Recombinant human IGF-I does not modify the ACTH and cortisol responses to hCRH and hexarelin, a peptidyl GH secretagogue, in humans

An inhibitory influence of insulin-like growth factor-I (IGF-I) on hypothalamus-pituitary-adrenal (HPA) axis has been hypothesized. In fact, it has been reported that the rhGH (recombinant human GH)-induced IGF-I increase inhibits both cortisol and GH response to MK-0677, a non-peptidyl GH secretagogue in animals. The aim of this study was to further clarify the inhibitory role, if any, of IGF-I on corticotroph function. We studied the effect of rhIGF-I (recombinant human IGF-I; 20 microg/kg s.c. at -180 min) or placebo on the ACTH and cortisol responses to hCRH (human CRH; 2.0 microg/kg i.v. at 0 min) or hexarelin (HEX; 2.0 microg/kg i.v. at 0 min), a peptidyl GHS, in normal young women. The effect of rhIGF-I on the GH response to HEX was also studied. The subjects were six normal young women [age: 26-35 yr; body mass index (BMI): 19-23 kg/m2] in their early follicular phase. The results showed that after s.c. rhIGF-I administration, circulating IGF-I levels increased approximately 77%, peaking at -60 min and persisting similar up to +120 min. The mean ACTH, cortisol and GH concentrations did not change from -180 to 0 min when evaluated after both placebo or rhIGF-I. CRH and HEX induced similar ACTH (peak vs baseline, mean+/-SE: 47.5+/-10.9 vs 21.3+/-3.0 pg/ml and 30.3+/-6.9 vs 19.2+/-3.8 pg/ml, respectively; p<0.04) and cortisol responses (177.5+/-5.4 vs 109.3+/-10.3 microg/l and 149.4+/-12.3 vs 119.8+/-16.4 microg/l, respectively, p<0.04). RhIGF-I pretreatment did not modify the ACTH and cortisol responses to hCRH (46.0+/-13.8 pg/ml and 181.1+/-16.9 microg/l, respectively) as well as those to HEX (28.8+/-5.0 pg/ml and 144.1+/-16.2 microg/l, respectively). On the other hand, the GH response to HEX was clearly reduced by rhIGF-I (23.9+/-4.7 vs 64.7+/-14.8 microg/l, p<0.05). Our findings show that rhIGF-I-induced increase of circulating IGF-I levels exerts negative feedback action on somatotroph secretion, while it does not modify the corticotroph and the adrenal responsiveness to CRH or hexarelin.     

Effects of the combined administration of hexarelin, a synthetic peptidyl GH secretagogue, and hCRH on ACTH, cortisol and GH secretion in patients with Cushing's disease

Hexarelin (HEX) is a peptidyl GH secretagogue (GHS) which markedly stimulates GH release but, like other GHS, possesses also CNS-mediated ACTH- and cortisol-releasing activity. Interestingly, the stimulatory effect of HEX on ACTH and cortisol release is exaggerated and higher than that of hCRH in patients with Cushing's disease (CD). To further clarify the mechanisms by which HEX stimulates the activity of hypothalamo-pituitary-adrenal (HPA) axis in man, in 6 patients with CD (6 women, 38-68 yr old) and in 7 control subjects (CS, 7 women, 22-29 yr old) we studied the effects of HEX (2.0 microg/kg i.v.) and/or hCRH (2.0 microg/kg i.v.) on ACTH and cortisol (F) secretion. The GH responses to HEX alone and combined with hCRH were also studied in all subjects. Basal ACTH and F levels in CD were higher than in CS (66.3+/-5.1 vs 16.5+/-0.6 pg/ml and 217.8+/-18.5 vs 134.4+/-4.6 microg/l, respectively; p<0.02). In CS, the ACTH and F responses to HEX, evaluated as deltaAUC (mean+/-SE: 128.7+/-39.2 pg x min/ml and 328.5+/-93.2 microg x min/l, respectively) were lower, though not significantly, than those after hCRH (375.8+/-128.4 pg x min/ml and 1714.2+/-598.0 microg x min/l, respectively), though the peak ACTH and F responses to both stimuli were similar. The co-administration of HEX and hCRH had an additive effect on both ACTH (1189.6+/-237.2 pg x min/ml) and F secretion (3452.9+/-648.6 microg x min/l). In fact, the ACTH and F responses to HEX+/-hCRH were significantly higher (p<0.01) than those elicited by single stimuli. In CD, HEX induced ACTH and F responses (3603.8+/-970.7 pg x min/ml and 10955.9+/-6184.6 microg x min/l, respectively) clearly higher (p<0.002) than those in CS. The HEX-induced ACTH and F responses in CD were higher, though not significantly, than those recorded after hCRH (1432.7+/-793.5 pg x min/ml and 4832.7+/-2146.5 microg x min/l, respectively). On the other hand, the hCRH-induced ACTH and F responses in CD were similar to those in CS. In CD, the coadministration of HEX and hCRH had an additive effect on ACTH (8035.7+/-1191.1 pg x min/ml) but not on F (10985.4+/-3900.8 microg x min/l) secretion. In fact, the ACTH, but not the F response to HEX+hCRH was significantly higher (p<0.02) than that elicited by single stimuli. In conclusion, the present study demonstrates that in patients with Cushing's disease as well as in subjects control Hexarelin and hCRH have an additive effect on ACTH secretion. Considering that, at least in humans, differently from hCRH, GHS have no interaction with AVP, our present findings further agree with the hypothesis that the ACTH-releasing activity of GHS is, at least partially, independent of CRH-mediated mechanisms.     

