In vitro thermogenic activity of rat brown adipose tissue in neonatal period.

The roles of noradrenaline (NA) and glucagon in ontogeny of nonshivering thermogenesis (NST) were investigated in rats. The relative brown adipose tissue (BAT) mass to body weight was larger in the neonates compared with those of adult animals. The NA level in BAT was low at birth and then increased rapidly to adult level, whereas glucagon level at birth was as high as that in the adult. The thermogenic function of BAT was estimated by measuring the in vitro oxygen consumption of the tissue blocks. NA and glucagon stimulated the oxygen consumption of BAT maximally in a dose of 1 microgram/ml, respectively. The response of the tissue to NA from the neonates just after birth was high compared with that in adult animals. The high values persisted throughout the early neonatal period, and decreased around the weaning period. The response to glucagon exhibited similar pattern. These results indicate that glucagon as well as NA play a significant role in NST in BAT during the early stage of neonatal period.