Repetitive and continuous administration of human corticotropin releasing factor to human subjects

ACTH secretion was studied in response to repetitive and continuous administration of human corticotropin releasing factor (CRF) in 14 healthy volunteers and 2 patients with secondary adrenal insufficiency. ACTH increases during repetitive CRF administration were within the same range in normal subjects independent of the intervals (60-180 min) between the CRF pulses (100 micrograms iv). When CRF was infused continuously (100 micrograms/h for 3 h) after an initial CRF bolus injection (100 micrograms iv), ACTH and cortisol remained elevated during the infusion at a nearly constant level (ACTH: 60 +/- 5 pg/ml; cortisol: 21.2 +/- 1 micrograms/dl; means +/- SE). A second CRF bolus injection at the end of the infusion did not lead to a significant further increase of ACTH and cortisol levels. This shows that there is no desensitisation or depletion of a ready releasable pool, as it is observed with other pituitary hormones after releasing hormone stimulation. Pulsatile administration of CRF in 2 patients with secondary adrenal insufficiency due to previous cortisol or glucocorticoid excess, respectively, revealed a blunted response to the first pulse which became normal after the following pulses. The latter could not be sustained until the next morning without CRF given overnight. These findings point to a hypothalamic defect being the cause of hypocortisolism after long-term cortisol suppression.     

Infusion of beta-endorphin has no suppressive effect on the releasing hormone-stimulated pituitary-adrenal-axis of normal human subjects

The existence of a short-loop feedback inhibition of pituitary ACTH release by administration of beta-endorphin was postulated. However, data on the effect of peripherally administered beta-endorphin in humans are highly controversial. We infused human synthetic beta-endorphin at a constant rate of 1 microgram.kg-1.min-1 or normal saline to 7 normal volunteers for 90 min. Thirty min after starting the beta-endorphin or placebo infusion, releasing hormones were injected as a bolus iv (oCRH and GHRH 1 microgram/kg, GnRH 100 micrograms, TRH 200 micrograms) and blood was drawn for measurements of beta-endorphin immunoreactivity, all other pituitary hormones, and cortisol. Infusion of beta-endorphin resulted in high beta-endorphin plasma levels with a rapid decrease after the infusion was stopped. During the control infusion, beta-endorphin plasma levels rose in response to CRH. Plasma ACTH and serum cortisol levels in response to the releasing hormone were not different in subjects infused with beta-endorphin or placebo. The PRL response to TRH was significantly higher after beta-endorphin than after placebo (area under the stimulation curve 1209 +/- 183 vs 834 +/- 104 micrograms.l-1.h). There was no difference in the response of all other hormones measured. Our data on ACTH and cortisol secretion do not support the concept of a short-loop negative feedback of beta-endorphin acting at the site of the pituitary.     

Adrenocorticotropin stimulation test: effects of basal cortisol level, time of day, and suggested new sensitive low dose test

Adrenal response to iv administration of 1-24 ACTH (250 micrograms) was examined in normal volunteers under various conditions. The effect of basal cortisol levels was examined by performing the tests at 0800 h with and without pretreatment with dexamethasone. The effect of time of day was evaluated by performing the tests at 0800 h and at 1600 h, eliminating possible basal cortisol influence by pretreatment with dexamethasone. In the first set of tests, despite significantly different baseline levels, 30-min cortisol levels were not different (618 +/- 50 vs. 590 +/- 52 nmol/L). Afternoon cortisol levels in response to ACTH were found to be significantly higher than morning levels at 5 min (254 +/- 50 vs. 144 +/- 36 nmol/L, p less than 0.01) and at 15 min (541 +/- 61 vs. 433 +/- 52 nmol/L, p less than 0.02). This difference in response was no longer notable at 30 min (629 +/- 52 and 591 +/- 52 nmol/L). We tried also to determine the lowest ACTH dose which will elicit a maximal cortisol response. No difference was found in cortisol levels at 30 and 60 min in response to 250 and 5 micrograms 1-24 ACTH. Using 1 micrograms ACTH, the 30-min response did not differ from that to 250 micrograms (704 +/- 72 vs. 718 +/- 55 nmol/L, respectively). However, the 60-min response to 1 microgram was significantly lower (549 +/- 61 vs. 842 +/- 110 nmol/L, p less than 0.01). Using this low dose ACTH test (1 microgram, measuring 30-min cortisol level), we were able to develop a much more sensitive ACTH test, which enabled us to differentiate a subgroup of patients on long-term steroid treatment who responded normally to the regular 250 micrograms test, but had a reduced response to 1 microgram. The stability of 1-24 ACTH in saline solution, kept at 4 C, was checked. ACTH was found to be fully stable after 2 hs in a concentration of 5 micrograms/ml in glass tube and 0.5 micrograms/ml in plastic tube. It was also found to be fully stable, both immunologically and biologically, for 4 months, under these conditions. We conclude that the 30-min cortisol response to ACTH is constant, unrelated to basal cortisol level or time of day. It is therefore the best criterion for measuring adrenal response in the short ACTH test. The higher afternoon responses at 5 and 15 min suggest greater adrenal sensitivity in the afternoon, but further studies are needed to clarify this issue.(ABSTRACT TRUNCATED AT 400 WORDS)     

