Cytologic and biochemical changes associated with inoculation of amniotic fluid and meconium into lungs of neonatal rats

Objective-To evaluate the effect of homologous amniotic fluid and meconium inoculated intratracheally into the lungs of neonatal rats. Animals-153 male 7-day-old Fischer-344 rats. Procedure-Amniotic fluid was obtained by cesarean section from the uterus o f pregnant rats and meconium was collected at the time of birth from the ga strointestinal tract of neonatal rats. Neonatal rats were randomly allocate d into 5 treatment groups. Two groups received 0.05 ml of saline (0.9% NaCl ) solution; the third and fourth groups received 0.05 ml of 50% or 100% amn iotic fluid, respectively; the fifth group was inoculated with 0.05 ml of a 20% suspension of meconium. Six or 7 rat pups/group were euthanatized by e xsanguination under halothane anesthesia at postinoculation days 1, 3, 7, a nd 14. The magnitude of injury and inflammatory response was determined by biochemical and cytologic analyses of bronchoalveolar lavage fluid. Results-Inoculation with saline solution and amniotic fluid did not induce pulmonary injury or inflammatory response. Inoculation with meconium induce d significant (P < 0.01) injury and inflammatory response, characterized by the release of cytosolic enzymes and recruitment of neutrophils in the lun g. Conclusions-Saline solution is an innocuous vehicle that can be safely used in intratracheal inoculations in neonatal rats. Homologous amniotic fluid, despite containing keratin and epidermal cells, does not cause acute injur y or inflammation in the lung. In contrast, meconium acts as a toxic substa nce injuring respiratory cells and causing a vigorous but transient leukocy tic inflammatory reaction in the lungs.