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Ghrelin is a novel brain-gut peptide that stimulates food intake and may secondarily increase body weight via a growth hormone secretagogue receptor (GHS-R). Tumor-bearing mice (MCG101), characterized by anorexia, fat loss and muscle wasting due to increased concentration of PGE2 and proinflammatory cytokines (IL-1beta, IL-6, TNF-alpha), were provided ghrelin i.p. at a low (20 microg/day) and high dose (40 microg/day) to examine the ability of ghrelin to counteract tumor-induced anorexia. Immunohistochemical staining and Western blot analyses were used to identify GHS-R expression in the brain as well as its relationship to NPY expression in hypothalamic neurons. GHS-R mRNA in hypothalamus and ghrelin mRNA in gastric fundus were quantified by RT-PCR. Body composition was determined by carcass extractions. GHS-R expression in hypothalamus and plasma ghrelin levels were significantly increased in freely-fed tumor-bearing mice, while gastric fundus expression of ghrelin was unaltered compared to non-tumor-bearing mice (controls). Ghrelin treatment increased food intake, body weight and whole body fat at both low and high doses of ghrelin in normal controls, while tumor-bearing mice showed improved intake and body composition at the high dose of ghrelin only. Exogenous ghrelin normalized the GHS-R expression in hypothalamus from tumor-bearing mice without alterations in the gastric fundus expression of ghrelin. Tumor growth was not altered by exogenous ghrelin. Our results indicate that MCG 101-bearing mice became ghrelin resistant despite upregulation of hypothalamic GHS-R expression, which confirms similar indirect observations in cancer patients. Thus, other factors downstream of the ghrelin-GHS-R system appear to be more important than ghrelin to explain cancer-induced anorexia.

Tumor growth leads to anorexia and decreased food intake, the regulation of which is via the integrated hypothalamic peptidergic and monoaminergic system. Serotonin (5-HT), an anorectic monoamine acts primarily via 5-HT 1B-receptors in hypothalamic nuclei while neuropeptide Y (NPY) acts an orexigenic peptide. We previously reported that 5-HT 1B-receptors are up regulated while NPY is down regulated in tumor-bearing (TB)-related anorexia, contributing to food intake reduction. In anorectic TB rats we hypothesize that after tumor resection when food intake has reverted to normal, normalization of 5-HT 1B-receptor and NPY will occur. The aim of this study was to demonstrate normalization of these hypothalamic changes compared to Controls. In anorectic tumor-bearing rats after tumor resection (TB-R) and in sham-operated (Control) rats, distribution of 5-HT 1B-receptors and NPY in hypothalamic nuclei was analyzed using peroxidase antiperoxidase immunocytochemical methods. Image analysis of immunostaining was performed and the data were statistically analyzed. Immunostaining specificity was controlled by omission of primary or secondary antibodies and pre-absorption test. Our results show that after TB-R versus Controls a normalization of food intake, 5-H-1B-receptor and NPY expression in the hypothalamus occurs. These data, discussed in context with our previous studies, support the hypothesis that tumor resection results not only in normalization of food intake but also in reversible changes of anorectic and orexigenic hypothalamic modulators.

