AN ULTRASTRUCTURAL-STUDY OF BROWN ADIPOSE-TISSUE IN PRETERM HUMAN NEWBORNS

The ultrastructure of brown adipose tissue (BAT), the thermogenic type of adipose tissue, was investigated in biopsies from 4 pre-term human new-borns delivered at 25-27 week's gestational age and compared with peri-renal brown fat from 2 adult patients with phaeochromocytoma (a condition of brown fat activation). The cell size of brown adipocytes was smaller in pre-term new-borns than in adult patients; adipocytes w ere almost exclusively multilocular, suggesting active thermogenesis. in 3 of the pre-term newborns, brown adipocyte ultrastructure indicate d a good to high degree of differentiation (in particular at the level of mitochondria) as compared with activated brown fat cells found in adult patients; in one pre-term infant the tissue morphology was obvio usly suggestive of an earlier, proliferative phase of development and the differentiation process of brown adipocytes could be traced in som e detail. The results suggest that (a) brown adipose tissue may be fai rly well-differentiated and thermogenetically active in pre-term human newborns weighing about 750 g at birth; (b) brown adipocytes apparent ly develop from vessel-associated cells, the early signs of adipocyte differentiation being glycogen and lipid accumulation; (c) the ultrast ructural morphology of mitochondria in well-differentiated BAT from pr e-term infants can strictly resemble that found in active brown adipos e tissue of adult phaeochromocytoma patients.