Gonadotropin inhibition during chronic stress: role of the adrenal gland

The effect of adrenalectomy, metyrapone and dexamethasone treatments on gonadotropin response to chronic stress were studied. Adult male rats were submitted to chronic restraint (6 h daily over 4 days). At the end of the last stress period animals were decapitated and trunk blood was collected. Chronic restraint evoked a decrease in plasma LH and to a lesser degree in plasma FSH in the intact rat. Adrenalectomy did not prevent the LH reduction induced by stress and magnified the inhibitory effect of restraint on FSH secretion. Administration of the corticosterone synthesis blocker metyrapone increased the inhibitory effect of restraint on plasma LH and to a lesser degree on plasma FSH. Dexamethasone treatment did not significantly modify plasma gonadotropin levels in adrenalectomized unstressed rats, but this treatment totally blocked plasma LH and FSH reduction after chronic restraint. These results indicate that plasma LH and FSH reduction during chronic restraint is not due to the increase in glucocorticoid secretion, but seems to be mediated by the increase of the hypothalamic-pituitary components of the adrenal axis.     

Evaluation of hypothalamic-pituitary function in a combination of tests with four hypothalamic releasing hormones and L-dopa in normal subjects and in patients with hypothalamic and/or pituitary disorders

Hypothalamic-pituitary function was evaluated in a combination of tests with four hypothalamic releasing hormones (4RHs) and L-dopa in normal subjects and in patients with hypothalamic and/or pituitary disorders. Plasma concentrations of anterior pituitary hormones (GH, ACTH, TSH, PRL, LH and FSH) were measured before and after simultaneous iv administration of GHRH, CRH, TRH and LHRH. In addition, changes in the plasma levels of GHRH and GH were investigated before and after oral administration of L-dopa. Normal subjects showed appreciable responses to both tests. In five patients with hypothalamic disorders, the response of plasma anterior pituitary hormones varied, but plasma GHRH and GH did not respond to L-dopa. Patients with idiopathic and postpartum hypopituitarism showed low response to 4RHs or none at all, but L-dopa evoked a normal GHRH response in 2 of the 4 cases having no GH response. In the patients with hypopituitarism due to resection of a pituitary tumor, the response of anterior pituitary hormones to 4RHs was low, and L-dopa administration induced a normal GHRH and low GH response in 5 out of the 7 cases. After 4RHs administration, the patients with ACTH deficiency syndrome showed different patterns of impaired ACTH secretion, and isolated, combined or limited ACTH reserve. Seven patients with anorexia nervosa showed exaggerated GH, delayed TSH and FSH, low ACTH and LH, that is, normal PRL response to 4RHs, but no response of plasma GHRH or GH to L-dopa, suggesting the presence of hypothalamic dysfunction. These results indicate that the combination of the 4RHs test and L-dopa test is a simple and useful means for evaluating hypothalamic-pituitary function by measuring the response of plasma GHRH and six anterior pituitary hormones in the patients with endocrine disorders.     

Plasma concentrations of pituitary hormones in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated male rats

Experiments were conducted to test the hypothesis that acute TCDD toxicity is associated with pituitary hypofunction. Sexually mature male Sprague-Dawley rats were given graded doses of TCDD (0-100 micrograms/kg) and evaluated 7 days later. Despite pronounced hypophagia and body weight loss, plasma concentrations of growth hormone (GH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were not significantly affected by any dose of TCDD. Only prolactin (PRL) concentrations were reduced, while, as previously reported, thyroid-stimulating hormone concentrations were elevated. Also, plasma LH, PRL, and adrenocorticotropic hormone (ACTH) concentrations were not significantly affected 1, 2, 3, 4, 5, or 7 days after a single dose of TCDD (50 micrograms/kg). We conclude that (1) pituitary hypofunction is not a major cause of the initial stages of acute TCDD toxicity, (2) growth retardation in TCDD-treated rats is not the result of a deficiency of GH, (3) alterations in plasma corticosterone concentrations are due to altered responsiveness of the adrenal to ACTH stimulation rather than to changes in plasma ACTH concentrations, and (4) that impaired spermatogenesis is not associated with a decrease in plasma FSH concentrations. In addition, the lack of a consistent effect on plasma PRL concentrations suggests that alterations in plasma PRL concentrations do not play a critical role in the toxicity of TCDD. Finally, because TCDD treatment causes a serious androgenic deficiency without increasing the rates at which androgens are catabolized or excreted, the fact that plasma LH concentrations were unaffected indicates that TCDD treatment must reduce the responsiveness of the testis to LH stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma LH, FSH, testosterone, prolactin and androstenedione in male white-tailed deer after ACTH and dexamethasone administration

