In vivo activation of pineal N-acetyltransferase but not type II thyroxine 5'-deiodinase by phenylephrine in young rats.

The regulation by alpha- and beta-adrenergic agonists of pineal N-acetyltransferase (NAT) and type II thyroxine 5'-deiodinase (5'-D) in rats at either 2 or 6 weeks of age was studied. The pattern of stimulation was different because NAT activity could be clearly activated by an alpha-adrenergic agonist, phenylephrine, only in 2-week-old rats. However, isoproterenol, a beta-adrenergic agonist, was able to stimulate NAT activity in rats at both 2 and 6 weeks of life. On the other hand, phenylephrine was always ineffective in stimulating 5'-D activity, while isoproterenol clearly activated it at both ages. These results strongly suggest a role for alpha-adrenergic receptors, in addition to beta-adrenergic receptors, in regulating rat pineal NAT activity during development.