Increase In Plasma ACTH Levels Research Articles

Increased plasma corticosterone levels in bovine growth hormone (bGH) transgenic mice: effects of ACTH, GH and IGF-I on in vitro adrenal corticosterone production.

Previous work from our laboratory provided evidence for increased plasma corticosterone levels in mice transgenic for human and bovine growth hormone (GH). Corticosterone was elevated in both sexes, under both basal and ether-induced stress conditions. The objectives of the present study were to investigate the in vitro adrenal sensitivity to ACTH, GH and/or IGF-I in normal and bGH transgenic mice, to examine plasma corticosterone levels at different times of the day, and to determine plasma levels of ACTH in these animals. For the measurement of plasma corticosterone and ACTH levels, transgenic and normal siblings were housed 2 per cage and decapitated simultaneously within 20 seconds of the first disturbance of the cage. The corticosterone production by in vitro adrenal incubations did not differ between adrenals from normal and transgenic mice at the basal level or in the presence of different doses of ACTH. Growth hormone or IGF-I did not have any effect on corticosterone production in vitro when given alone, and did not modify the effects of ACTH on the accumulation of corticosterone production in vitro when alone, and did not modify the effects of ACTH on the accumulation of corticosterone in the media. Plasma corticosterone concentrations were higher in transgenic than in normal animals in both morning and evening. Plasma concentrations of ACTH in animals killed in the morning were sharply increased in transgenic males as compared with their normal siblings. The results indicate that increased circulating levels of corticosterone in transgenic mice are not due to a potentiation of ACTH actions by GH or IGF-I, but rather to a chronic increase in plasma ACTH levels. The increase in ACTH is presumably a reflection of GH actions in the hypothalamic-pituitary system.

Central administration of saikosaponin-d increases corticotropin-releasing factor mRNA levels in the rat hypothalamus

Saiko agents, Chinese herbal drugs, stimulate corticotropin-releasing factor (CRF) release from the hypothalamus, adrenocorticotropin (ACTH) secretion and proopiomelanocortin (the precursor for ACTH) gene expression in the anterior pituitary. In the present study, the effect of intracerebroventricular injection of saikosaponin (SS)-a and -d, two of the main components of saiko agents, on hypothalamic CRF gene expression was examined in pentobarbital-anesthetized rats. Administration of SS-d, 0.2–2.0 μg/kg body wt, increased plasma ACTH levels, proopiomelanocortin mRNA levels in the anterior pituitary and the CRF mRNA level in the hypothalamus in a dose-dependent manner, whereas SS-a failed to have an affect on these levels. These findings indicate that SS-d stimulates both CRF gene expression and CRF release, which in turn increases ACTH release and proopiomelanocortin gene expression in the anterior pituitary. Therefore, SS-d is believed to have an important role both in saiko agent-induced CRF release and CRF gene expression in the hypothalamus.

Microinjection of norepinephrine into the paraventricular nucleus of the hypothalamus stimulates corticotropin-releasing factor gene expression in conscious rats.

To examine the physiological effects of norepinephrine (NE) in the paraventricular nucleus of the hypothalamus (PVH) on CRF gene expression and CRF release, NE was microinjected bilaterally into the PVH of conscious rats, and kinetic studies were performed on the levels of POMC messenger RNA (mRNA) in the anterior pituitary (AP), CRF mRNA in the PVH-containing hypothalamic fragment, and plasma ACTH. Plasma ACTH levels were increased dose dependently by NE (5-50 nmol/side) injection into the PVH. They reached their peaks after 30 min and returned to the basal values after 90 min. The POMC mRNA level in the AP and hypothalamic CRF mRNA level increased significantly 90 min after NE injection and increased further after 120 min. The POMC mRNA level in the AP and hypothalamic CRF mRNA level were increased dose dependently by NE (5-50 nmol/side) after 120 min. Intracerebroventricular pretreatment with prazosin abolished completely the increase in plasma ACTH levels after intrahypothalamic NE injection, whereas pretreatment with propranolol was without significant effect. These results suggest that NE stimulates CRF gene expression in the PVH and CRF secretion into the portal circulation, thus regulating positively the hypothalamic-pituitary-adrenal axis. alpha 1-Adrenergic receptors may mediate the action of NE on CRF neurons.

