Muscarinic control of histamine release from airways. Inhibitory M1-receptors in human bronchi but absence in rat trachea.

Isolated human bronchi and rat tracheae were incubated in organ baths to measure histamine release. The calcium ionophore A23187, 3 micromol/L in rat trachea and 10 micromol/L in human bronchi, stimulated histamine release by 145 +/- 50% (n = 6) and 270 +/- 48% (n = 7) above the prestimulation level, respectively. Acetylcholine (100 pmol/L; human bronchi) or oxotremorine (1, 100, 10,000 nmol/L; rat trachea) did not affect the spontaneous histamine release. In rat tracheae neither acetylcholine nor oxotremorine inhibited A23187-evoked histamine release, whereas 100 pmol/L acetylcholine significantly suppressed the evoked histamine release in human bronchi by 86%. For receptor characterization the following subtype-specific muscarinic receptor antagonists were applied: pirenzepine (M1 subtype), para-fluorohexahydrosiladifendiol (pFHHSiD; similar affinities at human cloned M1-, M3-, and M4-receptors), AF-DX 116 (M2 subtype), and clozapine (antagonist at cloned M1-, M2-, M3-receptors; agonist at cloned M4-receptors). Pirenzepine, pFHHSiD, AF-DX 116, and clozapine (100 nmol/L each) antagonized the inhibitory effect of 100 pmol/L acetylcholine by 83 +/- 20% (n = 6), 83 +/- 9% (n = 8), 50 +/- 14% (n = 6), and 35 +/- 7% (6). In conclusion, a species difference exists in the cholinergic control of histamine release between human and rat airways. In human airways muscarinic receptors most likely of the M1 subtype are involved in the inhibitory control of mast cell function, whereas such an inhibitory pathway does not exist in the rat trachea.