Characterization of the rabbit detrusor response to histamine through pharmacologic antagonism

The various effects of histamine on smooth muscles and other tissues are thought to be mediated by two pharmacologically distinct receptors, H1 and H2 types. These receptors are defined in terms of thier susceptibility to blockade by pyrilamine (type H1) or burimamide (type H2). In this study selective antagonism of the spasmodic effects of histamine on isolated strips of rabbit detrusor has shown that the response is mediated by H1 receptors, with no evidence of H2 activity. The p-A2 of the pyrilaminehistamine antagonism is 9.3. The histamine response is susceptible to muscarinic blockade (atropine and propantheline) but not to nicotinic blockade (hexamethonium). Adrenergic blocking agents propranolol (10 minus 4 M) and phenoxybenzamine (10 minus 8 M) do antagonize the contractile response, but this does not appear to be indicative of adrenergic mediation.