Bone marrow adipose tissue: Response to acute starvation

Adipose tissue is a major component of normal rabbit marrow. Its physiologic function has not been elucidated, but it is generally believed to be, essentially, a passive space filler. The response of marrow fat cells to lipolytic stimuli was studied by subjecting rabbits to acute starvation. Following 2 weeks of starvation and a weight loss of 28%, the mean marrow fat cell volume was 50.9 ± 9.6 pl (control, 42.8 ± 8.1 pl), and the mean volume of the perinephric fat cell 134.3 ± 87.8 picoliter (pl) (control, 318 ± 89.7 pl). Esterification capacity for labeled palmitate of the marrow fat cells did not change from control; the esterification capacity of the perinephric fat cells fell by about 60%. After 3 weeks of starvation and further weight loss to 34% of initial weight, the perinephric fat cells decreased their mean cell volume to 50.2 ± 33.6 pl. The marrow fat cell volume remained essentially unchanged from control. Esterification capacity of the marrow fat cells again did not differ from that of the control animals, but the esterification capacity of the perinephric fat cells fell further to 19% of that of the marrow fat cells. Despite the urgent energy requirements of the starved animals, the marrow fat cells did not yield their stored fat and continued to esterify free fatty acids at an unaltered rate. Drastic weight loss produced no change in volume, in esterification capacity, or in number of fat cells in the femoral marrow of the rabbit. Marrow adipocytes are metabolically active cells that are involved in the hematopoietic process rather than involved with the total energy needs of the animal.