Differential effects of histamine on protein permeability in dog lung and forelimb

In this study, the effects of histamine on the microvascular permeability of a canine, isolated perfused left lower lung lobe (LLL) and a forelimb preparation were evaluated by comparing the apparent filtered volumes (VF) calculated from the increases in hematocrit (Hct) and plasma protein concentration (Pr) observed during filtration. In the LLL and forelimb, the elevation of venous pressure (Pv) to 15.5 Torr resulted in a ratio of filtered volumes (VF,Pr/VF,Hct) of 0.97 and 0.99, respectively. In the LLL, histamine administration did not significantly change this ratio, whereas the addition of methylene blue decreased it to 0.62. In the forelimb, histamine transiently decreased VF,Pr/VF,Hct to 0.23. After recovery, the elevation of Pv to cause further filtration resulted in a ratio of 0.94. These data suggest that intrinsic differences in the regulation of microvascular permeability exist between blood vessels of the lung and forelimb, in that a histamine dose that significantly increased the protein permeability of the forelimb had no measurable effect on the LLL.