Aging is not accompanied by sympathetic hyperresponsiveness to air-jet stress

It has been postulated that sympathetic nervous system reactivity to acutely applied stress is increased with age. We investigated the autonomic and hemodynamic adjustments to air-jet stress in 9 mature (12-mo-old) and 11 senescent (24-mo-old) Fischer 344 rats. Rats were instrumented with arterial and venous catheters, flow probes around the renal artery, and nerve electrodes on the ipsilateral renal nerve. After the rats recovered from surgery, blood pressure, heart rate, renal blood flow, and renal sympathetic nerve activity were recorded during control conditions and during an 8-min continuous air-jet application. Renal resistance and the low (0.01-0.20 Hz)- and mid-frequency (0.20-0.50 Hz) power of blood pressure were computed off-line. The air jet induced an increase in blood pressure, heart rate, renal resistance, renal nerve activity, and blood pressure power in the low- and mid-frequency ranges in both groups. Blood pressure and low-frequency blood pressure power increased less, and the elevations in renal resistance and renal nerve activity were of shorter duration in senescent compared with mature rats. These data suggest that sympathetic responsiveness to air-jet stress is not enhanced with increasing age.