Effect of oral morphine and naloxone on pituitary-adrenal response in man induced by human corticotropin-releasing hormone

To further investigate the role of opioids in the regulation of the pituitary-adrenal axis we studied the effect of morphine and naloxone on human corticotropin-releasing hormone (hCRH)-induced ACTH, immunoreactive (ir) beta-endorphin, and cortisol release in normal subjects. Protocols: 1. 30 mg of a slow-release preparation of morphine or placebo was given orally 3 h prior to administration of hCRH (0.1 mg iv) (N = 7). 2. Naloxone (4 mg as bolus iv) or placebo was given 5 min prior to hCRH (N = 7). 3. Naloxone (4 mg iv as bolus followed by a continuous infusion of 6 mg over 75 min) or placebo was started 15 min prior to hCRH (N = 6). hCRH was injected at 11.00 h (protocol 1, 2) or at 17.00 h (protocol 3). Oral morphine not only suppressed basal hormone levels (P less than 0.02), but also the peak response to hCRH compared with placebo (cortisol: 270 +/- 50 vs 559 +/- 80 nmol/l; ACTH: 5.1 +/- 1.5 vs 13.1 +/- 2.7 pmol/l; ir beta-endorphin: 48.5 +/- 8.7 vs 88 +/- 14 pmol/l; mean +/- SEM, P less than 0.02). Similarly, the maximum incremental changes and the area under the curve were significantly reduced for all three hormones compared with placebo (P less than 0.05). After 4 mg of naloxone in the morning, no significant hormonal changes in response to hCRH were observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal responses to insulin-induced hypoglycemia in man

Insulin-induced hypoglycemia is a potent stress stimulating ACTH release, but the factors responsible for this ACTH secretion are not known. In this study, several ACTH-stimulating factors, such as CRH, arginine vasopressin (AVP), epinephrine (E), norepinephrine (NE), and dopamine, in addition to ACTH, cortisol, and glucose, were simultaneously measured in plasma before and 15, 30, 60, 90, and 120 min after iv administration of 0.1 U/kg BW regular insulin to seven normal subjects. Insulin administration resulted in significant rises in the mean plasma ACTH level from 4.6 +/- 1.1 (+/- SEM) to 21.6 +/- 4.8 pmol/L at 30 min (P less than 0.01) and in plasma cortisol from 330 +/- 60 to 720 +/- 50 nmol/L at 60 min (P less than 0.01). These increases were preceded by a 41.0 +/- 1.9% (P less than 0.001) fall in blood glucose levels. The mean plasma CRH level rose significantly from 1.0 +/- 0.1 to 1.2 +/- 0.1 pmol/L (P less than 0.01) at 30 min and remained elevated until 120 min. In addition, concomitant and significant rises in plasma AVP levels (basal, 1.5 +/- 0.01; peak, 4.5 +/- 1.1 pmol/L at 30 min; P less than 0.01), E (basal, less than 50; peak, 640 +/- 130 pmol/L at 30 min; P less than 0.01), and NE (basal, 0.07 +/- 0.01; peak, 0.17 +/- 0.03 nmol/L at 60 min; P less than 0.05), but not dopamine, also occurred. These results suggest that multiple ACTH-releasing factors, such as CRH, AVP, E, and NE, are involved in ACTH secretion induced by insulin-induced hypoglycemia in man.     

Effect of metyrapone pretreatment on adrenocorticotropin secretion induced by corticotropin-releasing hormone in normal subjects and patients with Cushing's disease

To examine the influence of endogenous cortisol on the ACTH response to CRH, we compared ACTH secretion during CRH tests before and after metyrapone administration in 9 normal subjects and 12 patients with Cushing's disease. The administration of 4.5 g metyrapone (750 mg, orally, every 4 h) resulted in a decrease in basal (pre-CRH) plasma cortisol levels and an increase in basal plasma ACTH levels in both normal subjects and Cushing's patients. The pretreatment with metyrapone significantly blunted the increase in plasma cortisol levels and markedly enhanced ACTH secretion after iv injection of 100 micrograms human CRH. The peak ACTH levels during CRH test before and after metyrapone administration were 8 +/- 1 and 58 +/- 8 pmol/L, respectively, in normal subjects (P less than 0.01) and 26 +/- 5 and 50 +/- 11 pmol/L, respectively, in Cushing's patients (P less than 0.05). Although the basal and peak ACTH levels as well as delta ACTH (peak ACTH - basal ACTH) during the CRH test before metyrapone administration were significantly higher in Cushing's disease patients than in normal subjects (P less than 0.01), no such difference was observed between the 2 groups after metyrapone administration. The results clearly indicate that the endogenous cortisol levels greatly influence the ACTH response to CRH, and that the CRH test as commonly performed does not allow a correct evaluation of potential responsiveness of normal pituitaries and Cushing's adenomas to CRH.     