In cancer anorexia, a decrease in food intake (FI) occurs concomitant with changes in orexigenic peptides such as neuropeptide Y (NPY) and anorexigenic peptides such as alpha-melanocyte-stimulating hormone (alpha-MSH) and anorexigenic neurotransmitter serotonin. omega-3 Fatty acid (omega-3FA) inhibits cytokine synthesis, and delays tumor appearance, tumor growth, and onset of anorexia in tumor-bearing rats. We hypothesize that, in cancer anorexia, omega-3FA is associated with quantitative reversal of hypothalamic NPY, alpha-MSH, and serotonin receptor (5-HT(1B)-receptor) enhancing FI. Fischer rats were divided into: MCA tumor bearing fed chow (TB-Chow) or omega-3FA diet (TB-omega-3FA) and controls: non-tumor bearing fed chow (NTB-Chow) or omega-3FA diet (NTB-omega-3FA). Rats were euthanized at anorexia and brains were removed for hypothalamic immunohistochemical study, using NPY, alpha-MSH, and 5-HT(1B)-receptor-specific antibodies and slides assessed by image analysis. Immunostaining specificity was controlled by omission of primary or secondary antibodies and pre-absorption test. At anorexia, FI decreased (P < 0.05) in TB-Chow but did not change in TB-omega-3FA rats. In TB-omega-3FA vs. TB-Chow, NPY immunoreactivity increased 38% in arcuate nucleus (ARC; P < 0.05), and 50% in magnocellular paraventricular nucleus (mPVN; P < 0.05). alpha-MSH decreased 64% in ARC and 29% in mPVN (P < 0.05). 5-HT(1B)-receptor immunoreactivity decreased 13% only in supraoptic nucleus (P < 0.05). No immunoreactivity was found in the control sections. omega-3FA modified hypothalamic peptides and 5-HT-(1B)-receptor immunoreactivity at anorexia, concomitant with an increase in FI, were probably mediated by omega-3FA inhibition of tumor-induced cytokines.

Paraventricular (PVN) concentrations of neuropeptide Y (NPY), serotonin (5-HT) and dopamine (DA) in anorectic tumor-bearing (TB) rats were measured before and after tumor resection. At onset of anorexia in TB versus non-tumor bearing (NTB) Controls 5-HT increased from 12.19+/-0.49 pg/microg to 14.89+/-0.81 pg/microg ( P<0.05 ) while DA and NPY decreased from 7.34+/-0.42 pg/microg to 4.97+/-0.56 pg/microg and 23.47+/-4.27 pg/microg to 13.64+/-1.44 pg/microg, respectively ( P<0.05 ). After tumor resection, these neuromediators normalized when compared to sham-operated NTB rats. NTB pair-fed Controls were also studied. We conclude that the increased 5-HT and the decreased DA and NPY concentrations in PVN are associated with cancer anorexia and that the NPY food stimulatory effect is linked to serotoninergic and dopaminergic systems in hypothalamus.

Gender differences of feeding pattern in normal male and female rats are well recognized. Differences in gender-related feeding patterns have also been established following a variety of experimental manipulations, such as hypothalamic lesions, nicotine infusion, and total parenteral nutrition administration. Anorexia is a common feature during tumor growth. The present study examined whether the feeding indices constituting the feeding patterns differed with the development of cancer anorexia in male and female rats. Sixteen male and 15 female Fischer-344 rats had their food intake (FI) and feeding indices, meal number (MN) and meal size (MZ), continuously measured by a computerized rat eater meter. Viable methylcholanthrene (MCA) sarcoma cells (10(6)) were inoculated subcutaneously in 10 male (M-TB) and 8 female (F-TB) Fischer rats, while the rest were controls and received an equal volume of vehicle. Tumor-bearing (TB) rats became anorectic by Day 18, when the weight of the tumor was approximately 8% of the total body weight (BW). A notable decrease in BW was observed in both M-TB and F-TB. A decrease in FI resulted from different feeding indices between male and female rats. In male rats, lower FI was due to a decrease in both MN and MZ. In female rats, lower FI was solely due to a decrease in MN. The data show that gender differences in feeding patterns, which are an external manifestation of biochemical changes in the brain, occur following development of cancer-related anorexia suggesting that besides other factors, cancer anorexia is also influenced by sex-related hormones.

Previous studies suggest that the dopaminergic system in the supraoptic nucleus (SON) is involved not only in the water balance control but also in the food intake regulation. Since we reported that an injection of the D2 receptor antagonist, sulpiride, into specific hypothalamic nuclei (e.g. the LHA, or the VMN) increases food intake in anorectic tumor-bearing rats, as well as in normal rats, we hypothesized that an injection of sulpiride into the SON would also improve cancer anorexia. Sulpiride injection (4 microg/0.5 microl) into bilateral SON of anorectic tumor-bearing male rats significantly improved food intake via increases in both meal size and meal number. These data suggest that pharmacological manipulation of the hypothalamic dopaminergic system is feasible in amelioration of cancer anorexia.

