Renal blood volume regulation in trained and untrained subjects during immersion

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Abstract
To study the cause of the increased blood volume of endurance-trained athletes we assessed the renal blood volume regulating mechanisms in eight untrained (UT) and eight endurance-trained (TR) male subjects during a 4 h head-out immersion. In TR plasma volume remained constant whereas it decreased in UT by 2.4 ml/kg (ppp<0.02) which was partly due to a delayed increase of glomerular filtration rate. Plasma osmolality, creatinine, and protein concentrations as well as hematocrit values were reduced during immersion to a similar extent in both groups. The results indicate a reduced renal response of endurance-trained subjects to congestion of the low-pressure system resulting in an increase in blood volume.