Characterization of mitochondrial-uncoupling protein in bovine fetus and newborn calf.

Development changes in the content of the mitochondrial-uncoupling protein (UCP) have been studied in adipose depots of bovine fetuses and a newborn calf as well as in adipose depots of newborn and aging lambs. The occurrence of UCP unique to brown adipose tissue (BAT) was investigated by GDP binding, photoaffinity labeling with 8-azidoadenosine 5'-triphosphate, and immunoblots using specific antibodies directed against rat UCP. A protein of 32,000 relative molecular weight was characterized in both species with properties similar to those of rodent UCP. In bovine, UCP became detectable in the perirenal adipose tissue at day -80 and its content increased until birth. Both in bovine (perirenal, subscapular, and retroperitoneal sites) and in ovine (perirenal, subscapular, retroperitoneal, and pericardiac sites), all adipose tissues except the subcutaneous adipose tissue contained at birth UCP and thus can be considered as BAT. The data indicate that the perirenal adipose depot should play in bovine and ovine a major thermogenic role at birth, whereas perirenal and pericardiac adipose tissues of lambs held under cold conditions for 45 days after birth did not show any immunoreactive UCP.