Spontaneous activity and adipose cellularity in the genetically obese Zucker rat (fafa).

The development of spontaneous activity was studied in obese and lean Zucker rats. Rats were given access to activity wheels for 3 hr/day before weaning and for 24 hr/day after weaning. Zucker obese rats are less active than lean rats. This decreased activity occurs at weaning and follows the onset of hyperphagia and obesity. At 8 wk of age exercised lean and obese rats have less total fat and fewer adipocytes than their appropriate controls. Adipose cell size is decreased only in exercised lean rats. When rats are exercised until 8 wk of age and then confined until 6 mo of age, body weight and fat is elevated in these formerly active rats compared to control rats. Adipose cell number is permanently decreased only in formerly active lean rats. Exercise has no long-term effect in decreasing cell number in obese rats.