Hyperoxia: A Stereologic Ultrastructural Examination of Its Influence on Cytoplasmic Components of the Pulmonary Granular Pneumocyte

Abstract

A B S T R A C T We used the technique of lineal analysis to study the influence of 48 h of hyperoxia on cytoplasmic organelles of pulmonary granular pneumocytes with particular reference to their lamellar bodies. We undertook this study because lamellar bodies are considered to be storage granules for pulmonary surfactant and because we had found that hyperoxia decreased [14C]leucine incorporation into protein of a surface-active lung fraction.We found that for lamellar bodies the percent cytoplasmic volume was 12.8±1.5 (mean+SEM) and 8.4+ 2.2, the organelle area (sm') per organelle was 0.98± 0.13 and 0.62±0.10 and the organelle volume (Am') was 0.35±0.04 and 0.18+0.01, for air-and oxygenexposed rats, respectively, (P = < 0.05). The surface density of the lamellar body membrane was 7.05±0.47 and 9.36±0.96 (P = <0.05) for air-and oxygen-exposed rats. There were no differences in lamellar body number per cytoplasmic area or per pneumocyte between air-and oxygen-exposed rats. There were no statistical differences in these parameters between mitochondria of air-or oxygen-exposed rats. The surface density of the rough endoplasmic reticulum was the same in both groups.This study indicates that granular pneumocytes of rats exposed to hyperoxia have the same number of lamellar bodies as control rats but the lamellar bodies are smaller. This findings is consistent with the hypothesis that the hyperoxia-induced decrease in protein synthesis by lung represents at least in part a decreased synthesis of the secretory lipoprotein-pulmonary surfactant.

Hyperoxia: Influence on Lung Mechanics and Protein Synthesis

“…We cannot disprove this contention. However, the decreased incorporation into the surface-active fraction is associated with a decrease in the size but no change in number of the lamellar bodies (25). Substantial evidence indicates that lamellar bodies are storage sites for surfactant.…”

Changes in Sedimentation of Surfactant in Ventilated Excised Rat Lungs

“…Pellets formed by centrifuging the lung lavage returns were fixed and prepared for electron microscope analysis as previously described in detail for lung tissue (14).…”

Adaption to Hyperoxia

“…The decrease in the synthesis of protein in a surface-active fraction is greater than the decrease in synthesis of protein in the whole lung homogenate. Within this time there is also a decrease in the volume fraction of lamellar bodies in the pulmonary granular pneumocyte (2); this latter finding is important in relation to the studies on protein biosynthesis because lamellar bodies are considered to be storage sites for pulmonary surfactant (3)(4)(5)(6)(7). These biochemical and morphological findings in concert suggest to us that hyperoxia decreases protein synthesis in general but also decreases the synthesis of proteins which are components of macromolecules made for export (secretory proteins), in this instance the apoproteins of pulmonary surfactant.…”

“…The tissue was prepared and samples were taken for electroni microscopy as described before except that four electron micrographs of granular pneumocytes were taken from each tissue block rather than two as in our previous paper (2). Granular pneumocytes were identified as round or cuboidal cells in the alveolar walls which had signs of attachment as evidenced by a tight junction between it and an adjacent cell.…”

“…Granular pneumocytes were identified as round or cuboidal cells in the alveolar walls which had signs of attachment as evidenced by a tight junction between it and an adjacent cell. In our initial definition of this cell for the present study, we decided not to require the presence of lamellar inclusion bodies as we had in our previous report (2). We did this because type I alveolar epithelial cells begin to be replaced by type II alveolar epithelial cells (granular pneumocytes) after exposure to hyperoxia for more than 72 h (14).…”