Difference in effects of pirenzepine and atropine on carbachol-induced pepsinogen secretion from isolated gastric glands

Abstract

The effect of pirenzepine on carbamylcholine (carbachol)-stimulated pepsinogen secretion was compared with that of atropine in the isolated guinea pig gastric glands. Pirenzepine and atropine caused a dose dependent inhibition of carbachol-stimulated pepsinogen secretion. Moreover, pirenzepine as well as atropine produced a rightward shift in the dose response curve of carbachol-stimulated pepsinogen secretion but did not alter the maximum increase in pepsinogen secretion. Results therefore demonstrate that pirenzepine acts as a specific receptor antagonist in the interaction of carbachol with its receptor on gastric chief cells. However, pirenzepine was 50 times less potent than atropine in inhibiting pepsinogen secretion. Half maximal inhibitory concentration of pirenzepine was 2×10 −5M when a maximally effective concentration of carbachol was used, while that of atropine was 4×10 −7M. Results, therefore, suggest that muscarinic receptor on gastric chief cells to which pirenzepine binds may be an intermediate affinity type.