INHIBIN-A AND INHIBIN-B SECRETION IN MOUSE PREANTRAL FOLLICLE CULTURE

Conditioned media from single mouse ovarian follicles cultured from th e early preantral stage up to complete maturity were analysed for diff erent immunoreactive inhibin forms. The inhibin assays measured (i) al pha-specific inhibin, as represented by a mix of 32 and and 57 kDa inh ibins, inhibin precursors, alpha-subunit and its precursors; (ii) dime ric inhibin A; and (iii) dimeric inhibin B. The validity of these assa ys for the measurement of mouse inhibin was established. All forms of inhibin were secreted in culture media from the preantral follicle sta ge onwards. Inhibin B was the most sensitive marker for proliferation of early stage follicles, while inhibin A secretion became predominant at later stages, when antral like cavities were formed in granulosa c ell masses. Supplementation of standard culture medium with recombinan t follicle stimulating hormone appeared to be the predominant regulato r of inhibin secretion; addition of recombinant luteinizing hormone th roughout the culture period did not cause any major shifts in the expr ession of dimeric inhibin or alpha-specific inhibin forms. In the abse nce of theca cells during isolation and culture (as reflected by absen ce of oestrogen secretion), follicles grew at a reduced rate, and prod uced lower inhibin concentration in conditioned medium. These data sug gest (i) that monitoring of dimeric inhibins can provide useful marker s of the growth and differentiation of cultured follicles and (ii) tha t dimeric inhibins A and B are secreted at an earlier stage in vitro t han in vivo.