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

Activation of cardiac sensory receptors with vagal afferents can resul t in inhibition of sympathetic outflow to the peripheral circulation. This study investigated whether the regulation of renal sympathetic ne rve activity (RSNA) during dynamic exercise was modulated by cardiac s ensory receptors. RSNA, blood pressure, and heart rate were measured i n seven New Zealand White rabbits during treadmill exercise while card iac receptors were intact (saline), during cardiac neural block with 2 % procaine (2% PCN), and during cardiac efferent receptor block with m ethscopolamine and atenolol (M + A). Drugs were infused into the peric ardial 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 potent iated RSNA response to exercise at 7 m/min (+/-134 +/- 37%) and 12 m/m in (+234 +/- 45%) relative to saline (+62 +/- 24 and +101 +/- 28%) or M + A (+19 +/- 9 and +52 +/- 19%, P < 0.05). These results suggest tha t cardiac sensory receptors attenuate sympathetic drive to the kidney during dynamic exercise in conscious rabbits.