Role of the sympathetic nervous system in regulating renin and aldosterone production in man.

Several lines of evidence have been developed indicating that the sympathetic nervous system may play a role in mediating the renal and adrenocortical secretory responses to upright posture and sodium deprivation. Despite concurrent increases in arterial blood pressure, the plasma renin activity of normal subjects increased both in response to the infusion of catecholamines (norepinephrine: epinephrine, 10:1) and in response to stimulation of the sympathetic nervous system by cold. Aldosterone excretion was also increased by catecholamine infusion. In normal subjects the stimuli of upright posture and of sodium depletion both resulted in increases in urinary catecholamines, plasma renin activity, and urinary aldosterone. A patient with severe autonomic insufficiency did not experience normal elevations of urinary catecholamines, plasma renin activity, or urinary aldosterone in response to upright posture or sodium deprivation, despite a substantial fall in arterial blood pressure. When orthostatic hypotension was prevented by infusion of catecholamines, however, increases in plasma renin activity and in aldosterone excretion were observed. We suggest that both upright posture and sodium depletion lead to decreases in effective plasma volume and increases in sympathetic nervous system activity. This increase in sympathetic activity is then responsible for an increase in renal afferent arteriolar constriction, leading to an increase in renin secretion and, ultimately, an increase in aldosterone secretion.

Dopamine inhibits angiotensin-stimulated aldosterone biosynthesis in bovine adrenal cells.

The possibility that dopamine may play a role in the in vivo control of aldosterone production in man was suggested to us by reports from others; (a) that bromocriptine, a dopaminergic agonist, inhibits the aldosterone response to diuresis and to the infusion of angiotensin or ACTH; and (b) that metaclopramide, a dopamine blocking agent, causes elevations in plasma aldosterone levels. To determine whether such effects were direct or indirect, we examined the action of dopamine on aldosterone biosynthesis in isolated, bovine adrenal cells. Dopamine significantly inhibits the aldosterone response to angiotensin (P < 0.001), but does not influence basal aldosterone biosynthesis. It has previously been reported that angiotensin stimulates both the early and late phases of aldosterone biosynthesis. The present experiments demonstrated that the enhancing effect of angiotensin on the conversion of deoxycorticosterone to aldosterone (late phase of aldosterone biosynthesis) was almost completely inhibited by dopamine (P < 0.001). A significant inhibitory effect of dopamine (10 nM) was seen even when aldosterone biosynthesis was stimulated by a grossly supraphysiological concentration of angiotensin II (10 muM). However, these studies did not demonstrate any direct effect of dopamine on the early phase of aldosterone biosynthesis (cholesterol to pregnenolone) basally or when stimulated, or on the late phase of aldosterone biosynthesis under basal conditions. These in vitro studies suggest a direct inhibitory role for dopamine on the late phase of aldosterone biosynthesis, which may account for the in vivo inhibition of the aldosterone response to angiotensin in subjects treated with a dopaminergic agent.

Radioimmunoassay of beta-MSH in human plasma and tissues.

A radioimmunoassay method for beta-melanocyte-stimulating hormone (beta-MSH) has been developed and utilized in the identification and quantification of this hormone in human plasma and tissues. The concentration of beta-MSH in two human pituitary glands was found to be approximately 350 mug/g. beta-MSH was identified in the tumor tissue of all 11 patients with the ectopic ACTH syndrome who were studied; concentrations in individual cases ranged from 3 to 1600 ng/g. In plasma of chronically hyperpigmented patients with Addison's disease, Cushing's disease (after bilateral adrenalectomy), and the ectopic ACTH syndrome, beta-MSH concentrations of 0.5-6 ng/ml were found. The degree of clinical hyperpigmentation was well correlated with the quantity of beta-MSH in the plasma. beta-MSH concentrations in the plasma of normal subjects were less than 0.09 ng/ml. In all of these circumstances, bioassays for MSH were also performed, and it was found that most of the biologic MSH activity of the plasma and tissues could be accounted for by beta-MSH.

Normal and abnormal regulation of beta-msh in man.

