Growth Pattern of Postnatally Developing Rat Parotid Gland ∗

Summary

The time course of postnatal growth and differentiation of rat parotid has been described, and the mechanisms involved in gland growth examined. An early phase of extensive cellular proliferation, which persists at levels of 17-23/1000 acinar cells through 23 days of age, was seen. This was accompanied by small increases in cell size; after 23 days of age, cell size became the prominent cellular event and mitotic rate decreased markedly. Changes after 64 days of age in gland weight, cell size, state of cellular differentiation, and cell number were not conspicuous. These determinations were based on histological examination and measurement of cell size, nuclear size, and mitotic indices. DNA-RNA content also increased with time postnatally, and both exhibited, like mitotic rate, the sharpest increment between 16–23 days of age. Parallels between the biphasic mechanism of postnatal parotid growth and that of heart and skeletal muscle were examined, and comparison was made to growth patterns exhibited under other conditions of growth.