Clara cells in the llama.

A study was made by light and electron microscopy of the Clara cells of two llamas born and bred at an altitude of 4,720 m in the Peruvian Andes. The Clara cells were numerous and prominent with big apical caps, many of which had been extruded into the terminal bronchioles. On electron microscopy the caps were found to contain vesicular endoplasmic reticulum. Previous studies have shown this to contain dipalmitoyl lecithin, a known pulmonary surfactant. Acute exposure to a simulated altitude of 4,270 m has been reported to increase surface tension in lung extracts of mice. Hence it may be that an animal, such as the llama, chronically exposed to high altitude requires a persistent secretion of pulmonary surfactant.