Hormonal and renal responses to water drinking in moderately trained and untrained humans
Freund, B.J.; Claybaugh, J.R.; Hashiro, G.M.; Dice, M.S.
American Journal of Physiology 254(3 Pt 2): R417-R423
1988
ISSN/ISBN: 0002-9513 PMID: 3348438 Document Number: 320470
Endurance exercise training alters the regulation of body fluids. To investigate specifics of these alterations, hormonal, electrolyte, and renal responses to water ingestion (1% of lean body wt) were studied in six moderately trained (T) and 6 untrained (UT) male subjects. No differences between groups for base-line hormonal, electrolyte, or renal measurements were found. After water ingestion, atrial natriuretic factor remained unaltered in both groups. Predrink plasma antidiuretic hormone (ADH) levels of 0.51 .+-. (SE) 0.19 (UT) and 0.47 .+-. 0.07 .mu.U/ml (T) remained unchanged in the T group but were reduced from min 9 through 90 in the UT group. At 30 min postdrink, UT subjects had lower ADH values than T subjects (0.18 .+-. 0.02 vs. 0.33 .+-. 0.05 .mu.U/ml), while plasma osmolality was similarly reduced by .apprx. 3 mosmol/kg in both groups. Urine flow rates increased in both groups from similar values of 0.85 .+-. 0.24 (UT) and 0.67 .+-. 0.11 ml/min (T) to peak flows of 4.6 .+-. 1.6 for UT and 2.7 .+-. 1.1 ml/min for T (UT vs. T, P .ltoreq. 0.05) at 60 min postdrink. Urine osmolality was reduced from similar values of 809.1 .+-. 62.1 and 867.0 .+-. 56.1 mosmol/kg to values of 248.8 .+-. 87.6 and 469 .+-. 146.1 mosmol/kg for UT and T, respectively (UT vs. T, P < 0.05), at 60 min. Reduced ADH before reductions in plasma osmolality in the UT but not the T subjects suggests that T subjects have a reduced oropharyngeal inhibition of ADH. The higher plasma ADH values in the T subjects are probably responsible for the blunted diuresis and are in spite of similar plasma osmolality values between groups. These findings suggest an alteration in the osmotic regulation of plasma ADH in endurance-trained subjects.