Evidence suggests that cytokines in the central nervous system are mediators behind anorexia in tumor-bearing hosts. We have therefore evaluated, by immunohistochemical image analyses, time course changes of interleukin (IL)-1beta, IL-6, tumor necrosis factor (TNF) alpha, IL-6 receptor (gp130), IL-1 receptor I, and cyclooxygenase (Cox)-2 protein in brain cortex, hippocampus and the ventromedial hypothalamic nucleus (VMH) in tumor-bearing mice with prostanoid-related anorexia. Pair-fed non-tumor-bearing mice were used as controls. Prostaglandin E(2) was provided systemically to freely fed, non-tumor-bearing mice to confirm a role for prostanoids in modulation of brain cytokines and food intake. Time course changes of IL-1beta were significantly different between tumor-bearing mice and pair-fed controls in the hippocampus but not in the VMH. TNF-alpha in the hippocampus and VMH did not show any significant difference between tumor-bearing mice and pair-fed controls, whereas TNF-alpha showed a small increase over time in brain VMH. IL-6 content did not show any significant alterations among tumor-bearing and pair-fed mice but increased significantly over time in both the study and control group. Cox-2 in brain hippocampus and VMH showed a statistically significant rise in both tumor-bearing and pair-fed controls, with no difference between animal groups. Systemic provision of exogenous PGE(2) to non-tumor-bearing mice altered brain cytokines significantly in the hippocampus and VMH with associated changes in food intake. Our results demonstrate that some differences (IL-1beta) occurred in brain cytokines comparing tumor-bearing and pair-fed, non-tumor-bearing mice but within unexpected decreased levels in brain tissue from tumor-bearing mice. Surprisingly, many time course changes in brain cytokines were similarly altered in tumor-bearing and pair-fed mice. Our observations do not support that up-regulation of brain cytokines explains or promotes anorexia in cancer disease. Rather, cytokine and Cox-dependent alterations in brain tissue seemed to be secondary to a decline in food intake and related to subsequent stress hormone activities.

Background: Tumor growth in animals and humans is associated with the onset of anorexia and reduced food intake. We previously demonstrated that the ventromedial nucleus of hypothalamus (VMN) plays a contributory role in mediating cancer anorexia. Because serotonin and interleukin-1 (IL-1) are putative mediators of cancer anorexia, we hypothesized that their influence on food intake during tumor growth might occur via their action within the VMN., Methods: To test this hypothesis, 12 Fischer rats injected subcutaneously with 10(6) viable MCA sarcoma cells (TB rats) and their nontumor-bearing controls (NTB, n = 13) were studied. When anorexia developed, TB and NTB rats received bilateral intra-VMN microinjections of the serotonin antagonist mianserin (200 nmol) or the IL-1 receptor antagonist (IL-1ra, 25 ng). Food intake and its determinants of meal number and size were continuously recorded via a computerized device., Results: In NTB rats, intra-VMN mianserin did not affect food intake, whereas after IL-1ra or vehicle a momentary decrease in food intake due to a predominant reduction of meal size occurred. In TB rats, intra-VMN mianserin or IL-1ra selectively increased meal number, leading to improved food intake., Conclusions: Data suggest that intra-VMN serotonin and IL-1 are involved in influencing cancer related anorexia.

Previous investigations suggest that neuropeptide Y (NPY) feeding mechanisms and corticotropin releasing factor (CRF) are altered in anorectic tumor-bearing (TB) rats. To better determine the relationship of NPY and CRF synthesis to cancer anorexia we measured mRNA for these peptides in medial and lateral hypothalamus of TB and control rats. NPY and CRF mRNA were reliably detected by Northern blot analysis only in medial hypothalamus, where NPY message was elevated significantly in TB rats. CRF mRNA tended to be reduced in both pair-fed (PF) and TB rats, but did not reach statistical significance. Concentrations of NPY or CRF were not altered significantly in either the lateral or medial hypothalamus of TB or PF rats. These results suggest that the transcription of NPY is elevated in PF rats and is increased further in anorectic TB rats. The lack of significant increases in levels of peptides may be related to dilution, due to measuring a relatively large block of hypothalamic tissue. Alternatively, translation of the signal for NPY production may be inhibited, or degradation of peptide levels may be increased.

