Antagonistic effect of polyphloretin phosphate and di-4-phloretin phosphate on the contractile responses of guinea-pig gastric muscles to prostaglandin E2.

Polyphloretin phosphate (PPP) and di-4-phloretin phosphate (DPP) were studied for their ability to antagonize the contractions produced by prostaglandin E2 (PGE2) on isolated guinea-pig gastric muscles. PPP (100, 200 and 300 micrograms/ml) and DPP (10, 30 60 and 100 micrograms/ml) inhibited reversibly the PGE2-produced excitatory effect in longitudinal fundus and corpus muscles but did not influence the PGE2-produced inhibitory effect in circular muscle strips. In the presence of PPP and DPP the concentration-effect curves for PGE2 were shifted to the right parallel to control curves. The antagonistic action of PPP and DPP appeared to be a specific one since the compounds had little, if any, effect on the responses to histamine, acetylcholine and BaCL2. Analysis of the data (1) showed that DPP is a more potent antagonist than PPP against PGE2 on guinea-pig gastric muscle with pA2 6,1 and 4,8, respectively.