Anorexigenic effects of d-amphetamine and 1-dopa in the rat

The effect of amphetamine and 1-dopa was compared in 22-hr food- and water-deprived rats. Amphetamine produced marked anorexia, and 1-dopa significantly reduced food intake at 200 mg/kg. Following pretreatment with RO 4-4602, a decarboxylase inhibitor, 100 mg/kg of 1-dopa, a dose that did not significantly affect eating, produced marked anorexia. The anorectic effect of both amphetamine and 1-dopa was antagonized by propranolol, a β adrenergic antagonist. Phentolamine, an a-adrenergic antagonist, potentiated the anorectic effect of amphetamine and 1-dopa. Haloperidol (0.1 mg/kg), a dopamine antagonist, failed to prevent the anorexia due to amphetamine but accentuated that due to 1-dopa. Methysergide, a serotonin antagonist, also failed to prevent the anorexigenic effect of amphetamine. Finally, the administration of 1-dopa with or without peripheral decarboxylase inhibition resulted in more than twice the increase in hypothalamic dopamine levels without significant changes in 5-HT or norepinephrine levels. The data show that the anorexigenic effect of amphetamine and 1-dopa are similar and indicate a functional role for both norepinephrine and dopamine neurons in feeding behaviour in the rat.