Thyroxine 5'-deiodinase type II activity in chick pineal and Harderian gland: nyctohemeral rhythmicity and its regulation by noradrenergic input.
Circadian rhythmicity of type II thyroxine 5'-deiodinase (5'-D) activity was studied in the pineal gland and Harderian glands of chicks. Only Harderian 5'-D activity showed a nyctohemeral rhythmicity with a maximal peak during the day time (1300), while no rhythm of enzyme activity was found in the pineal gland. Besides type II 5'-D activity, we found high basal levels of the type I isoenzyme in both glands; this activity was specifically suppressed by the addition of 6-n-propyl-thiouracil (PTU). However, day-night differences in Harderian 5'-D activity were maintained even after the addition of PTU. This activity was not affected for either continuous light exposure or darkness during the day. 5'-D activity seems to be regulated by the noradrenergic input, since the enzymatic activity was stimulated by a beta-adrenergic agonist, isoproterenol, and by the alpha-adrenergic agonist, phenylephrine, in both pineal and Harderian glands. Both drugs affected 5'-D activity in the Harderian gland by stimulating the enzyme activity over basal levels.
University of Texas Health Science Center, Department of Cellular and Structural Biology, San Antonio 78284-7762.
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Menendez-Pelaez
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D000818:Animals; D002645:Chickens; D002940:Circadian Rhythm / Q000502:physiology*; D003623:Dark Adaptation; D006243:Harderian Gland / Q000187:drug effects / Q000201:enzymology*; D007453:Iodide Peroxidase / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology*; D008027:Light; D010656:Phenylephrine / Q000494:pharmacology*; D010870:Pineal Gland / Q000187:drug effects / Q000201:enzymology*; D011441:Propylthiouracil / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism
D007527:Isoenzymes; D011941:Receptors, Adrenergic; D010656:Phenylephrine; D011441:Propylthiouracil; D007453:Iodide Peroxidase; D007545:Isoproterenol