Distribution and Characteristics of Histamine H1-receptors in Guinea-pig Airways Identified by [3H]mepyramine

The distribution and characteristics of histamine H1-receptors in various regions of guinea-pig airways have been studied using the antagonist [3H]mepyramine. A similar density of specific [3H]mepyramine sites was found in trachea, bronchi and parenchyma and these sites possessed pharmacological properties expected of a histamine H1-receptor. In addition, there was a large component of [3H]mepyramine binding that did not show stereoselectivity towards the isomers of chlorpheniramine and as such cannot be considered to represent binding to an H1-receptor. This non-specific component accounted for approximately 80% of total [3H]mepyramine binding when assays were performed in Tris-HCl buffer but was considerably reduced by the presence of sodium ions in the incubation buffer. The present results do not confirm previous reports on the heterogeneity of histamine H1-receptors in guinea-pig lung and suggest that this may, in part, be due to difficulties in accurately assessing true receptor specific binding.