Effects of prostaglandin F2.ALPHA. administration on the time of parturition and post-partum ovulation in rats.
The time relationship between delivery and post-partum ovulation in rats treated with PGF2α was investigated.PGF2α, 1.0 mg/rat, was s.c. injected at 21:00 on Day 19 (PG 19 group) or 09:00 on Day 20 (PG 20 group) of pregnancy.In the PGF2α-treated groups, first delivery occurred about 30 h after the treatment. About 90% of the rats delivered within 48 h after the treatment. Some rats which delivered from 11:00 to 19:00 on Day 21 of pregnancy in the PG 19 group had ovulated within 12 h after the delivery. In rats which delivered from 20:00 on Day 21 to 10:00 on Day 22 of pregnancy in the PG 20 group, ovulation was not detected until 23:00 on Day 22 of pregnancy.Serum gonadotrophin levels (LH and FSH) increased within 2 h after the delivery in the PG 19 group. In the PG 20 group, however, gonadotrophin levels did not change until 12:00 on Day 22 of pregnancy.These results suggest that the timing of the "critical period" for the release of gonadotrophins for post-partum ovulation in the PGF2α-treated rats is between 11:00 and 20:00. The "critical period" is similar to normally delivering rats and broader than that in cyclic rats.