Prolactin-releasing peptide releases corticotropin-releasing hormone and increases plasma adrenocorticotropin via the paraventricular nucleus of the hypothalamus

Intracerebroventricular (ICV) injection of prolactin-releasing peptide (PrRP) is known to increase plasma adrenocorticotropin (ACTH) and cause c-fos expression in the hypothalamic paraventricular nucleus (PVN). We hypothesize that this is the site at which PrRP acts to increase plasma ACTH. We have used ICV injection and direct intranuclear injection of PrRP into the PVN to investigate the sites important in the stimulation of ACTH release in vivo. To investigate the mechanism of action by which PrRP increases ACTH, we have used primary culture of pituitary cells and measured neuropeptide release from in vitro hypothalamic incubations. ICV administration of PrRP increased plasma ACTH 10 min post-injection (PrRP 5 nmol 81.0 +/- 23.5 pg/ml vs. saline 16.8 +/- 14.1 pg/ml, p < 0.05). Intra-PVN injection of PrRP increased ACTH 5 min post-injection (PrRP 1 nmol 22.9 +/- 5.0 pg/ml vs. saline 10.3 +/- 1.4 pg/ml, p < 0.05). This effect continued until 40 min post-injection (PrRP 1 nmol 9.9 +/- 1.5 pg/ml vs. saline 6.2 +/- 0.5 pg/ml, p < 0.05). In vitro PrRP (1-100 nmol/l) did not effect basal or corticotropin-releasing hormone (CRH)-stimulated ACTH release from dispersed anterior pituitary cells. PrRP increased hypothalamic release of CRH (PrRP 100 nmol/l 1.4 +/- 0.2 nmol/explant vs. the basal 1.1 +/- 0.2 nmol/explant, p < 0.05) but not arginine vasopressin. PrRP also stimulated neuropeptide Y release (PrRP 100 nmol/l 56.5 +/- 11.8 pmol/explant vs. basal 24.0 +/- 1.9 pmol/explant, p < 0.01), a neuropeptide known to stimulate the hypothalamo-pituitary-adrenal axis. Our data suggest that in vitro PrRP does not have a direct action on the corticotrope but increases plasma ACTH via the PVN and this effect involves the release of hypothalamic neuropeptides including CRH and neuropeptide Y.     

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

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

The responses of plasma adrenocorticotropin and cortisol to corticotropin-releasing hormone (CRH) and cerebrospinal fluid immunoreactive CRH in anorexia nervosa patients

Pituitary-adrenocortical responses to the iv injection of 100 micrograms synthetic ovine corticotropin-releasing hormone (CRH) were studied in 13 patients with anorexia nervosa, and the concentrations of immunoreactive CRH in cerebrospinal fluid were measured in 7 of them. Mean basal levels of plasma ACTH and cortisol were 32 +/- 5 pg/ml (+/- SEM) and 21.1 +/- 1.5 micrograms/dl, respectively. The latter value was significantly higher than that in age-matched normal women (P less than 0.005). The mean increments of plasma ACTH and cortisol in response to CRH injection in those 13 patients were 21 +/- 5 pg/ml and 5.3 +/- 1.7 micrograms/dl, respectively, significantly lower than those in normal women (58 +/- 6 pg/ml and 15.3 +/- 7.7 micrograms/dl, respectively; P less than 0.005). When 4 patients were reexamined after weight gains of between 3 and 22 kg, their responses to the CRH injection increased. The mean concentration of immunoreactive CRH in the cerebrospinal fluid of seven patients was 30.8 +/- 3.9 pg/ml (+/- SEM), which was higher than the value of 18.4 +/- 1.1 pg/ml (P less than 0.005) in control subjects with cervical spondylosis. These findings suggest the possibility that hypersecretion of CRH may occur in patients with anorexia nervosa.     

Responsivity of the baboon fetal pituitary to corticotropin-releasing hormone in utero at midgestation.

