Maintenance of carotid baroreflex function in advanced age in the rat.

To evaluate the influence of age per se on the carotid sinus baroreceptors in the absence of hypertension and atherosclerosis, we employed the Fischer 344 rat model. In 14 adult (A, 6-9 mo) and 9 senescent (S, 24-26 mo) normotensive male Fischer 344 rats the left carotid sinus region was vascularly isolated with sinus nerve intact and perfused with oxygenated modified Kreb's solution. Simultaneous measurements of intrasinus pressure and femoral arterial pressure response were obtained during linear pressure increases (20-200 mmHg) in the vascularly isolated sinus. There was no age difference in base-line arterial pressure or heart rate. Both age groups demonstrated similar positive relations between basal femoral arterial pressure and the magnitude of the femoral pressure response to equivalent carotid sinus pressures. There were similar estimated sinus volumes at onset of systemic response (39 +/- 1, A; 39 +/- 1 microliter, S), time to initial systemic pressure response (9 +/- 1, A; 7 +/- 1 s, S), mean rates of femoral pressure decline (1.8 +/- 0.3, A; 2.1 +/- 0.3 mmHg/s, S), and return to base line (1.5 +/- 0.3, A; 1.4 +/- 0.3 mmHg/s, S) as well as magnitudes of systolic (25 +/- 3, A; 26 +/- 4 mmHg, S) and diastolic (21 +/- 2 A; 22 +/- 4 mmHg, S) pressure drops. Thus, in the Fischer 344 rat model of aging, which differs from the human in that it is not complicated by hypertension or atherosclerosis, carotid sinus baroreflex function appears to be well maintained in senescence.