Comparative effects of prostaglandin E2 and prostaglandin E3 on water flow and cyclic AMP in the urinary bladder of the frog, Rana pipiens

Prostaglandins (PGs) modulate osmotic water flow in amphibian urinary bladders. Gas chromatographic analysis of prostaglandin precursors in bladders showed that arachidonic acid represented 13.0 +/- 0.6% and eicosapentaenoic acid 4.3 +/- 0.1% of the total fatty acid content. The effects of PGE2 and PGE3 on basal and arginine vasotocin (AVT) stimulated water flow were compared. Control water flow (1.1 +/- 0.2 mg/min) was increased to 4.6 +/- 0.3 mg/min with AVT (10(-6)M) present. PGE2 (10(-6)M) inhibited both basal and AVT stimulated water flow. In contrast, PGE3 (10(-6)M) stimulated basal water flow and further increased AVT stimulated water flow. Basal adenylate cyclase activity (ACA, 59 +/- 0.3 pmol cyclic AMP/mg protein/10 min) was stimulated by the addition of AVT in the absence or presence of exogenous guanosine 5' triphosphate (GTP, 10(-5)M). Both PGE2 and PGE3 stimulated basal ACA in the absence, but not in the presence of GTP. In the absence of exogenous GTP, PGE2 increased AVT stimulated ACA, whereas PGE3 decreased it. Both prostaglandins inhibited AVT stimulation when GTP was added. The effects of PGE2, PGE3 and AVT on tissue cyclic AMP levels in whole urinary bladders were similar to the effects seen on ACA in the absence of exogenous GTP. The contrasting effects of PGE2 and PGE3 on control water flow appear distinct from their similar effects on ACA. However, PGE2 and PGE3 may regulate AVT stimulation through mechanisms involving cyclic AMP.