|BRADY, KRISTEN - University Of Maryland
|PORTER, TOM - University Of Maryland
|LIU, HSIAO-CHIN - North Carolina State University
Submitted to: Molecular Reproduction and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2019
Publication Date: 1/24/2020
Citation: Brady, K., Porter, T.E., Liu, H., Long, J.A. 2020. Characterization of the hypothalamo-pituitary-gonadal axis in low and high egg producing turkey hens. Molecular Reproduction and Development. 99(2):1163-1173. https://doi.org/10.1016/j.psj.2019.12.028.
Interpretive Summary: Turkey hens have the capacity to lay an egg on a daily basis (every 24 to 26 hours or 6-7 eggs/week); however, there are hens that routinely produce fewer eggs (3-4 eggs per week). Understanding the mechanism of why low egg producing hens (LEPH) ovulate less frequently than high egg producing hens (HEPH) is important to improve reproduction in commercial operations. Ovulation is trigged by a preovulatory surge of luteinizing hormone (LH) and progesterone, and is governed by the hypothalamo-pituitary-gonadal (HPG) axis. The two hypothalamus hormones, gonadotropin releasing hormone (GNRH) and gonadotropin inhibitory hormone (GNIH), act on the pituitary gland to stimulate (GNRH) or inhibit (GNIH) the production of LH. This hormone in turn acts upon the ovarian follicles to produce either progesterone or estradiol. To determine if these mechanisms were altered in LEPH, pituitary cells collected from LEPH and HEPH were cultured in vitro, treated with GNRH or GNIH and then examined for changes in expression of genes related to ovulation. Similarly, ovarian follicles from LEPH and HEPH were treated in cell culture with LH or follicle stimulating hormone (FSH), followed by radioimmunoassay’s for to measure progesterone and estradiol production by the cells. Pituitary cells from HEPH had higher expression of genes associated with ovulation stimulation; whereas LEPH pituitary cells showed up-regulation of genes associated with the inhibition of ovulation. Moreover, the follicles from HEPH were more sensitive to LH and FSH treatment. Taken together, these results suggest possible physiological mechanisms for the poor egg production in some turkey hens.
Technical Abstract: Low egg producing hens (LEPH) ovulate less frequently than high egg producing hens (HEPH). Ovulation is trigged by a preovulatory surge of luteinizing hormone (LH) and progesterone and is governed by the hypothalamo-pituitary-gonadal (HPG) axis. Pituitary cell production of LH is stimulated by gonadotropin releasing hormone (GNRH) and inhibited by gonadotropin inhibitory hormone (GNIH). Granulosa cells from the largest follicle (F1G) respond to LH to produce progesterone while small white follicle cells (SWF) respond to follicle stimulating hormone (FSH) to produced estradiol. Pituitary cells from LEPH and HEPH were subjected to both GNRH and GNIH treatment followed by expression analysis for HPG axis genes related to ovulation while F1G and SWF from LEPH and HEPH were subjected to LH and FSH treatment, respectively, followed by radioimmunoassay’s for progesterone and estradiol production. Results were analyzed by a two-way ANOVA using the mixed models procedure of SAS. In response to GNRH and GNIH treatment, HEPH pituitary cells showed up-regulation of genes associated with ovulation stimulation, whereas LEPH cells showed up-regulation of genes associated with inhibition of ovulation. HEPH F1G and SWF cells displayed a higher sensitivity and responsiveness to LH and FSH treatment, respectively. Level of egg production impacted ovulation related gene expression in pituitary cells after neuropeptide treatment as well as steroid hormone production of F1G and SWF cells after gonadotropin treatment, with HEPH displaying a greater positive response to HPG axis stimulation.