Effects of isoprenaline and cooling on histamine induced changes of capillary permeability in the rat hindquarter vascular bed.

Histamine infused intra-arterially into artificially perfused, maximally dilated rat hindquarters markedly increased fluid filtration and CFC but had essentially no effect on the diffusion capacity to small molecules. Isoprenaline largely prevented the increase in fluid filtration and CFC if infused prior to the start of the histamine infusion and, if infused after the start of the histamine infusion, promptly reduced fluid filtration and CFC to near control levels. Additionally, it was noted that severe cooling of the perfusate also largely prevented the marked increase in fluid filtration and CFC by histamine. This antagonism of histamine induced increases in macromolecular permeability represents a direct action of isoprenaline on the microvascular membrane which effectively counteracts that of histamine. The data also suggest that the large pores created by histamine are different from the large pore through which macromolecules normally transverse the microvascular membrane, and that catecholamines may exert a regulatory function in the control of microvascular permeability to macromolecules in pathophysiological states associated with massive histamine release.