A quantitative morphological study of the carotid bodies of rats living at a simulated altitude of 4300 metres.

A quantitative histological study was carried out on the carotid bodies of 10 normal rats and 10 rats living in a hypobaric chamber at a pressure of 460 mm Hg from 25 to 96 days. In the chronically hypoxic rats there was a four-fold increase in the mean combined volume of the carotid bodies. Morphometric analysis disclosed a three-fold increase in the mean volume of specialised glomic cells and a ten-fold increase in the mean volume of capillaries, although the proportion of glomic cells was actually significantly decreased. In all our hypoxic rats there was evidence of both right and left ventricular hypertrophy. However, there was no linear relation between total carotid body volume or volume of glomic cells on one hand and the right and left ventricular weight, on the other hand. Although there was no linear relation between combined total carotid body volume and duration of hypoxia, the linear relation between glomic cell volume and duration of hypoxia was significant at the 5 per cent. level. The increase in vascularity of the hypoxic carotid body may be a mechanism to increase blood flow and thus oxygen transport to a hypoxic organ with increased metabolic activity. Small quantities of an amorphous hyaline material of unknown nature were found in relation to capillaries and type I cells in all the hypoxic rats.