Implication of maternal nitrogen balance in the regulation of circulating levels of insulin-like growth factor-I in human pregnancy.

Abstract

Nutrition plays an important role in regulating the circulating levels of insulin-like growth factor-I (IGF-I). We have demonstrated that reduced nitrogen balance is related to changes in serum IGF-I levels but not serum growth hormone levels in pregnant rats. In the present study, we investigated the effects of changes in nitrogen balance on serum IGF-I levels in normal and malnourished pregnant women (defined as having negative nitrogen balance). Forty-eight pregnant women (threatened miscarriage and premature labor, 39; pre-eclampsia, 3; hyperemesis, 3; ileus, 2; bleeding from the colon, 1) and 19 non-pregnant women admitted in Kobe University Hospital were enrolled in this study. Blood samples of normal pregnant controls were also obtained from 172 healthy pregnant women attending the outpatient clinic. Serum IGF-I levels and nitrogen balance were measured serially in 9 pregnant women with threatened miscarriage and premature labor and 9 malnourished pregnant women out of 48 pregnant women. Serum IGF-I and urinary nitrogen levels were measured by radioimmunoassay with acid-ethanol extraction and the Dumas method, respectively. Nitrogen balance was expressed as the difference between daily nitrogen intake and nitrogen excretion assessed by urinary nitrogen levels. Serum IGF-I levels in normal pregnant controls significantly increased in the third trimester of pregnancy compared with non-pregnant controls. No difference in serum IGF-I levels in any trimester of pregnancy was observed between normal pregnant controls and pregnant women with threatened miscarriage and premature labor. There was no significant difference in nitrogen balance between the pregnant women with threatened miscarriage and premature labor and non-pregnant controls. In the longitudinal study, no correlation was found between the changes in serum IGF-I levels and those in nitrogen balance in the 9 pregnant women with threatened premature labor (daily nitrogen balance > 0 g/day) on the basis of linear regression analysis. On the other hand, the changes in serum IGF-I levels in the 9 malnourished pregnant women were significantly correlated with those in nitrogen balance (y = 1.72x + 17.5; r = 0.60; P < 0.05: linear regression analysis). These results indicate that maternal nutritional states have a major effect on serum IGF-I levels in malnourished pregnant women, but not in pregnant women with daily nitrogen balance > 0 g/day. Serum IGF-I levels can be a potent index of nutritional states under malnutrition during human pregnancy.