Alterations in the binding characteristics of glucocorticoid receptors from obese Zucker rats

Obese Zucker rats appear to lack a circadian rhythm of serum corticosterone and maintain relatively high concentrations throughout the 24-h day. The binding characteristics of glucocorticoid receptors in lean and obese Zucker rats were examined in three tissues suggested to be involved in the feedback inhibition of corticosterone: the anterior pituitary, hypothalamus and hippocampus. Hepatic glucocorticoid receptors were also examined to determine if receptor alterations exist in a peripheral tissue. The dissociation constant (Kd) of glucocorticoid receptors in the anterior pituitary of obese rats was 50% greater than the Kd of receptors derived from lean rats. This suggests a decrease in the affinity of these receptors and could indicate a reduced feedback inhibition of corticosterone at the anterior pituitary. Hepatic glucocorticoid receptors of obese rats also showed an increase (150%) in the Kd of binding and a reduction (40%) in the number of receptors. No difference was observed in the Kd or maximal binding of receptors from the hypothalamus or hippocampus of lean and obese rats. It appears that glucocorticoid receptor alterations exist in obese Zucker rats and that these alterations may affect the drive of the pituitary-adrenal axis and possibly the expression of obesity.     

Prenatal exposure to dexamethasone alters hippocampal drive on hypothalamic-pituitary-adrenal axis activity in adult male rats

Glucocorticoids are essential for normal hypothalamic-pituitary-adrenal (HPA) axis activity; however, recent studies warn that exposure to excess endogenous or synthetic glucocorticoid during a specific period of prenatal development adversely affects HPA axis stability. We administered dexamethasone (DEX) to pregnant rats during the last week of gestation and investigated subsequent HPA axis regulation in adult male offspring in unrestrained and restraint-stressed conditions. With the use of real-time PCR and RIA, we examined the expression of regulatory genes in the hippocampus, hypothalamus, and pituitary, including corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), glucocorticoid receptors (GR), mineralcorticoid receptors (MR), and 11-beta-hydroxysteroid dehydrogenase-1 (11beta-HSD-1), as well as the main HPA axis hormones, adrenal corticotropic hormone (ACTH) and corticosterone (CORT). Our results demonstrate that the DEX-exposed group exhibited an overall change in the pattern of gene expression and hormone levels in the unrestrained animals. These changes included an upregulation of CRH in the hypothalamus, a downregulation of MR with a concomitant upregulation of 11beta-HSD-1 in the hippocampus, and an increase in circulating levels of both ACTH and CORT relative to unrestrained control animals. Interestingly, both DEX-exposed and control rats exhibited an increase in pituitary GR mRNA levels following a 1-h recovery from restraint stress; however, the increased expression in DEX-exposed rats was significantly less and was associated with a slower return to baseline CORT compared with controls. In addition, circulating levels of ACTH and CORT as well as hypothalamic CRH and hippocampal 11beta-HSD-1 expression levels were significantly higher in the DEX-exposed group compared with controls following restraint stress. Taken together, these data demonstrate that late-gestation DEX exposure in rats is associated with persistent changes in both the modulation of HPA axis activity and the HPA axis-mediated response to stress.     

Estrogens up-regulate type I and type II glucocorticoid receptors in brain regions from ovariectomized rats

The effects of 1-4 days of estradiol (E2) treatment on type I and type II glucocorticoid receptors (GCR) were determined in cytosolic fractions from brain regions of ovariectomized rats. Four days after E2 administration, type I GCR increased in septum, amygdala, hypothalamus and hippocampus, but decreased in the anterior pituitary. Type II GCR increased in septum and hypothalamus only. For both receptor types, changes occurred earlier in septum (1 day) than in the other regions. The E2 increment was due to an increase in Bmax, without changes in Kd. The up-regulation of type II GCR by E2 was also confirmed immunocytochemically in four nuclei of the septal area. In a parallel study, E2 receptors were determined in nuclear and cytosol fractions from the same regions analyzed for GCR. In rats receiving E2, estrogen receptors decreased in cytosol and increased in nuclei from septum, amygdala, hypothalamus and anterior pituitary, but did not change in hippocampus. The results suggest that GCR in certain neuroendocrine regions are regulated by E2, without taking into account whether the areas involved contain high (anterior pituitary), moderate (septum, hypothalamus, amygdala) or low (hippocampus) levels of E2 receptors. Our model may shed light on sex differences in GCR and on E2 regulation of glucocorticoid action in brain and the pituitary.     