Prenatal alcohol exposure alters the hypothalamic-pituitary-adrenal axis response of immature offspring to interleukin-1: is nitric oxide involved?

We have previously shown that following prenatal alcohol exposure, immature offspring showed blunted ACTH released in response to the peripheral administration of interleukin-1 beta (IL-1 beta). The present studies were conducted to investigate the role of changes in corticosteroid feedback (measured by altered adrenal responses to ACTH), corticotropin-releasing factor (CRF) content of the median eminence (ME), and the influence of endogenous nitric oxide (NO). The injection of several doses of ACTH failed to indicate measurable differences between the corticosterone responses of offspring born to dams fed ad libitum [control (C)], pair-fed (PF), or fed alcohol [ethanol (EtOH) = E]. CRF content in the ME, taken as an index of the amount of releasable peptide, showed a small, but statistically significant, decrease following prenatal alcohol exposure. A comparable change, however, was also noted in PF rats. As expected, the subcutaneous injection of IL-1 beta (0.5 microgram/kg) induced smaller increases in plasma ACTH levels of E than C pups. The response of PF animals was intermediate between that of E and C rats. Finally, we observed that inhibition of NO formation by the administration of the arginine derivative L omega nitro-L-arginine-methylester significantly augmented ACTH secretion in all three experimental groups, and reversed the decreased corticotrophs' response to IL-1 beta caused by prenatal alcohol. Taken together, our results suggest that the ability of prenatal alcohol exposure to alter ACTH released by immature pups in response to blood-borne IL-1 beta is probably not mediated through changes in adrenal responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex differences in endocrine response to hyperthermia in sauna.

Neuroendocrine response was investigated during and after a single 20 min bath in sauna (80 degrees C) in a group of 8 healthy men and 8 healthy women. In an additional group of 8 young men, the dynamics of plasma ACTH and cortisol levels were studied during a 30 min sauna exposure (90 degrees C). This dynamic study showed a biphasic response of plasma cortisol which decreased during the initial phase of sauna bath (15 min) and increased thereafter, reaching its maximum 15 min after the end of bathing. Maximal increase in plasma ACTH levels occurred 15 min earlier. In the first sauna exposed group the increase in body temperature was the same (about 2 degrees C) in both sexes. Nevertheless, the elevation in plasma ACTH concentration was significantly more pronounced in women than in men. In the plasma collected at the end of sauna bath inside the sauna room, a significant rise in both adrenaline and noradrenaline levels was found. Though the catecholamine responses were similar in both groups, the increase in heart rate during sauna bath was significantly higher in women. Sauna-induced prolactin release was also more pronounced in women compared with men. Thus hyperthermia induced by sauna exposure resulted in a more pronounced neuroendocrine activation in women compared with men. Moreover, it is evident that repeated blood sampling is necessary to reveal the sauna-induced activation of some hormonal systems.

Stimulatory effect of interleukin-1β on the hypothalamic-pituitary-adrenal axis of the rat: influence of age, gender and circulating sex steroids

The bilateral communication between the immune and neuroendocrine systems plays an essential role in modulating the adequate response of the hypothalamic-pituitary-adrenal (HPA) axis to the stimulatory influence of interleukins (ILs). It is thus reasonable to assume that inappropriate responses of the HPA axis to ILs might play a role in modulating the onset of pathological conditions such as infections. As part of our programme aimed at investigating the ability of ILs to release pro-opiomelanocortin-like peptides and corticosterone in rats exposed to alcohol, we observed that this stimulatory action appeared to be influenced by the gender of the animals. We therefore examined the ability of IL-1 beta, injected peripherally, to stimulate the HPA axis as a function of stage of sexual maturation and the presence or absence of circulating sex steroids. In immature (21 to 22-day-old) rats, both males and females responded to the i.p. administration of 0.5 or 2.0 micrograms IL-1 beta/kg with statistically comparable increases in plasma ACTH levels. In contrast, females released significantly (P < 0.01) more corticosterone in response to the lower dose of cytokine. Forty-day-old intact animals showed no sexual dimorphism in ACTH secretion, but the females again secreted significantly (P < 0.05-0.01) more corticosterone. Gonadectomy, performed 7-8 days prior to the assay, increased the absolute amount of corticosterone released over a 60-min period. A noticeable dimorphism of the ACTH response to IL-1 beta became apparent in 70-day-old intact rats, with females secreting more ACTH than males.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated plasma adrenocorticotropin concentration as evidence of limited adrenocortical reserve in patients with adrenomyeloneuropathy.

