When hysterectomized guinea pigs were treated daily with prostaglandin F2α, (0.058 mg PGF2α/100 g body weight per day), luteal volumes and systemic levels of progesterone were unaffected up to day 9 of the oestrous cycle, but the onset of luteolysis had occurred around day 12, 3–4 days earlier than normal. The treatment of hysterectomized animals on days 5–7 and 8–10 at the same dose did not result in luteal regression in any respect on day 14, but treatment on days 9–12 and days 9–13 induced luteolysis. A continuous treatment with 0.135 mg PGF2α/100 g body weight per day reduced the cycle length by 22%, but again luteal volume and progesterone level were unaffected up to day 9. The treatment with human chorionic gonadotropin (50 IU/day) or follicle-stimulating hormone (5 U/day) on days 8–13 had an antagonistic effect on the luteolytic action of PGF2α administered on days 9–13, but prolactin also administered at this time did not have this effect. It is postulated that, in guinea pigs, ovulation and the formation of corpus luteum (CL) are not affected by a low dose of PGF2α, the CL is protected from PGF2α by gonadotropins up to day 9, normal luteolysis is due to the withdrawal of gonadotropins and the upsurge of PGF2α, and the subsequent rate of luteal regression depends on the amount of available PGF2α.
The effect of continuous treatment with prostaglandin F-2 on oestrous cycle length and corpus luteum regression in hysterectomized guinea-pigs
