CEREBROCORTICAL AND MEDULLARY BLOOD-FLOW CHANGES AFTER GENERAL OPIATERECEPTOR BLOCKADE DURING HEMORRHAGIC-SHOCK IN CATS

The effect of centrally induced opiate receptor blockade on regional c erebral blood flow (rCBF) was studied in anesthetized, ventilated cats during the course of hemorrhagic shock. The blood flow of the medulla and the parietal cortex was measured with the H-2-gas clearance techn ique. Hemorrhagic shock was produced by lowering the systemic mean art erial pressure to 60 mmHg for 120 min by blood withdrawal. Central opi ate receptor blockade was induced by 10 mu g/kg intracerebroventricula rly (i.c.v.) injected naloxone at the 60th min of the bleeding period. Cortical blood flow showed no improvement after i.c.v. naloxone admin istration. Medullary blood flow, however, increased significantly and approached the pre-bleeding control flow values following central opia te receptor blockade. The results indicate involvement of endogenous o pioid mechanisms in the regulation of rCBF during hemorrhage and may p rovide an explanation for the previously described beneficial effects of naloxone in hemorrhagic shock.