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 hypertensive rats (BHR) and Wistar-Kyoto (WKY) rats. Male BHRs were divided into two groups; the maturation group (Mat) was not stressed, whereas the 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 norepinephrine (NE) levels were higher in the AJS group. In contrast, chronic stress failed to increase basal arterial pressure or HR in WKY rats. In response to acute foot shock, the Mat group had higher MAP increases, at which they plateaued, whereas the AJS rats displayed a progressive decline in MAP. This was associated with higher plasma NE and epinephrine levels but a smaller increase in adrenocorticotropic hormone in AJS versus Mat rats. This hyperactivity in the sympathoadrenal system of chronically stressed BHRs may, in part, account for their mild hypertension.