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Competition for Host Essential and Nonessential Fatty Acids by Ehrlich Ascites Carcinoma in Mice¹

Tumor-Lipid Laboratory, Research Service, Veterans Administration Wadsworth Hospital Center, Los Angeles 90073, and the Department of Medicine, UCLA School of Medicine, Los Angeles, California 90024

Mobilization of essential and nonessential free fatty acids (FFA) in control and Ehrlich ascites carcinoma-bearing mice was studied under varying nutritional conditions. Competition between tumor and host tissues for circulating FFA and the relationship between FFA transport rates (from blood to tumor) and FFA turnover in tumor extracellular fluid were also studied. Traders, [9,10-³H]palmitate and [1-¹⁴C]linoleate, complexed to mouse serum albumin were injected i.v. into unanesthetized animals. Plasma FFA radioactivity and pool sizes were measured. About 60 to 100% of plasma FFA was replaced per min. In no case was the mean fractional irreversible disposal rate greater in cancerous than in normal mice. Transport rates (µEq/min) of palmitate equalled those of linoleate and were the same in cancerous as in control mice. The total plasma FFA pool was replaced at a rate of approximately 1.3 µEq/min/mouse in all groups; only 0.01 µEq/min was transferred from blood to a 7-ml tumor. Thus, the presence of a large, rapidly growing ascites tumor did not increase FFA mobilization; a nearly negligible fraction of the FFA turning over in the extracellular fluid of the tumor (0.5 µEq/min/7-ml tumor) could have been derived from plasma FFA. Moreover, the cancer, the largest organ in the body of these mice, was unable to compete effectively with the host for plasma essential as well as nonessential FFA. Either the slow FFA transport from blood to tumor can support the net growth of the tumor and energy requirements or another source of tumor fatty acids exists.

¹ Supported in part by Veterans Administration Medical Research and NIH USPHS Grant CA 15813. Computing assistance was obtained from the Health Sciences Computing Facility, UCLA, sponsored by NIH Grant FR-3.

² To whom requests for reprints should be addressed, at Veterans Administration Wadsworth Hospital Center, Building 115, Room 316, Wilshire and Sawtelle Boulevards, Los Angeles, Calif. 90073.

Received 11/ 3/76. Accepted 4/ 7/77.