Lactate and pH mapping in calf muscles of rats during ischemia/reperfusion assessed by in vivo proton and phosphorus magnetic resonance chemical shift imaging.

Abstract

Metabolic images of phosphocreatine, inorganic phosphate (Pi), and pH formed by phosphorus 31 (31P) nuclear magnetic resonance (NMR) spectroscopy, that of lactate by proton (1H) NMR spectroscopy and 1H magnetic resonance imaging (MRI) were concurrently observed using the same ischemia/reperfusion model in the calf muscles of rats. From the multidimensional analyses, the correlation between tissue pH and lactate formation was examined. Six rats were used in the study. For the selective detection of lactate by 1H NMR, a multiple quantum coherence filter was used. The localization of the metabolites and pH was achieved by three-dimensional chemical shift imaging technique. These observations were repeated in 1-hour cycles during 6 hours of ischemia and after reperfusion. The tibialis anterior and gastrocnemius muscles, which are mainly composed of fast-twitch muscle fibers, showed severe tissue edema and irreversible phosphoenergetic change. These muscles became more acidic than other portions of the calf. In contrast, the central part of the calf including soleus muscle (slow-twitch muscle) showed reversible phosphoenergetic changes. Lactate accumulated mainly between the muscles showing reversible and irreversible phospho-energetic changes. Discrepancy between acidosis and lactate accumulation in calf muscles was observed in this ischemia/reperfusion model, although the exact reasons for this phenomenon could not be explained by this study.