AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 2 430-R435, Copyright © 1990 by American Physiological Society
Adrenergic effects on thyroxine 5'-deiodinase in brown adipose tissue of lean and ob/ob mice
A. L. Kates, G. Zaror-Behrens and J. Himms-Hagen
Department of Biochemistry, University of Ottawa, Ontario, Canada.
Genetically obese, ob/ob, mice have an impaired capacity to increase the
level of thyroxine 5'-deiodinase (T5'D) in their brown adipose tissue (BAT)
when they are exposed to cold. Yet they are able to secrete norepinephrine
(NE) from the nerves of their BAT in response to cold and are apparently
refractory to this action of NE. The principal objective was to find out
whether injected NE could increase T5'D in BAT of the ob/ob mouse. A
secondary objective was to elucidate the nature of the adrenergic
receptor(s) involved in this response in lean and ob/ob mice. Injection of
NE increased T5'D in BAT of lean mice within 3 h. It also increased T5'D in
BAT of ob/ob mice but to a lesser extent. Basal T5'D activity in BAT of
ob/ob mice was greater than that seen in BAT of lean mice because of the
greater size of the tissue. Neither isopropylnorepinephrine nor
phenylephrine alone could increase T5'D activity, but a combination
increased it almost as well as did NE, although to a lesser extent in ob/ob
mice than in lean mice. Both a beta-adrenergic antagonist (propranolol) and
an alpha 1-adrenergic antagonist (prazosin) could inhibit the effect of NE.
The acute effect of NE on metabolic rate of intact mice also involves an
action of both beta- and alpha 1-adrenergic receptors. The beta-adrenergic
component appears to be defective in the ob/ob mouse.
