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Brown adipose tissue thermogenic responses of rats induced by central stimulation: effect of age and cold acclimation

Brown adipose tissue thermogenic responses of rats induced by central stimulation: effect of age and cold acclimation

Journal of Physiology 426: 317-333

1. Urethane-anaesthetized, age-matched cold- (4 .degree.C) and room (21 .degree.C)-acclimated groups of Sprague-Dawley rats were given repeated (three) ventromedial hypothalamic electrical stimulations. Interscapular brown adipose tissue (IBAT), colonic, surface tail temperatures and blood pressure were monitored before and after each electrical stimulation. Propranolol HCl (2.cntdot.5 mg kg-1 i.v.) was given 10 min prior to the last (third) ventromedial hypothalamic stimulation. 2. Repeated electrical stimulation of the ventromedial hypothalamic (VMH) nucleus to either small or large rats (kept at 21 .degree.C) caused no significant change in interscapular brown fat, colonic or surface temperatures compared to respective pre-stimulation control values whereas mean arterial pressure was slightly but significantly increased during the 30 s stimulation period. 3. Electrical stimulation of the ventromedial hypothalamic nucleus of small or large rats, kept at 4 .degree.C for 3 weeks prior to testing, caused significant (> 0.cntdot.25 and > 0.cntdot.40 .degree.C, respectively) rises in interscapular BAT temperature from respective prestimulation control values. Colonic temperatures increased following ventromedial hypothalamic electrical stimulation only in the small, 4 .degree.C-acclimated group whereas surface tail temperatures did not significantly change after stimulation of either cold-exposed group. Mean arterial pressures were significantly increased during ventromedial hypothalamic electrical stimulation in both 4 .degree.C-acclimated groups, compared to pre-stimulation control levels and, in addition, were above those of age-matched rats kept at 21 .degree.C. Intravenous propranolol, which decreased interscapular brown fat and colonic temperatures in all groups, blocked the rise in interscapular brown fat and colonic temperatures of the 4 .degree.C-acclimated rats following the last electrical stimulation of the ventromedial hypothalamic nucleus. 4. In vitro biochemical analysis of the interscapular brown fat pads of another four groups of age-matched, small and large 21 and 4 .degree.C-acclimated rats revealed that the thermogenic capacity of the 4 .degree.C-acclimated groups was, in all cases, significantly increased from age-matched groups previously kept at 21 .degree.C, as shown by significant increases in brown adipose tissue mass, BAT DNA and protein content, BAT mitochondrial protein and BAT mitochondrial GDP binding. 5. Other experiments using urethane-anaesthetized, age-matched male Sprague-Dawley rats previously maintained at 21 or 4 .degree.C for 3 weeks prior to testing, with their core temperature maintained at 37 .degree.C during experimentation, revealed similar results as above. Interscapular brown fat temperatures were significantly elevated (> 0.cntdot.50 .degree.C) in the 4 .degree.C-acclimated group following electrical stimulation of the ventromedial hypothalamic nucleus but not in those rats kept at 21 .degree.C. However, intravenous infusion of noradrenaline HCl (20 .mu.g ml-1) for 10 min significantly raised interscapular brown rat temperatures (> 0.cntdot.80 .degree.C) in room (21 .degree.C)-acclimated rats, yet temperatures of the interscapular brown fat pad were raised significantly further (> 1.cntdot.5 .degree.C) following noradrenaline infusion in the 4 .degree.C-acclimated group. 6. Results suggest that chronic cold-acclimation of rats increased the thermogenic capacity of interscapular brown adipose tissue such that subsequent electrical stimulation of the ventromedial hypothalamic nucleus area evoked significant increases in interscapular brown adipose tissue temperature. Electrical stimulation of the ventromedial hypothalamic nucleus to age-matched groups kept at 21 .degree.C could not evoke significant rises in interscapular temperature even though I.V. noradrenaline infusion did raise interscapular temperatures in this group. The in vivo IBAT temperature responses of the 4 and 21 .degree.C-acclimated groups correlated with the differences found in the thermogenic ca.

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Accession: 007071454

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PMID: 2231401

DOI: 10.1113/jphysiol.1990.sp018140

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