Nutritional dependence of insulin-like growth factor (IGF) receptors in skeletal muscle: measurement by light microscopic autoradiography.
To determine the cellular location, capacity, and nutritional sensitivity of insulin-like growth factor (IGF) receptors, we measured the in vitro binding of [125I]-IGFs to skeletal muscle using light microscopic autoradiography. Muscle was collected from 8-month lambs that had received high or low nutrition diets (3% and 1.25% of body weight/day in pellets, respectively). Half of each group had also received growth hormone (0.25 mg/kg/day). Cryosections were incubated with [125I]-IGF alone or with unlabeled IGF-1, IGF-2, or insulin to characterize binding sites as probable Type 1 IGF, Type 2 IGF, or insulin receptors. [125I]-IGF-1 was found to bind to blood vessels and Type 1 receptors in connective tissue (p < or = 0.001), but not to muscle fiber or nerves. In muscle from 6-month lambs that were fed or fasted, [125I]-IGF-1 bound to Type 1 receptors in connective tissue (p < or = 0.01 fed; p < or = 0.05 fasted) and muscle fiber (p < or = 0.05). The binding to connective tissue was also greater in fasted than in fed animals (p < or = 0.05). Binding of [125I]-IGF-2 to the Type 2 receptor was located in blood vessels and connective tissue (p < or = 0.01) and did not alter with fasting. Therefore, these experiments have demonstrated that Type 1 and Type 2 receptors vary in their distribution and nutritional sensitivity in skeletal muscle.
Oldham
J M
JM
Department of Biological Sciences, University of Waikato, Hamilton, New Zealand.
Hodges
A K
AK
Schaare
P N
PN
Molan
P C
PC
Bass
J J
JJ
D000818:Animals; D001160:Arterioles / Q000378:metabolism; D001345:Autoradiography; D003238:Connective Tissue / Q000737:chemistry / Q000378:metabolism; D005215:Fasting; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D009747:Nutritional Physiological Phenomena; D017526:Receptor, IGF Type 1 / Q000032:analysis / Q000378:metabolism*; D017527:Receptor, IGF Type 2 / Q000032:analysis / Q000378:metabolism*; D012756:Sheep; D014699:Venules / Q000378:metabolism
D017527:Receptor, IGF Type 2; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone; D017526:Receptor, IGF Type 1