The present study was designed to determine whether the baboon fetal pituitary at midgestation was responsive in utero to a bolus injection of CRH. On day 100 of gestation (term = day 184), baboons were anesthetized with halothane/nitrous oxide, the fetus was exteriorized, and a cannula was inserted into a fetal carotid artery. Five minutes later (experimental time zero), a fetal carotid blood sample was obtained, and saline (0.5 ml) with (n = 6) or without (n = 3) ovine CRH (100 ng estimated to equal 500 ng/kg BW) was then infused via the fetal carotid over a 3-min period. Fetal blood samples were taken 5, 15, 30, 45, and 60 min post-CRH/saline treatment and assayed for ACTH. Mean (+/- SE) pretreatment fetal plasma ACTH concentrations were similar in animals that subsequently received saline (26 +/- 3 pg/ml) or CRH (29 +/- 6 pg/ml). Fetal plasma ACTH remained constant after the infusion of saline. In contrast, CRH increased (P less than 0.05) fetal plasma ACTH within 5 min in six of six baboons to a value (58 +/- 12 pg/ml) that exceeded (P less than 0.05) the zero time value and the respective mean value (27 +/- 5 pg/ml) in saline-treated fetuses. Fetal plasma ACTH concentrations continued to rise in four of six baboons 15 min after CRH injection to a level (68 +/- 15 pg/ml) which exceeded that in saline controls (27 +/- 2 pg/ml). In fetuses treated with CRH, overall mean fetal plasma ACTH concentrations from 0-60 min increased at a rate (1.47 pg/min) greater (P less than 0.05) than that in fetuses injected with saline (0.07 pg/min). In contrast to the effects of intracarotid CRH injection, fetal plasma ACTH was not increased after the infusion of 100 ng CRH into a fetal antecubital vein of three additional animals. Collectively, these findings indicate that intracarotid injection of a bolus of CRH into the baboon fetus rapidly increased fetal plasma ACTH concentrations. Moreover, the site of action of CRH was presumably the fetal pituitary. Therefore, we suggest that the baboon fetal hypothalamic-pituitary axis at midgestation has the capacity to secrete ACTH in response to a challenge of CRH.     

Corticotropin-releasing factor secretion increases in rat hypophysial portal blood during insulin-induced hypoglycemia

To study the possible involvement of hypothalamic corticotropin-releasing factor (CRF) in the stimulation of adrenocorticotropic hormone (ACTH) release caused by insulin-induced hypoglycemia (IIH), we measured CRF secretion in hypophysial portal blood (HPB) in rats anesthetized with sodium thiopental after injection of insulin. Before treatment, systemic ACTH levels (952 +/- SE 143 pg/ml; n = 12) were well above normal values, probably reflecting the anesthetic and surgical stress consecutive to the preparation for portal blood collection. Insulin injection induced a significant increase of ACTH release within 15 min (1,588 +/- 168 vs. 741 +/- 144 pg/ml; n = 6, in vehicle-injected rats) which lasted for at least 1 h. CRF levels in HPB were 857 +/- SE 168 pg/ml (n = 13) during the first-hour pretreatment collection. Vehicle injection did not modify CRF secretion (759 +/- 142 pg/ml; n = 6). Insulin injection provoked a significant increase in CRF release (1,449 +/- 257 pg/ml; n = 7). These data suggest that an increased hypothalamic CRF secretion is responsible for the stimulation of pituitary ACTH release following IIH. The possible involvement of central neuromediators in the IIH-induced CRF production is discussed.     

Immunoreactive corticotropin-releasing hormone present in human plasma may be derived from both hypothalamic and extrahypothalamic sources

