Histamine H1 and H2 effects on gastric acid and pepsin, heart rate and blood pressure in humans.

Gastric acid and pepsin secretion, heart rate and blood pressure were studied simultaneously during an infusion of histamine in eight patients with peptic ulcer or esophagitis. We found that histamine equally stimulated both acid and pepsin via H2 receptors. No evidence for any gastric H1 effect was found. Heart rate was increased modestly (12 beats/min) and this effect was reversed by diphenhydramine, an H1 antagonist, which did not by itself or in combination with the H2 antagonist cimetidine modify the hypotensive effect of histamine. The histamine effects in humans contrasts with those in the conscious dog where histamine inhibits pepsin secretion and strongly stimulates heart rate. The results emphasize major species and organ differences in both gastric and cardiac histamine effects.