1. In order to investigate the role of the adrenocortical system in the regulation of plasma levels of reproductive hormones, adult male white-tailed deer (five intact and one castrated) from a captive herd were sedated with xylazine and ketamine and then challenged with various doses of ACTH with and without dexamethasone (DX) pretreatment. 2. Plasma levels of LH, testosterone (T), FSH, prolactin (PRL) and androstenedione (A) were determined by RIA in serial samples taken from the jugular vein. 3. An increase of A levels detected after ACTH in both intact and castrated deer indicated stimulation of secretion of adrenal androgens by ACTH. 4. No effect on FSH and PRL levels was observed in either group. 5. A significant decline of LH and T observed in various treatments could not be attributed to ACTH or DX administration. It is speculated that the decrease may be caused by anaesthetics which alleviate the stress induced in deer by the pre-immobilization activities.     

Effect of dexamethasone on the release of pituitary hormones in monolayer cultures of rat pituitary cells

The effect of dexamethasone on the release of ACTH, GH, PRL, LH and TSH was studied in monolayer cultures of rat pituitary cells in 4-hour incubation. With or without the addition of rat hypothalamic extract, the release of GH was significantly inhibited by dexamethasone at concentrations higher than 10(-9) M, although less remarkably than that of ACTH. Intracellular ACTH and GH were unchanged. PRL, LH and TSH were not affected. These results indicate that dexamethasone, when exerted for 4 hours, suppressed the release of GH as well as ACTH, at least in part, at the pituitary level.     

Pituitary hormones dependent expression of insulin-like growth factors I and II in the immature hypophysectomized rat testis

Since insulin-like growth factors I (IGF-I) and II (IGF-II) appeared involved in paracrine or autocrine regulation of both cell multiplication and differentiation of the rat testis, we have investigated the pituitary hormonal dependence of IGF-I and IGF-II mRNA production in the testis of immature hypophysectomized rats (22 days old) supplemented with highly purified FSH, LH, GH or PRL. Our data show that testicular expression of IGF-I mRNA as measured by dot-blot hybridization, is increased by LH, FSH or GH treatments of 7-, 6-, and 4-fold, respectively, above controls. Intensity of the signal was 3-fold lower after PRL treatment than in hypophysectomized control rats. On the contrary, IGF-II mRNA expression, was found low in the immature hypophysectomized rat testis and unmodified by any hormonal treatment. In contrast to the increase of IGF-I expression in the testis no significant change in the IGF-I plasma concentration was observed after LH or FSH supplementation. GH treatment, as expected, increased 4-fold the IGF-I plasma concentration of the experimental animals. Since we have previously shown that LH, FSH, and GH exhibit selective cell multiplication and differentiation in the testis of our animal model, it is proposed that testicular IGF-I expression could be the tissue response to pituitary hormone in these phenomena.     

