Capillary size and density in the cerebral cortex of rats with a porto-caval anastomosis.

Morphometric investigation by automatic image analysis of alkaline phosphatase positive brain capillaries was performed in control rats and in rats with a 30 days old porto-caval anastomosis. Rats with a porto-caval anastomosis showed an increased capillary diameter Di and as a consequence of this a decreased capillary surface-to-volume ratio Si/Vi. The free capillary distance was increased and the capillary length per unit brain volume LVi was decreased in the shunted rats compared to the controls. There was no difference in the percentage of the projected capillary area AAi% between the two groups. It is suggested that the dilatation of the capillaries in rats with a porto-caval anastomosis is caused by the altered haemodynamic properteries with a low mean blood pressure although the cardiac output is increased and that the alteration in free capillary distance and length per unit brain volume LVi is caused by dispersion by cortical edema induced by the porto-caval anastomosis.