PRESSOR RESPONSES TO AMPHETAMINE IN THE SPINAL CAT AND ITS INFLUENCE ON TACHYPHYLAXIS TO TYRAMINE

¹ Department of Pharmacology, College of Medicine, Howard University, Washington, D. C.

Studies of the development of tachyphylaxis to amphetamine in spinal cats have shown that tachyphylaxis was developed rapidly, and was not accompanied by any change in cardiac catecholamine levels. The tachyphylaxis was specific, and could not be "crossed over" to tyramine. Amphetamine hastened the development of tachyphylaxis to tyramine. The development of tachyphylaxis to amphetamine was not altered by injections of tyramine. The rate of fall in specific activity of myocardial norepinephrine after administration of labeled catecholamine did not change in animals treated with successive doses of amphetamine, but increased in animals treated with tyramine. Amphetamine prevented the "escape" from tachyphylaxis to tyramine without influencing the tyramine-induced release of catecholamine from the heart. The mechanism of tachyphylaxis to amphetamine appears to differ from that to tyramine.