Gestational changes in prostaglandin synthase activity of ovine cotyledonary microsomes

The capacity of cotyledonary microsomes, prepared from pregnant ewes (20-145 days of gestation), to metabolize exogenous arachidonic acid was quantified using a radiolabel technique. During gestation, the capacity of microsomes to metabolize arachidonic acid increased 25-fold, from 0.36 +/- 0.06 mumol arachidonic acid/incubation (n = 8) at less than 100 days of gestation to 9.06 +/- 1.02 mumol arachidonic acid/incubation at 130-145 days of gestation (n = 5; P less than 0.05). Arachidonic acid was metabolized to prostaglandin E2 and F2 alpha, as determined by thin-layer chromatography and reverse-phase high performance liquid chromatography. The profile of prostaglandins synthesized by cotyledonary microsomes did not change throughout gestation. These data suggest that the increase in cotyledonary prostaglandin synthesis that occurs during late gestation and at term may reflect an increase in the tissue content of prostaglandin H2 synthase.