AN IMMUNOHISTOCHEMICAL AND IN-SITU HYBRIDIZATION STUDY OF THE POSTNATAL-DEVELOPMENT OF UNCOUPLING PROTEIN-1 AND UNCOUPLING PROTEIN-1 MESSENGER-RNA IN LAMB PERIRENAL ADIPOSE-TISSUE

In the lamb, the uncoupling protein-1 (UCP1) content of perirenal adip ose tissue at birth is an important factor in heat production by non-s hivering thermogenessis and the prevention of hypothermia. This study examines UCP1 gene expression and protein content in perirenal adipose tissue over the first 15 days of life by in situ hybridisation and im munohistochemistry. UCP1 mRNA was detected at birth in 30% of adipocyt es, and in approximately 24% of fat cells at 2 days of life. However, by 5 days of age and thereafter UCP1 mRNA was undetectable. Immunoreac tive UCP1 was present in all adipocytes at birth and at 2 days of age, and remained detectable in a decreasing proportion of cells until day 10 of life. By 15 days of age no immunoreactive UCP1 was detected and the perirenal adipose tissue had the appearance of white fat. It is c oncluded that UCP1 gene expression is suppressed in most adipocytes in perirenal adipose tissue of newborn lambs, and gene expression rapidl y falls in the remaining adipocytes over the first 5 days of postnatal life. In contrast, immunoreactive UCP1, a characteristic of brown adi pose tissue, was present in many adipocytes for up to 10 days of age, suggesting that UCP1 has a long half-life in lambs. All adipocytes in perirenal adipose tissue of newborn lambs appear to be functionally br own, but over the first 2 weeks of postnatal life there is a complete transformation to white adipocytes.