Dynamic Aspects of Glucocorticoid Receptors in the Spinal Cord of the Rat

In spite of biochemical and autoradiographic evidence for glucocorticoid binding sites in the spinal cord (SC), events occurring after the preliminary step of hormone binding were not studied. In this investigation, we have examined the transformation (activation) of the cytosolic receptor coupled to [3H]dexamethasone (DEX) and the in vivo interaction of adrenal hormone [corticosterone (CORT)] with purified nuclei from the SC, in addition to the CORT content of the SC before and after stress. Binding of [3H]DEX in the SC was 40% lower than in the hippocampus (HC), although the KD values were comparable. Transformation of [3H]DEX-receptor complexes in the cytosol was demonstrated by diethylaminoethane-cellulose chromatography, by DNA-cellulose binding, and by a combined minicolumn procedure including hydroxyapatite in addition to the last two techniques for separation of transformed, nontransformed, and meroreceptor complexes. In all these situations, SC glucocorticoid binding sites behaved similarly to those in the HC. Nuclear uptake of a tracer dose of [3H]CORT was much lower in the SC than in the HC; nuclear retention of CORT was more easily detected by radioimmunoassay after injection of 1 mg of CORT into adrenalectomized rats. Substantial amounts of CORT, which increased in level after stress, were measured in five regions in the SC, with higher concentrations in the cervical regions. These studies suggest that although SC and HC receptors show similar properties in vitro, differences emerged at the level of nuclear uptake in vivo, in that glucocorticoid action in the SC was similar to that in the optic nerve, where receptors seem to be localized mostly in glial cells.     

Brain corticosteroid receptor gene expression and neuroendocrine dynamics during aging

The present study examined the stress responsiveness of the hypothalamic-pituitary-adrenal axis in relation to the properties of corticosteroid receptors in the brain and pituitary in old (30 months) and young (3 months) male Brown Norway rats. The data demonstrate that circulating ACTH rather than the corticosteroid plasma level was elevated under basal conditions and following stress. Furthermore, a reduction of mineralocorticoid receptor (MR) number in the hippocampus and of glucocorticoid receptor (GR) number in the hypothalamus and the pituitary correspond to increased neuroendocrine responsiveness and negative feedback following stress. The changes in receptor binding do not parallel the changes in the amount of MR and GR mRNA measured with in situ hybridization. This suggests that the processing rather than the receptor gene expression is affected in senescence.     

Disruption of mineralocorticoid receptor function increases corticosterone responding to a mild, but not moderate, psychological stressor

Glucocorticoid negative feedback regulation of the hypothalamic-pituitary-adrenal (HPA) axis is mediated by corticosteroid receptors. It is widely thought that during stress, glucocorticoid receptors (GR) are essential for this negative feedback. In contrast, mineralocorticoid receptors (MR) are associated with HPA axis regulation in basal, nonstress conditions. Notions about the relative roles of MR and GR for HPA axis regulation during stressor challenge may not be complete. Recent work in our laboratory suggests that previous estimates of MR occupancy at resting plasma levels of corticosterone (CORT) may be overestimated. It is possible that a significant number of MR may be available to mediate negative feedback during stressor challenge. We hypothesized that this may be especially the case during mild stressor challenge when the plasma CORT response is weak. In the present studies, adult male Sprague-Dawley rats were first treated systemically or centrally with the selective MR antagonist RU28318 (50 mg/kg sc or 500 ng.10 microl(-1).2 h(-1) icv) or vehicle (300 microl propylene glycol sc or 10 microl/2 h sterile saline icv) and then challenged with 60-min novel environment or restraint. In vehicle controls, restraint resulted in a greater plasma CORT response than novel environment. Both systemic and central treatment with RU28318 significantly increased CORT responding to novel environment relative to vehicle controls. However, RU28318 treatment did not increase the CORT response to restraint. These data suggest that MR may be necessary for glucocorticoid regulation of HPA axis activity during mild stressors, but not during stressors that result in a more robust CORT response.     

