ロジェストロンと17α, 20β-ジヒドロオキシ-4-プレグネン-3-オンの変動

The time course changes in serum concentrations of gonadotropin (GtH), 17α-hydroxypro-gestrone and 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-diOHprog) during LH-RH-induced final oocyte maturation and ovulation in gravid ayu Plecoglossus altivelis were examined. The fish underwent GVBD one day following a single intraperitoneal injection of emulsified LH-RH and ovulated in 2 days. A slow and moderate increase in serum levels of GtH occurred 1-3 days after injection. The LH-RH treatment caused a prompt increase in hte serum levels of 17α-hydroxypro-geterone and 17α, 20β-diOHprog concomitant with final oocyte maturation and ovulation. The levels of 17α, 20β-diOHprog remained high for 1-3 day after injection, followed by a sharp decrease at 5-7 days. The elevation of 17-hydroxyprogesterone, which is a precursor for 17α, 20β-diOHprog occurred earlier and persisted longer than the changes in 17α, 20β-diOHprog. Thus, the changes in serum levels of these steroids during final maturation and ovulation are medizted through the secretion of pituitary GtH. These findings suggest that 17α, 20β-diOHprog is the major ovarian mediator of LH-RH-induced oocyte maturation in ayu.