Interaction between mental stress and baroreceptor control of heart rate and sympathetic activity in conscious spontaneously hypertensive (SHR) and normotensive (WKY) rats.

Spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY) were compared with regard to the interaction between cortico-hypothalamic alerting responses and the baroreflex influences on neurogenic cardiovascular control. Baroreceptor sensitivity was assessed as heart rate (HR) and renal sympathetic nerve activity (RSNA) reduction per mmHg mean arterial pressure (MAP) increase by phenylephrine infusion. Response to 'mental stress' was studied. Addition of 'mental stress' during baroreceptor activation (30 mmHg MAP increase) was also performed. RSNA was higher in SHR than in WKY during rest and increased more during stress. Baroreflex sensitivity was reduced in SHR compared with WKY concerning HR (0.44 +/- 0.06 versus 0.78 +/- 0.08%/mmHg). Percentage RSNA reduction was similar, while RSNA reduction appeared greater in SHR in comparison with WKY (0.10 +/- 0.02 and 0.06 +/- 0.01 microV/mmHg, P less than 0.12). During baroreflex activation 'mental stress' increased both HR (+24 +/- 7%) and RSNA (+114 +/- 21%) in SHR with almost no changes in WKY. The results suggest an increased cortico-hypothalamic activity in SHR, which is clearly augmented during 'mental stress' and readily overcomes baroreflex inhibitory influences on sympathetic activity.