Chest
Volume 122, Issue 4, October 2002, Pages 1407-1411
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Laboratory and Animal Investigations
Repeated Allergen Challenge in Rats Increases Vitamin A Consumption

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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.

Section snippets

Animals

Highly inbred BN rats (n = 24) were obtained from Harlan. The animals were housed in metal cages in a room with controlled temperature (25 ŷ 2ŶC), relative humidity (65 ŷ 5%), and light (8 am to 6 pm). Ethical permission was obtained for the study, and all procedures were conducted in full compliance with the strict guidelines of the Hebrew University Policy on Animal Care and Use. The rats were weighed at the beginning and end of the study, and their food intake was measured every other day.

Induction of Allergic Bronchitis

Results

There was no difference in food consumption or body weight at the beginning and end of the study between the sensitized (test group) and the naive (control group) rats. The mean NO, TNF-α, percentage of Penh, and concentration of vitamin A in liver, lung, and plasma for the test group and control group rats are shown in Table 1. Bronchoconstriction 5 min after allergen challenge was significantly higher in the sensitized rats compared to the naive rats (p < 0.001).

The plasma and lung vitamin A

Discussion

In this study, we demonstrated that recurrent allergen challenges result in a decrease of hepatic vitamin A stores in sensitized rats. Vitamin A intake was not different between the two groups as was measured by food intake and also expressed by body weight. The liver supplies vitamin A to the serum and the various organs and maintains normal serum and tissue concentration as long as vitamin A is not depleted.14 A decrease of hepatic vitamin A stores might be a result of an increased demand of

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