Adrenal insufficiency occurs in approximately two thirds of patients with adrenomyeloneuropathy. Its development may precede or follow the onset of neurological disease. To define the sensitivity of various tests of adrenal cortical function, we reviewed adrenocortical function tests in 28 patients with adrenomyeloneuropathy who had normal ACTH stimulation tests at the time of enrollment into an ongoing dietary study. Endocrine studies performed at 6-month intervals included a conventional ACTH stimulation test, plasma ACTH and cortisol concentrations, and 24-h urinary cortisol and aldosterone excretion rates. Eleven patients (39%) developed an elevated plasma ACTH concentration after a median follow-up of 3 yr. Their 24-h urinary cortisol and plasma basal and ACTH-stimulated cortisol concentrations were all normal. The mean basal cortisol level tended to be lower in patients who had increased plasma ACTH levels than in patients who maintained a normal plasma ACTH concentration during the study period (408 +/- 22 vs. 491 +/- 33 nmol/L; P = 0.05). Patients who had an increased plasma ACTH concentration and symptoms consistent with adrenal insufficiency had a lower mean 24-h urinary free cortisol level than those with normal plasma ACTH (196 +/- 22 vs. 281 +/- 30 nmol/day; P < 0.05). Plasma ACTH concentrations were persistently elevated in six patients in whom subsequent values were available. One individual later developed a subnormal ACTH-stimulated cortisol concentration consistent with overt adrenal insufficiency. Our results suggest that conventional provocative and integrative tests of adrenocortical function may not be sufficient to identify patients with adrenomyeloneuropathy who have compensated adrenal hypofunction. An elevated plasma ACTH concentration may represent an early marker for adrenocortical dysfunction and incipient adrenal insufficiency in AMN patients.

Patterns of ACTH response to oCRH in Cushing's disease: correlation with histological/immunocytochemical findings.

The most common lesion in Cushing's disease is an anterior pituitary adenoma. However, normal or hyperplastic corticotropic pituitary tissue has also been found in some cases. In an attempt to distinguish the patterns of ACTH response to oCRH in different forms of anterior pituitary hypersecretion, 17 patients with pituitary adenoma and 17 without pathological evidence of adenoma were studied. These patients underwent transsphenoidal pituitary surgery by the same surgeon and were retrospectively evaluated. The diagnosis of pituitary lesions was confirmed by microscopical and immunohistochemical studies. Patients without pituitary adenoma showed a higher and more prolonged mean plasma ACTH response than that observed in patients with pituitary tumors. In patients with pituitary adenoma, the peak ACTH response was observed within 30 min after oCRH administration, and was followed by a gradual decrease to basal levels in the following 30 min. In those cases in whom no pituitary adenoma was found, oCRH injection produced a marked increase in plasma ACTH levels during the first 60 min with a slower decline at the subsequent time points. The mean response curves of the two groups, analyzed by Beherens-Fischer nonparametric ANOVA, showed significant differences, either when they were compared globally (p < 0.01), or at single time points. Differences in ACTH response to oCRH stimulation support the hypothesis of different pathogenetic mechanisms leading to ACTH hypersecretion in Cushing's disease with and without pituitary adenoma.

Corticotropin-releasing hormone, proopiomelanocortin, and glucocorticoid receptor gene expression in adrenocorticotropin-producing tumors in vitro.

To differentiate between ectopic ACTH syndrome and Cushing's disease, gene expression of corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), and glucocorticoid receptor was examined in 10 pituitary adenomas (Cushing's disease) and in 10 ectopic ACTH-producing tumors. CRH increased plasma ACTH levels in all patients with Cushing's disease and in five patients with ectopic ACTH syndrome whose tumors contained CRH and CRH mRNA. In five CRH nonresponders, CRH was not detected in tumors that contained no CRH mRNA or that contained only long-size CRH mRNA. Dexamethasone (Dex) decreased plasma ACTH levels in all patients with Cushing's disease and in three patients with ectopic ACTH-producing bronchial carcinoid. These tumors contained glucocorticoid receptor mRNA. CRH increased and Dex decreased ACTH release and POMC mRNA levels in pituitary adenoma and bronchial carcinoid cells. PMA increased POMC mRNA levels only in carcinoid cells. These results reveal characteristics of ectopic ACTH-producing tumors: long-size CRH mRNA and PMA-induced POMC gene expression. In addition, there are two ectopic ACTH syndrome subtypes: tumors containing ACTH with CRH (CRH responder) and tumors without CRH. Dex decreases ACTH release and POMC mRNA levels in some bronchial carcinoids. Therefore, CRH and Dex tests have limited usefulness in differentiating between Cushing's disease and ectopic ACTH syndrome.

