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To better understand the role of the liver in the hypertriglyceridemia observed in a tumor-bearing state, we have examined tumor-induced alterations in hepatic lipogenesis and fatty acid oxidation. The effects of differing tumor burden as well as tumor excision on the activity and mRNA levels of malic enzyme and carnitine palmitoyltransferase were studied in Fisher 344 rats bearing a methylcholanthrene-induced sarcoma. Serum triacylglycerols and plasma nonesterified fatty acids (NEFA) levels were both elevated with increasing tumor burden (P < 0.05 vs control). The elevation disappeared with tumor removal. Malic enzyme activity of tumor bearers, compared with control rats, declined with an increase in tumor burden. These two variables were negatively correlated (r = -0.90, P < 0.01). The changes in activity were accompanied by positively correlated changes in mRNA levels (r = 0.73, P < 0.01). Carnitine palmitoyltransferase activity was not altered, even in the presence of a large tumor burden. Hepatic lipogenesis, reflected by malic enzyme activity, was tumor-dependent and was significantly reduced during the period of circulating hypertriglyceridemia. Fatty acid oxidation, reflected by carnitine palmitoyltransferase activity, was not enhanced in spite of an ample supply of NEFAs to the liver from the peripheral tissues. The data suggest that neither hepatic lipogenesis nor fatty acid oxidation contribute to hypertriglyceridemia in the tumor-bearing state.

Although blood flow is central to systemic metabolism, little is known about the effect of tumor on the perfusion of host tissues. This study evaluated the effects of a methylcholanthrene-induced sarcoma on blood flow to intra-abdominal organs and skeletal muscle of Fischer-344 rats anesthetized with pentobarbital sodium. Animals were studied by aortic injection of radiolabeled microspheres when the tumors reached 20% of body weight. Total-organ arterial flows in spleen, liver, small intestine, and pancreas were each increased to 50-150% in tumor bearers relative to controls (P less than 0.05). Portal venous flow and flow per gram to hindlimb muscle were 60 +/- 20 and 300 +/- 100% greater, respectively, in tumor-bearing animals (P less than 0.005). This study shows that tumor growth can be associated with large changes in organ flow and distribution of cardiac output. The increase in skeletal muscle flow in the tumor bearers, which lost normal tissue weight relative to pair-fed controls (P less than 0.05), is in marked contrast to decreased muscle flow previously observed in simple starvation.

Pretransplant blood transfusion has been shown to significantly affect the outcome of renal transplantation. Evidence regarding the association of blood transfusions with growth or recurrence of solid tumors is still conflicting both in clinical and in experimental studies, although diminished survival has been suggested in several studies. To determine the influence of blood transfusions and hypovolemia, as separate or combined factors, on tumor growth, we evaluated the weight of a subcutaneously implanted sarcoma (methylcholanthrene-induced) in 35 rats. After reaching 1% tumor burden (day 0), the animals were separated into two groups: hypovolemia (shed volume, 15 ml/kg) or normovolemia. These groups were further divided according to resuscitation: OO (no resuscitation), BL (receiving syngeneic blood stored in citrate phosphate dextrose for 4 days, 15 ml/kg), SL (receiving 0.9% sodium chloride, 45 ml/kg). Tumor dimensions were determined daily by external measurement, and tumor weight was calculated. Hypovolemia exerted a significant influence on tumor growth, independent of the resuscitation modality. The rats that received blood transfusions showed an increased rate of tumor growth, compared to the animals that received saline solution or no treatment. No interaction was noted between the effects produced by hypovolemia and blood transfusion. We conclude that the hypovolemic event enhanced tumor growth independently of the resuscitation, and transfusion of citrate phosphate dextrose-blood stored for 4 days did influence tumor growth in this model. We suggest that the effect of blood transfusion in patients with cancer has to be redefined to account for the influence of possible hypovolemic events.