The regulation of plasma beta-melanocyte-stimulating hormone (beta-MSH) in man has been studied utilizing a radioimmunoassay previously described (1). In normal subjects plasma beta-MSH values ranged from 20 to 110 pg/ml. Metyrapone increased and dexamethasone decreased plasma beta-MSH levels. Surgical stress stimulated beta-MSH secretion. Plasma beta-MSH levels were elevated in patients with untreated Addison's disease and untreated congenital adrenal hyperplasia, and these levels fell to normal during glucocorticoid therapy. In patients with Cushing's syndrome due to pituitary adrenocorticotropic hormone (ACTH) excess, plasma beta-MSH was slightly elevated before treatment. In those patients who developed pituitary tumors and hyperpigmentation after bilateral adrenalectomy, plasma beta-MSH was greatly elevated. In patients with Cushing's syndrome due to adrenal tumor, plasma beta-MSH was subnormal. In patients with the ectopic ACTH syndrome, the levels of plasma beta-MSH were high. Plasma beta-MSH had a diurnal variation in normal subjects, patients with Addison's disease, and patients with congenital adrenal hyperplasia; but the normal diurnal variation was lost in patients with Cushing's disease. In patients with high plasma beta-MSH, simultaneous determinations of plasma ACTH showed close correlation between the degree of elevation of ACTH and that of beta-MSH. In extracts of tumors from patients with the ectopic ACTH-MSH syndrome the quantities of the two hormones were roughly equivalent. In patients with hyperpigmentation due to a variety of disorders other than pituitary-adrenal abnormalities, plasma beta-MSH was normal. It is concluded that the secretion of beta-MSH is regulated by the same factors that regulate ACTH.

Biologic and immunologic characterization and physical separation of ACTH and ACTH fragments in the ectopic ACTH syndrome.

Extracts of tumors from 32 patients with the ectopic ACTH syndrome were subjected to simultaneous bioassay and radioimmunoassays for ACTH. Radioimmunoassays were performed using three antisera, one of which reacts with the extreme N-terminal 1-13 amino acid sequence of ACTH, the second with the N-terminal 1-23 sequence of the ACTH molecule, and the third with the C-terminal 25-39 amino acid sequence of ACTH. There was, in general, good correlation between bioactivity and N-terminal ACTH immunoreactivity. However, there were large excesses of both extreme N-terminal and C-terminal immunoreactive materials in most tumor extracts, which were not found in extracts of three human pituitaries. Three tumor extracts were subjected to molecular sieve chromatography on Sephadex G-50 fine resin. The bioactive ACTH eluted in the same fractions as pituitary ACTH (mol wt approximately 4,500 daltons) and reacted equally in all three ACTH radioimmunoassay systems. The bioactive tumor ACTH was neutralized by incubation with the C-terminal antiserum, indicating it has an intact C-terminal sequence of amino acids. The next several fractions from the Sephadex column contained a material, mol wt approximately 3,100, which was biologically inactive and had C-terminal immunoreactivity but no N-terminal or extreme N-terminal immunoreactivity. Incubation with the N-terminal 1-23 ACTH antiserum did not adsorb these C-terminal fragments, indicating they lacked an intact sequence of amino acids in this region. A smaller ACTH fragment (mol wt approximately 1,800 daltons) eluted in still later fractions and reacted with the extreme N-terminal antiserum but not with the N-terminal or C-terminal antisera. It had no steroidogenic activity, but appeared to have significant melanocyte-stimulating activity. It is concluded that, in addition to an ACTH similar, if not identical, to pituitary ACTH, tumors of patients with the ectopic ACTH syndrome contain both N-terminal and C-terminal ACTH fragments.

Effect of synthetic ovine corticotropin-releasing factor. Dose response of plasma adrenocorticotropin and cortisol.

