Increased capillary hydraulic conductivity induced by atrial natriuretic peptide

The small molecular weight peptide, atrial natriuretic peptide (ANP), produces marked sodium and water excretion. The peptide, extracted from several species of vertebrate heart, also has been shown to increase glomerular filtration and reduce plasma volume. Several mechanisms have been proposed to account for the action of the peptide but remain undefined. In the present report, the ANP-induced alterations in transcapillary water movement were directly assessed. The modified Landis technique was used to measure single capillary hydraulic conductivity (Lp) of vessels from the frog mesenteric circulation. In 6 individual microvessels, Lp was measured under control conditions and again during perfusion with 10 X 10(-6) M ANP. The Lp increased in each vessel by a mean of 3.79-fold (+/- 2.09 SD). In 4 of these vessels, an additional measurement of Lp was repeated under control conditions; the capillary filtration coefficient returned to control levels. It was concluded that ANP directly and reversibly elevates capillary hydraulic conductivity; this response is independent of changes in capillary hydrostatic pressure or surface area.