Effects of arterial hypotension on brain metabolism in normotensive and spontaneously hypertensive rats.

The effects of graded systemic hypotension induced by the combination of bleeding and trimethaphan camsylate infusion on brain metabolism were studied in normotensive rats (NTR) and spontaneously hypertensive rats (SHR). Metabolites such as lactate, pyruvate and adenosine triphosphate (ATP) of the brain frozen in situ were measured at the end of 1 hour of hypotension. In SHR, either cerebral lactate or the lactate/pyruvate (L/P) ratio increased rapidly and progressively with a concomitant decrease in ATP, when mean arterial blood pressure (MAP) fell below about 50 mm Hg. In NTR, on the other hand, the metabolites changed little until MAP fell to about 40 mm Hg. Metabolic derangements of the brain during profound hypotension were more marked and severe in SHR than in NTR. These results suggest that the SHR is more vulnerable to severe hypotension than NTR, probably due to hemodynamic difference of the cerebral circulation between the 2 groups. The increased cerebral vascular resistance and upward shift of cerebral autoregulation in hypertension might be responsible for this vulnerability.