Somatomedin activity and growth hormone levels in body fluids of the fetal pig: effect of chronic hyperinsulinaemia

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Abstract
Chronic hyperinsulinemia in the presence of euglycemia was obtained in pig fetuses between 90 and 104 days gestational age (term is 114 days) by the implantation of insulin-filled osmotic mimipumps. At 104 days these fetuses were compared with saline-implanted controls and with unoperated fetuses from the same sows. Mean plasma GH [growth hormone] levels were the same in all 3 treatment groups and were much greater than in the maternal peripheral venous circulation. Levels of GH in amniotic fluid were low, and even lower levels were measured in lung fluid. Glucose and protein levels were also lower in amniotic fluid than in plasma and lower still in lung fluid. Somatomedin activity was higher in amniotic and lung fluids than in fetal plasma and, when expressed relative to protein content, was highest in lung fluid. Insulin-treated fetuses had significantly (P < 0.05) higher levels of somatomedin activity than control fetuses, but despite this, were neither longer nor heavier than control fetuses. Evidently, neither insulin nor somatomedin directly affect fetal growth.