Airway hyperresponsiveness to histamine in mycoplasmal infection: role of histamine N-methyltransferase

To elucidate the modulatory role of histamine-degrading Enzymes in airway constrictor responses in mycoplasmal Infection, we studied hamster tracheal segments under isometric conditions in vitro. Nasal inoculation with Mycoplasma pneumoniae potentiated the contractile responses to histamine but not to methacholine. Pretreatment of tissues with the histamine N-methyltransferase inhibitor SKF 91488 abolished the infection-induced potentiation, whereas, the diamine oxidase inhibitor aminoguanidine had no effect. The histamine N-methyltransferase but not diamine oxidase activity in tracheal tissues was decreased in infected Animals. These results suggest that M. pneumoniae causes airway hyperresponsiveness to histamine probably through a reduction of endogenous histamine N-methyltransferase activity.