Synthetic ovine corticotropin-releasing factor (CRF) was administered to normal male volunteer subjects as an intravenous bolus or 30-s infusion. Doses of CRF ranging from 0.001 to 30 micrograms/kg body wt were administered, and plasma immunoreactive (IR)-ACTH and IR-cortisol concentrations were measured. The threshold dose appeared to be 0.01-0.03 micrograms/kg, the half-maximal dose 0.3-1 micrograms/kg, and the maximally effective dose 3-10 micrograms/kg. Basal concentrations of IR-ACTH and IR-cortisol were 14 +/- 7.6 pg/ml (mean +/- SD) and 5.6 +/- 2.2 micrograms/dl, respectively. IR-ACTH rose as early as 2 min after CRF injection, reached peak levels in 10-15 min, and declined slowly thereafter. IR-cortisol rose at 10 min or later and reached peak levels in 30-60 min. At a dose of 30 micrograms/kg, neither IR-ACTH nor IR-cortisol fell from peak levels of 82 +/- 21 pg/ml (mean +/- SE) and 23 +/- 1.4 micrograms/dl, respectively, during the 2-h course of the experiment, indicating that CRF has a sustained effect on ACTH release and/or a prolonged circulating plasma half-life. There was little or no increase in the levels of other anterior pituitary hormones. At doses of 1 microgram/kg and higher, facial flushing, tachycardia, and, in some subjects, a 15-29-mmHg decline in systemic arterial blood pressure were observed, even though blood volume was replaced and the subjects remained supine. These data indicate that synthetic ovine CRF is a very potent and specific ACTH secretagogue in man. Administered with caution until its vasomotor effects are more fully defined, CRF promises to be a safe and very useful investigative, diagnostic, and, possibly, therapeutic agent in man.

New mineralocorticoids: 5alpha-dihydroaldosterone and 5alpha-dihydro-11-deoxycorticosterone.

Mineralocorticoid activity of several delta4-3-ketosteroids and their 5alpha-dihydro analogs were evaluated by bioassay using urinary Na:K ratio of adrenalectomized rats as an index of mineralocorticoid activity. Among delta4-3-ketosteroids, aldosterone, 11-deoxycorticosterone, corticosterone, cortisol, 11-dehydrocorticosterone, and cortisone showed mineralcorticoid activity with aldosterone, the most potent of the series, showing virtually maximum activity at a dose of 0.25 microgram/rat. 5alpha-Dihydroaldosterone and 5alpha-dihydro-11-deoxycorticosterone possessed distinct mineralcorticoid activity, albeit less than aldosterone and 11-deoxycorticosterone. 5alpha-Dihydrocorticosterone, 5alpha-dihydrocortisol, 5alpha-dihydro-11-dehydrocorticosterone, and 5alpha-dihydrocortisone did not show mineralocorticoid activity in doses up to 100 microgram/rat. It is concluded that reduction of the 4.5 double bond diminishes mineralocorticoid activity of delta4-3-ketosteroids. Nevertheless, 5alpha-dihydroaldosterone has distinct mineralocorticoid activity with potency of 1.8% of that of aldosterone and approximately the same as that of 11-deoxycorticosterone.

Single subcutaneous doses of a luteinizing hormone-releasing hormone antagonist suppress serum gonadotropin and testosterone levels in normal men.

The ability of single doses of a LHRH antagonist [Ac-delta 3Pro1, 4F-D-Phe2, D-Trp3,6]LHRH (4F-antagonist) to suppress serum gonadotropin and testosterone levels was studied in six normal men. The 4F-antagonist was given sc at four doses: 40, 80, 160, and 320 micrograms/kg body weight. Serum immunoreactive LH, FSH, and testosterone and bioactive LH were measured at intervals for the subsequent 18 h. Serum LH decreased rapidly by (mean +/- SE) 39.7 +/- 2.7%, 41.6 +/- 5.4%, 45.5 +/- 4.7%, and 45.3 +/- 5.4% after each of the four doses. The mean number of LH pulses and their amplitude decreased after each dose and remained suppressed for at least 6 h. After each of the four doses, mean serum FSH levels decreased by 20.0 +/- 4.1%, 33.8 +/- 6.8%, 25.8 +/- 3.6%, and 33.3 +/- 5.7%, and mean serum testosterone levels decreased by 47.7 +/- 7.3%, 55.6 +/- 10.5%, 58.2 +/- 10.8%, and 76.0 +/- 6.0%. Serum testosterone remained low for at least 18 h after the two higher doses. LH bioactivity and the ratio of bioactive LH to immunoreactive LH decreased in all subjects, especially after higher doses of the 4F-antagonist. No side effects or adverse reactions occurred after 4F-antagonist administration, and toxicology studies were negative. These results demonstrate that a single sc injection of this potent LHRH antagonist inhibits the pituitary-gonadal axis in normal men.