Participation of voltage-sensitive calcium channels in pituitary hormone release

The role of extracellular Ca2+ in pituitary hormone release was studied in primary cultures of rat anterior pituitary cells. The basal levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH), and adrenocorticotropin (ACTH) secretion were independent of extracellular Ca2+ concentration ([Ca2+]e). In contrast, the basal levels of growth hormone (GH) and prolactin (PRL) release showed dose-dependent increases with elevation of [Ca2+]e, and were abolished by Ca2+-channel antagonists. Under Ca2+-deficient conditions, BaCl2 mimicked the effects of calcium on PRL and GH release but with a marked increase in potency, and also increased basal LH and FSH release in a dose-dependent manner. In the presence of normal [Ca2+]e, depolarization with K+ maximally increased cytosolic [Ca2+] ([Ca2+]i) from 100 to 185 nM and elevated LH, FSH, TSH, ACTH, PRL, and GH release by 7-, 5-, 4-, 3-, 2-, and 1.5-fold, respectively. These effects of KCl were abolished in Ca2+-deficient medium or in the presence of the Ca2+-channel antagonist, Co2+, and were diminished by the dihydropyridine Ca2+-channel antagonist, nifedipine. The Ca2+-channel agonist BK 8644 (100 nM) enhanced the hormone-releasing actions of 25 mM KCl upon PRL, LH, FSH, GH, TSH, and ACTH by 2.3-, 2.0-, 1.8-, 1.7-, 1.6-, and 1.4-fold, respectively. The dose- and voltage-dependent actions of BK 8644 were specific for individual cell types; BK 8644 enhanced GH, PRL, TSH, LH, and ACTH secretion in the absence of any depolarizing stimulus, with ED50 values of 8, 10, 150, 200, and 400 nM, respectively. However, in the presence of 50 mM KCl, the ED50 values for BK 8644 were 1.5, 2, 3, 5, and 7 nM for GH, PRL, ACTH, TSH, and LH, respectively. [3H]BK 8644 bound specifically to pituitary membranes with Kd values of 0.8 nM and concentrations of about 900 channels per cell. These observations provide evidence for the presence and participation of voltage-sensitive calcium channels in the secretion of all five populations of anterior pituitary cells.     

Cellular associations of pituitary gonadotrophs in a rodent (Lagostomus maximus maximus) with photoperiod-dependent reproduction

The morphological characteristics and percentage of the cellular associations between gonadotrophs (LH- and FSH-secreting cells) and other cellular types were studied in pituitary pars distalis of adult male viscachas (Lagostomus maximus maximus) by double immunohistochemistry using specific antibodies to LH, FSH, PRL, GH, ACTH, TSH and S-100 protein (by folliculostellate cells; FSC), during long and short photoperiods. Bihormonal gonadotrophs were observed in ventro-medial and dorsal regions, interspersed between monohormonal gonadotrophs, and their number increased in short photoperiod. LH- and FSH-gonadotrophs were found around lactotrophs, enclosed by somatotrophs in the dorsal region, and associated with irregular corticotrophs. Gonadotrophs and thyrotrophs were associated along blood vessels and follicular structures. The cytoplasmic prolongations of FSC were in contact with both gonadotrophs. The percentage of LH–FSH, LH–ACTH, LH–FSC, FSH–LH, FSH–PRL, FSH–GH, FSH–ACTH, FSH–TSH and FSH–FSC associations decreased, whereas LH–PRL increased in short as compared to long photoperiod. The most abundant associations were LH–GH and LH–TSH during long photoperiod, but LH–GH and LH–PRL during short photoperiod. FSH–GH and FSH–PRL were the most numerous associations, and LH–FSC and FSH–FSC were the less abundant ones in both photoperiods. These results provide the morphological evidence for specific cellular associations between gonadotrophs and other cellular types of viscacha pituitary.     

Inhibition of the ACTH adrenal response to stress by treatment with hydrocortisone, prednisolone and dexamethasone in the rat

