A quantitative study of the effects of chronic hypoxia on the histological structure of the rat major salivary glands.

Ten young adult female Wistar rats were placed in a decompression chamber at a simulated altitude of 5500 m for 28 days, after which they were killed and their salivary glands and thoracic organs were compared with those of eight matched control rats that had been maintained at sea-level atmospheric pressure. The prolonged hypoxic conditions were severe enough to induce structural changes in the heart and lungs of experimental rats, and their parotid and submandibular, but not sublingual, glands showed severe hyperaemic responses. However, no parenchymal changes occurred in any of the major salivary glands. The mean proportional volume of vascular tissue was increased by 57% in the parotid and 30% in the submandibular glands, and the mean intralobular capillary densities were also increased, by 29 and 18% respectively, in these two glands. The effectiveness of these vascular responses in protecting the salivary parenchymal elements against hypoxic degeneration probably reflects the high reserve potential normally present in salivary blood flow.