Luteal progesterone and prostaglandin F 2α production [formula omitted][formula omitted] during fluprostenol-induced luteolysis in the mare

Abstract

Prostaglandin F 2α (PGF 2α) release in vitro by luteal tissue from mares was quantified to determine if exogenous prostaglandin analog increased endogenous luteal PGF 2α production during induced luteolysis. On day 8 after ovulation, luteal tissue was collected by flank laparotomy and endometrium was collected by uterine biopsy. Mares were assigned to one of four treatments: (1) no intramuscular injection at 0-hr (n = 5), (2) 250 μg Fluprostenol (ICI 81008 PGF 2α analog) at 4-hr (n = 4), (3) 250 μg Fluprostenol at 12-hr (n = 5), or (4) 250 μg Fluprostenol at 28-hr (n = 5) prior to tissue collection at laparotomy. Blood was collected from a jugular vein at laparotomy. Luteal and endometrial tissues (100-mg minces) were incubated in duplicate in 5 ml of Krebs-Ringer bicarbonate buffer (pH 7.4) in an ice bath in an air atmosphere or at 37°C in an atmosphere of 95% O 2:5% CO 2. The incubation treatments consisted of: no treatment, indomethacin 1.3 × 10 −4M, 1 μg/ml of arachidonic acid, 10 μg/ml of Fluprostenol, and 100 μM dbc-AMP (Fluprostenol was not added to endometrial tissue incubations). The injection of Fluprostenol induced luteolysis in these mares as indicated by decreased plasma progesterone and luteal tissue progesterone production (P<0.01). Luteal PGF 2α production was only detectable in tissue from mares that had been injected with Fluprostenol; production reached a maximum by 12 hr post-injection and had returned to pre-treatment levels by 28 hr (P<0.01). Endometrial tissue produced PGF 2α, but this activity was not significantly affected by injection of mares with Fluprostenol. Increased production of PGF 2α by luteal tissue of mares during PGF 2α analog induced luteolysis was similar to that observed in the pig and ewe.