Abstract des Autors

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. Immersion diuresis of TR was only half as high as in UT (peak values: 3.22 ml/min in UT, 1.60 ml/min in TR). Free water clearance remained approximately constant in UT but temporarily decreased in TR. This points to poor or even absent inhibition of antidiuretic hormone secretion in the lattergroup. Osmolar clearance increased less in TR than in UT 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 bothgroups. The results indicate a reduced renal response of endurance-trained subjects to congestion of the lowpressure system resulting in an increase in blood volume.