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)     

Free fatty acids exert an inhibitory effect on adrenocorticotropin and cortisol secretion in humans

Free fatty acid (FFA) administration stimulates the hypothalamic-pituitary-adrenal (HPA) axis in rats, suggesting that the HPA axis and lipolysis may be linked by a positive-feedback loop. To clarify the influence of FFA on the HPA axis in humans, we studied the effect of lipid load on both basal and stimulated ACTH and cortisol secretion in normal subjects. In six young female volunteers [(mean +/- SEM) age, 24.4 +/- 2.1 yr; body mass index, 23.1 +/- 1.2 kg/m(2)), ACTH, cortisol, FFA, glucose, and insulin levels were measured every 30 min for 330 min during the following procedures: 1) i.v. saline infusion (from 0 to 330 min); 2) i.v. FFA infusion (Intralipid 10%, from 0 to 210 min) followed by saline infusion (from 210 to 330 min); 3) human CRH (hCRH) administration (2 microg/kg i.v. at 90 min) during saline infusion (from 0 to 330 min); and 4) hCRH administration during FFA infusion (Intralipid 10%, from 0 to 210 min, followed by saline infusion from 210 to 330 min). During saline infusion, ACTH and cortisol levels progressively declined. Lipid-heparin emulsion (LHE) infusion strikingly increased circulating FFA levels and, simultaneously, amplified the ACTH and cortisol decrease (P < 0.05). After LHE withdrawal, FFA decrease was associated with an increase (P < 0.05) in ACTH and cortisol levels (restored to baseline values within 60 min). The ACTH and cortisol responses to hCRH, however, were unaffected by LHE that, concomitantly, induced an increase (P < 0.05) in glucose but not in insulin levels. This study shows that an LHE-induced increase in FFA levels has an inhibitory effect on spontaneous ACTH and cortisol secretion in humans. Lipid load, however, does not affect the ACTH and cortisol responses to hCRH; this evidence would indicate that the negative influence of FFA on the HPA axis in humans takes place at the suprapituitary level.     

The relationship of saline-induced changes in vasopressin secretion to basal and corticotropin-releasing hormone-stimulated adrenocorticotropin and cortisol secretion in man

To investigate the effect of endogenous arginine vasopressin (AVP) on ACTH secretion, normal subjects were given infusions of either hypertonic saline (HS) or isotonic saline (NS) combined with human corticotropin-releasing hormone (CRH) or placebo. Basal plasma AVP was 2.3 +/- 0.3 (+/- SE) pg/ml, did not change with NS treatment, and rose to 5.4 +/- 0.6 pg/ml during HS infusion (P less than 0.01). Both basal and CRH-stimulated plasma ACTH and cortisol concentrations increased during HS infusion. Peak plasma ACTH and cortisol levels were 11.4 +/- 1.5 pg/ml and 8.6 +/- 0.8 micrograms/dl, respectively, during the HS (plus placebo) infusion. During the NS (plus placebo) infusion, plasma ACTH and cortisol gradually declined to 6.8 +/- 0.5 pg/ml and 2.6 +/- 0.4 micrograms/dl. The timing of the rise in ACTH during the HS infusion paralleled the rise in AVP. When an iv dose of 1 microgram/kg CRH was administered during the saline infusions, peak plasma ACTH and cortisol levels were 27.7 +/- 6.3 pg/ml and 17.5 +/- 1.0 micrograms/dl, respectively, during the HS infusion and 15.6 +/- 1.7 pg/ml and 13.4 +/- 1.2 micrograms/dl during the NS infusion. When the areas under the hormone response curves were compared, CRH stimulated ACTH and cortisol secretion to a greater extent than did HS (P less than 0.05). The hormonal stimulation due to combined CRH and hypertonic saline was greater than that attributable to either factor alone (P less than 0.025), but was not different than the sum of the effects of the individual factors. These results indicate that increases in endogenous AVP produced by HS are associated with increases in both basal and CRH-stimulated ACTH and cortisol release. The effect of HS appears to be additive to but not consistently synergistic with the effect of CRH.     