To elucidate the mechanisms of hypertriglyceridemia observed in the tumor-bearing rat, tissue lipoprotein lipase (LPL) activity and LPL mRNA levels were examined in the fed and fasted states at different degrees of tumor burden and after tumor removal. LPL activity in the epididymal fat pad and cardiac muscle in the 24-h-fasted rats was significantly decreased with increasing tumor burden (r = -0.53, P less than 0.05 and r = -0.72, P less than 0.01, respectively). Tumor removal completely reversed these changes. In contrast, no change in LPL activity was detected in the fed state since food intake stimulated LPL activity to the same extent in both tumor-bearing (TBR) and control rats. LPL activity in the diaphragm and skeletal muscle was only marginally altered in TBR, as compared to controls. LPL mRNA from the epididymal fat pad and cardiac muscle migrated to the same site on agarose gel and hybridized to a LPL-specific complementary DNA probe. The decline in LPL activity in epididymal fat pad observed in TBR was associated with a decrease in LPL mRNA levels. In contrast, there was no significant difference in LPL mRNA levels in cardiac muscle between the two groups despite significantly suppressed enzyme activity in tumor bearers. This study provides evidence that hypertriglyceridemia in TBR is due in part to tumor-dependent suppression of adipose and cardiac LPL activity in the fasted state, which is stimulated by the presence of tumor. Unlike cardiac LPL, the tumor-induced changes in adipose LPL activity are regulated at the mRNA level in this tumor model.

Cancer cachexia is frequently accompanied by hyperlipidemia. To identify the mechanisms underlying this alteration in lipid metabolism, free fatty acid (FFA) and very low density lipoprotein-associated triacylglycerol (VLDL-TG) kinetics were determined in tumor-bearing (subcutaneously implanted methylcholanthrene-induced sarcoma) Fischer 344 rats. The animals were studied after chronic vascular catheterization, in an unanesthetized, undisturbed state, after 24 hr of fasting. They were separated into three groups: control (n = 5), tumor-bearing (n = 5, tumor burden = 10% body weight), and 7 days after tumor excision (n = 5). VLDL-TG and FFA kinetics were assessed by a constant infusion of [3H]palmitate-labeled VLDL-TG and [14C]palmitate bound to albumin, respectively. FFA rate of appearance (FFA-Ra) and clearance (FFA-Cl) and VLDL-TG rate of appearance (VLDL-TG-Ra) and clearance (VLDL-TG-Cl) were determined at steady state. We observed that the tumor-bearing rats had significantly increased FFA-Ra and VLDL-TG-Ra, decreased VLDL-CL, and maintained FFA-Cl, when compared to control. These alterations returned to normal levels after tumor excision. The results suggest that the hyperlipidemia observed in tumor-bearing rats is due to elevated lipolysis rate, maintained rate of plasma FFA clearance, increased triacylglycerol production and VLDL secretion by the liver, and decreased VLDL-TG clearance from plasma. These alterations were reversed 7 days following tumor excision.

The accelerated mobilization of peripheral protein and subsequent increased gluconeogenesis are regarded as mechanisms of cancer cachexia. To determine the relation of gluconeogenesis to different degrees of tumor burden and subsequent tumor removal in the fed and fasted states, we examined the activity and mRNA levels of the key regulatory enzyme for gluconeogenesis: phosphoenolpyruvate carboxykinase (PEPck) in the liver of Fischer rats with a transplanted methylcholanthrene-induced sarcoma. PEPck activity in liver cytosol, after a 24-hour fast, was significantly higher in the tumor-bearing rats than in their pair-fed controls. The increase in enzyme activity was clearly evident at 8% tumor burden and correlated positively with the degree of tumor burden (r = 0.85, p less than 0.01). Removal of the tumor produced a complete reversal of PEPck activity 10 days after excision. Regular feeding also abolished this increased enzyme activity. A similar trend was seen in the mitochondria. PEPck mRNA levels of rats with greater than 11% tumor burden in the fed state were decreased more than those of controls. PEPck mRNA levels were equally elevated in tumor bearers and controls in the 24-hour-fasted state. These results suggest that tumor-bearing simulates the fasted state associated with hypoglycemia, which in turn triggers induction of the gluconeogenic enzyme, PEPck.