Stereospecific stimulation of brown adipocyte respiration by catecholamines via beta 1-adrenoreceptors.
Regulation of respiration by catecholamines was studied in adipocytes isolated from interscapular brown adipose tissue of warm-acclimated rats by rapid digestion of collagenase. (-)-Norepinephrine stimulated adipocyte respiration 10-12 times above basal values in less than 3 min. (Vmax = 410 +/- 29.5 nmol O2 . min-1 . 10(-6) cells-1). Stimulated respiration remained stable for at least 20 min, provided that cells were incubated in balanced salt media containing bicarbonate. The maximal capacity of total brown adipose tissue for norepinephrine-stimulated respitarion was estimated at 1.5 ml O2/min per rat. beta-Adrenergic agonists increased calorigenesis stereospecifically with an order of potency expected for respiratory stimulation via adrenoceptors of the beta 1-subtype: (-)-isoproterenol  (1/2 Vmax = 2 nM) greater than (-)-norepinephrine (1/2 Vmax = 20 nM) approximately equal to (-)-epinephrine (1/2 Vmax = 40 nM) greater than corresponding (+)-stereoisomers. The alpha-adrenergic agonist phenylephrine (1/2 Vmax = 5 microM) stimulated adipocyte respiration as rapidly and as effectively as beta-agonists. Although alpha-adrenoreceptors are present in brown adipose tissue, studies with alpha- and beta-adrenergic antagonists revealed that norepinephrine elicits thermogenesis at physiological concentrations (less than or equal to 1 microM) predominantely via beta 1-adrenergic pathways.
D000064:Acclimatization; D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000494:pharmacology*; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D006358:Hot Temperature; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects*; D010643:Phenoxybenzamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
D002395:Catecholamines; D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D010643:Phenoxybenzamine; D010656:Phenylephrine; D011433:Propranolol; D007545:Isoproterenol; D009638:Norepinephrine; D004837:Epinephrine