title: Thyroxine 5'-deiodinase activity in pineal gland and frontal cortex: nighttime increase and the effect of either continuous light exposure or superior cervical ganglionectomy.
abstract: Type II T4 5'-deiodinase (5'-D) activity was studied in pineal gland, frontal cortex, and anterior pituitary of male rats. Enzymatic activity was determined by the release of 125I using [3',5'-125I]T4 as substrate. Daytime levels of 5'-D activity were maximal for anterior pituitary (346.2 +/- 142.5 fmol 125I released/mg protein.h), followed by pineal gland (61.5 +/- 8.7 fmol 125I released/mg protein.h) and frontal cortex (3.1 +/- 0.5 fmol 125I released/mg protein.h). Twenty-four-hour fluctuations of 5'-D activity were apparent in the pineal gland and cortex. For pineal, peak 5'-D activity (43.4 +/- 11.4 fmol 125I released/gland.h) occurred at 0100 h, with values at this time being 8-fold greater than basal daytime levels. Superior cervical ganglionectomy (SCGX) or exposure to continuous light (LL) completely abolished the nocturnal rise of 5'-D activity. Treatment with iopanoic acid also inhibited 5'-D activity in pineal (32.1 +/- 3.5 vs. 18.8 +/- 1.7 fmol 125I released/gland.h) without influencing either the N-acetyltransferase activity or the melatonin content. In cortex, peak 5'-D activity occurred at 0500 h (5.3 +/- 0.4 fmol 125I released/mg protein.h), with values at this time being 1.5-fold greater than basal daytime levels. SCGX moderately depressed enzymatic activity, while LL exposure strikingly enhanced the nocturnal increase (11.7 +/- 1.1 vs. 19.3 +/- 2.4 fmol 125I released/mg protein.h at 0300 h). 5'-D activity exhibited no 24-h fluctuation in the anterior pituitary gland, and neither SCGX nor LL exposure affected enzyme levels in this tissue. Our data demonstrate the existence of a 24-h rhythm of type II T4 5'-D activity in pineal gland and cortex, with peak levels occurring at night; in pineal, the sympathetic neural input is indispensable for the rhythm, since SCGX prevented it. In cortex, the apparent paradoxical effect of LL and SCGX on 5'-D activity indicates that other mechanisms are involved in its regulation.
authors.affiliation: Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio 78284.
authors.forename: J M
authors.initials: JM
authors.lastname: Guerrero
authors.forename: M
authors.initials: M
authors.lastname: Puig-Domingo
authors.forename: R J
authors.initials: RJ
authors.lastname: Reiter
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology*; D002940:Circadian Rhythm; D003624:Darkness; D005727:Ganglia, Spinal / Q000502:physiology*; D007453:Iodide Peroxidase / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism; D010870:Pineal Gland / Q000201:enzymology*; D010903:Pituitary Gland, Anterior / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
chemical_list: D007453:Iodide Peroxidase; D008550:Melatonin