beta-Endorphin stimulates plasma renin and aldosterone release in normal human subjects

To determine the effect of beta-endorphin on the renin-angiotensin-aldosterone system, human synthetic beta-endorphin (0.3, 1.0, and 3.0 micrograms/kg X min) was infused iv in normal subjects. Each dose was administered for 30 min, and a control infusion of 5% dextrose and water was given on another day. Ten subjects were studied recumbent and in balance while ingesting a 10-meq Na+ diet. Plasma renin activity (PRA), plasma aldosterone (PA), and plasma cortisol (F) were measured basally and every 30 min for 210 min. The increments in PRA and PA above basal significantly (P less than 0.05) increased (3.1 +/- 1.2 ng/ml X h and 12.2 +/- 5.3 ng/dl, respectively; P less than 0.05) at the end of the beta-endorphin infusion. beta-Endorphin also significantly (P less than 0.01) suppressed F levels. Since in the low salt study, beta-endorphin suppressed F release while stimulating renin secretion, an additional five subjects were pretreated with dexamethasone (0.5 mg every 6 h) and were studied in balance while ingesting a 200-meq Na+ diet to suppress the renin-angiotensin system. Significant (P less than 0.025) increments in PRA (2.1 +/- 0.7 ng/ml X h) and PA (4.1 +/- 1.7 ng/dl) levels above basal were again found during the sequential dose infusion of beta-endorphin (0.3, 1.0, and 3.0 micrograms/kg X min). However, PA elevations were sustained for at least 120 min after the beta-endorphin infusion was stopped despite a drop in PRA 90 min earlier. In additional studies, an attempt was made to define the minimal effective dose of beta-endorphin by 60-min infusions (0.03, 0.1, and 0.3 micrograms/kg X min) in subjects on a 200-meq Na+ diet who were dexamethasone pretreated. The PRA and PA levels rose significantly (P less than 0.05) above basal at the 0.3 micrograms/kg X min dose, but not at the 0.03 or 0.1 micrograms/kg X min dosage levels. There were no changes in blood pressure or potassium during either the 10 or 200-meq Na+ studies. Thus, beta-endorphin stimulates aldosterone release in vivo. However, the underlying mechanisms are complex, since renin levels also increased. The data suggest that the early aldosterone rise may be secondary to an increase in renin release, but renin cannot account for the sustained postinfusion elevations of aldosterone.     

Prolactin stimulates adrenal androgen secretion in infant baboons

It has been suggested that pituitary factors other than ACTH modulate adrenal steroidogenesis during maturation of the pituitary-adrenocortical axis. Therefore, we determined whether hormones other than ACTH influence the production of cortisol (F), dehydroepiandrosterone (DHA), and DHA-sulfate (DHAS) in baboon infants studied between 8 and 24 months of age. Animals (three males, two females) were sedated with ketamine and peripheral blood samples taken 20, 10, and 0 min before a 90-min constant iv infusion of 448 pmol/min of either ACTH, ovine PRL, ovine GH, 2.4 nmol/min human CG (hCG), or normal saline. Serum F, DHA, and DHAS concentrations of blood samples obtained during the infusion (70, 80, 90 min) were averaged and compared with average pretreatment values. Each animal received each of the treatment protocols which included a minimum recovery period of 3-6 weeks. The serum concentrations of F, DHA, and DHAS did not vary with age and averaged (mean +/- SE) 24 +/- 2, 1.9 +/- 0.2, and 36 +/- 5 micrograms/dl, respectively. Compared to pretreatment values, ACTH increased (P less than 0.05) mean serum F concentrations by 155 +/- 20%; PRL, GH, hCG, and saline had no effect. In contrast, serum DHA concentrations were stimulated (P less than 0.05) by both ACTH (131 +/- 20%) and PRL (58 +/- 18%); GH, hCG, and saline had no effect. Similar findings were observed for serum DHAS concentrations. These findings indicate that the majority of serum androgens in young baboons is of adrenal origin. Therefore, we conclude that PRL, in addition to ACTH, may also be an adrenocorticotrophic factor in baboon infants. However, in contrast to ACTH, the action of PRL on the adrenal is apparently specific for androgen production.     

