Effect of growth hormone on basal and LH-stimulated steroid secretion by chicken yellow ovarian follicles. An in vitro study.

The aim of the present study was to determine the effect of growth hormone (GH) on basal and LH-regulated steroid secretion by yellow hierarchical follicles before and after maturation, and the granulosa and theca layers of the largest preovulatory follicles during the ovulatory cycle in the chicken. In the first experiment, whole yellow follicles (8-12 mm, 12-18 mm, 18-24 mm and 24-30 mm) isolated from 15 and 17-18 week-old chickens were used. In the second experiment, the granulosa and theca layers of the 3 largest yellow preovulatory follicles (F3<F2<F1) were isolated from the ovary of the laying hen (age 21 weeks) at stages 22 h and 3 h before F1 ovulation. The collected follicles and fragments of the granulosa and theca layers were randomly assigned to Eagle's medium containing 0 (control), chicken GH (cGH; 10 ng/ml), ovine LH (oLH; 10 ng/ml) or cGH+oLH (10 ng/ml+10 ng/ml) and incubated for 24 h at 38 degrees C. Following incubation, the progesterone and estradiol levels were determined in collected medias by RIA. It was found that cGH (1) elevated basal progesterone secretion by all classes of yellow follicles, (2) decreased estradiol secretion by the largest (18-30 mm) follicles and (3) attenuated to the control level the LH-stimulated estradiol secretion by the theca layer of F3 and F2 follicles at 22 h before ovulation. These results suggest that GH directly stimulates progesterone secretion and inhibits estradiol secretion by yellow hierarchical ovarian follicles in chicken. However, the effect of GH on separated granulosa and theca layers of the preovulatory follicles is not as pronounced as on whole follicles. It cannot be excluded that GH temporarily modulates LH action in estradiol production by the theca cells of chicken preovulatory ovarian follicles.