The potentiation of the pressor response to tyramine by amphetamine in the anesthetized dog.

It has been shown that amphetamine enhanced the acute pressor responses to tyramine. This enhancement was observed even after the development of tachyphylaxis to amphetamine. The response to tyramine peripherally in the perfused leg was not enhanced by amphetamine, i.e., the sensitivity to i.a. tyramine was unchanged, while the response of the perfused leg to i.v. tyramine was increased following amphetamine. The enhancement of the response to i.v. tyramine by amphetamine therefore may be due to an increase in the blood levels of active circulating tyramine following its injection. The increase in pressor responses to increased levels of circulating tyramine (result of either increased doses of tyramine or following amphetamine treatment) was shown to be primarily the result of an increase in peripheral resistance rather than an increase in cardiac output.