Inhibition of pituitary beta-endorphin by ACTH and glucocorticoids

beta-Endorphin and ACTH are secreted concomitantly in baseline conditions and in response to physiological and pharmacological stimuli. However, few and contradictory data are available on their feedback inhibition mechanisms. To investigate this aspect, the effects of exogenous ACTH1-24 and glucocorticoids on endogenous ACTH1-39 and beta-endorphin were tested in 18 patients with Addison's disease. Two main experimental protocols were employed: (1) 7 patients were given ACTH1-24 50 micrograms as an intravenous bolus followed by a 50-micrograms infusion in 90 min. Blood samples for beta-endorphin, ACTH and cortisol were obtained at 0, 15, 30, 45, 60, 90, 120 min. Six other patients were given oCRH 100 micrograms i.v. plus ACTH1-24, as described above. (2) In 5 other patients, hydrocortisone 37.5 mg was administered i.v. in 90 min. Blood samples for beta-endorphin, ACTH and cortisol were drawn at 0, 15, 30, 45, 60, 90, 120 min. One week later, the same patients were given oCRH 100 micrograms i.v. and hydrocortisone 37.5 mg, as described above. ACTH1-24 administration caused a significant (p less than 0.01) decrease in endogenous ACTH but not in beta-endorphin. oCRH injection significantly stimulated both ACTH and beta-endorphin. The response of both ACTH and beta-endorphin was inhibited by exogenous ACTH1-24. There was a potent inhibition by hydrocortisone on both basal and stimulated beta-endorphin, confirming that the feedback mechanism of glucocorticoids concomitantly inhibits ACTH and beta-endorphin. On the other hand, only CRH-stimulated but not basal secretion of beta-endorphin seems affected by ACTH ultrashort feedback, suggesting an intrapituitary regulation.     

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.     

Increased cortisol production in women runners

Because we previously found increased basal serum cortisol levels in women runners, we examined adrenocortical function in amenorrheic running women (AR), eumenorrheic running women (R), and normal nonexercising women (NC) in further detail. Mean 24-h urinary cortisol levels were significantly elevated (P less than 0.001) in six AR [45.1 +/- 7.2 (+/- SEM) micrograms/24 h] and eight R (38.5 +/- 6.9 micrograms/24 h) compared to four NC (13.9 +/- 2.8 micrograms/24 h). After adrenal suppression with 2 mg dexamethasone, integrated responses and absolute maximal elevations in serum cortisol levels in response to 10 micrograms/m2 exogenous ACTH (1-24) administered as an iv bolus dose, were not significantly different among six AR, six R, and six NC. This dose of ACTH results in maximal steroid release. The disappearance rates of cortisol (5 mg, iv) after dexamethasone suppression were similar in four AR, five R, and four NC and corresponded to a two-compartment model with mean half-lives of 4.9 and 93.8 min, respectively. Cortisol-binding globulin levels were also similar among the groups. These data document higher cortisol secretion and suggest increased ACTH secretion in running women.     

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.     

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.     

