VASCULAR ENDOTHELIAL GROWTH-FACTOR INCREASES HYDRAULIC CONDUCTIVITY OF ISOLATED-PERFUSED MICROVESSELS

These experiments report the first direct measurement of microvessel p ermeability coefficients after exposure to vascular endothelial growth factor (VEGF). The Landis technique was extended to enable measuremen t of the resistance of the microvessel wall to water flow, hydraulic c onductivity (L(p)), on the same microvessel in the frog mesentery duri ng the initial exposure to VEGF (acute) and 24 and 72 h after initial exposure (chronic). Control measurements of L(p) showed no change eith er acutely or chronically. Exposure to 1 nM VEGF rapidly and transient ly increased microvessel L(p) within 30 s (to 7.8-fold greater than ba seline values) and returned to control within 2 min. The baseline L(p) was fivefold greater after 24 h than the initial baseline as a result of VEGF perfusion and returned to its original value after 72 h. Thes e experiments confirm the hypothesis that VEGF acts both acutely (over a period of a few minutes) and chronically (over a few hours) to incr ease microvascular permeability.