P-31 MAGNETIC-RESONANCE SPECTROSCOPY DEMONSTRATES EXPANSION OF THE EXTRACELLULAR-SPACE IN THE SKELETAL-MUSCLE OF STARVED RATS

Starvation significantly alters the adistribution of body water. To st udy the effects of starvation on cellular energetics and water distrib ution in skeletal muscle, a novel P-31 magnetic resonance technique (P -31 MRS) was developed to measure water compartments. After P-31 MRS-v isible water space markers which distribute in total body water (dimet hyl methylphosphonate, DMMP) and extracellular water (phenylphosphonat e, PPA) were infused intravenously, P-31 MRS spectra were obtained fro m the gastrocnemius muscle of male virus-free Wistar rats at baseline and after starvation or ad libitum feeding for 4 days. Muscle water sp aces were also measured using the chloride method and Nernst's equatio n. Muscle water contents as determined by drying were equivalent in th e two groups. In vivo measurements of changes in DMMP relative to all of the MRS visible phosphates also demonstrated that the total water s pace was similar in control and starved rats. However, starvation sign ificantly increased the ratio of PPA/DMMP (0.67 +/- 0.05 vs 0.87 +/- 0 .04, Control vs Starvation; P < 0.001), and therefore the ratio of ext racellular water to total water in the gastrocnemius. Furthermore, bec ause muscle water contents were comparable between the groups, this ex pansion of the extracellular space was accompanied by contraction of t he intracellular compartment in starved animals. Equivalent changes we re detected in vitro using the chloride method. Lastly, phosphocreatin e/ATP ratios, which measured changes in high-energy phosphate stores, decreased after starvation (4.09 +/- 0.06 vs 3.61 +/- 0.06; P < 0.001) and were inversely related to changes in PPA/DMMP (r = -0.61; P < 0.0 01). We conclude that starvation alters the distribution of water with in skeletal muscle and these changes are related to the depletion of e nergy stores. These phenomena can be studied simultaneously in a nonin vasive fashion using in vivo P-31 MRS and MRS-visible water space mark ers. (C) Academic Press, Inc.