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Characterization of perfused periaortic brown adipose tissue from the rat

1994; NRC Research Press; Volume: 72; Issue: 4 Linguagem: Inglês

10.1139/y94-051

1205-7541

A. Matthias, Stephen M. Richards, Kim A. Dora, Michael G. Clark, Eric Q. Colquhoun,

Cancer, Hypoxia, and Metabolism

A technique was developed for the perfusion of periaortic brown adipose tissue (BAT) with a view to assessing vascular system involvement in BAT thermogenesis. The procedure involved cannulation of the thoracic aorta and ligation of the intercostal branches and the distal thoracic aorta. Perfusion was conducted in a buffer-filled chamber using constant flow at 37 °C. Lactate dehydrogenase leakage was less than 2%/h, and after 30 min of perfusion the energy charge was 0.72 ± 0.05 (n = 4) and differed little from freshly sampled interscapular BAT (0.71 ± 0.03 (n = 7)). Periaortic BAT was indistinguishable from interscapular BAT in enzyme content, mitochondrial size, mitochondrial cristae, lipid content, and cell size. Basal oxygen consumption [Formula: see text] was 64.3 ± 7.4 μmol∙h −1 ∙g −1 wet weight, and basal perfusion pressure was 65 ± 3 mmHg (1 mmHg = 133.3 Pa). Norepinephrine and isoproterenol each increased [Formula: see text] of perfused periaortic BAT in a time-dependent and reversible manner. Half-maximal stimulation of [Formula: see text] occurred at 12 nM norepinephrine and 8 nM isoproterenol; maximally stimulated tissue had a [Formula: see text] of approximately 150 μmol∙h −1 ∙g −1 wet weight. Norepinephrine (50 nM) had no consistent effect on perfusion pressure, but the increase in [Formula: see text] by this agonist was completely blocked by 10 μM DL-propranolol and unaffected by phentolamine (1–20 μM) or nitroprusside (0.01–1 mM). Increasing the perfusion flow rate increased pressure and had no effect on basal [Formula: see text] but increased the [Formula: see text] response due to norepinephrine. Several observations suggest that vascular thermogenesis and (or) vascular control of BAT thermogenesis were minimal in constant flow perfused periaortic BAT. These include (i) the failure of norepinephrine to consistently cause vasoconstriction or vasodilation in association with an increase in [Formula: see text]; (ii) isoproterenol-mediated increase in [Formula: see text]; (iii) the failure of increased flow to increase basal [Formula: see text]; (iv) the failure of nitroprusside or phentolamine to inhibit norepinephrine mediated increase in [Formula: see text]; and (v) the complete inhibition by propranolol of the norepinephrine- or isoproterenol-mediated increase in [Formula: see text]. Finally, the present findings provide no evidence for the presence of an α-adrenergic mechanism to control BAT thermogenesis directly, or indirectly by alterations in flow.Key words: brown adipose tissue, perfusion, thermogenesis, oxygen consumption, norepinephrine, isoproterenol.