Depressed baroreflex control of renal nerve activity in conscious WHHL rabbits

The baroreflex control of heart rate and renal nerve activity were examined in conscious Watanabe heritable hyperlipidaemic (WHHL) rabbits. Normal Japanese white rabbits were used as controls. The concentrations of serum cholesterol and triglyceride in WHHL rabbits were ten times higher than those in normal rabbits. The basal values of mean arterial pressure, pulse pressure and heart rate in WHHL rabbits were significantly higher than those in normal rabbits. Baroreceptors were stimulated or unloaded by raising or lowering arterial pressure with injections of phenylephrine or glyceryl trinitrate respectively. The peak changes in heart rate and renal nerve activity were plotted against the peak changes in mean arterial pressure, and a logistic function curve was fitted to the relationships between mean arterial pressure and heart rate, or mean arterial pressure and renal nerve activity. The slopes of both heart rate and renal nerve activity declined in WHHL rabbits. The response of renal nerve activity to acute volume expansion (10 ml.kg-1) with isotonic iso-oncotic dextran was further examined. In the normal rabbit, volume expansion caused renal nerve activity to decrease by 60 +/- 5%, while mean arterial pressure did not change. In the WHHL rabbit the decrease in renal nerve activity caused by volume expansion was significantly attenuated (42 +/- 3%). These results indicate that both sino-aortic and cardiopulmonary baroreceptor mediated changes in renal nerve activity were impaired in the WHHL rabbit.