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Experimental tumors induce a decline in food intake that may derive from changes in taste or the development of taste aversions. The preferences of tumor-bearing (TB) and non-tumor-bearing (NTB) rats for five chemicals (three palatable and two aversive taste stimuli) were studied in an animal model of experimental cancer employing the methylcholanthrene (MCA) sarcoma. In protocol 1, five groups of Fischer 344 rats were given 23-h, two-bottle preference tests (taste solution vs. water) daily from day 3 after tumor implantation until spontaneous death occurred. Both NTB and TB rats avoided quinine hydrochloride and hydrochloric acid solutions throughout the experiment indicating that tumor growth produced no disruption in the animals' perception of these normally aversive tastes. In both groups, preference for sucrose (88% to 97%) and saccharin (75% to 93%) remained high until days 22 and 17 respectively, but tended to decline with advanced tumor growth. In both cases, a reduction in total calorie intake preceded the changes in sucrose or saccharin preference by several days. With or without a tumor, rats exhibited approximately 50% preference for NaCl at all times. In protocol 2, a four-bottle preference test (sucrose vs. saccharin vs. NaCl vs. water) was administered before tumor implantation and again 3 weeks later when a decline in food intake was evident. Both TB and NTB rats displayed a dominant preference for sucrose over saccharin, NaCl, and water at the pre- and posttests. However, a comparison of the difference scores (pre- minus postimplantation) of NTB and TB rats showed a small but significant suppression of TB animals' preference for sucrose. The altered preferences for sweet but not salt taste stimuli suggest that food-related taste cues may be more susceptible to the development of taste aversions during cancer. However the contribution of taste changes to the anorexia of cancer remains unclear and it is possible that the changes in taste preference may be secondary to the reduction in food intake.

The cause of cancer cachexia is unclear. Tumors may be competing with the host for ingested nutrients or may be releasing some factor that actively inhibits energy utilization. To explore these questions, plasma was sterilely collected and pooled from 103 terminally cachectic Fischer 344 rats implanted with an experimental sarcoma. Control plasma was collected in similar fashion from 138 nontumor-bearing rats (NTBP). Plasma from tumor-bearing rats (TBP) or NTBP was continuously infused in a randomized, blinded fashion for 4 days into 20 normal rats. During infusion, food intake and nitrogen excretion were measured daily. At sacrifice, body weight and organ masses were determined. Rats receiving TBP demonstrated an immediate and profound anorexia compared with those receiving NTBP. Total food intake during treatment was 31.2 +/- 3.3 (g +/- SEM) in the TBP group versus 48.2 +/- 2.8 in the NTBP group (P less than 0.001 by t test). Likewise, the total decline in body weight was greater in the TBP group as compared with the NTBP group (-35.2 +/- 3.4 versus -14.6 +/- 4.0, P less than 0.001). Mean daily nitrogen balance during treatment was negative in the rats receiving TBP (-14.5 +/- 20.1 mg +/- SEM) while remaining highly positive in the rats receiving NTBP (110.7 +/- 19.3, P less than 0.002). Finally, cardiac and gastrocnemius muscle masses were decreased, while hepatic mass was unaffected. These data demonstrate that the syndrome of cancer-associated cachexia is transmissible in plasma and therefore may be mediated by a circulating molecule or molecules. Identification and purification of the molecule(s) responsible for this effect would have obvious clinical benefits.

As a model of surgical stress in the cancer-bearing animal, we resected large flank sarcomas from cachectic rats under ether anesthesia and closed wounds primarily. The metabolic cost of tumor resection was measured using a long-term continuous indirect calorimeter. In the immediate postresection period energy balance decreased and host energy expenditure increased significantly (P less than 0.005). In animals with similar tumor weights, mortality following resection was determined by the degree of cachectic depletion. We then considered whether improvement of preoperative host nutritional status with insulin treatment might improve a subsequent surgical outcome. Insulin, when administered exogenously to cachectic tumor-bearing rats, has been shown to stimulate food intake and preserve host weight and does not stimulate tumor growth. When individual rats bearing a cachexia-producing flank sarcoma demonstrated a decline in food intake to less than 75% of predicted (approximately 25 days after tumor implantation), they were randomized to receive either daily injections of NPH insulin (2 units/100 g/day) for 5 days or no treatment for 5 days. Animals then underwent tumor resection and 14-day survival was measured. All resections were performed in an unbiased manner without the surgeon's knowledge of each rat's treatment status. In an experiment using 59 rats, insulin-treated rats had a threefold higher 5-day preoperative food intake and did not lose weight in the preoperative period, while untreated rats lost 17 g (P less than 0.001). Mortality in the insulin-treated group was 10% versus 28% in the untreated group.(ABSTRACT TRUNCATED AT 250 WORDS)

The syndrome of cancer anorexia includes early satiety in man and a reduction in the duration of feeding in experimental animals. These aberrations suggest dysfunction of peripheral and/or central nervous system satiety mechanisms in tumor-bearing individuals. Since the gut peptide, cholecystokinin (CCK), has been implicated as a potent satiety cue in man and animals, plasma and brain concentrations of CCK were measured by radioimmunoassay in anorectic tumor-bearing rats. Plasma concentrations of immunoreactive CCK were not significantly altered in either an acute Walker 256 carcinosarcoma or more chronic methylcholanthrene-induced sarcoma animal model of cancer anorexia. However, levels of immunoreactive CCK were significantly reduced in the hypothalamus and cerebral cortex of animals bearing the methylcholanthrene sarcoma during both mild and severe anorexia. These data demonstrate that elevations in immunoreactive CCK are not a major factor in the etiology of cancer anorexia. If brain CCK is involved in satiety, tumor-bearing rats may be attempting to compensate for their anorexia by down-regulating CCK production.

Morphometric data on left ventricular papillary muscle structures have been determined in tumor-induced malnutrition and related to the maximum activities of key enzymes for energy production in the whole myocardium. Adult, nongrowing mice with a syngeneic sarcoma were used to represent a condition of cancer associated host tissue wasting. Hearts from mice 11 days after tumor implantation showed atrophy and a significantly reduced amount of myofibrillar, soluble, and collagen proteins than hearts from control animals. The cross-sectional area of myocardial cells was 33% smaller in tumor-bearing mice (p less than 0.025), but the total number of capillaries and the residual interstitial volume were similar in the two groups. The total number of subcellular structures per cell, such as mitochondria, myofibrils, and myosin filaments per myofiber, were significantly lower in the tumor-bearing animals (p less than 0.025). Conversely, the proportion of myofibrils was higher (p less than 0.05) in tumor-bearing animals while the proportion of mitochondria was lower. Maximum activities (Vmax) of selected regulatory key enzymes for energy production (glycogenolytic, glycolytic, and mitochondrial) were not significantly altered in hearts from tumor-bearing mice. The results support the conclusion that myocardial functional capacity is better preserved than overall structural components would imply in tumor-host associated malnutrition, which is probably secondary to deprived food intake. Teleologically, this may be a means by which functional deterioration of the heart is minimized during the induction of malnutrition.