Psychoneuroendocrine outcomes of short-term crowding stress

One-week exposure to crowding stress has been reported to affect body weight and pituitary-adrenal axis activity. This study has first evaluated whether the aforementioned changes are associated with altered exploratory activity. One-week crowding (16 rats/cage) diminished body weight gains, compared to the control situation (four rats/cage): actually, this difference was mainly due to a marked loss in food intake and body weight following the first day of crowding. On the other hand, 1-week crowded rats were not different from their controls when placed for the first time in an open field, as shown by the analysis of their exploratory activities, their number of grooming episodes, and their defecation. Psychoneuroendocrine effects of 1-day crowding were then investigated: actually, open field behaviors were not modified but basal plasma glucose levels were decreased. Moreover, neither plasma ACTH and corticosterone levels nor 2-min cold swim-induced increases in corticosterone levels were affected. Besides, cold swim-induced increases in plasma ACTH levels were amplified in crowded rats, and these increases were associated with hyperglycemia in crowded, but not in control rats. It is suggested that 1-day exposure to crowding has differential consequences upon feeding and exploratory behaviors while potentiating the responsiveness of stress hormones.

Ontogeny of insulin-induced hypoglycemia stimulation of adrenocorticotropin secretion in the rat: role of catecholamines.

We previously reported that insulin-induced hypoglycemia (IIH) induces a large increase in plasma ACTH and corticosterone levels in the developing rat during the stress hyporesponsive period and that this effect is mediated, at least partially, by arginine vasopressin (AVP), but not corticotropin-releasing factor. Nevertheless, ACTH secretion in response to IIH in rats immunoneutralized against AVP was still stimulated, suggesting that other regulatory factors participate in the stimulation of ACTH secretion during IIH. It has been suggested that, in the adult rat, during profound hypoglycemia, epinephrine may act at the pituitary level through beta 2-adrenergic receptors to stimulate ACTH secretion. In this report, we studied the effect of the blockade of beta-adrenergic receptors on the pituitary-adrenal axis response to IIH. Rats (20 or 8 day old) were pretreated with saline or 2.5 mg/kg propranolol (a beta-adrenergic receptors antagonist) and subsequently injected with 3 IU/kg insulin. In 20-day-old rats, insulin injection induced a large increase of plasma ACTH concentrations that were unaffected by propranolol pretreatment. In 8-day-old rats, the IIH-induced increase of plasma ACTH levels was significantly reduced by propranolol pretreatment. Pretreatment of 8-day-old rats with 5 mg/kg CGP 20712A (a selective beta 1-adrenergic receptor antagonist) did not change the plasma ACTH response to insulin injection, while pretreatment with 2.5 mg/kg ICI 118551 (a selective beta 2-adrenergic receptor antagonist) resulted in a significant decrease of the IIH-induced stimulation of ACTH secretion. We next studied the effect of the blockade of circulating AVP and/or beta-adrenergic receptors on the pituitary response to IIH. Pretreatment of 8-day-old rats with antiserum anti-AVP or propranolol was followed by a significant reduction of IIH-induced increase of plasma ACTH concentrations. No additive effect was found after pretreatment with both antiserum anti-AVP and propranolol, suggesting that the stimulatory effect of catecholamines during IIH in 8-day-old rats is mediated through a modulation of hypothalamic AVP secretion.

