The ultrastructure of rat type II pneumocytes: effects of age, sex, and strain.

Abstract

The morphology of type II pneumocytes was investigated in Fischer 344 and Sprague-Dawley rats to determine whether differences in age, sex, and/or genetic strain influence type II cell ultrastructure. In Fischer 344 rats the type II pneumocytes increased in size with age due to an increase in the cytoplasmic component of the cell. Although mitochondrial volume density increased with age no significant changes in lamellar body volume density or lamellar body size were detected. No ultrastructural differences were observed between the type II cells in 6-week-old male and female Fischer 344 rats. However, substantial ultrastructural differences were found to exist among type II cells from the Fischer and Sprague-Dawley strains. Lamellar body volume density was 60% greater, P less than 0.001, in the Fischer rats due to the larger size of individual lamellar bodies. While mitochondrial volume density was also 22% greater in the Fischer rats, P less than 0.01, type II cell size was similar in the two strains. These results indicate that the ultrastructure of type II cells can differ within a genetically inbred strain as a function of age as well as between genetically different strains of the same species.