title: Microscopic changes induced by the intratracheal inoculation of amniotic fluid and meconium in the lung of neonatal rats.
abstract: Meconium aspiration syndrome is a major contributor to neonatal respiratory distress in infants and it has been sporadically recognized in neonatal animals. This investigation was designed to study the short and long term effects of meconium and amniotic fluid in the lungs of neonatal rats. Seven-day-old rats (n = 123) divided in three groups were intratracheally inoculated with saline solution, amniotic fluid or meconium. Rats were euthanatized on 1, 3, 7, 14, 28, 56 and 112 postinoculation days (PID) and the lungs were examined by light microscopy. Saline solution did not induce any change while amniotic fluid elicited only a mild foreign body response which disappeared by PID 14. In contrast, meconium induced an exudative alveolitis characterized by recruitment of neutrophilsn in the bronchoalveolar spaces. Meconium also induced atelectasis, hyperinflation and thickening of alveolar septa all of which had disappeared by PID 14. Starting at PID 7, neutrophils were progressively replaced by macrophages, giant cells, and some fibroblasts. There were sporadic foci of mineralization starting at PID 14 and lasting up to PID 112. Some mineralized foci became lined with cuboidal epithelial cells at PID 28. Meconium was slowly degraded but still evident by PID 112. It was concluded that inoculation of meconium in neonatal rats induces acute microscopic changes typical of meconium aspiration syndrome. The long term lesions induced by meconium consisted of persistent multifocal histiocytic alveolitis and bronchiolitis reaction with occasional foci of calcification.
authors.affiliation: Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Canada. jmburnes@uat.edu.mx
authors.forename: J
authors.initials: J
authors.lastname: Martínez-Burnes
authors.forename: A
authors.initials: A
authors.lastname: López
authors.forename: G M
authors.initials: GM
authors.lastname: Wright
authors.forename: W P
authors.initials: WP
authors.lastname: Ireland
authors.forename: D W
authors.initials: DW
authors.lastname: Wadowska
authors.forename: G V
authors.initials: GV
authors.lastname: Dobbin
mesh_terms: D000653:Amniotic Fluid / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D004396:Coloring Agents; D005260:Female; D007442:Intubation, Intratracheal; D008168:Lung / Q000473:pathology*; D008297:Male; D008470:Meconium / Q000502:physiology*; D011014:Pneumonia / Q000473:pathology; D011247:Pregnancy; D011650:Pulmonary Alveoli / Q000473:pathology; D051381:Rats; D011916:Rats, Inbred F344; D016707:Tissue Fixation
chemical_list: D004396:Coloring Agents