CHRONIC STRESS INDUCES SENSITIZATION IN SYMPATHOADRENAL RESPONSES TO STRESS IN BORDERLINE HYPERTENSIVE RATS

The effects of acute foot shock on cardiovascular and sympathoadrenal responses were investigated in chronically stressed borderline hyperte nsive rats (BHR) and Wistar-Kyoto (WKY) rats. Male BHRs were divided i nto two groups; the maturation group (Mat) was not stressed, whereas t he chronic stress group (AJS) received 8 wk (5 days/wk, 30 min/day) of air-jet stress coupled with immobilization. After chronic stress, the rats were cannulated in the femoral artery and jugular vein. Resting mean arterial pressure (MAP), heart rate (HR), and plasma norepinephri ne (NE) levels were higher in the AJS group. In contrast, chronic stre ss failed to increase basal arterial pressure or HR in WKY rats. In re sponse to acute foot shock, the Mat group had higher MAP increases, at which they plateaued, whereas the AJS rats displayed a progressive de cline in MAP. This was associated with higher plasma NE and epinephrin e levels but a smaller increase in adrenocorticotropic hormone in AJS versus Mat rats. This hyperactivity in the sympathoadrenal system of c hronically stressed BHRs may, in part, account for their mild hyperten sion.