Effect of dexamethasone on immunoreactive corticotropin-releasing factor in the rat median eminence and intermediate-posterior pituitary

Strain-specific steroidal control of pituitary function

We have previously shown that 7B2 null mice on the 129/SvEvTac (129) genetic background die at 5 weeks of age with hypercorticosteronemia due to a Cushing's-like disease unless they are rescued by adrenalectomy; however, 7B2 nulls on the C57BL/6NTac (B6) background remain healthy, with normal steroid levels. Since background exerts such a profound influence on the phenotype of this mutation, we have evaluated whether these two different mouse strains respond differently to high circulating steroids by chronically treating wild-type 129 and B6 mice with the synthetic steroid dexamethasone (Dex). Dex treatment decreased the dopamine content of the neurointermediate lobes (NIL) of 129 mice, leading to NIL enlargement and increased total D(2)R mRNA in the 129, but not the B6, NIL. Despite the decrease in this inhibitory transmitter, Dex-treated 129 mice exhibited reduced circulating alpha-melanocyte-stimulating hormone (alpha-MSH) along with reduced POMC-derived peptides compared with controls, possibly due to reduced POMC content in the NIL. In contrast, Dex-treated B6 mice showed lowered cellular ACTH, unchanged alpha-MSH and beta-endorphin, and increased circulating alpha-MSH, most likely due to increased cleavage of NIL ACTH by increased PC2. Dex-treated 129 mice exhibited hyperinsulinemia and lowered blood glucose, whereas Dex-treated B6 mice showed slightly increased glucose levels despite their considerably increased insulin levels. Taken together, our results suggest that the endocrinological response of 129 mice to chronic Dex treatment is very different from that of B6 mice. These strain-dependent differences in steroid sensitivity must be taken into account when comparing different lines of transgenic or knockout mice.

Effects of corticotropin-releasing hormone (CRH) on the synthesis and secretion of proopiomelanocortin-related peptides in the anterior pituitary: a study using CRH-deficient mice

Corticotropin-releasing hormone (CRH) mainly regulates the synthesis and secretion of adrenocorticotropin (ACTH) in the anterior pituitary (AP). By using CRH-deficient mice (CRH KO), we investigated the role of CRH in the processing of proopiomelanocortin (POMC), a precursor of ACTH, beta-lipotropic hormone, and beta-endorphin (EP). In the basal condition, the plasma ACTH level was similar in CRH KO and wild-type mice (WT), while its response to pain stress in CRH KO was smaller than that in WT. Immunoreactive (ir) beta-EP contents in the AP of CRH KO were not significantly different from those of WT. In order to determine the different molecule profile of POMC-related peptides between WT and CRH KO, ir beta-EP contents extracted from AP of WT and CRH KO were assayed by gel filtration chromatography. The gel filtration analyses revealed that a higher molecular weight form of ir beta-EP, putative POMC, was increased in CRH KO, but the beta-EP peak level was small and similar between two groups. These results suggest that CRH has little influence on the basal release of ACTH and prohormone convertase-2 processing enzyme. On the other hand, it is essential for ACTH secretion under stress conditions, and CRH would affect on the prohormone convertase-1/3 processing enzyme in AP.

Novel glucocorticoid and cAMP interactions on the CRH gene promoter

Glucocorticoids inhibit corticotrophin releasing hormone (CRH) production in the hypothalamus but stimulate production from the placenta. We have sought to identify the key elements regulating the CRH gene. Mouse pituitary tumour-derived cells (AtT20 cells) were used in deletion and mutational analyses of the CRH promoter. Two cAMP responsive elements were identified: (I) a consensus cAMP response element (CRE) and (II) a previously unrecognised caudal-type homeobox response element (CDXRE). Glucocorticoids inhibit only the component of cAMP-stimulation occurring via the CRE through an action involving a negative glucocorticoid response element (nGRE). We also identified two regions that, in the absence of the nGRE, can be stimulated by glucocorticoids: (I) the CRE and (II) a region between -213 and -99 bps. Electrophoretic mobility shift assays (EMSAs) identified binding of the transcription factors CREB and Fos at the CRE in AtT20 cells while CREB and cJun were detected in placental cells. Tissue specific expression of transcription factors may mediate regulation of the CRH gene.

