Abstract
Effects of ONO-802 on maintenance of pregnancy, luteal function and ovulation were investigated. In pregnant rats, ONO-802 given i.p. showed antinidatory, abortifacient and strong labor-inducing effects with treatment on day 2, after day 17 and on day 21 of gestation, respectively. The abortifacient effect was not apparent when treatment was given from days 4 ?? 15. PGE1 had an antinidatory effect, PGF2α had an abortifacient and labor-inducing effects after implantation, and PGE2 had both these effects. PGF2α and PGE2 showed a luteolytic effect in rats, while ONO-802, similarly to the findings with PGE1, had no such effect. In pregnant rabbits, intraperitoneal ONO-802 exhibited antinidatory and abortifacient effects after implantation. Abortifacient effects were more potent with the progression of pregnancy though relatively large doses of ONO-802 were required. A significant decrease in peripheral blood progesterone level was observed in the group on high doses but the abortifacient effect of ONO-802 did not always depend on the decreases in the levels of progesterone. In cycling, spontaneously ovulating rats, the high doses of ONO-802 suppressed spontaneous ovulation when these doses were given two at 14:30 and 15:30 on the day of proestrus. ONO-802 did not inhibit the HCG-induced ovulation and the ovulation suppressed by ONO-802 was recovered by PGE2 or HCG.
