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

Open Access
Publisher Website
Google Scholar
Abstract
The possible temperature‐dependent interconversion of histamine H1‐ 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. Chlorpheniramine, an H1‐blocker, caused a rightward shift of the cumulative histamine dose‐response 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. 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. 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. Our results allow us to conclude that no temperature‐dependent interconversion of histamine H1‐ and H2‐receptors occurs in the guinea‐pig ileum.