Fluid control mechanisms after exercise dehydration

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Abstract
Since the osmocontrol- (osmolality), the renin-angiotensin- (PRA), and the volume control- (central venous pressure, CVP) systems are involved in the maintainance of the salt-water balance, we investigated the pattern of these parameters in the recovery period after exercise dehydration in 13 well trained long-distance runners. On average, after exercise the athletes had lost 3.1% of their body weight (BW). After eating and drinking the BW was still 1.3% below control value, indicative of continuing deficits. Plasma osmolality increased, however, from an average value of 286–290 mosmol/kg after exercise as well as postprandially, but the change was not significant. PRA-Levels rose significantly from 0.167–0.599 ng/ml·h after exercise and decreased to 0.333 ng/ml·h postprandially. CVP was significantly altered after exercise (−3.5 cm H2O) as well as postprandially (−2.4 cm H2O). The results suggest that the salt-water balance is maintained by the interplay of all the three systems. In conflicting situations, however, as when intercompartmental water- and solute-shifts take place during the recovery period, the volume control system triggered off by the CVP is the dominant corrective response to the prevailing deficits.