Immunoreactive CRH concentrations were determined in human plasma using an immunoaffinity chromatographic extraction procedure and sensitive RIA. Immunoreactive CRH was detectable in the plasma of all normal subjects (mean +/- SD, 6.2 +/- 2.4 pg/mL; n = 15). Basal (0800-1000 h) plasma immunoreactive CRH levels were significantly lower in patients with Cushing's syndrome due to adrenal (2.8 +/- 1.1 pg/mL; n = 4) or pituitary adenomas (2.9 +/- 0.8 pg/mL; n = 5), in patients with hypothalamic hypopituitarism (3.2 +/- 0.9 pg/mL; n = 5), and in glucocorticoid-treated patients (3.9 +/- 1.9 pg/mL, n = 8). Basal plasma CRH levels were also low in patients with acromegaly (2.8 +/- 0.8 pg/mL; n = 14) and insulin-treated diabetic patients whose pituitary-adrenal function was normal (3.6 +/- 1.0 pg/mL; n = 12). In normal subjects plasma CRH levels increased after insulin-induced hypoglycemia; this response was abolished by the prior administration of dexamethasone. In contrast, basal plasma CRH levels were not affected by prior administration of metyrapone or dexamethasone. No evidence for diurnal variation in plasma immunoreactive CRH was found in normal subjects. In addition, in normal subjects oral glucose administration elicited a significant increase in plasma CRH (basal, 7.3 +/- 0.9 pg/mL; peak 30 min after glucose, 16.7 +/- 5.8 pg/mL; n = 5; P less than 0.05) without concomitant changes in ACTH. Gel filtration of extracts of pooled plasma from normal subjects revealed a major component of immunoreactive CRH in the position of synthetic rat CRH. Immunoreactive CRH-sized material had the same retention time as authentic rat CRH in a reverse phase high pressure liquid chromatography system. The content of immunoreactive CRH in human placenta, pancreas, and adrenal gland was much larger than that in hypothalamus. These findings suggest that immunoreactive CRH is present in peripheral plasma; the increase in plasma immunoreactive CRH after insulin-induced hypoglycemia may reflect stimulation of hypothalamic CRH release; the increase in plasma immunoreactive CRH after glucose administration may reflect extrahypothalamic CRH release; and the lack of diurnal variation in plasma immunoreactive CRH together with the lack of suppression of CRH by dexamethasone suggest that basal plasma CRH is of extrahypothalamic origin.     

Ovine corticotropin-releasing hormone stimulation test in normal children

We administered ovine corticotropin-releasing hormone (CRH) as a bolus iv injection (1 microgram/kg) to 21 normal boys and girls, aged 6-15 yr. CRH stimulated release of immunoreactive ACTH and cortisol in all children. The peak plasma ACTH and cortisol levels after CRH were 15.7 +/- 9.4 (SD) pg/ml and 14.3 +/- 3.6 micrograms/dl, respectively, in the girls, and 20.7 +/- 9.7 pg/ml and 16.6 +/- 3.3 micrograms/dl, respectively, in the boys. Plasma ACTH and cortisol responsiveness to CRH did not differ between girls or boys, or between children and adults. Cortisol-binding globulin concentrations in plasma did not change with age. We conclude that CRH provides a safe means of stimulating the pituitary-adrenal axis in children.     

Differential effects of estradiol on the adrenocorticotropin responses to interleukin-6 and interleukin-1 in the monkey.

Endotoxin and the inflammatory cytokines interleukin (IL)-1 and IL-6 are potent activators of the hypothalamic-pituitary-adrenal (HPA) axis. Although estradiol (E(2)) has been shown to enhance the HPA response to certain types of stress, previous studies in the rodent have shown that HPA responses to endotoxin and to IL-1 were enhanced by ovariectomy and attenuated by E(2). The mechanisms underlying these observations are unclear, but there is evidence that E(2) may have direct inhibitory effects on IL-6 synthesis and release. Because endotoxin and IL-1 both stimulate IL-6, it is possible that the E(2)-induced suppression of the HPA response to endotoxin and IL-1 results from decreased IL-6 release. We have therefore examined the ACTH response to IL-6 and IL-1beta in six ovariectomized rhesus monkeys with and without 3 weeks of E(2) replacement. In the first study, plasma ACTH levels peaked at 60 min after iv injection of 6 microg recombinant human IL-6. Both the ACTH response, over time, and the area under the ACTH response curve were significantly higher in the E(2)-treated animals (P < 0.05). The peak ACTH level was 66 +/- 16 pg/ml without E(2) vs. 161 +/- 69 pg/ml with E(2). In the second study, iv infusion of recombinant human IL-1beta (400 ng) produced plasma IL-6 levels comparable with those seen after IL-6 injection in the first study. In the IL-1 study, however, there was a significant attenuation of the ACTH response, over time, in the E(2)-treated animals (P < 0.001); the peak ACTH level was 83 +/- 34 pg/ml vs. 13 +/- 4.4 pg/ml after E(2). The IL-6 response was similarly attenuated (P < 0.001); the peak IL-6 level was 614 +/- 168 pg/ml vs. 277 +/- 53 pg/ml after E(2) treatment. Our results demonstrate that physiological levels of E(2) enhance the ACTH response to IL-6 but attenuate the ACTH response to IL-1. The attenuated ACTH response to IL-1 was accompanied by a blunted IL-6 response. Our results suggest that the blunted HPA response to IL-1 can be explained, at least in part, by E(2)-induced alterations in IL-6 release. It remains to be determined whether E(2) affects other inflammatory mediators that also participate in this process.     

