Baroreceptor reflex effect on sympathetic nerve activity in stroke-prone spontaneously hypertensive rats

To elucidate the relationship between responses in sympathetic outflow to incremental changes in blood pressure, we performed baroreflex activation experiments in conscious, stroke-prone, spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. We gave incremental bolus injections of nitroprusside and methoxamine and measured mean blood pressure (MAP), heart rate, and splanchnic nerve activity (SpNA). Change in heart rate per change in blood pressure was greater in WKY rats than in SHRSP indicating the decrease in baroreceptor sensitivity displayed in the latter strain. In contrast, change in SpNA per change in blood pressure was greater in SHRSP than in WKY rats. These findings suggest that sympathetic outflow in SHRSP is more reactive to blood pressure changes than in WKY rats. The discordance in heart rate and SpNA changes supports the notion that central neural integration of autonomic function in SHRSP is impaired.