Effect of FSH and cell localization on dimeric inhibin-A secretion from bovine granulosa cells in culture

Abstract

We tested the hypotheses that the secretion of dimeric inhibin-A from cultured bovine granulosa cells is stimulated by FSH, and that antral cells secrete more inhibin-A than do mural cells. Cells from the antral or mural compartment of follicles were cultured in defined medium in two culture systems, and dimeric inhibin-A was measured by two-site ELISA or by Western immunoblotting. In the first culture system, dimeric inhibin-A secretion declined with time in culture, but was significantly (P<0·05) higher from antral than from mural cells (as was total inhibin-measured by RIA). The secretion of dimeric inhibin-A and inhibin-from antral but not mural cells was responsive to FSH. In the second culture system, dimeric inhibin-A secretion increased with time in culture, and was significantly stimulated by FSH, but FSH responsiveness was dependent on the concentrations of insulin in the culture medium. The major forms of inhibin-A secreted had molecular masses of approximately 58, 62, 103-116 and >116 kDa; the 32 kDa form was barely detectable. These different forms were all stimulated by FSH, but the >116 and 62 kDa forms were most responsive to FSH. We conclude that (i) FSH stimulates dimeric inhibin-A secretion from bovine granulosa cells, (ii) the 62 kDa form of inhibin-A may be more responsive to FSH than the 58 kDa form, and (iii) the spatial differentiation of granulosa cell function within the follicle previously observed for oestradiol secretion was also observed for inhibin-and dimeric inhibin-A secretion.

Interactions Between Follicle-Stimulating Hormone and Growth Factors in Modulating Secretion of Steroids and Inhibin-Related Peptides by Nonluteinized Bovine Granulosa Cells1

“…These discrepancies most likely reflect the fact that we used an assay that specifically detects dimeric inh A (␣-␤ A dimer), rather than ␣ subunit-directed RIAs as used by these authors. In agreement, Boudjemaa et al [48] recently reported an FSHinduced increase in inh A secretion by bovine granulosa cells cultured in conditions similar to ours; they also used a two-site immunoassay to specifically detect the ␣-␤ A dimer.…”

Ovarian follicle development in the laying hen is accompanied by divergent changes in inhibin A, inhibin B, activin A and follistatin production in granulosa and theca layers

“…Studies in mammals indicate that activin can promote proliferation, inhA and B production (Lanuza et al 1999, Boudjemaa et al 2000, Findlay et al 2001 and FSH receptor expression by undifferentiated rat G cells (Hasegawa et al 1988, Xiao et al 1992) and, in turn, promote FSH-induced stimulation of LH receptor expression and upregulation of steroidogenesis (Hillier et al 1994). From the present observations, 'activin tone' appears to decrease progressively as small follicles grow from 1-2 mm to 9 mm, the approximate point of recruitment into the preovulatory hierarchy.…”

Plasma Concentrations of Inhibin A and Follicle-Stimulating Hormone Differ Between Cows with Two or Three Waves of Ovarian Follicular Development in a Single Estrous Cycle1

“…Because the early growth of the follicle cohort would be stimulated by FSH, increases in the concentration of inhibin A may have been caused primarily by the increased number of newly emerged and growing follicles. FSH has also demonstrated a direct action on inhibin A production by antral follicle granulosa cells in culture [28]. The dominant follicle was approximately 8-9 mm in diameter on the day of peak plasma concentrations of inhibin A.…”