Hypothalamic amenorrhea with normal body weight: ACTH, allopregnanolone and cortisol responses to corticotropin-releasing hormone test

OBJECTIVE: Hypothalamic amenorrhea (HA) is a functional disorder caused by disturbances in gonadotropin-releasing hormone (GnRH) pulsatility. The mechanism by which stress alters GnRH release is not well known. Recently, the role of corticotropin-releasing hormone (CRH) and neurosteroids in the pathophysiology of HA has been considered. The aim of the present study was to explore further the role of the hypothalamic-pituitary-adrenal axis in HA. DESIGN: We included 8 patients (aged 23.16+/-1.72 years) suffering from hypothalamic stress-related amenorrhea with normal body weight and 8 age-matched healthy controls in the follicular phase of the menstrual cycle. METHODS: We measured basal serum levels of FSH, LH, and estradiol and evaluated ACTH, allopregnanolone and cortisol responses to CRH test in both HA patients and healthy women. RESULTS: Serum basal levels of FSH, LH, and estradiol as well as basal levels of allopregnanolone were significantly lower in HA patients than in controls (P<0.001) while basal ACTH and cortisol levels were significantly higher in amenorrheic patients with respect to controls (P<0.001). The response (area under the curve) of ACTH, allopregnanolone and cortisol to CRH was significantly lower in amenorrheic women compared with controls (P<0.001, P<0.05, P<0.05 respectively). CONCLUSIONS: In conclusion, women with HA, despite the high ACTH and cortisol levels and, therefore, hypothalamus-pituitary-adrenal axis hyperactivity, are characterized by low allopregnanolone basal levels, deriving from an impairment of both adrenal and ovarian synthesis. The blunted ACTH, allopregnanolone and cortisol responses to CRH indicate that, in hypothalamic amenorrhea, there is a reduced sensitivity and expression of CRH receptor. These results open new perspectives on the role of neurosteroids in the pathogenesis of hypothalamic amenorrhea.     

The effects of epinephrine on norepinephrine release in essential hypertension

The effects of endogenous epinephrine (E), released by glucagon injection, and exogenously infused E on plasma norepinephrine (NE) and cardiovascular responses before and after beta-blockade were studied in patients with essential hypertension and in age-matched normotensive controls. The resting plasma NE and E levels were significantly higher in the borderline hypertensive subjects (NE: 251 +/- 21 pg/ml [SEM], p less than 0.005; E: 57 +/- 5, p less than 0.05, n = 18) than in controls (NE: 129 +/- 12; E: 39 +/- 5, n = 18). An intravenous injection of glucagon (1.0 mg) induced a transient rise of both plasma catecholamine levels and blood pressure in every subject studied. Plasma E levels rose transiently and returned to the basal levels by 20 minutes after the injection, whereas plasma NE levels showed a more prolonged rise over 20 minutes. beta-Blockade with propranolol did not affect the plasma E response to glucagon, but inhibited the prolonged rise of plasma NE levels. An intravenous infusion of exogenous E (1.25-1.50 micrograms/min) for 30 minutes caused an apparent rise of both plasma NE levels and blood pressure, which lasted more than 60 minutes after stopping the E infusion. Propranolol did not affect the time course of plasma E but again inhibited the prolonged rise of both plasma NE levels and blood pressure. No significant differences could be observed in the cardiovascular or plasma NE responses to glucagon or to E infusion between normal and hypertensive subjects. These findings lend support to the view that plasma E can act physiologically as a sustained stimulator of presynaptic beta-adrenergic receptors, which leads to an enhanced NE release from peripheral sympathetic nerve terminals and a rise of blood pressure in humans.     

