Thyroid hormone-sensitive brown adipose tissue respiration in the newborn rabbit

The effects of thyroid hormone treatment on brown adipose tissue (BAT) and liver metabolism were assessed by measuring oxygen consumption, sodium-potassium adenosine triphosphatase (Na-K-ATPase), and mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) activities in tissues from triiodothyronine- (T3) and vehicle-injected (for 3 days) newborn and adult rabbits. In the newborns, basal BAT cellular respiration was increased [mean (%/- SE) = 119 +/- 18 vs. 65 +/- 4 microliter O2/10(6) cells-1 . h in controls (P less than 0.005)], whereas hepatic respiration was unchanged. Ouabain had no effect on basal BAT cellular respiration, but suppressed hepatic respiration by 30% in both newborn groups. T3 treatment had no effect on NE- (10(-6) M) stimulated BAT respiration, whereas adult hepatic respiration was increased almost twofold. alpha-GPD activities were increased in both newborn BAT and adult liver but not in newborn liver. Na-K-ATPase activity was significantly increased only in newborn liver. In conclusion, 1) both BAT and liver are thyroid-hormone sensitive in the newborn rabbit, but the responses to T3 treatment are different in the two tissues; 2) the failure to stimulate both hepatic alpha-GPD and respiration in the newborn appears to be a developmental phenomenon characteristic of the rabbit; 3) thyroid hormones have little effect on sodium transport-dependent respiration in either BAT of liver in the newborn rabbit.