|Ann. Medit. Burns Club - voL VII - n. 2 - June 1994
DYNAMIC CHANGES OF FIBRE CONTENT IN RABBIT LUNG AFTER SMOKE INHALATION INJURY
Er-fan X., Zong-cheng Y., Li Ao (Ngao)
Institute of Burn Research, Southwestern Hospital, Third Military Medical College, Chongelin, Sichuan, China
SUMMARY. On the basis of the autofluoreseence characteristics of elastic and collagenous fibres, microspectrofluorometry was used in this study to measure the dynamic changes of the fluorescent intensity of alveolar walls in rabbit lung after smoke inhalation injury. Such changes would indicate the alteration of amounts of fibre content in the lung. The concomitant changes of arterial blood gas levels, lung water volumes and pathomorphology of lung tissue were also observed. It was found that after injury the fluorescent intensity of alveolar walls decreased progressively denoting a substantial loss of elastin and collagen in the lung. Serious lung damage and pulmonary oedema were also found. The results indicated that the disrupting effects of proteolytic enzymes on lung tissue structures may contribute importantly to lung injury after smoke inhalation. A new method, rnicrospectrofluorometry, is thus provided for the study of fibre content in the lung.
Following studies in the pathogenesis of smoke inhalation injury, many achievements have been reported regarding the damage of pulmonary and capillary endothelial cells. However, no research on the extracellular interstitium, in particular regarding the quantitative description, has yet been conducted. This study concentrated on the dynamic changes of fibre content in rabbit lung after smoke inhalation with the application of microspectrofluorometry, in order to form a complete picture of pulmonary injury.
Materials and methods
Thirty healthy adult rabbits of either
sex weighing 2-3 kg were used, divided randomly into five groups. There was one control
group (6 rabbits) and four experimental groups (6 rabbits each). Conscious animals inhaled
smoke in a mildly hypoxic environment for a period of 7 min, according to the method
previously established in our Institute (1). All the animals in the exPerimental groups
were killed at respectively 2, 6, 12 and 24 h after smoke inhalation injury. Control
animals underwent similar procedures except that air replaced smoke.
Pa02 and S02C decreased progressively in the first 6 h after smoke inhalation injury. It then began to rise but had not returned to normal controls by the end of the experiment. PaC02 increased significantly after the injury with a peak at 6 h, and was still higher than normal level at 24 h (Table 1).
The fluorescent intensity of the alveolar walls decreased gradually throughout the entire experimental period after smoke inhalation. It was already significantly lower than normal control levels at 6 h, and the lowest value occurred at 24 h (Table II).
The causes of damage of smoke
inhalation injury are very complicated. Besides the direct destructive actions of noxious
chemical substances and particulate materials, the effects of local andlor systemic
factors, including neural, humoral and cellular factors, etc., are also very important
after injury. Among these factors, the roles of proteolytic enzymes, such as elastase,
collagenase, etc., released from polymorphonuelear leukoeytes (PMN) and alveolar
macrophages (AM), have received growing attention.
Both elastic and collagenous fibres have
their own autofluorescence characteristics (5). Under fluorescence microscopy, the
fluorescent light of elastic fibres is yellow-green, strong and concentrated, while that
of collagenous fibres is pale, weak and homogeneous. These characteristics were adopted in
the present study. The autofluorescent intensity of alveolar walls was measured by
microspectrofluorometry, the values of which indicated the amounts of elastic and
collagenous fibre content in the lung. The results showed that the autofluorescent
intensity of alveolar walls decreased gradually after smoke inhalation injury, and was
already apparently lower than that in normal controls 6 h post-injury. Pa02 and S02C
dropped, P.C02 was raised, TLW and EVLW increased, and serious lung damage was also
observed in pathological examinations. These changes suggested that the fibre content of
alveolar walls decreased markedly in the early post-injury stage, and a large amount of
elastin and collagen was digested, thus causing the destruction of lung tissue structures.
Twenty-four hours after injury, Pa02, PaC02, TLW and EVLW showed some improvement, but did
not return to normal levels. However, the fluorescent intensity of alveolar walls became
even weaker, indicating continuation of hydrolysis of proteases on fibre content. This was
consistent with the results of our previous studies, i.e. elastase activity in
bronchoalveolar lavage fluid was still significantly higher than normal control levels 24h
after smoke inhalation injury (1). Starcher (6) also suggested that elastase entering the
lung interstitium continues to attack the elastin fibre for several days at least. Total
clastin content can be replaced within a month, although severed alveolar walls clearly
cannot be rebuilt.
RESUME. Sur la base des caractéristiques de l'autofluorescence des fibres élastiques et collagènes, les auteurs de cette étude ont utilisé la microspectrofluorométrie pour mesurer les changements dynamiques de l'intensité fluorescente des parois alvéolaires dans le poumon de lapin après la lésion d'inhalation de fumée. Ces changements indiqueraient l'altération des quantités de contenu fibreux dans le poumon. Les auteurs ont aussi observé les changements concomitants des niveaux du gas hématique artériel, des volumes du liquide pulmonaire et de la pathomorphologie du tissu pulmonaire. Ils ont trouvé que, après le lésion, l'intensité fluorescente des parois alvéolaires diminuait progressivement, ce qui indiquait une perte considérable d'élastine et de collagène dans le poumon. Ils ont aussi trouvé de graves dommages pulmonaires et l'oedème pulmonaire. Les résultats indiquaient que les effets perturbateurs des enzymes protéolytiques sur les structures tissulaires pulmonaires peuvent contribuer en manière importante à la lésion pulmonaire après l'inhalation de fumée. En cette manière les auteurs fournissent une nouvelle méthode, la microspectrofluorométrie, pour l'étude du contenu fibreux du poumon.