[Arginine]vasopressin (AVP) stimulates maximal prostaglandin E2 production in cultured rat renal mesangial cells within 2 min. As early as 10s after addition of AVP (10(-6)M) a significant loss of radioactivity from phosphatidylinositol 4,5-bisphosphate but not from phosphatidylinositol 4-phosphate and phosphatidylinositol was observed in cells prelabelled with 32Pi. Cells labelled with [14C]arachidonic acid showed an increase of label in 1,2-diacylglycerol after 15 s and in phosphatidic acid after 30 s upon stimulation with AVP. Pretreatment of the cells with indomethacin (10(-5)M) did not abolish the effect of AVP on the increased labelling of phosphatidic acid.