Corticotropin-independent effect of ovine corticotropin-releasing hormone on cortisol release in man.

The effect of corticotropin-releasing hormone (CRH), independent of adrenocorticotropin hormone (ACTH), was evaluated in nine healthy individuals. Cortisol release and corresponding ACTH production were determined after separate intravenous administration of ovine-CRH (1 micrograms/kg BW) and insulin inducing hypoglycemia (0.1 u/kg BW). Adrenocorticotropin hormone (1-24; 250 micrograms intravenous bolus) revealed an adequate adrenal reserve capacity in all subjects. At the time of peak cortisol response following CRH and insulin administration, IR-cortisol increments were 14 +/- 1 micrograms/dl and 9 +/- 1 micrograms/dl (mean +/- SE), respectively (p less than .05); whereas ACTH (IR-ACTH) increments were 40 +/- 10 ng/l and 53 +/- 14 ng/l, respectively. The cortisol increment/ACTH increment ratios were 0.53 +/- 0.09 and 0/36 +/- 0.09, respectively (p less than 0.05), suggesting an ACTH-independent effect of CRH on cortisol production. The authors speculate that CRH may have a direct effect on the human adrenal gland or it may release ACTH-like factors that stimulate the human adrenal cortex.     

Response to corticotropin-releasing hormone during pregnancy in the baboon

CRH is secreted by the placenta into human maternal and fetal plasma during gestation. In the present study plasma CRH was measured in the plasma of five pregnant baboons and their fetuses to ascertain whether the baboon is a suitable model for study of placental CRH. Studies were performed in chronically catheterized animals that exhibited no behavioral or endocrinological signs of stress; maternal animals moved freely about the cage. Mean maternal plasma CRH was 620 +/- 110 pmol/L (2970 pg/mL) at 146 +/- 11 days gestation, and mean fetal plasma CRH was 133 +/- 29 pmol/L (640 pg/mL) at delivery in four animals. Plasma CRH was undetectable (less than 8.5 pmol/L; less than 41 pg/mL) in nonpregnant animals and in animals 8 h after delivery. Maternal and fetal plasma CRH levels in the chronically catheterized baboon were very similar to human maternal and umbilical cord CRH levels at comparable gestational ages. In addition, the majority of maternal plasma CRH eluted in the same position as synthetic human CRH by gel filtration. CRH stimulation tests were performed in the chronically catheterized maternal baboon to investigate whether pituitary-adrenal function during pregnancy is similar to that observed after chronic CRH infusion; blunted ACTH and cortisol responses to acute injections of CRH are observed after chronic CRH infusion. The administration of 0.5 micrograms/kg ovine CRH (oCRH) failed to result in an ACTH or cortisol rise in four pregnant baboons. Baseline ACTH levels were 5.2 +/- 0.4 pmol/L (23.5 pg/mL), and baseline cortisol levels were 800 +/- 55 nmol/L (29.1 micrograms/dL); neither rose after CRH administration. In contrast, 0.5 micrograms/kg oCRH did result in significant ACTH and cortisol elevations in five nonpregnant baboons [ACTH: baseline, 5.9 +/- 1.4; peak, 16 +/- 4.8 pmol/L (P less than 0.05); cortisol: baseline, 430 +/- 55 nmol/L; peak, 960 +/- 200 nmol/L (P less than 0.05)]. In contrast, the administration of a larger dose of oCRH (5.0 micrograms/kg) led to stimulation of ACTH release in five pregnant baboons (baseline, 6.6 +/- 1.3 pmol/L; peak, 34.1 +/- 6.4; P less than 0.001). After this dose cortisol levels also rose in the pregnant animals (baseline = 1040 +/- 30 nmol/L; peak, 1620 +/- 130); however, this response was blunted compared to that in the nonpregnant animals (P less than 0.05). CRH (5.0 micrograms/kg) significantly stimulated both ACTH and cortisol in the nonpregnant animals.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pituitary-adrenal responses to CRH and insulin hypoglycemia in patients with idiopathic GH deficiency

