ABSTRACT
Isometric tension changes in 22 isolated segmental human pulmonary arteries obtained from 17 patients at thoracic surgery were studied after histamine challenge. Cumulative dose-response contraction curves were constructed. A slight potentiation could be found with the H2 antagonist cimetidine, whereas the H1 blocker mepyramine moved the log dose-response curve for histamine to the right indicating competitive antagonism at specific receptors. When mepyramine was added after maximal contraction with histamine, a relaxation occurred that could be blocked by adding cimetidine prior to mepyramine. The in vitro tests reveal a dual action of histamine with a dominating H1 receptor mediated contraction, but with the possibility of relaxation via specific H2 receptors in human pulmonary arteries.
