Central effect of histamine and peripheral effect of histidine on food intake in rabbits

Histidine is an amino acid precursor of neuronal histamine. It is evident that peripheral injection of histidine produces effects that resemble to centrally administered histamine. The aim of the present study was to compare the effects of intracerebroventricular (ICV) injection of histamine and inraperitoneal (IP) injection of histidine on food intake in rabbits. ICV injections of histamine (12.5, 25, 50,100 and 200 ?g/rabbit) were performed through a permanent cannula, which was implanted into the right lateral ventricle of brain. IP injection of histidine (31.25, 62.5, 125, 250, and 500 mg/kg) were injected using a 23-gauge injection needle. Cumulative food intake was measured at 1, 2, 3, 6 and 24 h after injections. The results showed that histamine (ICV, 12.5 and 25 ?g) and histidine (IP, 31.25 and 62.5 mg/kg) had no effect on food intake. A short-time (2 h) reduction of food intake was observed when the doses of 50 ?g of histamine and 125 mg/kg of histidine were applied. The highest reduction (total 24h) of food intake occurred at the 200 ?g of histamine and 500 mg/kg of histidine. Based on the results of the present study it is concluded that activation of brain histamine in rabbits induces anorexia. Histidine, a precursor of histamine, mimics effects of the centrally administered histamine. This may be due to conversion of histidine into histamine in the brain.