Atrial peptide potentiates renal responses to volume expansion in conscious dogs

Experiments were performed to compare the renal responses to atrial peptide infusion in conscious dogs with normal and expanded extracellular fluid volumes to test the hypothesis that the renal responses to atrial peptide infusions are dependent on the prevailing fluid and electrolyte status in the animal. Atrial peptide-(99-126) was infused intravenously in doses of either 0, 5, 25, or 100 ng.kg-1.min-1 in conscious dogs prepared with chronic catheters in the femoral artery and vein and the urinary bladder. In dogs with normal extracellular fluid volume, atrial peptide caused small increases in urinary sodium excretion with the high physiological (25 ng.kg-1.min-1) and pharmacological (100 ng.kg-1.min-1) doses. Urine volume and potassium excretion were increased only at the highest pharmacological dose. In contrast, atrial peptide infusion in dogs that were volume expanded by infusion of hypertonic saline showed dramatic, dose-dependent increases in sodium excretion and urine flow with all doses tested. The low, physiological dose of atrial peptide (5 ng.kg-1.min-1) increased sodium excretion and urine flow rate in volume-expanded dogs more than the pharmacological dose in normal dogs (n = 4). These results demonstrate that the renal responses to atrial peptide infusion are potentiated in dogs that are volume expanded and suggest that under conditions where atrial peptide secretion would be enhanced, small changes in plasma atrial peptide concentration can have significant effects on renal function.