title: Effect of physical fitness on vanillylmandelic acid excretion during immersion.
abstract: 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 occurred (4 h value: +2.7 +/- 10.9 ng/ml GFR), but there was a highly significant increase in the UT (+29.0 +/- 17.2 ng/ml GFR). VMA values during control experiments in supine position tended to decrease in both groups. Systolic and diastolic blood pressure 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 intolerance (o.i.) after immersion is not effected by decreased sympathetic innervation of vessels; in contrast it seems to be partly compensated 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 decrease in renin activity.
mesh_terms: D000328:Adult; D001794:Blood Pressure; D006801:Humans; D007101:Immersion / Q000503:physiopathology; D008297:Male; D010809:Physical Fitness; D010953:Plasma Volume; D011187:Posture; D013564:Sympathetic Nervous System / Q000503:physiopathology; D013575:Syncope; D014642:Vanilmandelic Acid / Q000652:urine*; D014893:Weightlessness
chemical_list: D014642:Vanilmandelic Acid