Hormonal changes in normal and polycythemic high-altitude natives.

Acute and chronic exposure to high-altitude (HA) hypoxia inhibits the renin-angiotensin-aldosterone system and may modify the release of atrial natriuretic peptide (ANP) in sea-level (SL) natives. In HA natives, the release of these hormones could be influenced by changes in blood volume or pulmonary arterial pressure. Twenty-four men residing in La Paz, Bolivia, at 3,600 m were separated into two groups: one normocythemic (HAN; with hematocrit < 57%; n = 13) and the other polycythemic (HAP; with hematocrit > 57%; n = 11). A control group of 9 SL residents was studied in normoxia (SLN) as well as after 4 days spent at 4,350 m (SLH). The groups were tested for plasma active renin (PAR), plasma aldosterone concentration, ANP, and potassium and norepineprine concentrations at rest and after a maximal exercise. Pulmonary arterial systolic pressure was assessed by a Doppler technique. It was observed that PAR and plasma aldosterone concentration at rest and after exercise were lower in the SLH than in the SLN group. PAR and norepineprine concentration were higher among highlanders than in the SLN group. Renin response to exercise was normal among the HAN group and slightly decreased among the HAP group, and an exercise-induced increase in aldosterone was attenuated in both HA groups. Aldosterone response to renin was maintained among the SLH group but was attenuated in the HA groups, possibly owing to a protective mechanism against salt and water retention. Resting and exercise ANP was lower in the HA groups than in the SLN group.(ABSTRACT TRUNCATED AT 250 WORDS)