Corticotropin-releasing hormone links pituitary adrenocorticotropin gene expression and release during adrenal insufficiency

Corticotropin-releasing hormone (CRH)-deficient (KO) mice provide a unique system to define the role of CRH in regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Despite several manifestations of chronic glucocorticoid insufficiency, basal pituitary proopiomelanocortin (POMC) mRNA, adrenocorticotrophic hormone (ACTH) peptide content within the pituitary, and plasma ACTH concentrations are not elevated in CRH KO mice. The normal POMC mRNA content in KO mice is dependent upon residual glucocorticoid secretion, as it increases in both KO and WT mice after adrenalectomy; this increase is reversed by glucocorticoid, but not aldosterone, replacement. However, the normal plasma levels of ACTH in CRH KO mice are not dependent upon residual glucocorticoid secretion, because, after adrenalectomy, these levels do not undergo the normal increase seen in KO mice despite the increase in POMC mRNA content. Administration of CRH restores ACTH secretion to its expected high level in adrenalectomized CRH KO mice. Thus, in adrenal insufficiency, loss of glucocorticoid feedback by itself can increase POMC gene expression in the pituitary; but CRH action is essential for this to result in increased secretion of ACTH. This may explain why, after withdrawal of chronic glucocorticoid treatment, reactivation of CRH secretion is a necessary prerequisite for recovery from suppression of the HPA axis.

Opposing effects of androgen and estrogen on pituitary-adrenal function in nonpregnant primates

Maternal administration of androstenedione produces a sustained fall in maternal plasma adrenocorticotropic hormone (ACTH) concentrations in the pregnant nonhuman primate. We hypothesize a negative feedback influence on the maternal hypothalamo-pituitary-adrenal (HPA) axis by androgens in primates. This may reflect an important maternal adaptation during pregnancy in primates preventing premature induction of labor by maternal stress. However, androstenedione is precursor for placental estradiol-17beta synthesis, and infusion of androstenedione into pregnant primates elevates maternal plasma estradiol-17beta to term concentrations. Thus, it could be argued that 1) the effects attributed to androstenedione on the maternal HPA axis are mediated by estrogen rather than by androgen and 2) the negative influence of androgens may be on placental ACTH rather than, or in addition to, pituitary ACTH. To discriminate between androgenic and estrogenic effects of androstenedione on pituitary and/or placental ACTH function in primates we measured plasma ACTH, cortisol, and dehydroepiandrosterone sulfate (DHEAS) concentrations in nonpregnant baboons after treatment with either androstenedione or estradiol-17beta. Nine female baboons were studied between 14 and 22 days postpartum prior to estrous cycling. After 2 days of baseline, a continuous i.v. infusion of androstenedione (1.5 mg/kg per h in 10% intralipid, IL) was started at 0900 h and maintained for 9 days in 3 baboons. A similar protocol was carried out in another 3 baboons that received a continuous i.v. infusion of estradiol-17beta (10 microg/kg per h in 10% IL) instead of androstenedione. Three additional baboons received continuous i.v. IL vehicle alone and served as controls. Arterial blood samples (0.5 ml) for measurement of plasma hormones were taken during baseline and after 1, 3, 5, 7, and 9 days of infusion. Baseline plasma ACTH, DHEAS, and cortisol concentrations were similar among all groups. Plasma ACTH did not change during IL, increased following estradiol-17beta, and fell during androstenedione treatment. Accordingly, plasma cortisol and DHEAS concentrations were also unaltered by IL, and both steroids increased during estradiol-17beta treatment. In contrast, plasma cortisol and DHEAS remained unaltered from baseline during androstenedione treatment, despite the fall in plasma ACTH measured at this time. These data in the nonpregnant baboon 1) are consistent with negative feedback on pituitary ACTH by androgens and 2) demonstrate a positive influence on pituitary-adrenal function by estrogen in primates.

Fetal sheep pituitary proopiomelanocortin in late gestation: effect of bilateral lesions of the paraventricular nucleus on regional and cellular messenger ribonucleic acid levels

Previous experiments have clearly indicated that the successful completion of ovine gestation is dependent upon fetal adrenocortical maturation and the associated preterm rise in fetal plasma cortisol. The purposes of this study were to: 1) examine pituitary POMC messenger RNA (mRNA) levels during normal fetal development; and 2) examine the effects of bilateral lesion of the fetal paraventricular nucleus (PVN) on levels and spatial distribution of pituitary POMC mRNA. Pituitary glands were collected from intact fetal sheep of four gestational ages [100-107 days gestational age (dga), n = 8; 117-121 dga, n = 9; 126-130 dga, n = 9; 144-147 dga, n = 8]. Lesions of the PVN (PVN Lx; n = 4) or sham lesions (Sham; n = 5) were performed at 118-122 dga. Pituitary glands from PVN Lx and Sham fetuses were collected at 139-142 dga (term approximately 147 dga). POMC mRNA levels were determined by in situ hybridization. POMC transcript levels were determined by both regional analysis (20x magnification) and analysis of individual corticotropes (400x magnification). There was no difference among gestational age groups in superior anterior pituitary (AP) POMC mRNA levels determined by regional or cellular analysis. POMC mRNA levels were significantly greater in the inferior AP at 144-147 dga, compared with other gestational ages, using regional analysis (P = 0.003) or analysis of individual corticotropes (P < 0.01). POMC mRNA levels in the neurointermediate lobe in 126- to 130-dga fetuses were significantly greater than those in younger fetuses (P = 0.005) but not those in 144- to 147-dga fetuses. There was no difference in POMC mRNA levels in the superior AP between PVN Lx and Sham, using regional analysis or analysis of individual corticotropes. In the inferior AP, there was a significant decrease in POMC mRNA levels in PVN Lx, compared with Sham, using both regional analysis (P < 0.01) and cellular analysis (P < 0.01). There was no difference in POMC mRNA levels in the neurointermediate lobe as the result of bilateral PVN Lx. Our findings support that basal AP POMC mRNA levels are heterogenously distributed in the ovine fetal AP, with POMC mRNA levels in the inferior AP being significantly greater than in superior AP, by 144-147 dga. We further found that the higher POMC mRNA levels in the inferior AP reflect significantly higher corticotrope POMC transcripts and not simply a greater density of corticotropes in this AP region. The increase in POMC mRNA levels at 144-147 dga in the inferior AP seems unrelated to the onset of adrenocortical maturation (at approximately 125-130 dga). Finally, we report that increase in corticotrope POMC transcripts during late gestation in the inferior AP requires an intact PVN.

