Pressure diuresis and autonomic function in conscious dogs

Pressure diuresis is thought to be a major long-term regulator of arterial blood pressure (AP). Previously, pressure diuresis has been characterized using pharmacological or surgical blockade of other mechanisms known to affect renal function. This study evaluated pressure diuresis in conscious dogs with minimal experimental interference. Dogs were chronically instrumented under pentobarbital anesthesia with aortic and urinary bladder catheters. AP was increased by 10% in resting dogs by exposure to increased light and sound intensity (arousal) for 90 min. During arousal, urine flow (UV) and Na+ excretion (UNa+ V) correlated with AP (UV vs. AP, r = 0.12, P less than 0.05; UNa+ V vs. AP, r = 0.19, P less than 0.005; 17 trials in 7 dogs). Arousal did not affect the plasma concentration of atrial natriuretic factor, suggesting that this hormone did not contribute to the correlations between UV or UNa+ V and AP. Because arousal may induce an autonomically mediated antidiuresis, studies were repeated during autonomic ganglionic blockade with hexamethonium. During autonomic blockade, the correlations between UV or UNa+ V and AP were increased (UV vs. AP, r = 0.72; UNa+ V vs. AP, r = 0.72, P less than 0.001; 6 trials in 4 dogs). We conclude that the effect of pressure diuresis on UV and UNa+ V can be detected in the intact animal, during normal operation of all the mechanisms that control renal function. Furthermore, when autonomic reflexes are blocked, the pressure-diuresis mechanism is a major determinant of UV and UNa+ V.