A short negative feedback mechanism regulating corticotropin-releasing hormone release

The effect of ACTH administration on plasma CRH levels was studied. In five patients with Addison's disease and three patients with hypopituitarism, bolus iv injection of 0.25 and 0.5 mg ACTH-(1-24) reduced plasma CRH levels (that had become elevated 48 h after discontinuation of corticosteroid replacement) to near-normal levels at 30-60 min in a dose-dependent manner. Plasma immunoreactive beta-endorphin levels were similarly decreased in patients with Addison's disease. ACTH-(1-24) (0.25 and 0.5 mg) injection failed to inhibit plasma CRH levels in five normal subjects. Basal CRH release from the rat hypothalamic median eminence in vitro was inhibited by 0.22 and 2.2 nM ACTH-(1-24) and ACTH-(1-39) in a dose-dependent manner. These results suggest that in the absence of negative feedback control of ACTH secretion by glucocorticoids, ACTH can regulate its secretion by inhibition of hypothalamic CRH release.     

Failure of somatostatin and octreotide to acutely affect the hypothalamic-pituitary-adrenal function in patients with corticotropin hypersecretion

Although somatostatin inhibits a variety of pituitary and non-pituitary hormones, not univocal data on its effects on ACTH release have been reported so far. In this study we investigated the effects of somatostatin or octreotide on ACTH levels of patients with corticotropin hypersecretion: 7 patients with Addison's disease, 2 patients previously adrenalectomized for Cushing's disease, 4 patients with Cushing's disease and 3 patients with ectopic ACTH syndrome. Plasma ACTH and cortisol levels were determined after somatostatin (500 micrograms over 60 min) infusion or octreotide (100 micrograms sc) injection. In 5 other patients with Cushing's disease ACTH and cortisol responses to CRH (1 microgram/kg iv) were evaluated in basal conditions and after octreotide acute administration. In no patients with Addison's disease any inhibitory influence of somatostatin (delta % = -21, -25) or octreotide (delta % = -38 +/- 12 vs -39 +/- 12 after saline) on plasma ACTH was found. Somatostatin did not significantly inhibit plasma ACTH in the two patients previously adrenalectomized for Cushing's disease and in 3 patients with Cushing's syndrome; in other 4 patients with Cushing's syndrome octreotide did not affect plasma ACTH levels. In 5 patients with Cushing's disease the plasma ACTH and cortisol responses to CRH were similar both before (ACTH from 9.9 +/- 1.7 pmol/L to 19.4 +/- 6.1 pmol/L; cortisol from 496 +/- 43.9 nmol/L to 923 +/- 355 nmol/L) and after octreotide injection (ACTH from 8.8 +/- 2.4 pmol/L to 19.1 +/- 8.2 pmol/L; cortisol from 510 +/- 54.6 nmol/L to 735 +/- 220 nmol/L). In conclusion, the acute administration of somatostatin or octreotide is not able to modify ACTH levels in patients with corticotropin hypersecretion either due to hypocortisolemic state or consequent to ACTH-secreting pituitary or ectopic tumors; moreover, octreotide does not affect the pituitary-adrenal responsiveness to CRH in patients with Cushing's disease.     

Responses of the hypothalamic-pituitary-adrenal and renin-angiotensin axes and the sympathetic system during controlled surgical and anesthetic stress

We studied the responses of plasma CRH, ACTH, cortisol, norepinephrine, epinephrine, and renin activity in 11 patients undergoing parathyroid or thyroid surgery after identical preoperative sedation and during isoflurane (Forane) anesthesia. During surgical exploration, plasma CRH levels [10 +/- 2 (+/- SEM) pg/mL] remained at basal (unstimulated) levels, and plasma ACTH (11.5 +/- 1.4 pg/mL), cortisol (24 +/- 4 micrograms/dL), and epinephrine (35 +/- 10 pg/mL) concentrations remained within their normal morning ranges. The majority of the patients had no evidence of pulsatile ACTH secretion during the operation, but, rather, secreted ACTH and cortisol continuously. There was a small elevation of plasma norepinephrine and PRA which was associated with a small increase in heart rate and decrease in blood pressure. Anesthesia reversal, endotrachial extubation, and the early recovery period were associated with marked mean peak increases in plasma ACTH (173 +/- 45 pg/mL), cortisol (35 +/- 6 micrograms/dL), and epinephrine (220 +/- 56 pg/mL) and the return of plasma norepinephrine and PRA to basal levels. All hormones returned to basal levels by the first post-operative day. The data suggest that with modern anesthetic techniques patients undergoing neck surgery had mildly elevated plasma ACTH, cortisol, and epinephrine levels. Glucocorticoid secretion during the operation was maintained primarily by continuous rather than pulsatile ACTH secretion. The immediate postoperative period was associated with profound elevations of plasma ACTH, cortisol, and epinephrine. The major determinant of ACTH, cortisol, and epinephrine secretion was anesthesia reversal and recovery and not surgical trauma.     

