Inhibitory effect of androgen on estrogen-induced prolactin messenger ribonucleic acid accumulation in the male rat anterior pituitary gland

The maternal hormone in the male brain: Sexually dimorphic distribution of prolactin signalling in the mouse brain

Research of the central actions of prolactin is highly focused on females, but this hormone has also documented roles in male physiology and behaviour. Here, we provide the first description of the pattern of prolactin-derived signalling in the male mouse brain, employing the immunostaining of phosphorylated signal transducer and activator of transcription 5 (pSTAT5) after exogenous prolactin administration. Next, we explore possible sexually dimorphic differences by comparing pSTAT5 immunoreactivity in prolactin-supplemented males and females. We also assess the role of testosterone in the regulation of central prolactin signalling in males by comparing intact with castrated prolactin-supplemented males. Prolactin-supplemented males displayed a widespread pattern of pSTAT5 immunoreactivity, restricted to brain centres showing expression of the prolactin receptor. Immunoreactivity for pSTAT5 was present in several nuclei of the preoptic, anterior and tuberal hypothalamus, as well as in the septofimbrial nucleus or posterodorsal medial amygdala of the telencephalon. Conversely, non-supplemented control males were virtually devoid of pSTAT5-immunoreactivity, suggesting that central prolactin actions in males are limited to situations concurrent with substantial hypophyseal prolactin release (e.g. stress or mating). Furthermore, comparison of prolactin-supplemented males and females revealed a significant, female-biased sexual dimorphism, supporting the view that prolactin has a preeminent role in female physiology and behaviour. Finally, in males, castration significantly reduced pSTAT5 immunoreactivity in some structures, including the paraventricular and ventromedial hypothalamic nuclei and the septofimbrial region, thus indicating a region-specific regulatory role of testosterone over central prolactin signalling.

Prolonged in vivo administration of testosterone-enanthate, the widely used and abused anabolic androgenic steroid, disturbs prolactin and cAMP signaling in Leydig cells of adult rats

This study was designed to systematically analyze and define the effects of 1-day, 2-weeks, 10-weeks intramuscular administration of testosterone-enanthate, widely used and abused anabolic androgenic steroid (AAS), on main regulators of steroidogenesis and steroidogenic genes expression in testosterone-producing Leydig cells of adult rats. The results showed that prolonged (10-weeks) intramuscular administration of testosterone-enanthate, in clinically relevant dose, significantly increased prolactin, but decreased Prlr2 and Gnrhr in pituitary of adult rat. The levels of testosterone, Insl3, cAMP and mitochondrial membrane potential of Leydig cells were significantly reduced. This was followed by decreased expression of some steroidogenic enzymes and regulatory proteins such as Lhcgr, Prlr1/2, Tspo, Star, Cyp11a1, Cyp17a1, Dax1. Oppositely, Hsd3b1/2, Hsd3b5, Hsd17b4, Ar, Arr19 increased. In the same cells, transcriptional milieu of cAMP signaling elements was disturbed with remarkable up-regulation of PRKA (the main regulator of steroidogenesis). Increased prolactin together with stimulated transcription of Jak2/Jak3 could account for increased Hsd3b1/2 and Hsd3b5 in Leydig cells following 10-weeks in vivo treatment with testosterone-enanthate. In vitro studies revealed that testosterone is capable to increase level of Prlr1, Prlr2, Hsd3b1/2, Hsd3b5 in Leydig cells. Accordingly, testosterone-induced changes in prolactin receptor signaling together with up-regulation of PRKA, Hsd3b1/2, Hsd3b5, Ar in Leydig cells, could be the possible mechanism that contribute to the establishment of a new adaptive response to maintain homeostasis and prevent loss of steroidogenic function. Presented data provide new molecular insights into the relationship between disturbed testosterone homeostasis and mammalian reproduction and are important in terms of wide use and abuse of AASs and human reproductive health.

Pituitary androgen receptor signalling regulates prolactin but not gonadotrophins in the male mouse

Production of the androgen testosterone is controlled by a negative feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. Stimulation of testicular Leydig cells by pituitary luteinising hormone (LH) is under the control of hypothalamic gonadotrophin releasing hormone (GnRH), while suppression of LH secretion by the pituitary is controlled by circulating testosterone. Exactly how androgens exert their feedback control of gonadotrophin secretion (and whether this is at the level of the pituitary), as well as the role of AR in other pituitary cell types remains unclear. To investigate these questions, we exploited a transgenic mouse line (Foxg1^Cre/+; AR^fl/y) which lacks androgen receptor in the pituitary gland. Both circulating testosterone and gonadotrophins are unchanged in adulthood, demonstrating that AR signalling is dispensable in the male mouse pituitary for testosterone-dependent regulation of LH secretion. In contrast, Foxg1^Cre/+; AR^fl/y males have a significant increase in circulating prolactin, suggesting that, rather than controlling gonadotrophins, AR-signalling in the pituitary acts to suppress aberrant prolactin production in males.

