Effect of Histamine on the Permeability of the Ocular Vessels

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Abstract
Although many endogenous substances are known which promote an increase in capillary permeability, controversy still exists as to the precise mechanism of their action,1-3 it having been variously suggested that the leakage occurs through the endothelial cells themselves, or through the intercellular cement, or through gaps resulting from a reversible separation of the endothelial cell margins. Nor is there agreement about the exact site within the vascular tree at which these permeability changes primarily occur. The recent work of Majno and Palade4 and of Majno, Palade, and Schoefl5 goes far to resolve these problems. By injecting histamine or serotonin into the cremaster muscle of rats, in which colloidal carbon or mercuric sulphide had previously been introduced into the circulation, they demonstrated, by both light and electron microscopy, the site and structural mechanism of the resulting changes in permeability. It was seen that the endothelial cells first partially