Ontogeny of insulin-induced hypoglycemia stimulation of adrenocorticotropin secretion in the rat: role of catecholamines

We previously reported that insulin-induced hypoglycemia (IIH) induces a large increase in plasma ACTH and corticosterone levels in the developing rat during the stress hyporesponsive period and that this effect is mediated, at least partially, by arginine vasopressin (AVP), but not corticotropin-releasing factor. Nevertheless, ACTH secretion in response to IIH in rats immunoneutralized against AVP was still stimulated, suggesting that other regulatory factors participate in the stimulation of ACTH secretion during IIH. It has been suggested that, in the adult rat, during profound hypoglycemia, epinephrine may act at the pituitary level through beta 2-adrenergic receptors to stimulate ACTH secretion. In this report, we studied the effect of the blockade of beta-adrenergic receptors on the pituitary-adrenal axis response to IIH. Rats (20 or 8 day old) were pretreated with saline or 2.5 mg/kg propranolol (a beta-adrenergic receptors antagonist) and subsequently injected with 3 IU/kg insulin. In 20-day-old rats, insulin injection induced a large increase of plasma ACTH concentrations that were unaffected by propranolol pretreatment. In 8-day-old rats, the IIH-induced increase of plasma ACTH levels was significantly reduced by propranolol pretreatment. Pretreatment of 8-day-old rats with 5 mg/kg CGP 20712A (a selective beta 1-adrenergic receptor antagonist) did not change the plasma ACTH response to insulin injection, while pretreatment with 2.5 mg/kg ICI 118551 (a selective beta 2-adrenergic receptor antagonist) resulted in a significant decrease of the IIH-induced stimulation of ACTH secretion. We next studied the effect of the blockade of circulating AVP and/or beta-adrenergic receptors on the pituitary response to IIH. Pretreatment of 8-day-old rats with antiserum anti-AVP or propranolol was followed by a significant reduction of IIH-induced increase of plasma ACTH concentrations. No additive effect was found after pretreatment with both antiserum anti-AVP and propranolol, suggesting that the stimulatory effect of catecholamines during IIH in 8-day-old rats is mediated through a modulation of hypothalamic AVP secretion.

Effects of metyrapone infusion on corticotropin-releasing factor and arginine vasopressin secretion into the hypophysial portal blood of conscious, unrestrained rams.

The effects of rapid changes of circulating cortisol levels on ACTH secretion and on corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) concentrations into hypophysial portal blood were studied in six adult rams. Pharmacological adrenalectomy was obtained by 3 h metyrapone infusion (100 mg.kg-1.h-1). Blockade of cortisol synthesis induced a tenfold increase of plasma ACTH levels accompanied by a moderate increase of CRF secretion (150% vs preinjection levels) and a large increment of AVP secretion (535% vs preinjection levels). ACTH levels remained high during the 3 h following the end of metyrapone infusion. During the same period, CRF secretion was still elevated (231% vs preinjection levels), while AVP secretion was further stimulated (2,151% vs preinjection levels). Subsequent hydrocortisone infusion (66 micrograms.kg-1.h-1) for 2 h induced a rapid decrease of both ACTH and AVP secretion, while CRF levels in hypophysial portal blood still remained elevated. These data suggest that changes in ACTH secretion induced by acute modifications of the negative glucocorticoid feedback are, in addition to the well documented direct effect of cortisol on the corticotropes, mainly mediated by variations of hypothalamic AVP secretion.

Cocaine-induced ACTH secretion: Dependence of plasma levels of the drug and mode of exposure

To determine whether changes in pituitary responsiveness might account for the lack of corticotropin (ACTH) stimulation following 6 consecutive days of continuous cocaine administration (5 or 25 mg/kg/day, via osmotic minipumps), the hormonal response of vehicle- or cocaine-pretreated male rats was compared. Intravenous injections of synthetic corticotropin-releasing factor (CRF) (0.2, 1, or 5 μg/Kg) elicited dose-dependent increases in ACTH secretion irrespective of whether rats had been previously exposed to cocaine or not. Similarly, in both vehicle- and cocaine-pretreated rats ACTH response to acute injections of the drug was identical, indicating that pituitary corticotrophs remained responsive following continuous administration of cocaine. To determine and compare plasma concentrations of cocaine and its metabolites after continuous or acute administration of the drug, pharmacokinetics analysis of concentration vs. time was ascertained. Circulating concentrations of cocaine from rats continuously exposed to the drug were relatively low throughout the 6 days of exposure. In contrast, intravenous injections of cocaine produced peak concentrations of the drug that were significantly higher than those measured during continuous cocaine infusion. Such peak concentrations in cocaine correlated with marked increases in plasma ACTH levels. Plasma concentrations of the metabolites benzoylecgonine and methyl ester ecgonine followed a pharmacokinetic clearance similar to that of the parent compound, with low concentrations detected during continuous exposure whereas high concentrations were observed following intravenous injections of the drug. Our results suggest two nonmutually exclusive conclusions. First, there may be a critical threshold of cocaine plasma concentrations (as indicated by our results as being over 800 ng/ml) that are necessary for activation of the hypothalamic-pituitary-adrenal axis to occur. Second, stimulation of ACTH secretion may only occur during rapid systemic increases in drug concentrations.

