Chronic hypoxia and chemodectomas in bovines at high altitudes.

A severe degree of hyperplasia of the chief cells occurs in bovine carotid bodies at high altitudes, compared to sea level. As a result, the carotid body from an animal at high altitudes is significantly heavier and larger than the carotid body from an animal at sea level (P less than .001). In eight of 20 (40%) animals at high altitudes, the hyperplastic reaction had progressed to form chemodectomas. The findings suggest that neoplasia can result from chronic stimulation by a biologically essential environmental factor (atmospheric PO2) that acts pharmacologically on the target tissues (chief cells of the carotid body).