Capillary perfusion in the brain.

The density of the total and the perfused capillary network was determined in the brains of awake, normocapnic rats. Perfused capillaries were marked by i.v. Evans blue. Existing capillaries were made visible by antibodies directed against the fibronectin portion of the capillary walls. Comparison of perfused and existing capillaries in identical brain sections by double staining showed a high degree of congruence between perfused and existing brain capillaries. The results show a continuous perfusion of all capillaries in the brain of the awake normocapnic rat. In the second group of experiments capillary perfusion was investigated during a reduction of cerebral blood flow induced by incomplete forebrain ischaemia. These experiments showed a gross preservation of capillary flow in the brain capillaries, although the velocity of perfusion was reduced. Finally, a method was developed which allows the distribution pattern of brain capillary plasma flow to be examined. The third group of experiments which used this method indicates a heterogeneous distribution of capillary flow in the brain under normocapnic conditions and a reduction of heterogeneity during hypocapnic hyperaemia.