EFFECT OF EXOGENOUS PHOSPHOLIPASE-A2 AND TRIACYLGLYCEROL LIPASE ON THE SYNTHESIS AND RELEASE OF MONOENOIC AND BISENOIC PROSTAGLANDINS FROM ISOLATED RAT UTERUS

The possible existence of a selective and independent mechanism subserving the formation of prostaglandin E1 (PGE1) and of prostaglandin E2 (PGE2) has been reported in previous studies from our group. In the present experiments we have demonstrated that neutral lipid lipases play an important role yielding dihomo-gamma-linolenic acid for the formation of PGE1. Indeed, exogenous triglyceride lipase added to the incubation bathing solution at a concentration of 150 U/ml increased several fold the production of PGE1 by isolated uterine strips obtained from spayed rats. Nevertheless the presence of the enzyme did not modify significantly the synthesis and release of bisenoic PGs (PGE2 and PGF2-alpha). When triarachidonin was added, as an artificial substrate into the incubating medium in order to detect the presence of endogenous triacylglycerol lipase, we observed a significant increment in the generation of PGE2 (p < 0.005) and of PGF2-alpha (p < 0.001) without evident changes in the basal release of PGE1. On the other hand, the addition of phospholipase A2 (PLA2) at 0.2 U/ml, increased significantly the production of PGE2 (p < 0.001) but failed to alter the concentration of PGE1 in the incubating solution. Surprisingly, PLA2 did not enhance the synthesis of PGF2-alpha in the present experiments, a situation for which we do not have a clear explanation. Exogenous bradykinin (10(-6) M), a well known stimulant of PLA2 activity in several tissues, also increased significantly (p < 0.001) the production of PGE2 Without altering that of PGE1. Results presented herein provide strong support to the notion that different enzyme mechanisms and different lipid stores are linked to the formation of PGE1 and PGE2 in isolated rat uteri.