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 development of rat intestine and its induction by zinc and cortisteroids were studied. Pregnant rats from d 17 to 22 of gestation and rats at 2, 4, 13 and 21 d of postnatal life were injected with saline solution (control) or with zinc (10 mg/kg body wt) or corticosteroids (1 mg/kg body wt). After 6 h, tissues were removed for analysis. Northern hybridization of polyA⁺RNA to ³²P-MT-cDNA revealed that MT was expressed already at d 17 of fetal life, increased afterwards (reaching the maximal expression around birth) and decreased soon after until weaning. Metallothionein mRNA was markedly induced by zinc at d 18 of fetal life to a level that remained constant throughout postnatal life. Corticosteroids were ineffective in inducing MT gene expression during prenatal and postnatal development. In 21-d-old adrenalectomized rats the level of MT 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 expression can be induced by zinc during fetal life and that its expression without exogenous inducers cannot be ascribed to circulating corticosteroids.