Inhibition of cytochromeP-450 C17 enzyme by a GnRH agonist in ovarian follicles from gonadotropin-stimulated rats

Abstract

Irusta G, Parborell F, Tesone M. Inhibition of cytochrome P-450 C17 enzyme by a GnRH agonist in ovarian follicles from gonadotropin-stimulated rats. Am J Physiol Endocrinol Metab 292: E1456 -E1464, 2007; doi:10.1152/ajpendo.00226.2006.-Our objective was to study the direct action of a GnRH-I agonist, leuprolide acetate (LA), on ovarian steroidogenesis in preovulatory follicles obtained from equine chorionic gonadotropin (eCG)-treated rats. Previously, we have demonstrated an inhibitory effect of LA on steroidogenesis and follicular development. In this study, we tested the hypothesis that gonadotropin-releasing hormone (GnRH) exerts its negative effect on follicular development by inhibiting thecal cytochrome P-450 C17 (P450C17) ␣-hydroxylase expression and, consequently, androgen synthesis. Studies were carried out in prepubertal female rats injected with either eCG (control) or eCG plus LA (LA) and killed at different time points. Immunohistochemical studies indicated that LA induced steroidogenic acute regulatory protein (StAR) expression mainly in theca cells of preantral and antral follicles. In addition, serum progesterone levels increased significantly (P Ͻ 0.05), whereas those of androsterone decreased (P Ͻ 0.05) after 8 h of LA treatment. This inhibition caused by LA seemed to be a consequence of the decreased expression of follicular P450C17 ␣-hydroxylase, as demonstrated by Western blot and RT-PCR techniques. In vitro studies using follicles isolated from 48-h-eCG-treated rats and cultured with LA showed a significant (P Ͻ 0.05) inhibition of FSH-induced androsterone follicular content as well as P450C17 ␣-hydroxylase protein levels, as determined by Western analysis. However, LA increased StAR protein expression in these follicles without significant changes in P450scc enzyme levels. Taking all these findings into account, we suggest that GnRH-I exerts a direct inhibitory action on gonadotropininduced follicular development by decreasing the temporal expression of the P450C17 enzyme and, consequently, androgen production, thus reducing the supply of estrogens available to developing follicles. ovary; follicle; gonadotropin-releasing hormone agonist; steroidogenesis THE SUPPRESSION OF GONADOTROPINS exerted by the administration of gonadotropin-releasing hormone (GnRH) analogs on the pituitary-gonadal axis is well known. The agonists initially stimulate the secretion of large amounts of gonadotropins, followed by a desensitization of the pituitary and the subsequent inhibition of gonadal steroid production (33, 62). However, in the last several years there has been increasing evidence that GnRH is an intraovarian regulatory factor. A GnRH-like peptide, GnRH receptors, and transcription products from their genes have been found in ovarian tissue (3,7,31,65), and a direct inhibitory effect of this decapeptide has been observed on steroidogenesis in both granulosa cells (Gc) (31,32,35,38,40,43,58) and in corpus luteum (1,62,64). In addition, we (57) have demonstrated that in vitro treatment with a GnRH-I ...

A link between Notch and progesterone maintains the functionality of the rat corpus luteum

“…3Aa) showed a low immunoreactivity for this protein. Active CASP3 staining was more evident in the nuclei of the CL sections, in coincidence with the fact that, once activated, active CASP3 translocate to the nucleus (Irusta et al 2007, Parborell et al 2008. Interestingly, the presence of progesterone in the culture medium not only reversed the increase in the immunoreactivity for active CASP3 observed with DAPT but also significantly decreased active CASP3 with respect to the control values ( Fig.…”

Noradrenaline modulates the presence of gonadotropin-releasing hormone in ovary. The importance of its interrelation on the ovarian steroidogenesis and apoptosis on dioestrus II in rat.

“…In this work, the increase of GnRH in ovary incubation might cause the fall of E 2 in coincidence with previous reports that indicate an inhibitory effect of GnRH on LH-stimulated androgen biosynthesis in ovarian interstitial cells through the inhibition of the 17-a-hydroxylase, 17, 20 lyase enzymes and aromatase [48]. This E 2 decrease might trigger mechanisms leading to cell apoptosis as mentioned before [14].…”

Role of the Dll4-Notch System in PGF2alpha-Induced Luteolysis in the Pregnant Rat.

“…Interestingly, CASP3 staining was more evident in the nuclei of the CL of the sections obtained from DAPT-treated ovaries than in those of the control group, in line with the fact that once activated, CASP3 translocates to the nucleus [36,37].…”