Effects of ovine corticotropin-releasing hormone on adrenocorticotropin secretion in the absence of glucocorticoid feedback inhibition in man.

We studied 1) the nature of the plasma ACTH response to ovine CRH (oCRH) in the absence of normal glucocorticoid negative feedback inhibition and 2) the cause of the diminished circadian peak in plasma ACTH in normal men the morning after 3-30 micrograms/kg BW doses of oCRH. Placebo or oCRH (3 micrograms/kg BW, iv) was administered as iv injections to five normal men given metyrapone to produce acute glucocorticoid deficiency. Four studies were performed: 1) placebo oCRH plus placebo hydrocortisone (HC), 2) oCRH plus placebo HC, 3) placebo oCRH plus HC, and 4) oCRH plus HC. HC was given as a variable rate iv infusion to mimic the plasma cortisol response to the same dose of oCRH in normal men. Plasma cortisol levels rose only slightly after oCRH, indicating nearly complete blockade of cortisol biosynthesis. Plasma cortisol levels during the HC infusion were similar to those in normal men given 3 micrograms/kg oCRH. There was an exaggerated rise in both the first and second peaks of the plasma ACTH response to oCRH in the metyrapone-treated men. HC infusion did not alter the plasma ACTH response during the first 60 min after oCRH, but markedly attenuated the response thereafter; however, it did not affect the timing of the second peak. This inhibitory effect continued for up to 11 h, which was 2-3 h longer than the period that plasma cortisol levels were increased. Thus, cortisol secreted in response to ACTH released by oCRH modulates, after about a 60-min delay, the continuing release of ACTH. Despite the greater oCRH-induced release of pituitary ACTH in the metyrapone-treated men, the magnitude of their next morning's circadian plasma ACTH peak was similar to that after they received placebo oCRH. Thus, depletion of pituitary ACTH did not appear to explain the diminished circadian peak. Its magnitude was reduced by the combination of oCRH and HC, but not by HC alone. Administration of oCRH, alone or in combination with HC, delayed the onset of the circadian rise, while oCRH, HC, or the combination thereof delayed the time of the circadian peak. Thus, it appears that both the glucocorticoid response to oCRH and direct or indirect effect(s) of oCRH are required to produce these two phenomena.

Effect of altered thyroid hormone levels on hypothalamic-pituitary-adrenal function.

To determine whether alterations in serum thyroid hormone levels affect hypothalamic-pituitary-adrenal function, we measured the plasma immunoreactive (IR) ACTH and IR-cortisol responses to 1 microgram/kg BW ovine CRH (oCRH) given iv in the late afternoon and the plasma IR-ACTH, IR-cortisol, and IR-11-deoxycortisol responses to 2 g metyrapone given orally at midnight in 10 athyreotic patients during T4 treatment and 1 month after stopping T4 when they were biochemically, but not clinically, hypothyroid. Mean serum TSH increased from 0.7 +/- 0.9 (+/- SD) mU/L (normal range 0.5-4.9 mU/L) during T4 therapy to 107 +/- 82 mU/L after stopping T4. The serum total T4 level and free T4 index fell from 165 +/- 37 nmol/L and 1.9 +/- 0.4, respectively (normal range, 59-154 nmol/L and 0.9-2.5, respectively), to 19 +/- 9 and 0.2 +/- 0.1, respectively, after stopping T4. Basal plasma IR-ACTH and IR-cortisol levels at 0800 and 1630 h were similar during and after stopping T4 therapy. Peak plasma IR-ACTH and IR-cortisol levels after oCRH were significantly greater after stopping T4 (20 +/- 9.2 pmol/L and 880 +/- 260 nmol/L, respectively) than during T4 therapy (9.7 +/- 4.7 pmol/L and 720 +/- 190 nmol/L; P less than 0.01 and P less than 0.05, respectively). The mean integrated plasma IR-ACTH and IR-cortisol responses to oCRH were also significantly greater P less than 0.01 and P less than 0.05, respectively) after stopping T4 than during T4 therapy. Plasma IR-ACTH the morning after metyrapone was slightly (1.6-fold) but not significantly greater during therapy than after stopping T4 therapy (100 +/- 86 vs. 65 +/- 54 pmol/L, respectively). The plasma IR-11-deoxycortisol responses to metyrapone during and after stopping T4 therapy were similar (720 +/- 250 and 750 +/- 330 nmol/L, respectively), presumably because plasma IR-ACTH concentrations were maximally stimulating in both instances. These results indicate that thyroid hormone deficiency of short duration 1) increases corticotroph sensitivity to oCRH, 2) may diminish the plasma ACTH response to metyrapone-induced hypocortisolemia, and 3) has no apparent effect on the acute adrenal response to ACTH. These data together with those of previous studies that have shown reduced responses of the hypothalamic-pituitary-adrenal axis to metyrapone and hypoglycemia in hypothyroid patients suggest that the release of hypothalamic CRH and/or other ACTH secretagogues may be decreased in hypothyroidism.

