Influence of sympathetic nervous system on surfactant production. An ultrastructural study

The influence of the sympathetic nervous sytem on pulmonary surfactant was investigated in an ultrastructural study of normal and chemically sympathectomized rat lungs. Chemical sympathectomy was accomplished by administration of 6- hydroxydopamine (6-OHDA). The 6-OHDA did not have any systemic influence on the experimental animals. These animals grew normally and were killed at intervals of three, four, six, and seven weeks. The mean weight of the controls at three weeks was 41.75 +/- 3.12; at four weeks, 77.00 +/- 2.68; at six weeks, 169.25 +/- 11.29; and at seven weeks, 182.25 +/- 4.94. The mean weight of the 6-OHDA treated group at three weeks was 48.50 +/- 1.04; at four weeks, 76.25 +/- 1.93; at six weeks, 171.75 +/- 3.40; and at seven weeks, 180.25 +/- 2.36. The body/ lung weight ratio was about the same in both groups. In the control animals, the alveolar capillary membranes were intact, the alveoli were well expanded, and epithelial cells appeared normal. The cytoplasm of the granular II pneumocytes contained their characteristic osmiophilic lamellated bodies as well as multiple transition forms between the multivesicular and lamellated bodies. It is these lamellated bodies that are the suspected site of surfactant production in the lung and they appear to migrate towards the alveolar lumen. In addition to the lamellated bodies, multiple lattice-like tubular myelin figures were abundant in the alveoli of the normal rat lung. Following sympathectomy, structural alterations occurred within the cytoplasm of the granular II pneumocytes, involving mainly the lamellated bodies. There was a decrease of osmiophilic content as well as loss of organization of the bodies. This change was quantitated by scoring the degree of osmiophilia in the control and sympathectomized animals. The mean score in the control animals was 4.43 +/- 0.03 S.E., whereas in the sympathectomized group it was 3.77 +/- 0.16 S.E. It was concluded that the lamellated bodies, the site of phospholipid synthesis in the granular II pneumocyte, arise from the multivesicular bodies and are extruded into the alveolus. They then participate in the formation of the alveolar acellular lining layer. Sympathectomy alters the structure of the lamellated bodies, thereby influencing the development of the surfactant system.