Preferential Blockade of Pre-Synaptic Alpha-Adrenoceptors on the Rat Isolated Vas Deferens by Cryptolepine, 7: Studies on Cryptolepine

Abstract

The twitch response of the rat isolated vas deferens to electrical field stimulation, (1 to 10 Hz, 1 to 2 m. sec.), reduced by noradrenaline (1 to 2 µg ml^-1) was further enhanced by cryptolepine (5 to 10 µg ml^-1). Cryptolepine (0.1 to 0.2 µg ml^-1) antagonised the inhibition of the twitch produced by clonidine (1 to 2 ng ml^-1) but did not antagonise the phenylephrine effect. Cryptolepine (1 to 2 µg ml^-1) inhibited the potentiation of the twitch response and contraction of the muscle produced by phenylephrine (0.3 µg ml^-1). Potentiation of the twitch produced by cocaine (1 to 5 µg ml^-1) was also enhanced by Cryptolepine (1 to 2 µg ml^-1).

The results demonstrated by the difference in the concentration of Cryptolepine required to block pre-and post-junctional α-adrenoceptor effects of clonidine and phenylephrine suggest that cryptolepine has preferential presynaptic α-adrenoceptor blokking action.

Key Word Index

Cryptolepis sanquinolenta - Asclepiadaceae - Alkaloids - Alpha-Adrenoceptors