Inhibition of prostaglandin synthesis by ovine allantoic fluid: acute reduction in inhibitory activity during late gestation

Abstract

The capacity of ovine allantoic fluid to modulate prostaglandin (PG) synthesis was measured in fluid taken from ewes at 100–140 days gestation. An inhibitor of PG synthesis was found in allantoic fluid from ewes at 100–130 days gestation. The inhibitor had the capacity to inhibit PGF2α, PGE2, and 6-keto-PGF1α synthesis by endometrial cotyledon microsomes in a concentration-dependent manner. At 140 days gestation, the inhibitory potency of the fluid was significantly less than that present at 100–130 days gestation, at concentrations greater than 20% (v/v) (p < 0.001). The inhibitor is not albumin and remained active after boiling, dialysis, and protease treatment. It was extracted with chloroform–methanol, indicating that the active portion of the molecule is a lipid. We suggest that parturition in the sheep may be associated with a local withdrawal of inhibition of prostaglandin synthesis.