Kisspeptin regulates tuberoinfundibular dopaminergic neurones and prolactin secretion in an oestradiol-dependent manner in male and female rats

Prolactin (PRL) secretion is inhibited by hypothalamic dopamine. Kisspeptin controls luteinising hormone (LH) secretion and is also involved in PRL regulation. We further investigated the effect of kisspeptin-10 (Kp-10) on the activity of tuberoinfundibular dopaminergic (TIDA) neurones and the role of oestradiol (E2 ) in this mechanism. Female and male rats were injected with i.c.v. Kp-10 and evaluated for PRL release and the activity of dopamine terminals in the median eminence (ME) and neurointermediate lobe of the pituitary (NIL). Kp-10 at the doses of 0.6 and 3 nmol increased plasma PRL and decreased 4-dihydroxyphenylacetic acid (DOPAC) levels in the ME and NIL of ovariectomised (OVX), E2 -treated rats but had no effect in OVX. In gonad-intact males, 3 nmol Kp-10 increased PRL secretion and decreased DOPAC levels in the ME but not in the NIL. Castrated males treated with either testosterone or E2 also displayed increased PRL secretion and reduced ME DOPAC in response to Kp-10, whereas castrated rats receiving oil or dihydrotestosterone were unresponsive. By contrast, the LH response to Kp-10 was not E2 -dependent in either females or males. Additionally, immunohistochemical double-labelling demonstrated that TIDA neurones of male rats contain oestrogen receptor (ER)-α, with a higher proportion of neurones expressing ERα than in dioestrous females. The dopaminergic neurones of periventricular hypothalamic nucleus displayed much lower ERα expression. Thus, TIDA neurones express ERα in male and female rats, and kisspeptin increases PRL secretion through inhibition of TIDA neurones in an E2 -dependent manner in both sexes. These findings provide new evidence about the role of kisspeptin in the regulation of dopamine and PRL.

Lack of anti-androgenic effects of equol on reproductive neuroendocrine function in the adult male rat

Equol (EQ), a metabolite of the soy isoflavone daidzein, has well known estrogenic properties. Data from animal studies suggested that EQ may act also as an anti-androgen. However, data regarding how EQ may affect brain functions like the regulation of neuroendocrine activity and reproductive outcomes in adult male rats are still lacking. We therefore investigated the effects of EQ on sex-steroid regulated gene expression in the brain [medial preoptic area/anterior hypothalamus (MPOA/AH) and medial basal hypothalamus/median eminence (MBH/ME)], pituitary, and prostate as a reference androgen-dependent organ. Furthermore reproductive outcomes were evaluated. The anti-androgen flutamide (FLUT) served as reference compound. Male rats (n=12 per group) were treated by gavage for 5 days with either EQ (100 or 250 mg/kgBW/day), or FLUT 100 mg/kgBW/day. All vehicle- and EQ-treated males showed successful reproductive outcomes, whereas FLUT-exposed males had severe reproductive impairments resulted in infertility. FLUT decreased relative weights of prostate, seminal vesicles and epididymides, and increased serum levels of luteinizing hormone, follicle-stimulating hormone, testosterone and 5α-dihydrotestosterone without altering prolactin levels, whereas EQ exerted opposite effects. Both EQ and FLUT decreased gonadotropin releasing hormone (GnRH) expression in the MPOA/AH. Only FLUT upregulated levels of GnRH receptor expression both in the MBH/ME and pituitary. While EQ downregulated the hypothalamic ERα and ERβ expressions, but FLUT did not. In the prostate, only FLUT upregulated both ERα and AR mRNA expression levels. Taken together, our findings are the first data that EQ did not induce anti-androgenic effects on brain, prostate and male reproductive parameters, however, estrogenic neuroendocrine and reproductive effects of EQ were observed.

Effects of the natural endocrine disruptor equol on the pituitary function in adult male rats

