ANTAGONISM OF RESERPINE-INDUCED SUBSENSITIVITY TO TYRAMINE BY METHYLDOPA

¹ Department of Pharmacology, McGill University, Montreal, Canada

The cardiovascular actions of tyramine in spinal cats and its inotropic action on the cat isolated papillary muscle were tested following methyldopa, reserpine, and reserpine injected after methyldopa. It was found that reserpine reduced the pressor and inotropic effects of tyramine and stellate ganglion stimulation in spinal cats and the inotropic actions of tyramine and butyrylcholine on the papillary muscle, whereas methyldopa did not inhibit these responses. However, in cats pretreated with methyldopa, reserpine did not reduce the actions of tyramine.

As the effects of stellate ganglion stimulation and butyrylcholine were inhibited when reserpine had been injected after methyldopa, it is concluded that methyldopa did not interfere with the release of endogenous catecholamine by reserpine. On the basis of these results, the cause of the subsensitivity to tyramine following reserpine is suggested to be an antagonism between reserpine and tyramine at the receptor level.