AJP - Endocrinology and Metabolism, Vol 263, Issue 5 E884-E889, Copyright © 1992 by American Physiological Society
Adrenergic regulation of type II 5'-deiodinase circadian rhythm in rat harderian gland
C. Osuna, J. Jimenez, R. J. Reiter, A. Rubio and J. M. Guerrero
University of Seville School of Medicine, Department of Medical Biochemistry and Molecular Biology, Spain.
This paper reports on the regulation of the nyctohemeral profile of type II
thyroxine 5'-deiodinase (T45'D) activity in the rat harderian gland.
Harderian gland T45'D activity exhibits a nighttime increase with maximal
values late in the dark period (0200-0400 h) and basal values during the
daytime. The nocturnal rise of the deiodinating activity was prevented by
either exposure of animals to light at night, injecting the animals with
both alpha- and beta-adrenergic receptor blockers, or bilateral superior
cervical ganglionectomy (SCGx). However, adrenalectomy did not affet the
enzyme activity in the harderian gland. In brown adipose tissue (BAT),
where thyroid hormone metabolism is extremely dependent on alpha
1-adrenergic stimulation by blood-circulating catecholamines, adrenalectomy
significantly decreased T45'D activity. Deiodinating activities in brain
frontal cortex (BFC) and pituitary gland were unaffected by adrenalectomy.
Unlike in the harderian gland, SCGx did not modify the T45'D activity in
either BAT, BFC, or the pituitary gland. The results suggest that elevated
plasma catecholamines are not required for harderian gland T45'D activation
and that the nyctohemeral profile of the enzyme activity in the harderian
gland is dependent on the noradrenergic input from the superior cervical
ganglia.