Equol (EQ), a potent biologically active metabolite of the soy isoflavone daidzein, interacts with estrogen receptors (ERs), however, as suggested recently, EQ may also exert anti-androgenic actions in androgen regulated tissues like prostate and seminal vesicles in adult male rats. However, data regarding a putative anti-androgenic activity of EQ on pituitary function in male individuals are still lacking. Therefore, we investigated the effects of EQ on androgen- and estrogen-regulated gene expressions in the pituitary and circulating luteinizing hormone (LH) and prolactin (PRL) levels in adult male rats. 3-Month-old male Sprague-Dawley rats (n=12 per group) were treated by gavage for 5 days with either EQ (100 and 250 mg/kg BW/day) or vehicle olive oil (1 ml/rat/day). As reference compound, the pure anti-androgenic drug flutamide (FLUT) was employed at a dose of 100 mg/kg BW/day. At day 5, animals were sacrificed. Levels of pituitary hormones and gene expression were measured by radioimmunoassays and quantitative TaqMan(®) real-time reverse transcription polymerase chain reaction, respectively. The present findings revealed that the pituitary mechanisms involved in the effects of EQ and FLUT were different due to the opposite changes in the mRNA expression levels of estrogen receptor subtype alpha (ERα)-, truncated estrogen receptor product-1 (TERP-1)- and -2 (TERP-2)-, gonadotropin releasing hormone receptor (GnRH receptor)-, beta-subunit of LH (LHβ)-, and gonadotropin alpha subunit (α-subunit) genes. EQ displayed typical ER-agonistic actions as shown by the significant increases in ERα-, TERP-1/-2 mRNA expressions and serum PRL levels along with the significant reduction in serum LH levels, whereas FLUT exerted opposite effects on gonadotropin secretion and expression. Taken together, our findings are the first in vivo data that upon sub-acute oral exposure of EQ show an estrogenic effect on reproductive endocrine activity of the pituitary in adult male rats. However, EQ did not exert anti-androgenic effects on male rat pituitary function as observed at the levels of mRNA expression of androgen- and estrogen-regulated genes and circulating pituitary hormones.

Sexually dimorphic basal water absorption at the isolated pelvic patch of Japanese tree frog, Hyla japonica

Frogs ingest little water orally, but absorb the majority of the water needed for normal physiological performance through a specific region of the ventral skin, the pelvic patch. We observed non-stimulated (basal water absorption, BWA) water flux through the isolated pelvic patch in vitro in Japanese tree frog (Hyla japonica). We found that water flux through non-stimulated skin from the pelvic patch was greater in males than females. This water flux was confirmed as BWA by observing no effect following the in vitro administration of propranolol and [adamantaneacetyl(1), O-Et-D-Tyr(2), Val(1), aminobutyryl(6), Arg(8, 9)] vasopressin, which are a beta-adrenergic receptor antagonist and a vasopressin V2 receptor antagonist, respectively. We further examined this phenomenon following gonadectomy, treatment with sex hormones (E2, 17beta-estradiol; TP, testosterone propionate), estrogenic chemicals (BPA, bisphenol A; MTX, methoxychlor) or prolactin (PRL, a hormone regulated by sex hormones that has osmoregulatory activity). Ovariectomy increased BWA in females. Injection (in vivo treatment) of E2 or PRL reduced BWA in males, whereas TP injection increased BWA in females. However, the in vitro addition of E2, TP, or PRL to the Ringer's solution on the serosal side of the ventral skin patch did not alter BWA. Subsequently, we injected (in vivo treatment) BPA or MTX, environmental chemical contaminants with known hormonal actions in mammals. Injection of BPA or MTX reduced BWA in males as observed following treatment with E2. These results provide the first evidence of sexual dimorphism in BWA through the isolated pelvic patch. The gonad appears essential for observed sexual dimorphism in BWA, and we hypothesize that sex hormones regulate the release of PRL, that in turn influences BWA indirectly. E2 is known to exert a specific stimulatory effect on PRL secretion. In addition, we have observed that some endocrine disrupting contaminants also eliminate the sexual dimorphism in BWA observed in the Japanese tree frog.

Effects of anabolic implants of oestradiol alone or in combination with trenbolone acetate on the ultrastructure of mammary glands in female lambs regarding their interference in prolactin secretion

The side-effects of anabolic steroid implants on mammary gland ultrastructure were evaluated in female lambs treated with oestradiol (n = 10) and with oestradiol plus trenbolone acetate (n = 10). Ten non-implanted lambs were used as controls. Apart from the ultrastructural study of the mammary gland, an assessment of the prolactin pituitary cell population was carried out by immunological methods. Our results showed that oestrogenic implants exert stimulating effects on mammary gland development, both by activating the synthesis process at mammary gland cell levels and by increasing prolactin pituitary production. Nevertheless, there was no evidence of secretory products in the lumen of the gland. Implants containing trenbolone acetate counteracted the mammary stimulus of oestrogens showing ultrastructural images of cell autolysis and necrosis.

