Continuous intravenous infusion of ghrelin does not stimulate feeding in tumor-bearing rats.

The development of anorexia continues to be a serious treatment issue for cancer patients. Because the orexigenic peptide, ghrelin, is active through systemic routes and activates hypothalamic neuropeptide systems known to be refractory in anorectic tumor-bearing (TB) rats, we investigated whether it would prevent the development of cancer anorexia when infused continuously intravenously. The 24-h food intake was increased in nontumor-bearing (NTB) rats at a dose of 288 microg/day ghrelin. However, no tested dose of ghrelin, up to 576 microg/day, elicited increased feeding in TB rats prior to or subsequent to the development of anorexia. In hypothalamus, ghrelin-infused TB rats exhibited significantly increased concentration of neuropeptide Y (NPY) as compared to saline-infused TB rats. Hypothalamic expression of NPY and agouti-related protein (AgRP) messenger RNA were elevated in ghrelin-infused TB rats as compared to NTB rats, but saline-infused TB rats also exhibited increased expression of AgRP. Proopiomelanocortin message was reduced in ghrelin-infused and saline-infused TB rats as compared to noninfused TB control rats. Although ghrelin infusion did not preserve muscle protein, a significant saving in body fat was observed in TB rats. Thus, the adiposity effects of ghrelin did not require an orexigenic response to the peptide. These results suggest that continuous ghrelin infusion may not be an effective treatment for cancer anorexia.

Alteration of NPY and Y1 receptor in dorsomedial and ventromedial areas of hypothalamus in anorectic tumor-bearing rats.

Although previous studies have implicated NPY in the etiology of experimental cancer anorexia, the results have been difficult to interpret. Studies have suggested that although NPY level and message were decreased in the dorsomedial hypothalamic area (DMA), they were elevated in the ventromedial hypothalamic area (VMA). To better assess specific intra-area alterations of NPY, Y(1) receptor (Y(1) R), and agouti-related peptide (AgRP) in TB rats, we used radioimmunoassay, quantitative real-time RT-PCR, and immunohistochemistry. We found that NPY and AgRP mRNA were elevated significantly in whole hypothalamus of anorectic TB rats, while Y(1) R mRNA was decreased. Based on two replicates of four pooled samples each, both NPY and AgRP mRNA appeared to be elevated in the VMA of anorectic TB rats, while only AgRP exhibited a similar increase in the DMA. Levels of NPY were elevated in the VMA of both TB and pair-fed (PF) rats, but in the DMA only PF rats exhibited a significant NPY increase. NPY and Y(1) R immunohistochemistry revealed reduced NPY staining in PVN and ARC nucleus of TB and PF rats. Y(1) R immunostaining was also reduced in the ARC and PVN of TB rats, while PF rats exhibited elevated immunostaining in the PVN. These results continue to implicate dysfunction of NPY feeding systems in experimental cancer anorexia and suggest down-regulation of Y(1) R receptors as well as possible problems in NPY translation.

Mediation of burn-induced hypermetabolism by CRF receptor-2 activity.

Hypermetabolism and anorexia are significant problems associated with major burn trauma. Recent studies have implicated hypothalamic peptides and receptors of the corticotropin releasing factor (CRF) family as putative mediators of burn-induced hypermetabolism. Increased neuronal activity at the CRF type 2 receptor (CRF R-2) appeared particularly involved in the expression of elevated resting energy expenditure (REE) following major burn trauma. In the present study we continued these investigations of CRF R-2 mediation of burn-induced hypermetabolism, demonstrating that 3rd ventricle injection of CRF R-2 antisense oligodeoxynucleotide (ODN) normalized REE in burned rats. Similar treatments with CRF or CRF R-1 antisense ODNs had no significant effect in burned rats. In addition, 3rd ventricle injection of the selective CRF R-2 antagonist, antisauvagine-30, also reduced REE significantly in burned rats, while similar treatment with the selective CRF R-1 antagonist, antalarmin, was without effect. To determine which endogenous peptide was altered following burn we measured hypothalamic levels of urocortin (UCN) and CRF 15 days after burn injury, finding UCN was significantly elevated by nearly 3-fold, while CRF level tended to be decreased. We also assessed hypothalamic mRNA peptide and receptor expression by real-time PCR 7, 14, and 21 days post-burn, observing decreased CRF expression 7 and 21 days post-burn, decreased UCN-2 expression 7 days post-burn, and no significant alteration in UCN-1 at any time point. However, CRF R-2 mRNA was elevated at each post-burn time point. These results continue to suggest that increased neuronal activity is integrally involved in the mediation of burn-induced hypermetabolism, and that one of the UCN peptides may be the endogenous ligand affecting this receptor.

