In the present study, the expression of inhibin/activin subunits in the mouse ovary from 13 days post-coitus (dpc) to 30 days postpartum (dpp) was investigated. Circulating FSH, LH, inhibin A, and inhibin B in neonatal to 30 dpp ovaries were measured. Inhibin/activin subunits (α, βA, βB ) were weakly stained in 13 dpc ovarian stromal cells and increased with age. Inhibin α subunit was immunolocalized in follicular granulosa cells at each developmental stage. In 30 dpp ovaries, several large

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... al follicles were strongly stained for inhibin α subunit. Inhibin βA subunit was weakly immunolocalized in granulosa cells until 20 dpp. Moreover, 2 to 3 antral follicles from 20 to 30 dpp were strongly stained for inhibin βA subunit. There was relatively high immunoactivity for inhibin βB subunit in neonatal to 30 dpp mouse ovaries. All three inhibin subunits were stained in thecainterstitial cells from 15 dpp onward. RIA data showed that a temporal increase in circulating FSH occurred around 10 dpp, while the plasma concentrations of LH were sustained at a relatively higher level from 8 to 15 dpp. Inhibin B was detectable in circulation early at 1 dpp (day of birth), and a clear increase in inhibin B occurred around 8 dpp. Circulating inhibin B gradually increased from 20 dpp to 30 dpp, indicating a negative correlation with FSH. Inhibin A levels were only measured on 25 and 30 dpp, and the levels were low. These results suggest that inhibins play an important role in early folliculogenesis in mice. In addition, inhibin B seems to be the main functional isoform from the neonatal to prepubertal stage in the mouse ovary. he dimeric proteins formed from the inhibin/ activin subunits are members of the TGF β superfamily of growth and differentiation factors. T h e s e p r o t e i n s h a v e b e e n i s o l a t e d a n d characterized as gonadal-derived regulators of FSH secretion [1] . Previous evidence suggests that the inhibin/activin subunits could exert local autocrine and paracrine roles on steroidogenesis and folliculogenesis in developing ovaries [2] [3] [4] [5] [6] . The temporal expression patterns of the inhibin/activin subunits have been investigated in immature mice [7] , rats [8-10], and lambs [11] . Expression of inhibin mRNAs and proteins has also been found