Regulation of endometrial prostaglandin synthesis during early pregnancy in cattle: Effects of phospholipases and calcium In vitro

In experiment 1, endometrial explants from 3 cyclic (Day 17) cows were incubated with arachidonic acid (AA), phospholipase A-2 (PLA-2) and calcium ionophore A23187 (CaI) or control. AA (0.2 mg), PLA-2 (1 U/ml) and CaI (4 micrograms/ml) increased PGF and PGE secretion. In experiment 2, endometrial explants from cyclic (n = 4) and pregnant (n = 3) cows were incubated +/- Ca++ and with either: control, AA, PLA-2, CaI, PLA-2 + CaI, or AA + CaI. PG secretion was higher in cultures with Ca++. In presence of Ca++, PGF secretion was lower for pregnant than cyclic endometrium. AA with Ca++ stimulated PGF and PGE secretion, indicating that AA availability may limit PG secretion. The stimulatory effect of PLA-2 on PGF and PGE secretion was greater in pregnant than cyclic endometrium. However, CaI inhibited the PLA-2 response of pregnant, but not cyclic endometrium. In experiment 3, endometrium (4 cyclic cows) failed to convert 3H-PGF2 alpha to PGE2 or 3H-PGE2 to PGF2 alpha. Responsiveness of PG secretion to PLA-2, and CaI is altered by reproductive status suggesting that these factors may be involved in the differential regulation of PG production during early pregnancy in cattle.