Effect of activin A and inhibin A on expression of the inhibin/activin beta-B-subunit and gonadotropin receptors in granulosa cells of the hen.

Activin A has been shown to be abundant in the theca layer of the large pre-ovulatory follicles of the hen whereas inhibin A is produced in the granulosa layer. The purpose of this study was to investigate the effects of activin A and inhibin A on granulosa cell expression of inhibin beta-B-subunit, FSH receptor (FSHR), and LH receptor (LHR). Granulosa cells were isolated from the F1, F3+F4, and small yellow follicles (SYF; 6-12 mm diameter) of laying hens and pooled according to size. The cells were dispersed and plated in the presence of 0, 10, or 50 ng/ml recombinant human activin A (n=5 replicate cultures). RNA was subsequently extracted from the cells and Northern blots performed. Cell proliferation was determined for all treatments. An identical set of experiments was performed in which the granulosa cells were treated with recombinant human inhibin A (n=4 replicate cultures). Treatment with activin A at 50 ng/ml significantly (p<0.05) increased expression of beta-B-subunit for granulosa cells from all follicles. This dose also significantly increased expression of FSHR in granulosa cells from all follicles (p<0.05) and increased expression of LHR in cells from F1 and F3+F4 follicles (p<0.01) with no significant effect on cells from the SYF. Overall, activin A treatment significantly (p<0.05) decreased cell proliferation at the 50 ng/ml dose. Inhibin A had no significant effect on expression of beta-B-subunit, FSHR or LHR at any dose. There was a moderate stimulatory effect of inhibin A on granulosa cell proliferation. These results suggest that activin A may have an important role in regulating granulosa cell responsiveness to gonadotropins while also modulating follicle development by attenuating cell proliferation.