Hemodynamic Response Variability in Dahl Salt‐Sensitive‐mcw and Brown‐Norway‐mcw Rats Following Acute and Chronic Stress

We have identified differences in hemodynamic response patterns to both an acute pharmacological stressor, cocaine, and an acute behavioral stressor, startle with cold water, in two unrelated strains of rats. Following cocaine administration (5 mg/kg, i.v.), Dahl salt‐sensitive‐mcw (DSS) rats have an increase in arterial pressure (AP) that is entirely due to an increase in cardiac output (CO). We named these rats cardiac responders. Brown‐Norway‐mcw (BN) rats have a similar peak increase in AP following cocaine that is due entirely to an increase in systemic vascular resistance (SVR). We call these rats vascular responders. Likewise, startling rats with cold water (1 cm deep) elicited a pressor response due to an increase in CO in DSS rats and an increase in SVR in BN rats. Since vascular responders (human or rat) have been shown to have an increased risk for developing hypertension, we examined the hemodynamic responses of each strain to chronic pharmacological or behavioral stress. We subjected DSS and BN rats to 10 days of either repeated binge cocaine administration or a behavioral stress paradigm consisting of 1 hr of restraint and 1 hr of resident‐intruder stress each day, and monitored changes in AP. BN rats had greater increases in AP over the 10‐day stress period in response to both types of stressors than did DSS rats. We propose that genetic differences in central neurochemicals are responsible for producing the hemodynamic response variability. This work was supported by grants from the USPHS DA13256 and GM008306.