Effect of isoproterenol and dibutyryl cyclic AMP on thyroxine type-II 5'-deiodinase and N-acetyltransferase activities in rat pineal organ cultures.

The effects of either isoproterenol or dibutyryl cyclic AMP on rat pineal thyroxine type-II 5'-deiodinase (5'-D) and N-acetyltransferase (NAT) activities were studied using an organ culture technique. Moving the animals to light at night dramatically inhibited the NAT with no change in the 5'-D activity. The subsequent incubation of pineal glands with either isoproterenol or dibutyryl cyclic AMP restored the NAT activity and caused a further rise in 5'-D activity. In animals maintained under light conditions during the night, both isoproterenol and dibutyryl cyclic AMP were able to stimulate the 5'-D and NAT activities. The results suggest that the beta-adrenergic activation of the 5'-D activity is mediated by cyclic AMP in the rat pineal gland.