Unlabelled: Based on reports that increased hypothalamic ventromedial nucleus (VMN)-serotonin (5-HT) is associated with cancer anorexia and recent findings in our laboratory that low levels of dopamine (DA) in the VMN are associated with prolonged inter meal intervals thus decreased food intake, and reports that setting up satiation is concomitant with descending levels of DA in the rostromedial hypothalamus, we hypothesized that an elevated 5-HT to low DA ratio in the VMN modulates food intake in cancer anorexia., Methods: In Expt 1: A microdialysis cannula guide was placed stereotactically into the VMN of methylcholanthrene (MCA) sarcoma tumor-bearing (TB) Fischer rats and in non-tumor-bearing (NTB) and pair-fed (PF) controls. When TB rats manifested anorexia by a decrease in food intake, VMN-5-HT, its metabolite 5-hydroxyindolacetic acid (5-HIAA), and DA with its metabolite 3,4,-dihydroxyphenylacetic acid (DOPAC) were measured by in vivo microdialysis using HPLC during baseline, in response to food, and after feeding. In Expt 2: TB rats had tumor removed and VMN microdialysis performed 7 days later., Results: Increased 5-HT release and turnover, and significantly reduced DA release with increased DOPAC occurred in TB vs NTB or PF rats. When food was offered, intake in TB rats was significantly lower than in NTB control rats. During eating, VMN-5-HT rose and peaked significantly earlier in TB vs NTB rats, while DA release was significantly reduced. With eating, the 5-HT and DA metabolism became reduced in all rats. Seven days after surgical removal of the tumor, 24 h food intake had increased to the level of controls; and when food was offered during microdialysis, intake in TB rats increased (ns relative to control), but was not yet normal. VMN microdialysis showed that 5-HT was normal at baseline, as well as during and after eating, while DA remained depressed. The metabolic turnover of 5-HT and DA was significantly lower in TB-r and PF vs NTB rats. We conclude that increased 5-HT/DA ratio is related to the development of cancer-induced anorexia.

Although isoproterenol stimulated adenylate cyclase activity in hypothalamic membranes taken from freely-feeding, food-restricted or nonanorectic tumor-bearing rats, the response was greatly reduced in anorectic tumor-bearing rats. The addition of NPY to the membrane preparation inhibited adenylate cyclase activity in hypothalamus taken from freely-feeding and food-restricted rats, but NPY-inhibitory activity was significantly reduced in both groups of tumor-bearing rats. These results suggest that cyclic AMP formation is refractory in anorectic tumor-bearing rats, and that NPY-induced inhibition of hypothalamic adenylate cyclase is reduced in tumor-bearing rats prior to the onset of significant anorexia. Therefore, NPY-induced feeding may be reduced in tumor-bearing organisms due to a dysfunction in the cyclic AMP second messenger system.

Interleukin-1 (IL-1) induces anorexia via direct action in the brain, and its participation in the pathogenesis of cancer-associated anorexia has been hypothesized. Because the functional ablation of the ventromedial nucleus of hypothalamus (VMH), where IL-1 receptors have been detected, reverses cancer-associated anorexia in tumor-bearing (TB) rats, we hypothesize that cancer anorexia involves the direct effect of IL-1 on the VMH. To test this hypothesis, we investigated whether the intra-VMH injection of the IL-1 receptor antagonist (IL-1ra) improves food intake in anorectic TB rats. Sixteen Fischer rats (approximately 300 g/BW) were injected s.c. with 10(6) trypan-blue viable methylcholanthrene sarcoma cells, and then individually caged. Chow and water were freely available, and food intake was recorded throughout the study. Normal food intake was measured in 8 more rats, injected s.c. with normal saline. Tumor developed in all rats. When TB rats became anorectic, they were randomly assigned to either treatment or control groups. Using stereotaxic techniques, 25 ng of IL-1ra dissolved in normal saline (TB-IL-1ra; n = 8), or an equal volume of normal saline (TB-NS; n = 8) was injected bilaterally into the VMH. After surgery, rats were caged and changes in food intake recorded. At study's end, rats were sacrificed and brains removed for histological confirmation of injection sites. In the TB-NS group, food intake decreased with the occurrence of anorexia. In contrast, the intra-VMH injection of IL-1ra reduced the severity of cancer anorexia, significantly improving food intake in TB-IL-1ra rats. Data indicate that centrally acting IL-1 plays a significant role in the development of cancer anorexia.

