Submitted to: Journal of Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/1996
Publication Date: N/A
Citation: Interpretive Summary: Growth hormone (GH) promotes bone growth and body weight gain in mammals and most vertebrates. Many of the growth-promoting actions of GH are mediated by insulin-like growth factor-I (IGF-I), which is produced by the liver and other tissues under the influence of GH. In these species, removal of GH by hypophysectomy greatly reduces blood IGF-I levels, while GH supplementation restores circulating IGF-I concentrations. In poultry species, both hypophysectomy and GH replacement therapy are relatively ineffective in altering circulating IGF-I levels during growth. The present study was designed to determine if adult chickens, which have low circulating concentrations of GH and IGF-I, are responsive to administered chicken GH. Results showed that continuous administration of GH to adult male chickens elevated circulating IGF-I concentrations up to 3-fold, and increased expression of another hepatic GH-regulated gene. GH treatment had no effect on blood levels of thyroid or reproductive hormones. These findings demonstrate an important age difference in the physiological response of chickens to GH. Scientists will use these results to better understand the growth process in poultry, and to design further research which will explore the physiological basis for the growth differences between chickens and other meat-producing animals.
Technical Abstract: In young birds, growth hormone (GH) administration has been found to have only a small or even no effect on circulating concentrations of insulin-like growth factor - (IGF_)I. This is in obvious contrast to the situation in mammals. The present study examines the effect of continuous administration of GH in adult male chickens. Plasma concentrations of IGF-I were markedly elevated (2.5-2.0 fold, P < .001) in GH-treated chickens. There were also some transient increases in the circulating levels of IGF binding proteins. Adult chickens showed other manifestations of increased responsiveness to GH including elevated haptic expression of GH regulated gene-I with GH treatment (P < .05), and decreased GH receptor mRNA. In contrast to the changes in circulating concentrations of GH and IGF-I with GH treatment, no changes in plasma concentrations of thyroid hormones, reproductive hormones, glucose, or non-esterified fatty acids were evident.