It is well known that the activation of the hypothalamus-pituitary-adrenal axis (HPA) by insulin-induced hypoglycemia (IIH) is more potent and multifactorial than that caused by CRH administration. In this study we compared the clinical value of both tests in assessing the integrity of the HPA system. Plasma ACTH and cortisol responses to oCRH (1 microgram/kg iv) and IIH (insulin 0.1 U/kg iv, glycemia less than 40 mg/dl) were compared in 15 patients with idiopathic GH deficiency. The CRH-induced mean ACTH response was lower, but not significantly, in patients than in controls (peak: 8.8 +/- 1.7 vs 13.4 +/- 2.2 pmol/l), while the mean cortisol response was significantly lower than in normals (peak: 585.7 +/- 49.5 vs 764.5 +/- 52.2 nmol/l, p less than 0.005). Plasma ACTH and cortisol responses to IIH were significantly lower than in normal subjects (peak: 22.3 +/- 5.3 vs 35.8 +/- 5.2 pmol/l, p less than 0.05 and peak: 566.5 +/- 55 vs 803 +/- 38.5 nmol/l, p less than 0.02, respectively). Both in controls and in patients the CRH-induced mean ACTH response was significantly lower (p less than 0.02) than that after insulin, while cortisol peaks were not different. In conclusion, in patients with GH deficiency the impairment of ACTH secretion is not evident in basal condition, but it is disclosed after appropriate dynamic tests. It is confirmed that insulin hypoglycemia is a more potent stimulus than CRH for ACTH release.     

Alterations of the adrenocorticotropin-cortisol axis in normal weight bulimic women: evidence for a central mechanism

We studied pituitary-adrenal function in eight women with normal weight bulimia and seven normal women by measuring plasma ACTH and serum cortisol levels at 20-min intervals for 24 h and the responses to human CRH (hCRH) and to a noon meal. The bulimic women had increased 24-h transverse mean plasma ACTH [1.09 +/- 0.06 (+/- SE) vs. 0.75 +/- 0.14 pmol/L; P less than 0.05] and serum cortisol (235 +/- 21 vs. 152 +/- 9 nmol/L; P less than 0.005) concentrations. While the 24-h ACTH and cortisol pulse frequencies were unaltered, the bulimic women had higher (P less than 0.05) mean peak ACTH (1.46 +/- 0.09 vs. 1.03 +/- 0.15 pmol/L) and cortisol values (331 +/- 33 vs. 239 +/- 17 nmol/L). Despite having higher mean and peak plasma ACTH and serum cortisol values, the bulimic women had a blunted response of both ACTH (P less than 0.001) and cortisol (P less than 0.005) to hCRH, which included a lower mean maximal plasma ACTH response, decreased (P less than 0.05) integrated area under the ACTH response curve (161 +/- 12 vs. 231 +/- 23 pmol/min.L), a lower (P less than 0.05) maximum cortisol response (284 +/- 35 vs. 413 +/- 19 nmol/L), and decreased (P less than 0.05) area under the cortisol curve (11.1 +/- 1.9 vs. 15.9 +/- 1.3 X 10(3) nmol/min.L). The circadian variations of both ACTH and cortisol were maintained in the bulimic women; the nadir and acrophase times were similar to those of the normal women. However, the rise in serum cortisol that occurred within 1 h after the lunch meal in the normal women (104 +/- 35 nmol) did not occur in the bulimic women (P less than 0.05). These data demonstrate that marked changes in hypothalamic-pituitary-adrenal function occur in bulimia in the absence of weight disturbance and suggest central activation of CRH and/or synergistic factors as well as alterations in signals from gut to brain in this syndrome.     

Effect of ovine corticotropin-releasing hormone administered during insulin-induced hypoglycemia on plasma adrenocorticotropin and cortisol

The factors that mediate the hypothalamic-pituitary response to hypoglycemia in man are unknown. To investigate the role of CRH in the plasma ACTH response to hypoglycemia, two different doses of ovine CRH (oCRH) were given to normal men during insulin-induced hypoglycemia. We hypothesized that if the endogenous CRH response to hypoglycemia were less than maximally stimulating, administration of oCRH during hypoglycemia would result in a greater peak plasma immunoreactive (IR) ACTH response. Six normal men were given 1) 0.15 U/kg regular insulin, iv; 2) insulin plus 1 microgram/kg oCRH, iv, 5 min after serum glucose fell to 40 mg/dL or less; and 3) oCRH alone. The degree and duration of hypoglycemia were the same when insulin was given alone or with oCRH. Plasma IR-ACTH after insulin alone and insulin plus oCRH rose at the same rate to similar peaks of 226 +/- 37 (mean +/- SEM) and 213 +/- 53 pg/mL, respectively, both of which were greater (P less than 0.05) than the peak plasma IR-ACTH after oCRH alone (61 +/- 19 pg/mL). The peak plasma IR-cortisol levels after insulin alone (24 +/- 4 micrograms/dL), insulin plus oCRH (27 +/- 3 micrograms/dL), and oCRH alone (18 +/- 2 micrograms/dL) were not significantly different. In a second study, six normal men were given 0.15 U/kg regular insulin, iv; insulin plus 10 micrograms/kg oCRH, iv; and 10 micrograms/kg oCRH alone. Administration of oCRH 5 min after serum glucose fell to 40 mg/dL or less did not affect the degree or duration of hypoglycemia. Plasma IR-ACTH after insulin alone and insulin plus oCRH rose at the same rate to similar peaks of 258 +/- 14 and 290 +/- 33 pg/mL, respectively, both of which were greater (P less than 0.01) than the peak (54 +/- 6 pg/mL) after oCRH alone. After insulin alone, plasma IR-ACTH declined to baseline by 3 h. However, after insulin plus oCRH, plasma IR-ACTH fell gradually until 2 h, rose to a second peak at 2.5-3 h, and remained greater (P less than 0.01) than after insulin or oCRH alone for the 4-h duration of the study. The mean peak plasma IR-cortisol level after insulin plus oCRH (33 +/- 4 micrograms/dL) was similar to that after insulin alone (28 +/- 3 micrograms/dL), but was greater (P less than 0.05) than that after oCRH alone (18 +/- 2 micrograms/dL).(ABSTRACT TRUNCATED AT 400 WORDS)     

