOS subjects. Design Pilot prospective study. Patients Seven obese PCOS women and seven age–weight matched controls. Measurements Hormonal measurements, oral glucose tolerance test (OGTT) and a ghrelin test (1 µg/kg i.v. bolus). PCOS patients repeated the clinical work‐up after 4 months of metformin treatment (1500 mg/day orally). Results At baseline, PCOS women showed a significantly higher insulinaemic response to the OGTT compared to controls (P < 0·05). In basal conditions, PCOS women exhibited lower NPY levels than controls (P < 0·01). Ghrelin injection markedly increased NPY in controls (P < 0·01), whereas PCOS women showed a deeply blunted NPY response to the stimulus (area under the curve – AUC–NPY: P < 0·01 vs. controls.). Metformin treatment induced a significant decrease in insulin levels (P < 0·01) and the concomitant recovery of NPY secretory capacity in response to ghrelin (AUC–NPY: P < 0·05 vs. baseline) in PCOS women. Leptin levels, which were similar in the two groups, were not modified by ghrelin injection; metformin did not affect this pattern. Conclusion Hyperinsulinaemia seems to play a pivotal role in the alteration of NPY response to ghrelin in obese PCOS women. This derangement could be implicated in the physiopatology of obesity in these patients.     

PLASMA CORTICOTROPHIN-RELEASING FACTOR AND VASOPRESSIN RESPONSES TO HYPOGLYCAEMIA IN NORMAL MAN

The plasma cortisol, ACTH, AVP and corticotrophin-releasing factor (CRF) responses to insulin-induced hypoglycaemia were investigated in six normal men using a controlled, randomized, cross-over design. Hormonal concentrations were determined following insulin or saline injection. The maximum cortisol response was seen at 90 min while plasma ACTH, AVP and CRF concentrations peaked at 45 min following insulin injection. The responses of the insulin-treated and control groups were compared by assessing the incremental response from baseline (pre-injection) to peak hormone levels. A significant increase was observed for each hormone following insulin injection. The mean of the incremental responses between 30 and 120 min in each subject was also statistically greater for each hormone in the insulin-treated group when compared with the control group. These results are consistent with the hypothesis that AVP and CRF are both physiological mediators of ACTH secretion induced by a hypoglycaemic stress.     

The counterregulatory response to hypoglycaemia in women with the polycystic ovary syndrome

OBJECTIVE The pathogenetic mechanisms behind insulin resistance in polycystic ovary syndrome (PCOS) are far from fully elucidated. Aberrant counterregulatory responses to hypoglycaemia have been reported in patients with insulin resistance, and recent reports suggest that plasma glucose may be regulated at lower levels in women with PCOS. In this study we investigated the complete hormonal counterregulatory response to hypoglycaemia in women with PCOS. DESIGN Prospective cross-sectional study. PATIENTS Eight obese (BMI 25) and 10 non-obese (BMI < 25) women with PCOS, diagnosed by means of ultrasonography and clinical signs of chronic anovulation. Eight obese and 9 non-obese controls. MEASUREMENTS Hypoglycaemia was induced by an intravenous bolus of soluble insulin (0.15 IU/kg body weight). The counterregulatory responses of cortisol, GH, catecholamines, glucagon, chromogranin A (CGA), and neuropeptide Y (NPY) were studied together with symptoms of hypoglycaemia. RESULTS The obese women with PCOS had a more pronounced truncal-abdominal body fat distribution (waist hip ratio, WHR) and were hyperinsulinaemic, compared with the obese controls. All the women exhibited blood glucose levels (< 2 mmol/l) well below the threshold for the hormonal counterregulatory response and for the appearance of clinical symptoms. The non-obese women with PCOS showed a greater increase in serum concentrations of GH than the lean controls. The obese women with PCOS exhibited blunted responses of noradrenaline and NPY, but similar increases of adrenaline and CGA, compared with the obese controls. They also showed a lower symptom score during hypoglycaemia. The response of noradrenaline to hypoglycaemia correlated inversely with fasting insulin levels in the women with PCOS. Among all the obese women (PCOS and controls pooled) basal levels of noradrenaline correlated inversely with the WHR. CONCLUSIONS All the women with PCOS, independent of BMI, body fat distribution and insulin levels, showed preserved counterregulatory responses to hypoglycaemia. The reduced plasma levels of noradrenaline and the lower perception of hypoglycaemic symptoms in the obese women with PCOS could both reflect a lower activation of the sympathetic nervous system. This aberration seems related to truncal-abdominal obesity and hyperinsulinaemia. The finding of an increased response of GH in the lean women with PCOS could support previous suggestions of an altered activity of the GH/IGF-I system in these women.     

