CAPILLARY PERFUSION DURING INCOMPLETE FOREBRAIN ISCHEMIA AND REPERFUSION IN RAT-BRAIN

Previous studies have shown a complete plasma perfusion of all capilla ries in the rat brain under normal physiological conditions. This rais es the question under which experimental conditions nonperfused capill aries may show up in the brain. Two experimental models were investiga ted in rats. 1) Reduced cerebral blood flow (CBF) during incomplete fo rebrain ischemia: hemorrhagic hypotension was maintained for 30 min at a mean arterial blood pressure of 41 mmHg. During the final 5 min of hypotension both carotid arteries were ligated. 2) Reperfusion after i ncomplete forebrain ischemia: reperfusion lasted for 4 h after either 15 or 30 min of incomplete forebrain ischemia. Under both experimental conditions, the density of the existing as well as the plasma-perfuse d brain capillary network was quantified using fluorescent double stai ning. Local CBF was measured during incomplete forebrain ischemia usin g the quantitative autoradiographic 4-iodo-[N-methyl-C-14]antipyrine t echnique. The results showed a decrease in CBF during incomplete foreb rain ischemia, which amounted up to 94%. Whereas normotensive control animals showed a complete staining of all capillaries within 5 s after the intravenous injection of Evans blue, this period of time was incr eased to 10 s during incomplete forebrain ischemia, indicating a delay ed capillary perfusion. Four hours of reperfusion after 15 min of inco mplete forebrain ischemia resulted in a complete capillary staining, w hereas reperfusion after 30 min of ischemia was followed by intracereb ral bleedings and a few nonperfused capillary areas (circulation time of Evans blue: 10 s). The data show 1) during incomplete forebrain isc hemia, which was verified by a drastic reduction of CBF, all brain cap illaries investigated remained perfused with plasma, although at a low ered velocity; 2) during reperfusion occasional perfusion deficits sho wed up.