title: Water and electrolyte balance in the vascular space during graded exercise in humans.
abstract: We analyzed the changes in water content and electrolyte concentrations in the vascular space during graded exercise of short duration. Six male volunteers exercised on a cycle ergometer at 20 degrees C (relative humidity = 30%) as exercise intensity was increased stepwise until voluntary exhaustion. Blood samples were collected at exercise intensities of 29, 56, 70, and 95% of maximum aerobic power (VO2max). A curvilinear relationship between exercise intensity and Na+ concentration in plasma ([Na+]p) was observed. [Na+]p significantly increased at 70% VO2max and at 95% VO2max was approximately 8 meq/kgH2O higher than control. The change in lactate concentration in plasma ([Lac-]p) was closely correlated with the change in [Na+]p (delta[Na+]p = 0.687 delta[Lac-]p + 1.79, r = 0.99). The change in [Lac-]p was also inversely correlated with the change in HCO3- concentration in plasma (delta[HCO3-]p = -0.761 delta[Lac-]p + 0.22, r = -1.00). At an exercise intensity of 95% VO2max, 60% of the increase in plasma osmolality (Posmol) was accounted for by an increase in [Na+]p. These results suggest that lactic acid released into the vascular space from active skeletal muscles reacts with [HCO3-]p to produce CO2 gas and Lac-. The data raise the intriguing notion that increase in [Na+]p during exercise may be caused by elevated Lac-.
authors.affiliation: Department of Physiology, Kyoto Prefectural University of Medicine, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Nose
authors.forename: A
authors.initials: A
authors.lastname: Takamata
authors.forename: G W
authors.initials: GW
authors.lastname: Mack
authors.forename: Y
authors.initials: Y
authors.lastname: Oda
authors.forename: T
authors.initials: T
authors.lastname: Okuno
authors.forename: D H
authors.initials: DH
authors.lastname: Kang
authors.forename: T
authors.initials: T
authors.lastname: Morimoto
mesh_terms: D000328:Adult; D001639:Bicarbonates / Q000097:blood; D015444:Exercise / Q000502:physiology*; D006801:Humans; D006955:Hypernatremia / Q000097:blood / Q000209:etiology; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008297:Male; D009994:Osmolar Concentration; D010949:Plasma / Q000378:metabolism; D010953:Plasma Volume; D012964:Sodium / Q000097:blood; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D001639:Bicarbonates; D007773:Lactates; D019344:Lactic Acid; D012964:Sodium