GROWTH-HORMONE INCREASES INSULIN-LIKE GROWTH FACTOR-I (IGF-I) AND DECREASES IGF-II IN PLASMA OF GROWING-PIGS

Insulin-like growth factor I (IGF-I) and IGF-II have been measured in plasma obtained from male and female pigs of two strains during daily administration of pituitary-derived porcine GH (pGH; 100 μg/kg) from 60 to 90 kg body weight. Each plasma sample was first chromatographed to separate the IGF from binding proteins in order to obtain reliable measurements. IGF-I concentrations showed no differences between strains, but were higher in untreated males (497 ± 43 (S.E.M.) μg/l) than females (299 ± 15 μg/l). GH-treated animals had two-fold higher concentrations of IGF-I. IGF-II concentrations were not significantly different between sexes or strains, but were decreased in pigs treated with pGH (299 ± 28 μg/l) compared with controls (431 ± 32 μg/l). Binding protein concentrations, measured as interference in the IGF-I and IGF-II assays, were not different between sexes of strains, but were increased in pGH-treated animals. Taken together, these results indicate that in addition to the expected increase in IGF-I concentrations, exogenous administration of pGH to pigs leads to an increase in IGF-binding protein and a depression in IGF-II concentrations.