Pulsatile human corticotropin-releasing hormone prevents dexamethasone-induced suppression of the plasma cortisol response to hypoglycemia in normal men.

Insulin-induced hypoglycemia causes a sequential stimulation of all three components of the hypothalamic-pituitary-adrenal axis. States of acute glucocorticoid excess, such as the overnight (1 mg) dexamethasone suppression test (DST), inhibit both the basal cortisol level and the response to an insulin tolerance test (ITT). However, whether this negative feedback effect is exerted primarily at the hypothalamic or the pituitary level is not clear. To explore this question further we have examined the cortisol response to insulin-induced hypoglycemia in three experimental settings, in the following order: 1) a control ITT performed at 0900 h after an overnight hospital stay (cITT); 2) an ITT at 0900 h after oral dexamethasone, 1 mg, at 2300 h on the previous evening (DST + ITT); and 3) an ITT at 0900 h after dexamethasone, 1 mg, at 2300 h and hCRH, 1 microgram/kg iv, at 90 min intervals from 0100-0700 h (DST+hCRH + ITT). The response to ITT was defined as the peak cortisol increment (peak minus baseline). Since the study objective was to test whether overnight pulsatile hCRH could prevent dexamethasone-induced suppression of the response to a morning ITT, only subjects that demonstrated a greater than 25% decrease in the cortisol response to DST + ITT vs. cITT received the full protocol (five of nine normal men). Basal ACTH and cortisol secretion remained suppressed throughout the night during both the Dex + ITT and Dex + hCRH + ITT studies when compared to the control study (cITT, P < 0.05). However, the cortisol response to hypoglycemia during DST + hCRH + ITT was significantly greater than during DST+ITT (P < 0.05) and was similar to the cITT response. Thus, pulsatile hCRH, administered during the 10 h between dexamethasone and the subsequent hypoglycemic stimulus, prevented acute suppression by dexamethasone of the cortisol response to hypoglycemia. We conclude that the dexamethasone-induced inhibition of the cortisol response to hypoglycemia results primarily from suppression by dexamethasone of basal hypothalamic corticotropin-releasing factor and the consequent impairment of corticotroph responsiveness to exogenous and endogenous corticotropin-releasing factor.     

Serotoninergic receptor activation by dextrofenfluramine enhances the blunted pituitary-adrenal responsiveness to corticotropin-releasing hormone in obese subjects.

To explore the interrelationships between the serotoninergic system and the hypothalamic-pituitary-adrenal (HPA) axis in human obesity, we evaluated cortisol and adrenocorticotropic hormone (ACTH) response to synthetic human corticotropin-releasing hormone (hCRH, 1 microgram/kg intravenously [IV]) before and after stimulation of the serotoninergic system by dextrofenfluramine (d-FF, 30 mg/d for 3 months) in nine obese women. These responses were compared with a CRH test (1 microgram/kg) carried out in nine age-matched normal-weight women. Plasma cortisol of obese subjects did not significantly increase after CRH (peak value 127.1 +/- 11.2 ng/mL v 104.1 +/- 9.5 ng/mL). This response was lower (P less than .005) than in the controls, in whom the basal cortisol value of 120.6 +/- 11.8 ng/mL reached a peak value of 221.2 +/- 13.4 ng/mL. However, after administration of d-FF, CRH significantly increased (P less than .0001) plasma cortisol (peak value 170.6 +/- 18.0 ng/mL v 111.5 +/- 10.8 ng/mL) and the response was enhanced (P less than .05) as compared with that obtained before d-FF. The ACTH levels of our patients showed a small increment after CRH injection (peak value 13.5 +/- 1.7 pg/mL v 9.6 +/- 1.1 pg/mL), but the hormonal response was lower (P less than .005) than in controls (peak value 38.1 +/- 5.5 pg/mL v 13.8 +/- 0.8 pg/mL). However, after d-FF, CRH induced a significant increment (P less than .05) in plasma ACTH at 30 minutes (20.4 +/- 3.7 pg/mL v 10.9 +/- 0.9 pg/mL) and 45 minutes (18.0 +/- 2.6 pg/mL), even though this response was not significantly different from that observed before d-FF administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of pulsatile human corticotropin-releasing hormone administration on the adrenal insufficiency that follows cure of Cushing's disease