Evidence for Glucocorticoid Target Cells in the Rat Optic Nerve. Hormone Binding and Glycerolphosphate Dehydrogenase Induction

Abstract: Biochemical evidence suggests that neuroglia are responsive to glucocorticoids, yet previous studies of glucocorticoid localization have typically failed to demonstrate significant uptake by neuroglial cells. To further investigate this problem, we measured glycerol-3-phosphate dehydrogenase (GPDH) activity and glucocorticoid receptor binding capacity in normal rat optic nerves and in those undergoing Wallerian (axonal) degeneration. Binding studies were also performed on hippocampus and anterior pituitary for comparison purposes. Normal optic nerve preparations possessed a high level of GPDH activity that was glucocorticoid-inducible and that increased further following axonal degeneration. Antibody inactivation experiments demonstrated the presence of more enzyme molecules in the degenerating nerve preparations. Correlative immunocytochemical studies found GPDH-positive reaction product only in morphologically identified oligodendrocytes, a result that is consistent with the previously reported localization of this enzyme in rat brain. Optic nerve cytosol fractions displayed substantial high-affinity binding of both dexamethasone (DEX) and corticosterone (CORT) that, like GPDH, was elevated approximately twofold in degenerating nerves. Finally, in vivo accumulation of [³H]DEX and [³H]CORT by optic nerve and other myelinated tracts was examined using nuclear isolation and autoradiographic methods. Although neither steroid was found to be heavily concentrated by these tissues in vivo , a small preference for DEX was observed in the nuclear uptake experiments. These results are discussed in terms of the hypothesis that glial cells are targets for glucocorticoid hormones.     

Effect of alcohol on the content of sex steroid receptors in the hypothalamus and hypophysis of male rats

In experimental dipsomania model (formation of physical dependence by method of intensive alcoholization) we have studied receptor binding of testosterone (T) and estradiol (E2) in the hypothalamus and pituitary body of mature male rats. Administration (at 10 and 16 h) of 25% ethanol-saline solution at a dose of 7.5 g/kg of body weight in the course of 5 days significantly decreased serum T level but did not change serum LH and FSH levels. Essential reduction of the nuclear androgen receptors in the preoptic-anterior hypothalamic area (POA), mediobasal hypothalamus (MBH) and adenohypophysis was noted in alcohol-treated rats. Unlike androgen receptors the number of the nuclear E2-binding sites in PaO was significantly increased in these males. Thus the results of the present paper demonstrate that multiple administration of ethanol stipulates deficit of serum T, androgen receptors in MBH and pituitary body that possibly results in separation of negative feedback mechanism between the gonads and pituitary body. Increase of specific binding of E2 to nuclear receptors in PoA might appear to explain feminization of alcohol-treated rats.     

Corticosterone regulation of brain and lymphoid corticosteroid receptors

Circulating lymphocytes are often used as a model for brain corticosteroid receptor regulation in clinical disease states, although it is not known if lymphoid receptors are regulated in a similar manner as brain receptors. In the present study the regulation of brain (hippocampus, frontal cortex, hypothalamus and striatum), lymphoid (circulating lymphocytes, spleen and thymus) and pituitary glucocorticoid receptors in response to alterations in circulating corticosterone levels was examined. Seven days following adrenalectomy, type II corticosteroid receptors (i.e. glucocorticoid receptors) were significantly increased in the hippocampus, frontal cortex and hypothalamus, but not in any other tissues. Administration of corticosterone (10 mg/kg) for 7 days significantly decreased type II as well as type I (i.e. mineralocorticoid receptors) receptors in the hippocampus. Type II receptors in the frontal cortex, circulating lymphocytes and spleen were also significantly decreased by chronic corticosterone treatment. Immobilization stress (2 h a day for 5 days) failed to alter receptor density in any of the tissues. These results demonstrate that homologous regulation of corticosteroid receptors by corticosterone does not invariably occur in all tissues and emphasize the complex degree of regulation of these receptors. However, the simultaneous downregulation of both hippocampal and lymphocyte glucocorticoid receptors by corticosterone provides support for the hypothesis that circulating lymphocytes do reflect some aspects of brain glucocorticoid receptor regulation.     

