Abstract
Adult female rats continuously exposed to androgens from prepuberty have reproductive and metabolic features of polycystic ovary syndrome (PCOS). We investigated whether such exposure adversely affects estrous cyclicity and the expression and distribution of gonadotropin-releasing hormone (GnRH), GnRH receptors, and corticotrophin-releasing hormone (CRH) in the hypothalamus and whether the effects are mediated by the androgen receptor (AR). We also assessed the effect of low-frequency electro-acupuncture (EA) on those variables. At 21 days of age, rats were randomly divided into three groups (control, PCOS, and PCOS EA; n = 12/group) and implanted subcutaneously with 90-day continuous-release pellets containing vehicle or 5α-dihydrostestosterone (DHT). From age 70 days, PCOS EA rats received 2-Hz EA (evoking muscle twitches) five times/week for 4–5 weeks. Hypothalamic protein expression was measured by immunohistochemistry and western blot. DHT-treated rats were acyclic, but controls had regular estrous cycles. In PCOS rats, hypothalamic medial preoptic AR protein expression and the number of AR- and GnRH-immunoreactive cells were increased, but CRH was not affected; however, GnRH receptor expression was decreased in both the pituitary and hypothalamus. Low-frequency EA restored estrous cyclicity within 1 week and reduced the elevated hypothalamic GnRH and AR expression levels. EA did not affect GnRH receptor or CRH expression. Interestingly, nuclear AR co-localized with GnRH in the hypothalamus. Thus, rats with DHT-induced PCOS have disrupted estrous cyclicity and an increased number of hypothalamic cells expressing GnRH, most likely mediated by AR activation. Repeated low-frequency EA normalized estrous cyclicity and restored GnRH and AR protein expression. These results may help explain the beneficial neuroendocrine effects of low-frequency EA in women with PCOS.
Highlights
Polycystic ovary syndrome (PCOS) is characterized by hyperandrogenism and anovulation
Decreased androgen receptor (AR) protein expression in the hypothalamus Hypothalamic AR protein expression was higher in PCOS rats than in controls (p,0.001) (Fig. 2), and so was AR immunoreactivity (AR-ir) in the medial preoptic area (MPO) (p,0.05) (Fig. 3A, 3B)
This study shows that continuous DHT exposure, starting before puberty, inhibits normal estrous cyclicity and increases hypothalamic AR expression and the number of gonadotropin-releasing hormone (GnRH)-ir cells in adult female rats
Summary
Polycystic ovary syndrome (PCOS) is characterized by hyperandrogenism and anovulation. Its origin appears to be multifactorial, as increased concentrations of luteinizing hormone (LH) and insulin stimulate the ovaries and increase androgen secretion [1]. Regardless of the etiology, increased androgen concentrations appear to result in neuroendocrine dysfunction. The resulting increase in pituitary synthesis of LH contributes to excessive LH pulsatility and a relative deficiency in follicle-stimulating hormone (FSH) [2]. High LH concentrations increase ovarian androgen production, and FSH deficiency contributes to impaired follicular development [3]. In adult female rats prenatally exposed to androgen, androgen receptor (AR) activation appears to contribute directly to the development of a hyperactive GnRH pulse generator [4]. After continuous exposure to the nonaromatizable androgen dihydrotestosterone (DHT) from prepuberty, adult rats have polycystic ovaries, an increased number of apoptotic follicles, and irregular cycles [6]
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