Effects of high altitude exposure on the lungs of young rats

Adaptation of the growing lung to increased oxygen consumption. II. Morphometric analysis

This paper is the second part of a study investigating the effect of increased O2 consumption on the lungs of growing animals. By means of injections of the drug IDPN (imino-betabeta'-dipropionitrile) hyperkinesia was permanently induced in white mice aged 3 weeks, thus increasing their Vo2 per gram body weight (= specific VO2) by 50%. 3 1/2 months later the lungs of these animals were fixed by standardized procedure, analysed by morphometric techniques and the results compared with those of control mice originating from the same litters. Whereas the specific weights (= weights per gram body weight) of various organs did not differ significantly in the two groups, the specific volume of the lungs fixed with standardized techniques was up by 23% in IDPN mice. The relative composotion of lung parenchyma was also altered: air space volume density was slightly but significantly reduced, whereas tissue and capillary volume densities were both increased by 15%. An analogous increase was detected in alveolar and capillary surface densities. These changes led to significantly higher specific capillary and tissue volumes, as well as higher specific gas exchange surface areas in DIPN mice. Therefore the morphometrically determined specific pulmonary diffusion capacity was increased by more than 40% in the IDPN-treated animals. The findings are compared with those hitherto reported, where a structural adaptation of the gas exchange apparatus to exercise or altered PO2 had been found. In view of our present knowledge of the postnatal lung growth the quantitative structural alterations found in this experiment indicate that the higher O2 requirements in IDPN mice induced an alteration in the septal morphology. This consisted in an augmentation of septal volume possibly due to a lengthening and corrugation of the intralveolar septa. This change is reflected by the increased alveolar surface area in IDPN mice and by the increase of the ratio Sa/Va estimating the air space surface complexity.

Adaptation of the growing lung to increased VO2. I. IDPN as inducer of hyperactivity

This paper is the first part of a study aiming to further analyse the hypothesis that in growing animals an increased VO2 due to a high physical activity leads to a quantitative adaptation of the gas exchange apparatus. Trying to avoid the tedious treadmill exercises we tested the applicability of the drug IDPN (imino-beta,beta'-dipropionitrile) as an inducer of increased VO2. Three intraperitoneal injections of IDPN permanently transform normal white mice into 'waltzing mice'. In our experiments ten male mice were injected with IDPN at the age of 20, 21 and 23 days. A control group was simultaneously injected with saline. The typical 'IDPN' hyperkinetic syndrome' appeared within five days from the first injection. The treated mice lost weight and grew at a slower rate than the controls. Their physical activity, as measured by Animex activity meters, was about twice that of the controls and was accompanied by a 50% increase in specific VO2 (VO2/body weight). At the age of about 4 months all animals were killed, their lungs fixed by intratracheal instillation of glutaraldehyde for a complete morphometric analysis. The body weights and the weights of heart, liver, kidneys, viscera, skin and carcass as well as the skin surface area were determined. IDPN mice were significantly lighter than the controls (-16%). All the other parameters cited above were reduced in about the same proportions, so that, when related to body weight, no significant changes could be detected. Specific lung volumes (VL/body weight) of IDPN mice were however up by 23%. These findings confirm that IDPN treatment represents a suitable way to increase VO2 in mice and may therefore allow to avoid more cumbersome methods of enforced exercise. The complete morphometric analysis will be published in a following paper.

Postnatal growth of the mammalian lung: lack of influence by carbon monoxide exposure

The growth and internal partitioning of the lung are increased in young animals exposed to high altitude. Neither the mechanism whereby O2 lack brings this about nor the anatomic site of action of hypoxia is known. To test whether extrapulmonary tissue hypoxia can stimulate lung growth in the prescence of normal alveolar PO2, pulmonary morphology was studied quantitatively in young rats exposed to 208 ppm carbon monoxide for 29-30 days. The results show no effect of this exposure on lung dimensions and thus argue against extrapulmonary tissue hypoxia as the relevant stimulus in the increased lung growth that occurs at high altitude.