title: Rhythmicity of triiodothyronine generation by type II thyroxine 5'-deiodinase in rat pineal is mediated by a beta-adrenergic mechanism.
abstract: Type II T4 5'-deiodinase plays an essential role in converting T4 to T3 in extrathyroidal tissues, thus allowing the full development of a cellular effect of thyroid hormone. This enzyme is one of the most important factors in regulating local action of thyroid hormone. Its activity in the rat pineal was 20-30 times higher at midnight than at noon; this nocturnal rise was abolished by the beta-adrenergic blocker, propranolol. The beta-agonist isoproterenol, caused a 3-fold increase in diurnal enzyme activity. There is thus a marked nyctohemeral variation in T4 activation in the pineal, probably mediated by a beta-adrenergic mechanism. Since the temporal peak of pineal T4 activation corresponds to that of pineal function, our data suggest a previously unrecognized role of thyroid hormone in pineal regulation.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D007453:Iodide Peroxidase / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D008027:Light; D008297:Male; D010870:Pineal Gland / Q000201:enzymology* / Q000528:radiation effects; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D014284:Triiodothyronine / Q000096:biosynthesis*
chemical_list: D011943:Receptors, Adrenergic, beta; D014284:Triiodothyronine; D011433:Propranolol; D007453:Iodide Peroxidase; D007545:Isoproterenol