Repeated allergen challenge in rats increases vitamin A consumption

Background: Vitamin A plays an important role in airways epithelial repair and differentiation. Allergen challenge induces epithelial damage and shedding, which cause an increase in repair activity. Objective: To examine whether repeated allergen challenges could increase vitamin A consumption in a rat model. Design: Allergic bronchitis was induced in 12 animals, and 12 rats remained naive. After 14 days, repeated allergen inhalation challenges were performed in the sensitized rats for 2 weeks. On day 16, allergen challenge was performed and bronchoconstriction was measured in all 24 rats. On day 30, all rats were killed. BAL was performed and ex vivo tumor necrosis factor (TNF)-α and nitric oxide (NO) production was measured in the lavage cells. Liver, lung tissue, and serum were collected for measurement of vitamin A concentration. Results: The study rats showed severe bronchoconstriction after allergen challenge compared to the naive rats, and ex vivo TNF-α and NO production was significantly higher in the sensitized rats. Serum and lung concentrations of vitamin A were not different among the two groups. However, the vitamin A liver concentration in the study rats was significantly lower compared to the naive rats. Conclusions: We conclude that vitamin A utilization is increased during repeated allergen challenge and allergic bronchitis, most probably due to increased demand for epithelial repair.