The corticotropin-releasing hormone test in normal short children: comparison of plasma adrenocorticotropin and cortisol responses to human corticotropin-releasing hormone and insulin-induced hypoglycemia

The human corticotropin-releasing hormone (hCRH) tests were performed in twelve normal short children, and the responses of plasma ACTH and cortisol to iv administration of 1 micrograms/kg hCRH were compared with those to insulin-induced hypoglycemia. After administration of hCRH, the mean plasma ACTH level rose from a basal value of 3.3 +/- 0.4 pmol/l (mean +/- SEM) to a peak value of 9.2 +/- 0.8 pmol/l at 30 min, and the mean plasma cortisol level rose from a basal value of 231 +/- 25 nmol/l to a peak value of 546 +/- 30 nmol/l at 30 min. The ACTH response after insulin-induced hypoglycemia was greater than that after hCRH administration; the mean peak level (P less than 0.01), the percent maximum increment (P less than 0.01), and the area under the ACTH response curve (P less than 0.01) were all significantly greater after insulin-induced hypoglycemia than those after hCRH administration. Although the mean peak cortisol level after insulin-induced hypoglycemia was about 1.3-fold higher than that after hCRH administration (P less than 0.01), neither the percent maximum increment in plasma cortisol nor the area under the cortisol response curve after insulin-induced hypoglycemia was significantly different from that after hCRH administration. Consequently, the acute increases in plasma ACTH after the administration of 1 microgram/kg hCRH stimulated the adrenal gland to almost the same cortisol response as that obtained with a much greater increase in plasma ACTH after insulin-induced hypoglycemia. These results suggest that a plasma ACTH peak of 9-11 pmol/l produces near maximum acute stimulation of adrenal steroidogenesis.     

GHRP-6 is able to stimulate cortisol and ACTH release in patients with Cushing's disease: comparison with DDAVP

It has been shown that hexarelin stimulates ACTH and cortisol secretion in patients with Cushing's disease. The ACTH release induced by this peptide is 7-fold greater than that obtained by hCRH. The mechanism of action of hexarelin on the hypothalamic-pituitary-adrenal axis has not been fully elucidated. Although controversial, there is evidence that it might be mediated by arginine vasopressin (AVP). The aim of this study was to evaluate the ACTH and cortisol releasing effects of GHRP-6 in patients with Cushing's disease and to compare them with those obtained with DDAVP administration. We studied 10 patients with Cushing's disease (8 female, 2 male; age: 36.7 +/- 4.2 yr), 9 with microadenomas, who were submitted to both GHRP-6 (2 microg/kg iv) and DDAVP (10 micro g i.v.) in bolus administration on 2 separate occasions. ACTH was measured by immunochemiluminometric assay and cortisol by radioimmunoassay. The sensitivities of the assays are 0.2 pmol/l for ACTH, and 11 nmol/l for cortisol. GHRP-6 was able to increase significantly both ACTH (pmol/l, mean +/- SE; basal: 15.5 +/- 1.7 vs peak: 45.1 +/- 9.3) and cortisol values (nmol/l, basal: 583.0 +/- 90.8 vs peak: 1013.4 +/- 194.6). ACTH AUC (pmol/l min(-1)) and cortisol AUC (nmol/l min(-1)) values were 1235.4 and 20577.2, respectively. After DDAVP administration there was a significant increase in ACTH (basal: 13.0 +/- 1.4 vs peak: 50.5 +/- 16.2) and cortisol levels (basal: 572.5 +/- 112.7 vs peak: 860.5 +/- 102.8. AUC values for ACTH and cortisol were 1627.6 +/- 639.8 and 18364.7 +/- 5661.4, respectively. ACTH and cortisol responses to GHRP-6 and DDAVP did not differ significantly (peak: 45.1 +/- 9.3 vs 50.5 +/- 16.2; AUC: 1235.4 +/- 424.8 vs 1627.6 +/- 639.8). There was a significant positive correlation between peak cortisol values after GHRP-6 and DDAVP administration (r = 0.87, p = 0.001). Our results show that GHRP-6 is able to stimulate ACTH and cortisol release in patients with Cushing's disease. These responses are similar to those obtained after DDAVP injection. These findings could suggest the hypothesis that both peptides act by similar mechanisms, either at hypothalamic or pituitary level.     

ACTH and cortisol responses to glucagon stimulation.

