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Am J Physiol Regul Integr Comp Physiol 271: R586-R592, 1996;
0363-6119/96 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 271, Issue 3 586-R592, Copyright © 1996 by American Physiological Society

ARTICLES

Alpha-adrenergic stimulation of thermogenesis in a rat kangaroo (Marsupialia, Bettongia gaimardi)

J. M. Ye, S. J. Edwards, R. W. Rose, J. T. Steen, M. G. Clark and E. Q. Colquhoun
Department of Biochemistry, University of Tasmania, Hobart, Australia. Y.Jiming@bioch.utas.edu.au

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 O2 consumption (Vo2) 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 Vo2 was 22.9 +/- 1.9 mmol.kg-1.h-1. Norepinephrine (10-80 micrograms.kg-1.min-1) stimulated Vo2 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 Vo2 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 Vo2 elicited by norepinephrine. As a dose of 10 micrograms.kg-1.min-1, the alpha-adrenergic blocker phentolamine abolished the effects of naphazoline and phenylephrine and reduced norepinephrine-induced Vo2 by 45.5%. The beta-adrenergic blocker propranolol inhibited the norepinephrine-induced Vo2 by 58.8% at 20 micrograms.kg-1.min-1. A combination of the two antagonists blocked 82.5% of the norepinephrine-induced Vo2. Pretreatment of the animal with indomethacin (1 mg/kg), a known inhibitor of prostaglandin cyclooxygenase, had no effect on phenylephrine-elicited Vo2. Taken together, these results indicate that alpha 1-adrenoceptors are directly involved in norepinephrine-induced thermogenesis in non-BAT tissue(s).


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