16- and 4-week-old intact and adrenalectomized rats have been treated with different doses of the three glucocorticoids hydrocortisone, prednisolone and dexamethasone by gavage. The delayed feedback effect on plasma ACTH and corticosterone response to an ether stress have been assessed. Almost complete suppression of corticosterone response 20 min after an ether stress and an ACTH suppression to 20% of control values 5 min after an ether stress were observed with 25 micrograms of dexamethasone, 10 mg of prednisolone and 20 mg of hydrocortisone. Although the percent inhibition of corticosterone and ACTH response to stress was comparable, a striking dissociation of the ACTH and corticosterone release was observed in terms of absolute concentrations. A mean ACTH concentration of 462 ng/l after 25 micrograms of dexamethasone was measured together with a barely measurable corticosterone concentration of 3 micrograms%. Similarly, after 10 mg of prednisolone, the mean ACTH concentration was 404 ng/l, whilst the mean corticosterone concentration was 3 micrograms%. This dissociation demonstrates that the corticosterone concentration on its own does not necessarily reflect the ACTH release. At 4 weeks of age, the ACTH response to stress is more difficult to suppress than in adult animals. This is more obvious after adrenalectomy, where the excessive ACTH secretion was less inhibited by all glucocorticoids used. The time between the last steroid gavage and stress must be considered. In 4-week-old animals the ACTH response 16 h after 12.5 micrograms of dexamethasone was inhibited by 22%, whereas 4 h after the same dexamethasone dose the inhibition was 85%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of corticotropin releasing factor and growth hormone releasing factor on pituitary hormone secretion in patients with congenital thyrotropin deficiency. Abnormal response of growth hormone to corticotropin releasing factor

Blood concentrations of anterior pituitary hormones, ACTH, GH, TSH, PRL, LH, and FSH were determined in corticotropin releasing factor (CRF) test (synthetic ovine CRF 1.0 microgram per kg body weight) and growth hormone releasing factor (GRF) test (synthetic human pancreatic GRF-44 100 micrograms) in 2 female sibling patients with congenital isolated TSH deficiency, in their mother, in 2 patients with congenital primary hypothyroidism and in 8 normal controls. The patients with isolated TSH deficiency showed normally increased plasma ACTH and serum GH after CRF and GRF, respectively, and also showed an abnormal GH response to CRF. The serum GH showed a rapid increase to maximum levels (12.9 ng/ml) within 30 to 60 min followed by decrease. The possibility of secretion of abnormal GH could be excluded by the fact that on serum dilution, GH value gave a linear plot passing through zero. In addition, serum PRL, LH and FSH levels after CRF administration in case 1 and PRL after GRF in case 2 were also slightly increased but these responses were marginal. The mother of the patients, patients with congenital primary hypothyroidism, and normal healthy controls showed normal responses of pituitary hormones throughout the experiment. Data from the present study and a previous report show that abnormal GH response to the hypothalamic hormones (CRF, TRH and LHRH) may be observed in patients with congenital isolated TSH deficiency.     

ACTH and corticosterone response to naloxone and morphine in normal, hypophysectomized and dexamethasone-treated rats

The effect of opiate receptors blocker naloxone on ACTH and corticosterone secretion in normal, dexamethasone-treated and hypophysectomized rats was studied. A dose-related increase in plasma corticosterone level was found at 45 min after s.c. injection of naloxone in a dose range of 0.25-2.0 mg kg-1. The rise in plasma corticosterone was preceded by a slight increase in plasma ACTH. Acute morphine administration in a relatively low dose (6 mg kg-1 s.c.) induced a significant rise in both plasma ACTH and corticosterone levels. Dexamethasone treatment was followed by low basal corticosterone level, by total inhibition of the stress response and response to morphine injection, while the response to ACTH administration was normal. Under these circumstances as well as in rats 6 days after hypophysectomy, naloxone failed to increase plasma corticosterone levels. It is concluded that a direct stimulation of corticosteroid biosynthesis in adrenal cortex is not involved in the mechanism of naloxone-induced activation of pituitary-adrenocortical function.     

Spontaneous recovery from hypopituitarism due to postpartum hemorrhage

A rare case is presented of a woman with spontaneous recovery from hypopituitarism following postpartum hemorrhage. One month after delivery, serum thyroid hormone, TSH, LH and FSH levels were low, and their secretion from the pituitary gland responded poorly to the TRH and LH-RH tests. Pituitary TSH response was normal 3 months after delivery. In the LH-RH test, pituitary LH and FSH response returned to normal at 2 months. Pituitary GH secretion and serum cortisol levels induced by ITT already responded normally one month postpartum. Excessive secretion of pituitary PRL was observed 3 months after delivery and improved gradually thereafter. These results indicate that the secretion of pituitary tropic hormones was sensitive to pituitary ischemia in the following order: TSH, gonadotropin, GH and ACTH. The disturbance of these hormones also persisted in the same order.     

