Histamine receptors in the lower esophageal sphincter (LES)

The motor response of histamine on the lower esophageal sphincter and the receptors involved were investigated on isolated preparations from rats, guinea pigs and humans. Histamine exerted a spasmogenic effect through excitation of H1-receptors. H1-receptor selective agonists in the rat but not in the guinea pig seem to act through release of prostaglandin-like substances. Apparently H2-receptors, whose stimulation causes relaxation of the sphincter, do not occur in the LES of rat and human whereas they are present in the guinea pig. H2-receptor antagonists exerted different and sometimes opposite effects and this suggests that their actions depend on the specific molecules and not on the H2-receptor blockade. The significance and the importance of the above findings are discussed.