Chan_1988_Pharmacology_37 Suppl 1_17

Stimulation of acid secretion by muscarinic agents involves receptors with a higher apparent affinity to the M1-antagonists, pirenzepine and telenzepine, than those regulating heart rate and salivary secretion. However, the localization of the proposed M1-receptors regulating acid secretion remains unclear. Studies with parietal cells isolated from several species indicate that parietal cells have a muscarinic receptor with low affinity for the M1-antagonists. Our studies with somatostatin cells isolated from canine fundic mucosa indicates that the muscarinic receptor inhibiting somatostatin release also is of low affinity for M1-antagonists. We have found no evidence for regulation of histamine release from canine fundic mast cells, whereas there is evidence that acetylcholine induces histamine release from the enterochromaffin-like cells of the rat and rabbit fundic mucosa. Further studies will be necessary to determine which of the muscarinic receptors potentially involved in the regulation of acid secretion is responsible for the M1-behavior of this pathway.