Feedback effects of dexamethasone on adrenocortical responses in rats with fornix section.

To investigate the sites of the negative feedback of corticoids in the regulation of ACTH secretion, the effect of 10 mug of dexamethasone on adrenocortical responses to ether stress was studied in intact and fornix-sectioned rats. Dexamethasone pretreatment in both groups depressed significantly both the basal and stress plasma corticosterone levels. However, in rats with fornix section the amount of depression of the adrenocortical response was much smaller than in intact animals, when compared to the non-treated group. These data would inicate that extrahypothalamic regions play a role in the action of glucocorticoids in the feedback control of pituitary-adrenal function and that the hippocampus participates in this mechaism.     

Localization of Carboxyl Ester Lipase in Human Pituitary Gland and Pituitary Adenomas

Carboxyl ester lipase (CEL) is an enzyme that hydrolyzes a wide variety of lipid substrates, including ceramides, which are known to show inhibitory regulation of pituitary hormone secretion in experimental models. Because no studies on CEL expression in human pituitary and pituitary adenomas have been reported in the literature, we investigated CEL expression in 10 normal pituitary glands and 86 well-characterized pituitary adenomas [12 FSH/LH cell, 17 α-subunit/null cell, 6 TSH cell, 21 ACTH cell, 11 prolactin (PRL) cell, and 19 GH cell adenomas] using IHC, immunoelectron microscopy, Western blotting, and quantitative RT-PCR. In normal adenohypophysis, CEL was localized in GH, ACTH, and TSH cells. In adenomas, it was mainly found in functioning GH, ACTH, and TSH tumors, whereas its expression was poor in the corresponding silent adenomas and was lacking in FSH/LH cell, null cell, and PRL cell adenomas. Ultrastructurally, CEL was localized in secretory granules close to their membranes. This is the first study demonstrating CEL expression in normal human pituitary glands and in functioning GH, ACTH, and TSH adenomas. Considering that CEL hydrolyzes ceramides, inactivating their inhibitory function on pituitary hormone secretion, our findings suggest a possible role of CEL in the regulation of hormone secretion in both normal and adenomatous pituitary cells. (J Histochem Cytochem 58:881–889, 2010)     

Effect of ACTH, dexamethasone, and adrenalectomy on the secretion of testosterone in the rat

The effect of ACTH (100 micrograms/animal/day, i.p.), dexamethasone (75 micrograms/animal/day, s.c.), both for three consecutive days, and adrenalectomy, with or without dexamethasone, maintained according to the group, one, two or three days, on the plasmatic testosterone and corticosterone levels, has been studied in adult male Wistar rats. ACTH and adrenalectomy produced a high decrease in testosterone levels (p less than 0.001 for the three days studied). Dexamethasone produced lower testosterone levels in the first day followed by partial recuperation between the second and the third days of its administration. Dexamethasone produced the effects mentioned for intact animals. The changes in corticosterone levels were according to an adequate response of the hypothalamus-pituitary-adrenal system under these experimental circumstances. ACTH exerts an inhibitory effect on testosterone secretion in the rat, so that such an effect from the data obtained after adrenalectomy and simultaneous dexamethasone injections, does not seems to be mediated either by the presence of adrenals or high corticosterone levels.     

Inhibitory effects of cysteamine on neuroendocrine function

The action of cysteamine on anterior pituitary hormone secretion was studied in vivo using conscious, freely moving male rats and in vitro using anterior pituitary cells in monolayer culture. Administration of 500 micrograms cysteamine into the lateral cerebral ventricles of normal rats caused the complete inhibition of pulsatile GH secretion for a minimum of 6 h. This treatment also significantly decreased plasma concentrations of LH for at least 6 h in orchiectomized rat, TSH in short-term (0.5 month) thyroidectomized rats, and PRL in long-term (6 months) thyroidectomized rats. The in vivo stimulation of GH, LH, TSH and PRL with their respective releasing hormones 60 min after administration of cysteamine was not different from the response observed in rats pretreated with saline except for PRL where cysteamine pretreatment significantly inhibited the expected PRL increase. In vitro, 1 mM cysteamine decreased basal and TRH stimulated PRL release while not affecting basal or stimulated GH, LH, TSH and ACTH secretion. These data demonstrate the dramatic and wide-ranging effects of cysteamine on anterior pituitary hormone secretion. This action appears to be mediated through hypothalamic pathways for GH, LH and TSH and through a pituitary pathway for PRL.     