Effects of corticosterone on CRH mRNA and content in the bed nucleus of the stria terminalis; comparison with the effects in the central nucleus of the amygdala and the paraventricular nucleus of the hypothalamus

We previously reported that corticosterone (CORT) increased corticotropin-releasing hormone (CRH) mRNA in the central nucleus of the amygdala (CEA), while reducing it in the paraventricular nucleus (PVN) of the hypothalamus by using in situ hybridization histochemistry. The bed nucleus of the stria terminalis (BNST) is closely related to the amygdala, and it is also a source of extrahypothalamic CRH; therefore, we examined CRH mRNA changes in the BNST following systemic treatment with CORT in adrenally-intact rats. Effects of adrenalectomy on CRH mRNA in the BNST, PVN and CEA were also examined. In addition, CRH content in these nuclei and in the median eminence (ME) were determined by micropunch dissection technique combined with CRH radioimmunoassay in CORT pellet implanted rats. Subcutaneous injections of high CORT (5 mg/day, over 14 days) increased CRH mRNA in the dorsal part of the lateral BNST (BSTLD) at 2, 4 and 8 days, although the low dose of CORT (1 mg/kg/day) had no significant effects. By contrast, in the ventral part of the BNST (BSTV) neither the high nor low dose of CORT altered CRH mRNA levels. In a second experiment, a slowly-releasing CORT pellet (200 mg, 60-day release) produced an elevation of CRH mRNA at both 1 and 2 weeks or at 1 week in the BSTLD or in the BSTV, respectively. These results show that glucocorticoids can facilitate CRH mRNA expression in the BSTLD in the same manner as seen in the CEA, and that CRH mRNA in the BSTLD can respond to CORT more than in the BSTV. In a third experiment, bilateral adrenalectomy, however, did not affect CRH mRNA in the BNST although there was a modest decrease in the CEA and a robust increase in the PVN. Finally, in CORT pellet (200 mg, for 2 weeks) implanted rats, CRH content in the ME significantly decreased and modestly increased in the CEA compared with control rats, whereas it did not change in the PVN and BNST. Taken together, these results suggest that (1) CRH in the BNST and the CEA may share some common functions in neuroendocrine and behavioral changes, but that (2) mechanisms of CRH synthesis or its releasing sites may be different in the BNST and CEA.

Glucocorticoids potentiate the adenylyl cyclase-cAMP system mediated immunoreactive beta-endorphin production and secretion from hypothalamic neurons in culture

Beta-endorphin(beta EP)1-31, a potent opioid peptide of proopiomelanocortin (POMC) derivatives, is produced and released from neurons at arcuate nuclei of the rat hypothalamus. Although dexamethasone (DM) suppresses the production and secretion of POMC related peptides from rat pituitary corticotrophs, the effect of glucocorticoids on the function of hypothalamic beta EP neurons remains unclear. Employing long term monolayer cultures of neonatal rat hypothalamic cells, we report here that 4 day treatment with 10 microM of forskolin increased ir-beta EP levels in cell content and culture media by approximately 1.7 (P < 0.05) and 4.1 times (P < 0.01) above vehicle treated control cultures (mean +/- S.E.M., 47.3 +/- 2.6 pg/well and 40.4 +/- 3.0 pg/well; n = 3) respectively. Although 4 day treatment with DM alone had little effect on the release and the cell content of ir-beta EP, it significantly enhanced forskolin-induced elevation of ir-beta EP levels in cell content and in culture media. The effect of DM was dose-related and time-dependent, with an EC50 of about 1 nM; at this concentration DM enhanced ir-beta EP secretion about 2.1 times (P < 0.01) above that induced by 10 microM of forskolin alone. Furthermore, the potentiating effect of DM was specifically suppressed by 100 nM of RU38486 (P < 0.01), a glucocorticoid receptor antagonist, but not by an equivalent dose of RU28318, a mineralocorticoid receptor antagonist. In addition, Northern blot analysis showed that forskolin (10 microM) increased the abundance of POMC mRNA 1.4 fold above that of vehicle treated control cultures. Whereas by itself, DM (10 nM) had little effect on the level of POMC mRNA, it enhanced forskolin-stimulated increase of the abundance of POMC mRNA approximately 2.6 times. Moreover, DM also augmented 1.6 times (P < 0.05) forskolin-induced but not 3-isobutyl-1-methylxanthine (IBMX)-induced increase of cAMP production (5.5 +/- 0.4 pmol/well; mean +/- S.E.M., n = 3) in the cultures. Taken together, our findings suggest that in contrast to the inhibitory effect on pituitary corticotrophs, glucocorticoids enhance the production and secretion of beta EP from rat hypothalamic neurons by facilitating the stimulatory effect mediated, in part, through the adenylyl cyclase-cAMP system.

