Appearance of D2O in Sweat after Oral and Oral-Intravenous Rehydration in Men

Abstract

Intravenous (IV) rehydration is common in athletics, but its thermoregulatory benefits and ergogenicity have not been elucidated. Availability of orally ingested fluid is dependent on gastric emptying and intestinal absorption rate. Deuterium oxide (D2O) has been used to demonstrate that fluid ingested during exercise appears in sweat within 10 minutes. The purpose of this study was to determine the effect of concurrent IV rehydration on D2O appearance in sweat samples after per ora rehydration with D2O labeled fluid. We hypothesized that the combination method would not be superior to the oral method. Ten fit men (age 23 ± 4, VO2max 59.49 ± 4.09 L·min(-1)) underwent 20 hours of fluid restriction resulting in 1.95 ± 0.25% body weight loss before beginning treadmill exercise and cycling. Exercise was performed in an environmental chamber (35.6 ± 0.2° C, 35.0 ± 1.8% relative humidity) for 2 hours at 55% VO2max, and the participants exhibited a mean body weight deficit of 4.50 ± 0.04%. Thermoregulatory measures were recorded while subjects were rehydrated with oral (OR) or oral combined with intravenous (IVO) fluid traced with D2O. After 30 minutes of rehydration and 30 minutes of seated recovery, the subjects began treadmill exercise at 55-60% VO2max. Forehead sweat samples were collected 0, 5, 10, 20, and 75 minutes from the start of rehydration. The samples were analyzed for D2O via isotope ratio mass spectrometry. D2O did not appear in the sweat within 20 minutes of rehydration; however, it did appear during the subsequent exercise bout. There was no significant difference between rehydration modes. Plasma volume increases and decreased volume of orally ingested fluid did not significantly alter transit time from ingestion to appearance in excreted sweat. The IVO method does not appear to be superior to the traditional OR method of rehydration.

Historical and contemporary stable isotope tracer approaches to studying mammalian protein metabolism

“…Building upon the knowledge generated by researchers utilizing heavy water for measurement of body water pool size (Hevesy & Hofer, ), energy expenditure (Lifson, Gordon, & McClintock, ; Schoeller & van Santen, ) and aspects of plant protein metabolism (Humphrey & Davies, , ), it was soon realized, through the dedicated work of Marc Hellerstein and Stephen Previs (working independently of each other), that D 2 O could overcome a number of the issues related to the use of traditional substrate‐specific stable isotope tracers. Administered either orally (Previs et al, ; Gasier, Fluckey, & Previs, ; Robinson et al, ; Gasier et al, ; MacDonald et al, ; Wilkinson et al, , ; Decaris et al, ) or intravenously (Emmanuel et al, ), continuously (Robinson et al, ; Brook et al, ; Decaris et al, ) or as a single bolus (MacDonald et al, ; Wilkinson et al, , ), D 2 O rapidly equilibrates with body water (within ∼20 min in rodents; Dufner et al, and up to 1–2 hr in adults humans (IAEA Human Health Series, )), this creates a homogenous, slowly turning over, precursor pool available for use by multiple substrates. The deuterium from the body water can then be incorporated onto different substrates at stable CH positions through biological reductions during de novo synthesis, and the metabolic flux of these substrate pools can be calculated from the measurement of the amount of the label that is incorporated (Hellerstein, ).…”

Intravenous Fluid Use in Athletes

“…21 A follow-up study compared ingestion of labeled oral fluid versus a combination of oral and IV labeled D2O. After dehydration, subjects were rehydrated and exercised until D2O was measured in sweat.…”

“…There were no differences in the groups despite an apparent increase in plasma volume afforded by IV rehydration. 21 …”

“…39 Studies utilizing labeled deuterium oxide (D2O) fluid show that during exercise D2O appears in sweat 10 minutes after oral ingestion. 21 A follow-up study compared ingestion of labeled oral fluid versus a combination of oral and IV labeled D2O. After dehydration, subjects were rehydrated and exercised until D2O was measured in sweat.…”