Effect of upright posture on the aldosterone responses to dopamine, metoclopramide, angiotensin II, and adrenocorticotropin

Aldosterone secretion in man is stimulated by potassium (K), ACTH, and angiotensin II (AII) and inhibited by dopamine (DA). In normal sodium-replete supine individuals, aldosterone secretion is under maximum tonic inhibition by DA and is not inhibited further by DA administration. Sodium depletion alters plasma aldosterone responses to secretogogues. Upright posture, another physiological stimulus to aldosterone secretion, recently was demonstrated to sensitize the adrenal cortex to inhibition of aldosterone secretion by a large quantity of DA (4.0 micrograms/kg X min). The effect of upright posture on aldosterone responses to other secretogogues is unknown. In this study, we investigated the effect of upright posture on aldosterone responses to low infusion rates of DA, to the DA antagonist metoclopramide (M) and to AII and ACTH. Fourteen normal men eating a normal sodium diet were studied. In eight, PRA, plasma aldosterone (PAC), plasma cortisol (F), and serum K concentrations were determined after 4 h of upright posture and infusion of vehicle (D5W) or DA at 0.1, 0.4, and 2.0 micrograms/kg X min. Six other normal men were kept supine for 3 h and, on separate days, upright for 3 h and given iv M (10-mg bolus dose), AII (1 and 4 pmol/kg X min for 30 min), and ACTH (20 and 120 mU/h for 30 min). PAC, PRA, F, and K were measured before and after these three secretogogues were administered. In the presence of vehicle, mean PAC increased by 15.1 +/- 4.3 (+/- SEM) ng/dL after 4 h of upright posture. In the presence of DA infused at 0.1, 0.4, and 2.0 micrograms/kg X min, the PAC response to upright posture was decreased to 9.7 +/- 2.5 (P = NS), 7.5 +/- 3.9 (P less than 0.05), and 8.1 +/- 2.0 (P less than 0.05) ng/dL, respectively. This occurred without a decrease in PRA, F, or K. The stimulation of PAC 10 and 20 min after a 10-mg bolus dose of M was 9.6 +/- 3.3 and 9.3 +/- 2.6 ng/dL, respectively, in supine subjects and 8.3 +/- 2.3 and 10.8 +/- 3.4 ng/dL 10 and 20 min after the M dose in upright subjects. The responses of PAC to ACTH and AII also were unchanged after 3 h of upright posture. We conclude that upright posture sensitizes the adrenal cortex to inhibition of aldosterone secretion by DA without affecting other modifiers of aldosterone secretion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Adrenal steroid responses to continuous intravenous adrenocorticotropin infusion compared to bolus injection in normal volunteers

We compared the adrenal steroid responses after synthetic ACTH-(1-24) (Cosyntropin) administration given by either continuous iv infusion or bolus injection in 11 normal women and 6 normal men. Each subject received 250 micrograms Cosyntropin as a bolus iv injection on 1 occasion and as a continuous 2-h iv infusion on another occasion, in random order. There was a 1-week interval between the studies. We measured the plasma levels of cortisol, 11-deoxycortisol, 17-hydroxyprogesterone, progesterone, pregnenolone, 17-hydroxypregnenolone, dehydroepiandrosterone, dehydroepiandrosterone sulfate, delta 5-androstenediol, androstenedione, and testosterone by RIA 15 and 0 min before and 30, 45, 60, and 120 min after administering ACTH. The steroid concentrations and their increments, ratios, or areas above baseline did not differ significantly between the bolus injection and the continuous infusion. Thus, at the dose of 250 micrograms, a bolus ACTH injection stimulates adrenal steroid secretion as effectively as a 2-h continuous ACTH infusion.     

Effect of androgen on adrenal steroidogenesis in normal women

Ovarian hyperandrogenism may induce adrenal enzymatic defects that mimic true inherited disorders of adrenal hormone biosynthesis. To assess the effect of hyperandrogenism on adrenal steroidogenesis, seven normal ovulatory women were studied on 2 days during the early follicular phase of their cycles. Plasma 17-hydroxyprogesterone (17-Prog), 17-hydroxypregnenolone, dehydroepiandrosterone (DHEA), DHEA sulfate, androstenedione (Adione), testosterone (T), 11-deoxycortisol, and cortisol concentrations were measured every 15 min for 3 h after iv injection of 0.25 mg ACTH (day 1) and pretreatment with dexamethasone on each day. On the second study day, T (80 micrograms/h) was infused iv for 5 h, and ACTH was given after 2 h of T infusion. The T infusion raised mean serum T levels from 1.2 +/- 0.3 (+/- SE) to 8.6 +/- 0.6 nmol/L. The maximum incremental (delta max) plasma Adione response to ACTH was significantly higher (2.6 +/- 0.3 to 3.2 +/- 0.4 nmol/L; P less than 0.009) during the T infusion, while the delta max responses of the other steroids did not change. There was an increase in the delta max 17-Prog to cortisol ratio (4.9 +/- 0.7 to 7.0 +/- 1.0; P less than 0.05), but no change in the delta max 17-Prog to Adione or 17-hydroxypregnenolone to DHEA ratios and no changes in the delta max delta 5- to delta 4-steroid ratios. These data suggest that acute T elevations result in subtle inhibition of 21-and/or 11 beta-hydroxylase activities, but not in 17-20-desmolase or 3 beta-ol activities.     

