The use of a deuterium tracer technique to follow the fate of fluids ingested by human subjects: Effects of drink volume and tracer concentration andcontent

Deuterium oxide ((H2O)-H-2) has been added to drinks as a tracer for water to estimate the availability to the body water pool of ingested fluids, but doubts have been raised as to the reliability of the method. The present i nvestigation evaluated the effects of systematic variations in the volume o f fluid consumed and the amount and concentration of added tracer on the ra te of accumulation of tracer in arterialized blood after ingestion of a lab elled drink. Three separate experiments were undertaken. In expt 1, six hea lthy men ingested on separate occasions 200, 400 and 800 ml of a dilute glu cose-electrolyte solution: all test drinks contained the same concentration (40 g l(-1)) of (H2O)-H-2. In expt 2, six healthy men ingested 200, 400 an d 800 ml of the same glucose-electrolyte drink: each drink contained 8 g of (H2O)-H-2 so that the concentration, bur not the amount, of (H2O)-H-2 diff ered between treatments. In expt 3, six healthy men ingested 400 ml of the same drink on three separate occasions: each drink contained 8, 16 or 32 g of tracer so that amount and concentration of (H2O)-H-2 both varied. Arteri alized venous blood samples were collected for the determination of deuteri um (H-2) concentration before ingestion of the test drink and at intervals for 120 min after ingestion. All trials for each of the experiments were co nducted in the morning after an overnight fast and trials were in randomize d order and separated by 7 days. In expt 1, the blood H-2 concentration at all time points from 2 min after ingestion of the test drink onwards was hi gher for the drink containing 32 g (H2O)-H-2 than for the drink containing 16 g (H2O)-H-2, which in turn was higher than after ingestion of the drink containing 8 g of (H2O)-H-2. In expt 2, no significant differences between treatments were observed at any time. In expt 3, the rare of H-2 accumulati on was greater after ingestion of the drink containing 32 g of (H2O)-H-2 th an after either of the other two drinks, and the H-2 accumulation rate was greater after ingestion of the drink containing 16 g of (H2O)-H-2 than afte r thr drink containing 8 g of (H2O)-H-2. When data from all three experimen ts were combined, significant correlations were observed between the rate o f accumulation of H-2 in the circulation (p.p.m. min(-1)) and the amount (r (s) = 0.75, P < 0.001) and concentration (r(s) = 0.69, P < 0.001) of (H2O)- H-2 in the test drink, but there was no relationship (r(s) = 0.09, P = 0.5) between the rate of H-2 accumulation in the blood and the volume of the dr ink consumed. Thr result, suggest that the rate of tracer accumulation in t he blood after ingestion of different volumes of test drinks is not a relia ble indication of the availability of the ingested fluid, but that the meth od gives at least a qualitative measure of the sum of the effects of gastri c emptying and intestinal water absorption.