Thyroid hormone suppression of hepatic levels of phenobarbital-inducible P-450b AND P-450e and other neonatal P-450S in hypophysectomized rats

Abstract

Mechanism of developmental suppression of cytochrome P-450 (P-450) in rat livers was studied using Western blots. The contents of phenobarbital (PB)-inducible P-450b and P-450e, expressed constitutively in livers, were higher in neonate than in adult rats. The contents were also 10∼50 fold higher in hypophysectomized than in intact adult male rats. Administration of L-triiodothyronine (T 3, 50 μg/kg) or human growth hormone (4U/kg) reversed almost completely the increased amounts of P-450b and P-450e. T 3-induced suppression was also observed on two other neonatal P-450s (P-450 6β-1 and P-448-H), which are expressed in neonatal periods in livers. The postnatal developmental profiles of hepatic P-450b were correlated inversely with that of serum free T 3 level in rats reported ( Walker et al. (1980) Pediat. Res. 14, 249 ). These results suggest, in addition to pituitary growth hormone ( Yamazoe et al. (1987) J. Biol. Chem. 262, 7423 ), the possible involvement of T 3 on the suppressive regulation of PB-inducible and other neonatal P-450s.