Immunoreactive corticotropin-releasing hormone levels in the hypothalamus of female Wistar fatty rats

We have studied immunoreactive corticotropin-releasing hormone (CRH) levels in the hypothalamus of female Wistar fatty rats, a strain with the fa gene transferred from the Zucker rat to the Wistar Kyoto rat, in an attempt to understand the role of CRH in the development of obesity. A study was conducted with 5-week- and 12-week-old female Wistar fatty rats and lean littermates. There was no significant difference in hypothalamic CRH levels between lean and obese rats at the age of 5 weeks (1887 +/- 99.6 vs. 1767 +/- 124 pg/tissue; mean +/- S.E.M.). Hypothalamic CRH immunoreactivities, however, were significantly lower in 12-week-old obese rats (2361 +/- 132 pg/tissue) than those in lean littermates (2992 +/- 118 pg/tissue; P less than 0.05). The difference of CRH contents between the lean and obese group becomes apparent as they grow up and develop obesity.

Hypothalamic and suprahypothalamic effects of prolonged treatment with dexamethasone in the rat

Corticosteroid type I and II receptors mediate the negative feedback effects of these hormones at various central nervous system sites involved in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. To examine the effects of chronic treatment with dexamethasone (DEX), a type 2 receptor agonist, on the regulation of this axis, male Sprague-Dawley rats weighing 200-250 g were given daily injections of DEX for 1,2,3, and 4 weeks or were treated with a subcutaneously implanted DEX-releasing minipump for one week. At the end of treatment, the animals were weighed and brains and truncal blood were collected. Daily intermittent DEX treatment reduced the body weight of the rats in a time-dependent fashion, but had little or no effect on their wet brain weight. Plasma ACTH and corticosterone, measured by RIA, were fully suppressed after one week of intermittent treatment and did not show any further reduction in rats treated for longer periods. In these animals, the content of immunoreactive corticotropin-releasing hormone (iCRH), arginine vasopressin (AVP), ACTH and beta-endorphin (beta-EP) in the hypothalamus, hippocampus, cerebral cortex and cerebellum and pituitary ACTH content did not show any difference compared to vehicle-treated rats. In contrast, continuous DEX treatment increased iCRH content in the cortex, reduced AVP content in the cerebellum, increased ACTH content in the hippocampus, decreased ACTH and beta-EP content in the hypothalamus, and reduced pituitary ACTH content. Hypothalami explanted from rats treated with DEX for one week released lower basal amounts of iCRH in vitro and did not respond to a maximally stimulatory concentration of serotonin (5-HT), a known CRH secretagogue. Continuous DEX administration suppressed also potassium chloride-induced iCRH release. Interestingly, hypothalami explanted from rats receiving daily injection of vehicle, but not from unhandled, untreated controls, did not respond to 5-HT with an increase of iCRH release in vitro. In conclusion, prolonged and continuous, but not intermittent, administration of DEX had a strong effect on brain neuropeptide content. Both regimens of DEX reduced the hypothalamic iCRH responsiveness to stimuli in vitro. Chronic handling also decreased the responsiveness of the hypothalamus to a stimulatory neurotransmitter and may confound the interpretation of data pertinent to inhibitory mechanisms.

Effects of cortisol treatment on brain and adrenal corticotropin-releasing hormone (CRH) content and other parameters regulated by CRH

Corticotropin-releasing hormone (CRH) has been found in both hypothalamic and extrahypothalamic sites of the brain and also in the adrenal medulla. To study the timing and location of delayed glucocorticoid action in rats, we measured the effects of 2-day and 7-day cortisol treatment on immunoreactive CRH concentrations in hypothalamus, cerebral cortex, hippocampus, cerebellum, and adrenal gland. The activity of the hypothalamo-pituitary-adrenal (HPA) axis and the sympathoadrenal system were also measured. Studies were carried out both in the afternoon and/or in the morning, to get information about possible circadian changes. CRH contents were not changed in any brain areas studied, except there was a trend of decrease in the hypothalamus compared to vehicle in the afternoon due to the lack of circadian increase after 7-day cortisol treatment. Pituitary ACTH content decreased significantly after 7-day treatment, while beta-endorphin did not. Plasma levels of ACTH, corticosterone, norepinephrine and epinephrine and adrenal ACTH and beta-endorphin contents decreased after 2-day, adrenal CRH content after 7-day treatment with cortisol. Our findings suggest, that chronic cortisol treatment inhibits the circadian activation of the HPA axis at all levels but has variable effects on baseline measures because it causes different changes in release and synthesis at different sites.

