Effect of rat atriopeptin III on renal function in dogs during water diuresis and hydropenia

Experiments have been performed in conscious male beagle dogs under maximal water diuresis or hydropenia to determine the effects of synthetic rat atriopeptin III [r-AP III = r-ANF- (103-126)] (Geller et al. 1984), in an intravenous dose of 50 micrograms/kg body weight, on renal function and plasma renin activity. Intravenous injection of r-AP III resulted in an increase in urine and sodium excretion lasting up to 20 minutes, while the glomerular filtration rate and renal plasma flow were hardly influenced under either of the experimental conditions. r-AP III induced an increase in free water clearance from 7.51 +/- 2.45 ml/min in controls to 12.15 +/- 2.25 ml/min in the first clearance period, whereas the free water reabsorption was only slightly reduced (5.56 +/- 1.22 vs. 5.02 +/- 1.23 ml/min). r-AP III caused a slight increase in plasma renin activity from 0.65 +/- 0.46 in controls to 1.02 +/- 0.47 ng X ml-1 X h-1 in water diuretic dogs and from 3.19 +/- 0.51 in controls to 3.72 +/- 0.81 ng X ml-1 X h-1 in hydropenic dogs. These experiments show that the r-AP III-induced salidiuretic response seems not to be mediated by changes in the glomerular filtration rate and renal plasma flow. Moreover, the increase in free water clearance and the absence of change in free water reabsorption indicate a proximal site of action of r-AP III.