Comparative effects of prostaglandin E 2 and prostaglandin E 3 on water flow and cyclic AMP in the urinary bladder of the frog, [formula omitted

Abstract

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 PGE 2 and PGE 3 on basal and arginine vasotocin (AVT) stimulated water flow were compared. Contol water flow (1.1 ± 0.2 mg/min) was increased to 4.6 ± 0.3 mg/min with AVT (10 −6M) present. PGE 2 (10 −6M) inhibited both basal and AVT stimulated water flow. In contrast, PGE 3 (10 −6M) 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 −5M). Both PGE 2 and PGE 3 stimulated basal ACA in the absence, but not in the presence of GTP. In the absence of exogenous GTP, PGE 2 increased AVT stimulated ACA, whereas PGE 3 decreased it. Both prostaglandins inhibited AVT stimulation when GTP was added. The effects of PGE 2, PGE 3 and AVT on tissue cycilc AMP levels in whole urinary bladders were similar to the effects seen on ACA in the absence of exogenous GTP. The contrasting effects of PGE 2 and PGE 3 on control water flow appear distinct from their similar effects on ACA. However, PGE 2 and PGE 3 may regulate AVT stimulation through mechanisms involving cyclic AMP.