Effect of Water Immersion on Renal Natriuretic Peptide (Urodilatin) Excretion in Humans

We examined 1) the effect of thermoneutral (34 +/- 0.5 degrees C) water immersion to the neck in humans on the temporal profile of renal urodilatin (atrial natriuretic peptide (ANP)-(95-126)) excretion and 2) the relationship between urodilatin and urinary fluid and sodium excretion. Eight normal subjects underwent 12 h of water immersion, and another group of eight were studied during seated control conditions. The subjects ingested 200 ml of tap water hourly. Water immersion induced an increase in renal urodilatin and guanosine 3`.5`-cyclic monophosphate (cGMP) excretion, urinary fluid and sodium. After peak values were attained between the 2nd and 5th h of water immersion, urodilatin and cGMP excretion, urinary fluid and sodium returned toward preimmersion and control values. At the 12th h of water immersion, urodilatin and cGMP excretion and urinary fluid were indistinguishable from preimmersion values but were significantly elevated compared with the control values. Sodium was maintained elevated compared with both preimmersion and control values. During water immersion, positive and statistically significant linear correlations could be established between urinaryfluid and renal urodilatin excretion in six subjects and between sodium and urodilatin excretion in four subjects. We conclude that water immersion induces an increase in the rate of renal urodilatin excretion, attaining a peak value at the 3rd h followed by an attenuation toward preimmersion and control levels. Furthermore, urodilatin might participate as one of several mechanisms of the natriuresis and diuresis of water immersion in humans