Inhibition of brain histamine synthesis increases food intake and attenuates vasopressin response to salt loading in rats.

Alpha-fluoromethylhistidine (FMH), a histamine synthesis inhibitor, was infused into the lateral cerebral ventricle of male Long-Evans rats for 7 days at a dose of 60 mcg/day. During this period animals were housed in metabolic cages; water and food consumption were measured and urine samples were collected. FMH-treated rats ate significantly more than controls and had a significantly greater weight increase. Concomitantly, sodium and potassium excretion increased. On the seventh day, rats were injected i.p. with 6.67 ml/kg of either 5.8% NaCl or physiological saline. Animals were decapitated 1 h after injection and plasma vasopressin, corticosterone and posterior pituitary vasopressin levels were determined by radioimmunoassay. NaCl loading significantly increased plasma vasopressin in control rats but not in rats pretreated with FMH. FMH alone had no effect. There were no significant changes in pituitary vasopressin or plasma corticosterone. These results clearly suggest an inhibitory role for the histaminergic system in the regulation of food intake. They also agree with, although not proving, the stimulatory control of vasopressin release by the histaminergic system in rat brain.