Oxytocin-induced prostaglandin release from perifused bovine caruncular and intercaruncular endometrial tissue on days 20, 30 and at first estrus postpartum.

Twenty-two multiparous Brahman x Hereford F1 cows were utilized to determine the effect of oxytocin (OT) on prostaglandin F2 alpha (PGF) release from caruncular and intercaruncular endometrial tissues and prostaglandin E2 (PGE) release from intercaruncular tissue. The previously gravid uterine horn was removed on d 20 postpartum (n = 7), on d 30 postpartum (n = 7) or the uterine horn ipsilateral to the dominant follicle was removed 12-18 h after onset of first behavioral estrus postpartum (ES; n = 8). Tissues (200 mg wet wt) were cultured in Nutrient Mixture F-10 medium in a perifusion system. The medium and tissues were aerated with 95% O2: 5% CO2 and temperatures were maintained at 39 degrees C. The flow rate was 100 microliters/min and fractions were collected at 20 min intervals for 400 min. After a 2 h settling phase, the tissues were challenged with 1, 2 or 4 micrograms [Asu1,6]-OT/ml of media for 1 h. Basal release of PGE and PGF on d 20 was greater than on d 30 and at ES (P less than .02) which were similar. All doses of OT increased PGE and PGF with both remaining elevated throughout the duration of the perifusion (P less than .008). However, there were no differences among doses. Release of PGE in response to OT on d 20 and 30, was higher than at ES (P less than .008). More PGF was released in response to OT from intercaruncular than caruncular tissue on d 20 (P less than .0001) and at ES (P less than .003). Release of PGF in response to OT on d 20 was higher (P less than .0001) than on d 30 and d 30 was higher than at ES (P less than .007). Basal and OT-induced release of PGE and PGF declined as day postpartum increased. We conclude that intercaruncular tissue released more PGF than caruncular tissue and both intercaruncular and caruncular tissue responded to OT with a sustained release of prostaglandins in a non-dose-dependent manner on d 20, 30 and at ES postpartum.