A comparison of the effects of pirenzepine and atropine on gastric acid secretion, salivary secretion and pupil diameter in the rat.

The ability of pirenzepine and atropine, given i.v., to inhibit gastric acid and salivary secretion and increase pupil diameter has been assessed in the rat. Pirenzepine had a similar potency against acid secretion, ED 50 0.71 (0.41 to 1.1) mg.kg-1, and salivary secretion, ED 50 (0.43 to .59) mg.kg-1, whilst its potency was less in the eye, ED 50 1.8 (1.6 to 2.1) mg.kg-1. Atropine however, was more potent in reducing salivary secretion, ED 50 0.012 (0.010 to 0.016) mg.kg-1 and increasing pupil diameter, ED 50 0.028 (0.025 to 0.031) mg.kg-1 than in inhibiting gastric acid secretion, ED 50 0.056 (0.037 to 0.083) mg.kg-1. Therefore, that quantity of pirenzepine which inhibits gastric acid secretion by 50% will have only a slight effect on the eye and will inhibit salivary secretion by a similar magnitude. In contrast, the amount of atropine required to inhibit acid secretion by 50% will significantly increase pupil diameter and abolish salivary secretion.