Postnatal differentiation of the immunohistochemical expression of aromatase P450 in the rat pituitary gland

Relation among Aromatase P450 and Tumoral Growth in Human Prolactinomas

The pituitary gland is part of hypothalamic-pituitary–gonadal axis, which controls development, reproduction, and aging in humans and animals. In addition, the pituitary gland is regulated mainly by hormones and neurotransmitters released from the hypothalamus and by systemic hormones secreted by target glands. Aromatase P450, the enzyme responsible for the catabolization of aromatizable androgens to estrogens, is expressed in different parts of body, including the pituitary gland. Moreover, aromatase P450 is involved in sexual dimorphism where alteration in the level of aromatase can initiate a number of diseases in both genders. On the other hand, the direct actions of estrogens, mainly estradiol, are well known for stimulating prolactin release. Numerous studies have shown that changes in the levels of estrogens, among other factors, have been implicated in the genesis and development of prolactinoma. The pituitary gland can produce estradiol locally in several types of endocrine cells, and it is possible that aromatase could be responsible for the maintenance of the population of lactotroph cells and the modulation of the action of central or peripheral regulators. Aromatase overexpression due to inappropriate gene regulation has clinical effects such as the pathogenesis of prolactinomas. The present study reports on the synthesis of pituitary aromatase, its regulation by gonadal steroids, and the physiological roles of aromatase on pituitary endocrine cells. The involvement of aromatase in the pathogenesis of pituitary tumors, mainly prolactinomas, through the auto-paracrine production of estradiol is reviewed.

Prenatal exposure to low doses of bisphenol A increases pituitary proliferation and gonadotroph number in female mice offspring at birth

The pituitary gland is composed of hormone-producing cells essential for homeostasis and reproduction. Pituitary cells are sensitive to endocrine feedback in the adult and can have altered hormonal secretion from exposure to the endocrine disruptor bisphenol A (BPA). BPA is a prevalent plasticizer used in food and beverage containers, leading to widespread human exposure. Although prenatal exposure to BPA can impact reproductive function in the adult, the effects of BPA on the developing pituitary are unknown. We hypothesized that prenatal exposure to low doses of BPA impacts gonadotroph cell number or parameters of hormone synthesis. To test this, pregnant mice were administered 0.5 μg/kg/day of BPA, 50 μg/kg/day of BPA, or vehicle beginning on Embryonic Day 10.5. At parturition, pituitaries from female offspring exposed in utero to either dose of BPA had increased proliferation, as assessed by mKi67 mRNA levels and immunohistochemistry. Coincidently, gonadotroph number also increased in treated females. However, we observed a dichotomy between mRNA levels of Lhb and Fshb. Female mice exposed to 0.5 μg/kg/day BPA had increased mRNA levels of gonadotropins and the gonadotropin-receptor hormone (GNRH) receptor (Gnrhr), which mediates GNRH regulation of gonadotropin production and release. In contrast, mice treated with 50 μg/kg/day of BPA had decreased gonadotropin mRNA levels, Gnrhr and Nr5a1, a transcription factor required for gonadotroph differentiation. No other pituitary hormones were altered on the day of birth in response to in utero BPA exposure, and male pituitaries showed no change in the parameters tested. Collectively, these results show that prenatal exposure to BPA affects pituitary gonadotroph development in females.

Effect of androgen treatment during foetal and/or neonatal life on ovarian function in prepubertal and adult rats

We investigated the effects of different windows of testosterone propionate (TP) treatment during foetal and neonatal life in female rats to determine whether and when excess androgen exposure would cause disruption of adult reproductive function. Animals were killed prepubertally at d25 and as adults at d90. Plasma samples were taken for hormone analysis and ovaries serial sectioned for morphometric analyses. In prepubertal animals, only foetal+postnatal and late postnatal TP resulted in increased body weights, and an increase in transitory, but reduced antral follicle numbers without affecting total follicle populations. Treatment with TP during both foetal+postnatal life resulted in the development of streak ovaries with activated follicles containing oocytes that only progressed to a small antral (smA) stage and inactive uteri. TP exposure during foetal or late postnatal life had no effect upon adult reproductive function or the total follicle population, although there was a reduction in the primordial follicle pool. In contrast, TP treatment during full postnatal life (d1-25) resulted in anovulation in adults (d90). These animals were heavier, had a greater ovarian stromal compartment, no differences in follicle thecal cell area, but reduced numbers of anti-Mullerian hormone-positive smA follicles when compared with controls. Significantly reduced uterine weights lead reduced follicle oestradiol production. These results support the concept that androgen programming of adult female reproductive function occurs only during specific time windows in foetal and neonatal life with implications for the development of polycystic ovary syndrome in women.

