Adipose tissue cellularity in woodchucks: effects of season and captivity at an early age.

The objectives of this study were to determine the roles of adipocyte hypertrophy and hyperplasia in the prehibernatory weight gain of adult woodchucks and in the increased body weight of woodchucks born in captivity. The seasonal increase in weight in wild adult woodchucks was associated with an increase approaching tenfold in both body fat and in subcutaneous and retroperitoneal adipocyte size. There was no increase in total adipocyte number. Four groups of woodchucks were used in the study of the effect of captivity: I) animals born to females bred in the laboratory; II) those born to females captured just before parturition; III) those captured at weaning; and IV) animals captured at 12 months of age. At 14 months non-fat body weight and subcutaneous adipocyte size were equal in the four groups. The males but not the females in Groups I, II, and III had both an increased body fat content and a significantly increased total adipocyte number in comparison to the males in Group IV and the adults in the seasonal study. This study demonstrates that captivity at an early age, unlike prehibernatory weight gain, is associated with an increased adipocyte number in male woodchucks, and this increase can occur after weaning.