Abstract
The precise mechanisms for catecholamine release at birth are not well established. Labor and delivery, cold, cord clamping, hypoxia and acidosis are stimuli of catecholamine release. Lung liquid resorption is in relationship with catecholamine release. To study the effect of the different stress applied on lung tissue, we investigated the different phases of birth simulation in utero focused only on lung distension, ventilation with Nitrogen(N2) without modifications of fetal blood gases, then with air and oxygen. We studied 16 ewes at 134,75±4 days of gestational age. Mean fetal weight was 3,63±0,63 kg. Pressure of db tension was 25±10 cm of water. For rhythmic ventilation with N2, pressure of inflation was 27±6 mm Hg, PEEP 4±5 and I/E 36±13%. Catecholamine samples were withdrawn after 15 min following modifications. Catecholamine concentrations were measured by high-performance liquid chromatography with electrochemical detection. Statistical analysis compared the consecutive steps analyzed by the non-parametric Wilcoxon test and considered significant for a p<0,01 Ventilation increased 4,6 fold epinephrine concentrations. However distension did not increase catecholamine release. Ventilation with air and O2 decreased concentrations and placental blood flow was abolished. The precise mechanism which induces catecholamine release during rhythmic ventilation with N2 is not elucidated.
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