Stress-Related Changes in beta-Endorphin Processing: The Limitations of Slaughterhouse Material

Abstract In the sheep, unlike many other species, a significant proportion (>25%) of immunoreactive beta-endorphin in the anterior pituitary is post-translationally modified to opioid-inactive, alpha-N-acetylated forms. In a study to determine the precise molecular nature of alpha-N-acetylated beta-endorphin immunoreactivity, we noted a striking difference in high-performance liquid chromatography profiles of anterior pituitary extracts between sheep killed on the farm, and age-, sex- and strain-matched slaughterhouse animals. These altered patterns of a-N-acetylated beta-endorphin processing were reproduced in farm animals by chronic (</= 4 days) treatment with the synthetic glucocorticoid dexamethasone; in contrast dexamethasone had no effect on a-N-acetylated beta-endorphin processing in hypothalamo-pituitary disconnected sheep. These data suggest that (1) the change in processing is a stress response, mediated by prolonged glucocorticoid exposure, (2) this effect is central, rather than a direct effect on the pituitary, and (3) the relative abundance of various peptide sequences in slaughterhouse-derived material may not reflect their abundance under more physiological conditions.

Differential steroid hormone and neural influences on peptide mRNA levels in CRH cells of the paraventricular nucleus: a hybridization histochemical study in the rat

The three major classes of neurons in the paraventricular nucleus (PVH) provide a rich model for studying hormonal and neural influences on multiple neuropeptides expressed in individual cells. A great deal of previous work has examined this problem at the immunohistochemical level, where hormonal and neural influences on peptide levels have been established. In situ hybridization methods were used here to determine whether these effects are accompanied by measurable changes in neuropeptide mRNA levels. In the first series of experiments, the time-course of corticosterone replacement effects on corticotropin-releasing hormone (CRH) mRNA levels in parvicellular neuroendocrine cells of adrenalectomized animals were determined, and a dose-response curve was established. CRH mRNA hybridization remains maximal with plasma levels of steroid up to about 50 ng/ml, then declines sharply between about 60-130 ng/ml, and is just detectable at higher levels. We confirmed that corticosterone decreases vasopressin mRNA levels in this cell group and showed that levels of preproenkephalin mRNA are also decreased, whereas no significant changes in cholecystokinin, beta-preprotachykinin, and angiotensinogen mRNA levels could be detected. Thus, corticosterone decreases some neuropeptide mRNA levels and has no influence on others in this cell group. Tyrosine hydroxylase mRNA hybridization is also unaffected in this part of the nucleus. In a second group of experiments, the cell-type specificity of corticosterone influences was examined. It was found that while the hormone depresses CRH mRNA levels in parvicellular neurons, it increases such levels in PVH neurons with descending projections, in certain magnocellular neurosecretory neurons, and in a part of the central nucleus of the amygdala, whereas no influence was detected in the rostral lateral hypothalamic area. Furthermore, the stimulatory effects of corticosterone have different threshold levels in different cell groups. Thus, in different types of neurons, corticosterone may increase, decrease, or have no influence on CRH mRNA levels. In contrast, while corticosterone depresses vasopressin mRNA levels in parvicellular CRH neurons, it has no obvious effects on vasopressin mRNA levels in magnocellular or descending neurons; as with CRH, the effects of corticosterone on vasopressin mRNA levels are cell-type specific. In a third series of experiments it was shown that glucocorticoid receptor and mineralocorticoid receptor mRNAs are found in all three cell types in the PVH and that corticosterone tends to produce modest increases in mRNA levels for both receptors. Finally, it was shown that unilateral catecholamine-depleting knife cuts do not change mRNA levels for any of the neuropeptides (or steroid hormone receptors) examined here, although dramatic changes in neuropeptide levels themselves have been shown.4+

Dexamethasone suppresses ACTH release without attenuating pituitary cyclic AMP response to stress in vivo

Dexamethasone, a synthetic glucocorticoid, has been shown to decrease basal and stress-elevated levels of the pituitary hormone ACTH. Glucocorticoids are known to bind to multiple sites within the brain and pituitary and it is not known which site(s) is most important in mediating the observed inhibition of ACTH release. At the level of the corticotroph, there is contradictory data from in vitro studies regarding whether dexamethasone acts proximal or distal to the formation of the cyclic AMP second messenger that has been shown to be involved in CRF-stimulated ACTH release. In the present report, we have examined the effects of dexamethasone pretreatment on stress-induced elevations in pituitary cyclic AMP and the release of ACTH in vivo. Acute stress (15 min of intermittent footshock) elevated levels of pituitary cyclic AMP and plasma ACTH consistent with previous studies. Dexamethasone administration (0.4 mg/kg 24 hr prior to sacrifice plus 0.2 mg/kg 2 hr prior to sacrifice) inhibited stress-induced elevations in plasma ACTH but did not affect pituitary cyclic AMP response to acute stress. These findings suggest that dexamethasone inhibits the release of ACTH via an action distal to the generation of cyclic AMP.

