Effects of alkyl analogs of histamine and metiamide on gastric acid secretion.

Histamine and metiamide analogs with alkyl, methyl, ethyl or isopropyl groups on the imidazole ring in position 5, not previously tested on an in vivo preparation, were studied for their effects on gastric acid secretion in cats with gastric fistulas. Our findings confirmed that the methyl group appears to be optimal for an effect on gastric acid secretion as regards both agonism and antagonism. Ethyl substitution apparently did not change the pharmacological activity of histamine but modified the inhibitory effect of metiamide from competitive to non-competitive kinetics. Isopropyl analogs were inactive on gastric secretion under our experimental conditions.