The effect of the intramuscular injection of various doses of glucagon in 15 healthy subjects was studied. Significant elevations of plasma ACTH, and cortisol were found to occur 3 h after the administration of 4 mg of crystalline glucagon. Mean levels in 7 subjects were for ACTH 44 +/- 30 (SD) pg/ml, and for cortisol 14 +/- 6 (SD) mug/100 ml at the beginning of the test, and rose to 109 +/- 48 (SD) pg/ml and to 23 +/- 5 (SD) mug/100 ml respectively following glucagon. The peak response of ACTH and cortisol was preceded by a significant rise of plasma insulin, by a fall of the blood glucose, which was initially increased by the administration of glucagon, and by the symptoms of nausea and sweating. This study demonstrates that the intramuscluar administration of glucagon (4 mg) provids a potent stimulus to ACTH and cortisol secretion in healthy subjects.     

Plasma adrenocorticotrophin, cortisol and aldosterone responses to ovine corticotrophin-releasing factor and vasopressin in sheep

Ovine corticotrophin-releasing factor (oCRF) (1 microgram/kg) and arginine vasopressin (AVP) (1 microgram/kg) were injected iv in sheep, both separately and in combination. Plasma levels of immunoreactive ACTH (IR-ACTH), cortisol, and aldosterone were measured for 3 h after the injections. Mean levels before injections were 8 +/- 4 pmol/l for ACTH, 7 +/- 3 nmol/l for cortisol, and 28 +/- 9 pmol/l for aldosterone. CRF caused a rapid rise in IR-ACTH and a peak level of 125 +/- 52 pmol/l was obtained 15 min after injection. Highest values for cortisol and aldosterone levels were 40 +/- 9 nmol/l and 64 +/- 13 pmol/l, respectively, 30 min after injection. AVP also increased IR-ACTH (maximum level: 202 +/- 77 pmol/l at 5 min) and aldosterone (128 +/- 36 pmol/l at 15 min), whereas the cortisol increase was lower than after CRF. Simultaneous injection of CRF and AVP produced an addition of the IR-ACTH response (295 +/- 82 pmol/l at 15 min), but the changes in cortisol levels were similar to those obtained after CRF alone and those in aldosterone levels resembled those induced by AVP alone. Plasma Na and K, osmolality, and plasma renin activity (PRA) were not modified by either CRF or AVP. It is suggested that the increase in aldosterone levels after CRF could be mediated by ACTH and that after AVP by an IR-ACTH peptide with less effect on cortisol secretion.     

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)     

Alprazolam, a benzodiazepine, blunts but does not abolish the ACTH and cortisol response to hexarelin, a GHRP, in obese patients

GH secretagogues (GHS) act on specific receptors at the pituitary and hypothalamic level and possess potent GH-releasing activity but also stimulate prolactin (PRL), ACTH and cortisol (F) secretion. However, hyperactivity of the HPA axis in obesity has been reported. The objective of this study was to clarify the endocrine activity of GHS in obesity. In nine obese patients (obese OB), 9 F, age, (34.8 +/- 3.7 y, body mass index (BMI), 35.0 +/- 2.2 kg/m2; WHR, 0.9 +/- 0.02), 14 controls (normal subjects, NS), 14 F, 30.4 +/- 0.9 y, 20.0 +/- 0.4 kg/m2), we studied the ACTH, F and GH responses to hexarelin (HEX, 2.0 microg/kg), a peptidyl GHS, alone and preceded by alprazolam (ALP, 0.02 mg/kg), and a benzodiazepine which has an inhibitory effect on corticotroph secretion. The HEX-induced ACTH response in OB was higher than that in n.s., but this difference did not attain statistical significance. In n.s. the HEX-induced ACTH response was abolished by ALP (P < 0.03) which, however, only blunted that in OB (P < 0.02). The GH response to HEX in OB was lower (P < 0.02) than that in n.s.. ALP blunted the GH response to HEX in n.s. (P < 0.03) while it did not modify that in OB. The GABAergic activation by alprazolam abolishes the ACTH response to hexarelin in normal subjects, while it only blunts that in obese subjects. Moreover, alprazolam blunts the GH response to hexarelin in normal but not in obese subjects. Thus, obese patients show partial refractoriness to the inhibitory effect of alprazolam on both corticotroph and somatotroph function.     

ACTH and vasopressin responses to insulin-induced hypoglycemia in intact and neurohypophysectomized conscious dogs.