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)

Gonadotropins and testosterone escape from suppression during prolonged luteinizing hormone-releasing hormone antagonist administration in normal men.

The ability of prolonged administration of a LHRH antagonist, [Ac-delta 3Pro1,4F-D-Phe2,D-Trp3,6]LHRH (4F-antagonist), to suppress serum gonadotropin and testosterone levels was studied in normal men. The 4F-antagonist was given either as a continuous 13.3 micrograms/kg X h sc infusion for 72 h or as intermittent sc injections of 100 micrograms/kg every 6 h for 7 days. Serum FSH, LH, and testosterone levels decreased in the period immediately following initiation of 4F-antagonist administration. However, an escape toward baseline levels for each of these hormones occurred during prolonged antagonist administration. When men receiving the continuous infusion were challenged with iv bolus doses of 50 micrograms LHRH, the response of LH after the first 12 h of 4F-antagonist administration was similar to that before its administration. This gonadotropin and testosterone escape suggests that, at the doses used, the inhibitory action of the antagonist on gonadotropin secretion is progressively lost. The initial decrease in androgen levels could serve to augment endogenous LHRH release, which, in turn, overcomes the pituitary effects of the antagonist, or to augment endogenous LH secretion directly. These results demonstrate that the pituitary can escape from the suppressive effects of prolonged LHRH antagonist administration and partially restore serum gonadotropin and testosterone levels to normal in man.

Suppression of pituitary-gonadal function by a potent new luteinizing hormone-releasing hormone antagonist in normal men.

LHRH antagonists compete with endogenous LHRH for binding to receptors on pituitary gonadotrophs and thereby inhibit gonadal function by suppressing gonadotropin secretion. We studied the effects of a recently developed LHRH antagonist on the pituitary-gonadal axis in man. The antagonist Detirelix [( N-Ac-D-Nal(2)1, D-pCl-Phe2,D-Trp3, D-hArg(Et2)6, D-Ala10]LHRH) was given as a single sc injection to nine normal men at three dose levels (5, 10, and 20 mg) at intervals of at least 7 days. Serum FSH, LH, and testosterone levels were measured before treatment, at frequent intervals for 48 h, and 72, 96, and 168 h after administration of the antagonist. Mean serum FSH levels decreased (P less than 0.001) from 6.9 +/- 0.5 (+/- SEM) mIU/mL to nadirs of 4.4 +/- 1.1, 3.6 +/- 0.9, and 4.1 +/- 0.9 after the 5-, 10-, and 20-mg doses, respectively. Serum LH levels decreased (P less than 0.001) from 6.2 +/- 0.3 mIU/mL to nadirs of 3.3 +/- 0.4, 2.8 +/- 0.3, and 2.7 +/- 0.3 after all three doses. Serum testosterone levels decreased (P less than 0.001) in a dose-dependent fashion from 5.1 +/- 0.2 ng/mL to nadirs of 1.3 +/- 0.3, 0.9 +/- 0.3, and 0.6 +/- 0.1 after the same doses. After the initial testosterone decrease, however, escape occurred 12-28 h after the lower doses. The area under the response curve, describing hormone concentrations as a function of time during the study, diminished by 23 +/- 2%, 36 +/- 4%, and 36 +/- 3% for FSH, by 14 +/- 6%, 30% +/- 6%, and 34 +/- 5% for LH, and by 41 +/- 5%, 58 +/- 6%, and 68 +/- 4% for testosterone with the same doses, respectively. The apparent plasma disappearance half-life of Detirelix by RIA was at least 41 h after all three doses. Detirelix elicited only a minor local reaction; no systemic side-effects were observed within the dose range used. These results indicate that this LHRH antagonist is a safe, highly potent inhibitor of the human pituitary-gonadal axis with an exceptionally long duration of action.

