Metabolism of a chylomicron-like emulsion in rats with Walker 256 tumor: influence of a polyunsaturated (n-6) compared with a saturated fatty acid-rich diet.

OBJECTIVE: Defects in lipid metabolism secondary to development of cancer are frequently observed and, in experimental animals, manipulation of the lipid content of the diet can significantly influence tumor growth. The effects of a high polyunsaturated fat vs a high saturated fat diet upon the chylomicron metabolism of rats bearing Walker 256 tumor were examined. METHODS: Chylomicron-like emulsions labeled with radioactive lipids were injected into rats bearing the tumor and control rats. The two groups were previously given a high polyunsaturated (n-6) (15% fat) or a high saturated fat diet (15% fat) for 6 weeks. Following injection, plasma samples were collected at 8 time intervals in 60 minutes and tissue fragments were excised after the animals were killed, for determination of the plasma fractional clearance rate (FCR, min-1) and organ uptake of radioactive lipids. RESULTS: FCR of the emulsion triacylglycerols (TG) and cholesteryl oleate ether (CE) decreased in the tumor-bearing rats fed the polyunsaturated fat-rich diet (FCR-TG control = 0.26 +/- 0.09, tumor = 0.11 +/- 0.04; FCR-CE controls = 0.18 +/- 0.05, tumor = 0.10 +/- 0.02), as did activity of the lipoprotein and hepatic lipases (p < 0.05). This indicates that in this group, the presence of the tumor elicited defective lipolysis and delayed removal of the emulsion from the plasma. In the group fed the saturated fatty acid-rich diet, however, these alterations were not observed (FCR-TG control = 0.21 +/- 0.11, tumor = 0.20 +/- 0.08; FCR-CE control = 0.13 +/- 0.06, tumor = 0.10 +/- 0.05). The uptake by several tissues of the emulsion CE was similar in all rat groups. CONCLUSION: The saturated fat-rich diet avoids the deficiency in chylomicron lipolysis elicited by the implanted Walker 256 tumor.