Characterization of growth hormone binding sites in granulosa and theca layers at different stages of follicular maturation and ovulatory cycle in the domestic hen.

The currently available evidence points to a possible influence of growth hormone (GH) on avian folliculogenesis, which can be mediated by both hepatic- and ovarian-derived IGF-I. Therefore, the purpose of the present study was to reveal GH-binding sites in granulosa and theca layers of preovulatory follicles and to determine the binding characteristics depending on the degree of follicular maturation and the stage of the ovulatory cycle in the hen. Hens were killed 2 h (stage I), 9 h (stage II), 16 h (stage III), and 23 h (stage IV) after oviposition, and the five largest yellow follicles (from F1 to F5) were removed. GH-binding sites in granulosa and theca layers from F1 to F5 follicles were characterized using a radioreceptor assay. Equilibrium dissociation constants (K(d)) and binding capacities (B(max)) were determined by Scatchard analysis of saturation curves, which revealed a single class of high-affinity GH-binding sites in both theca tissue and granulosa cells. In F1, F2, and F5 follicles, B(max) and K(d) for GH-binding sites in the granulosa layer changed during the ovulatory cycle, decreasing between stages I and III, to increase again at stage IV, with alterations in K(d) being less profound. No significant differences in binding capacities and affinities of GH-binding sites in the theca layer were found between various stages of the cycle. Furthermore, the concentration of GH-binding sites in the granulosa layer rose, whereas that in the theca layer fell with follicular enlargement. These findings indicate the presence of high-affinity GH-binding sites in both granulosa and theca layers of hen preovulatory follicles. Data also demonstrate that GH-binding sites in these tissues are regulated in a tissue-specific manner. Furthermore, the regulation of binding capacity of GH binding in granulosa cells by hormonal factors associated with ovulatory cycle is apparently not dependent on the state of follicular maturation.