Effects of some putative amino acid neurotransmitters on the stimulated TSH secretion in male rats

The importance of several amino acids (glycine, L-glutamic acid, L-serine, taurine and beta-alanine) in the regulation of the stimulated secretion of TSH was studied in male rats using both peripheral and central administration of the amino acids. Glycine (10-200 mg/kg i.p.), L-glutamic acid (10-500 mg/kg i.p.) and L-serine (500 mg/kg i.p.) decreased significantly the cold-induced TSH secretion whereas beta-alanine (1-500 mg/kg i.p.) and taurine (10-100 mg/kg i.p.) were not effective. The effect of L-glutamic acid (100 mg i.p.) was partially antagonized by bicuculline (1 mg/kg i.p.) but not by picrotoxin (1 or 2 mg/kg i.p.). Only glycine (50 and 100 mg/kg i.p.) inhibited the TRH-stimulated TSH secretion. When the intracerebroventricular route was used, L-serine (50 micrograms/rat) decreased the TSH could response whereas glycine and L-glutamic acid (1-50 micrograms/rat) had no clear effect. We conclude that glycine, glutamate and serine inhibit the cold-induced TSH secretion in the male rat. The action of serine and glycine is possibly mediated through the periventricular hypothalamus and the anterior pituitary, respectively. The inhibition caused by glutamate seems to be partially mediated through the bicuculline-sensitive GABA receptors in the hypothalamus. Taurine and beta-alanine play no role in the control of rat TSH secretion.     

Correlation between LH and estrogen receptor turnover in pituitary and hypothalamus of castrate rats following estrogen agonists and antagonists

A series of studies was undertaken to correlate the short-term dynamics of LH secretion and depletion-replenishment patterns of estrogen receptors (ER) in hypothalamic and pituitary cytosols of ovariectomized rats. Animals castrated for 2 weeks were administered various test compounds and analyzed at 1, 3, 5, 10 and 15 h post-treatment. A single injection of 10 micrograms 17 beta-estradiol (E2) to ovariectomized rats elicited a rapid depletion of ER in both pituitary and hypothalamus and a dramatic, though delayed, fall in serum LH. ER replenishment occurred in both tissues through 15 h and LH recovered in a similar manner. When cycloheximide was administered along with E2, ER replenishment was completely inhibited in both tissues; serum LH fell and failed to recover. Actinomycin D injected with E2 blocked replenishment in pituitary but not hypothalamus; serum LH recovered in parallel with the hypothalamic ER pattern. 17 alpha-E2 elicited only slight changes in ER and LH was suppressed 10-20% through 15 h. CI-628 caused a near total depletion of pituitary ER with no subsequent replenishment, whereas hypothalamic ER content was virtually unaltered; serum LH was suppressed and later recovered. Orchidectomized rats given 5 micrograms E2 demonstrated a less complete ER depletion in hypothalamus, and an earlier replenishment than that seen in pituitary or hypothalamus of similarly treated ovariectomized females. Serum LH rebounded to 157% of control levels at 15 h. The results indicate that the acute feedback suppression of LH by exposure to estrogens correlates with binding to ER and nuclear translocation. Replenishment and/or retention of cytoplasmic ER in hypothalamus appears to be required for full resumption of LH secretion, following acute suppression.     

