title: Alpha 2-adrenoceptor-mediated effects on resting energy expenditure.
abstract: The effects of the alpha 2-adrenoceptor agonist guanfacin, other alpha-adrenoceptor agonists, beta-adrenoceptor agonists and alpha- and beta-adrenoceptor antagonists on resting energy expenditure (REE) were studied in female Wistar rats at 23 degrees C. Guanfacin produced a maximum change of -20% (-1.2 W/kg0.75, P < 0.001) in REE in rats with a mean +/- s.d. pre-treatment REE of 6.0 +/- 0.9 W/kg0.75. The dose producing half the maximum effect was 0.4 mg/kg. Other alpha 2-adrenoceptor agonists, clonidine, UK14304 and the peripherally acting alpha 2-agonist, p-aminoclonidine, also decreased REE. The effects of guanfacin were antagonized by idazoxan, yohimbine and RX821002 (all selective for alpha 2-adrenoceptors) but not prazosin (selective for alpha 1-adrenoceptors). Prazosin used alone lowered REE indicating a role for alpha 1-adrenoceptors in normal REE. To determine whether guanfacin was acting directly on oxygen-consuming tissues or if it was acting by lowering sympathetic tone, rats were treated with selective beta 1-, beta 2- and beta 3-agonists and antagonists both alone and in combination with guanfacin. The results of these experiments support the hypothesis that guanfacin lowered REE through a decrease in sympathetic tone (noradrenaline release) which in turn lessened the normal resting stimulation of alpha 1- and beta 1-adrenoceptors.
authors.affiliation: Queensland Department of Primary Industries, Tropical Cattle Research Centre, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Gazzola
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D005260:Female; D016316:Guanfacine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D016316:Guanfacine