EFFECTS OF 17-BETA-ESTRADIOL ON PITUITARY AND TESTICULAR FUNCTION IN MALE GOLDFISH

The potential involvement of 17beta-estradiol in the regulation of pit uitary and testicular function was investigated in male goldfish at va rious times during the seasonal reproductive cycle. Serum levels of te stosterone, 11-ketotestosterone, and 17beta-estradiol were 10, 16, and 4 times higher in mature males (tubercles on the pectoral fins and mi lt production; March) than in sexually regressed males (no tubercles o r milt production; July). Intraperitoneal injection Of [D-Arg6,Trp7,Le u8,Pro9-NEt]gonadotropin releasing hormone (sGnRH-A, 0.01 mug/g) eleva ted serum gonadotropin II levels within 6 h, and there was a concomita nt increase in testosterone but not 17beta-estradiol levels in sexuall y regressing male goldfish (October). Males in the early stage of test icular recrudescence (November) had increased serum levels of gonadotr opin II and testosterone in response to [D-Ala6,Pro9-NEt]GnRH (LHRH-A, 0.1 mug/g) or the dopamine antagonist domperidone (5 mug/g). Males im planted intraperitoneally for 10 days with solid Silastic pellet impla nts containing 17beta-estradiol (100 mug/g) had lower basal testostero ne levels and a reduced testosterone response to both LHRH-A and dompe ridone. The serum gonadotropin II response to LHRH-A but not domperido ne was enhanced by 17beta-estradiol. Male goldfish in mid-recrudescenc e receiving 17beta-estradiol implants for 4 days had lower basal testo sterone and 11-ketotestosterone levels than controls. Combined treatme nt with sGnRH-A (0.1 mug/g) and domperidone (10 mug/g) elevated serum testosterone and 11-ketotestosterone levels at 24 h; the serum androge n response was reduced in 17beta-estradiol-implanted fish. These studi es support the concept that 17beta-estradiol plays a role in the regul ation of reproduction in male goldfish by enhancing pituitary gonadotr opin II release and by reducing testicular androgen production.