Possible role of CRF peptides in burn-induced hypermetabolism.

Hypermetabolism and anorexia are significant problems associated with major burn trauma. Recent studies have shown that hypothalamic corticotropin releasing factor (CRF) elevates metabolic rate, while neuropeptide Y (NPY) reduces it. CRF also elicits anorexia, while NPY stimulates feeding. We hypothesized that elevation of CRF and decrease of NPY may be mediators of these negative effects of burn trauma. Therefore, we assessed concentrations of CRF and NPY in hypothalamus of burned rats one, three, and twenty-one days after a 30% body surface area, full-thickness, open flame burn. In addition we determined whether a biochemical lesion of CRF receptors using 3rd ventricle injections of a saporin-CRF conjugated peptide would decrease resting energy expenditure (REE). We found a three-day period of anorexia, with REE significantly increasing three days after the burn trauma. Concentrations of NPY were increased in the PVN-containing dorsomedial region of the hypothalamus 1 and 3 days after burn trauma, but were increased further in the day 1 pair-fed rats suggesting this change was a consequence of the anorexia. Levels of CRF were decreased in the ventromedial region of the hypothalamus in day 1 and day 3 burned and PF rats. Treatment with the saporin-CRF conjugate normalized REE and reduced CRF receptor-2 density in the hypothalamus of burned rats, and blocked CRF-induced hypermetabolism in sham-burned rats. Although these results suggest a role of CRF receptors in mediating burn-induced hypermetabolism, CRF itself may not be the principle ligand, as suggested by the significant elevation of hypothalamic urocortin 15 days after burn injury.

The role of polyamines in glucagon-like peptide-2 prevention of TPN-induced gut hypoplasia.

Total parenteral nutrition (TPN) of rats has been demonstrated to produce hypoplasia of gut mucosa, and to be associated with reduced immune response and elevated translocation of bacteria from gut to mesenteric lymph nodes, spleen and liver. Treatment of rats being maintained on TPN with the proglucagon fragment, glucagon-like peptide-2 (GLP-2), has been shown to totally prevent small intestine mucosal hypoplasia. In the present study, we found that depletion of polyamines with alpha-difluromethylornithine (DFMO) significantly reduced the efficacy of GLP-2 in preserving gut mucosa in rats maintained on TPN for 8 days. Co-infusion of GLP-2 with TPN prevented loss of protein and mucosa in duodenum, jejunum and ileum, but not in colon. Addition of DFMO to the infusate prevented the protective effects of GLP-2 in the duodenum and jejunum. In the jejunum, putrescine and spermidine were reduced in DFMO-treated rats, while the ileum exhibited reductions of these polyamines in rats infused with TPN or TPN plus GLP-2. DFMO infusion further reduced these polyamines in the ileum, while levels of spermine were increased. Concentrations of ornithine decarboxylase were elevated in jejunum of rats infused with TPN or TPN plus GLP-2, but were reduced significantly in DFMO-treated rats. These results suggest that normal levels of polyamines are necessary for the expression of GLP-2-induced hyperplasia. Differential effects of GLP-2 and DFMO across gut segments may relate to regional differences in proliferative and anti-apoptotic effects of the treatments.

Elevated blood lactate is not a primary cause of anorexia in tumor-bearing rats.

Tumor-bearing (TB) rats exhibit elevated concentrations of lactate in blood contiguous with the development of anorexia. Continuous intravenous infusion of lactate into non-TB rats reduced food intake at plasma concentrations lower than those observed in anorectic TB rats. Levels of neuropeptide Y (NPY) were elevated in the ventromedial (VMH) and dorsomedial hypothalamic regions of lactate-infused rats. The addition of the enhancer of pyruvate dehydrogenase activity, dichloroacetate (DCA), to the drinking water of TB rats (0.1-0.4%) normalized blood lactate concentration but had no significant effect on anorexia. However, the elevated concentration of NPY in the VMH of anorectic TB rats was also normalized by the DCA treatment. No alterations in regional hypothalamic levels of corticotropin-releasing factor were observed within any treatment conditions. These results suggest that, although hyperlactatemia may be involved in maintaining elevated NPY concentrations in anorectic TB rats, it does not appear to be a significant factor in the etiology of experimental cancer anorexia.