METALLOTHIONEIN GENE IS EXPRESSED IN DEVELOPING RAT INTESTINE AND IS INDUCED BY ZINC BUT NOT BY CORTICOSTEROIDS

The expression of metallothionein (MT) mRNA during perinatal developme nt of rat intestine and its induction by zinc and cortisteroids were s tudied. Pregnant rats from d 17 to 22 of gestation and rats at 2, 4, 1 3 and 21 d of postnatal life were injected with saline solution (contr ol) or with zinc (10 mg/kg body wt) or corticosteroids (1 mg/kg body w t). After 6 h, tissues were removed for analysis. Northern hybridizati on of polyA+RNA to P-32-MT-cDNA revealed that MT was expressed already at d 17 of fetal life, increased afterwards (reaching the maximal exp ression around birth) and decreased soon after until weaning. Metallot hionein mRNA was markedly induced by zinc at d 18 of fetal life to a l evel that remained constant throughout postnatal life. Corticosteroids were ineffective in inducing MT gene expression during prenatal and p ostnatal development. In 21-d-old adrenalectomized rats the level of M T mRNA was similar to that of control rats of the same age and was not changed by hormone treatment. The results indicate that MT gene expre ssion can be induced by zinc during fetal life and that its expression without exogenous inducers cannot be ascribed to circulating corticos teroids.