Effects of age and anatomic site on preadipocyte number in rat fat depots.

Preadipocytes are cells which are capable of either replication or of differentiation into fat cells. As with other stem or progenitor cell types, the replicative capacity of preadipocytes declines with increasing age; however, little information about effects of age on preadipocyte cell number in vivo is available. We determined preadipocyte number in the perirenal and epididymal fat depots of 3-, 17-, and 27-month-old Fischer 344 rats in 23 experiments. Increasing age was not associated with a decrease in preadipocyte number; indeed, the number of preadipocytes increased in epididymal depots throughout maturation and senescence. Hence, the tenet that aging causes a decline in the size of stem cell or progenitor pools is not generalizable to all tissues, even if the cells exhibit reduced replicative capacity in culture.