Trends of reproductive hormones in male rats during psychosocial stress: role of glucocorticoid metabolism in behavioral dominance

Stress in socially subordinate male rats, associated with aggressive attacks by dominant males, was studied in a group-housing context called the visible burrow system (VBS). It has been established that subordinate males have reduced serum testosterone (T) and higher corticosterone (CORT) relative to dominant and singly housed control males. The relationship of the decreased circulating T levels in subordinate males to changes in serum LH concentrations has not been evaluated previously. Since decreases in LH during stress may cause reductions in Leydig cell steroidogenic activity, the present study defined the temporal profiles of serum LH, T, and CORT in dominant and subordinate males on Days 4, 7, and 14 of a 14-day housing period in the VBS. The same parameters were followed in serum samples from single-housed control males. Leydig cells express glucocorticoid receptors and may also be targeted for direct inhibition of steroidogenesis by glucocorticoid. We hypothesize that Leydig cells are protected from inhibition by CORT at basal concentrations through oxidative inactivation of glucocorticoid by 11beta-hydroxysteroid dehydrogenase (11betaHSD). However, Leydig cell steroidogenesis is inhibited when 11betaHSD metabolizing capacity is exceeded. Therefore, 11betaHSD enzyme activity levels were measured in Leydig cells of VBS-housed males at the same time points. Significant increases in LH and T relative to control were observed in the dominant animals on Day 4, which were associated with the overt establishment of behavioral dominance as evidenced by victorious agonistic encounters. Serum LH and T were lower in subordinate males on Day 7, but T alone was lower on Day 14, suggesting that lowered LH secretion in subordinates may gradually be reversed by declines in androgen-negative feedback. Serum CORT levels were higher in subordinate males compared to control at all three time points. In contrast, oxidative 11betaHSD activity in Leydig cells of dominant males was higher relative to control and unchanged in subordinates. These results suggest the following: 1) failure of Leydig cells of subordinate males to compensate for increased glucocorticoid action during stress, by increasing 11betaHSD oxidative activity, potentiates stress-mediated reductions in T secretion; and 2) an inhibition of the reproductive axis in subordinate males at the level of the pituitary.     

The immunostaining for the hypothalamic vasoactive intestinal peptide, but not for beta-endorphin, dynorphin-A or methionine-enkephalin, is affected by the glucocorticoid milieu in the rat: correlation with the prolactin secretion

Effects of the glucocorticoid milieu on the basal and ether stress-induced prolactin (PRL) release and on the immunostaining for hypothalamic vasoactive intestinal peptide (VIP), beta-endorphin (beta-EP), dynorphin-A (DYN-A) and methionine-enkephalin (Met-ENK), were examined in separate groups of male rats. After colchicine treatment in intact rats, VIP-containing cell bodies were observed only in the suprachiasmatic nucleus (SCN). Adrenalectomy (ADX), performed 7 days previously, resulted in the additional appearance of VIP-immunoreactive neurons in the parvocellular subdivision of the paraventricular nucleus (PVN), as well as in significantly higher basal and stressed PRL levels than intact values. Treatment of intact rats with a high dose (500 micrograms/kg body weight (s.c.) daily for 7 days) of dexamethasone (DEX), but not with a low dose (50 micrograms/kg) of DEX, significantly reduced both the basal and stressed PRL release. Administration of either the low or high dose of DEX to ADX rats prevented the appearance of the PVN-VIP neurons. In addition, the ADX-induced high basal and stressed PRL levels were restored to intact values by the low dose of DEX, and completely suppressed by the high dose of DEX. The staining of SCN-VIP-, beta-EP-, DYN-A or Met-ENK neurons was not affected by any treatment employed in this study. These results suggest that the appearance of PVN-VIP immunostaining in ADX rats may, at least in part, be responsible for the enhanced PRL secretion observed in this group. However, SCN-VIP-, beta-EP-, DYN-A- or Met-ENK neurons do not seem to play a pivotal role in the glucocorticoid regulation of PRL secretion.     

Melatonin effects on glucocorticoid receptors in rat brain and pituitary: significance in adrenocortical regulation

1. The effects of chronic melatonin treatment on glucocorticoid binding sites in hippocampus, hypothalamus and pituitary were investigated in rats, subjected to long-term manipulation of circulating corticosterone concentrations. 2. Melatonin treatment decreased the affinity of glucocorticoid receptors. 3. The effect of melatonin was apparent in the presence of normal or enhanced systemic corticosterone levels, but not in long-term adrenalectomized animals.     

