Morphometric Analysis of Foilicular Development in the Rat

Ovarian follicular development was examined in the cycling rat using histological techniques. The number and size distribution of follicles was determined for each day of the estrous cycle. While the number of follicles in the early stages of growth did not appear to vary dramatically throughout the estrous cycle, the final stages of growth and differentiation showed great variation throughout the cycle. No follicles of 390–500 μm were seen on proestrus, bus many appeared the next day suggesting that there was a discontinuous movement of follicles into the largest size range. Follicular atresia was most marked in follicles 200–400 μm in diameter suggesting that there may be a critical stage during follicular development when, unless rescued, most follicles become atretic.