Estrogen modulates the hypothalamic-pituitary-adrenal and inflammatory cytokine responses to endotoxin in women

Endotoxin stimulates the release of the inflammatory cytokines interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF)-alpha, which are potent activators of the hypothalamic-pituitary-adrenal (HPA) axis. Recent studies in the rodent and in the primate have shown that the HPA responses to endotoxin and IL-1 were enhanced by gonadectomy and attenuated by estradiol (E2) replacement. In addition, there is some evidence, in the rodent, that estrogen modulates inflammatory cytokine responses to endotoxin. To determine whether estrogen has similar effects in humans, we studied the cytokine and HPA responses to a low dose of endotoxin (2--3 ng/kg) in six postmenopausal women with and without transdermal E2 (0.1 mg) replacement. Mean E2 levels were 7.3 +/- 0.8 pg/mL in the unreplaced subjects and increased to 102 +/- 13 pg/mL after estrogen replacement. Blood was sampled every 20 min for 1--2 h before, and for 7 h after, iv endotoxin administration. Endotoxin stimulated ACTH, cortisol, and cytokine release in women with and without E2 replacement. E2 significantly attenuated the release of ACTH (P < 0.0001) and of cortisol (P = 0.02). Mean ACTH levels peaked at 190 +/- 91 pg/mL in the E2-replaced group vs. 411 +/- 144 pg/mL in the unreplaced women, whereas the corresponding mean cortisol levels peaked at 27 +/- 2.9 microg/dL with E2 vs. 31 +/- 3.2 microg/dL without E2. Estrogen also attenuated the endotoxin-induced release of IL-6 (P = 0.02), IL-1 receptor antagonist (P = 0.003), and TNF-alpha (P = 0.04). Mean cytokine levels with and without E2 replacement peaked at 341 +/- 94 pg/mL vs. 936 +/- 620 pg/mL for IL-6, 82 +/- 14 ng/mL vs. 133 +/- 24 ng/mL for IL-1 receptor antagonist, and 77 +/- 46 pg/mL vs. 214 +/- 87 pg/mL for TNF-alpha, respectively. We conclude that inflammatory cytokine and HPA responses to a low dose of endotoxin are attenuated in postmenopausal women receiving E2 replacement. These data show, for the first time in the human, that a physiological dose of estrogen can restrain cytokine and neuroendocrine responses to an inflammatory challenge.     

Response to corticotropin-releasing hormone during pregnancy in the baboon

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

Cerebrospinal fluid immunoreactive corticotropin-releasing hormone and adrenocorticotropin secretion in Cushing's disease and major depression: potential clinical implications.

To explore whether possible differences in central nervous system neuromodulators contribute to the differential presentation of affective symptomatology in Cushing's disease and major depression, we examined the levels of immunoreactive CRH and ACTH in the cerebrospinal fluid (CSF) of 11 patients with Cushing's disease, a patient with ectopic ACTH secretion, 34 patients with major depression, and 60 healthy subjects. We elected to measure these peptides not only because both are classically involved in pituitary-adrenal regulation, but also because their primarily arousal-producing and anorexigenic behavioral effects in experimental animals suggest that they may play a role in the symptom complex of depressive syndromes. We also explored whether the CSF levels of these peptides were more helpful in determining the often difficult differential diagnosis between major depression and Cushing's disease than the plasma ACTH response to ovine CRH, a currently used but somewhat insensitive laboratory means of distinguishing these disorders. CSF levels of immunoreactive CRH and ACTH were significantly lower in Cushing's disease patients [21.9 +/- 2.7 and 15.4 +/- 1.8 pg/mL, (mean +/- SEM), respectively] compared to patients with major depression [38.4 +/- 2.3 pg/mL (P less than 0.01) and 24.5 +/- 1.6 pg/mL (P less than 0.01), respectively] and controls [38.4 +/- 1.6 pg/mL (P less than 0.001) and 26.3 +/- 1.1 pg/mL (P less than 0.001), respectively]. The coexistence of high plasma ACTH and low CSF ACTH in Cushing's disease yielded a CSF/plasma ACTH ratio consistently less than that in depressed patients, with only 2 of 31 subjects comprising both groups showing values that overlapped. In contrast, 9 of the combined patients showed ACTH responses to ovine CRH that overlapped. These data suggest that differences in centrally directed CRH secretion may account for the differential presentation of the dysphoric syndromes seen in major depression and Cushing's disease. Hence, the classic form of major depression (melancholia), is often associated with evidence of pathological hyperarousal, such as intense anxiety, sleeplessness, and anorexia, while that of Cushing's disease is associated with evidence of pathological hyperarousal, including hyperphagia, fatigue, and inertia. Moreover, measurement of the CSF/plasma ACTH ratio may serve as a clinically useful adjunct to the ovine CRH stimulation test and other laboratory measures in determining the differential diagnosis between major depression and Cushing's disease.     