Vasopressin mediates the interleukin-1 alpha-induced decrease in luteinizing hormone secretion in the ovariectomized rhesus monkey.

Arginine vasopressin (AVP) has previously been shown to participate in the neuroendocrine control of the adrenal axis. In this study we investigated the role of AVP in the mechanisms linking stress and decreased gonadotropin secretion and evaluated the action of an AVP antagonist on interleukin-1 alpha (IL-1 alpha)-induced changes in gonadotropin and cortisol release in the primate. Adult ovariectomized rhesus monkeys were given a 30-min intracerebroventricular infusion of IL-1 alpha (2.1 micrograms/30 min; n = 5) or IL-1 alpha plus an AVP antagonist (240 micrograms/120 min; [deamino-Pen1,O-Me-Tyr2,Arg8] vasopressin; n = 7); the AVP antagonist infusion was started 30 min before IL-1 alpha and continued for 2 h. Controls included intracerebroventricular infusions of physiological saline (n = 5) or AVP antagonist alone (n = 3). LH concentrations were measured at 15-min intervals during a 3-h preinfusion morning baseline control period and a 5-h postinfusion period. Cortisol concentrations were determined at 45-min intervals. Pulsatile LH release remained unchanged after a control saline or AVP antagonist infusion. Overall LH concentrations decreased significantly after IL-1 alpha infusion, from a morning control baseline of 109.9 +/- 8.8 to 53.7 +/- 3.2 ng/ml after the infusion (P less than 0.05). Concomitant infusion of the AVP antagonist prevented the IL-1 alpha-induced LH inhibition (morning control baseline, 144.5 +/- 6.8; postinfusion, 132.3 +/- 5.8; P = NS vs. saline; P less than 0.0001 vs. IL-1 alpha). While cortisol concentrations decreased throughout the experimental period in the animals receiving saline, they increased after IL-1 alpha infusion: mean +/- SE postinfusion cortisol concentrations were 29.6 +/- 1.9 micrograms/dl (saline) vs. 44.0 +/- 1.7 micrograms/dl (IL-1 alpha; P less than 0.0001). Coinfusion of AVP antagonist and IL-1 alpha did not block the IL-induced cortisol increase (46.8 +/- 1.5 micrograms/dl; P less than 0.0001 vs. morning). After the infusion of AVP antagonist alone, cortisol concentrations significantly decreased from a morning control value of 40.2 +/- 1.6 to 34.9 +/- 1.6 micrograms/dl (P less than 0.05). The results confirm our previous demonstration of an inhibitory effect of IL-1 alpha on gonadotropin secretion in the ovariectomized rhesus monkey and indicate for the first time an important inhibitory role for AVP in the control of gonadotropin secretion during stress. The data also suggest that in this species, the adrenocortical response to IL-1 does not require AVP.     

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)     

Arginine stimulates growth hormone secretion by suppressing endogenous somatostatin secretion

