GROWTH-RATES AND ANTRUM FORMATION OF MOUSE OVARIAN FOLLICLES IN-VITROIN RESPONSE TO FOLLICLE-STIMULATING-HORMONE, RELAXIN, CYCLIC-AMP AND HYPOXANTHINE

The culture of individual intact follicles in vitro, from small pre-an tral to pre-ovulatory stages, will improve our ability to perform cont rolled experiments studying follicle growth and female gamete developm ent. This study was undertaken to characterize further the conditions required for physiological follicle growth in vitro. We cultured a tot al of 398 pre-antral follicles of immature mice (aged 26-28 days) with an initial diameter of 140-340 mu m for 4 days in vitro, using indivi dual micro-cultures under paraffin oil. Summarizing the results of all groups, 50 follicles were damaged (12.6%) and, of those remaining int act (n = 348), 60 (17.2%) became atretic, 195 (56.0%) became antral an d 26 (7.5%) ovulated. The most advanced follicles grew to 400-500 mu m diameter. The presence of follicle-stimulating hormone (FSH) in the m edium significantly stimulated follicle growth in vitro (P < 0.03), in a manner proportional to the initial diameter over the range of 140-2 50 mu m initial diameter, with larger follicles being refractory. FSH also significantly increased the proportion of follicles forming antra (P < 0.001) and their likelihood of ovulating in vitro (P < 0.01), an d reduced the frequency of atresia (P < 0.01). Dibutyryl-cyclic AMP mi micked FSH, significantly stimulating growth of large follicles (P < 0 .05) and antrum formation (P < 0.01). Hypoxanthine also stimulated ant rum formation (P < 0.01) but did not significantly affect follicle gro wth. Porcine relaxin had no significant effect on mouse follicle growt h or antrum formation. The optimal conditions for mouse follicle growt h in vitro have not yet been defined, but selection of follicles of < 250 mu m diameter and inclusion of FSH or dibutyryl-cyclic AMP in the culture medium are recommended.