High‐Altitude trekking in the Himalayas increases the activity of circulating endothelial cells

Circulating endothelial progenitor cells (EPCs) are believed to contribute to vascular homeostasis; unfortunately, the response of EPCs in physiological conditions remains largely unknown. Herein we report our observations of a 44-year-old healthy subject after a trek in the Himalayas that support high-altitude hypoxia and exercise oxygen demands are strong stimuli for clonogenic endothelial cell activation and activity, as shown by the increase in the number of mature EPCs and in the endothelial colony-forming unit capacity. Both of these effects were completely reverted at sea level, 45 days after the subject’s trek. Am. J. Hematol. 79:76–78, 2005. a 2005 Wiley-Liss, Inc.