Arterial baroreceptor reflexes in young and old racing greyhounds

The characteristics of the carotid sinus baroreceptor (CSB) reflex control of arterial pressure-flow relations were studied in young (18 mo) and old (10.5 yr) racing greyhounds anesthetized with chloralose. Pressure and flow were simultaneously measured in the ascending aorta, the celiac, superior mesenteric, renal, and iliac arteries under steady-state conditions of pulsatile perfusion of the isolated carotid sinuses before and after bilateral cervical vagotomy. Operating-point (OP) values of mean pressure were not significantly different between the young or old greyhounds, but OP values of cardiac output were lower and of peripheral resistance were higher in the older animals. OP values of regional resistances were higher in the older animals, but only those of the celiac and mesenteric beds were significantly different. Values of OP sensitivity of central hemodynamic variables were not decreased in the older animals. OP values of renal and iliac resistance sensitivity tended to be lower in the older animals. The overall range of control of the various hemodynamic variables by the CSB was lower in the older group only in the case of iliac resistance. The characteristics of the CSB were not uniformly depressed in the older animals but were relatively well maintained compared with those of the younger group.