Effect of growth hormone on steroid content, proliferation and apoptosis in the chicken ovary during sexual maturation

Abstract

The present study was undertaken to examine in vivo the effect of growth hormone (GH) on progesterone and estradiol levels and on cell proliferation and apoptosis in the chicken ovary during sexual maturation. Hy-Line chickens (10 weeks old) were injected three times a week with 200 μg recombinant chicken GH (cGH) per kilogram body weight until sexual maturity. GH treatment significantly increased ovarian weight at 16 weeks of age, i.e., ~1 week before onset of egg laying. The progesterone content in the ovary just before and at the time of sexual maturity and the estradiol content before onset of egg laying were also elevated after cGH injections. The highest number of proliferating (positive for proliferating cell nuclear antigen) and apoptotic (positive for terminal-deoxynucleotidyl-transferase-mediated dUTP nick-end labeling) cells was found in the ovarian stroma and white follicles (>1-4 mm diameter), whereas the lowest number of these cells was detected in yellow (>8-30 mm) follicles. Administration of cGH significantly stimulated cell proliferation and inhibited cell apoptosis in the ovarian stroma and small ovarian follicles. The number of ovarian follicles and the weight of the ovary prior to the first oviposition were also higher in cGH-injected hens. Thus, prior to and after the onset of egg laying, GH participates in the growth, maturation and hormonal activity of ovarian follicles in the chicken, via the regulation of steroidogenesis, proliferation and apoptosis processes.

Gonads directly regulate growth in teleosts

“…GH is produced primarily in the pituitary by the somatotrophic cells of the mesoadenohypophysis, although it is well established that some extrapituitary tissues express the GH gene, and that its product is not released into the systematic circulation but acts locally in an autocrine or paracrine manner (26). Although GH is expressed in the gonads of mammals (13,14), birds (15)(16)(17)(18), and fish (27,28), the function of gonadal GH in regulating growth has not been determined. Our results indicate that the gonads play an important role in the regulation of body growth in both male and female tilapia.…”

“…These results suggest that the release of GH from ectopically transplanted gonads stimulates growth. GH and IGF-I are expressed in the testis of human and chicken (17)(18)(19)(20)(21), and the gonads might produce both GH and IGF-I, although there might be differences between species. The roles of these hormones produced from the gonads in growth are not clearly understood, however.…”

“…These two hormones are known to directly stimulate growth. Although GH is classically associated with the pituitary, and the major source of IGF-I is the liver, recent studies have demonstrated that these hormones are expressed in other tissues as well (12)(13)(14)(15)(16)(17)(18), where their functions are unclear. In tilapia, both hormones are expressed as mRNA and protein in the testis and the ovary (Fig.…”

Growth hormone production and role in the reproductive system of female chicken

“…Moreover, yellow hierarchical follicles were present in the ovaries of most GH treated hens but not in the control hens ( Fig. 1), suggesting the involvement of GH in the selection of small prehierarchical follicles into hierarchy of yellow preovulatory follicles (Hrabia et al, 2011). In other experiments Donoghue et al (1990) found that GH injections for 3 weeks to older egg laying White Leghorn hens did not affect egg production, but significantly improved eggshell quality.…”

“…Moreover, a role for pituitary GH in the function of the ovary is also supported by an increase in the number of small ovarian follicles after GH administration to laying hens (Williams et al, 1992). Similarly, injections of recombinant chicken GH (cGH) to chickens prior to the onset of egg laying resulted in increased ovarian weight (13.5 ± 6.14 g vs 0.89 ± 0.14 g or 7.70 ± 4.17 g vs 1.10 ± 0.12 g, dependently on experiment) about one week before sexual maturity (Hrabia et al, 2011). Moreover, yellow hierarchical follicles were present in the ovaries of most GH treated hens but not in the control hens ( Fig.…”