Effects of fetal bovine serum, FSH and 17beta-estradiol on the culture of bovine preantral follicles.

We describe a 7-d culture in droplets of collagen gel of isolated small bovine preantral follicles in medium with or without 10% fetal bovine serum (FBS). In addition, the effect of human recombinant FSH and 17beta-estradiol on the morphology and growth of the preantral follicles was investigated in medium without FBS. After culture in medium with 10% FBS, the increase in follicle diameter was 13.1 +/- 8.4 microm, the percentage of BrdU-labeled cells was 49.9 +/- 11.3 and the number of cells per area granulosa was 11.1 +/- 1.8. Omission of serum from the culture medium had no effect on the percentage of labeled cells, but the diameter increase was lower and the cells were smaller. Apparently, serum affects the size of the granulosa cells from small preantral follicles rather than the stimulation of cell proliferation. Addition of human recombinant FSH and/or 17beta-estradiol to serum-free medium resulted in a larger diameter increase during culture compared with that of the control. With FSH, this was due to an increase in cell proliferation, while with estradiol this was caused by an increase in granulosa cell size. The effects of simultaneous treatment with FSH and estradiol was simply the combination of their individual effects. In conclusion, small bovine preantral follicles can be cultured for 7 d in the absence of serum and hormones. The follicles increase in diameter and react to FSH with enhanced cell proliferation and to estradiol with an increase in cell size.