Differential effects of central and peripheral injection of interleukin-1β on brain c- fos expression and neuroendocrine functions

Cytokines such as interleukin-1β (IL-1β) alter the activity of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes in the rat. However, the brain sites at which IL-1β exerts these effects have not been well identified. The present study sought to identify some of these sites, using c- fos protein expression as an index of cellular activation. We also attempted to determine possible differences between the effects of peripheral and central injection of IL-1β on the activation of specific brain areas. Castrated male rats received intravenous (i.v.) or intracerebroventricular (i.c.v.) injections of IL-1β through a jugular catheter or a permanent cannula implanted in the right lateral ventricle, respectively. Blood samples were taken before, as well as 30 and 120 min after i.v. or i.c.v. IL-1β infusion in order to measure plasma ACTH and LH levels. Immediately thereafter, the rats were anesthetized with pentobarbital, then perfused. Their brains were removed and postfixed for one hour. Thirty-μm frozen sections were cut and approximately every fourth tissue section was processed for c- fos expression by an avidin-biotin-peroxidase method. Both i.v. (1 μg) and i.c.v. (100 ng) injection of IL-1β significantly increased plasma ACTH levels, but only i.c.v. treatment measurably inhibited LH secretion. I.c.v. infusion of the cytokine markedly augmented c- fos expression in the paraventricular nucleus (PVN) and the arcuate nucleus (ARC) of the hypothalamus. A large amount of CRF cells in the PVN contained labelled c- fos protein (as measured by a double labelling technique), which indicates that CRF perikarya in this hypothalamic region are activated by the central administration of IL-1β. In contrast, i.v. injection of IL-1β did not significantly alter c- fos expression in the PVN or the ARC of the hypothalamus. These results suggest that the increased HPA axis activity which follows the peripheral IL-1β administration, a phenomenon previously shown to depend on endogenous CRF, does not require immediate activation of hypothalamic CRF perikarya. Thus our results indicate that the stimulatory effect of blood-born cytokine may be exerted at the level of nerve terminals in the median eminence. In contrast, i.c.v.-injected IL-1β appears to activate the HPA axis through a stimulation of CRF neurons within the parvocellular part of PVN. Finally, we postulate that the increase in cellular activity observed in the ARC of the hypothalamus may be involved in the decrease in LH secretion observed after i.c.v. infusion of IL-1β.

Changes in Proopiomelanocortin Primary Transcript Levels in the Anterior Pituitary Accompany Increased Adrenocorticotropin Secretion During the Diurnal Surge

Proopiomelanocortin (POMC) gene transcription in the anterior pituitary varies during stress and glucocorticoid feedback. These changes appear to parallel alterations in peptide release. The diurnal rhythm of the hypothalamo-pituitary-adrenal axis also involves the periodic excursion of adrenocorticotropin (ACTH) levels in plasma, but it is not clear whether the diurnal release is accompanied by changes at the transcriptional level. In the present study, we have initially characterized the heteronuclear species of POMC (hnPOMC) RNA found in the anterior pituitary by a Northern blot analysis and subsequently used this method to quantitate relative changes in the levels of heteronuclear transcript during diurnal stimulation. Two species of RNA migrating at 6.0 kb and 4.1 kb were found in the nuclear fraction of the anterior pituitary. Successive probing by various POMC cRNAs indicated that the 6.0 kb fragment was the primary transcript and the 4.1 kb fragment corresponded to the intron A-containing processing intermediate of POMC. The nuclear species were quantitated after acute swim stress and during the diurnal ACTH secretion. Acute swim increased plasma ACTH levels by 243% after 30 min. This was paralleled by a 214% increase in the primary transcript RNA levels. Endogenous circadian stimulation in the evening produced a smaller rise of plasma ACTH (79%), and was accompanied by a 34% increase in POMC hnRNA levels. Nuclear processing intermediate (4.1 kb) and the mRNA levels did not vary during the evening. These results suggest that the diurnal mechanism transiently increases ACTH release as well as POMC gene transcription in the anterior pituitary. Release and transcription appear to be tightly coupled during circadian activation as well as during stress.