Aromatase cytochrome P450 enzyme expression in human pituitary

Aromatase (P450AROM) converts testosterone to estrogen. This conversion could be important in normal physiology and estradiol-induced tumorigenesis in human pituitary. The objective of this study was to examine the expression of P450AROM in normal human pituitary and determine the gender difference. We examined aromatase expression in 19 normal human pituitary glands [13 males, 6 females, median age: 30 years (interquartile ranges, IQR: 23-63)] obtained from autopsy. We demonstrated aromatase gene expression levels by quantitative RT-PCR and aromatase protein with immunohistochemical staining in normal male and female human pituitary. Although median relative expression level of aromatase mRNA of male individuals [median DeltaCt = 42.6 (IQR: 7.6-93.9)] was higher than the female individuals [median DeltaCt = 3.9 (IQR:0-44.8)], we could not determine a significant gender difference in aromatase mRNA levels (p = 0.2). The difference between the aromatase protein density by immunohistochemistry was not significant between genders (p = 0.78). The aromatase levels were also not correlated with the age of the study subjects (p = 0.42 r = -0.21). The results indicate that aromatase enzyme is present in human pituitary. The amount and the density of the enzyme show a large variance among different individuals. Although higher mRNA expression was observed in male pituitary compared to female pituitary, there was no statistically significant difference for gender or age.

Dehydroepiandrosterone restoration of growth hormone gene expression in aging female rats, in vivo and in vitro: evidence for actions via estrogen receptors

A decline in dehydroepiandrosterone (DHEA) and GH levels with aging may be associated with frailty and morbidity. Little is known about the direct effects of DHEA on somatotropes. We recently reported that 17beta-estradiol (E2), a DHEA metabolite, stimulates the expression of GH in vitro in young female rats. To test the hypothesis that DHEA restores function in aging somatotropes, dispersed anterior pituitary (AP) cells from middle-aged (12-14 months) or young (3-4 months) female rats were cultured in vitro with or without DHEA or E2 and fixed for immunolabeling or in situ hybridization. E2 increased the percentage of AP cells with GH protein or mRNA in the aged rats to young levels. DHEA increased the percentages of somatotropes (detected by GH protein or mRNA) from 14-16 +/- 2% to 29-31 +/- 3% (P < or = 0.05) and of GH mRNA (detected by quantitative RT-PCR) only in aging rats. To test DHEA's in vivo effects, 18-month-old female rats were injected with DHEA or vehicle for 2.5 d, followed by a bolus of GHRH 1 h before death. DHEA treatment increased serum GH 1.8-fold (7 +/- 0.5 to 12 +/- 1.3 ng/ml; P = 0.02, by RIA) along with a similar increase (P = 0.02) in GH immunolabel. GHRH target cells also increased from 11 +/- 1% to 19 +/- 2% (P = 0.03). Neither GH nor GHRH receptor mRNAs levels were changed. To test the mechanisms behind DHEA's actions, AP cells from aging rats were treated with DHEA with or without inhibitors of DHEA metabolism. Trilostane, aminogluthemide, or ICI 182,780 completely blocked the stimulatory effects of DHEA, suggesting that DHEA metabolites may stimulate aging somatotropes via estrogen receptors.

Expression of aromatase P450 is increased in spontaneous prolactinomas of aged rats

We have recently reported the presence of aromatase P450 in the rat hypophysis. This enzyme is responsible for the aromatization of testosterone to estradiol. Since the induction of prolactinomas has been demonstrated in the rat following chronic treatment with estradiol, the aim of the present study was to analyze whether a relationship exists between the presence of pituitary aromatase and the appearance of spontaneous prolactinomas in aged rats. Of a series of 90 adenomas studied, 53% showed prolactin immunoreactive cells and were classified as prolactinomas; only 33% of the adenomas were pure prolactinomas and the other 20% were multi-hormonal protactinomas. Moreover, 60% of the adenomas were aromatase-positive tumors. Interestingly, 100% of the pure prolactinomas were aromatase-positive while only 60% of the multi-hormonal prolactinomas expressed the enzyme. Western blotting with anti-aromatase antibodies revealed a 3.8-fold increase in expression of aromatase in pituitary tumors as compared to normal rat pituitary gland. Double immunohistochemical labeling detected the coexistence of prolactin and aromatase P450 in prolactinoma cells. ACTH- and LH-positive adenomas were considered as controls; only multi-hormonal ACTH and LH tumors display aromatase-positive cells and all of these also contained prolactin-positive cells. Our results demonstrate for the first time that aromatase is expressed in pituitary adenomas and that it is related to the functional nature of the tumor, especially in the case of pure prolactinomas, suggesting the possibility that an abnormally high conversion of testosterone into estradiol in pituitary cells may contribute to the genesis of spontaneous prolactinomas in aged rats.