Glucose tolerance, insulin secretion, insulin sensitivity and glucose effectiveness in normal and overweight hyperthyroid women

OBJECTIVE Inter-relationships between insulin sensi-tivity and body weight in patients with hyperthyroidism remain incompletely understood. We have examined whether a mild excess of body weight exacerbates the metabolic abnormalities of spontaneous hyperthyroidism. DESIGN AND PATIENTS Insulin-modified intravenous glucose tolerance tests were performed on 14 hyperthy-roid women with body mass indices (BMI) ranging from 21 to 31 kg/m². A control group of 19 healthy women matched for age and BMI was also studied. MEASUREMENTS Intravenous glucose tolerance (KG), first and second-phase integrated insulin responses to glucose, the integrated glucose area under the curve (AUC), and minimal model parameters of insulin sensitivity (SI) and glucose effectiveness (SG) were determined. RESULTS Hyperthyroid women had mean KG, glucose-induced insulin secretion and SG values similar to those in control women. The mean glucose AUC was higher in hyperthyroid patients (P<0.05). Lower insulin sensitivity was observed in hyperthyroid patients than in control women (SI=0.38±0.07 vs 0.59±0.07 l/min pmol 10⁴ (mean±SEM), P<0.05). A steeper decline in insulin sensitivity with increase in body mass index was found in hyperthyroid women when compared with the control group, after adjusting for age. When groups were compared according to their BMI, hyperthyroid women with normal weight (BMI≤25 kg/m², n=8) had mean KG, insulin response to glucose, glucose AUC, SG and SI values similar to those in normal weight control women (n=11). Overweight hyperthyroid patients (BMI>25 kg/m², n=6) had a higher (P<0.05) second-phase insulin response to glucose than normal weight patients, a higher glucose AUC (P<0.05) than normal weight patients and overweight controls (n=8), and a lower SI (P<0.05) than normal weight patients and overweight controls. SG was not influenced by BMI in hyperthyroid patients. CONCLUSIONS These results suggest that overall glucose tolerance was not significantly affected in normal weight hyperthyroid women. However, when a moderate excess of weight is also present, a state of clear insulin resistance occurs.     

The effects of alcoholism on the hypothalamic-pituitary-adrenal axis: interaction with endogenous opioid peptides

