Potential role of skeletal muscle glycerophosphocholine in response to altered fluid balance in humans: an in vivo nuclear magnetic resonance study.

Many cells adapt to hyperosmolal conditions by upregulation of organic osmolytes to maintain cell function and integrity. Glycerophosphocholine (GPC), a recognized osmolyte in renal medullary cells, is the major phosphodiester (PDE) in human skeletal muscle, wherefore we hypothesized muscular GPC to be associated with surrogate parameters of fluid status and osmolality in healthy humans. The objective of this study was to investigate the relationship of muscular GPC with surrogate parameters of body fluid status and osmolality. We analyzed data of 30 healthy volunteers who underwent noninvasive 31P-magnetic resonance spectroscopy of either calf (n = 17) or thigh (n = 13) muscle. Therefore, we conducted correlation analyses between phosphor metabolites, and blood values depicting body fluid status and osmolality. Relevant parameters were further implemented in a multivariable regression model to evaluate if GPC concentrations can depict variations in fluid and electrolyte balance. Uric acid (0.437, P = 0.018) and urea (0.387, P = 0.035) were significantly correlated with GPC, which in case of uric acid was independent of sex. Considering sex, following multivariable regression reported GPC as suitable parameter to predict uric acid (R2 = 0.462, adjusted R2 = 0.421; P < 0.001). Our data indicate a connection between muscular GPC concentrations and uric acid, which is a marker of body fluid status, in healthy human subjects, suggesting that skeletal muscle might regulate GPC content in adaptation to changes in fluid status.NEW & NOTEWORTHY Using in vivo magnetic resonance spectroscopy, our study is the first one indicating fluid balance-dependent properties of glycerophosphocholine concentrations in human skeletal muscle. In vivo examination of GPC as organic osmolyte in human skeletal muscle marks a novel approach, which might give further insight on how water and electrolyte balance affect muscle tissue. Beside this main finding, glycerophosphocholine of both calf and thigh muscle correlated remarkably with blood laboratory parameters of lipid metabolism in our study population.