Effects of nomegestrol acetate administration on central and peripheral beta-endorphin and allopregnanolone in ovx rats

The aim of this study was to investigate the effects of nomegestrol acetate (NOMAc) on the central nervous system by analyzing the neurosteroid allopregnanolone and the opioid beta-endorphin (beta-endorphin). 104 Wistar female rats were used in this study; one group of fertile and one group of ovariectomized rats were used as control. The others were ovariectomized and they underwent a 2-week oral treatment of NOMAc (0.05, 0.1, 0.2, 0.5, 1mg/kg/day), alone or with 0.05 mg/kg/day of estradiol valerate (E2V). Allopregnanolone and beta-endorphin were assessed in different brain areas and in circulation. Ovariectomy decreased allopregnanolone anywhere except in the adrenal gland and E2V reversed the effects of ovariectomy. 0.5 and 1mg/kg/day of NOMAc increased allopregnanolone levels in hippocampus. Combined administration of 1mg/kg/day of NOMAc plus E2V induced a further increase of allopregnanolone levels in hippocampus, hypothalamus, and anterior pituitary. NOMAc (1mg/kg/day) decreased the adrenal content of allopregnanolone, both by itself and associated with E2V. NOMAc increased hippocampal and hypothalamic content of beta-endorphin at the highest doses, and it increased positively E2V action, at 1mg/kg/day, also in anterior pituitary and plasma. These findings reinforce the clinical data regarding the capability of NOMAc to modulate the pathways involved in mood and behaviour. In fact, due to the NOMAc action on hippocampus, hypothalamus, and anterior pituitary, our results highlight the selectivity of NOMAc on part of the limbic system and the anterior pituitary, regarding both allopregnanolone and beta-endorphin.     

Neuroendocrine changes in female rats born from streptozotocin-diabetic mothers

In adult female rats born from Streptozotocin-diabetic mothers, blood glucose measured under basal conditions or 30 min after glucose administration was similar to controls; however at 180 min 50% of offspring from diabetics was moderately hyperglycemic whereas 100% of controls were normoglycemic. The time of vaginal opening, and after maturity, the number of rats with regular estrous cycles was in the range of controls. After ovariectomy, control rats receiving estradiol showed a sharp increase of serum LH at 4 pm following progesterone treatment at 10 am, while rats born from diabetic mothers failed to modify serum LH. Estradiol receptors in cell nuclei and cytosolic progestin receptors were determined in anterior pituitary, hypothalamus and preoptic area of rats subjected to a 4-day estradiol treatment. Changes were statistically significant in the hypothalamus only, in that rats born from diabetic mothers showed reduced induction of progestin receptors coupled to increased binding of (3H)-estradiol in cell nuclei. These findings bring support for a hypothalamic defect in rats born from diabetic mothers, the reduction of hypothalamic progestin receptors being reflected in the reduced sensitivity to the positive feedback action of progesterone to release LH.     

Regulation of anterior pituitary and brain beta-adrenergic receptors by ovarian steroids

