Mechanism of carotid-occlusion diuresis

In anaesthesized dogs given large doses of ADH and DOC and subjected to acute left renal denervation, urine flow (V) and sodium excretion (UNaV) rose significantly in response to bilateral carotid artery clamping in both the intact (p less than 0.05) and the denervated kidney (p less than 0.001). This was associated with significant (p less than 0.05) increases of the tubular rejection fraction of sodium (TRFNa) while creatinine clearance (Ccr) remained unchanged. Following a second control period, carotid occlusion was repeated, while perfusion pressure in the left kidney was kept constant by aortic constriction. In this case the diuretic and natriuretic response in the right kidney occurred in the same fashion as previously, and no significant change in V, UNaV, or TRFNa was observed in the left kidney. The amount of free water reabsorbed in the collecting duct (TcH2O) was not consistently altered by carotid occlusion. It is concluded that acute renal denervation augments the pressure diuresis that follows carotid occlusion. The failure of carotid polyuria to occur when renal perfusion pressure is kept constant points to the importance of mechanical factors. Still, a wash-out of the medullary osmotic gradient seems to be an unlikely mechanism.