Modulation of pituitary gonadotropins and prolactin secretion by testosterone in vitro

4-Nitro-3-phenylphenol has both androgenic and anti-androgenic-like effects in rats

To investigate the effect of endocrine disruption of 4-nitro-3-phenylphenol (PNMPP) on immature male Wistar-Imamichi rats, the rat pituitary was exposed to PNMPP (10^–5–10^–9 M) for 24 h with or without gonadotropin-releasing hormone (GnRH) in experiment I. In addition, the Leydig cells (10^–5–10^–9 M) were exposed to PNMPP for 24 h with or without human chronic gonadotropin (hCG) in experiment II. Our results showed that the PNMPP at 10^–5–10^–7 M suppressed follicle-stimulating hormone (FSH) and luteinizing hormone (LH) productions from GnRH-stimulated pituitary cells. At the same time, PNMPP 10^–5–10^–7 M induced an increase in testosterone production from the Leydig cells treated with or without hCG. Based on our results, it can be concluded that that PNMPP might have both androgen agonist action by decreasing FSH and LH production in the pituitary and anti-androgenic action by increasing testosterone production in the Leydig cell.

Effects of testosterone on hormonal content and calcium-dependent basal secretion in female rat pituitary cells

In vivo and in vitro effects of elevated androgens on agonist-induced gonadotropin secretion have been addressed previously. Here we investigated the effects of testosterone on hormonal content and basal (in the absence of agonists) hormone release in pituitary lactotrophs, somatotrophs and gonadotrophs from female rats. Furthermore we tested the hypothesis that testosterone action is dependent on the pattern of spontaneous and Bay K 8644 (a L-type calcium channel agonist) -induced calcium signalling. Mixed anterior pituitary cells were cultured in steroid containing or depleted media, and testosterone (1pM to 10nM) was added for 48h. Cells were studied for their spontaneous and Bay K 8644-induced calcium signalling pattern and total hormone levels (release and hormonal content). In lactotrophs, somatotrophs and gonadotrophs testosterone did not affect the pattern of spontaneous calcium signalling. Bay K 8644-induced calcium signalling and hormone release were not affected by testosterone. In both steroid-depleted and -containing medium, testosterone inhibited prolactin (PRL), luteinizing hormone (LH) and growth hormone (GH) cellular content and release in a dose-dependent manner, with IC(50)s in a sub-nanomolar concentration range. These results indicate that testosterone inhibits basal hormone release from lactotrophs, somatotrophs and gonadotrophs without affecting intracellular calcium signalling. This action of testosterone is not dependent on the presence of other steroid hormones.

Developmental changes in the hormonal identity of gonadotroph cells in the rhesus monkey pituitary gland

To help elucidate the regulatory mechanism responsible for divergent gonadotrophin secretion during sexual maturation, we examined the gonadotroph population and hormonal identity of gonadotroph subtypes in pituitary glands of juvenile (age, 1.7 +/- 0.2 yr) and adult (age, 12.3 +/- 0.8 yr) male rhesus monkeys (Macacca mulatta). Serum LH and testosterone concentrations were, respectively, 3 and 7 times lower in juveniles than in adults, thus confirming the different stages of development. Immunohistochemistry revealed that the proportion of LH gonadotrophs in relation to the total pituitary cell population in the juvenile animals was significantly smaller than in the adults. In a subsequent study, double immunofluorescent labeling identified three distinct gonadotroph subtypes in both age groups: ones expressing either LH or FSH and another one expressing a combination of both gonadotrophins. Whereas the number of monohormonal LH cells per unit area was greater in the adults than in the juveniles, the number of monohormonal FSH gonadotrophs was remarkably lower. However, the proportion of FSH cells (whether mono- or bihormonal) within the gonadotroph population was similar between groups. Interestingly, the proportion and number of bihormonal gonadotrophs as well as the LH/FSH gonadotroph ratio were significantly greater in the adults than in the juveniles. Taken together, these data reveal that during the juvenile-adult transition period, not only does the pituitary gonadotroph population increase, but a large number of monohormonal FSH gonadotrophs are likely to become bihormonal. Because this morphological switch occurs when marked changes in plasma gonadotrophins are known to occur, it may represent an intrapituitary mechanism that differentially regulates gonadotrophin secretion during sexual development.

Castration differentially regulates nitric oxide synthase in the hypothalamus and pituitary

Mammalian reproductive function is under control of the integrated hypothalamic-pituitary-gonadal (HPG) axis. Castration in male rats has been utilized as an effective tool to investigate hormonal interactions in the mammalian HPG axis. Recently, nitric oxide (NO) has been suggested to play a role in HPG hormonal regulation. In order to gain further insight into the function of the NO-NOS system in reproductive neuroendocrine control, particularly in the gonadal feedback regulation of the hypothalamic-pituitary unit, we examined steady state levels of nNOS mRNA, nNOS protein, and the important physiological index, NOS enzyme activity, of the intrinsic NOergic system in both hypothalamus and pituitary in castrated male rats and their sham-operated counterparts one week after surgery. In the pituitary, we found a significant four-fold increase in nNOS mRNA, p < 0.0003 compared to sham. Castration also resulted in a four-fold rise in pituitary nNOS protein, p < 0.02 compared to sham. Pituitary NOS enzyme activity was stimulated 2 fold, p < 0.003 after castration. In the hypothalamus, conversely, we observed no significant castration-modulated difference in either nNOS mRNA, nNOS protein or NOS enzyme activity. Thus, it appears that the hypothalamic NO-NOS system is either not required for hypothalamic adaptations to castration, although important in the release of LHRH under normal physiological conditions, or alternatively, the hypothalamus may become more sensitive to the effects of NO in the castrated state. In the pituitary, NO may attenuate the gonadotropin response to castration as a local balancing mediator.

A prolactin-secreting tumor in a patient with Klinefelter's syndrome: a case report

We report the case of a patient with Klinefelter's syndrome who developed a prolactin (PRL)-secreting tumor. The patient developed headaches, visual alterations and also symptoms of hypogonadism despite appropriate testosterone (T) replacement therapy. The diagnosis of hyperprolactinemia was then suspected. The laboratory findings confirmed the hypothesis, showing high levels of serum PRL. The patient was initially treated with oral bromocriptine, and afterwards with the injectable form. There was a marked decrease in PRL levels and in tumor size. Although some neoplasms, like breast carcinoma and germ cell tumors, are known to occur more frequently in patients with Klinefelter's syndrome, an association with PRL-secreting tumor has not been reported yet. In conclusion, symptoms of hypogonadism in patients with Klinefelter's syndrome receiving appropriate T replacement therapy can suggest the presence of hyperprolactinemia.