Plasma proANP1-98 Response During High Altitude Stress: Effect of Age and Ethnicity

Abstract

Objective: Acclimatization to high altitude (HA) is accompanied by decrease in plasma atrial natriuretic peptide (ANP). On the other hand, circulating levels of the hormone are known to be influenced by age and ethnicity. The impact of these factors on ANP response during prolonged HA exposure remains unexplored. Hence, this study was conducted to examine possible age and ethnic variation in plasma proANP1-98 levels in men after 3 to 4 weeks at HA. Methods: Lowlanders (LL) were studied at sea level (SL) and after 3 to 4 weeks at an altitude of ∼4500 m. The LL group comprised Rajput (n = 48), Gorkha (n = 40), and South Indian (n = 43) ethnicities. Another group of HA natives (Ladakhi, n = 40) were studied at ∼4500 m only. Subjects were between 20 and 50 years of age. Estimation of plasma proANP1-98 and biochemical, hematologic, and physiologic evaluation was done. Results: In LL at HA, proANP1-98 levels decreased (P < .001); plasma arginine vasopressin decreased (P < .05 in Rajputs and South Indians); and total protein, hemoglobin, and hematocrit increased (P < .05). Heart rate increased (P < .05), whereas arterial oxygen saturation decreased (P < .05) in all LL at HA. Ethnicity but not age variation in proANP1-98 was observed under HA stress. In HA natives, plasma proANP1-98 was higher than LL at HA and did not exhibit any age variation. Conclusions: Plasma proANP1-98 levels, reflecting medium-term ANP secretion, decrease during prolonged exposure to HA in LL. This is due to diuresis leading to plasma volume reduction that occurs during the acclimatization process. Ethnicity but not age variation is associated with plasma proANP1-98 under HA stress. © 2010 Wilderness Medical Society.