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 β-adrenergic activation of the 5′-D activity is mediated by cyclic AMP in the rat pineal gland.