Pretranslational regulation of rhythmic type II iodothyronine deiodinase expression by beta-adrenergic mechanism in the rat pineal gland

It has been demonstrated that type II iodothyronine deiodinase is present i n rat pineal gland, and the deiodinase activity markedly increases during t he hours of darkness, primarily through beta-adrenergic mechanism. We have studied the relationship between pineal type II iodothyronine deiodinase me ssenger RNA (mRNA) and the deiodinase activity to elucidate the mechanisms involved in the nocturnal rise in pineal deiodinase activity. Northern anal ysis has demonstrated that type II iodothyronine deiodinase mRNA is express ed in rat pineal gland, and the mRNA markedly increases during the hours of darkness. The nocturnal increase in pineal type II iodothyronine deiodinas e activity is preceded by the increase in its mRNA. Daytime isoproterenol a dministration resulted in a rapid increase in pineal type II iodothyronine deiodinase mRNA followed by the increase in deiodinase activity. Propranolo l treatment, bilateral superior cervical ganglionectomy, or constant light exposure significantly suppressed the nocturnal rise in type II iodothyroni ne deiodinase mRNA as well as the deiodinase activity. Moreover, isoprotere nol or (Bu)(2)AMP stimulated type II iodothyronine deiodinase mRNA and the deiodinase activity in cultured rat pineal glands. These results suggest th at the rhythmic change in pineal type II iodothyronine deiodinase activity is regulated at least in part at the pretranslational level by a beta-adren ergic mechanism transmitted through superior cervical ganglia.