Interactions of cryptosin with mammalian cardiac beta-adrenoceptors

Cryptosin - a new cardenolide from the leaves of Cryptolepis buchanani R & S was found to be a potent positive inotropic agent. In experiments with dog heart ex vivo, the rise in the cardiac rate associated with an increase in dP/dtmax and left ventricular pressure (LVP) correlated with changes in the beta-adrenoceptor densities as measured by the binding of 3H-Dihydroalprenolol (DHA). A significant change in the beta-adrenoceptor densities was observed when cryptosin was incubated with guinea pig and dog heart sarcolemmal membranes in vitro. Analysis of the binding of 3H-DHA in post-cryptosin treated membranes indicated a non-specific type of interaction of cryptosin with mammalian cardiac beta-adrenoceptors.