EFFECTS OF DIET AND ACUTE NORADRENALINE TREATMENT ON BROWN ADIPOSE TISSUE DEVELOPMENT AND MITOCHONDRIAL PURINE-NUCLEOTIDE BINDING

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Abstract
Feeding rats a highly palatable cafeteria diet resulted in a 2-fold increase in interscapular brown adipose tissue (BAT) mass after only 3 d [day] on the diet. No significant difference in DNA content of BAT was noted between control and cafeteria-fed rats at this time but DNA content was elevated 2- to 3-fold in the latter group by d 30, and incorporation rates of tritiated thymidine into DNA were elevated in these animals after 5, 15 and 30 d of cafeteria feeding. A doubling of specific GDP binding (per mg protein) to BAT mitochondria was seen in cafeteria-fed rats on d 3, 15 and 30 and total GDP binding in the interscapular depot was increased by 3- to 4-fold. Injection of the animals with noradrenaline [norepinephrine] (25 .mu.g/100 g body wt) 1 h before killing caused 180 and 430% increases in BAT mitochondrial GDP binding in control and cafeteria-fed rats, respectively. Linear Scatchard plots of binding data obtained from 15 d control and cafeteria groups indicated a single class of receptor, with the same affinity for GDP in all animals, but the maximum number of binding sites was markedly elevated in cafeteria rats and was increased further after treatment with noradrenaline 1 h prior to sacrifice. When cafeteria-fed rats were returned to stock diet alone the differences in BAT mass and GDP binding diminished but after 10 d brown fat mass and noradrenaline-stimulated GDP binding were still significantly higher than control levels. These data provide further evidence for the involvement of BAT and its mitochondrial proton conductance pathway in diet-induced changes in thermogenic capacity.

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