Alpha-adrenergic stimulation of thermogenesis in a rat kangaroo ( marsupialia: bettongia gaimardi). Ye, Ji-Ming, Stephen J. Edwards, Randy R. Rose, John T. Steen, Michael G. Clark, and Eric Q. Colquhoun. Departments of Biochemistry and Zoology, University of Tasmania, Hobart, Tasmania, 7001, Australia
APStracts 3:0091R, 1996.
The Tasmanian bettong (Bettongia gaimardi) is a small rat kangaroo without detectable brown adipose tissue (BAT). In view of our previous findings of norepinephrine-mediated increase in oxygen consumption (O2) in the perfused hindlimb of this species, the present study examined the effect of [alpha]-adrenoceptors on the thermogenesis of conscious bettongs at rest by infusing adrenergic agents via an indwelling catheter in the tail vein. The resting O2 was 22.9 +/- 1.9 mmol.kg-1.h-1. Norepinephrine (10-80 [mu]g.kg-1.min -1) stimulated O2 in a dose-dependent manner with the maximal increment of 46.7%. Naphazoline (an [alpha]1, [alpha]2-adrenergic agonist) and phenylephrine (an [alpha]1-adrenergic agonist) also elicited increases in O2 with maximal values of 29.6% and 34.8%, respectively. In contrast, the [alpha]2-adrenergic agonist clonidine had no significant effects. Both [alpha]- and [beta]-adrenergic blockers were used to antagonize the submaximal increase in O2 elicited by norepinephrine. At a dose of 10 [mu]g.kg-1.min-1, the [alpha]-adrenergic blocker phentolamine abolished the effects of naphazoline and phenylephrine and reduced norepinephrine-induced O2 by 45.5%. The [beta]-adrenergic blocker propranolol inhibited the norepinephrine-induced O2 by 58.8% at 20 [mu]g.kg-1.min-1. A combination of the two antagonists blocked 82.5 % of the norepinephrine-induced O2. Pretreatment of the animal with synthesis indomethacin (1 mg.kg-1), a known inhibitor of prostaglandin cycloxygenase had no effect on phenylephrine-elicited O2. Taken together, these results indicate that [alpha]1-adrenoceptors are directly involved in norepinephrine -induced thermogenesis in non-BAT tissue(s). 

Received 20 June 1995; accepted in final form 28 February 1996.
APS Manuscript Number R378-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96