Effects of androgens on bioactivity and immunoreactivity of pituitary FSH in GnRH antagonist-treated male rats

Abstract

The effects of androgens on the bioactivity and molecular composition of pituitary FSH were examined in intact and GnRH antagonist-suppressed male rats. Eight groups of adult Sprague-Dawley rats were subjected to the following treatments: antagonist (75 \g=m\g/day by osmotic minipumps; sc), testosterone-filled Silastic implants (3\m=x\5cm, sc), dihydrotestosterone-filled Silastic implants (3\m=x\5cm, sc), E2 benzoate (15 \g=m\g/day,sc), and combined administration of antagonist with either steroid for 3 weeks. At the end of the treatment period, pituitaries were dissected out and homogenised. FSH content was determined in the pituitary extracts by an in vitro bioassay and a radioimmunoassay. Individual pituitary extracts from rats treated with vehicle, testosterone and testosterone + antagonist were subjected to isoelectric-focusing on sucrose density gradients performed in the pH range from 3.5 to 7.0. Individual isoelectric-focusing fractions (100-120) were analysed for bioactive and immunoreactive FSH. Treatment with antagonist, E2 or antagonist + E2 caused a significant decrease in pituitary FSH, whereas testosterone and dihydrotesterone alone or in combination with antagonist prevented the decrease in pituitary FSH. The effects of all treatments on both bioactive and immunoreactive FSH were similar. Testosterone treatment not only maintained FSH synthesis but also altered the molecular composition of pituitary FSH. Following treatment with testosterone there was a shift of maximal FSH bioactivity to the more acidic pH range. On the other hand, less bioactivity was recovered than corresponding immunoreactivity in the higher pH region, resulting in significantly reduced ratios of bioactivity to immunoreactivity of FSH. No significant differences were found in the isoelectric-focusing profiles or bioactivity to immunoreactivity ratios of pituitary FSH in animals treated with testosterone alone or in combination with antagonist. The results demonstrate that testosterone not only maintained the synthesis of both bioactive and immunoreactive FSH in male rats, but also influences the molecular composition of pituitary FSH. These effects of testosterone on pituitary FSH appear not to be mediated through hypothalamic GnRH.Follicle-stimulating hormone exists in multiple mo¬ lecular forms within the anterior pituitary gland of several animal species and man (1-5). These isoforms of FSH differ not only in charge properties (isoelectric point; pi) but also in receptor binding activity (6), circulating half-life (7) and in vitro bi¬ ological potency (8,9). Furthermore, the relative abundance of these isoforms in the pituitary is af¬ fected by the endocrine status of the animal, such as castration (4,10,11), pubertal development (12), and during different phases of the reproductive cycle in the female (13), suggesting that gonadal factors might be involved in the regulation of mo¬ lecular heterogeneity of FSH (2,5,6,14,15). It has previously been demonstrated in our lab¬ oratory that testosterone (T) administration to male...

Microheterogeneity of pituitary follicle-stimulating hormone in male rats: differential effects of the chronic androgen deprivation induced by castration or androgen blockade

“…Since the pituitary gland is situ¬ ated outside the blood-brain barrier and casodex is believed not to enter the central brain tissue (Freeman et al 1986), the androgen blockade should occur only (or mainly) at the pituitary level. On this basis, our data suggest that the effect of androgen deprivation on the molecular heterogeneity of pitui¬ tary FSH does not involve hypothalamic GnRH, in accordance with previous evidence obtained in GnRH antagonist-treated rats supplemented with testosterone (Sharma et al 1990). …”

“…Bioactive FSH was measured in the IEF pools, in pituitary homogenates and in serum samples using a highly sensitive and specific in-vitro bioassay based on the conversion of androgen sub¬ strates to oestradiol by immature rat Sertoli cells (Van Damme et al 1979;Padmanabhan et al 1987), as previously described (Jockenhövel et al 1990;Sharma et al 1990). Sertoli cells from 7-10-day-old male Sprague-Dawley rats were cultured for 72 h in medium (Ham's F12 : Dulbecco's modification of Eagle's medium, 1:1; Flow Laboratories, Irvine, Strathclyde, U.K.) enriched with antibiotics and hormones in 96 microwell plates, in an atmosphere of 95% air and 5% C02 at 32°C.…”

“…In the male rat, micro¬ heterogeneity of pituitary FSH changes during sex¬ ual maturation; at the inception of spermatogenesis (45 days of age) there is a shift in the relative distri¬ bution of the different molecular isoforms towards the more acidic components, a situation which is partially reversed 15 days after orchidectomy (UlloaAguirre et al 1986). Moreover, in FSH-suppressed rats, testosterone can stimulate pituitary and serum FSH (Rea et al 1986a,b) and also influences the molecular composition of the gonadotrophin via a mechanism which probably does not involve hypo¬ thalamic gonadotrophin-releasing hormone (GnRH; Sharma et al 1990).…”

Metformin versus flutamide in the treatment of metabolic consequences of non-obese young women with polycystic ovary syndrome: a randomized prospective study

“…Specific androgen-receptor blockade by flutamide has been shown to increase gonadotropin synthesis in rats [62][63][64][65][66] and men 67,68 by reversing the effect of androgen. In PCOS, gonadotropin secretion is altered 69 and the majority of patients have elevated LH levels in plasma and a persistent rapid frequency of LH (GnRH) pulse secretion [70][71][72] , the mechanisms of which are unclear.…”

Effects of administration of testosterone and gonadotrophin-releasing hormone (GnRH) antagonist on basal and GnRH-stimulated gonadotrophin secretion in orchidectomized monkeys

“…This observation markedly differs from the testosterone-induced time-and dose-dependent stimulation of serum and pituitary concentrations of FSH observed in GnRH antagonist-treated orchidec¬ tomized rats (Bhasin et al 1987;Arslan et al 1989). Such positive feedback effect of testosterone on FSH has also been observed in intact rats (Rea et al 1986;Rea, Weinbauer, Marshall & Nieschlag, 1987; Sharma, Khan, Weinbauer et al 1990). Under these conditions, in the intact and orchidectomized rat, testosterone also selectively stimulated the mRNA expression for FSH-ß (Wierman & Wang, 1990).…”