Capillary size, density and ultrastructure in brain of rats with urease-induced hyperammonaemia.

The capillary diameter, the capillary area as percentage of brain area, the minimal intercapillary distance, the harmonic mean basement membrane thickness and the mitochondrial content of capillary endothelium were estimated in the striatum of normal rats and after 4 days' urease-induced hyperammonaemia. Electronic image analysis, planimetry and classification with a ruler were the methods used. The capillary diameter was increased after 4 days' hyperammonaemia. The mitochondrial content of capillary endothelium was decreased after hyperammonaemia, while all other parameters were unchanged. Using an inverse logarithmic transformation, the distribution of the basement membrane intercepts was approximately normal. The increased capillary diameter could be a result of vascular paralysis induced by hyperammonaemia. The metabolic working capability is decreased in hyperammonaemia but the diffusion properties across the basement membrane and in the brain parenchyma appear from a morphological point of view to be unchanged.