It has been postulated that sympathetic nervous system reactivity to acutely applied stress is increased with age. Therefore, we investigated the autonomie and hemodynamic adjustments to air jet stress in conscious, freely-moving mature (12-month-old; n=9) and senescent (24-month-old; n=11) male 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 recovery from surgery, pulsatile blood pressure (BP), heart rate (HR), renal blood flow (RBF), and renal sympathetic nerve activity (RNA) were recorded during control conditions and an eight minute continuous air jet application. Renal resistance (RR) and the low (LF, 0.01 - 0.20 Hz) and mid frequency (MF, 0.20-0.50 Hz) power of BP were computed off-line. Air jet induced an increase in BP, HR, RR, RNA, and BP power in the LF and MF ranges in both groups. BP and LF BP power increased less and the elevations in RR and RNA were of shorter duration in senescent compared with mature rats. A significant correlation between the air jet-induced changes in RNA and RR was found for the senescent but not for the mature rats. These data suggest that sympathetic responsiveness to air jet stress is blunted rather than enhanced with increasing age, while the translation from sympathetic activation to hemodynamic effects is improved and may partly compensate for the reduced sympathetic responsiveness.
|State||Published - 1996|