Activity of phospholipase C and release of prostaglandin F2 alpha by endometrial tissue from ewes during the oestrous cycle and early pregnancy.

Oxytocin appears to play an important role in regulating uterine secretion of prostaglandin F2 alpha (PGF2 alpha) in sheep. Changes in uterine secretion of PGF2 alpha throughout the oestrous cycle and early pregnancy may be due to changes in the intracellular regulatory pathways that control synthesis of PGF2 alpha in response to oxytocin. In this experiment, caruncular endometrial tissue was collected from ewes throughout the oestrous cycle and early pregnancy. Endometrial tissue was incubated in vitro to assess release of PGF2 alpha and activity of phospholipase C (PLC) in response to oxytocin. Release of PGF2 alpha in the presence of arachidonic acid was used to assess the activity of prostaglandin H2 endoperoxide synthase (PGS). In non-pregnant ewes, oxytocin stimulated release of PGF2 alpha from endometrial tissue collected on days 14 and 16, but not on days 4-7, 10 or 12 after oestrus. This coincided with times when oxytocin stimulated the activity of PLC. Release of PGF2 alpha was enhanced by the addition of arachidonic acid to tissues collected on days 12, 14 and 16 after oestrus. As with tissue from nonpregnant ewes, oxytocin could stimulate release of PGF2 alpha on days 14 and 16 of early pregnancy. Yet, oxytocin had no effect on activity of PLC in tissue from pregnant ewes. Release of PGF2 alpha in the presence of arachidonic acid by tissue from pregnant ewes was similar to that in nonpregnant ewes at comparable times after oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)