Structure and steroidogenic activity of the granulosa layer of F1 preovulatory ovarian follicles of the hen (Gallus domesticus)

The study was performed to determine the structure and steroidogenic activity of granulosa cells derived from the germinal disc region, proximal region and distal region of the largest preovulatory ovarian follicle (F1) of the hen. The study was carried out on 34 Hy-Line Brown egg-laying hens aged 40 weeks. Morphology of the granulosa cells was studied by histological assessment and scanning electron microscopy. Moreover, the level of P4, histochemical activity of 3beta-HSD and expression of 3beta-HSD gene mRNA in granulosa cells of F1 follicle were determined. The findings indicate that the morphology and steroidogenic activity of the granulosa layer in F1 preovulatory ovarian follicle are associated with the region of the follicle. This is consistent with earlier studies. In the germinal disc region the granulosa cells form a multilayer while in the proximal and distal regions granulosa cells form a single layer. Analysis of P4 concentration revealed that its level in granulosa cells was markedly reduced closer to the germinal disc. Moreover, our study demonstrates for the first time the lower histochemical activity of 3beta-HSD and expression of 3beta-HSD mRNA in granulosa cells from the germinal disc region compared with the proximal and distal region.