Factors from the neurohypophysis are important in the control of anterior pituitary function. This study evaluated the hypothesis that the neurophypophysis is an integral component of the adrenocorticotropin (ACTH) response to certain stimuli. Furthermore, we investigated the possibility that the importance of the neurohypophysis during corticotropic stimuli can be classified by the magnitude of the systemic vasopressin response induced. The ACTH response to insulin-induced hypoglycemia (INS), nitroprusside hypotension (NP), or ovine corticotropin-releasing factor (CRF) infusion (20 ng/kg/min) was measured in dogs before (intact) and greater than 2 weeks after selective transbuccal neurohypophysectomy (NHX). INS (0.2 U/kg) resulted in a significant decrease in plasma glucose from 93 +/- 1 to 33 +/- 2 mg/dl at 30 min and a significant increase in plasma ACTH from 53 +/- 10 to 306 +/- 33 pg/ml in intact dogs whereas the vasopressin (AVP) response was small (2.8 +/- 0.3 to 5.5 +/- 0.7 pg/ml). NHX had no effect on the blood glucose or ACTH response to INS. NP resulted in large increases in ACTH from 54 +/- 8 to 351 +/- 89 pg/ml and in AVP from 2.7 +/- 0.2 to 272 +/- 98 pg/ml. In contrast to INS, NHX significantly attenuated the ACTH and AVP responses to NP. The ACTH response to CRF was not attenuated by NHX, indicating normal pituitary corticotropic function. In summary, NHX attenuated the ACTH response to hypotension (large peripheral AVP response) but not to INS or CRF (small peripheral AVP response).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of an antiserotoninergic drug, metergoline, on the ACTH and cortisol response to insulin hypoglycemia and lysine-vasopressin in man.

The effect of metergoline, a specific antiserotoninergic drug, on ACTH secretion was investigated in 29 normal volunteers and in 4 patients with increased ACTH production (3 with Addison's disease, 1 with Cushing's disease). In 15 normal subjects, a 4-day treatment with 10 mg daily of metergoline significantly blunted the ACTH response to insulin hypoglycemia. Mean peak ACTH values before and after treatment were, respectively, 333 +/- 39.2 (SE) and 235 +/- 38.8 pg/ml (P less than 0.05). The corresponding values of plasma cortisol were 29.6 +/- 2.96 and 20.5 +/- 2.67 mug/100 ml (P less than 0.05). In contrast, metergoline failed to affect the ACTH response to lysine-vasopressin (LVP) administered iv (8 subjects studied) and im (6 subjects studied). In 3 patients suffering from Addison's disease, an appreciable although not statistically significant lowering of the plasma ACTH levels was noted during metergoline administration. The mean pre- and post-treatment values of plasma ACTH in these patients were, respectively, 1116 +/- 192.2 and 666 +/- 100.8 pg/ml, 4240 +/- 50.0 and 3398 +/- 368.0 pg/ml, and 431 +/- 44.0 and 352 +/- 23.9 pg/ml. In one patient with Cushing's disease caused by a pituitary adenoma, metergoline did not appreciably modify plasma ACTH levels. Taken together, these results lend support to the concept of a physiological stimulating effect of serotonin on ACTH secretion. Moreover, they are compatible with the view that serotonin exerts its action chiefly at the hypothalamic level while LVP promotes ACTH release by a primary action on the pituitary.     

Glucagon administration elicits blunted GH but exaggerated ACTH response in obesity

Reduction in both spontaneous and stimulated GH secretion in obesity has been clearly demonstrated. Mild hyperactivity of hypothalamus-pituitary-adrenal (HPA) axis has been also reported. Glucagon, at least after im administration, induces clear increase in either GH or ACTH and F levels but its effect on somatotroph and corticotroph secretion in obesity has never been studied. In 7 patients with abdominal obesity (OB, aged 24-42 yr, BMI: 29.1-43.9 kg/m2, waist/hip ratio [WHR]: 0.86-1.00) we studied the GH, ACTH and F responses to the im administration of glucagon (0.017 mg/kg at 0 min). The results in OB were compared with those in a group of 6 age-matched controls normal subjects (Ns aged 26-32 yr, BMI 19.7-22.5 kg/m2). In Ns glucagon administration induced clear increase in GH (peak vs baseline, mean+/-SE: 11.6+/-3.4 vs 3.3+/-0.7 microg/l, p<0.02), and ACTH (52.9+/-15.2 vs 19.0+/-1.5 pg/ml, p<0.02) levels which peaked at +150 and +165 min, respectively. Increase in F levels (222.3+/-23.8 vs 158.3+/-7.0 ng/ml, p<0.05) was also recorded but peaked at +180 min. In OB glucagon administration induced GH response (7.4+/-2.3 vs 0.8+/-0.6 microg/l) lower (p<0.05) than that recorded in Ns; when the GH responses were evaluated by co-variance analysis, a significant difference between the 2 groups was recorded in term of peaks but not of AUCs. On the other hand, the ACTH response to glucagon in OB was higher than that in Ns (11452.6+/-2447.7 vs 4892.2+/-719.4 pg/ml x min, p<0.05). The F response to glucagon in OB and Ns was, however, similar (24057.9+/-4109.1 vs 29835.9+/-1566.0 ng/ml x min). In conclusion, this study demonstrates that in obese patients the im administration of glucagon elicits blunted GH response but exaggerated ACTH increase which is uncoupled with the adrenal response. These findings agree with the existence of concomitant GH insufficiency and altered corticotroph function in obesity.     