Hyponatremia-Induced Inhibition of Magnocellular Neurons Causes Stressor-Selective Impairment of Stimulated Adrenocorticotropin Secretion in Rats*

Chronically hyponatremic rats were subjected to various stressors in order to evaluate the possible contribution of magnocellular neurons to the regulation of ACTH secretion, since such rats have markedly inhibited secretion and synthesis of magnocellular arginine vasopressin (AVP) and oxytocin (OT). Stress caused by a novel environment or by insulin-induced hypoglycemia resulted in moderate increases in plasma ACTH, which were of similar magnitude in both hyponatremic and normonatremic rats, and these stressors caused no increase in plasma AVP and OT levels in either group of rats. However, when exposed to ether, hyponatremic rats exhibited a significantly blunted ACTH response compared to normonatremic controls (331 +/- 49 vs. 740 +/- 124 pg/ml; P less than 0.01, respectively), and plasma AVP levels were markedly increased in the normonatremic, but not in the hyponatremic, rats. Intravenous infusion of 2 M NaCl also caused an ACTH release in hyponatremic rats that was significantly smaller than that in their normonatremic counterparts (228 +/- 52 vs. 479 +/- 85 pg/ml; P less than 0.05, respectively), and in this case both plasma AVP and OT levels were markedly increased in the normonatremic, but not in the hyponatremic, rats. However, hyponatremic rats exhibited greatly increased plasma ACTH levels 2 and 96 h after adrenalectomy (ADX), which were statistically equivalent to the increases in ACTH levels in normonatremic rats after ADX. Seven days after ADX parvocellular neurons of the paraventricular nucleus showed strongly increased CRF-41 and AVP-neurophysin, but not OT-neurophysin, immunoreactivities in both normonatremic and hyponatremic rats. These results show that parvocellular CRF-41/AVP-producing neurons in the paraventricular nucleus are not inhibited by chronic hyponatremia, in contrast to magnocellular neurons, and suggest that ACTH secretion induced by ether or hypertonic saline, but not by novel environment or insulin-induced hypoglycemia, is partially mediated by magnocellular AVP and/or OT.

Prolonged exposure to alcohol: effect on CRF mRNA levels, and CRF- and stress-induced ACTH secretion in the rat

We have conducted studies in intact adult male rats, designed to examine the effect of a 3- or 7-day exposure to alcohol (EtOH) on the pituitary's response to corticotropin-releasing hormone (CRF) or stress, and on CRF expression in the hypothalamus. In a first series of experiments, rats exposed to EtOH vapors for 7 days had mean blood alcohol levels (BAL) of 127 ± 12mg%. At the end of the 7-day period, basal plasma ACTH levels were 69 ± 10pg/ml in control rats and 121 ± 23pg/ml in EtOH animals ( P ⩽ 0.01). Resting corticosterone levels were 39 ± 11ng/ml in control animals, and 101 ± 24ng/ml in EtOH rats ( P ⩽ 0.01). In all experiments described here, there was no statistical difference ( P > 0.05) between the body weights of controls (animals kept in chambers with normal atmosphere) and EtOH-exposed animals. In control animals, the injection of 0.3–10 μg ovine CRF per rat caused dose-related increases in plasma ACTH levels measured 10 min later. All doses of CRF also significantly ( P ⩽ 0.01) stimulated ACTH secretion by EtOH rats, but there was no clear dose-response curve. Though EtOH-treated animals responded to the lower dose of CRF (0.3 μg) with larger increases in plasma ACTH levels than control rats, the only statistical difference ( P ⩽ 0.01) between control and EtOH rats was observed following administration of 10 μg CRF, which caused a blunted response in EtOH animals. These results suggested that alcohol caused an increased sensitivity and decreased maximum responsiveness of the pituitary to CRF. In a second series of experiments, we examined the effect of a 7-day exposure to EtOH on the hypothalamic-pituitary-adrenal response to mild electroshocks (1.0 mA, 0.5 s duration, 2 shocks/min, 10 min total duration). At the end of the 7-day period, BAL were 158 ± 20mg%, and basal ACTH values were 58 ± 9pg/ml for control rats and 175 ± 52pg/ml for EtOH animals ( P ⩽ 0.01). Resting corticosterone levels for control and EtOH rats were 32 ± 10and115 ± 26ng/ml, respectively ( P ⩽ 0.01). Though stress-induced ACTH levels were statistically equivalent ( P > 0.05) in control and EtOH rats (978 ± 220vs768 ± 153pg ACTH/ml), the increase over basal values were significantly ( P ⩽ 0.01) smaller in rats exposed to alcohol. A third series of experiments investigated the effect of a 3- or 7-day exposure to EtOH on CRF expression in the hypothalamus. Both periods of EtOH exposure caused an approximate 2-fold increase ( P ⩽ 0.01) in CRF mRNA levels in the hypothalamus. These results indicate that exposure of male rats to alcohol vapors for 7 days significantly alters the activity of the hypothalamic-pituitary-adrenal axis.