BACKGROUND Abnormal baseline hypothalamic-pituitary-adrenal axis function and dexamethasone suppressibility seen in withdrawing alcoholics returns to normal on abstinence, but some studies report blunting of the ACTH response to CRH persisting during the early abstinence phase. Reduced central levels of endogenous oplold peptides have been postulated to have an aetiological role In alcohol addiction. AIMS To evaluate hypothalamic-pituitary-adrenal axis function in a group of recently abstinent alcoholics using basal hormone data, naloxone (an oplold receptor antagonist), and ovine CRH. SUBJECTS Nine alcoholics (age 41.4±3.1 years) studied more than one week after the acute withdrawal period but within 6 weeks of cessation of drinking, and nine age and sex matched non-alcoholic controls. PROTOCOL Cortisol, ACTH, CRH and AVP levels were measured every 20 minutes for 2 hours between 0900 and 1100h. Twenty mg naloxone I.v. was administered at 1100h (0 minutes) and further samples for the above hormones were taken at 15, 30, 45, 60, 90 and 120 minutes. On a separate occasion, again at 1100h, oCRH 1μg/kg (n= 7 alcoholics, n = 6 controls) was administered, with samples for cortisol, ACTH and AVP taken at the same times. STATISTICS Results were examined by analysis of variance for repeated measures (ANOVA), while Incremental hormone response and area under the secretory curve (AUC) in alcoholics versus controls were compared by the two-tailed Student's t-test. Linear regression analysis was carried out to examine the relation between basal cortisol and hormone responses to naloxone and oCRH. RESULTS Basal hormone levels did not differ between the groups. The alcoholics had a blunted ACTH incremental response to naloxone (11.4±3.0 vs 21.1±25 pmol/l, P< 0.05) but the cortisol response was not signiflcantly different (205±51 vs 305±42 nmol/l, P= 0.15). The alcoholics also had a blunted ACTH incremental response to oCRH (28.7 ± 4.2 vs 41.2 ± 3.7 pmol/l, P= 0.052) and by ANOVA a significant main effect of group (alcoholic vs control) was seen (P < 0.02) for the ACTH response to oCRH. There was no difference between the groups in the cortisol Incremental response to oCRH. In the control subjects, a negative correlation was found between basal cortisol and the cortisol Increment (r=-0.82, P< 0.05) and ACTH Increment (r=-0.81, P = 0.052) following oCRH, while In contrast, basal cortisol correlated positively with cortisol increment (r= 0.72, P < 0.05) following naloxone. There was also a trend for basal cortisol to correlate positively with ACTH increment following naloxone In the controls (r= 0.63, P < 007). In the alcoholics, the normal negative effect of basal cortisol on the cortisol Increment after oCRH was reversed, with a positive correlation between basal cortisol and cortisol increment (r= 0.75, P= 0.05). CONCLUSIONS Recently abstinent alcoholics with normal basal HPA axis hormone levels have a blunted ACTH response to naloxone and oCRH. While reduced levels of central endogenous oplold peptides may be a factor in the blunted ACTH response to naloxone In the alcoholics, it Is proposed that the alcoholics have reduced pituitary responsiveness to CRH. This may be via a direct pituitary effect of the chronic ethanol exposure or by a reduction in hypothalamic-hypophyseal vasopressin levels.     

alpha2-adrenoceptor regulation of the hypothalamic-pituitary-adrenocortical axis in obesity

BACKGROUND: Abdominal obesity is associated with hyper-responsiveness of the hypothalamic-pituitary-adrenocortical (HPA) axis to stimulatory neuropeptides and to stress. Catecholamines are involved in the regulation of the HPA axis, particularly during stress, via alpha-adrenoceptor modulation. DESIGN: In this study, we investigated the effects of pre-treatment with an alpha2-adrenoceptor agonist, clonidine (2 microg/kg over 10 minutes) and antagonist, yohimbine (0.125 mg/kg bolus, followed by 0. 001 mg/kg/minutes per 90 minutes infusion) on the HPA axis, measured by ACTH and cortisol response to combined CRH (human, 100 microg) plus AVP (0.3 IU) administration, and on noradrenalin (NA) and adrenalin (A) blood levels, in a group of obese women with abdominal (A-BFD) or peripheral (P-BFD) body fat distribution and in nonobese controls. RESULTS: During the control CRH + AVP test the ACTH but not the cortisol response was higher (P < 0.05) in obese A-BFD women than in controls, with minor and transient variations of NA levels. Neither the control test nor clonidine or yohimbine influenced basal or post CRH + AVP A concentrations. Clonidine pretreatment similarly and significantly decreased NA levels in all women and, compared to the control test, marginally influenced the ACTH response to CRH + AVP. Conversely, during yohimbine infusion NA levels steadily and similarly increased to values more or less double baseline values in all groups. Compared to the control test, however, the ACTH response to the CRH + AVP test performed during yohimbine infusion significantly decreased in the control subjects whereas a tendency to a further increase occurred in the obese groups and, specifically, in the A-BFD group significantly (P < 0.05) more than in the P-BFD group. CONCLUSIONS: This study shows that alpha2-adrenoceptor regulation of the HPA axis is different in obese and nonobese women, particularly in stressed conditions. We suggest that the abnormal ACTH response to CRH + AVP challenge with increased noradrenergic tone may represent a specific pathophysiological aspect of the abnormal response to stress or to other specific stimulatory factors in obese women, particularly those with abdominal body fat distribution.     

