Cell size and plamitate-1-14c turnover of rabbit marrow fat

Adipose tissue is a major component of normal rabbit marrow. Morphological considerations suggest an active role for this tissue in hematopoiesis. This hypothesis was tested by injecting 50 micronCi of palmitate-1-14C intravenously into fed, hematologically normal New Zealand rabbits. The animals were sacrificed 24 hr later and the femoral marrow removed. Samples of subcutaneous and perinephric fat were taken for comparison. The fat cells were isolated by the Rodbell method and the diameters measured. Incorporation of the 14C-palmitate in the triglyceride fraction was determined and the composition of the fatty acids was measured by gas chromatography. The mean diameter of the marrow fat cell was 46 micronm (mean cell volume 55 pl); the mean diameter of the perinephric fat cell 70 micronm (mean cell volume 200 pl). 14C-Palmitate turnover per gram triglyceride was some fivefold greater in the marrow fat; however, when expressed on a cell basis, the turnover for the marrow and perinephric fat cell was similar. The marrow fat contained a higher concentration of unsaturated fatty acids. These findings suggest that there is greater lipolysis and lesser storage in the marrow fat than in the perinephric.