Postnatal development of uncoupling protein, uncoupling protein mRNA, and GLUT4 in adipose tissues of goats.

Adipose tissues have been characterized in newborn goats on the basis of the presence of the 32,000-M(r) mitochondrial uncoupling protein (UCP) diagnostic of brown fat, and early postnatal developmental changes have been determined. Both internal (perirenal, pericardial, and omental) and subcutaneous (hindlimb and neck regions) adipose tissues in newborn goats contained UCP and are therefore brown fat. The insulin-sensitive glucose transporter, GLUT4, was also present in adipose tissues of newborn goats, implying a potential for insulin-stimulated glucose uptake at birth. UCP was still evident in the perirenal fat of goats at 3 wk of age, but the mitochondrial concentration was only 4%, and the amount per cell a mere 0.2%, of that in the newborn. UCP was not detectable, however, in either the omental or subcutaneous adipose tissue at 3 wk of age and had disappeared from the subcutaneous fat before 2 wk. In contrast to UCP, GLUT4 remained throughout the initial 3 wk of postnatal life. The mRNA for UCP was detected in perirenal adipose tissue of newborn goats, indicating that the gene coding for the protein is being expressed at around birth. UCP mRNA was not, however, detectable in the other fat depots; nor was it evident in the perirenal adipose tissue at > or = 2.5 days of age. It is concluded that the adipose tissues of newborn goats (both internal and subcutaneous) represent brown fat and that there is a rapid transition toward white fat over the first weeks of life. This transition occurs at different rates in different depots but is not markedly faster in goats than in other ruminants.(ABSTRACT TRUNCATED AT 250 WORDS)