Preventing hemodilution abolishes natriuresis of water immersion in humans.
The hypothesis was tested that hemodilution is one of the determinants of the water immersion (WI)-induced natriuresis. Eight males were subjected to 3 h of 1) WI to the midchest (Chest), 2) WI to the neck combined with thigh cuff-induced (80 mmHg) venous stasis (Neck + stasis), and 3) a seated time control (n = 6). Central venous pressure and left atrial diameter increased to the same extent during Chest and Neck + stasis (P < 0.05), whereas renal sodium excretion only increased during Chest from 77 +/- 7 to 225 +/- 13 micromol/min (P < 0.05). During Chest, plasma colloid osmotic pressure (COP) decreased from 27.7 +/- 0.7 to 25.1 +/- 0.7 mmHg (P < 0.05), and plasma volume (PV) increased from 3,263 +/- 129 to 3,581 +/- 159 ml (P < 0.05), whereas these variables remained unchanged during Neck + stasis. Plasma norepinephrine concentration decreased similarly during Chest and Neck + stasis by 45 +/- 7 and 34 +/- 4%, respectively (P < 0.05), whereas plasma renin activity decreased only during Chest (P < 0.05). In conclusion, during WI in humans 1) hemodilution (decrease in COP and increase in PV) is a pivotal stimulus for the natriuresis and 2) central blood volume expansion without hemodilution does not augment renal sodium output.
Johansen
L B
LB
Danish Aerospace Medical Centre of Research, Rigshospitalet 7805, DK-2200 Copenhagen, Denmark.
Pump
B
B
Warberg
J
J
Christensen
N J
NJ
Norsk
P
P
D000328:Adult; D000450:Aldosterone / Q000097:blood; D001794:Blood Pressure; D003102:Colloids; D006339:Heart Rate; D006438:Hemodilution; D006801:Humans; D007101:Immersion; D007700:Kinetics; D008297:Male; D009318:Natriuresis / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood; D009997:Osmotic Pressure; D010953:Plasma Volume; D012083:Renin / Q000097:blood
D003102:Colloids; D000450:Aldosterone; D012083:Renin; D009638:Norepinephrine