ISSN:
1600-079X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: 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 β-adrenergic agonist, isoproterenol, and by the α-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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1600-079X.1993.tb00485.x
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