Altitude diuresis: endocrine and renal responses to acute hypoxia of acclimatized and non-acclimatized subjects.

As a result of our recently published studies we have thought that altitude diuresis resulting from hypoxic stimulation of the arterial chemoreceptors reduces the cardiac volume overload. To test this hypothesis, cardiovascular, endocrine and renal responses to stepwise acute exposure to simulated altitude (6,000 m) were compared in ten acclimatized recumbent mountaineers a mean of 24 days, SD 11, after descending from Himalayan altitudes of at least 4,000 m, with those found in ten non-acclimatized recumbent volunteers. The results showed that natriuresis and diuresis typified the renal responses to altitude exposure of both the acclimatized as well as non-acclimatized subjects, as long as altitude was well tolerated. It was concluded that the renal effects were mediated by atrial natriuretic peptide release and slight suppression of arginine-vasopressin (AVP) secretion, that the increased urine flow at altitude offset the cardiac (volume) overload resulting from hypoxic stimulation of the arterial chemoreceptors, and that enhanced AVP secretion, as found in the non-acclimatized subjects at and above 4,000 m, coincided with subjective and objective distress, i.e. with inadequate altitude adjustment owing to insufficient chemoreflex effects and central hypoxia.