EFFECTS OF EXOGENOUS AND ENDOGENOUS PROSTAGLANDINS ON THE FAST PHASE OF CONTRACTION OF THE GUINEA-PIG VAS-DEFERENS PRODUCED BY ELECTRICAL-FIELD STIMULATION

The initial, fast phase of contraction of the guinea-pig vas deferens produced by electrical field stimulation (10 pulses) was dose-dependen tly and completely inhibited by prostaglandin (PG) E(2), sulprostone a nd, at high concentrations, by cicaprost. Sulprostone was more potent than PGE(2) indicating that the EP(3) receptor was involved. Cicaprost (a PGI(2) analogue) apparently had weak EP(3) receptor against activi ty. At low concentrations, cicaprost potentiated the contractions of t he vas deferens, presumably by acting on an IP receptor. Exogenous ara chidonic acid also dose-dependently and completely inhibited contracti ons of the guinea-pig vas deferens. The action of arachidonic acid was delayed when compared to PGE(2) and was inhibited by indomethacin, su ggesting that the arachidonic acid was converted to PGE(2) by the vas deferens. Indomethacin (1.4 to 6.0 mu M) had no significant, potentiat ing effect on the contractions of the guinea-pig vas deferens which su ggests that endogenous PGs do not normally inhibit this fast phase of contraction, In higher concentrations, the contractions were reduced b y indomethacin. The fast phase of contraction of the guineapig vas def erens consisted of 3 components. PGE(2), sulprostone and arachidonic a cid inhibited all components. The order of inhibition of the component s was component 2, then component 3, followed by component 1.