EVIDENCE FOR HISTAMINE INVOLVEMENT IN THE EFFECT OF HISTIDINE LOADS ON FOOD AND WATER-INTAKE IN RATS

We examined the hypothesis that histidine is a regulator of short-term food and water intake in rats and that this control is through histid ine's action as a precursor for histamine. The primary objectives were to measure food and water intake after histidine monohydrochloride mo nohydrate (His-HCI) given by intragastric (IG) and intraperitoneal (IP ) routes of administration and to measure feeding and drinking respons es to histidine when given after blockade of the histaminergic pathway by chlorpheniramine (CPA) and alpha-fluoromethylhistidine (FMH). Eigh t experiments were conducted using a back-to-back design. Rats were gi ven treatment by IP or IG administration, and food and water intake wa s measured during time periods of 0-1, 1-2, 2-3 and 3-14 h. Histidine consistently reduced food intake with the sensitivity to IP much great er than to the IG route. The effect of histidine given by IP or IG on water intake was similar, generally causing an increase at least in th e first hour. Histidine's action was not accounted for by its energy, pH or nitrogen content. Because FMH, which blocks the enzyme convertin g histidine to histamine, partially reversed the effect of histidine o n food and water intake, these results support the hypothesis that his tidine regulates food and water intake, at least in part, through its precursor control of histamine.