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Sodium regulating hormones at high altitude: basal and post-exercise levels
M Zaccaria1, S Rocco, D Noventa
1Institute of Semeiotica Medica, University of Padua, Italy.
The Journal of Clinical Endocrinology and Metabolism
|February 19, 1998
Summary
High altitude exposure alters sodium and water hormones, with exercise responses changing over time. Hypoxia may suppress the renin-angiotensin-aldosterone system (RAAS), impacting fluid balance at high altitudes.
Area of Science:
- Environmental Physiology
- Endocrinology
- Human Physiology
Background:
- High altitude (HA) diuresis involves significant hormonal shifts, particularly in the renin-angiotensin-aldosterone system (RAAS) and atrial natriuretic hormone (ANH).
- Physical exercise, common at HA, also stimulates these sodium and water regulating hormones.
- The precise relationship between hormonal changes, HA diuresis, and exercise remains unclear.
Purpose of the Study:
- To investigate the response of sodium-regulating hormones to exhaustive exercise during prolonged exposure to high altitude.
- To evaluate changes in plasma hematocrit, total body water, sodium excretion, and urinary volume.
- To determine the effects of acute and chronic HA exposure on basal and exercise-induced hormonal levels.
Main Methods:
- Seven males underwent four study phases: sea level (SL1), 7 days at 5050m (P1), 21 days at 5050m (P2), and return to sea level (SL2).
- Measurements included plasma hematocrit (Ht), total body water (TBW), 24-hr sodium excretion (uNa), urinary volume (uV), plasma renin activity (PRA), plasma aldosterone, and ANH.
- Samples were collected basally and post-maximal graded exercise at each phase.
Main Results:
- Sodium excretion (uNa) and urinary volume (uV) increased at P1 then decreased at P2, with parallel TBW reduction and Ht increase.
- Basal PRA and aldosterone were suppressed at P1 and P2 and unresponsive to exercise at HA, unlike at sea level.
- ANH levels were unchanged at P1 but significantly decreased at P2 (basally and post-exercise) compared to SL1.
Conclusions:
- Renin-angiotensin-aldosterone system (RAAS) hormones (PRA and aldosterone) are suppressed and unresponsive to exercise during HA exposure.
- Atrial natriuretic hormone (ANH) response is stimulated during acute HA exposure but blunted during chronic exposure.
- Hypoxia-induced chemoreceptor stimulation may directly suppress RAAS, contributing to natriuresis at high altitude.