Reactivity of the cerebrocortical vasculature and energy metabolism to direct cortical stimulation in haemorrhagic shock.

Direct electrical stimulation of the cerebral cortex was used to determine the changes of cortical carbohydrate and oxidative metabolism and of vascular reactivity during haemorrhagic shock. The results were as follows. 1. Electrical stimulation of the brain cortex applied in the control period led to a marked vasodilation and NAD reduction that was preceded in part of the experiments by a transient NADH oxidation. It is suggested that the increase in cortical NADH fluorescence observed during direct stimulation is due to the fact that the rate of cytoplasmic NADH production exceeded the rate of mitochondrial NADH oxidation and of the rate of H+-transport from the cytoplasm into the mitochondria. 2. The cerebrocortical vascular and NAD/NADH redox state responses induced by electrical stimulation changed in the early hypovolaemic phase of shock. At this time, electrical stimulation of the brain cortex led to NADH oxidation in the majority of the experiments or in some experiments, the stimulation did not bring about changes in the redox state of the cortex. The total loss of the reactivity to direct stimulation of the cerebrocortical vessels and of energy metabolism preceded the occurrence of cortical ischaemia during the hypovolaemic phase of shock. 3. Since after reinfusion of the shed blood, redox state and vasculature remained unresponsive to stimulation even in those experiments in which the cortical ischaemia improved, it is concluded that the carbohydrate and oxidative metabolism of the brain cortex were already irreversibly damaged in the early phase of hypovolaemic shock.