Postulating that central IL-1 is involved in the pathogenesis of cancer anorexia we measured IL-1 alpha in cerebrospinal fluid (CSF) from anorectic tumor bearing (TB) rats and non-tumor bearing controls, and correlated their CSF IL-1 alpha with food intake and tumor weight. Food intake in controls was significantly higher than that in anorectic TB rats. Eight of the 13 anorectic TB rats had detectable CSF IL-1 alpha; no CSF IL-1 alpha was detected in controls. In anorectic TB rats a negative correlation existed between CSF IL-1 alpha and food intake and a positive correlation between CSF IL-1 alpha and tumor weight. Data suggest a link between CSF IL-1 alpha and the pathogenesis of cancer anorexia.

The efficacy of NPY to elicit feeding in TB rats was reduced prior to the onset of overt anorexia, with the feeding response decreasing further as anorexia developed. Hypothalamic concentration of NPY was reduced in TB rats, with the magnitude of the decrease paralleling the degree of anorexia. Binding affinity of NPY to hypothalamic membranes taken from TB rats suggested decreased binding affinity with no change in receptor number. Infusing ammonium salts at a concentration and rate necessary to increase blood ammonia levels to the degree observed in TB rats, produced anorexia and decreased NPY feeding. These results suggest that NPY feeding systems are abnormal in TB rats and that hyperammonemia may be of primary importance in this dysfunction.

Tumor growth is accompanied by an anorexia mediated by humoral factors that appear to influence appetitive mechanisms in the brain. Because tumor resection is followed by resumption of normal food intake, the circulating anorexigenic substance(s) are produced either by the neoplastic tissue or by the host in response to the tumor. Increased levels of plasma free tryptophan and plasma ammonia have been proposed to mediate cancer anorexia. With animal models, it is often difficult to ascertain whether changes in food intake depend upon metabolic changes or the progressively increasing tumor mass per se. The feeding patterns and biochemical changes that occur during tumor growth were evaluated in 96 male Fischer rats that were inoculated with 10(6) methylcholanthrene sarcoma cells or saline (controls). Rats were placed into metabolic cages equipped with an Automated Computerized Rat Eater Meter to continuously determine meal size and meal number. Plasma free tryptophan and ammonia were evaluated 6, 10, 16, 18, 22, and 26 days after tumor inoculation. Anorexia developed by day 17-18, when food intake started to decrease via a decrease in meal size but not meal number and reached 60% of control by day 26. However, long before anorexia developed, free tryptophan was significantly higher 6 days after tumor inoculation, and the greatest increase occurred after 18 days. Ammonia did not differ from control at any time. Data confirm tumor-associated increases in plasma free tryptophan that occurred before the manifestation of anorexia and support a possible role of brain serotonin in cancer anorexia.

Consistent anorexia was first observed 33 days after inoculating Fischer 344 rats with methylcholanthrene-induced sarcoma. Daily treatment of a similar group of rats with the glutamine synthetase inhibitor, methionine sulfoximine, elicited significant reductions of feeding by day 29 at a dose that had no effect on nontumor-bearing rats. Blood concentrations of ammonia were elevated in both groups of tumor-bearing rats and brain ammonia level was increased in the methionine sulfoximine-treated tumor-bearing rats. Forebrain concentrations of tyrosine, tryptophan, DOPAC and 5-HIAA were elevated in both groups of tumor-bearing rats. Since ammonia is detoxified through the glutamine synthetase reaction, these results suggest that blood and brain ammonia concentrations are more important than the neurochemical consequences of ammonia detoxification for the etiology of cancer anorexia.

