Histaminergic pharmacology of primate lower esophageal sphincter

We have studied the lower esophageal sphincter (LES) response to exogenous histamine and to H1- and H2-blocking agents in the awake baboon. Increasing intravenous bolus doses of histamine produce an increase in LES pressure with a maximum response at a dose of 12 microgram/kg. H1-receptor blockade with chlorpheniramine over a wide dose range did not alter basal LES pressure but did abolish the response of the LES to exogenous histamine. H2-receptor blockade with cimetidine at doses markedly inhibiting gastric acid secretion (2 mg/kg.h) did not alter basal LES pressure or the response of the LES to exogenous histamine. In addition, cimetidine did not alter the response of the LES to pentagastrin and bethanechol. Although histamine and histamine receptors are important in gastric secretion, they appear to have no identifiable role in the maintenance of basal LES smooth muscle tone in the baboon. These results demonstrate the presence of a stimulatory H1 receptor on baboon LES smooth muscle, but provide no evidence for the presence of an H2-inhibitory receptor. As opposed to the parietal cell, the LES response to pentagastrin and bethanechol does not require a H2 receptor.