Agouti-related protein stimulates the hypothalamic-pituitary-adrenal (HPA) axis and enhances the HPA response to interleukin-1 in the primate

alpha-MSH antagonizes many of the immune and neuroendocrine effects induced by inflammatory cytokines. Studies have shown that alpha-MSH attenuates the stimulatory effect of IL-1 on the hypothalamic-pituitary-adrenal (HPA) axis and plays a physiological role in limiting the HPA response to IL-1. Recently an alpha-MSH antagonist, agouti-related protein (AGRP), has been identified in the hypothalamus, which stimulates food intake by antagonizing the effects of alpha-MSH at specific melanocortin receptors. It is unknown whether AGRP can also modulate neuroendocrine responses to inflammatory cytokines. We have therefore examined the effects of AGRP on the HPA axis and on prolactin (PRL) at baseline and in response to stimulation by IL-1 beta in nine ovariectomized rhesus monkeys. In the first study, the effects of intracerebroventricular (i.c.v) infusion of 20 microg (n = 6) and 50 micro g (n = 4) of human AGRP (83-132)-NH(2) were compared with icv saline infusion. There was a significant stimulatory effect of 20 microg AGRP on cortisol release over time (P < 0.001). The area under the hormone response curve (AUC) for cortisol increased by 29% after 20 microg AGRP vs. saline; the AUC for ACTH increased by 166% (P = 0.028); the AUC for PRL increased by 108% (P = 0.046). There was a significant stimulatory effect of 50 microg AGRP on ACTH (P < 0.001), cortisol (P < 0.001), and PRL (P < 0.001) release over time. The AUC for ACTH after 50 microg AGRP increased by 98%; the AUC for cortisol increased by 37%; the AUC for PRL increased by 161%. The effects of AGRP on ACTH, cortisol, and PRL release were prevented by alpha-MSH infusion. In the second study, animals received icv either 50 ng of human IL-1 beta or 20 microg of AGRP followed by 50 ng IL-1 beta. AGRP significantly enhanced the ACTH (P < 0.05) response to IL-1 beta. The peak ACTH response to IL-1 beta alone was 124 +/- 55 pg/ml vs. 430 +/- 198 pg/ml after IL-1 beta plus AGRP; the peak cortisol response was 70 +/- 8.2 microg/dl vs. 77 +/- 6.2 microg/dl, but this was not significantly different. In conclusion, AGRP stimulated ACTH, cortisol, and PRL release in the monkey and enhanced the ACTH response to IL-1 beta. These studies suggest that, in addition to its known orexigenic effects, AGRP may play a role in neuroendocrine regulation and specifically that AGRP may interact with alpha-MSH to modulate neuroendocrine responses to inflammation.     

Elderly subjects show severe impairment of dehydroepiandrosterone sulphate and reduced sensitivity of cortisol and aldosterone response to the stimulatory effect of ACTH(1-24)

OBJECTIVE: Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis in ageing has been reported both in humans and in animals and may be involved in age-related changes in body composition, structure functions and metabolism, as well as in brain ageing. Despite the supposed HPA hyperactivity and its refractoriness to negative glucocorticoid feedback, low levels of dehydroepiandrosterone (DHEA) and its sulphate have been clearly demonstrated in human ageing and may suggest another cause of age-related changes in structure function and metabolism. Thus, our aim was to verify the adrenal responsiveness to various ACTH doses in normal elderly subjects. DESIGN: We studied cortisol (F), aldosterone (A) and DHEA responses to the sequential administration of very low, low and supramaximal ACTH1-24 doses (0.06 microg or 0.5 microg followed by 250 microg ACTH1-24 i.v. at 0 and +60 minutes) in healthy elderly subjects (ES) [six females and two males, aged 63-75 years, body mass index (BMI) 22-26 kg/m2]. The results in ES were compared with those recorded in healthy young subjects (YS) (six females and six males, aged 22-34 years, BMI 20-25 kg/m2). RESULTS: Basal DHEA levels in ES were lower (P < 0.05) than in YS, while F and A levels were similar in both groups. DHEA, F and A responses to ACTH were dose-dependent in both groups. In ES, however, DHEA levels showed no response to the 0.06 microg dose, a modest increase after 0.5 microg and a clearer rise after 250 microg ACTH; at any dose, the DHEA response in ES was clearly lower than in YS (P < 0.04). The F responses to 0.5 microg and 250 microg ACTH in ES were similar to those in YS; whereas, in ES, 0.06 microg ACTH elicited a non significant F increase which was significantly lower than in YS (P < 0.05). Similarly, the A responses to the highest ACTH doses were similar in both groups but, in ES, 0.06 microg ACTH elicited no increase in A secretion, which was clearly lower than in YS (P < 0.03). CONCLUSIONS: Normal elderly subjects show severe reduction of DHEA response to a wide range of ACTH doses, in agreement with peculiar impairment of the activity of the adrenal reticularis zone in ageing. In contrast to young adults, elderly subjects also show no cortisol and aldosterone response to a very low ACTH dose. This evidence indicates a reduced sensitivity to ACTH in the fasciculata and glomerulosa zones of the adrenal gland in ageing.     

