Cerebrospinal fluid and blood concentrations of luteinizing hormone, follicle stimulating hormone and prolactin following castration of adult male rats

Autocrine/paracrine roles of extrapituitary growth hormone and prolactin in health and disease: An overview

Growth hormone (GH) and prolactin (PRL) are both endocrines that are synthesized and released from the pituitary gland into systemic circulation. Both are therefore hormones and both have numerous physiological roles mediated through a myriad of target sites and both have pathophysiological consequences when present in excess or deficiency. GH or PRL gene expression is not, however, confined to the anterior pituitary gland and it occurs widely in many of their central and peripheral sites of action. This may reflect "leaky gene" phenomena and the fact that all cells have the potential to express every gene that is present in their genome. However, the presence of GH or PRL receptors in these extrapituitary sites of GH and PRL production suggests that they are autocrine or paracrine sites of GH and PRL action. These local actions often occur prior to the ontogeny of pituitary somatotrophs and lactotrophs and they may complement or differ from the roles of their pituitary counterparts. Many of these local actions are also of physiological significance, since they are impaired by a blockade of local GH or PRL production or by an antagonism of local GH or PRL action. These local actions may also be of pathophysiological significance, since autocrine or paracrine actions of GH and PRL are thought to be causally involved in a number of disease states, particularly in cancer. Autocrine GH for instance, is thought to be more oncogenic than pituitary GH and selective targeting of the autocrine moiety may provide a therapeutic approach to prevent tumor progression. In summary, GH and PRL are not just endocrine hormones, as they have autocrine and/or paracrine roles in health and disease.

Prolactin and male fertility: the long and short feedback regulation

In the last 20 years, a pituitary-hypothalamus tissue culture system with intact neural and portal connections has been developed in our lab and used to understand the feedback mechanisms that regulate the secretions of adenohypophyseal hormones and fertility of male rats. In the last decade, several in vivo rat models have also been developed in our lab with a view to substantiate the in vitro findings, in order to delineate the role of pituitary hormones in the regulation of fertility of male rats. These studies have relied on both surgical and pharmacological interventions to modulate the secretions of gonadotropins and testosterone. The interrelationship between the circadian release of reproductive hormones has also been ascertained in normal men. Our studies suggest that testosterone regulates the secretion of prolactin through a long feedback mechanism, which appears to have been conserved from rats to humans. These studies have filled in a major lacuna pertaining to the role of prolactin in male reproductive physiology by demonstrating the interdependence between testosterone and prolactin. Systemic levels of prolactin play a deterministic role in the mechanism of chromatin condensation during spermiogenesis.

Temporal effect of tamoxifen on cytochrome P450 side chain cleavage gene expression and steroid concentration in adult male rats

Adult male rats when treated with 0.4 mg tamoxifen (tam)/kg per day for 90 days show reduced circulating testosterone (T) and LH. The present study was designed to have an in depth understanding of tam induced androgen reduction in adult male rats. Adult male rats were orally administered 0.4 mg tam/kg per day for 30, 60 or 90 days and the temporal effects on intratesticular concentrations of pregnenolone (P(5)), progesterone (P(4)), T, 5 alpha-dihydrotestosterone (5 alpha-DHT) and estradiol (E(2)) were estimated. Control group rats were fed saline. Serum hormonal profile of LH, FSH, T and E(2) was also followed on these days. Testicular levels of cytochrome P450 scc mRNA transcripts on 30, 60 and 90 days of treatment with the same dose were quantitated by biplex RT-PCR using beta Actin as internal control followed by analysis using GelPro Analysis software.A significant reduction in intratesticular P(5), P(4), T, 5 alpha-DHT and E(2) was observed from day 30 of treatment. The P450 scc gene expression in the testis was reduced during treatment period from day 60 of treatment. This study demonstrates for the first time that tam reduces testicular pregnenolone biosynthesis through an effect on cholesterol transport and downregulation of P450 scc gene expression. In confirmation of the observed estrogenic effects of tam in this study, it is suggested that E(2) may have a role in cholesterol transport and testicular pregnenolone biosynthesis at the level of cytochrome P450 scc as shown by us.

