Effect of Pirenzepine Compared with Atropine and L-Hyoscyamine on Esophageal Peristaltic Activity in Humans

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Abstract
The effects of atropine, L-hyoscyamine, and pirenzepine on distal esophageal peristalsis induced by standardized liquid swallows were compared in 10 healthy volunteers. In the first series each subject underwent two experiments on separate days. After control swallows the effect of 0.5 mg atropine and 10 mg pirenzepine intravenously, respectively, was studied. In the second series, the same volunteers were premedicated with either 50 mg pirenzepine or 0.6 mg L-hyoscyamine perorally twice daily for 4 days, which are equipotent doses with regard to inhibition of gastric acid secretion. This series was double blind and randomized, and the experiments were carried out 2 h after the last drug administration. The serum levels of atropine, L-hyoscyamine, and pirenzepine during the experiments were measured by radio-immunoassay. After administration of atropine or pirenzepine the esophageal peristaltic amplitude decreased significantly. However, there was a highly significant difference (atropine inhibition versus pirenzepine inhibition) between the two drugs beginning 20 min after drug injection and continuing for the rest of the recording period of 90 min. In the peroral series, there was a 51% decrease of the peristaltic amplitude (p < 0.01) after L-hyoscyamine, whereas the peristaltic pressure was reduced by 15% (n.s.) after pirenzepine. Primary peristalsis induced by swallowing was absent in the distal esophagus in 10% (p < 0.05) after L-hyoscyamine orally; this effect was not seen in the controls or after pirenzepine perorally. These results show that therapeutic doses of conventional antimuscarinic drugs markedly decrease esophageal peristaltic pressure, in contrast to pirenzepine. This is in agreement with the concept of different subclasses of muscarinic receptors, in which pirenzepine has a lower affinity for muscarinic receptors of esophageal smooth muscles than atropine or L-hyoscyamine.