Quantitative changes of CRF-like immunoreactivity in eels treated with reserpine and cortisol

Immunocytochemical techniques were applied to brain and pituitary sections of European eels after experimental manipulation of the pituitary-interrenal activity. A corticotropin-releasing factor (CRF) antiserum allowed the identification of a CRF-like peptide in the preoptic nucleus (PON) and rostral and caudal neurohypophysis (NH). CRF-immunoreactivity (ir) was not affected in solvent-injected eels compared to noninjected eels. Reserpine induced a stimulation of the pituitary interrenal axis, decreased ir-CRF in the rostral NH, but did not affect hypothalamic ir-CRF. Cortisol reduced the immunostaining of hypothalamic CRF-ir perikarya and perikarya cross-sectional area. In the rostral NH, CRF-ir fibers decreased in number and almost disappeared in long-term treated eels. The immunostaining of ACTH cells with ACTH antiserum was greatly reduced. These data suggest that cortisol induces a marked reduction in the activity of the CRF-corticotrop axis. The intensity of the ir-CRF staining observed in the caudal NH, close to the intermediate lobe (IL) was not significantly affected in reserpine-treated eels, and only slightly reduced in long-term cortisol-treated eels. The intensity of ir-CRF staining in the caudal NH did not correlate with melanocorticotropic activity or plasma cortisol level. These data suggest that immunoreactive CRF fibers in the rostral and caudal NH are differently regulated.

Steroid inhibition of canine ACTH: in vivo evidence for feedback at the corticotrope

We infused submaximal feedback doses of either dexamethasone (DEX; 0.1 microgram.kg-1.min-1) or corticosterone and cortisol (B+F; 1.5 micrograms.kg-1.min-1) intravenously for 40 min into conscious dogs and measured the adrenocorticotropic hormone (ACTH) responses to hypoglycemia induced by insulin (0.1 U/kg) or to ovine corticotropin-releasing factor (oCRF; 1 microgram/kg); both agents were injected at 120 min. The dose of DEX was chosen to produce suppression of the ACTH response to oCRF equivalent to that produced by B+F. The purpose of the study was to determine 1) whether CRF- and hypoglycemia-induced ACTH secretion are equally inhibited by glucocorticoid treatment and 2) whether DEX and B+F have differential effects in the inhibition of stress-induced ACTH secretion. We found that peak ACTH responses to hypoglycemia and CRF were equally inhibited by DEX (36 +/- 6 and 52 +/- 9%, respectively). The peak ACTH responses to hypoglycemia and CRF were also equally inhibited after B+F infusion (45 +/- 13 and 65 +/- 5%, respectively). There was no significant interaction between the steroid administered and the stimulus given in controlling the ACTH response (by 2-way analysis of variance). The results suggest that pituitary feedback is of primary importance in suppression of canine ACTH secretion by delayed feedback and that the natural and synthetic steroids both act at this site.

Multiple feedback regulatory loops upon rat hypothalamic corticotropin-releasing hormone secretion. Potential clinical implications

To examine whether the hypothalamic corticotropin-releasing hormone (CRH) neuron is regulated by CRH, by products of the proopiomelanocortin (POMC) gene, and/or by glucocorticoids, we used a rat hypothalamic organ culture system in which rat CRH secretion from single explanted hypothalami was evaluated by an RIA (iCRH) specific for rat CRH. The effects of graded concentrations of ovine CRH (oCRH), adrenocorticotropin hormone (ACTH), beta-endorphin (beta-EP), alpha-melanocyte-stimulating hormone (alpha-MSH), corticotropin-like intermediate lobe peptide (CLIP), ovine beta-lipotropin (ovine beta-LPH), and dexamethasone (DEX) upon unstimulated and serotonin- (5HT), acetylcholine- (ACh), and norepinephrine-(NE) stimulated CRH secretion were determined. oCRH and DEX inhibited unstimulated iCRH secretion with ID50 at the 10(-8) M range. ACTH had no detectable suppressive effect at 10(-8) M. oCRH, ACTH, and DEX inhibited 5HT-, ACh-, and NE-stimulated iCRH secretion in a dose-dependent fashion. beta-EP, alpha-MSH, and CLIP also inhibited 5HT-induced iCRH secretion. Of the latter peptides, the strongest inhibitor was beta-EP and the weakest was CLIP. Ovine beta-LPH had only a weak inhibitory effect on 5HT-induced iCRH secretion. Generally, the concentrations required for 50% suppression of neurotransmitter-stimulated iCRH secretion were significantly lower than those required for a similar suppression of unstimulated iCRH secretion. In conclusion, these data suggest the presence of multiple negative feedback loops involved in the regulation of the hypothalamic CRH neuron: an ultrashort CRH-mediated loop, a short, hypothalamic POMC-derived peptide loop, and a long, glucocorticoid-mediated negative feedback loop. The potency of these negative feedback loops may be determined by the state of activation of the CRH neuron.

