Abstract
The role of meconium in the respiratory system was studied in newborns, who died from various causes (250 up to 3000 g of weight). We monitored tracheal rings response to dopamine, serotonin and ethanol in different concentrations (dopamine: 0,05 mg/ml, 0,5 mg/ml, 5 mg/ml; serotonin (5-HT): 10-4, 10-3, 10-2, 10-1 mol/dm3; ethanol: 0,02 ml, 0,5 ml, 1,0 ml; 96%). Tracheal smooth musculature tonus (TSM) was examined in 48 tracheal preparations taken after the newborn exitus due to different reasons. Based on functional researche of isolated preparations of tracheas, it may be concluded that: aspiration of meconium has not changed the response of TSM to dopamine, serotonin and ethanol (p>0,1) in comparison with the control group, which have died due to different lung inflammatory processes (e.g. pneumonia, bronchopneumonia, atelectasis, cerebral hemorrhage). The results suggest that meconium does not potentiate the constricting action of dopamine, serotonin and ethanol in tracheobronchial system. Meconium causes mild relaxation of the TSM through a mechanism that is not intermediated by the products of cyclooxygenases (prostaglandins, prostacyclins) from the tracheal epithelium or proteins. Also, as it seems, the direct activity of many tested acids in the smooth musculature has no significant impact on increase of the airways tonus in MAS syndrome.
Highlights
Syndrome of the aspiration of the meconium liquid (MAS) is an important cause of respiratory mortality and morbidity in newborn
Mechanisms that do contribute in increase of the airways reactibility at MAS syndrome are quite unclear
Meconium contains high concentrations of fatty acids ( ) and biliar acids ( ), which can induce the contraction of airways smooth musculature
Summary
Syndrome of the aspiration of the meconium liquid (MAS) is an important cause of respiratory mortality and morbidity in newborn. Meconium composition includes different bile acids (e.g. choline, Chenodeoxycholic and lithocholic acid) and minerals such copper, zinc, manganese, calcium, iron, and phosphorus that are the frequent ( , ) It contains plasmatic proteins (alpha- antitrypsin) ( , ). Meconium contains many other different substances such interleukins IL- ß, IL- and IL , necrotizing tumoral factor (TNF-alpha) ( ) and phospholipases A (PLA ) ( ) that may induce either direct or indirect pulmonary inflammation by increasing the production of cytokines and by activating leukocytes or epithelial and endothelial cells in the lung. In vitro exposure to meconium increases the release of IL- , TNF-alpha ( ), endothelium- , trombocytes activating factor (PAF), leukotrienes, thromboxane A , induces synthetase NO ( ), NO ( ), PLA and other substances that influence reactivity of the airways and inflammation. This shows interdependence with cholinergic nervous fibres that innervate airways smooth musculature ( )
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