Effects of meconium on airway reactivity to histamine and acetylcholine in vitro.

To better understand the mechanisms contributing to altered airway reactivity in the meconium aspiration syndrome, in this study we investigated whether there could be a meconium dose-dependent response of tracheal smooth muscle and lung tissue reactivity to histamine and acetylcholine in vitro. Tracheal and lung tissue strips from healthy guinea pigs were incubated for 1 hour in organ chambers with three different concentrations of meconium (1, 2, and 5 mg/ml) or in Krebs-Henseleit solution. Thereafter, the contractile responses to histamine and acetylcholine were recorded. Cumulative doses of histamine and acetylcholine increased reactivity of the strips in all groups. Tracheal smooth muscle reactivity to histamine and acetylcholine (10(-5)-10(-3) mol/l) was highest with the highest meconium concentration. In contrast, lung tissue reactivity tended to decrease with increasing meconium concentration. The mechanisms influencing the airway smooth muscle contractile response to meconium require further studies.