To determine how arginine (Arg) stimulates GH secretion, we investigated its interaction with GHRH in vivo and in vitro. Six normal men were studied on four occasions: 1) Arg-TRH, 30 g arginine were administered in 500 mL saline in 30 min, followed by an injection of 200 micrograms TRH; 2) GHRH-Arg-TRH, 100 micrograms GHRH-(1-44) were given iv as a bolus immediately before the Arg infusion, followed by 200 micrograms TRH, iv; 3) GHRH test, 100 micrograms GHRH were given as an iv bolus; and 4) TRH test, 200 micrograms TRH were given iv as a bolus dose. Blood samples were collected at 15-min intervals for 30 min before and 120 min after the start of each infusion. Anterior pituitary cells from rats were coincubated with Arg (3, 6, 15, 30, and 60 mg/mL) and GHRH (0.05, 1, 5, and 10 nmol/L) for a period of 3 h. Rat GH was measured in the medium. After Arg-TRH the mean serum GH concentration increased significantly from 0.6 to 23.3 +/- 7.3 (+/- SE) micrograms/L at 60 min. TRH increased serum TSH and PRL significantly (maximum TSH, 11.1 +/- 1.8 mU/L; maximum PRL, 74.6 +/- 8.4 micrograms/L). After GHRH-Arg-TRH, the maximal serum GH level was significantly higher (72.7 +/- 13.4 micrograms/L) than that after Arg-TRH alone, whereas serum TSH and PRL increased to comparable levels (TSH, 10.2 +/- 3.0 mU/L; PRL, 64.4 +/- 13.6 micrograms/L). GHRH alone increased serum GH to 44.9 +/- 9.8 micrograms/L, significantly less than when GHRH, Arg, and TRH were given. TRH alone increased serum TSH to 6.6 +/- 0.6 mU/L, significantly less than the TSH response to Arg-TRH. The PRL increase after TRH only also was lower (47.2 +/- 6.8 micrograms/L) than the PRL response after Arg-TRH. In vitro Arg had no effect on basal and GHRH-stimulated GH secretion. Our results indicate that Arg administered with GHRH led to higher serum GH levels than did a maximally stimulatory dose of GHRH or Arg alone. The serum TSH response to Arg-TRH also was greater than that to TRH alone. We conclude that the stimulatory effects of Arg are mediated by suppression of endogenous somatostatin secretion.     

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.     

Dose-response effects of exogenous pulsatile human corticotropin-releasing hormone on adrenocorticotropin, cortisol, and gonadotropin concentrations in agonadal women

Acute activation of the hypothalamic-pituitary axis with CRH has been reported to suppress gonadotropin secretion in women of reproductive age. In this study we specifically examined the effects of increasing doses of human CRH (hCRH) on circulating concentrations of ACTH, cortisol, and gonadotropins in five agonadal women, aged 46-65 (mean, 51.2) yr. The subjects had undergone either natural menopause or surgical removal of their ovaries at least 1 yr before study. Each woman was studied on four separate occasions and received either saline or hCRH at a dose of 0.5, 1.0, or 2.0 micrograms/kg BW through an indwelling iv catheter in a randomized, single blind fashion. During each experiment, five sequential iv injections of the same dose of hCRH or saline were administered at 90-min intervals over an 8-h period, followed by a 10-micrograms iv bolus of GnRH to test for pituitary gonadotropin responsiveness. Blood samples for measurement of LH, FSH, PRL, ACTH, and cortisol were obtained at 15-min intervals through an indwelling iv in the contralateral arm. Episodic pulses of LH secretion were analyzed using the Cluster computer program. Transverse mean LH, FSH, and PRL levels did not change with increasing hCRH doses. Mean (+/- SEM) LH pulse frequency [saline, 5.2 +/- 0.4/8 h; hCRH, (0.5 micrograms/kg), 4.8 +/- 0.2; hCRH (1 microgram/kg), 5.2 +/- 0.2; hCRH (2 micrograms/kg), 5.4 +/- 0.2] and amplitude [saline, 14.4 +/- 4.2 IU/L; hCRH (0.5 microgram/kg), 14.0 +/- 2.4; hCRH (1 microgram/kg), 15.8 +/- 2.5; hCRH (2 micrograms/kg), 17.2 +/- 2.9] did not differ among groups. Although the transverse mean levels of ACTH [saline, 8.7 +/- 0.2 pmol/L; hCRH (0.5 microgram/kg), 12.4 +/- 0.3; hCRH (1 microgram/kg), 11.5 +/- 0.4; hCRH (2 micrograms/kg), 12.8 +/- 0.4] did not change with increasing doses of hCRH, the duration of cortisol peaks after hCRH was longer and accounted for the increased transverse mean at each dose [saline, 152.8 +/- 4.1 nmol/L; hCRH (0.5 microgram/kg), 265.4 +/- 10.5; hCRH (1 microgram/kg), 329.7 +/- 14.3; hCRH (2 micrograms/kg), 348.2 +/- 12.1]. These findings suggest that ever larger doses of pulsatile hCRH continue to increase adrenal output of cortisol secondary to more sustained ACTH responses. However, hCRH-induced acute hypercortisolism does not alter gonadotropin secretion in agonadal women.     

