Postnatal age and food intake alter insulin-like growth factor-II/mannose-6-phosphate receptors in ovine skeletal muscles.
In female lambs aged from 2 days to 2 years, specific binding of 125I-IGF-II in muscle fibre and connective tissue of M. biceps femoris and M. gastrocnemius was demonstrated using histological autoradiography. The binding site was characterized as the IGF-II/M6P receptor in membrane preparations using competitive displacement assay and SDS-PAGE. In both muscles, 125I-IGF-II binding was more abundant in connective tissue than muscle fibre (P < or = 0.001). Levels changed significantly with age in all cell types studied (P < or = 0.001), while changes as a result of fasting were limited to a decrease in binding to the connective tissue of M. biceps femoris (P < or = 0.01). The overall decline of 125I-IGF-II binding with increasing age is correlated with a slowing of postnatal growth, while the reduction in 125I-IGF-II binding with fasting may be associated with modulating growth and composition of connective tissue, or increasing the bioavailability of IGF-II to specific muscles.
Oldham
J M
JM
AgResearch Ruakura, Hamilton, New Zealand.
Martyn
J A
JA
Napier
J R
JR
Bass
J J
JJ
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D001682:Biological Availability; D003238:Connective Tissue / Q000378:metabolism; D004435:Eating / Q000502:physiology*; D005260:Female; D007457:Iodine Radioisotopes; D008566:Membranes / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D012756:Sheep
D007457:Iodine Radioisotopes; D017527:Receptor, IGF Type 2