Nicotine is a competitive antagonist for H1-receptors in smooth muscles.

The effects of nicotine on histamine-induced contractions in the aortic strip from rabbit and in the intestinal and airway smooth muscles from guinea-pig were examined. Nicotine inhibited the contractile effects of histamine in a concentration-dependent manner in all investigated smooth muscle preparations having identical pA2 values. Data obtained in this study indicate that nicotine has a histamine H1-receptor antagonistic property with a lower activity than mepyramine for H1-receptors as verified by the calculated pA2 values.