Evidence against the temperature‐dependent interconversion of histamine H₁‐ and H₂‐receptors in the guinea‐pig ileum

Abstract

1The possible temperature-dependent interconversion of histamine Hl-and H2-receptors in the guinea-pig ileum suggested from previous studies was re-investigated by use of new and selective H2-receptor agonists and antagonists. 2 Chlorpheniramine, an H1-blocker, caused a rightward shift of the cumulative histamine doseresponse curve at both 37°C and 12°C. Conversely cimetidine and tiotidine, two H2-receptor blockers, were ineffective at both temperatures. Metiamide behaved as a non competitive antagonist at 12°C but only in very high concentrations. 3 Dimaprit and impromidine, two selective H2-receptor agonists, were inactive at both 37°C and 12°C when given alone, whereas at both temperatures they elicited the already described relaxation of the contractions induced by histamine. 4 Similar results were obtained on the guinea-pig whole ileum and on the longitudinal muscle strip: this indicates a lack of interference of the circular smooth muscle. 5 Our results allow us to conclude that no temperature-dependent interconversion of histamine H1-and H2-receptors occurs in the guinea-pig ileum.