Time course study on the effect of reserpine on hypothalamic immunoreactive CRF levels in rats

A time course study on the changes of rat hypothalamic corticotropin-releasing factor (CRF) levels and ACTH levels in plasma, pituitary and hypothalamus after an acute treatment with reserpine was examined using a rat CRF RIA. The massive and prolonged depletion of hypothalamic norepinephrine and dopamine levels provoked by a single injection of reserpine (2 and 8 mg/kg, i.p.) caused a transient decrease of hypothalamic CRF levels and ACTH levels in the anterior pituitary glands, and an increase in plasma ACTH levels. There was a strong correlation between the depletion of hypothalamic CRF and norepinephrine levels. These results suggest that: acute depletion of hypothalamic norepinephrine levels cause the initial release of CRF that stimulates pituitary ACTH secretion, and the depletion of CRF and ACTH stores at the early stage; and noradrenergic pathways may be involved in the inhibitory mechanism of CRF release.

Stimulatory effect of acetylcholine on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of acetylcholine (Ach) and gamma-aminobutyric acid (GABA) on immunoreactive corticotropin-releasing factor (CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. Ach stimulated CRF release in a dose-dependent manner (1 pM-1 nM). One nM Ach-induced CRF release was inhibited by atropine in a dose-dependent manner (1-100 nM), but was inhibited by only a high concentration (100 nM) of hexamethonium. In addition, such Ach-induced CRF release was inhibited by norepinephrine. GABA did not influence basal CRF release. These results suggest that Ach stimulates CRF release mainly through muscarinic receptors at least under our conditions.

Escape from dexamethasone-induced ACTH and cortisol suppression by corticotrophin-releasing hormone: modulatory effect of basal dexamethasone levels

The response of ACTH and cortisol to corticotrophin-releasing hormone (CRH) after pretreatment with various doses of dexamethasone was investigated in five healthy subjects. The five subjects participated in six experiments. In each experiment 200 micrograms ovine CRH was administered as an i.v. bolus injection at 0900 h after pretreatment with respectively: (A) 1 mg dexamethasone orally at 2300 h in the evening before CRH injection, (B) 2 mg dexamethasone orally at 2300 h in the evening before CRH injection, (C) 4 mg dexamethasone orally at 2300 h in the evening before CRH injection, (D) 2 mg dexamethasone orally at 2300 h in the evening before CRH injection, followed by 2 mg dexamethasone orally 1 h before CRH, (E) no dexamethasone and (F) 1 mg dexamethasone orally 1 h before CRH injection. In spite of overnight suppression with a single dose of dexamethasone CRH elicited cortisol rises in all individuals (experiments A-C). Dexamethasone pretreatment in experiment D abolished the CRH-induced stimulation of the pituitary-adrenal axis. There was a significant and negative correlation between the basal dexamethasone levels (i.e. the dexamethasone levels immediately before CRH administration) in the experiments A-D and the areas under the individual ACTH (R = -0.62; P less than 0.01 by Spearman's rank correlation test) and cortisol (R = -0.81; P less than 0.001 by Spearman's test) curves, i.e. the lower the basal dexamethasone levels, the greater the rise in ACTH and cortisol levels after CRH administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of serotonin, cyproheptadine and reserpine on corticotropin-releasing factor release from the rat hypothalamus in vitro

We investigated the effects of serotonin, cyproheptadine and reserpine on corticotropin-releasing factor (CRF) release from the rat hypothalamus, and the effect of cyproheptadine on CRF-induced adrenocorticotropic hormone (ACTH) secretion from the anterior pituitary (AP) in vitro using a perifusion system for rat hypothalami and AP, and a rat CRF radioimmunoassay. Cyproheptadine, 10(-8) M, had a direct inhibitory effect on both basal and 10(-9) M CRF-induced ACTH secretion from the rat AP in vitro. In addition, 10(-9)-10(-7) M cyproheptadine inhibited basal CRF release in a dose-dependent fashion, and also suppressed serotonin- and KCl-induced CRF release. Conversely, 10(-9)-10(-7) M reserpine failed to influence CRF release from the rat hypothalamus. These results indicate that a serotonergic mechanism may be involved in the CRF-releasing mechanism, and inhibition of depolarization-dependent calcium entry into cells and/or nerve endings. In addition an anti-serotonergic mechanism is involved in the inhibitory action of cyproheptadine.