Successful transsphenoidal surgery for Cushing's disease leads to secondary adrenal insufficiency in most patients. This form of transient adrenal insufficiency is thought to result from hypothalamic and pituitary suppression due to the preceding hypercortisolism. Whether the rate-limiting step in the recovery of adrenal function in this setting is the hypothalamic CRH neuron or the pituitary corticotroph cell, however, is not known. We studied this question by examining the response to ovine CRH (oCRH) before, during, and after prolonged pulsatile administration of human CRH (hCRH) beginning 1-2 weeks after curative microadenomectomy for Cushing's disease. Five patients cured of Cushing's disease received eight hCRH injections (1 microgram/kg) daily for 7 days. This CRH regimen was found previously to normalize plasma ACTH and cortisol patterns in patients with secondary adrenal insufficiency who had normal ACTH responses to a single injection of oCRH (hypothalamic adrenal insufficiency). The plasma ACTH and cortisol responses to oCRH (1 microgram/kg at 2000 h) were assessed immediately before, 2.5 h after, and 7 days after the end of pulsatile hCRH administration. To control for time-related improvement in the hormonal response to ovine CRH, an additional five patients cured of Cushing's disease underwent oCRH tests 1-2 and 3-4 weeks after transsphenoidal surgery, but did not receive hCRH. There was no significant difference in basal or oCRH-stimulated plasma ACTH and cortisol levels among any of the three oCRH tests in the patients who received hCRH. The baseline and oCRH-stimulated plasma ACTH and cortisol levels 1-2 and 3-4 weeks after surgery in the patients who did not receive pulsatile hCRH were similar to the values at those times in the patients who received pulsatile hCRH. Compared to normal subjects, however, both the hCRH-treated and non-hCRH-treated patients had significantly decreased peak and time-integrated plasma ACTH and cortisol responses to oCRH. We conclude that an impaired pituitary response to CRH contributes to the postoperative hypocortisolism of patients recently cured of Cushing's disease, and that this impaired pituitary response to CRH is not reversible by 1 week of pulsatile hCRH administration.     

Pituitary adrenal recovery following short-term suppression with corticosteroids.

To provide clinical guidelines for the use of high-dose short-term glucocorticoid therapy, we studied recovery of the hypothalamic-pituitary-adrenal axis in 10 normal men following the administration of suppressive doses of prednisone (25 mg twice daily for five days). Cortisol responses to insulin-induced hypoglycemia and synthetic ACTH before treatment were compared with responses two and five days after concluding the prednisone course when adrenal function was not influenced by the presence of exogenous steroid. Two days after prednisone therapy, peak cortisol responses to both hypoglycemia (11.0 +/- 0.9 microgram/dl mean +/- SEM) and synthetic ACTH (13.3 +/- 1.4 microgram/dl) were significantly reduced compared to pretreatment (20.6 +/- 1.6 and 27.3 +/- 2.5 microgram/dl, respectively, p less than 0.001). Five days after concluding the prednisone therapy, peak cortisol response to hypoglycemia had returned to near pretreatment levels although peak cortisol response in the adrenal gland to synthetic ACTH (22.3 +/- 1.1 microgram/dl) remained reduced (p less than 0.05). These data suggest that brief courses of high-dose prednisone therapy may limit the adrenal component of the hypothalamic-pituitary-adrenal response to stress for up to five days.     

Effects of a V1-vasopressin antagonist on ACTH release following vasopressin infusion or insulin-induced hypoglycemia in normal men

Experimental evidence indicates that arginine vasopressin contributes to the release of adrenocorticotropic hormone under certain conditions. We studied for the first time the AVP antagonist [d(CH2)5 Tyr(Me)AVP] in 6 normal men in order to evaluate the possible role of AVP as an ACTH-releasing hormone during insulin-induced hypoglycemia. To test the agent's capacity to inhibit an ACTH release by exogenous AVP, we compared the ACTH response to an infusion of 300 ng AVP/min a. 30 min after injection of 5 micrograms/kg of the antagonist, b. after injection of placebo (0.9% NaCl). Plasma ACTH levels during AVP infusion rose from 17.2 +/- 1.6 ng/l (3.8 +/- 0.35 pmol/l) to 31.7 +/- 4.2 ng/l (7.0 +/- 0.92 pmol/l) at 40 min after injection of the antagonist, the difference to the control-group (increment from 16.5 +/- 1.2 ng/l (3.6 +/- 0.26 pmol/l) to 41.8 +/- 3.5 ng/l) (9.2 +/- 0.77 pmol/l) being significant (p less than 0.05). Peak plasma cortisol levels were 323 +/- 42 and 529 +/- 52 nmol/l, respectively (p less than 0.05). We then tested the compound in the same subjects during an insulin-induced hypoglycemia; 30 min after administration of 10 micrograms/kg of the AVP antagonist or placebo, all subjects received 0.12 IU/kg of normal insulin, thus inducing a fall of blood glucose levels below 2 mmol/l. The AVP antagonist caused a moderate but insignificant reduction of the rise in plasma ACTH and a slightly greater, significant reduction of the increment in plasma cortisol (350 +/- 19 nmol/l with antagonist and 469 +/- 90 nmol/l with placebo, p less than 0.05) during insulin-induced hypoglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

