CARDIAC RECEPTORS MODULATE THE RENAL SYMPATHETIC RESPONSE TO DYNAMIC EXERCISE IN RABBITS

Activation of cardiac sensory receptors with vagal afferents can result in inhibition of sympathetic outflow to the peripheral circulation. This study investigated whether the regulation of renal sympathetic nerve activity (RSNA) during dynamic exercise was modulated by cardiac sensory receptors. RSNA, blood pressure, and heart rate were measured in seven New Zealand White rabbits during treadmill exercise while cardiac receptors were intact (saline), during cardiac neural block with 2% procaine (2% PCN), and during cardiac efferent receptor block with methscopolamine and atenolol (M + A). Drugs were infused into the pericardial space via a chronic catheter. Two exercise protocols were used: 7 m/min (5 min) and 12 m/min (2 min) at 0% grade. The increases in HR during exercise at 7 and 12 m/min were attenuated with 2% PCN or M + A. At 12 m/min, blood pressure was significantly lower with 2% PCN (76 +/- 4 mmHg) or M + A (76 +/- 3 mmHg) than with saline (86 +/- 2 mmHg). Abolition of cardiac afferent input with 2% PCN resulted in a potentiated RSNA response to exercise at 7 m/min (+/-134 +/- 37%) and 12 m/min (+234 +/- 45%) relative to saline (+62 +/- 24 and +101 +/- 28%) or M + A (+19 +/- 9 and +52 +/- 19%, P < 0.05). These results suggest that cardiac sensory receptors attenuate sympathetic drive to the kidney during dynamic exercise in conscious rabbits.