Atrial natriuretic factor reduces vasopressin and angiotensin II but not the ACTH response to acute hypoglycaemic stress in normal men

OBJECTIVE We determined the effects of physiological (non-hypotensive) increments of plasma atrial natriuretic factor (ANF) on the vasopressin and hypothalamic-pituitary-adrenal response to insulin induced hypoglycaemia. DESIGN Single blind, placebo controlled, randomized study of the effect of vehicle alone or ANF (2.5 pmol/kg/min for 120 minutes) commencing 30 minutes before bolus administration of insulin (0 15 U/kg body weight). RESULTS ANF infusion raised venous plasma ANF levels four to five-fold (mean level 32 ± 0.3 pmol/l at time of insulin injection) without affecting resting blood pressure or heart rate. After insulin, the fall in plasma glucose and rise in plasma adrenaline and noradrenaline were similar in both studies. In contrast, the responses in plasma arginine vasopressin (P < 0.02) and in plasma angiotensin II (P<0.05) were inhibited by ANF. Plasma corticotrophin releasing factor, ACTH and Cortisol responses to hypoglycaemic stress did not differ significantly in the presence and absence of ANF. CONCLUSION We conclude that four to five-fold acute increase in plasma ANF, while attenuating vasopressin and angiotensin II responses to hypoglycaemia, does not inhibit the hypothalamic, pituitary and adrenal responses or inhibit sympathetic nervous activation in normal men.     

Interactions of CRH, AVP and cortisol in the secretion of ACTH from perifused equine anterior pituitary cells: "permissive" roles for cortisol and CRH

To further elucidate the interaction of CRH, AVP and cortisol in the control of ACTH secretion, we used an in vitro perifusion model with dispersed equine anterior pituitary cells. To approximate the in vivo milieu in the horse, CRH was perifused continuously (at 0, 2 and 20 pmol/L) and 5-min pulses of AVP (0, 1, 3 and 10 nmol/L) were given every 30 min in the presence of 0 or 100 nmol/L cortisol. Total (baseline + incremental) ACTH secretion increased as both the CRH (p<0.001) and the AVP (p<0.001) concentration increased and interaction between CRH and AVP was significant (p=0.042). Cortisol reduced total ACTH secretion in the presence of 2 pmol CRH/L (p=0.001) but not 0 or 20 pmol CRH/L. For incremental ACTH there was interaction between CRH and AVP (p<0.0001), with increased secretion at higher concentrations, and no significant main effect of cortisol. There was significant (p=0.001) interaction between cortisol and CRH, with cortisol attenuating ACTH release at 0 pmol CRH/L (p=0.008), having no effect at 2 pmol CRH/L and potentiating it at 20 pmol CRH/L (p=0.026). We conclude that (1) CRH at high physiological levels has a "permissive" role in preventing the cortisol inhibition of the ACTH response to AVP, and (2) basal cortisol levels have a "permissive" action in priming the HPA axis for maximal responsiveness to stimulated levels of CRH and AVP.     