Progestin regulation of galanin and prolactin gene expression in oestrogen-induced pituitary tumours

Galanin is a peptide widely distributed in the hypothalamic-pituitary axis. In the female rat pituitary, galanin is mainly present in lactotrophs, where it regulates their secretion and proliferation. Galanin expression is increased in oestrogen-induced prolactinomas, and it has been proposed that oestrogen effects on lactotroph function and proliferation could be mediated by galanin. Previous studies from our laboratory demonstrated that the synthetic progestin levonorgestrel antagonizes pituitary tumorigenesis of rats given oestrogen, reducing the number of proliferating cells and increasing cell death by nonapoptotic mechanism(s). To elucidate the role of galanin in levonorgestrel effects on the tumours, we examined galanin and prolactin mRNA and peptide expression in prolactinomas of rats receiving the progestin. Levonorgestrel reduced the pituitary weight and serum prolactin concentrations in oestrogen-treated rats. Galanin mRNA expression (determined by in situ hybridization), and the number of galanin expressing cells (determined by immunocytochemistry) were also reduced by the progestin in tumour-bearing rats. However, neither prolactin mRNA content, nor the number of prolactin-expressing cells, were modified by levonorgestrel treatment of oestrogen-receiving rats. The present study suggests that levonorgestrel controls pituitary growth by diminishing galanin expression. In contrast, changes in serum prolactin concentration seem to be more related to the reduction in tumour size, since the reduction in galanin expression was not large enough to regulate prolactin mRNA expression or the percentage of lactotrophs.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Influence of adrenal glands on the modulation of prolactin gene expression by the endogenous benzodiazepine ligand octadecaneuropeptide in the male rat pituitary gland

Recently, an 86-amino acid polypeptide with high affinity for diazepam binding sites, termed diazepam-binding inhibitor (DBI), has been found in the rat brain. DBI, as well as a peptide derived from DBI, the octadecaneuropeptide DBI[33-50] (ODN), interacts with the GABA(A) receptor complex. To investigate the role of these endogenous ligands for GABA(A) receptors on prolactin gene expression, we studied the effects of acute intracerebroventricular administration (4 h before sacrifice) of ODN on prolactin mRNA levels in the male rat. Because, in some neuropeptidergic systems, glucocorticoids play a role in the response to ODN, we also studied the influence of adrenal glands and the effect of dexamethasone administration in the response of prolactin gene expression to ODN. ODN injection produced an increase in prolactin mRNA levels. Adrenalectomy performed 5 days before sacrifice resulted in an increase in prolactin gene expression and also potentiated the stimulating effect of ODN. Because castration has been shown to decrease prolactin gene expression in the male rat, we used castrated and adrenalectomized animals to study the role of dexamethasone in the response of lactotrophs to ODN. In these steroid-deprived animals, dexamethasone treatment (for 4 days) decreased prolactin mRNA levels but did not modify the response to ODN. These data indicate that an endogenous neuropeptide interacting with the GABA(A) receptor complex can stimulate prolactin gene expression and suggest that the adrenal glands may produce factor(s) capable of decreasing prolactin mRNA. On the other hand, it does not appear that glucocorticoid hormones play a role in the effect of ODN on lactotroph activity.

Mechanisms in progestin antagonism of pituitary tumorigenesis

Chronic exposure of F344 rats to diethylstilbestrol (DES) induces pituitary tumors (DES-T) composed of proliferating lactotrophs. Presently, we studied the effect of progestins on parameters related to tumor growth and function, due to previous evidences of progesterone antagonism of pituitary tumorigenesis acting at pituitary and hypothalamic levels [Piroli, G., Grillo, C., Ferrini, M., Lux-Lantos, V. and De Nicola, A. F., Antagonism by progesterone of diethylstilbestrol-induced pituitary tumorigenesis in Fischer 344 rats: Effects on sex steroid receptors and tyrosine hydroxylase mRNA, Neuroendocrinology, 1996, 63, 530-539]. In search of a quantitatively more important effect, animals bearing DES-T were treated with synthetic progestins. Competition assays using DES-T as source of progestin receptors indicated that levonorgestrel (LNG), gestodene and R5020 showed higher affinities (IC50 1-2 nM) than progesterone, norethisterone and medroxyprogesterone (IC50 10-25 nM). Treatment with LNG reduced DES-T weight by 45%, and serum PRL by one half. Small (monomeric) and big (polymeric) PRL increased 5- and 2.5-fold, respectively, in DES-T in comparison with pituitaries of ovariectomized (OVX) rats. However, LNG produced no changes indicating that synthesis and storage of PRL was conserved in rats receiving both hormonal treatments. DES induced a 15-fold increase in cell proliferation, measured as bromodeoxyuridine incorporation into cell nuclei, in comparison to OVX rats, while LNG treatment of DES-T bearing rats reduced this index by 72%. Electron microscopic images showed that LNG markedly reduced hypertrophy and hyperplasia of lactotropes, increasing the proportions of degenerating cells and cells of high electronic density with alterations of cytoplasmic organelles. However, histopathological signs of apoptosis were absent. Therefore, reduced cell proliferation and non-apoptotic cell death are part of the mechanisms employed by progestins to antagonize tumorigenesis at the pituitary level. The results may open a new therapeutic strategy for treatment of PRL secreting adenoma in humans.

