Mitotic Activity in the Epithelium of the Epididymis in Young and old Adult Rats

Abstract

The proliferative activity of epithelial cells lining the epididymis as judged from labeling indices in ³H-thymidine-injected animals and from mitotic indices was evaluated in three groups of adult albino rats, respectively, aged 2.5, 4, and 12 months. The labeling indices of principal and basal cells were relatively high in 2.5-month-old rats (2.2% of principal cells and 1.4% of basal cells for the whole epididymis) but low (below 0.6%) in 4-and 12-month-old animals. In the 2.5-month-old animals the cells labeled with ³H-thymidine stayed within the epithelium for a long period of time thereafter (up to 50 days when the experiment was terminated). There was no appreciable labeling of the nonstereociliated narrow columnar and light cells and no sign of cell loss. Mitotic indices were appreciable in 2.5-month-old rats but insignificant in older animals. Mitotic indices obtained from 4-month-old animals injected with colchicine were similar to that of noncolchicine-injected animals. These data indicated that in sexually mature but young adult rats growth was still taking place in the epididymis. In older rats growth of the epididymis continued but at a considerably lower rate. In these animals the low mitotic and labeling indices of the epididymal epithelial cells classified this cell population amongst the expanding rather than amongst the renewing ones. No holocrine secretion must therefore take place in the epididymis of adult rats.