Aspects of regulation of uterine secretion of prostaglandins during the oestrous cycle and early pregnancy

Abstract Evidence that the pattern of secretion of prostaglandin E 2 (PGE 2 ) by the uterus: conceptus unit is consistent with that compound playing a role in the local antiluteolytic effect of the embryo is reviewed briefly. Utero-ovarian venous concentrations of PGE 2 increased on day 13 in pregnant compared to non-pregnant ewes, both absolutely and in relation to prostaglandin F 2α (PGF 2α ). The roles of oestrogen and progesterone in regulation of utero-ovarian venous concentrations of PGF 2α were examined during two intervals of the oestrous cycle and on day 13 of the cycle or pregnancy. The first interval (Experiment l, days 10 to 14) was chosen to study the initial rises of PGF 2α that precede luteolysis. At laparotomy on day 9, a catheter was inserted into a utero-ovarian vein. Eight ewes received no further treatment. At surgery, 12 ewes were given 10 mg of progesterone (i.m.) along with an intravaginal pessary containing 30 mg flurogestone acetate and were either ovariectomized (n=5) or lutectomized (n=7). Five ewes were ovariectomized only. The second interval (Experiment 2, days 14 to 17) was chosen to study the maximal rises of PGF 2α associated with the completion of luteal regression and the preovulatory increase of oestrogen. Ewes were laparotomized and catheterized on day 14 and either received no further treatment (n=5), or were lutectomized (n=6), ovariectomized (n=5) or ovariectomized and implanted with oestradiol-17β (n=5). Five utero- ovarian venous samples were collected, every 30 min for 2 hours beginning at 0600 and 1800 on each day in each experiment, and assayed for PGF 2α . In a third experiment, 15 bred and 12 nonbred ewes were laparotomized and catheterized on day 12. One third of each type remained intact, while two thirds were ovariectomized and half of those received 10 mg of progesterone (s.c.) and an intravaginal sponge containing 30 mg of progesterone on day 12. Utero-ovarian samples were collected at 15-minute intervals for 3 hours on day 13. Neither the average day of occurrence of the first peak of PGF 2α (control, 12.1; lutectomy plus progesterone, 11.6; ovariectomy plus progesterone, 12.0; ovariectomy, 12.2) nor the mean number of peaks detected in each ewe during the sampling periods on days 10 to 14 (2.8, 3.7, 3.2 and 3.4, respectively) differed among groups in Experiment 1. The mean number of peaks of PGF 2α detected in each ewe during days 14 to 17 did not differ among groups in Experiment 2. Neither of the patterns of concentrations of PGF 2α studied (mean within sampling period over time and natural logarithm of the variance within sampling period over time) differed among groups in either experiment. Concentrations of PGF 2α increased after ovariectomy in Experiment 3 and were restored to values similar to intact ewes by replacement therapy with progesterone. These data do not support the idea that increases in oestrogen are involved in regulating patterns of uterine secretion of PGF 2α during the ovine oestrous cycle or the initiation of maternal recognition of pregnancy. In addition, progesterone may not be necessary after day 9 for initial rises of PGF 2α to occur on days 12 and 13, but does appear to be necessary to sustain normal patterns of secretion of PGF 2α beyond day 14.