The effect of prostaglandin on iridial blood vessel permeability.

Light and electron microscopy is used to examine the effect of exogenous PGE1 on the permeability and reactivity of rat iridial blood vessels. Results show that topical PGE1 causes an increase in the permeability of iridial vessles to carbon particles (200 A diameter). The technique of carbon labelling is used to quantitate increases in permeability caused by varying concentrations of PGE1 (0.001-1.0 mg/ml). Regression analysis shows that there is a linear relationship (P less than 0.02) between carbon labelling and PGE1 concentration over the range of concentrations tested. In other experiments rats were treated with the systemic histamine liberator Compound 48/80, or with topical applications of histamine diphosphate in order to examine the effects of exogenous and endogenous histamine upon iridial blood vessel permeability. These procedures produce only minimal labelling of iridial vessels. It therefore seems likely that PGE1 has a direct effect on iridial vessels and does not act indirectly by bringing about the liberation of endogenous histamine.