The effect of spinal cord transection on lung development in fetal sheep.

The relationship of breathing movements to lung development in the ovine fetus was investigated by transecting the fetal cervical spinal cord above (C2-C3; n = 4) or below (C7-C8; n = 4) the phrenic nucleus at 114 days of gestation. The fetuses were delivered by hysterotomy at term and compared with a group of intact term fetuses (n = 8). Cord transection at C2-C3 resulted in a significant (P less than 0.05) reduction in wet weight of the lungs to 1.56 +/- 0.23% of body weight from 2.59 +/- 0.83% in the C7-C8 group. The diaphragms of the two groups did not differ in weight or histological appearance. Distensibility of the left lung with air at 40 cmH20 was significantly less in the C2-C3 group (6.8 +/- 3.5 ml.kg-1 body weight) than the C7-C8 group (19.9 +/- 3.7 ml.kg-1) or the intact controls (15.2 +/- 5.4 ml.kg-1). DNA content in the C2-C3 group (0.63 +/- 0.12 g) was less than in controls (0.99 +/- 0.19 g) but it was not different from the C7-C8 group (0.82 +/- 0.33 g.) DNA concentration, water content and saturated phosphatidylcholine concentration in lung tissue and lavage fluid were similar in the three groups. It is concluded that the absence of breathing movements caused by transection of the spinal cord above the phrenic nucleus is associated with retarded lung growth and maturation.