Rapid sequential intravenous administration of four hypothalamic releasing hormones as a combined anterior pituitary function test in normal subjects.

Normal subjects were studied to test the feasibility of a combined anterior pituitary function test using iv administration of four hypothalamic releasing hormones: ovine corticotropin-releasing hormone, human GH-releasing hormone, GnRH, and TRH. Initially, nine normal men were studied with various combinations of these four hormones to exclude the possibility that they might inhibit or synergize with each other in releasing the individual anterior pituitary hormones. When given in combination, the releasing hormones were administered as sequential 20-sec iv infusions in the following order and doses: ovine corticotropin-releasing hormone, 1 microgram/kg; GnRH, 100 micrograms; human GH-releasing hormone, 1 microgram/kg; and TRH, 200 micrograms. Plasma or serum samples were assayed for ACTH, cortisol, GH, PRL, FSH, LH, and TSH at multiple times for 120 min after injection. Compared to individual administration, combined administration of these four hypothalamic releasing hormones caused no apparent inhibition or synergism with respect to the individual hormone responses of these normal subjects. Side-effects of the combined test were the same as those observed with individual hormone administration. No unusual or dangerous side-effects were observed. Having confirmed the efficacy of combined administration of the four releasing hormones, we administered the combination to five additional normal men and 12 normal women. Anterior pituitary hormone and cortisol responses were the same in men and women, except for a lower LH and a greater PRL response in women. There was a rapid increase in all hormones, with peak levels usually reached by 60 min. Adequate assessment of individual hormone responses can be achieved by assaying a basal and only 2 (or 3 in the case of ACTH and GH) postinfusion samples. A rapid, safe, and useful test of combined anterior pituitary function appears to be feasible using these four hypothalamic releasing hormones.

Diurnal variation in the response of plasma adrenocorticotropin and cortisol to intravenous ovine corticotropin-releasing hormone.

To determine whether the plasma immunoreactive ACTH (IR-ACTH) and IR-cortisol responses to ovine corticotropin-releasing hormone (oCRH) depend on the time of day, we administered 1 microgram/kg BW synthetic oCRH as an iv bolus dose to five normal men at their usual time of awakening between 0530-0740 h, at 1600 h, and at 2300 h. Mean basal plasma IR-ACTH and IR-cortisol levels were highest upon awakening, intermediate at 1600 h, and lowest at 2300 h, reflecting the diurnal rhythm of ACTH secretion. There was no significant difference in the plasma IR-ACTH response to oCRH at different times of the day. In contrast, the mean maximum plasma IR-cortisol increment and mean integrated response were 2- and 2.6-fold greater (P less than 0.05), respectively, at 2300 h than upon awakening. In another study, oCRH was given in the morning (0700-0900 h) to 22 normal men and in the late afternoon (1600-1800 h) to 24 normal men. Mean basal plasma IR-ACTH and IR-cortisol levels were significantly higher (P less than 0.001) in the morning [24 +/- 3 pg/ml (mean +/- SEM) and 10.6 +/- 0.8 micrograms/dl, respectively] than in the afternoon (13 +/- 2 pg/ml and 5.6 +/- 0.6 micrograms/dl, respectively). Mean peak plasma IR-ACTH was slightly greater in the morning (60 +/- 5.5 pg/ml) than in the afternoon (47 +/- 5.5 pg/ml), the mean maximum plasma IR-ACTH increments were the same (35 +/- 4 and 34 +/- 5 pg/ml, respectively), and the mean integrated IR-ACTH response was slightly less in the morning (2036 +/- 414 vs. 2365 +/- 358 pg . min/ml), but none of these differences was statistically significant. Mean peak plasma IR-cortisol concentrations in the morning and afternoon were similar (18.7 +/- 0.7 and 17.3 +/- 0.9 micrograms/dl, respectively), but the mean maximum plasma IR-cortisol increments (8.1 +/- 0.8 and 11.7 +/- 0.9 micrograms/dl, respectively; P less than 0.005), and the mean integrated IR-cortisol responses (588 +/- 115 and 976 +/- 95 micrograms . min/dl, respectively; P less than 0.01) were greater in the afternoon. There was an inverse correlation between basal plasma IR-cortisol concentration and the integrated IR-ACTH response (P less than 0.05), the maximum IR-cortisol increment (P less than 0.001), and the integrated IR-cortisol response (P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of synthetic ovine corticotropin-releasing factor: prolonged duration of action and biphasic response of plasma adrenocorticotropin and cortisol.