Ovariectomy of adult female rats (200-230g) resulted in an increase in beta-adrenergic receptors in the cerebral cortex, hypothalamus and anterior pituitary. The anterior pituitary had the largest overall increase as well as the most rapid increase in beta-adrenergic receptor density of the tissues examined. The increase in hypothalamic or cerebral cortical beta-adrenergic receptors became apparent only long after ovariectomy (7-14 days). Fourteen days after ovariectomy, the density of beta-adrenergic receptors was 79%, 40%, and 24% in excess of control values in crude membranes prepared from anterior pituitary, hypothalamus and cerebral cortex, respectively. Over the same interval, the plasma concentration of luteinizing hormone (LH) increased 28-fold, while the concentration of follicle-stimulating hormone (FSH) rose 5-fold compared to control levels. Estradiol replacement (20 micrograms/kg/day) in these animals for four days before sacrifice concomitantly reduced plasma levels of the gonadotropins as well as the density of beta-adrenergic receptors in both the anterior pituitary and the hypothalamus. Long-term steroid replacement during the fifth and sixth week after ovariectomy, with implants of estradiol and progesterone which released the steroids in approximately physiological concentrations, significantly reduced beta-adrenergic density in anterior pituitary, but not in the hypothalamic membranes. This treatment significantly reduced plasma LH, but not FSH. Beta-adrenergic receptor density was also found to fluctuate significantly during the 4-day estrous cycle. The highest values were found on proestrus, and the lowest on diestrus 1. These studies indicate that changes in plasma concentrations of gonadal steroids (e.g. during the estrous cycle) influence the density of beta-adrenergic receptors in tissues involved in the control and release of anterior pituitary gonadotropins.     

Gonadal steroids and anterior lobe dynorphin in the male rat

Immunoreactive (ir)-dynorphin levels were measured, and the species characterized by high performance liquid chromatography (HPLC), in the pituitary and hypothalamus of intact and castrate male rats. On HPLC, ir-dynorphin co-eluted with authentic dynorphin A 1-8, dynorphin A 1-17 and dynorphin 1-32 in the hypothalamus and intermediate lobe; in two different reversed phase (RP)-HPLC systems, anterior lobe ir-dynorphin co-eluted uniquely with dynorphin 32 (4K dynorphin). Anterior lobe levels of total ir-dynorphin were significantly lowered 7 days after castration, while HPLC profiles in all tissues remained unchanged. The change in anterior pituitary ir-dynorphin levels was reversed in a dose-related manner by dihydrotestosterone (15-500 micrograms/100 g b. wt/day); estradiol benzoate (3 micrograms/100 g/day) was without effect. The changes on castration and androgen administration suggest that gonadal steroids play a role in the regulation of dynorphin, as well as gonadotrophins and prolactin, within the anterior pituitary gland.     

Dexamethasone treatment increases neuropeptide Y levels in rat hypothalamic neurones

Immunoreactive glucocorticoid receptors (GR) have previously been demonstrated in neuropeptide Y (NPY) neurones of the rat hypothalamus. To determine whether NPY synthesis is influenced by glucocorticoids, the effect of dexamethasone (DEX) on the levels of immunoreactive NPY in rat hypothalamic neurones was investigated in vivo and in vitro. Daily injections of DEX (0.1 mg/day) for 5 days increased the NPY content of the mediobasal hypothalamus in female rats by 117% (p less than 0.002). Primary cultures of hypothalamic neurones were also sensitive to the effect of glucocorticoids. Intracellular NPY levels were significantly increased (p less than 0.001) compared to control values by 151%, 222% and 268% when cultures were maintained in a defined serum free medium containing DEX 10(-9), 10(-8) and 10(-7) M respectively.     

Effect of 5 alpha-dihydrotestosterone and dexamethasone on estrogen receptors of the anterior pituitary and uterus.

The administration of 5 alpha-dihydrotestosterone (5 alpha-DHT) and dexamethasone has been shown to attenuate estrogen-induced prolactin release in the estrogen-primed rat. Therefore, the effect of these compounds was studied on anterior pituitary and uterine estrogen receptors. Injection of 0.8 mg/kg body weight of 5 alpha-DHT to ovariectomized adult rats treated with 2 micrograms estradiol/d for 4 days resulted in a significant decrease in occupied nuclear estrogen receptors of the anterior pituitary but not the uterus. Estrogen priming was essential for 5 alpha-DHT effect on occupied nuclear anterior pituitary estrogen receptors because this effect did not occur in ovariectomized vehicle-treated control animals. The administration of 1 mg/kg body weight of dexamethasone brought about a decrease in uterine but not anterior pituitary nuclear estradiol receptors. These results provide further evidence that the regulation of estrogen receptor dynamics is different in the anterior pituitary and the uterus and that different steroids can exert tissue-specific effects.