Starvation significantly alters the distribution of body water. To study the effects of starvation on cellular energetics and water distribution in skeletal muscle, a novel 31P magnetic resonance technique (31P MRS) was developed to measure water compartments. After 31P MRS-visible water space markers which distribute in total body water (dimethyl methylphosphonate, DMMP) and extracellular water (phenylphosphonate, PPA) were infused intravenously, 31P MRS spectra were obtained from the gastrocnemius muscle of male virus-free Wistar rats at baseline and after starvation or ad libitum feeding for 4 days. Muscle water spaces were also measured using the chloride method and Nernst’s equation. Muscle water contents as determined by drying were equivalent in the two groups. In vivo measurements of changes in DMMP relative to all of the MRS visible phosphates also demonstrated that the total water space was similar in control and starved rats. However, starvation significantly 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 extracellular water to total water in the gastrocnemius. Furthermore, because muscle water contents were comparable between the groups, this expansion of the extracellular space was accompanied by contraction of the intracellular compartment in starved animals. Equivalent changes were detected in vitro using the chloride method. Lastly, phosphocreatine/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 < 0.001). We conclude that starvation alters the distribution of water within skeletal muscle and these changes are related to the depletion of energy stores. These phenomena can be studied simultaneously in a noninvasive fashion using in vivo31P MRS and MRS-visible water space markers.
ASJC Scopus subject areas