Afferent pathways in cardiovascular adjustments induced by volume expansion in anesthetized rats

The role of baroreceptors, cardiopulmonary receptors, and renal nerves in t he cardiovascular adjustments to volume expansion (VE) with 4% Ficoll (Phar macia; 1% body wt, 0.4 ml/min) were studied in urethan-anesthetized rats. I n control animals, VE produced a transitory increase in mean arterial press ure (MAP), which peaked at 10 min (17 +/- 4 mmHg) and increases in renal (1 28 +/- 6 and 169 +/- 19% of baseline at 10 and 40 min, respectively) and hi ndlimb vascular conductance (143 +/- 6 and 150 +/- 10%). These cardiovascul ar adjustments to VE were unaffected by bilateral vagotomy. After sinoaorti c denervation, the increase in MAP induced by VE was greater than in contro l rats (30 +/- 4 mmHg). However, renal vasodilation in response to VE was b locked, whereas hindlimb vasodilation was similar to that observed in contr ol rats. After unilateral renal denervation (ipsilateral to flow recording) , the initial renal vasodilation was blocked. However, 40 min after VE, a s ignificant renal vasodilation (125 +/- 4%) appeared. The hindlimb vasodilat ion and MAP responses were unaffected by renal denervation. These results d emonstrate that the baroreceptor afferents are an essential component of ca rdiovascular adjustments to VE, especially in the control of renal vascular conductance. They also suggest that renal vasodilation induced by VE is me diated by neural and hormonal mechanisms.