19‐Norandrostenedione (4‐estrene‐3,17‐dione) Inhibits Porcine Oocyte Maturation In Vitro

Abstract

Recent work has shown that 19-norandrostenedione is a major steroidal component of porcine follicular fluid; however, little is known about its role(s) in the regulation of follicular function. This study was designed to examine the effect of 19-norandrostenedione on porcine oocyte maturation in vitro. Oocyte-cumulus complexes were isolated from medium (3–6-mm diameter)-sized prepubertal pig follicles and incubated for 12 h in medium with or without dibutyryl cyclic AMP ((Bu)2cAMP, 1 mM) with or without testosterone (5 x 10−7 M) or 19-norandrostenedione (5 x 10−7 M). In medium alone, 70.8% of oocytes spontaneously resumed meiosis as evidenced by the occurrence of germinal vesicle breakdown. Oocyte maturation was inhibited by (Bu)2cAMP (44.6% of oocytes matured). Although neither steroid alone affected maturation, both testosterone and 19-norandrostenedione enhanced the effect of (Bu)2cAMP (22.5 and 19.6%, respectively, resumed meiosis). The effects of testosterone and 19-norandrostenedione on (Bu)2cAMP-inhibited oocyte maturation were dose dependent and there was no significant difference between the actions of the steroids. The effect of 19-norandrostenedione was reversible and dependent on the presence of an intact cumulus. Hydroxyflutamide (SCH-16423), a nonsteroidal compound known to block androgen receptors, abolished the effects of both testosterone and 19-norandrostenedione on germinal vesicle breakdown, indicating that the actions of these steroids are truly androgenic. The results of this study suggest that 19-norandrostenedione may be of physiological importance in the regulation of porcine oocyte maturation.