The development of cold-induced thermogenesis in hamsters.

The onset of the thermogenic response to cold exposure in hamsters was studied in relation to the development of brown adipose tissue. The daily weight increment of hamsters reared in animal house conditions was first determined. Organ weights in animals with body weights within +/- 1 SD of mean were obtained at intervals between 0 and 20 days of age. Adipose tissue increased rapidly in weight between days 10 and 15, but the fat content of cervical adipose tissue fell. Electronmicroscopic studies reveal that there had been a dramatic increase in the number and size of the mitochondria. Serial measurement of the rate of oxygen consumption showed an initial increase in minimal rate over the first 4 days of life followed by a larger increment from 8 to 16 days of age. On day 12 most hamsters shivered vigorously but had a poor and variable thermogenic response to cold. By day 16 all showed an impressive increase in heat production in the cold. It would appear that thermogenesis in response to cold exposure awaits the development of brown adipose tissue.