Does the histaminergic system mediate bombesin/GRP-induced suppression of food intake?

Bombesin (BN) and its mammalian homologue, gastrin-releasing peptide (GRP), are potent satiety agents and have been implicated in the physiological regulation of food intake. The mechanism(s) of action of this effect remains unclear. There is a functional and anatomic overlap between histamine and BN in relationship to feeding, which led us to hypothesize that BN may mediate its satiety effects through activation of the histaminergic system. To assess this contention, we examined the effects of R-α- methylhistamine (α-MH) and Imetit, selective H₃-receptor agonists that inhibit the release and synthesis of histamine, on BN- or cholecystokinin (CCK)-induced satiety. In this report we present the first evidence for the role of histamine H₃ receptors in the mediation of BN-elicited satiety. During the first hour of the 4-h daily feeding session, BN reduced food intake by >50% relative to the control condition; this suppression was blocked by prior treatment with the H₃-receptor agonist, α-MH. This blockade of BN-induced satiety was dose related and selective to BN as α-MH failed to attenuate sulfated CCK-8-induced satiety. When α-MH was administered alone, it failed to significantly affect food intake. The specificity of this effect was further supported by the demonstration that another H₃ agonist, Imetit, was also able to block the feeding-suppressant effects of BN. Furthermore, thioperamide, an H₃-receptor antagonist, blocked these effects of Imetit. These data support our working hypothesis that BN elicits its satiety effect by facilitating histaminergic activity at yet to be determined relevant sites and that H₃-receptor agonists attenuate its effect on food intake by inhibiting the release of histamine.