In vivo phosphorus 31 magnetic resonance spectroscopy of rat hind limb skeletal muscle during sepsis

D. O. Jacobs, J. Maris, R. Fried, R. G. Settle, R. R. Rolandelli, M. J. Koruda, B. Chance and J. L. Rombeau
Department of Surgery, University of Pennsylvania School of Medicine, Philadelphia.

High-energy phosphate metabolism in skeletal muscle is altered during sepsis, although the chronology of events is uncertain. Phosphorus 31 magnetic resonance spectroscopy was used to measure changes in muscle energy stores of the left hind limb musculature of adult male rats during sepsis. Following control scans, cecal ligation and puncture were performed and scanning was repeated 6, 24, and 48 hours after surgery. The ratios of phosphocreatine (PCr) to inorganic phosphate (Pi), a measure of energy stores, and adenosine triphosphate (ATP) to Pi ratio, a measure of the energy available for immediate use, were determined from peak heights. Intracellular pH was calculated using the distance between Pi and PCr peaks. In surviving animals, a 40% decrease in PCr/Pi ratio (+/- SEM) was observed by 24 hours (22.3 +/- 3.0 at time 0 vs 13.3 +/- 2.8 at 24 hours), whereas energy availability (beta-ATP/Pi) was statistically unchanged (18.2 +/- 2.2 at time 0 vs 15.2 +/- 1.2 at 48 hours). Intracellular pH did not change. Both PCr/Pi and ATP/Pi ratios were inversely correlated with time. In this model of documented peritonitis, skeletal muscle energy metabolism is rapidly altered following severe infection, and these changes can be detected using 31P magnetic resonance spectroscopy.