Pituitary Sex Steroid Receptors: Localization and Function

The pituitary contains estrogen receptor (ER), progesterone receptor (PR), and androgen receptor (AR). In accordance with immunocytochemistry, it is agreed that sex hormone receptors reside into the nucleus. All three receptors are found predominantly in gonadotrophs and lactotrophs, and less frequently in other cell types. ER plays a major role in prolactin (PRL) production and lactotroph proliferation, and protracted estrogen administration induces lactotroph hyperplasia and adenoma in rodents. Most research on PR and AR is focused on their role in the fine-tuning of gonadotropin secretion during estrous cycle. Contrary to the effect in nontumorous pituitary, estrogens can inhibit the proliferation of transplantable rat pituitary tumors and of cell lines derived from them. In humans, despite the presence of ER in all types of adenohypophysial tumors, the role of estrogen in tumor cell proliferation is still unclear. Few results indicate that tumor growth is stimulated by estrogen, and inhibited by progesterone and androgen. Novel data reveal that steroid hormones can act directly on plasma membrane or via other receptors, and interact with growth factors, oncogenes, and other transcription factors. The mechanisms by which steroid hormones control cell proliferation remain a major challenge for future research.

Effects of dehydroepiandrosterone (DHEA) on pituitary prolactin and arcuate nucleus neuron tyrosine hydroxylase mRNA levels in the rat

It is well documented that dehydroepiandrosterone (DHEA), an adrenal androgen, is converted into potent androgens and/or estrogens in peripheral tissues. Since sex steroids are involved in the regulation of prolactin (PRL) secretion, we have studied the effect of DHEA administration on PRL mRNA levels in both adult male and female rats. Since tuberoinfundibular dopaminergic (TIDA) neurons are involved in the negative regulation of PRL, we have also evaluated the effects of DHEA on the genetic expression of tyrosine hydroxylase (TH), the limiting enzyme in catecholamine biosynthesis in TIDA neurons. Sham-operated and castrated animals of both sexes received during 2 days DHEA at the dose of 6 mg/kg/day, starting on the first day after castration. PRL and TH mRNA levels were measured by quantitative in situ hybridization. In the male rat, orchiectomy performed 3 days earlier did not modify PRL mRNA levels. DHEA administration increased the hybridization signal in both sham-operated and orchiectomized animals. In the female, ovariectomy decreased PRL mRNA levels and, as observed in the male, DHEA treatment induced an increase in the hybridization signal in both control and ovariectomized rats. In TIDA neurons, castration increased TH mRNA levels as evaluated by number of grains over labelled neurons and the number of TH-labelled cells per section in both male and female animals. In both sham-operated male rats and orchiectomized animals, DHEA decreased the hybridization signal. In the female, DHEA administration completely prevented the increase in TH mRNA levels due to ovariectomy. In sham-operated female rats, the treatment had no effect. These data clearly indicate that in both male and female rats DHEA exerts an estrogenic influence on both PRL and TH gene expression. Although these in vivo experiments do not allow to establish whether the stimulation of PRL gene expression is due to an action of the steroid on the pituitary or at the hypothalamic level or alternatively at both sites, it is likely that one of the mechanisms of action of DHEA might be related to a decrease in dopamine release following a depression of TIDA neuron activity.

Involvement of the Y2 receptor subtype in the regulation of prolactin gene expression by neuropeptide Y in the male rat

In order to determine the influence of neuropeptide Y (NPY) on the biosynthesis of prolactin (PRL), we have studied the effects of NPY and some NPY analogs on PRL gene expression in the male rat anterior pituitary gland. The following peptides (4 micrograms/100 g body wt): NPY, peptide YY (PYY), NPY13-36 (a Y2 receptor agonist) and [Leu31,Pro34]NPY (a Y1 receptor agonist) were injected into the left lateral ventricle of adult male rats. Control animals received only the vehicle (0.9% NaCl). All the animals were perfused with 4% paraformaldehyde 4 h after injection and processed for in situ hybridization. The intracerebroventricular injection of NPY, PYY, and NPY13-36 induced a significant increase in the hybridization signal (22-40% over control). On the other hand, the Y1 receptor agonist [Leu31,Pro34]NPY did not influence PRL mRNA levels. These data then suggest that activation of the Y2 NPY receptor subtype at the central level can positively regulate PRL gene expression.

