Antagonism of some contractile responses to prostaglandins by cyproheptadine.

In the present study antagonism of the contractile responses to PGE1 and PGF2 alpha, by cyproheptadine on isolated rat stomach strip, rabbit uterus, guinea-pig ileum and rabbit jejunum is documented. Cyproheptadine blocks the responses to PGE1, PGF2 alpha, acetylcholine, 5-hydroxytryptamine in extremely small concentrations varying from 10 ng to 1 microgram/ml. The blockade is persistant, provided the exposure is prolonged. However, it does not antagonise the responses of adrenaline on guinea-pig seminal vesicle. Polyphloretine phosphate was used in the concentration of 2.5 to 100 micrograms/ml on the rat stomach strip, rabbit jejunum and rabbit uterus; it failed to produce any blockade of contractile responses to prostaglandins. It is concluded that cyproheptadine nonspecifically antagonised the responses to acetylcholine, 5-hydroxytryptamine, PGE1 and PGF2 alpha in extremely small concentrations.