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 I-125 -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 memb rane preparations using competitive displacement assay and SDS-PAGE. I n both muscles, I-125-IGF-II binding was more abundant in connective t issue than muscle fibre (P less than or equal to 0.001). Levels change d significantly with age in all cell types studied (P less than or equ al to 0.001), while changes as a result of fasting were limited to a d ecrease in binding to the connective tissue of M. biceps femoris (P le ss than or equal to 0.01). The overall decline of I-125-IGF-II binding with increasing age is correlated with a slowing of postnatal growth, while the reduction in I-125-IGF-II binding with fasting may be assoc iated with modulating growth and composition of connective tissue, or increasing the bioavailability of IGF-II to specific muscles.