Characterization of dissimilar steroid productions by granulosa, theca interna and theca externa cells during follicular maturation in the turkey (Meleagris gallopavo)

Unlike the established models for steroidogenesis in the rat and human, we have previously demonstrated that in the turkey progesterone (P), androgen (A), and estrodiol (E) are primarily produced by the granulosa, theca interna, and theca externa cells, respectively. In the present study, experiments were conducted to further characterize steroid productions by these cell types during follicular maturation. In Experiments 1 and 2, granulosa cells and theca internal cells, respectively, from the largest (F1) and fifth largest (F5) preovulatory follicles were incubated (1 × 10⁵ cells/ml) with ovine luteinizing hormone (oLH) or porcine follicle stimulating hormone (pFSH) for 5 hr. Granulosa production of P from both follicles was stimulated in response to oLH, with both basal and LH-stimulated P production greater in the larger F1 than in the smaller F5 follicle. No A or E production was detected in granulosa cells from either follicle size tested. Theca interna cell productions of P and A were stimulated by oLH in the smaller F5, but not in the larger F1, with both basal and stimulated levels of A greater in F5 than in F1. Medium content of E was non-detectable in cultures of theca interna cells from all follicles tested. In Experiment 3, theca externa cells were incubated (1 × 10⁶ cells/ml) from F1 and F5 follicles. The theca interna cells from F5 and the seventh largest follicle (F7) were pooled (1 × 10⁵ cells/ml) to provide substrate(s) for theca externa steroidogenesis. Theca externa cells were incubated alone and in combination with the pooled theca interna cells and with or without oLH or pFSH. Secretion of E by F5 theca externa cells was greater than that by F1 theca externa cells. Moreover, no significant response to LH was observed without the coincubation of the theca externa cells with the pooled theca interna cells. In Experiment 4, all follicular cells from the small white follicles (2-7 mm diameter) of ovaries were incubated together (1 × 10⁶ cells/ml) and with oLH or pFSH for 5 hr. Secretions of P, A, and E were stimulated in the presence of oLH. In the tissues tested, stimulations of steroidogenesis by pFSH may be explained by the reported LH content of the pFSH preparation. The greatest amounts of P, A, and E were produced by the F1 granulosa, F5 theca interna cells, and the F5 theca externa cells, respectively. However, the levels of E production by F5 theca externa cells were lower than those by coincubations of all cells from the small white follicles. Thus with follicular maturation, the predominant steroid produced by a follicle shifts from E to A and finally to P. This shift in predominant steroid was also associated with a change in the predominately active cell type in the follicle from the theca externa and theca interna cells in concert in the smaller follicles to the granulosa cells of the largest F1 follicle.