Kinetics of follicle growth in the prepubertal gilt

Follicular growth rates were determined by histological examination of ovaries of five prepubertal gilts following treatment with the stathmokinetic agent colchicine. One ovary from each of five gilts was removed surgically and then colchicine (n = 3) or saline (n = 2) was infused i.v. Precisely 2 h after treatment with colchicine, the remaining ovary was removed. Ovaries were processed for histological analyses and sectioned at 10 micrometer; every twentieth section was stained with hematoxylin and periodic acid-Schiffe's. Sections were viewed with a projection microscope and individual follicles were measured. Eight classes of follicles were established such that the number of granulosa cells per cross section doubled in each class. Diameters of follicles for each class were as follows: 1) less than 106 micrometers, 2) 106-148 micrometers, 3) 148-206 micrometers, 4) 206-287 micrometers, 5) 287-400 micrometers, 6) 400-657 micrometers, 7) 657-1480 micrometers, and 8) 1480-3130 micrometers. A layer of thecal cells was first seen in class 2 follicles, and 76% of class 3 follicles had a thecal layer. Oocyte diameter increased through the first four classes and reached a maximum diameter of approximately 110 micrometers. Almost all follicles greater than 400 micrometers had an antrum. Preantral follicles had a lower mitotic index and a higher mitotic time and class time than antral follicles. Growth rate increased with increasing size of follicles. Preantral follicles grew at a rate of 5.2 micrometers/day whereas antral follicles grew at 313 micrometers/day. Based on estimated growth rates, an activated primordial follicle required 84 days to reach the antral stage and a newly formed antral follicle grew to a diameter of 3.13 mm in 14 days