Roles of LH and insulin resistance in lean and obese polycystic ovary syndrome

OBJECTIVE The relationship between insulin resistance and hyperandrogenism led us to study insulin resistance in polycystic ovary syndrome (PCOS) in order to determine its prevalence and pathogenesis. DESIGN Blood samples were taken on the 8th day after menses commenced. PATIENTS Sixty-one women with PCOS, 30 with normal weight (BMK25 kg/m²) (group 1) and 31 with obesity (BMI<26 kg/m₂) (group 2) were studied. They were divided also according to LH level: group A, low or normal LH (n==23) and group B, high LH (n= 38). Twenty lean control women and 16 obese control women were studied. MEASUREMENTS Serum LH, testosterone, free testosterone, dehydroepiandrosterone, sex-hormone binding globulin, androstenedione, and fasting insulin were measured. Insulin sensitivity was explored by the insulin tolerance test (ITT). ITT was performed by bolus i.v. insulin of 0 1 IU/kg. Blood glucose was measured before (– 5, 0) and after injection (3, 5, 7, 10, 15 minutes). Insulin sensitivity was given by the ratio of glycaemic variation to initial blood glucose (AG/G index). RESULTS ΔG/G was correlated with other insulin resistance parameters, particularly fasting insulin r=–0.40, P<0.01. The PCOS groups had the following insulin resistances (mean ± SEM) compared to matched groups: ΔG/G lean PCOS vs lead controls: 0.45 ± 0.02 vs 0.61 ± 0.01, P< 0.001; ΔG/G obese PCOS vs obese controls: 0.32 ± 0.02 vs 0.40 ± 0.01, P<0.02. Insulin resistance was higher in group A than in group B: ΔG/G 0 29 ± 002 vs 0 45 ± 0 02, P < 0.001. The prevalence of insulin resistance was 63% in lean PCOS and 51% in obese PCOS. Positive correlations between AG/G index and LH were found in group 1 and 2, respectively r= 0.45, P<0.01 and r= 0.55, P<0.01. CONCLUSION PCOS was associated with a significant decrease of insulin sensitivity, independent of obesity. The correlation between LH and insulin sensitivity suggests a complementary action in PCOS.     

The effects of cortisol, vasopressin (AVP), and corticotropin-releasing factor administration on pulsatile adrenocorticotropin, alpha-melanocyte-stimulating hormone, and AVP secretion in the pituitary venous effluent of the horse

Plasma ACTH, arginine vasopressin (AVP), and alpha MSH were measured in pituitary venous effluent at 5-min intervals from five unanesthetized horses during cortisol infusion and after an iv bolus of AVP or ovine (o) CRF. In control experiments (no hormone) there was a significant overall correlation between the timing of concentration changes in ACTH and alpha MSH. Cortisol infusion increased jugular cortisol levels by 70% and was associated with a reduction in mean ACTH, AVP, and alpha MSH secretion rates and ACTH peak secretion rate, but did not alter the observed pulse frequencies of these hormones. Administration of AVP raised plasma concentrations to a level comparable to the spontaneous peaks in pituitary venous blood and resulted in an increase in the secretion of ACTH and alpha MSH in all horses. Furthermore, spontaneous AVP peaks occurred in pituitary venous blood between 90 and 180 min after AVP injection, indicating that the exogenous hormone did not suppress AVP secretion. oCRF administration led to a prolonged elevation in plasma CRF and an increase in secretion of ACTH and alpha MSH, but not AVP, in all horses. The pulsatile secretion of ACTH and alpha MSH was maintained despite plasma CRF levels in excess of 400 pmol/liter, and the timing of concentration changes in AVP and ACTH continued to be highly correlated. It is concluded that pulsatile ACTH secretion continues during cortisol, oCRF, or AVP administration. Like that of ACTH, alpha MSH secretion is stimulated by oCRF and AVP administration and suppressed by cortisol. Although the timing of concentration changes in ACTH and alpha MSH is highly correlated, the correlation of the actual concentrations of these two hormones varies considerably in different animals.