title: Chronic treatment with bovine growth hormone upregulates high-affinity hepatic somatotropic receptors in sheep.
abstract: We evaluated the effect of chronic bovine growth hormone treatment on the hepatic somatotropic receptor. Growing lambs were treated with bGH at 0, 0.05, 0.15, 0.25 or 0.55 mg.kg-1.day-1 daily (N = 5/group) for 56 days. The binding of ovine GH to hepatic membranes washed with 4 mol/l MgCl2 and prepared in the presence of aprotinin was examined. The specific binding of oGH was increased (p less than 0.01) from 7.1 +/- 1.2% in saline-treated controls to 17.4 +/- 1.5% in the 0.55 mg.kg-1.day-1 group. Scatchard analysis showed curvilinear plots that best fitted a two-site model in 22/25 livers. The two sites had estimated dissociation constants (Kd) of 3 to 13 nmol/l for the low-affinity site and a Kd ranging from 0.17 to 0.31 nmol/l for the high-affinity site. Treatment with bGH had no consistent effect on the affinity of either binding site. However, bGH therapy was associated with a dose-dependent increase (p less than 0.01) in the number of high-affinity somatotropic receptors. There was no effect of bGH therapy on the concentration of low-affinity binding sites. The concentration of high-affinity receptors correlated with weight gain (r = 0.54, p less than 0.01), fat content (r = -0.54, p less than 0.01), protein content (r = 0.40, p less than 0.05), and plasma IGF-I (r = 0.57, p less than 0.005). The concentrations of low-affinity binding sites showed no such correlations.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Paediatrics, University of Auckland, New Zealand.
authors.forename: H
authors.initials: H
authors.lastname: Sauerwein
authors.forename: B H
authors.initials: BH
authors.lastname: Breier
authors.forename: J J
authors.initials: JJ
authors.lastname: Bass
authors.forename: P D
authors.initials: PD
authors.lastname: Gluckman
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001835:Body Weight; D002417:Cattle; D013006:Growth Hormone / Q000008:administration & dosage*; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008099:Liver / Q000187:drug effects*; D008297:Male; D011869:Radioligand Assay; D011986:Receptors, Somatotropin / Q000187:drug effects*; D012756:Sheep; D015854:Up-Regulation / Q000187:drug effects*; D015430:Weight Gain
chemical_list: D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone