Modulation of intrafollicular oestradiol in explanted hamster follicles does not affect oocyte meiotic status

Mature antral follicles were collected from PMSG-primed hamsters before the LH surge on Day 4 of the oestrous cycle and were incubated individually for 6 or 10 h under 95% O2 and 5% CO2. The relationship between follicle size and follicular fluid volume was established, and both the oestradiol output during incubation and the LH sensitivity of the follicle with respect to induction of meiotic resumption were determined. The data obtained from these initial studies were then applied to experiments in which the oestrogenic status of follicles was altered by pressure injection of solutions into the antral cavity to result in known concentrations in follicular fluid of oestradiol (0-500 microM), the anti-oestrogens, tamoxifen (0-200 microM) or enclomiphene citrate (0-500 microM), or an oestradiol-specific antiserum (1:200 dilution of serum). The proportion of immature oocytes (% GV) was determined cytogenetically after follicular incubation. Significant correlations were established between follicle size and both follicular fluid volume (r = 0.90) and follicular oestradiol accumulation (r = 0.96). The minimum concentration of LH tested which induced maximal meiotic resumption (0% GV) was 0.5 microgram/ml. The % GV was not significantly reduced by intrafollicular injection of either of the anti-oestrogens over the concentration ranges tested, or of the oestradiol-specific antiserum, which was injected in an amount adequate to bind all oestradiol accumulated during the incubation. Intrafollicular injection of oestradiol failed to increase the % GV after follicular incubation in the presence of 0.5 microgram LH/ml. From these results we conclude that it is unlikely that oestradiol plays a primary role in the maintenance of meiotic arrest in follicle-enclosed hamster oocytes in vitro.