The importance of decreased food intake as the mechanism behind altered protein metabolism in skeletal muscle in cancer was evaluated. A methylcholanthrene-induced sarcoma (MCG 101) transplanted in weight-stable and nongrowing mice (C57BL/6J) was used as the tumor-animal model. Three study groups with appropriate control groups were used: sarcoma-bearing mice; pair-fed mice; and starved mice. The synthesis of myofibrillar and sarcoplasmic proteins was decreased in sarcoma-bearing mice. This was correlated to decreased content of RNA in the muscles and caused a net loss of muscle tissue was measured by dry weight of skeletal muscles. The incorporation rate of amino acids into myofibrillar and sarcoplasmic proteins was decreased to the same extent in the pair-fed mice as that in the sarcoma-bearing mice. This probably reflected decreased protein synthesis, since the radioactivity (dpm/mg) did not differ significantly in the crude transfer RNA fraction between the groups. Separation of soluble proteins from muscle tissue by means of ion-exchange chromatography showed that the pattern of decreased protein synthesis was not tumor specific when compared to muscle affected by starvation. The decrease in protein synthesis was more or less selective, since the synthesis of basic proteins was considerably decreased and was influenced more than were neutral and acidic proteins in both cancer and starvation. Anorexia of a tumor-bearing host is a sufficient trigger to induce decreased protein synthesis in skeletal muscles, but other factors may also be of quantitative importance.

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.

Assessment of biochemical parameters in methylcholanthrene sarcoma-bearing rats 2 days after the onset of anorexia revealed several biochemical aberrations in blood and brain. Plasma levels of glucose were decreased and lactate concentrations were increased. The plasma and brain amino acid profiles were also greatly altered in these rats, characterized by increased brain concentrations of glutamine and large neutral amino acids. Analysis of regional neurotransmitter and metabolite levels by high-performance liquid chromatography suggested increases in the neuronal activity of dopamine and serotonin in each brain region examined. Surgical removal of the tumors in another group of anorectic tumor-bearing rats was followed by the return of normal feeding within 6 days. Associated with the normalization of food intake was the reversal of these biochemical aberrations in blood and brain. It is hypothesized that the utilization of glutamine and excretion of ammonia by tumor tissue is the precursor of these alterations in brain amino acids and neurotransmitters, which may be causing anorexia.

Plasma concentrations of ammonia were elevated significantly in tumor-bearing rats prior to the onset of anorexia and continued to increase as the tumor grew and anorexia developed. Associated with this hyperammonemia were elevated levels of brain glutamine and large neutral amino acids (phenylalanine, tyrosine, tryptophan, methionine, histidine). Concentrations of the dopamine metabolites, DOPAC or HVA were elevated in the corpus striatum, nucleus accumbens, hypothalamus and amygdala of anorectic tumor-bearing rats only, while levels of the serotonin metabolite, 5-HIAA, were increased in these brain regions in both anorectic and non-anorectic tumor-bearing rats. Infusing ammonium salts into non-tumor-bearing rats elicited anorexia and alterations in brain amino acid profile and neurotransmitter metabolism that were similar to those observed in anorectic tumor-bearing rats. Therefore, we conclude that ammonia released by tumor tissue may have a direct role in the etiology of experimental cancer anorexia.

This study was designed to ascertain whether the overall availability of whole-body lipids and nitrogen is a limiting factor for survival in tumor-bearing mice suffering from anorexia and cachexia. Three-month-old nongrowing mice (C57BL/6J) were given s.c. transplants of a methylcholanthrene-induced sarcoma. Freely fed, starved, and pair-fed animals were used. Body and lipid composition, tumor growth, and survival time were measured. Freely fed sarcoma-bearing mice died with profoundly altered body composition. This was not explained by the anorexia assessed in pair-feeding experiments. Starvation had caused a more severe depletion in body composition in both tumor-bearing and nontumor-bearing animals than the tumor alone did in freely fed tumor-bearing mice. Freely fed tumor-bearing animals had normal proportions of whole-body triglycerides, cholesterol, and polar lipids, but they lost palmitic acid quantitatively more than any other fatty acid. It is unlikely that any single fatty acid became limiting during tumor growth. The results show that the overall availability of lipids, nitrogen, and glucose precursors is not a limiting factor for survival in experimental tumor cachexia. Other factors considered to be more likely as determining factors for the death of tumor-bearing animals are discussed.