Effects of chronic food restriction and treatments with leptin or ghrelin on different reproductive parameters of male rats

The existence of a close relationship between energy status and reproductive function is well-documented, especially in females, but its underlying mechanisms remain to be fully unfolded. This study aimed to examine the effects of restriction of daily calorie intake, as well as chronic treatments with the metabolic hormones leptin and ghrelin, on the secretion of different reproductive hormones, namely pituitary gonadotropins and prolactin, as well as testosterone, in male rats. Restriction (50%) in daily food intake for 20 days significantly reduced body weight as well as plasma PRL and T levels, without affecting basal LH and FSH concentrations and testicular weight. Chronic administration of leptin to rats fed ad libitum increased plasma PRL levels and decreased circulating T, while it did not alter other hormonal parameters under analysis. In contrast, in rats subjected to 50% calorie restriction, leptin administration increased plasma T levels and reduced testis weight. Conversely, ghrelin failed to induce major hormonal changes but tended to increase testicular weight in fed animals, while repeated ghrelin injections in food-restricted males dramatically decreased plasma LH and T concentrations and reduced testis weight. In sum, we document herein the isolated and combined effects of metabolic stress (50% food restriction) and leptin or ghrelin treatments on several reproductive hormones in adult male rats. Overall, our results further stress the impact and complex way of action of different metabolic cues, such as energy status and key hormones, in reproductive function also in the male.     

Effect of ACTH and glucocorticoids on plasma prolactin levels in the male rat

Relationships between prolactin and adrenal secretion were studied in the adult male rat by different experimental approaches. Administration of a long acting 1-24 ACTH preparation during 11 days induced a significant decrease in plasma prolactin levels. Adrenalectomy on the contrary resulted in an increase of prolactin levels that were not affected by ACTH treatment. Dexamethasone administration to intact or adrenalectomized animals resulted in a significant reduction of plasma prolactin in both cases. In order to elucidate if the inhibitory effect of the adrenal stimulation on prolactin was mediated through the blockade of endogenous ACTH, stimulation of hypothalamic-pituitary-adrenal axis with chronic intermittent immobilization stress was performed. Stress induced a significant elevation in plasma corticosterone levels, together with a decrease in prolactin values. These data indicated that the inhibitory role of ACTH and stress on prolactin secretion was mediated through the adrenal glucocorticoid stimulation.     

Validation of the mechanisms proposed for the stimulatory and inhibitory effects of progesterone on gonadotropin secretion in the estrogen-primed rat: a possible role for adrenal steroids.

The stimulatory and inhibitory effects of progesterone on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion were found to be dependent on the length of estrogen exposure in ovariectomized estrogen-primed rats. Progesterone suppressed LH and FSH secretion when administered 16 hours after a single injection of estradiol to ovariectomized rats. If the estradiol treatment was extended over 40 hours by two injections of estradiol 24 hours apart, progesterone administration led to a highly significant elevation of both serum LH and FSH levels 6 hours later. In addition to the direct stimulatory effect on LH and FSH release, progesterone, when injected 1 hour before, was able to antagonize the suppressive effect of a third injection of estradiol on LH and FSH release. In the immature ovariectomized estrogen-primed rat, 10 IU of ACTH brought about a release of progesterone and corticosterone 15 minutes later and LH and FSH 6 hours later. Progesterone, but not corticosterone, appeared to be responsible for the effect of ACTH on gonadotropin release. The synthetic corticosteroid triamcinolone acetonide brought about LH and FSH release in the afternoon, while cortisol, similar to corticosterone, was unable to do so. Nevertheless, triamcinolone acetonide and cortisol brought about increased secretion of FSH the following morning.