Developmental changes in insulin-like growth factor-I (IGF-I) receptor levels and plasma IGF-I concentrations in...

The developmental pattern of insulin-like growth factor-I receptor (IGF-IR) and plasma IGF-I concentrations were examined in longissimus dorsi (LD), trapezius (TR), and liver from the last third of gestation up to 1 year of age in male Large White (LW) and Meishan (MS) pigs. Plasma IGF-I concentrations increased between 75 days of gestation and 180 days of age with a 100-fold increase and decreased thereafter. At 180 and 365 days of age, plasma IGF-I concentrations were higher in LW than in MS pigs. 125I-IGF-I specific binding was detected in liver and skeletal muscle (not determined in fetal TR) from 75 days of gestation until the adult stage in both breeds. Affinity cross-linking experiments followed by electrophoresis under reducing conditions revealed the presence of one band with an apparent molecular weight of 140 kDa in fetal liver and LD. In displacement experiments, data indicated that IGF-I bound specifically to IGF-IR in both prenatal and postnatal tissues. Specific binding increased between 75 and 90 days of gestation in both liver and LD. It remained elevated until 103-113 days of gestation and tended to be higher in MS than in LW fetal liver. After birth, it decreased to remain stable thereafter. The developmental pattern of IGF-IR is concluded to be similar in liver and skeletal muscle of LW and MS pigs. The few differences observed between LW and MS pigs cannot account for their different growth performances. The high binding in fetus suggests that IGF-IR may play an important role in fetal growth and development.