Effects of temperature on the wall strength and compliance of frog mesenteric microvessels

In single perfused mesenteric microvessels of pithed frogs, we assessed wall strength from the critical pressure, PB, which has to be applied within the vessel in order to induce openings in the walls through which fluid and cells can extravasate. PB was determined in capillaries and venules of tissues at 12-20 The P(B) (mean +/- S.E.M.) in 22 vessels between 12 and 20 degrees C, P(B) was 92.0 +/- 7.40 cm H2O which was significantly higher than at room temperatures (P<0.001). The compliance of the vessel wall was estimated using both the red cell method and the oil meniscus technique. There was no measurable effect of temperature on wall compliance. The compliance of vessels from which the cells had been removed by previous perfusion with detergent solutions was very similar to that of intact vessels between 12 and 20 degrees C and between 0 and 5 degrees C. The negligible effects of temperature upon compliance suggest that microvessel walls have to be distended to a greater extent in cold tissue before P(B) is reached. This, together with their rapid closure, is consistent with the hypothesis that pressure-induced openings in microvascular walls are dependent on an active response of the endothelium rather than being the result of stress failure of the basement membrane.