Capillary and Cellular Permeability to Some Compounds Related to Antipyrine

Abstract

The permeability of the capillaries in the isolated, blood-perfused hindleg of the cat to a series of derivs. of 5-pyrazolone, including antipyrine and aminopyrine, and to urea was studied by the method of osmotic transients. Measurements were made at 8-36[degree]. Permeability to the test compounds was found to be directly related to their lipid-solubilities. No effect of chemical structure was apparent, except as it influenced lipid-solubility; and molecular wt. affected permeability only for the least lipid-soluble compounds. The rate at which these substances penetrated into the cells of the perfused tissues was also found to be dependent on their lipid-solubilities. At low temps. capillary permeability to the more lipid-soluble derivs. of 5-pyrazolone was found to be decreased to a much greater extent than capillary permeability to the lipid-insoluble substance urea. These observations are discussed in relation to the hypothesis that there are 2 routes by which molecules may penetrate the capillary endothelium: a system of discrete pores, penetration through which is restricted only by molecular dimensions, and the lipoid membranes of the endothelial cells, which provide an additional pathway for lipid-soluble molecules. The properties of the endothelial cell membranes are shown to be in accord with the well-known lipoid-film hypothesis of cell membrane structure.