ABSTRACT
Acute lung injury induced by meconium aspiration is characterized by rapidly developing
pulmonary inflammation with influx of activated polymorphonuclear cells. To evaluate
the role of meconium in the activation of these invading cells, we described the oxidative
capacity of circulating neutrophils after intratracheal administration of thick human
meconium in pigs. We also examined the direct effects of varying meconium concentrations
on the oxidative burst of human neutrophils in vitro. In neutrophils isolated from
meconium-insufflated pigs, phorbol myristate acetate stimulation led to an average
11.7-fold increase in production of reactive oxygen species, measured by chemiluminescence,
whereas the increase in control cells from saline-instilled pigs was only 3.1-fold,
p = .012 between the groups. Activation of unstimulated human leukocytes by meconium
resulted in a dose-dependent response. The lowest meconium concentration (0.2 mg/mL)
had an inhibitory effect on neutrophil activation, whereas higher concentrations of
meconium (1 and 2 mg/mL) increased neutrophil oxygen radical production progressively.
These results thus indicate that moderate and high concentrations of aspirated meconium
rapidly activate circulating neutrophils with a resulting oxidative burst contributing
to pulmonary tissue injury, whereas low contamination of the aspirated material may
in fact suppress the development of oxidative lung injury.
KEYWORDS
Lung - meconium - neutrophil - oxidative burst