The duration of the response to synthetic ovine corticotropin-releasing factor (CRF) was studied in 13 healthy male volunteer subjects. Placebo or CRF (0.3, 3, or 30 micrograms/kg BW) was administered as an iv bolus or, in the case of the largest dose, a 30-sec infusion in single blind fashion in the late afternoon. Basal plasma immunoreactive ACTH (IR-ACTH) and IR-cortisol were 10.8 +/- 7.7 pg/ml and 5.0 +/- 1.8 micrograms/dl (mean +/- SD), respectively. IR-ACTH rose rapidly after CRF, reached an initial peak at 15 min, fell rapidly until 1.5 h after CRF, and then either fell more slowly (after the lowest dose) or rose to a second major peak at 2-3 h before falling back to baseline. After 0.3, 3, and 30 micrograms/kg CRF, IR-ACTH remained elevated for 4, 7, and 8 h, respectively. The effect on plasma IR-cortisol was similar, but more prolonged. The magnitude of both peaks of IR-ACTH, the duration of the response, and the area under the curve all appeared dose dependent. The same was true for IR-cortisol, except that the first peak height was similar after all three doses. The duration of CRF's action is probably due to its long circulating half-life. The biphasic response curve may reflect initial secretion of a readily releasable pool of ACTH, followed by later secretion of a second pool of newly synthesized and/or matured peptide. The next morning's normal circadian rise in both IR-ACTH and IR-cortisol was delayed and diminished after 3 micrograms/kg CRF; there was no increase in IR-ACTH after 30 micrograms/kg CRF, and the IR-cortisol level was diminished. Inhibition of the normal circadian rise may reflect inhibition of ACTH secretion by the sustained high plasma cortisol levels.

Effect of subcutaneous and intranasal administration of ovine corticotropin-releasing hormone in man: comparison with intravenous administration.

