Insulin reverses ammonia-induced anorexia and experimental cancer anorexia

Previous experiments suggest that experimental cancer-induced anorexia is associated with hyperammonemia and that daily injections of insulin may attenuate the anorexia for several days. In the present study, we determined whether similar daily insulin treatments would correct anorexia induced by the infusion of ammonium salts and compared this feeding response with that of insulin-treated tumor-bearing (TB) rats. Daily treatment of control and anorectic TB rats with systemically administered insulin for six days increased feeding in all control rats and 40% of the TB rats. All insulin-treated groups exhibited equal degrees of hypoglycemia irrespective of anorexia. Basal concentrations of lactate and glucagon were elevated in saline-treated TB rats. Plasma lactate levels were normalized by insulin treatment, whereas glucagon was normalized only in the TB rats that fed to insulin and increased further in TB rats that did not feed to insulin. Elevated hypothalamic tyrosine was reduced in insulin-treated TB rats that ate, and 5-hydroxy-indoleacetic acid was increased further when the rats did not eat. Insulin also blocked anorexia resulting from the intravenous infusion of ammonium salts. Hypothalamic concentrations of tyrosine and tryptophan were increased by the ammonia infusion and reduced significantly in insulin-treated infused rats. These results indicate that insulin treatment can reverse experimental cancer-induced anorexia and hyperammonemia-induced anorexia. Neurochemical changes associated with these treatments are also similar, but not identical.