Effect of growth hormone on steroid concentrations and mRNA expression of their receptor, and selected egg-specific protein genes in the chicken oviduct during pause in laying induced by fasting

This study was undertaken to examine the effect of growth hormone (GH) treatment during pause in laying on (1) the concentration of steroids in blood plasma and oviduct tissues, (2) the expression of mRNA of steroid receptors, and (3) the mRNA expression of selected egg-specific proteins in the chicken oviduct. A pause in egg laying was induced by food deprivation for 5 d, followed by feeding every other day, and then feeding daily from Day 10 onward. Birds were divided into three groups: control (n = 18) fed ad libitum, subjected to pause in laying (n = 18), and subjected to pause in laying and injected every day with 200 μg/kg BW of chicken GH (chGH; n = 18). The oviduct was isolated from hens of each group on Days 6 (when the oviduct was regressed), 13 (during oviduct recrudescence), and 17 or 20 (rejuvenated oviduct) of the experiment. Fasting caused a decrease in plasma concentrations of progesterone (P4), testosterone, and estradiol on Day 6 and a reduction in tissue concentrations of these steroids on Days 6 and 13. Fasting also caused an increased relative expression of estrogen receptor α and β (ERα, ERβ) and progesterone receptor (PR) in the magnum and shell gland on Day 6, increased ERα and PR in the magnum on Days 13 and 17 or 20, and increased androgen receptor (AR) mRNA in the magnum on Days 6 and 13 and in the shell gland on Day 13. A fasting-induced elevation in ovocalyxin-36 mRNA expression on Day 6 and a decrease in avidin mRNA on Days 6 and 13 and in ovocleidin-116 on Day 13 were also observed (P < 0.05 to P < 0.001). Administration of chGH abolished the fasting-induced decrease in the concentration of steroids in plasma and tissues. Furthermore, chGH enhanced the effect of fasting on mRNA expression of PR, ERα, and avidin in the magnum on Day 6, and ERα in the shell gland on Day 13. The gene expression of ovalbumin on Days 6 and 13, ovocalyxin-36 and ovocleidin-116 on Day 6 was decreased in chGH-treated chickens. In contrast, the expression of ovalbumin on Day 17 or 20 was increased (P < 0.05 to P < 0.001). The results obtained indicate that, by alterations in the concentration of steroid hormones and their receptor expression in the chicken oviduct, GH determines the rate of regression and rejuvenation of this organ during molting. Moreover, changes in the expression of selected egg proteins indicate that GH might be the regulator of the secretory activity of the hen oviduct.