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

Abstract

Background: Many cells adapt to hyperosmolal conditions by upregulation of organic osmolytes to maintain cell function and integrity. Glycerophosphocholine (GPC), a recognised 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. Objectives: To investigate the relationship of muscular GPC with surrogate parameters of body fluid status and osmolality. Methods: We analysed data of 30 healthy volunteers who underwent non-invasive 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. Results: 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). Conclusion: 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.