Responsivity of adrenocorticotropin to corticotropin-releasing hormone and lack of suppressibility by dexamethasone are related phenomena in Cushing's disease

The ACTH and cortisol responses to 100 micrograms ovine corticotropin-releasing hormone (CRH) in 19 consecutive patients with Cushing's disease were compared with those in 13 normal subjects. In 2 patients with Cushing's disease, plasma ACTH and cortisol did not increase after CRH administration. Compared to the normal subjects, maximal ACTH increments [135 +/- 25 (+/- SEM) vs. 42 +/- 6 pg/ml; P less than 0.001, by Wilcoxon's two-sample test] and maximal cortisol increments (17.7 +/- 1.8 vs. 9.4 +/- 1.1 micrograms/100 ml; P less than 0.01 by Wilcoxon's test) after CRH were significantly higher in the 17 CRH-responsive patients with Cushing's disease. In the normal subjects, there was a significant negative correlation between the basal cortisol level and the maximal ACTH (r = -0.65; P less than 0.05, by Spearman's rank correlation test) and cortisol (r = -0.95; P less than 0.001, by Spearman's test) responses to CRH. In contrast, in the CRH-responsive Cushing patients, there was no significant correlation between the basal cortisol level and the maximal ACTH (r = 0.10; P greater than 0.10, by Spearman's test) and cortisol (r = 0.14; P greater than 0.10, by Spearman's test) increments after CRH treatment. In the normal subjects, there was no significant correlation between the basal ACTH level and the maximal ACTH increments after CRH administration (r = -0.24; P greater than 0.10, by Spearman's test). Again in contrast, in the CRH-responsive Cushing patients, maximal ACTH increments after CRH treatment correlated positively with basal ACTH levels (r = 0.69; P less than 0.005, by Spearman's test). Moreover, in these patients, the maximal ACTH increments after CRH were positively correlated with the ACTH levels after suppression with higher and lower doses of dexamethasone. We conclude that in Cushing's disease, unlike in normal subjects, circulating cortisol is not the major modulator of ACTH and cortisol responses to CRH, and that in these patients, responsivity of ACTH to CRH and lack of suppressibility by dexamethasone are related phenomena.     

A central mechanism is involved in the secretion of ACTH in response to IL-6 in rats: comparison to and interaction with IL-1 beta.