FK 33-824, a met-enkephalin analog, blocks corticotropin-releasing hormone-induced adrenocorticotropin secretion in normal subjects but not in patients with Cushing's disease

To further elucidate the site of action of opioids on the pituitary-adrenal axis, we studied the effect of D-Ala2,MePhe4,met-(O)enkephalin-ol (Sandoz, FK 33-824) on plasma ACTH and beta-endorphin immunoreactivity and serum cortisol in 7 normal subjects and 11 patients with Cushing's syndrome (Cushing's disease, n = 7; adrenal adenoma, n = 2; ectopic Cushing's syndrome, n = 2) after administration of human corticotropin-releasing hormone (hCRH). hCRH (0.1 mg; Bachem) was injected iv after pretreatment with 0.5 mg FK 33-824, im, or 0.9% saline. In normal subjects, the hCRH-induced ACTH, beta-endorphin, and cortisol increases were almost completely abolished by pretreatment with FK 33-824. Mean peak (+/- SEM) hormone concentrations were significantly reduced (ACTH, 16.7 +/- 3.5 vs. 45.3 +/- 7.8 pg/ml; beta-endorphin, 151 +/- 25 vs. 277 +/- 51 pg/ml; cortisol, 8.1 +/- 1.2 vs. 19.5 +/- 2.6 micrograms/dl; P less than 0.02), as were secretory areas (P less than 0.02). These results indicate a direct pituitary action of the synthetic met-enkephalin. In contrast, in patients with Cushing's disease, FK 33-824 did not inhibit hCRH-induced hormone release. Instead, maximum ACTH and beta-endorphin concentrations were slightly but not significantly higher after the administration of FK 33-824 (ACTH, 292 +/- 143 vs. 131 +/- 32 pg/ml; beta-endorphin, 2409 +/- 763 vs. 1921 +/- 600 pg/ml). These findings indicate a defect in inhibitory opiodergic control of ACTH secretion in patients with Cushing's disease, which may contribute to the pathological ACTH hypersecretion. In patients with Cushing's syndrome due to an adrenal adenoma or ectopic ACTH secretion, neither hCRH nor FK 33-824 altered hormone concentrations.     

Recovery of responses to ovine corticotropin-releasing hormone after withdrawal of a short course of glucocorticoid.

To characterize the recovery of the hypothalamic-pituitary-adrenal axis from suppression by short-term glucocorticoid treatment, we examined the responses to ovine CRH (oCRH) before and after prednisolone administration. Eight normal male volunteers were studied before (control) and after administration of 25 mg prednisolone twice daily orally for 14 days. Data are mean +/- SEM. The ACTH basal level was suppressed 24 h after prednisolone withdrawal (1.7 +/- 0.4 pmol/L vs. control, 3.5 +/- 0.6, P less than 0.02), but the ACTH response to oCRH was not significantly different from control (peak 12.8 +/- 2.0 pmol/L vs. 13.5 +/- 12.1, respectively). Seventy-two h post prednisolone basal ACTH levels had recovered to pretreatment values. Cortisol levels, both basal and in response to oCRH, were significantly suppressed 24 h post prednisolone (P less than 0.001). By 72 h post prednisolone, both basal and oCRH-stimulated cortisol had recovered to pretreatment levels. Dehydroepiandrosterone (DHEA), both basal and stimulated, was significantly suppressed 24 h post prednisolone (P less than 0.001). In contrast to cortisol, basal and peak DHEA remained suppressed 72 h post prednisolone (basal DHEA 9.1 +/- 1.1 nmol/L, P less than 0.05 vs. control; peak DHEA 20.0 +/- 3.3 nmol/L, P less than 0.01 vs. control). When expressed as percent rise, however, the DHEA response to oCRH was not significantly different from control. DHEA sulfate (DHEAS) was significantly lower than control at both 24 and 72 h post prednisolone (1.8 +/- 0.3 and 3.3 +/- 0.4 mumol/L respectively; control 7.2 +/- 0.7 mumol/L; P less than 0.001). The ratio of basal DHEA to DHEAS was significantly higher than control 72 h post prednisolone, indicating that DHEAS was more profoundly suppressed than DHEA. We conclude that after a short course of prednisolone pituitary ACTH secretion is the first parameter of the hypothalamic-pituitary-adrenal axis to recover. Hypothalamic secretion of CRH recovers next, followed by recovery of cortisol secretion. Secretion of DHEA and DHEAS remain suppressed after recovery of cortisol. This suppression may be caused by inhibition of sulfokinase activity by glucocorticoid.     

