Dysfunctional inhibitory muscarinic receptors mediate enhanced histamine release in isolated human bronchi

In human airways mucosal mast cells are under the control of inhibitory muscarinic receptors. The described experiments tested, whether the inhibitory potency of two muscarinic receptor agonists (oxotremorine, acetylcholine) becomes impaired in advanced chronic obstructive pulmonary disease (COPD). Isolated human bronchi obtained from 26 patients with lung cancer were separated into two groups. Group 1 patients suffered from moderate COPD (mean FEV1 56%; range 34–71%; mean pack years of cigarette smoking 50, range 20–96; one non-smoker). Group 2 patients had no or only a mild form of COPD; mean FEV1 was 82% (62–97%) and the number of pack years 22 (6–45; 3 non-smoker). The calcium ionophore A23187 induced a maximal histamine release of 4100 ± 870 pmol/g/5 min in group 1 bronchi, in contrast to only 1730 ± 240 pmol/g/5 min in group 2 bronchi (p < 0.02). Oxotremorine (1 nmol/L) reduced the stimulated histamine release by 81 ± 5% in group 2 bronchi, but did not produce a significant effect in group 1 bronchi (11 ± 14%). In conclusion, the present experiments show an enhanced histamine release in advanced COPD, which can be explained by a dysfunction of inhibitory muscarinic receptors.