title: Alpha-adrenergic stimulation of thermogenesis in a rat kangaroo (Marsupialia, Bettongia gaimardi).
abstract: 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).
authors.affiliation: Department of Biochemistry, University of Tasmania, Hobart, Australia. Y.Jiming@bioch.utas.edu.au
authors.forename: J M
authors.initials: JM
authors.lastname: Ye
authors.forename: S J
authors.initials: SJ
authors.lastname: Edwards
authors.forename: R W
authors.initials: RW
authors.lastname: Rose
authors.forename: J T
authors.initials: JT
authors.lastname: Steen
authors.forename: M G
authors.initials: MG
authors.lastname: Clark
authors.forename: E Q
authors.initials: EQ
authors.lastname: Colquhoun
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology*; D005260:Female; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D008394:Marsupialia / Q000502:physiology*; D009278:Naphazoline / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D010656:Phenylephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D009278:Naphazoline; D009638:Norepinephrine; D007213:Indomethacin