Abstract des Autors

The effects of 4 - 6 h head - out immersion on excretion of vanillylmandelic acid (VMA), blood pressure and plasma volume were estimated in 8 endurance - trained (TR) and 8 untrained (UT) subjects. In the trained only a slight increase of VMA excretion occured (4 h value: + 2.7 +/- 10.9 ng/ml GFR), but there was a highly significant increase in the UT (+29.0 +29.0 +/- 17.2 ng/ml GFR). VMA values during control experiments in supine position tended to decrease in both groups. Systolic and diastolic bloodpressure fell by 20 mm Hg after beginning of immersion; in the UT plasma volume was reduced while it remained constant in TR. The results indicate that orthostatic (o.i.) after immersion is not effected by decreased sympathetic innervation of vessels; in contrast it seems to be partly copensated for by an elevated sympathetic activity at least in the UT. As a main cause for the post - immersion o.i. one might suggest a decrrease in renin activity.