Fast feedback control of canine corticotropin by cortisol

These experiments test whether the rapid inhibition of ACTH responses in dogs fits the criterion for fast feedback. The ACTH response to hypoglycemia was measured after infusion of vehicle or cortisol at a rate of 9 or 18 micrograms/kg.min beginning at the time of injection of insulin or after infusion of 18 micrograms/kg.min beginning 20, 30, or 60 min later. Plasma ACTH was increased from 30-90 min after insulin treatment in all experiments. The ACTH responses to hypoglycemia were inhibited by cortisol infusions of 9 or 18 micrograms/kg.min beginning at 0 min [mean ACTH from 30-90 min: after vehicle, 557 +/- 57 (+/- SEM); after cortisol, 221 +/- 20 and 201 +/- 48 pg/ml, respectively], but the overall responses were not significantly reduced by infusions beginning 20, 30, or 60 min after the injection of insulin. The latency of the inhibition was 30 min after the infusions beginning at 0 min and 40-50 min after cortisol infusions beginning at later times. The infusion of cortisol also significantly reduced basal ACTH; however, this inhibition was not significant until 40 min. In further experiments the ACTH response to insulin-induced hypoglycemia was measured after infusing 45 micrograms/kg cortisol over 2, 5, or 15 min at rates of 22.5, 9, or 3 micrograms/kg.min. These infusions caused suppression of plasma ACTH by 30 min, but there was no significant difference in the degree of suppression (mean ACTH from 30-90 min: after vehicle, 532 +/- 34; cortisol for 2 min, 223 +/- 34; cortisol for 5 min, 197 +/- 18; cortisol for 15 min, 181 +/- 36 pg/ml). Thus, the inhibition of stimulated ACTH secretion in the dog is dependent on the feedback signal occurring at the initiation of the stimulus, but is not related to the rate of increase in plasma cortisol.     

The role of adrenocorticotropin in the cortisol and aldosterone responses to angiotensin II in conscious dogs

The role of ACTH in the cortisol and aldosterone responses to iv angiotensin II (AII) infusion, (5, 10, and 20 ng kg-1 min-1) in dogs was evaluated by examining the effect of AII infusion in conscious dogs pretreated with dexamethasone to suppress endogenous ACTH secretion. AII infusion in untreated dogs produced dose-related increases in plasma cortisol and aldosterone concentrations. The plasma ACTH concentration also increased. Dexamethasone treatment lowered the basal cortisol concentration from 1.7 +/- 0.1 to 0.7 +/- 0.1 micrograms/dl (P less than 0.05) and the ACTH concentration from 52 +/- 3 to 41 +/- 4 pg/ml (P less than 0.05), and abolished the cortisol response to all doses of AII, indicating that ACTH was necessary for the response. On the other hand, the basal aldosterone concentration was not significantly affected by dexamethasone, although the aldosterone response to the highest dose of AII was reduced. Additional experiments were performed to determine if the cortisol and aldosterone responses to AII (20 ng kg-1 min-1) in dexamethasone-treated dogs are restored if the ACTH concentration is maintained near control levels by iv infusion of synthetic alpha ACTH-(1-24) (0.3 ng kg-1 min-1). AII still failed to increase the plasma cortisol concentration in this group of dogs; however, the aldosterone response was fully restored. To evaluate the effect of elevated ACTH levels on the steroidogenic effects of AII, dogs were treated with dexamethasone and a higher dose of ACTH (0.4 ng kg-1 min-1). This dose of ACTH increased the plasma cortisol concentration from 1.7 +/- 0.1 to 3.5 +/- 0.8 micrograms/dl (P less than 0.05), but did not significantly affect the plasma aldosterone concentration. In the presence of constant elevated levels of ACTH, AII (10 and 20 ng kg-1 min-1) increased the plasma cortisol concentration in dexamethasone-treated dogs, although the response to the 10 ng kg-1 min-1 dose was smaller than the response in untreated dogs. Infusion of AII at 5 ng kg-1 min-1 did not increase the plasma cortisol concentration. In contrast, the increased plasma aldosterone produced by AII infusion in dexamethasone-treated dogs was not altered in the presence of elevated ACTH levels. Finally, AII infusion did not alter the clearance of cortisol. Collectively, these results demonstrate that an increase in plasma ACTH is necessary for the cortisol response to AII infusion.(ABSTRACT TRUNCATED AT 400 WORDS)