Influence of the compound NA872 on cardiopulmonary maturation in the unanaesthetised fetal lamb.

15 fetal lambs were instrumented on approximately day 100 (term 147 days) with small catheters in their jugular veins, carotid arteries and tracheas and fine electrodes in their diaphragms and on the lateral surfaces of their thoraces. Measurements were made intermittently of carotid arterial pressure, jugular venous pressure, amniotic fluid pressure, ECG and electrical activity in the diaphragm for 2-hour periods up to day 120. From day 120, two hourly recordings were made daily and samples of lung liquid taken until day 130. On this day, studies of lung mechanics were made on selected fetuses. From day 120, 8 animals were treated with the compound NA872 and 7 animals were given a control infusion of normal saline. In comparison to control animals the lecithin-sphingomyelin (L:S) ratio increased in the test fetuses from days 125--130; respiratory activity (diaphragmatic EMG) was suppressed in the test animals suggesting a more mature respiratory system; but resting lung volume on the test animals was smaller. Heart rate decreased as rapidly in the test animals while changes in systemic vascular pressures were similar. These results indicate that while the lungs are more 'mature' in that L:S ratio is increased, resting lung volumes are smaller, and respiratory activity is decreased. They raise the interesting questions of the influence of fetal respiratory activity on lung and thoracic cage development and the possible direct action of the drug NA872 on the respiratory pattern generator and the lung.