INTERACTION BETWEEN HISTAMINE AND NITRIC-OXIDE IN RAT MAST-CELLS AND IN ISOLATED GUINEA-PIG HEARTS

Background: Histamine and nitric oxide (NO) are present in guinea pig hearts and in rat mast cells (MCs) of the serosal phenotype. Histamine and NO are simultaneously released upon immunological challenge of is olated hearts of actively sensitised guinea pigs. MCs release histamin e in response to antigen and NO in response to stirring. This has prom pted us to study the interaction between histamine and NO in rat MCs a nd in guinea pig hearts. Methods: The experiments have been carried ou t in isolated purified rat serosal MCs and in isolated perfused guinea pig hearts. The generation of NO by both preparations has been evalua ted as nitrites (NO2-) by means of the Griess reaction. Results: Hista mine upregulates the generation of NO both in rat MCs and in guinea pi g hearts. The effect is abolished by blocking NO synthase and preferen tially mimicked by a selective H-2-receptor agonist. A selective H-3-r eceptor agonist downregulates the generation of NO in lipopolysacchari de-pretreated MCs and in bradykinin-pretreated guinea pig hearts. Conc lusion: A mutual relationship between histamine and NO in allergic inf lammation could be envisaged.