Regulation of basal adrenocorticotropin and cortisol secretion by arginine vasopressin in the fetal sheep during late gestation.

This study tested the hypothesis that arginine vasopressin (AVP) is involved in the regulation of basal ACTH secretion in the ovine fetus near term. In five fetuses challenged with AVP (1 microgram/ml, iv bolus) plasma ACTH concentrations increased to an 8-fold peak within 10 min of the preceding baseline (55 +/- 6 to 403 +/- 241 pg/ml). Cortisol in fetal circulation subsequently increased 2-fold (11 +/- 1 to 28 +/- 5 ng/ml) within 15 min of the AVP injection. The AVP-induced rise in plasma ACTH and cortisol concentrations was blocked when the fetus was pretreated with the AVP V1 receptor antagonist d(Ch2)5Tyr(Me)AVP. In a total of seven studies, antagonist (10 micrograms/kg estimated BW, iv bolus) was administered to three fetuses, aged 137-147 days gestation, followed 40 min later by the exogenous AVP challenge, as described above. After AVP antagonist treatment, basal ACTH and cortisol concentrations were not significantly different from the preinjection baseline levels (P greater than 0.05, by analysis of variance). Moreover, plasma ACTH and cortisol remained unchanged after the AVP challenge. To further define the role of endogenous AVP in basal ACTH and cortisol secretion, the AVP antagonist was administered (five studies in two fetuses) at 30-min intervals for a total of three injections per fetus. This extended AVP antagonist regimen also failed to alter fetal circulating concentrations of ACTH or cortisol (P greater than 0.05). Cortisol in the maternal circulation was not affected by any of the fetal AVP or AVP antagonist treatments. Lambs were born at 146 +/- 2 days gestation (n = 5), within the range for the normal duration of pregnancy. These data do not support the hypotheses that AVP is involved in the regulation of basal ACTH secretion in the fetal sheep during the 10 days preceding parturition. Rather, the ability of AVP antagonist to block the AVP-induced rise in plasma ACTH and cortisol in the fetus suggests that basal and stimulated ACTH secretion are under separate regulatory mechanisms.     

Beta-endorphin attenuates the serum cortisol response to exogenous adrenocorticotropin

Controversy surrounds the issue of whether beta-endorphin affects adrenal steroidogenesis. Recent work has both supported and refuted the claim that beta-endorphin stimulates a rise in serum aldosterone. We investigated the role of beta-endorphin in adrenal steroidogenesis by examining its potential modulation of the response of serum cortisol to exogenous ACTH (Cosyntropin). Four of five normal men received: 1) synthetic beta-endorphin (1 microgram/kg X min) for 30 min, followed by a bolus dose of 0.2 micrograms ACTH; 2) beta-endorphin (100 micrograms, iv), followed by 0.2 micrograms ACTH iv; 3) 0.2 micrograms ACTH iv; and 4) beta-endorphin (100 micrograms iv) alone. The integrated cortisol response to exogenous ACTH, calculated as the area under the cortisol response curve, was significantly less when the ACTH infusion was preceded by the 30-min beta-endorphin infusion than when administered alone [163 +/- 50 (SE) microgram/dl X min vs. 282 +/- 51 micrograms/dl X min, respectively; P less than 0.01]. By contrast, there was no difference between the integrated cortisol response to exogenous ACTH alone and exogenous ACTH after the bolus dose of beta-endorphin (282 +/- 51 vs. 293 +/- 39 micrograms/dl X min, respectively). Beta-Endorphin (30-min infusion or 100-micrograms bolus dose alone) caused no change in serum aldosterone, dehydroepiandrosterone, or PRA. Serum PRL levels, however, were raised significantly (P less than 0.05) by the 30-min infusion of beta-endorphin. The infusion and bolus doses of beta-endorphin raised plasma beta-endorphin levels to over 100,000 pg/ml and 5,000 pg/ml, respectively. We conclude that very high plasma levels of beta-endorphin may influence the response of cortisol to ACTH through a direct effect on the adrenal cortex. However, even in disease states such as Addison's and Nelson's diseases, such levels of plasma beta-endorphin are not known to be achieved.     

Corticotropin-releasing effect of hexarelin, a peptidyl GH secretagogue, in normal subjects pretreated with metyrapone or RU-486, a glucocorticoid receptor antagonist, and in patients with Addison's disease.

