Effects of Diet and Acute Noradrenaline Treatment on Brown Adipose Tissue Development and Mitochondrial Purine‐nucleotide Binding

Abstract

Feeding rats a highly palatable 'cafeteria' diet resulted in a two-fold increase in interscapular brown adipose tissue (b.a.t.) mass after only 3 d on the diet. No significant difference in DNA content of b.a.t. was noted between control and cafeteria-fed rats at this time but DNA content was elevated 2-3-fold in the latter group by day 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 (per mg protein) to b.a.t. mitochondria was seen in cafeteria-fed rats on days 3, 15 and 30 and total GDP binding in the interscapular depot was increased by 3-4-fold. Injection of the animals with noradrenaline (25 micrograms/100 g body weight) 1 h before killing caused 180 and 430% increases in b.a.t. 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 b.a.t. 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 b.a.t. and its mitochondrial proton conductance pathway in diet-induced changes in thermogenic capacity.

Body Weight and Brown Fat Activity in Hyperphagic Cafeteria-Fed Female Rats and Their Offspring

“…Purine nucleotide binding capacity is now routinely used to assess the activity of the mitochondrial proton conductance path way, and is increased in rats exhibiting dietinduced thermogenesis [3], and correlates [2] with changes in the concentration of the unique uncoupling protein associated with the high proton conductance of BAT mito chondria. GDP binding was increased by 50% in brown fat from cafctcria-fcd dams, indicating that thermogenesis was greater in the tissue of these animals.…”

“…2) and throughout lactation chondria were prepared by differential centrifugation [16] and the activity of the proton conductance path way was estimated from the binding of 3H-guanosine diphosphate (3H-GDP, lOCi/mmol, Amersham In ternational, Bucks, UK), using 2 \iM of the ligand [3], Non-specific binding was assessed from binding in the presence of excess (200 pAf) unlabelled nucleotide. Tissue and mitochondrial proteins were determined by a dye reagent method (Bio-Rad Labs, Watford, UK).…”

Effects of denervating brown adipose tissue on the responses to cold, hyperphagia and noradrenaline treatment in the rat.

“…is activated in rats exhibiting either non-shivering thermogenesis in response to cold exposure, or diet-induced thermogenesis in response to hyperphagia (see Girardier, 1983;Rothwell & Stock, 1983 for reviews). Both thermogenic stimuli produce rapid and sustained increases in the activity of the mitochondrial proton conductance pathway in brown fat (Nicholls & Locke, 1983;Brooks, Rothwell & Stock, 1982), and this is now considered to be the major thermogenic mechanism in the tissue (Nicholls & Locke, 1983). Cold exposure and hyperphagia also cause hypertrophy and hyperplasia of b.a.t.…”

“…Cold exposure and hyperphagia also cause hypertrophy and hyperplasia of b.a.t. (Tulp, 1981;Brooks et al 1982;Bukowiecki, Collet, Follea, Guay & Jahjah, 1982).…”

“…depot were dissected separately, weighed and homogenized in 0-2 M-sucrose. Mitochondria were prepared by the method of Slinde, Pedersen & Flatmark (1975), and the activity of the proton conductance pathway was assessed from the binding of [3H]guanosine-5'-diphosphate (GDP) (0-25 /sM) in the presence of 2 /iM-unlabelled nucleotide, or 200 1zM-GDP to assess non-specific binding (Brooks et al 1982). Tissue and mitochondrial protein were determined by a dye-reagent method (Bio-Rad) using bovine serum albumin standards.…”