RESUMO
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.