Cellularity of rat adipose tissue: effects of growth, starvation, and obesity.

The size, number, and rate of formation of mature adipocytes were studied in the epididymal pads and retroperitoneal adipose depots of the Sprague-Dawley rat. Early growth of these depots was accompanied by progressive enlargement of adipose cells as well as by increases in number. Beyond the 15th wk of life, the depot grew exclusively by the process of cellular enlargement, with no further change in cell number. Severe starvation during the 6th wk of life followed by normal feeding had no lasting effect on cell size or cell number; prolonged semistarvation beginning in the 15th wk greatly reduced cell size while cell number was unaffected. Likewise, extreme increases in depot size produced by hypothalamic lesions did not change cell number, but only cell size. The concept of a fixed number of mature adipocytes in the adult organism may be of central importance in caloric and metabolic equilibrium.