Exercise-associated hyponatremia: the effects of glycogen and hydration status on IL-6, ADH, and sodium concentrations

Abstract

Background: Exercise-associated hyponatremia (EAH) is a rare, but serious life-threatening condition that has been identified in marathoners, ultra-endurance athletes, and others engaging in prolonged, physical activity conducted in a hot environment. Hyponatremia is diagnosed when serum sodium concentrations fall below 135 mmol/L. Purpose: The purpose of this study was to evaluate the effect of hydration status and glycogen level on venous IL-6, ADH, and sodium concentrations during and after prolonged exercise in the heat. Method: Ten male participants completed four trials: a glycogen depleted, euhydrated condition (DE); a glycogen depleted, dehydrated condition (DD); a glycogen loaded, euhydrated condition (LE); and a glycogen loaded, dehydrated condition (LD). Each condition consisting of cycling at 60% VO2 max in a 35?C environment for 90 minutes followed by a 3 hour rehydration period. Body mass was measured before and after exercise and after rehydration. Blood and sweat samples were collected during exercise. Blood and urine samples were collected during the rehydration period. Blood was analyzed for glucose, IL-6, ADH, and Na+. Sweat and urine samples were analyzed for [Na+]. Results: The LD and LE conditions had significantly higher plasma glucose concentrations than the DD and DE conditions for all time points except for pre-exercise. There was a significant glycogen by hydration by time interaction for plasma [Na+] (p=0.022). The LD and DD conditions showed the greatest overall [Na+] changes from post exercise to post rehydration (-6.85 and -6.7 mmol/L, respectively) compared to the DE and LE conditions (-1.45 and 0.10 mM, respectively). [Na+] in the dehydrated conditions was significantly higher than the euhydrated conditions at the mid, post, 30, 60, and 90 time points. There was a main effect for time (p=0.00) for IL-6 with the highest concentrations occurring immediately post-ex.

There was a significant hydration by time interaction (p=0.000) for ADH with the post exercise time point being significantly different from all other time points. The dehydrated conditions showed the largest post-exercise increase in ADH concentrations with the DD conditions having an average ADH concentration ? 40.552 pg/mL and the LD conditions having an average of 55.46 ?of 50.16 68.124 pg/mL. Significant correlations were detected between post-exercise [IL-6] and 30 minutes post-exercise [Na+] (r=-0.077 p=0.008) in the DE condition and between change in body mass and total urine volume in the DD and LE conditions (r=-0.907 p= 0.000 and r=-0.88 p=0.001, respectively). Summary: Despite our glycogen, hydration, and exercise manipulations we did not observe a relationship between these variables. Glycogen status had no significant impact on IL-6 and ADH concentrations. We only observed a significant time effect for IL-6 concentrations and a significant hydration status and time effect for plasma sodium and ADH concentrations. A volume of 100% fluid replacement during exercise and a rehydration volume of 150% of fluid lost during exercise were enough to cause a tendency toward decreased plasma sodium concentrations.