The cytokines interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha are known to be potent effectors of ACTH secretion. Some of the peripheral effects of IL-1 beta appear to be related to the secretion of IL-6 induced by IL-1 beta. Thus, we evaluated the effect of IL-6 on ACTH secretion and its interaction with IL-1 beta. Rats received recombinant human (rhIL-6) or murine (rmIL-6) IL-6 through indwelling jugular cannulae. rhIL-6 (200 ng or 2 micrograms/rat) produced peak plasma ACTH levels which were 3- to 4-fold greater than basal levels. rmIL-6 produced similar responses. Neither species of IL-6 affected plasma prolactin levels. Comparison of rhIL-1 beta (200 ng) to rhIL-6 (200, 100 or 50 ng) showed that IL-6 elevated ACTH in a dose-dependent manner and that IL-1 beta was significantly more effective. IL-1 beta was also administered concomitantly with or 10 min after IL-6. Delivered together, IL-1 beta (100, 30 or 10 ng) and IL-6 (100 ng) produced significantly higher ACTH levels than when given alone. This additivity was also evident when IL-6 was given 10 min prior to IL-1 beta. The coadministration of IL-6 (2 micrograms) with corticotropin-releasing factor (CRF, 1 micrograms/kg, b.w.) also had an additive effect on ACTH secretion (at 20 min: 300 +/- 40 pg/ml for CRF; 320 +/- 83 pg/ml for IL-6; and 540 +/- 44 pg/ml for CRF + IL-6), whereas a higher dose of CRF (10 micrograms/kg b.w.) yielded ACTH levels of 1,000 +/- 107 pg/ml at 20 min, with no further enhancement by IL-6. Incubation of pituitary cells with IL-6 alone (0.1, 1.0 or 3.0 nM) produced a slight but significant stimulation of ACTH secretion within 2 h in response to the higher doses of IL-6 only (p < 0.05), but did not modify the effect of CRF in vitro. To determine if the action of IL-6 was at a site(s) within the brain, IL-6 (30 or 100 ng/0.5 microliters) was injected into the third cerebroventricle of alert rats. 100 ng IL-6 elicited peak plasma ACTH levels (300 +/- 65 pg/ml) within 30 min; these were significantly higher than the buffer responses (90 +/- 25 pg/ml, p < 0.01), and lower than the responses to 30 ng IL-1 beta (530 +/- 50 pg/ml, p < 0.001). 30 ng IL-6 was ineffective.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distinct classes of corticotropes mediate corticotropin-releasing hormone- and arginine vasopressin-stimulated adrenocorticotropin release.

ACTH release from the anterior pituitary gland is principally driven by the two hypothalamic hormones, corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP). Using the reverse hemolytic plaque assay, we have compared the effects of CRH and AVP on ACTH release from individual, dispersed pituitary cells. A small percent (0.36 +/- 0.06%) of pituitary cells formed plaques when exposed to medium alone. AVP caused 3.44 +/- 0.10% of cells to form plaques (P less than 0.01 compared with medium alone), CRH produced 4.85 +/- 0.20% plaque-forming cells (P less than 0.01 compared with AVP), and the combination of CRH and AVP produced a still greater percent of plaque-forming cells (5.80 +/- 0.20%, P less than 0.01 compared with CRH alone). A double reverse hemolytic plaque assay was then employed to examine whether some cells formed plaques only in the presence of one or other secretagogue. Using this technique we found clear evidence of cells that formed plaques in response to CRH but not AVP (P less than 0.005); CRH or AVP (P less than 0.0001), and CRH and AVP (P less than 0.05). There was no evidence of a corticotrope forming a plaque with AVP but not CRH (P = 0.52). Thus there appears to be functionally distinct classes of corticotropes. These findings have important implications for our understanding of the relative responsiveness of the pituitary to hypothalamic secretagogues and provide a new physiological perspective on recent reports of stress-specific hypothalamic responses regulating ACTH release.     

The combined dexamethasone-suppression/CRH-stimulation test in alcoholics during and after acute withdrawal

BACKGROUND: Chronic alcoholism is often accompanied by disturbances of the hypothalamic-pituitary-adrenal (HPA) system. Patients with alcoholism frequently show nonsuppression in the dexamethasone (Dex) suppression test and also a blunted increase of adrenocorticotropin (ACTH) after injection of corticotropin-releasing hormone (hCRH). However, the underlying mechanisms have not been fully elucidated. The combined Dex/CRH test (pretreatment with 1.5 mg dexamethasone at 2300 hr, injection of 100 microg hCRH at 1500 hr the next day) has been established as a more sensitive tool to investigate HPA system regulation in depressed patients. METHODS: We studied the effect of the combined Dex/CRH test in 19 alcoholic inpatients (9 male, 10 female) during and after withdrawal along with 19 healthy controls. RESULTS: Compared to normal controls, patients showed a severely dysregulated HPA system during withdrawal, with significantly elevated cortisol and ACTH response to hCRH after pretreatment with dexamethasone. After completed withdrawal, cortisol levels after injection of hCRH were almost normalized while ACTH values were partially lower in patients, compared to controls. CONCLUSIONS: We conclude that the HPA system is severely disturbed during alcohol withdrawal, possibly reflecting an exaggerated release of hypothalamic corticotropin and vasopressin.