Chronic Effects of Interleukin-1 on Hypothalamus, Pituitary and Adrenal Glands in Rat

To assess the chronic effects of interleukin-1 (IL-1) and IL-2 on the hypothalamo-pituitary-adrenal axis in vivo, we administered recombinant human (rh) IL-1 alpha, rhIL-1 beta or rhIL-2 (2.0 micrograms/day) repetitively to adult male rats for 10 days. In rhIL-1 beta-treated rats, adrenocorticotropic hormone-like immunoreactivity (ACTH-LI) of the anterior pituitary appeared to increase first on day 3 followed by an increase of corticotropin-releasing hormone (CRH)-LI both in the hypothalamus and in the adrenal gland after day 7. At the end of the 10-day treatment, wet weights of the adrenal glands of rhIL-1 beta-treated rats increased significantly compared with those of control rats. Plasma ACTH levels in rhIL-1 beta-treated rats at the sampling time continued to be elevated throughout the experimental period. Under the same experimental design, rhIL-1 alpha increased plasma ACTH levels at the sampling time without changes in adrenal weight or in the peptide contents investigated. The same amount of rhIL-2 had no effect on these measured variables during the 10-day treatment. These data indicate that the repetitive administration of IL-1 beta resulted in chronic effects in the hypothalamo pituitary-adrenal axis to increase the activities in these organs during the treatment and, moreover, IL-1 possibly has a positive direct effect on the CRH-containing cells in the adrenal glands.

In the Mouse, the Activation of the Hypothalamic Pituitary-Adrenal Axis by a Lipopolysaccharide (Endotoxin) Is Mediated through Interleukin-1*

The mechanisms through which endotoxin stimulates the hypothalamic-pituitary-adrenal axis are not well understood. In the studies reported here we tested the hypothesis that endotoxin increases plasma ACTH levels by releasing interleukin-1 (Il-1). Two experimental tools reported to interfere with the biological activity of IL-1 were used: antibodies directed against IL-1 receptors and alpha MSH. In a first series of experiments, adult male mice were injected with a lipopolysaccharide (LPS; 25 micrograms), antibodies against IL-1 receptor, alpha MSH (1-30 micrograms), or LPS and either IL-1 antibodies or alpha MSH. All treatments were administered ip. The endotoxin LPS caused a marked increase in plasma ACTH levels, measured 6 h later. Both alpha MSH and the Il-1 receptor antibodies, while having no effect by themselves, significantly (P less than or equal to 0.01) blocked LPS-induced ACTH release. In a second series of experiments, mice were injected ip with 500 ng recombinant human (rh) Il-1 alpha or 100 ng rhIl-1 beta in the presence or absence of alpha MSH (1-30 micrograms, ip). While not altering ACTH secretion induced by rhIl-1 alpha, 10-30 micrograms alpha MSH significantly (P less than or equal to 0.01) interfered with the effect of rhIl-1 beta. These results suggest 1) that endotoxin activates the hypothalamic-pituitary-adrenal axis through a mechanism involving the activation of interleukin-1 receptors; and 2) that the effect of rhIl-1 beta, but not -alpha, on ACTH secretion by the mouse can be partially blocked by alpha MSH.