Lead-induced permeability changes in immature vessels of the developing cerebellar microcirculation.

The ultrastructure and microcirculatory permeability changes of lead encephalopathy were studied in an animal model using horseradish peroxidase as an intravascular tracer. The fine structure of capillary sprouts in the developing cerebellar microcirculation of lead-poisoned rats were described. Immature vessels, characterized by the presence of endothelial sprouts, were found to have focal areas of endothelial injury with degenerating endothelial cells. These disruptions of the microcirculatory endothelium had tracer extending from the vessel lumen to the surrounding neuropil. The degenerating endothelial cells were found as early as 24-28 h after the first administration of lead acetate by gastric lavage (2-3-day-old rats). The early injury to endothelial cells of immature vessels in the developing microcirculation is suggested as an important component of the vascular permeability changes which characterize lead encephalopathy. Older animals (5-10 days old) had microaneurysmal vascular dilatations which had a complex internal structure formed by endothelial cells. These microaneurysmally dilated vessels may represent an endothelial response to preceding endothelial injury of immature vessels.