Nicotine-induced prenatal overexposure to maternal glucocorticoid and intrauterine growth retardation in rat

Overexposure to glucocorticoid during fetal development can result in intrauterine growth retardation (IUGR) as well as other diseases after birth. The purpose of this study is to investigate the possibility of glucocorticoid disturbance-mediated nicotine-induced IUGR after chronic prenatal exposure. Nicotine at 1.0 mg/kg twice a day was administered subcutaneously to pregnant rats from gestational day (GD) 8 to GD 15 (mid-gestation) or GD 21 (late-gestation). Placental weights and fetal developmental parameters were recorded. Corticosterone levels were determined by radioimmunoassay. The mRNA expressions of adrenal steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side chain cleavage (P450scc) and placental 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD-2) were determined using real-time quantitative RT-PCR. The results showed that prenatal chronic nicotine exposure causes IUGR in rats (P<0.01); in response to nicotine exposure, maternal serum corticosterone levels were elevated at mid- and late-gestations (P<0.05); mRNA expressions of StAR and P450scc increased in maternal adrenals (P<0.05 or 0.01) but decreased in fetal adrenals (P=0.16 or 0.11). Furthermore, the mRNA levels of placental 11β-HSD-2 were reduced at mid- and late-gestations (P<0.05). These results suggest that nicotine-induced IUGR is associated with the disturbances of glucocorticoid homeostasis in maternal and fetal rats. A possible underlying mechanism is that long term nicotine administration leads to fetal overexposure to maternal glucocorticoid by the combined effect of increased maternal glucocorticoid level and impaired placental barrier to it, all of which eventually leads to the fetal adrenocortical dysfunction and IUGR.