Quantitative analysis of anaerobic metabolism in resting anoxic muscle by 31P and 1H MRS

31P and 1H MRS high resolution measurements at 4.7 T were carried out in isolated frog (Rana esculenta) gastrocnemius muscle during anoxia to assess, using reference compounds, the concentration of high energy phosphates (apprx P = phosphocreatine (PC) plus adenosinetriphosphate (ATP)), inorganic phosphate (Pi), phosphomonoesters (PME) and lactate (La). Two sets of measurements were performed, with (p) and without (up) muscle IAA poisoning and the time course of the metabolite concentration changes was described. The rate of phosphocreatine hydrolysis during the first phase of anaerobiosis, when no lactate is accumulated in either case, appears to be greater in p than in up preparations. This finding can be explained with the sizeable accumulation of phosphomonoesters (PME) in the former. The efficiency of anaerobic glycolysis, i.e. the apprx P/La ratio, recalculated taking into account also PME changes, was found to be 1.48 +- 0.28, a value higher than that obtained by previous chemical measurements and close to the maximum stoichiometric apprx P/La value. Hence, the in vivo substrate of glycolysis, in the resting anoxic frog gastrocnemius, appears to be almost exclusively glycogen.