EFFECTS OF INHIBITION OF CHOLESTEROL SYNTHESIS BY SIMVASTATIN ON THE PRODUCTION OF ADRENOCORTICAL STEROID HORMONES AND ACTH

Simvastatin, a derivative of lovastatin, is a potent inhibitor of cholesterol biosynthesis and may interfere with steroid hormone production, for which cholesterol is required. In a single-blind, placebo-controlled study, 24 patients with severe primary hypercholesterolaemia (mean serum cholesterol +/- SD = 10.74 +/- 1.59 mmol/l) were treated with simvastatin 40 mg per day for 8 weeks. Before and after treatment, the following parameters were evaluated: basal levels of ACTH, cortisol, androstenedione, dehydroepiandrosterone and 17-hydroxyprogesterone; urinary excretion of free cortisol; the cortisol response after short-term infusion of ACTH; the ACTH and cortisol response during insulin-induced hypoglycaemia. Total serum cholesterol decreased by 35.0 +/- 8.1% (P less than 0.001) and low-density lipoprotein (LDL) cholesterol by 39.8 +/- 9.8% (P less than 0.001); high-density lipoprotein (HDL) increased by 9.2 +/- 11.1% (P less than 0.001). Basal levels of ACTH were higher after simvastatin (2.9 +/- 1.9 pmol/l vs 4.1 +/- 2.9 pmol/l; P less than 0.05) whereas basal levels of steroid hormones were not significantly changed. The excretion of free cortisol was unaltered. The peak cortisol after ACTH infusion was lower after treatment (0.87 +/- 0.23 mumol/l vs 0.78 +/- 0.10 mumol/l; P less than 0.05), but was unaltered during insulin-induced hypoglycaemia. We conclude that simvastatin lowers serum cholesterol without clinically relevant effects on the adrenocortical steroid hormone secretion and the hypothalamic-pituitary-adrenal axis.     

RECOVERY FROM GLUCOCORTICOID INHIBITION OF THE RESPONSES TO CORTICOTROPHIN-RELEASING HORMONE

We have characterized the recovery of the hypothalamic-pituitary-adrenal (HPA) axis from inhibition by short-term prednisolone administration. Prednisolone was given in a dosage averaging 25 mg at 12 h intervals orally for up to 2 weeks to adult volunteers. Human corticotrophin releasing hormone (hCRH) tests were performed at 0901 h using a bolus injection of 1 microgram/kg before and 24-48 h after discontinuing the prednisolone. In the initial control study, hCRH stimulated a two-fold rise in plasma ACTH and a 30% rise in plasma cortisol within 30 min (ACTH rose from 18.5 +/- 4.5, SEM, pg/ml to 36.5 +/- 12.6 pg/ml and cortisol from 415 +/- 58 to 531 +/- 69 nmol/l in response to hCRH. One dose of prednisolone had no effect on the ACTH or cortisol response to hCRH administered 24 h later. Twenty-four hours after discontinuing a 1 week course of prednisolone, baseline plasma ACTH (3.9 +/- 0.6 pg/ml) and cortisol (146 +/- 17 nmol/l) were markedly suppressed, as was the cortisol response to hCRH (peak 198 +/- 22). However, the plasma ACTH response to hCRH was not significantly suppressed. Forty-eight hours after discontinuing prednisolone, the recovery of ACTH secretion was complete (baseline 10.9 +/- 4.2, peak 36.4 +/- 14.8 pg/ml), but the cortisol response to hCRH was still depressed (peak 294 +/- 66 nmol/l). Recovery from a 2 week course of prednisolone had similar characteristics except plasma cortisol was depressed more profoundly. Plasma dehydroepiandrosterone (DHA) during hCRH tests and dehydroepiandrosterone sulphate (DHAS) paralleled plasma cortisol.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of infused hypertonic saline on the response to insulin-induced hypoglycemia in man