Antagonism of oestrogen-induced prolactin release by medroxyprogesterone acetate

Previous studies conducted at our clinic suggested that the administration of hormone replacement therapy (HRT) in postmenopausal women could result in the inhibition of oestrogen-induced prolactin (PRL) release. The aim of this study was to determine how the pituitary function is affected by the sequential addition of medroxyprogesterone acetate (MPA) to oestrogen replacement therapy. Twenty-one postmenopausal women receiving no other medication were treated with a standard dose (0.625 mg/day) of conjugated equine oestrogens (CEE) for a period of 24 days, plus 5 mg/day MPA added sequentially during the last 12 days of the oestrogen therapy. Blood samples were collected before treatment, during oestrogen and oestrogen-progestogen administration and after cessation of treatment. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), 17 beta-oestradiol (E2) and PRL levels were studied. During treatment gonadotrophin concentrations decreased significantly, while after cessation of HRT the levels of FSH and LH increased. These gonadotrophin fluctuations indicated a sharp rise in E2 levels during therapy and a significant decrease during the treatment-free period. PRL levels were found to be higher during CEE therapy, but they fell when patients received CEE in combination with MPA. These observations suggest that the role of progestogens in a variety of experimental and clinically relevant situations needs to be investigated not only as regards their direct action but also their modulation of the effect of oestrogen.

Transcriptional and translational regulation of LH, prolactin and their testicular receptors by hCG and bromocriptine treatments in adult and neonatal rats

Effects of altered gonadotropin and prolactin (PRL) secretion on luteinizing hormone (LH), PRL and their testicular receptors (R) were studied in neonatal and adult rats. Changes in gene expression were monitored by measurements of steady-state mRNA levels. Five-day and 90-day-old male rats received a single s.c. injection of hCG (600 IU/kg), 1 mg/kg bromocriptine (BR) twice daily, or their combination. After 2 or 8 days, the responses of LH, PRL, their testicular R, and testosterone (T) were assessed, including measurements of the appropriate mRNA levels. Vehicle-treated age-matched animals served as controls. hCG suppressed serum LH in 2 days in adult rats from 0.85 +/- 0.16 to 0.04 +/- 0.01 microg/l, and in neonates from 0.59 +/- 0.29 to levels below 0.01 microg/l (p < 0.01 for both). This was accompanied at both ages by a 60% decrease in pituitary content of the LH beta-subunit mRNA (p < 0.01), but a decrease in the alpha-chain (40%, p < 0.05) occurred only in neonates. hCG increased serum PRL in adult rats in 8 days over 2-fold (p < 0.01); this did not occur in neonates. In neonates, BR increased the LH subunit mRNAs 2-fold in 8 days (p < 0.01) without a concomitant effect on serum LH; no BR effects on the LH parameters were seen in adult animals. BR decreased pituitary PRL protein and mRNA levels at both ages (p < 0.01-0.05), but serum PRL decreased only in the adults. The homologous down-regulation of testicular LHR (near 100%) was accompanied in adults by a 30% decrease in LHR mRNA (p < 0.05). Also BR at this age decreased LHR binding (75% in 8 days, p < 0.01), but in this case no change occurred in the cognate mRNA. hCG and BR slightly up-regulated in adults PRLR binding, but only the 2-day effect of BR was accompanied by a 60% increase in PRLR mRNA (p < 0.05). In neonates, both hCG and BR increased testicular LHR and PRLR mRNA levels (p < 0.01-0.05). In adult animals, both hCG and BR suppressed testicular and serum T levels after 8 days (40-70%, p < 0.01-0.05); only BR was inhibitory to T by 8 days in the neonates (p < 0.05). In conclusion, the homologous and heterologous regulatory effects of hCG and BR on LH, PRL and their testicular R levels were only partly explained by changes in steady-state levels of the respective mRNAs. In general, the autoregulatory effects on LHR and PRLR appeared to affect steady-state levels of cognate mRNAs, whereas heteroregulation predominately involved changes at the protein level. The responses of the neonatal pituitary-gonadal axis to hCG and/or BR differed greatly from those observed in the adult, indicating that the mechanisms involved in these regulatory events in adult animals are a result of gradual postnatal development.

Role of serotonin in the regulation of prolactin gene expression in the male rat as evaluated by in situ hybridization

It is well documented that serotonin (5-HT) is involved in the regulation of prolactin (PRL) release as a stimulator. To evaluate the role of 5-HT on PRL gene expression, we have investigated the effects of repeated administration (during 2 days) of 5-HT, the 5-HT1 + 2 receptor antagonist methysergide, the 5-HT2 receptor antagonist ketanserin, and a combination of 5-HT and methysergide on PRL mRNA levels as measured by in situ hybridization in the adult male rat. The treatment with 5-HT induced a 14% increase in the hybridization signal, although the administration of methysergide produced a small reduction (5%) in PRL mRNA levels. On the other hand, ketanserin had no effect on the hybridization signal. The stimulatory effect of 5-HT was completely prevented by the concomitant administration of methysergide. The present results, together with previous data, indicate that 5-HT exerts a positive tonic influence not only on the release of PRL but on the biosynthesis of the hormone as evaluated by mRNA level measurements. They also strongly suggest that the role of 5-HT in the regulation of PRL secretion is mediated via activation of 5-HT1 receptors, although a dopaminergic effect of methysergide on PRL secretion cannot be totally excluded.

