CHANGES IN TISSUE BLOOD-FLOW AND SYMPATHETIC ACTIVITIES TO VARIOUS ORGANS DURING PROLONGED HEMORRHAGIC HYPOTENSION IN MONKEYS

This experiment was designed to determine whether prolonged hemorrhagi c hypotension in anesthetized monkeys produces differential control of tissue blood flow and sympathetic nerve activities to various organs (heart, kidney, liver, spleen, and hind-limb). We performed simultaneo us multifiber recording of sympathetic nerve activity to the kidney (R NA), heart (CNA), spleen (SpNA), liver (HNA), and hind-limb (LNA) duri ng sustained hemorrhagic hypotension at a mean blood pressure of 40 mm Hg for 2 h. Immediately after bleeding, all of the sympathetic nerve a ctivities increased significantly (Stage I) and then gradually decreas ed towards the prebleeding levels (Stage II). Thereafter, the secondar y sympathetic excitation was observed (Stage III), followed by a gradu al decrease in sympathetic activities below the prebleeding levels (St age IV). The shed blood started to return to the animals at this final stage. Time course of changes in sympathetic nerve activities did not differ among organs innervated. However, tissue blood flow of the ren al cortex, liver, skeletal muscle and spleen significantly decreased a t Stage I and remained at low levels until the end of the experimental period. In contrast, blood flow of the renal medulla and heart was pr eserved until Stage In and Stage TV, respectively. These results indic ate that although the sympathetic response to prolonged hemorrhagic hy potension of 40 mmHg did not differ among organs, changes in tissue bl ood flow were variable and blood flow to the heart and renal medulla w as maintained at a steady level until a late stage of hemorrhage.