Mitochondrial lamellated bodies and surfactant depots in the Type II cells of the lung compared by bimetallic staining and X-ray analysis.

After heavy dosages of sensory irritants osmiophilic whorls (mitochondrial lamellated bodies) are found in the mitochondria of the Type II cells of the lung. To obtain evidence of their nature, the lead/osmium (Pb/Os) ratio in these and other bodies after bimetallic staining was studied by electron probe X-ray analysis during transmission electron microscopy. To allow for inter-specimen variation the Pb/Os ratio was divided by the Pb/Os ratio for chromatin in the same cell, to give a "relative ratio". The values of the latter ranged from 1.4 for granules in an eosinophil leucocyte to 0.60-0.77 for lamellated osmiophilic bodies of Type II cells, 0.4 for nerve myelin, and 0.05 for fat globules. The Pb/Os ratio for mitochondrial lamellated bodies did not differ significantly from that for lamellated osmiophilic bodies (which are depots of lung surfactant) in the same cell. This is compatible with the mitochondrial lamellated bodies consisting of excess surfactant produced in response to stress. the method is capable of extension.

Maturity of fetal lungs tested by production of stable microbubbles in amniotic fluid.

Lung surfactant in amniotic fluid, and hence the maturity of the fetal lungs, can be assessed by observation of stable microbubbles (less than 15 micron diameter). Bubbles are formed by agitation with a Pasteur pipette and examined in hanging drops under the 10 x power of a microscope. Either after a count of bubbles, or after a general survey of hanging drops, the fluid is given a stable microbubble rating. A 'strong' rating indicates that the idiopathic respiratory distress syndrome will not occur after delivery, and that the lecithin/sphingomyelin ratio will indicate maturity. Complete absence of stable microbubbles suggests a high risk of respiratory trouble for the newborn infant, as does a weak or lower rating in the 30 to 37 week gestational age group. The test takes 5 to 10 minutes to perform, is cheap and easy, is not affected by blood, but may be affected by meconium. If a 'strong' rating is found, measurement of the L/S ratio can safely be omitted.

Postmortem changes in the surpellic activity of lung surfactant.

The surpellic activity of lung surfactant in mouse lungs stored in the cadaver persists for times much longer than those after which gross morphological changes at electron microscope level have been recorded.

The relation between surface tension and area in the alveolar lining film.

1. The properties of the rat alveolar lining film have been studied by observing the behaviour in a hanging drop, under reduced or increased ambient pressure, of bubbles derived from the lung.2. When such a bubble, covered by a metastable film of surfactant, is made to shrink, the material displaced from the surface usually remains in a form in which it can be re-adsorbed to the surface and retains its surpellic properties.3. When an excess of surfactant is available for adsorption to the surface of such a bubble in water, an increase in area to about 1.25 (varphi) times the metastable area is both necessary and sufficient for additional adsorption to the surface to take place.4. No significant variation of the ratio varphi with temperature between 22 and 37 degrees C has been found.5. It is concluded that during quiet breathing (involving a twofold change in lung volume in the rat) the variation in alveolar surface area is less than 25%. This finding is compatible with the extant morphometric data, but not with any assumption that the surface area is proportional to the 2/3 power of the gas volume.6. The behaviour of the bubbles in blood serum is similar to that in water. In a 2% solution of the detergent Tween 80, further adsorption of surfactant to the bubble surface does not take place.7. The fact that bubbles obtained from the lung by instillation of a solution of Tween 80 have surfactant linings similar to those of bubbles obtained with water or saline demonstrates that the bubble lining layer consists of the original alveolar lining layer detached.8. When a metastable bubble is stretched, it sometimes behaves as if some or all of its surfactant had been lost from the surface. The causes of this are unknown.9. The amount of surfactant associated with metastable bubbles freshly squeezed from a fragment of lung varies from bubble to bubble; the amounts found have ranged from 1 to 4.5 times (mean, 2) that required to cover the original bubble area with a metastable film. This would be compatible with an alveolar lining film of very uneven thickness.10. The maximum surface tension reached in the early stages of expansion of a lung bubble from the metastable state is about 34 mN/m.

The development of the lung and its surfactant in the foal and in other species.

The development of the lung from the glandular through the canalicular to the alveolar stages in the horse fetus is described. Traces of surfactant and occasional lamellated osmiophilic bodies representing intracellular surfactant were found at 150 days of gestation, some 40 to 60 days before the transition to the canalicular stage. During this transition some of the cuboidal cells of the glandular rosettes are transformed into cells of Types I and II, but the surfactant is not fully developed until 300 days or, in some foals, until after delivery.