THE EFFECT OF PROSTAGLANDIN F2α ON PROGESTERONE, OESTRADIOL AND LUTEINIZING HORMONE SECRETION IN SHEEP WITH OVARIAN TRANSPLANTS

SUMMARY The luteolytic properties of prostaglandin F2α (PGF2α) were studied in experiments on sheep with ovarian autotransplants. PGF2α was infused at the rate of 40, 10 and 2 μg/h for 4·0, 7·0 and 9·5–18·0 h respectively. At rates of 40 and 10 μg/h, progesterone secretion decreased to 50% of the control levels in 2·6 ± 1·4 h and fell to 8–30 μg/h within 36–52 h from the start of infusion. The onset of oestrus occurred 42–66 h after the infusions had started and a typical pre-ovulatory surge of luteinizing hormone (LH) was observed 52–66 h after infusing PGF2α. On occasions, this surge was accompanied by a brief peak of oestradiol-17β secretion and shortly thereafter ovarian steroidogenesis decreased to very low levels. In four sheep infused at a rate of 2 μg/h, peripheral progesterone values decreased gradually and only one animal returned to oestrus. It would seem that 2 μg/h is close to the minimum intra-arterial dose to cause luteolysis in the sheep.