Effects of morphine and naloxone on prolactin and growth hormone gene expression in the male rat pituitary gland

It is generally admitted that opioids can stimulate the release of both prolactin (PRL) and growth hormone (GH). In order to investigate the role of opioids in the regulation of PRL and GH gene expression in the rat pituitary, we studied the effects of chronic administration of the opioid drug morphine and an opiate receptor antagonist naloxone on both PRL and GH gene expression as measured by in situ hybridization. Four-day treatment with morphine (40 mg/kg/day) produced a 12% increase in PRL mRNA levels. Conversely, naloxone (4 mg/kg/day) decreased the autoradiographic reaction by 10%. The concomitant administration of morphine and naloxone induced no significant changes in PRL gene expression. On the other hand, treatment with morphine produced a 22% decrease in GH mRNA levels, an effect which was prevented by the concomitant administration naloxone. When injected alone, naloxone did not modify the hybridization signal. These results clearly indicate that opioids are involved not only in the regulation of GH and PRL release but also in the gene expression of the two hormones. The discordance observed between the acute effects of morphine on GH release and the effect of the opioid drug on mRNA levels remains to be clarified.

Progesterone inhibits the estrogen-induced prolactin gene expression in the rat pituitary

The present study examines the inhibitory action of progesterone (P) on prolactin (PRL) gene expression in the anterior pituitary of ovariectomized, estradiol (OVX+E) treated adult rats. A single injection of P (1 mg) was administered s.c. to OVX+E treated rats, and animals were killed at 3, 6, 9, and 36 h following P administration. Northern blot analysis showed that P suppressed the E-enhanced PRL mRNA level at 3, 6, and 9 h, but not at 36 h following P administration. When the second injection of P (1 mg) was given at 30 h after the first P, it again suppressed the E-induced PRL mRNA level, indicating that the inhibitory effect of P may not last until 36 h. The inhibitory action of P was dose-dependent, and the pretreatment of RU486 (100 micrograms/rat), a P receptor antagonist at 1 h before P injection partially restored PRL mRNA level which was inhibited by P. These data indicate that P plays a crucial role in the regulation of PRL gene expression in the rat pituitary.

Regulation of Prolactin Messenger Ribonucleic Acid Levels by Estradiol and Dihydrotestosterone as Evaluated by in situ Hybridization Performed on Implanted Pituitary Glands and Anterior Pituitary Cells in Culture in the Male Rat

We have recently demonstrated that 17ß-estradiol (E(2) ) administration increases protactin (PRL) mRNA levels in the male rat anterior pituitary gland and that this stimulatory effect is partially inhibited by concomitant administration of dihydrotestosterone. In order to gain more information about the site(s) of action of E(2) and dihydrotestosterone on PRL gene expression, we have studied the effects of these two hormones in pituitaries implanted under the kidney capsule as well as in anterior pituitary cells in culture. In implanted pituitaries, PRL mRNA levels were increased by 90% as compared to values obtained in the stalk-connected pituitaries from the same animals. Administration of E(2) induced a further increase of PRL mRNA levels in implanted pituitaries, while dihydrotestosterone did not produce any change in animals which had been treated or not with E(2) . In anterior pituitary cells in culture, addition of E(2) to the culture medium resulted in a 60% increase of PRL mRNA levels over control values. Supplementation with dihydrotestosterone did not induce any variation in the concentration of PRL mRNA in cells which were treated or not with E(2) . These results indicate that E(2) exerts a direct action on PRL cells at the pituitary level and strongly support the key role of the hypothalamus in the inhibitory effect of androgens on estrogen-induced stimulation of PRL mRNA in the male rat pituitary.

In vivo Regulation of Prolactin Gene Expression in the Male Rat: Role of Sex Steroids and Dopamine

Abstract The influence of sex steroids and the dopaminergic system on the in vivo modulation of prolactin (PRL) mRNA levels was investigated by quantitative in situ hybridization in the male rat anterior pituitary gland. In situ hybridization was performed using a [(35)S]-labeled cDNA probe encoding PRL. Orchiectomy performed 14 days earlier did not modify PRL mRNA levels. In orchiectomized rats treatment with the dopaminergic agonist bromocriptine for 14 days decreased PRL mRNA levels by 30%, while in intact animals the same treatment did not induce any changes in PRL mRNA levels. Administration of the dopamine D(2) receptor antagonist haloperidol in both intact and orchiectomized rats induced a 4-fold increase in mRNA levels. Administration of dihydrotestosterone to orchiectomized animals which had been treated or not with haloperidol or bromocriptine did not modify PRL mRNA levels. In orchiectomized animals administration of 17ss-estradiol (0.25 mug twice daily) for 14 days caused a 4-fold increase in amounts of PRL mRNA. Administration of bromocriptine to 17ss-estradiol-treated animals induced a 15% decrease of PRL mRNA levels compared to those obtained by 17ss-estradiol administered alone. The concomitant administration of 17ss-estradiol and haloperidol resulted in a 50% increase in PRL mRNA levels compared to those measured in animals treated with haloperidol alone. The present results clearly demonstrate that in vivo estrogen as well as dopamine-mediated mechanisms play a regulatory role in PRL mRNA levels in the male rat.

