The effects of ganglionic blockade on tracheobronchial muscle in fetal and newborn lambs

Abstract Changes in diameters of the trachea and bronchi of fetal and newborn lambs were studied by cineroentgenograms and histological sections after administration of a ganglionic blocking agent. Mean increases in diameters of the trachea and left and right bronchi were 90 %, 69 % and 62 %, respectively, in the fetal lambs. In the newborn lambs, the mean increases in tracheal and left and right bronchial diameters (51 %, 38 % and 60 %, respectively) were considerably less than those observed in the fetal lambs. This suggests that after birth the enhanced activity of the sympathetic component of the autonomic nervous system under normal circumstances overcomes the parasympathetic dominance over the respiratory tract which is characteristic of fetal life.