Continuous [3H] thymidine infusion: a method for the study of follicular dynamics.

Cycling rats were given continuous infusions of [3H] thymidine [( 3H] TdR) by means of osmotic minipumps, and autoradiographs of ovaries were prepared. Silver grains were distributed in a diffuse and uniform fashion over the granulosa layer of growing follicles. Nearly 100% of granulosa cells in large healthy follicles were labeled within 24 h. This uniform labeling makes possible detailed cell cycle analysis, as well as other kinetic studies. Follicles which were already atretic before the minipumps were inserted remained unlabeled. Follicles which became atretic after the minipumps were inserted were heavily labeled. Thus, with continuous labeling, it is possible to deduce retrospectively the viability of a particular follicle as it had been at the time the minipumps were inserted. Short-term continuous infusion of [3H] TdR, therefore, provides a valuable temporal component to morphometric studies of the ovary and should be useful for the study of other rapidly growing tissues as well.