Abstract
The effects of secretin vasodilation on peritubular capillary Starling forces and absolute proximal reabsorption were examined in the rat. Secretin was infused at 75 mU/kg per min into the aorta above the left renal artery. Efferent plasma flow increased from 125 +/- 28 to 230 +/- 40 nl/min with secretin infusion. Single nephron filtration rate (44 +/- 6 vs. 44 +/- 7 nl/min) and absolute proximal reabsorption (21 +/- 5 vs. 21 +/- 4 nl/min) were not significantly changed. Peritubular capillary and interstitial hydrostatic pressures increased with secretin infusions (from 9 +/- 0.4 to 15 +/- 0.7 mmHg and from 3 +/- 0.2 to 4 +/- 0.2 mmHg, respectively). Both peritubular capillary and interstitial oncotic pressures decreased (from 25 +/- 2 to 20 +/- 2 mmHg and from 10 +/- 1 to 4 +/- 1 mmHg, respectively) during secretin infusion. The net reabsorption pressure for peritubular capillary uptake significantly decreased from 9 +/- 2 to 5 +/- 2 mmHg and the coefficient of reabsorption increased from 3 +/- 1 to 6 +/- 2 nl/min per mmHg. We conclude that although secretin causes a vasodilation and decreases net reabsorption pressure, absolute proximal reabsorption is unchanged. Peritubular capillary uptake is maintained, and since net reabsorption pressure is decreased, the coefficient of reabsorption is increased.