CARDIAC SEASONAL VARIATION, A QUALITATIVE CHANGE IN PHARMACOLOGIC RESPONSE TO ETHYLENEDIAMINE

¹ Departments of Pharmacology, Schools of Medicine, Marquette University, Milwaukee, Wisconsin, and University of Michigan, Ann Arbor, Michigan

Ethylenediamine is a unique chemical agent in that it produces a negative inotropic action in isolated perfused turtle hearts during winter months; however, during summer months it manifests a positive inotropic action. Both responses appear to be correlated with the same physical form of ethylenediamine, the monocation. It is possible to convert summer turtle hearts to winter hearts in terms of their response to ethylenediamine by exposing the summer turtles to a cold environment (5°C) for a period of 2 to 3 wk.