Effect of hyperprolactinaemia as induced by pituitary homografts under kidney capsule on gastric and duodenal ulcers in rats

The effect of hyperprolactinaemia, induced by two or four pituitary homografts under the kidney capsule, on gastric and duodenal ulcers has been studied. The acute gastric ulcer models used were pylorus ligation, indometacin-induced and ethanol-induced gastric ulcers. Chronic gastric ulcers were induced using acetic acid and duodenal ulcers by mercaptamine hydrochloride. After pylorus ligation, there was an approximate 30-40% increase in gastric secretion, a significant increase in total acidity (P < 0.01) and in the ulcer index (P < 0.01) in rats bearing pituitary homografts under the kidney capsule when compared with the sham-operated control. Hyperprolactinaemia did not affect the formation of ethanol-induced gastric ulcers but showed a 40% reduction in the development of indometacin-induced gastric ulcers. It also produced a 20% increase in the ulcer index in acetic acid-induced chronic gastric ulcers and a 30% increase in ulcer area in mercaptamine-induced duodenal ulcers. Our results showed that hyperprolactinaemia induced gastric acid secretion and thereby aggravated gastric and duodenal ulcers in rats. Hyperprolactinaemia did not affect gastric cytoprotection.

Antifertility effects of estradiol in adult male rats

The dose-related effects of estradiol 17-beta at the doses 0.1 pg, 10 microg, 100 microg, 200 microg, 300 microg, 400 microg, 1,000 microg/kg/day were determined on sperm motility, potency, fertility parameters, serum levels of LH, FSH, PRL and testosterone, weights of testes and accessory sex organs, weights of pituitary and adrenal glands. The drug was administered daily via sc route for a period of 60 days. Dose-related effects on fertility parameters of the estradiol-treated male rats were ascertained by allowing them to mate with normal cycling female rats. Estradiol at 0.1 microg/kg/day dose significantly reduced sperm motility with no effects seen on potency or fecundity, serum LH, FSH, PRL or testosterone, weights of testes and accessory sex organs while pituitary weight increased. Estradiol at 10 microg/kg/day dose significantly reduced motility, serum LH, FSH, weights of testes and accessory sex organs, while pituitary weight increased with no effects seen on potency, fecundity, PRL or testosterone. Estradiol at 100-1,000 microg/kg/day dose significantly reduced motility, potency and fecundity, serum LH, FSH and testosterone, weights of testes and accessory sex organs while serum PRL and the weights of pituitary and adrenal glands increased significantly. Histology of the testes revealed disorganization of the cytoarchitecture in the seminiferous tubules, vacuolation, absence of lumen and compartmentalization of spermatogenesis. Estradiol withdrawal, testosterone propionate at 100 pg/kg/day or antiestrogen (tamoxifen citrate) at 400 microg/kg/day prevented the histological changes. It is conduded that estradiol reduces sperm motility even at a low dose. Low doses (<10 microg/kg/ day) appear to maintain whilst high doses (>10 microg/kg/day) reversibly disrupt spermatogenesis. Prevention of disruption by testosterone or antiestrogen indicates crosstalk between androgen and estrogen receptors in Sertoli cells. Loss of potency and fecundity also suggests effects on crosstalk between these receptors in other male reproductive organs.

Effect of centrally administered prolactin on gastric and duodenal ulcers in rats

The effect of centrally administered prolactin on gastric acid secretion and experimentally-induced gastric and duodenal ulcers was studied. The acute gastric ulcer models used were pylorus ligation, indomethacin-induced and ethanol-induced gastric ulcers. Chronic gastric ulcers were induced using acetic acid and duodenal ulcers by cysteamine hydrochloride. In pylorus ligated rats, prolactin (1 microg/kg icv) produced 45% increase in gastric content volume, significant increase in free acidity (P < 0.001), total acidity (P < 0.001) and ulcer index (P < 0.001). It did not show any significant effect on ethanol-induced and indomethacin-induced gastric ulcers. Prolactin increased the ulcer index (P < 0.001) and ulcer score (P < 0.05) in acetic acid-induced chronic gastric ulcers. It also increased ulcer area (P < 0.05) in cysteamine-induced duodenal ulcers. Therefore, the proulcerogenic activity of prolactin was due to its gastric hypersecretory effect.

Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion

Concentrations of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion. Further, gonadotrophin concentrations in geldings are reported to return to values within the normal range of the entire stallion. In an attempt to characterize this species-specific reversal, the gonadotrophin concentrations of 6 male ponies castrated on 25 March were monitored for 4 months, and 4 stallions were used to generate control data. Blood samples were collected daily, from 3 d before to 10 d after castration (Day 0), and weekly thereafter until Day 122. The pituitary response to castration was immediate. Castration resulted in a previously unreported, dramatic (13-fold) but transient (3 d) surge in circulating concentrations of LH. Concentrations of LH and FSH increased in a logarithmically scaled (LH, R2 = 0.77; FSH, R2 = 0.93) manner over the subsequent 5 wk, during which temporal changes in concentrations of both hormones were strongly correlated (R2 = 0.97). The ratio of plasma gonadotrophin concentrations was consistent throughout (LH:FSH, 1.43 +/- 0.04). Maximal concentrations of LH (20.58 +/- 1.97 ng/mL, Day 34.8 +/- 3.2) were attained approximately 2 wk before the peak in FSH (16.99 +/- 1.97 ng/mL, Day 49.7 +/- 3.0). Plasma gonadotrophin concentrations exceeded those of entire stallions throughout the study. The equine testes inhibited LH secretion during the early breeding season, and no chronic decrease in plasma gonadotrophin concentrations was recorded. However, the LH surge evident for 3 d immediately afer castration, may be related to the dynamic seasonal interaction between gonadal steroids and the regulation of pituitary gonadotrophin release.

Localization of receptors for luteinizing hormone/chorionic gonadotropin in neural retina

Although the expression of the luteinizing hormone (LH)/human chorionic gonadotropin (CG) receptor gene has been traditionally thought to be restricted to gonadal tissue, recent studies have shown that LH/CG receptors are present in many regions of the central nervous system (CNS), as well as in peripheral tissues. We now report the characterization of LH/CG receptor gene expression in the neural retina, a component of the CNS. Transcript levels in the retina are approximately equal to levels present in the cerebral cortex, but are at least 100 fold lower than the levels in testis. The density of LH/CG receptor transcripts, receptor protein and 125I-CG binding is the highest in the photoreceptor cells and then decreased throughout the inner retina. Our study is the first to demonstrate the presence of LH/CG receptors in the neural retina. This finding raises the possibility that photoreceptor cells have the potential to mount cellular responses to LH/CG that may impact on visual processing, and poses an intriguing connection to the proposed role of gonadotropins in the progression of proliferative retinopathy.

Gonadotropin, ACTH, prolactin, sexual steroid and cortisol levels in postmenopausal women's cerebrospinal fluid (CSF)

In CSF and serum of 24 fertile (34.9 +/- 12.2 years) and 15 postmenopausal (58.9 +/- 6.9 years) female patients with non-inflammatory neurologic diseases, LH, FSH, ACTH, prolactin (Prol), estradiol (E), progesterone (P), testosterone (T), and cortisol (C) levels were determined by RIA. In postmenopause, serum levels of FSH and LH had 8- and 6-fold increases in comparison to those in reproductive age. In postmenopause, serum levels of E, P, ACTH and Prol had 8-, 5-, 3- and 2-fold decreases. Serum levels of T and C remained statistically unchanged during the whole life span. In postmenopause, CSF levels of FSH and LH had 3- and 2-fold increases, while E, P, Prol, ACTH CSF levels remained statistically unchanged compared to those in reproductive age (CSF-C levels were under the test sensitivities). CSF/serum ratio of FSH had a 4-fold decrease while that of E had a 4-fold increase in the postmenopause. CSF and serum levels of estradiol and ACTH as well as the logarithmic values of FSH, Prol and P concentrations correlated significantly regarding the whole reproductive postmenopausal life span, however, the CSF-blood barrier seemed to protect the brain from the effects of peripheral estradiol-progesterone deficiencies.