Quantitative (stereological) study of the epididymis and seminal vesicle in the rat from young to old.

There is a scarcity of morphometric data on the developmental and ageing changes in the epididymis and seminal vesicle in young and old rats. Eighty-six normal male Sprague-Dawley rats were randomly sampled from a cohort of animals aged 1-36 months (7-9 animals each age group). The epididymis and seminal vesicle (with the closely attached coagulating gland) were removed, and methacrylate resin-embedded sections were prepared for quantitative study of key histological structures by light microscopy. Stereological methods (point counting and optical disector) were used to estimate the total volumes of sperm mass, secretion (glandular lumen) and other structures and the number of spermatozoa. The results showed that the rapid growth of the reproductive organs was between 1 and 4 months of age. The epididymis stored the largest volume of sperm mass or number of spermatozoa at 12 months of age, but thereafter until 36 months of age, the sperm storage did not markedly diminish. The volume of secretion stored in the seminal vesicular gland declined by more than 35% from a plateau at 12-18 months until 36 months of age while that in the coagulating gland declined by more than 30% from a plateau at 18-24 months until 36 months of age.