A series of experiments have been carried out to determine whether follicles secrete factors able to affect the growth and development of other, like-sized follicles. Late preantral mouse ovarian follicles were either cocultured or cultured in media conditioned by previously cultured follicles. In particular, the experiments examined whether follicles do secrete such factors, whether the level of FSH in the culture media can affect that process, and what the nature of such secretory factor(s) might be. First, pairs of follicles were cocultured across a polycarbonate membrane containing pores. This showed that communication between the follicles resulted in the stimulation of growth and that the stimulation was due, at least in part, to the production of secretory factor(s). In subsequent experiments, follicles were cultured in media that had been preconditioned by previously cultured follicles. The concentration of FSH in the cultures determined the effect of the conditioned media: conditioned media was stimulatory to follicle growth when levels of FSH remained high throughout the culture, but inhibitory when FSH levels were dropped midway through the cultures. Heat inactivation removed this inhibitory effect, showing that the factor was likely to be a protein; addition of follistatin to the conditioned media did not alter its effect, indicating that the factor was unlikely to be activin. We have shown through a series of culture experiments that mouse follicles secrete factor(s) that can affect the development of other like-sized follicles when cultured from the late preantral to Graafian stages. Furthermore, we have shown that the effect (or production) of such factors is dependent on the FSH environment of the follicles.

The effects of androgens on ovarian follicular development have been investigated using a whole follicle culture system. Follicles obtained from mouse ovaries and cultured in the presence of anti-androgen serum grew more slowly than control follicles. This effect was reversed by the addition of androstenedione to the medium. A similar effect was obtained when receptor-mediated effects of androgens were blocked using an androgen receptor antagonist. When follicles were grown in concentrations of FSH that are marginal for follicle development, they developed faster in the presence of a non-aromatizable androgen, dihydroxytestosterone. The results indicate that androgens exert a direct, stimulatory role on the growth and development of mouse antral follicles, in vitro.

A whole follicle culture system has been used to investigate the actions of gonadotrophic hormones, oestrogen and progesterone in the regulation of follicular development and steroidogenesis. Recombinant human FSH was required for the growth of preantral follicles and for Graafian morphogenesis, whereas recombinant LH was ineffective. While pure FSH was sufficient for growth and morphogenesis, production of oestrogen was greater when androstenedione or LH was present in combination with FSH, confirming that there is a two-cell mechanism for oestradiol production in the mouse follicle. When an antiserum to oestrogen or to progesterone or an oestrogen receptor antagonist were added to the culture medium, there was no significant effect on either follicular growth or oestradiol production. Thus, physiological concentrations of oestradiol are not needed for follicle development, although a role cannot be completely ruled out. In conclusion, the obligatory role of FSH was demonstrated. It appears to be sufficient for follicle development even in the absence of LH, and the paracrine or autocrine effects of oestradiol and progesterone, if any, appear to be minor in the mouse ovary.