beta-Adrenergic induction of tyrosine aminotransferase organ culture of fetal rat and fetal human liver.

Isoproterenol, phenylephrine, and salbutamol (all 100 microM) induced the activity of tyrosine aminotransferase (TAT; EC 2.6.1.5) by 109%, 72%, and 141%, respectively, in organ culture of fetal human liver. Propranolol (100 microM) inhibited the effects of isoproterenol and phenylephrine. In organ culture of fetal rat liver, the induction of TAT activity by phenylephrine (100 microM) was not significantly affected by phentolamine (100 microM), whereas it was abolished by a combination of phentolamine and propranolol (both 100 microM). Isoproterenol and salbutamol caused significant increases in TAT activity, which were not affected by 100 microM atenolol but were completely inhibited by propranolol (100 microM). The results show that the fetal human liver has developed responsiveness to adrenergic stimuli at the 12th week of gestation. The adrenergic induction of TAT in fetal human liver is mediated solely by beta-adrenergic mechanisms. In the fetal rat liver, the adrenergic induction of TAT is mediated by beta 2-adrenergic receptors.