Aim
Obese diabetic (ZDF fa/fa) rats with genetic leptin resistance suffer chronic lipotoxicity associated with age-related lung restriction and abnormal alveolar ultrastructure. We hypothesized that these abnormalities impair adaptation to ambient hypoxia.
Methods
Male fa/fa and lean (+/+) ZDF rats (4-months old) were exposed to 21% or 13% O2 for 3 weeks. Lung function was measured under anesthesia. Lung tissue was assayed for DNA damage and ultrastructure measured by morphometry.
Results
In normoxia, lung volume, compliance, and diffusing capacity were lower while blood flow was higher in fa/fa than +/+ rats. In hypoxia, fa/fa animals lost weight, circulating hematocrit rose higher, and lung volume failed to increase compared to +/+. In fa/fa, the hypoxia-induced increase in postmortem lung volume was attenuated (19%) vs. +/+ (39%). Alveolar ducts were 35% smaller in normoxia but enlarged two-fold more in hypoxia compared to +/+. Hypoxia induced broad increases (90–100%) in the volumes and surface areas of alveolar septal components in +/+ lungs; these increases were moderately attenuated in fa/fa lungs (58–75%), especially that of type-II epithelium volume (16% vs. 61% in +/+). In fa/fa compared to +/+ lungs, oxidative DNA damage was greater and hypoxia induced efflux of alveolar macrophages. Harmonic mean thickness of the diffusion barrier was higher, indicating higher structural resistance to gas transfer.
Conclusion
Chronic lipotoxicity impaired hypoxia-induced compensatory lung expansion and growth with disproportionate effect on resident alveolar progenitor cells. The moderate structural impairment was offset by physiological adaptation primarily via a higher hematocrit.