Effects of a synthetic atrial natriuretic polypeptide on intrarenal hemodynamics in dogs

The effects of a synthetic human atrial natriuretic polypeptide (alpha-hANP) on the intrarenal distribution of blood flow were examined in anesthetized dogs. Intrarenal infusion of alpha-hANP at a rate of 0.05 microgram/kg per min resulted in a significant increase in renal blood flow, urine flow and urinary excretion of sodium with no change in renal perfusion pressure. Measurement of the intrarenal blood flow by the microsphere method indicated a greater increase in flow rate in the juxtamedullary than in the superficial area. A significant correlation was observed during alpha-hANP infusion between changes in both urine flow and sodium excretion and inner cortical blood flow; changes in inner cortical blood flow may reflect changes in medullary blood flow. However, a smaller dose of alpha-hANP (0.01 microgram/kg per min) increased urine flow and electrolyte excretion but had no effect on the distribution of renal blood flow. Thus, neither the increased inner cortical blood flow nor the redistribution of blood flow is the sole cause of the natriuresis during infusion of alpha-hANP. Changes in intrarenal hemodynamics could contribute to the natriuresis induced by alpha-hANP, via washout of medullary solutes.