Hypoalbuminemia, a frequent finding in cancer patients, can be demonstrated in the tumor-bearing rat. In actuality, the circulating amount of albumin is maintained in tumor-bearing rats, although total body water and plasma volume are increased. The fractional degradation rate of newly synthesized albumin labelled by the injection of carbon-14-carbonate was significantly increased in tumor-bearing rats (half-life 55 hours) as compared with control rats (half-life 85 hours). These findings indicate maintained synthesis of albumin in the tumor-bearing rats, a finding consistent with an increased ratio of specific activity in albumin to that in plasma urea after the injection of carbon-14-carbonate. Hypoalbuminemia in cancer seems to be the net result of an increased turnover rate of albumin and dilution of the maintained albumin mass. Despite the presence of cancer anorexia, the flux of substrates from the degradation of peripheral tissues is sufficient to supply the liver and, in turn, to enable an increased protein synthesis with maintenance of the synthetic rate of albumin.

Anorexia can occur when a specific diet is associated with a developing illness. The studies reported here show that the decline in food intake which accompanies tumor growth is accompanied by the development of aversions to the specific diet consumed during tumor growth. An immediate elevation in food consumption occurred when a novel diet was introduced. Therefore, the development of learned aversions to the specific diet eaten during tumor growth may be a causal factor in the development of tumor anorexia.

Injection of norepinephrine into the hypothalamus of methylcholanthrene sarcoma-bearing rats elicited a normal feeding response both prior to and following the development of anorexia. Feeding elicited by cholinergic stimulation of the hypothalamus of tumor-bearing rats with carbachol was normal prior to the onset of anorexia, but decreased in magnitude as the anorexia became more severe. These data indicate that noradrenergic feeding mechanisms in the hypothalamus of tumor-bearing rats are functioning normally during anorexia. However, cholinergic feeding mechanisms in the hypothalamus of tumor-bearing rats appear to be depressed to the same degree as ad lib intake, possibly through adaptation or depletion of endorphin systems that mediate stress-induced feeding.

The association of elevated brain serotonergic activity with cancer anorexia was investigated in three experiments. Significant increases in whole brain tryptophan, serotonin and 5-hydroxyindoleacetic acid in anorectic rats bearing methylcholanthrene sarcomas demonstrated the general nature of this phenomenon. In the Walker 256 sarcoma model, significant increases in whole brain serotonin and 5-hydroxyindoleacetic acid immediately preceded the onset of anorexia, suggesting that these changes in serotonin activity were not caused by decreased food intake. Investigations of regional brain changes in serotonin activity of rats bearing Walker 256 tumors revealed widespread increases in tryptophan, while serotonin was increased in the diencephalon and cerebellum and 5-hydroxyindoleacetic acid was increased in the cortex, hippocampus, diencephalon, pons-medulla and cerebellum. Therefore, these experiments demonstrate that increased brain serotonin activity is a general phenomenon, being observed in two lines of anorexia-producing tumors, that it precedes the onset of anorexia and that selective increases in serotonin activity occur within different regions of the brain.

Plasma ammonia concentrations were significantly elevated by 150% in anorectic rats bearing methylcholanthrene sarcomas. Assessment of ammonia levels in blood draining these sarcomas indicated nearly a 20-fold increase as compared with venous blood in control rats, suggesting the tumor mass as the source of this increase in ammonia. Infusing increasing concentrations of ammonium salts produced anorexia and alterations in brain amino acids in normal rats that were similar to those observed in anorectic tumor-bearing rats. Therefore, these results suggest that ammonia released by tumor tissue may be an important factor in the etiology of cancer anorexia.