The relationship between the changes in insulin-like growth factor-1 (IGF-1) and the nutritional states evaluated by nitrogen balance in pregnant rats

Abstract

The effects of nutrition on serum insulin-like growth factor-1 (IGF-1) concentrations during pregnancy of rats were investigated by using rat cultured hepatocytes in vitro, and by the assessment of nitrogen balance in vivo. IGF-1 concentration was measured by radioimmunoassay, and nitrogen balance was calculated by Pregl-Dumas method. The results were as follows: (1) Cultured rat hepatocytes produced IGF-1 in medium and it was significantly stimulated by the addition of various concentrations of glucose (1.1-4.4 mM) and/or several amino acid concentrations in a dose-related manner. (2) Serum IGF-1 concentrations, which indicated 368.6 +/- 143.8 ng/ml in a non-pregnant fed state, markedly decreased in a fasted state, reaching the levels of 143.8 +/- 30.4 ng/ml after 72 hours fasting. Nitrogen balance in these fasted rats also decreased according to the fasted period. (3) In early pregnancy (Day 0-12), serum IGF-1 concentrations were indistinguishable from those of non-pregnant fed rats. It gradually declined after the 13th day of pregnancy and reached the minimum levels of 77.0 +/- 12.1 ng/ml on the 21st day. On the other hand, mean nitrogen balance which was calculated from the difference of nitrogen retention in the maternal body and that in the fetal body, also decreased after 13 days of pregnancy and reached the levels of 14.9 g/day on the 21st day of pregnancy. These results suggested that IGF-1 concentrations in rat serum and conditioned medium might be regulated by nutritional factors, i.e., glucose and/or several amino acids. The curious profiles of IGF-1 concentrations observed in pregnant rats might be due in part to the effects of nutritional changes between the maternal and fetal body, especially, the changes of protein metabolism represented by the nitrogen balance.