STRESS AND COCAINE ELICIT SIMILAR CARDIAC-OUTPUT RESPONSES IN INDIVIDUAL RATS

Cocaine use and behavioral stress elicit variable cardiovascular respo nses in individuals. In the present study, we examined the effects of cocaine or stress on arterial pressure, heart rate, and cardiac output in conscious rats. Rats were instrumented for determination of ascend ing aortic blood flow as an index of cardiac output using pulsed Doppl er flowmetry. Cocaine administration elicited consistent decreases in cardiac output in some rats, whereas others had increases. In contrast , the pressor and heart rate responses were similar in these two group s of animals. Air jet stress also elicited a decrease in cardiac outpu t only in a subset of conscious rats, yet produced equivalent pressor responses in all rats. Cardiac output responses to cocaine and air jet stress were closely correlated in individual rats, indicating that th ese stimuli evoke similar hemodynamic responses in individual rats. Th ese observations suggest that the rat may provide a model for understa nding differential cardiovascular sensitivity to cocaine and/or stress in humans.