Effects of opioid peptides on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of opioid peptides on immunoreactive corticotropin-releasing factor (I-CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. beta-Endorphin (0.3 - 30 nM), dynorphin (0.3 - 30 nM) and FK 33-824 (1 - 10 microM) suppressed basal I-CRF release in a dose-dependent fashion. At 2.2 nM concentrations of these peptides, mean percent inhibition was 56% for beta-endorphin; less than 5% for alpha-endorphin; 44% for dynorphin; 23% for leucine-enkephalin; 6% for methionine-enkephalin; less than 5% for FK 33-824; and less than 5% for D-ala2, D-leu5-enkephalin. The inhibitory effects of beta-endorphin and enkephalins were completely blocked by naloxone, but those of dynorphin were only partially blocked. These results suggest that opioid peptides act through opioid receptors and inhibit I-CRF release from the hypothalamus under our conditions. Therefore, endogenious opioid peptides may have a physiological role in the CRF-releasing mechanism of the hypothalamus.

Corticotropin-releasing factor (CRF)--a review

Corticotropin-releasing factor (CRF), a 41 amino acid polypeptide, has been isolated from ovine hypothalamic extracts, sequenced, and synthesized. It has a high potency for stimulating the secretion of corticotropin-like and beta-endorphin-like immunoactive substances in vitro and in vivo in laboratory animals and humans. The high concentration of CRF-like immunoactivity in hypophyseal portal plasma supports the hypothesis that CRF is the physiological hypothalamic factor. Human and rat CRF (rCRF) also have been purified and synthesized. They have an 83% sequence homology with ovine CRF (oCRF). oCRF-like activity has been found in human hypothalamus, pituitary stalk, posterior pituitary, thalamus, cerebral cortex, cerebellum, pons, medulla oblongata, spinal cord and in the adrenal, lung, liver, stomach, duodenum and pancreas. oCRF-like activity also has been found in the human placenta and in tissues producing ectopic ACTH. The action of CRF can be potentiated by vasopressin, oxytocin, epinephrine, norepinephrine, VIP, and angiotensin II. Intracerebroventricular administration of CRF in the rat produces prolonged elevations of plasma epinephrine, norepinephrine, glucose and glucagon; elevates mean arterial pressure and heart rate; increases motor activity and exploration in familiar surroundings and oxygen consumption; and decreases feeding and sexual behavior. Testing with CRF has enabled the separation of patients with hypothalamic and pituitary adrenal insufficiency. The CRF stimulation test has been useful in distinguishing pituitary from ectopic causes of Cushing's disease. The distribution of CRF within and beyond the hypothalamus provides an anatomical context for the observation that CRF can simultaneously activate and coordinate metabolic, circulatory and behavioral responses that are adaptative in 'stressful' situations. CRF not only stimulates the pituitary-adrenal axis in man, but it also influences several aspects of CNS function which may be of relevance to psychiatric illnesses.

Immunoreactive corticotropin-releasing factor in human plasma

Plasma immunoreactive corticotropin-releasing factor (I-CRF) levels were determined by using a human CRF radioimmunoassay and an immunoaffinity procedure. The basal plasma I-CRF level in normal subjects was 6 +/- 0.5 pg/ml (mean +/- SD). We found that most plasma I-CRF levels were affected by stress, negative feedback, and circadian rhythm. Basal I-CRF levels were high in patients with Addison's disease, Nelson's syndrome, hypopituitarism stemming from pituitary macroadenoma, and CRF- and adrenocorticotropic hormone-producing tumors. A very low, but significant, amount of I-CRF was detected (1-3 pg/ml) in patients with Cushing's syndrome, in corticosteroid-treated patients, and in a patient with hypothalamic hypopituitarism. These results suggest that a major component of plasma I-CRF is of hypothalamic origin, however, other extrahypothalamic tissues cannot be ruled out as a minor source of plasma I-CRF.

In vitro study of immunoreactive corticotropin-releasing factor release from the rat hypothalamus

Immunoreactive corticotropin-releasing factor (I-CRF) release from rat hypothalami was studied in vitro utilizing a perifusion of rat hypothalami and a rat CRF RIA. Basal release of I-CRF from the hypothalamus of adrenalectomized or hypophysectomized rats was higher than in that of normal rats. K+-induced I-CRF release was completely suppressed by omission of Ca++ from the medium. Dexamethasone suppressed I-CRF release from hypothalami, but not from median eminence (ME). C-AMP and angiotensin II had mild stimulatory effects on I-CRF release. These results suggest that 1) the feedback mechanism acts mainly on a higher level than ME, and 2) c-AMP and angiotensin II may be involved in CRF-releasing mechanism(s).