FSH bioactivity is strongly enhanced by kinetic incubation of pre-antral hamster follicles.

Unlabelled: Isolation of meiotic arrested oocytes from mammalian ovaries involves a resumption of the meiosis. Studying the effect of FSH on this process it was found that doses up to of 0.1 IU/ml did not maintain the meiotic arrest in hamster oocytes in pre-antral follicles during static incubation conditions. However, when the FSH medium was replaced at 120, 60 and 30 min the resumption of the meiosis gradually decreased. Using a replacement frequency of 30 min a complete log dose-curve was constructed (ED50: 0.5 mU/ml; minimum effective dose: 0.1 mU/ml). The lack of a FSH response during static incubation was not caused by exhaustion of its bioactivity: mixing of the FSH containing medium, obtained from a 4 hours' static incubation, resulted in an inhibition similar to the inhibition that occurred during the replacement procedure.

In Conclusion: FSH is able to maintain the meiotic arrest in pre-antral follicle enclosed oocytes at low doses only when the medium is in circulation.