ENDOTHELIN-1 AND ENDOTHELIN-3 STIMULATE OVARIAN STEROIDOGENESIS

The possible direct involvement of endothelin (ET) in preovulatory follicular steroidogenesis was investigated in vitro. Follicular development in immature rats was induced by pregnant mare's serum gonadotropin (PMS). Twenty-four and 48 h after PMS injection, ovarian follicles were incubated in vitro with or without 4 x 10(-11) to 4 x 10(-5) M endothelin-1 (ET-1) or endothelin-3 (ET-3) for 2 h, or perifused in vitro with 4 x 10(-7) M of ET-1 or ET-3 for 3 h. In the incubation study, ET-1 and ET-3 significantly stimulated progesterone, testosterone, and 17-beta-estradiol production by follicles 24 and 48 h after PMS injection. Progesterone, testosterone, and 17-beta-estradiol were increased in a dose-dependent manner by 4 x 10(-11) to 4 x 10(-6) M ET-1 or ET-3; in the case of ET-3, this increase occurred only at 24 h after PMS injection. In addition, ET-1 stimulated ovarian steroid production more effectively than ET-3. In addition to their effects on ovarian steroidogenesis, both ET-1 and ET-3 increased tissue cyclic adenosine-3',5'-monophosphate (cyclic AMP) production. The steroidogenic effect of ET-1 or ET-3 was most pronounced by follicles 48 h after PMS injection. In the perifusion experiment, ET-1 and ET-3 also stimulated progesterone, testosterone, and 17-beta-estradiol secretion. These indicate the involvement of ET-1 or ET-3 in the regulation of ovarian differentiation by stimulating steroidogenesis, at least partially through the mediation of cyclic AMP.