Effects of tumor bearing and removal on blood levels of lipids, lipolytic activity, and glycerol and on carcass weight in the rat.

In this animal model we investigated the effects of sarcoma bearing and complete or incomplete tumor excision on blood levels of lipids, lipolytic activity, and glycerol and on carcass weight. We also sought causes that could account for the apparent increase in lipid mobilization. Tumor-bearing (TB) rats had depleted retroperitoneal fat stores, elevated blood triglycerides and cholesterol, and normal thyroid, hepatic, and renal function during tumor bearing. Catecholamine, growth hormone, and glucagon levels were not different between TB and nontumor-bearing (NTB) groups. Serum lipolytic activity and glycerol levels, which were elevated during tumor bearing, returned to NTB levels after complete tumor excision, along with restoration of retroperitoneal fat depots and carcass weight. The elevated serum lipolytic activity of animals that had tumors only incompletely excised rose significantly higher after the tumor regrew; this was accompanied by a failure to regain carcass weight. Previous work has shown that elevated lipolytic activity can also be demonstrated in culture media conditioned by growth of certain animal or human tumor cell lines in cell culture, free of host influences. This suggests that the actual tumor cell and not the host may be at least partly responsible for the lipid derangements seen in this model.