[Nutritional adaptation in brown adipose tissue thermogenesis--with special reference to overfeeding and iron...

The effect of sucrose overfeeding and low iron diet on brown adipose tissue (BAT) thermogenesis of rats has been investigated from the view point of in vitro BAT oxygen consumption and BAT fatty acids (FA) compositions in rats. Control group was fed on a standard diet with tap water, sucrose group was on the standard diet and 32% sucrose solution, and iron deficient group on a low iron diet with tap water. In vitro interscapular BAT thermogenesis as estimated by oxygen consumption was measured in minced tissue blocks in Krebs-Ringer phosphate buffer using a Clark oxygen electrode. In sucrose overfeeding rats, caloric intake was greater than in controls, but did not differ body weight. Interscapular BAT weight and DNA content were greater. Colonic and tail skin temperatures were higher. Basal oxygen consumption was higher. Noradrenaline- and glucagon-stimulated oxygen consumptions did not differ when expressed per DNA, but significantly greater per whole tissue pad. Both BAT-triglyceride (TG) and -phospholipid (PL) levels were higher. Polyunsaturated FA were lower, while monosaturated FA were higher in both BAT-TG and -PL. In iron deficient rats, BAT weight and DNA content were higher. Colonic and tail skin temperatures did not differ. Although basal oxygen consumption did not differ, noradrenaline-stimulated oxygen consumption was less per DNA, but did not differ per whole tissue pad, while glucagon-stimulated oxygen consumption was less when expressed per DNA, as well as whole tissue pad. Cold-tolerance as assessed by the fall in colonic temperature at 0 degree C was decreased. BAT-TG and -PL levels did not differ. Polyunsaturated FA were higher in both BAT-TG and -PL. These findings indicated that sucrose-induced overfeeding enhances BAT thermogenesis mainly by tissue hyperplasia, while iron deficiency suppresses BAT thermogenic response, although it causes the compensatory tissue hyperplasia.