A system has been developed for performing 31P-n.m.r. studies on cerebral tissues superfused in vitro, and gives results comparable with those reported from studies in vivo. Under optimal superfusion conditions [10 mM-
glucose and O2/CO2 (19:1)] the tissue concentrations of
phosphocreatine and
ATP were calculated to be approx. 3.1 and 1.3 mumol/g respectively. When the
glucose of the superfusing medium was lowered to 0.5 mM, slightly decreased
sugar phosphate peaks were observed, but there was no detectable change in [
ATP] or [
phosphocreatine]. At 0.2 mM-
glucose, significantly decreased concentrations of
phosphocreatine and
ATP were observed. Substitution of
pyruvate plus
malate for
glucose did not decrease levels of
phosphocreatine and
ATP. When the superfusing medium was gassed with air/CO2 (19:1; 'mild
hypoxia'), there was an appreciable fall in
sugar phosphates and
phosphocreatine with no detectable effect on
ATP. In the presence of N2/CO2 (19:1; 'severe
hypoxia', since O2 was not completely excluded), concentrations of
phosphocreatine fell considerably, but with little effect on
ATP. The results demonstrate the feasibility of studying cerebral energy metabolism in vitro using the non-invasive 31P-n.m.r. technique and are discussed in relation to the sensitivity of cerebral tissues to metabolic insults in vitro and in vivo.