GH secretagogues (GHS) are peptidyl and nonpeptidyl molecules which possess strong GH-releasing activity but also stimulatory effect on hypothalamo-pituitary-adrenal axis. The ACTH and cortisol responses to Hexarelin (HEX), a peptidyl GHS, are abolished by low-dose dexamethasone pretreatment in normal subjects but are exaggerated and higher than those after hCRH in patients with pituitary ACTH-dependent Cushing's disease, in spite of their hypercortisolism. Based on the foregoing, we studied the ACTH, cortisol and GH responses to HEX (2.0 microgram/kg i.v. at 0 min) alone and after metyrapone (2 g p.o. at 23:00 h the night before) or RU-486 (400 mg p.o. at 02:00 h), a glucocorticoid receptor antagonist, in 6 normal women (NS, age 26-34 years). The endocrine responses (mean +/- SEM) to HEX alone were also studied in 8 patients with Addison's disease (AD, 6 males, 2 females, age 30-77 years; last hydrocortisone administration the day before testing). In NS, HEX stimulated basal ACTH (peak, mean +/- SEM: 26.0 +/- 7.8 vs. 10.7 +/- 2.0 pg/ml, p < 0. 05), cortisol (163.2 +/- 18.3 vs. 137.4 +/- 15.4 microgram/l, p < 0.05) and GH (72.6 +/- 23.5 vs. 3.7 +/- 1.3 microgram/l, p < 0.01) levels. Metyrapone markedly increased basal ACTH (294.4 +/- 61.6 pg/ml, p < 0.05), reduced basal cortisol (19.6 +/- 7.2 microgram/l, p < 0.05), while it did not modify GH levels. After metyrapone pretreatment the ACTH response to HEX was clearly increased (DeltaAUC: 2,857.4 +/- 901.9 vs. 367.3 +/- 274.0 pg/ml/h, p < 0.05), while the GH response was not modified. HEX did not stimulate the low cortisol levels after metyrapone pretreatment. RU-486 significantly increased basal ACTH (76.6 +/- 12.5 pg/ml, p < 0.05) and cortisol (312.7 +/- 22.2 microgram/l, p < 0.05), while it did not modify basal GH levels. RU-486 pretreatment did not modify the ACTH, cortisol and GH responses to HEX. In AD, HEX elicited a marked ACTH response (6,619.4 +/- 3,365.8 pg/ml/h; p < 0.01), which was clearly higher (p < 0.01) than that in NS after HEX alone but not significantly different from that after HEX+MET. The GH response to HEX in AD (1,325.6 +/- 284.1 microgram/l/h) was similar to that in NS (1,519.7 +/- 483.8 microgram/l/h). In conclusion, our present data demonstrate that the ACTH-releasing activity of HEX is increased in primary hypoadrenalism as well as in normal subjects after metyrapone but not after RU-486 pretreatment. These findings indicate that in normal subjects as well as in hypocortisolemic patients the ACTH-releasing activity of GHS is enhanced by the lack of negative glucocorticoid feedback.     

Development of pituitary-adrenal endocrine function in the marmoset monkey: infant hypercortisolism is the norm

Early life stress, involving activation of the hypothalamic-pituitary-adrenal (HPA) system, is associated with altered functioning of stress-related systems in adulthood. In the rat, postnatal development is characterized by low basal HPA activity and stress hyporesponsiveness, and infant exposure to atypical glucocorticoid levels leads to chronic alteration of HPA function and HPA-dependent peripheral and central processes. There have been few studies of primate HPA ontogeny, and here we report a study of changes in pituitary-adrenal function between birth and adulthood in the common marmoset monkey. In this simian primate, basal plasma ACTH and cortisol levels were actually elevated in neonates (ACTH, 141 +/- 28 pg/ml; cortisol, 1903 +/- 326 microg/dl) and wk 4 infants (ACTH, 114 +/- 9 pg/ml; cortisol, 290 +/- 8 microg/dl) relative to month 2 infants, juveniles (month 6), subadults (month 12), and adults (>2 yr; ACTH, 37 +/- 4 to 61 +/- 8 pg/ml; cortisol, 101 +/- 2 to 195 +/- 4 microg/dl). In contrast to older life stages, neonates lacked circadian change in their plasma cortisol levels, and this state of consistently high cortisol was associated with large adrenal glands in addition to high ACTH levels. Cerebrospinal fluid cortisol levels were, in accord with plasma levels, higher in wk 4 infants than in juveniles and subadults. In terms of stress response, month 2 infants demonstrated ACTH and cortisol peak stress responses similar to those at older life stages (infant stress cortisol, 185 +/- 36% of basal; subadult stress cortisol, 174 +/- 6% of basal); whereas infant ACTH recovery was also similar to that in older subjects, their cortisol poststress recovery was retarded. This primate, it is proposed, provides an excellent complementary model in which to test hypotheses derived from the rat model relating to HPA system ontogeny and the chronic effects and biomedical implications of hypercorticoidism during early life.