Elevated level of serum retinol-binding protein 4 in pregnancy-induced hypertension

Recent progress in adiposcience has revealed several important adipose-tissue-originated factors, so-called adipokines. Retinol-binding protein 4 (RBP4), a protein expressed and secreted by adipocytes, has been identified as a novel regulator of insulin resistance. Physiological insulin resistance occurs during the pregnancy of mammals to accommodate fetal growth, and it has been suggested that insulin resistance and hyperinsulinemia might also be associated with pregnancy-induced hypertension (PIH). In order to shed light on the role of RBP4 during pregnancy, we attempted to assess RBP4 levels during pregnancy. Fetal growth could be affected by aberrant regulation of RBP4 levels in fetal circulation per se, so we examined the RBP4 levels in cord blood samples of growth restricted cases. Circulating RBP4 levels were examined in non-pregnant and pregnant healthy women using Western blotting. Also, RBP4 levels in normal pregnancy and PIH were quantitated using Dot-blot analysis. RBP4 levels in cord blood samples also were evaluated in selected cases. RBP4 levels tended to decrease after early gestation with no obvious difference between mid- to late-gestation. RBP4 levels were increased in pregnant women with PIH compared with normal pregnancies (P < 0.01). RBP4 levels were decreased in the cord blood of PIH pregnancies and light-for-dates infants without obvious causes for intrauterine growth restriction compared with normal pregnancies (P < 0.01). These results suggest that circulating RBP4 could be elevated in PIH, where maternal glucose metabolism is perturbed, and that RBP4 levels in cord blood might be closely associated with fetal growth.