1994 Volume 58 Issue 2 Pages 136-142
Effects of α-human atrial natriuretic polypeptide (α-hANP) on renal function were studied in anesthetized dogs and isolated perfused rat kidneys. Two doses of α-hANP were used to determine whether renal hemodynamics or tubular reabsorption is tha major factor in the diuretic action of α hANP. The excretion rates of sodium (Na) and inorganic phosphate (PO4) were evaluated to determine the site of diuretic action in the renal tubule. In dogs that received the smaller dose of α-hANP (5 ng.kg-1.min-1) infused into the renal arteries without changes in systemic or renal hemodynamics, urine volume (UV) and urinary Na excretion (UNaV) increased significantly. Fractional excretion of Na (FENa) was increased, while fractional excretion of PO4 (FEpo4) was unchanged, following the infusion of α-hANP. The calculated fractional Na reabsorption in the distal tubule (DTRNa) during the infusion of α-hANP was significantly suppressed. In dogs that received the a larger dose of α-hANP (50 ng.kg-1.min-1), the glomerular filtration rate (GFR), UV, and FENa were increased and DTRNa was decreased. In isolated rat kidneys perfused at a constant pressure, a lower concentration of α-hANP (0.5 ng.ml-1) in the perfusate caused diuresis and increased Na and PO4 excretion without any renal hemodynamic alterations. A higher concentration of α-hANP (5 ng.ml-1) increased GFR, Na and PO4 excretion. Since PO4 reabsorption is believed to occur primarily in the renal proximal tubule, these findings suggest that the diuretic action of α-hANP in smaller doses is induced by direct action on renal distal nephron. However, the site of action of α-hANP in larger doses was not determined in the renal tubule because GFR and FEPO4 increased and DTRNa decreased following infusion of α-hANP.
