Effect of dimaprit on gastric acid secretion in conscious cats

Gastric acid secretion was studied in conscious cats with gastric fistulas. Dimaprit and Nalpha,5-dimethylhistamine produced higher maximal responses than histamine. In the presence of pyrilamine, the maximal response to histamine was equal to that of dimaprit. Pyrilamine increased submaximal but not maximal responses to pentagastrin. Cimetidine decreased the potency of dimaprit but did not alter the maximal response. Gastric acid secretion continued for 90 min after infusion of dimaprit was stopped. Possible mechanisms for the enhancement of acid secretion by pyrilamine include: (a) blocking of an inhibitory histamine H1-receptor and (b) inhibition of histamine methyltransferase.