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

Abstract

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.