Histochemical localization of delta 5-3 beta-HSDH activity in preovulatory rat follicles.

Rat ovarian follicles were isolated at 3 different hours before ovulation (at 16, 24 and 2 h) and the activity of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSDH) was examined by means of a new embedding technique. The activity of the enzyme in the theca interna cells, though the most intense one, was constant throughout the period of the time examined. It was the granulosa cells that showed the changing pattern of the activity: the reaction was strong there at 16 h and much weaker at 24 and 2 h (i.e. just before ovulation). The granulosa cells lying near the antrum displayed usually weaker reaction than those in the mural region. These differences in the enzyme activity between the mural and antral regions correlated with the morphological differenciation of granulosa cells into the two regions.