Localization of peripheral benzodiazepine binding sites and diazepam-binding inhibitor (DBI) mRNA in mammary glands and dimethylbenz(a)antracene (DMBA)-induced mammary tumors in the rat

An association of diazepam-binding inhibitor (DBI), an endogenous ligand at the benzodiazepine (BZD) receptor, with the peripheral type BDZ receptor (PBR) has been reported in the brain and a few peripheral tissues. In order to verify whether or not DBI and PBR are present in the mammary tissue, we have proceeded to the localization of DBI mRNA and PBR in rat mammary glands and DMBA-induced mammary tumors. DBI mRNA was detected by in situ hybridization using a 35S-labelled single-stranded RNA probe complementary to DBI mRNA and PBR by in vitro autoradiography using [3H]PK11195 as the ligand. In mammary glands from virgin and lactating animals, both DBI mRNA and PBR were detected in acinar cells. In dimethylbenz(a)anthracene (DMBA)-induced tumors, hybridization signal was not detected in all the cells whereas PBR appeared to be present in all the tumoral cells, although non uniformly distributed. These data indicating that mammary DMBA-induced tumoral cells contain both DBI and PBR suggest that BZD receptors might be involved in the regulation of mammary glands as well as mammary tumoral cells.

Effects of in vivo dihydrotestosterone treatment on changes in nocturnal surge of prolactin, luteal ultrastructure and P-450scc mRNA and protein content in pregnant rats

We have demonstrated previously that the administration of dihydrotestosterone (DHT) decreases plasma progesterone levels within 24 h and thus, results in abortion during the first half of pregnancy (Am. J. Physiol. 241 (1981) E444-E448). The purpose of this study was to determine (a) if the administration of DHT suppresses plasma prolactin levels or its nocturnal surge within 24 h after the treatment, (b) how soon after the commencement of treatment do the concentrations of DHT increase and progesterone levels decrease in the circulation, (c) the ultrastructural changes that occur in corpora lutea, and (d) the changes in luteal P-450 side-chain cleavage (P-450scc) enzyme and mRNA content upon DHT treatment. Within 24 h after the commencement of DHT treatment, the nocturnal surge of prolactin, detected in both groups on day 10 at 03.30 h, was inhibited in DHT-treated rats as compared to controls. The non-surge levels of prolactin at 05.00 and 06.00 h were not different between groups. The intraovarian DHT pellet increased plasma levels of the steroid 3-fold within 2 h (blood samples were taken at 2-hourly intervals) when compared to controls. By 24 h DHT levels were decreased but were still higher than controls. Plasma progesterone levels began to fall 6 h after the commencement of treatment. Luteal tissue from animals treated with DHT appeared steroidogenic, and contained more lipid droplets than controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of human chorionic gonadotropin (hCG) and prolactin (PRL) on 3 beta-hydroxy-5-ene-steroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) expression and activity in the rat ovary

Using a recently cloned rat ovary 3 beta-HSD cDNA and antibodies raised against purified human placental 3 beta-HSD, we have studied the effects of treatment with human chorionic gonadotropin (hCG) and hyperprolactinemia achieved by pituitary implants, alone or in combination, on the expression and activity of ovarian 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) in intact adult rats. 32P- and 35S-labeled cDNA probes were used to evaluate the effects of treatments on 3 beta-HSD mRNA levels by dot blot and in situ hybridization, respectively, while enzymatic activity was measured by the conversion of [14C]dehydroepiandrosterone into [14C]androstenedione. The present data show that hCG exerts a marked trophic effect on rat corpora lutea with an increase in total ovarian 3 beta-HSD mRNA levels, 3 beta-HSD protein content as well as enzymatic activity, resulting in an increase in serum progesterone levels. Prolactin-secreting pituitary implants alone, on the other hand, while exerting small effects on 3 beta-HSD expression and activity, led to a marked potentiation of the stimulatory effect of hCG on all parameters. The present data show that hCG and PRL act synergistically to stimulate ovarian progesterone secretion via an increase in 3 beta-HSD mRNA levels, protein content and enzymatic activity.