CHRONIC ADMINISTRATION OF GROWTH-HORMONE (GH) TO ADULT CHICKENS EXERTS MARKED EFFECTS ON CIRCULATING CONCENTRATIONS OF INSULIN-LIKE GROWTH-FACTOR-I (IGF-I), IGF BINDING-PROTEINS, HEPATIC GH REGULATED GENE-I, AND HEPATIC GH RECEPTOR MESSENGER-RNA

In young birds, growth hormone (GH) administration has been found to h ave only a small or even no effect on circulating concentrations of in sulin-like growth factor-I (IGF-I). This is in obvious contrast to the situation in mammals. The present study examines the effect of contin uous administration of GH in adult male chickens. Plasma concentration s of IGF-I were markedly elevated (2.5-3.0-fold, p < 0.001) in GH-trea ted chickens. There were also some transient increases in the circulat ing levels of IGF binding proteins. Adult chickens showed other manife stations of increased responsiveness to GH, including elevated hepatic expression of GH-regulated gene-I (mRNA) with GH treatment (p < 0.05) , and a tendency (p < 0.08) for decreased GH-receptor mRNA. In contras t to the changes in circulating concentrations of GH and IGF-I with GH treatment, no changes in plasma concentrations of thyroid hormones, r eproductive hormones, glucose, or nonesterified fatty acids were evide nt.