We studied the influence of a hypertonic saline infusion on the counterregulatory response to insulin-induced hypoglycemia in nine normal men. When given hypertonic saline, the men had less hypoglycemia in response to insulin, both acutely and in the recovery phase (P less than 0.01), and released 34% more glucagon (P less than 0.05) than when they were water loaded. The total integrated ACTH, cortisol, epinephrine, norepinephrine, and GH responses to hypoglycemia were similar after saline and water loading. After the saline load, the mean plasma vasopressin level rose from 11.0 +/- 2.2 (+/- SEM) to 20.9 +/- 2.9 pg/mL in response to insulin-induced hypoglycemia. In contrast, after the water load, vasopressin levels were undetectable (less than 2 pg/mL) and they increased only to 2.6 +/- 0.4 pg/mL with hypoglycemia. There was a significant positive correlation between basal plasma vasopressin and nadir glucose concentrations and a significant negative correlation between basal plasma vasopressin and the integrated fall in glucose after insulin administration (P less than 0.01 and P less than 0.025, respectively). The difference in the glycemic response to insulin may be related to the high vasopressin levels after saline loading, which could, either directly and/or through enhanced glucagon release, increase hepatic glucose production and thus limit the hypoglycemic response to insulin.     

Corticotropin response to combined administration of human corticotropin-releasing hormone and small-dose arginine vasopressin in normal subjects.

Arginine vasopressin (AVP) is known to potentiate corticotropin (ACTH) secretion by human corticotropin-releasing hormone (hCRH), and a combined administration of hCRH and AVP appears useful as a pituitary ACTH reserve test. This study was designed to evaluate the appropriate dose of AVP and its route of administration, for better estimation of pituitary ACTH reserve in humans, when used in combination with a conventional hCRH stimulation test. First, intravenous (IV) doses of hCRH (100 micrograms) and AVP (0, 0.1, and 0.3 U) were administered simultaneously in six normal subjects. Second, IV hCRH was administered with intramuscular (IM) AVP (0, 1.0, 3.0, and 5.0 U) in 10 normal subjects. Blood samples for measurement of plasma ACTH were obtained at 0, 15, 30, 45, 60, 90, and 120 minutes after the hCRH with and without AVP administration. The order of AVP doses was randomly chosen in each subject. The peak plasma ACTH level was 65.0 +/- 16.0 pg/mL (30 minutes) with hCRH alone and 139.5 +/- 35.6 pg/mL (15 minutes) with hCRH plus 0.3 U IV AVP in six normal subjects. Similarly, the peak plasma ACTH level was 43.5 +/- 5.6 pg/mL (30 minutes) with hCRH alone and 116.0 +/- 19.6 (15 minutes) and 96.6 +/- 24.0 pg/mL (15 minutes) with hCRH plus 3.0 and 5.0 U IM AVP in 10 normal subjects, respectively. The hCRH-induced ACTH responses (delta ACTH) with both IV and IM AVP were significantly (P less than .05) greater than the respective control values with hCRH alone. The responses (delta ACTH) were comparable between the two phases of 3.0 and 5.0 U IM AVP.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of the specific serotonin antagonist ICI 169, 369 on the pituitary hormone response to insulin-induced hypoglycaemia in humans

OBJECTIVE: To examine the role of serotonin in pituitary hormone release by studying the effect of a specific 5HT2 receptor antagonist, ICI 169,369, on the ACTH, prolactin, growth hormone and AVP response to insulin-induced hypoglycaemia in healthy humans. DESIGN: A double-blind, within-subject trial using a crossover design to compare the effect of placebo with two doses of ICI 169,369 on pituitary hormone responses to insulin-induced hypoglycaemia. PATIENTS: Ten healthy subjects were studied in the low-dose (30 mg x 2) limb and 11 healthy volunteers in the high-dose (80 mg x 2) limb. MEASUREMENTS: Plasma concentrations of prolactin, growth hormone, ACTH, cortisol and AVP, and blood glucose. RESULTS: In the low-dose study, pretreatment with 30 mg ICI 169,369, 10 and 2 hours before the study, had no effect on the fall in blood glucose or the rise in plasma ACTH, prolactin, growth hormone, AVP or plasma cortisol following insulin injection, when compared with placebo. In the high-dose study the effect of a higher dose (80 mg) of ICI 169,369 on the pituitary hormone response to hypoglycaemia was compared with that of placebo. Although the fall in blood glucose was similar following drug (4.3 +/- 0.1 to 1.5 +/- 0.5 mmol/l, mean +/- SEM, P less than 0.001) and placebo (4.3 +/- 0.1 to 1.4 +/- 0.4 mmol/l, P less than 0.001), the rise in plasma AVP was lower (P less than 0.05) following pretreatment with drug (0.5 +/- 0.2 to 2.1 +/- 0.6 pmol/l, P less than 0.05) than with placebo (0.7 +/- 0.2 to 3.4 +/- 0.9 pmol/l, P less than 0.01). CONCLUSIONS: The ACTH, prolactin, growth hormone and cortisol responses were unaffected by ICI 169,369. The data are compatible with an inhibitory effect of the serotonin antagonist ICI 169,369 on the AVP, but not the ACTH, prolactin or growth hormone response to insulin-induced hypoglycaemia in humans.