Long term use of ovine corticotropin-releasing hormone (oCRH) requires a convenient route of administration. The effects of 0.3, 3, and 30 micrograms/kg BW synthetic oCRH given as a sc injection and of 10 and 30 micrograms/kg given as an intranasal spray were studied in 10 normal men in the late afternoon. Basal plasma immunoreactive ACTH (IR-ACTH) and IR-cortisol levels were 14 +/- 1.9 pg/ml and 4.3 +/- 0.4 microgram/dl (mean +/- SEM). Peak IR-ACTH levels (mean +/- SEM) were 43 +/- 5.5, 53 +/- 8.1, and 64 +/- 8.9 pg/ml after the 0.3, 3, and 30 micrograms/kg doses of oCRH given sc, respectively, and 23 +/- 4.3 and 36 +/- 4.8 pg/ml after the 10 and 30 micrograms/kg doses of oCRH given intranasally, respectively. The lowest sc dose and both intranasal doses caused only single IR-ACTH peaks. After 3 and 30 micrograms/kg sc oCRH, IR-ACTH rose by 15 min, reached an initial peak at 45-60 min, fell rapidly until 90-120 min, and rose to a second peak at 3-5 h. This biphasic response is similar to that previously found after iv administration. IR-ACTH levels remained elevated for 4, 10, and at least 16 h after 0.3, 3, and 30 micrograms/kg sc oCRH, respectively, and for 1.5 and 3 h after 10 and 30 micrograms/kg intranasal oCRH respectively. The effect on IR-cortisol was similar, but more prolonged. Compared to the iv route, sc oCRH produced similar mean peak IR-ACTH and IR-cortisol levels and had a slightly longer duration of action. Intranasal oCRH was only about 1% as effective. Peak plasma IR-oCRH levels in 2 subjects receiving 3 micrograms/kg sc oCRH were 13 and 17 ng/ml at 90 min. These peaks were lower than those after iv administration of the same dose, but the levels remained elevated longer, probably accounting for the longer duration of action of sc oCRH. Peak plasma IR-oCRH levels in 4 subjects given 10 microgram/kg intranasal oCRH were only 64-122 pg/ml, presumably reflecting poor absorption through the nasal mucosa. These results demonstrate that sc injection of oCRH is at least as effective as the iv route with respect to plasma IR-ACTH and IR-cortisol responses. The convenience of this route of administration and the prolonged duration of action of oCRH suggest the feasibility of long term oCRH use.

Stimulation of rat liver 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity by o,p'-DDD.

To investigate the mechanism by which o'p'-DDD (2,2-bis [2-chlorphenyl-4-chlorophenyl]-1,1-dichloroethane; Mitotane) produces hypercholesterolemia in man, we studied the effect of the drug on hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity in reverse light-cycled rats. o,p'-DDD markedly stimulated reductase activity in vivo and in vitro in a dose-dependent manner. This effect was not associated with demonstrable adrenocortical toxicity or changes in plasma corticosterone concentrations. Thus o,p'-DDD may elevate circulating cholesterol levels in man by increasing endogenous cholesterol synthesis. In addition, the o,p'-DDD may elevate circulating cholesterol levels in man by increasing endogenous cholesterol synthesis. In addition, the o,p'-DDD-treated rat may serve as a useful model for testing other agents for the ability to suppress endogenous cholesterol synthesis and lower circulating cholesterol levels.

Are there unknown mineralocorticoids in low-renin essential hypertension?

The blood pressure elevation of primary aldosteronism is caused by excessive production of the known mineralocorticoid, aldosterone. The blood pressure elevation of low-renin essential hypertension may also be caused by mineralocorticoid excess, but which which mineralocorticoid is responsible is uncertain. Normal levels of aldosterone, found in this disorder despite suppressed plasma renin, and the presence of an unknown mineralocorticoid have been hypothesized to explain low-renin essential hypertension. We contrasted the blood pressure responses and changes in aldosterone seen in patients with low-renin essential hypertension and primary aldosteronism during treatment with two adrenal enzyme inhibitors. The results demonstrate the similarity between decrease in blood pressure and in aldosterone during early adrenal inhibition in both primary aldosteronism and in low-renin essential hypertension. During treatment with a distal adrenal blocker, patients with primary aldosteronism demonstrated decreases in both aldosterone and blood pressure, whereas patients with low-renin essential hypertension showed a decrease in aldosterone without significant change in blood pressure. This suggested that aldosterone was not the major mineralocorticoid responsible for low-renin essential hypertension. Unknown mineralocorticoid excretion decreased (along with blood pressure) during early inhibition but failed to decrease (along with blood pressure) during late inhibition at a time when aldosterone excretion decreased. This suggests that unknown mineralocorticoids play significant roles in the blood pressure elevation of low-renin essential hypertension.

Effects of dietary lecithin on hormonal and neurobehavioral profiles in normal subjects.

Four normal subjects received lecithin supplements sufficient to elevate serum choline levels 3-fold. Despite persistent hypercholinemia over 48 hours of close observation, no increase was observed in serum ACTH, cortisol, and insulin concentrations, or in free urinary catecholamine excretion. Screening of a large group of other pituitary and gonadal hormones also failed to reveal any influence of lecithin supplements. EEG patterns and results of psychometric tests were also unaltered.