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Article

Nutritional Status Affects Intestinal Carotene Cleavage Activity and Carotene Conversion to Vitamin A in Rats

National Institute of Nutrition, Indian Council of Medical Research, Jamai-Osmania Hyderabad - 500 007, India

²To whom correspondence should be addressed.

Validation of an in vivo method we developed recently and its application to assess the role of dietary factors in carotene conversion were tested in rats. We compared the ratio of area under plasma vitamin A time-curves (AUC_0–12h) obtained after a dose of ß-carotene to that after a dose of vitamin A, with the in vitro intestinal supernatant ß-carotene dioxygenase activity. In separate experiments, vitamin A (AD) and protein deficiencies (PD) were produced in male WNIN weanling rats. Corresponding food-restricted (AR and PR) and unrestricted rats (AA and PA) served as controls. Three rats in each of the AD, AR and AA groups received oral doses of 50–300 µg ß-carotene or 25–150 µg vitamin A and four rats in each of the PD, PR and PA groups received only 100 µg ß-carotene or vitamin A. The plasma vitamin A AUC_0–12h with ß-carotene or vitamin A were significantly and positively correlated (r = 0.714–0.918, n = 9–12, P < 0.05) with the dose in AD, AR and AA groups. The AUC_0–12h slope ratios in AD, AR and AA rats were 0.33, 0.20 and 0.26, respectively. The ß-carotene dioxygenase activity (pmol retinal · h^-1 · mg protein^-1) was significantly higher in the AD group (14.9 ± 2.43) compared to both AR (6.7 ± 0.62) and AA (6.3 ± 1.37) groups and was parallel with in vivo conversion of ß-carotene to vitamin A. The AUC_0–12h ratio was lower in PD rats (0.13) compared to PR (0.26) and PA (0.5) groups. Similarly, the in vitro enzyme activity (pmol retinal · h^-1 · mg protein^-1) in PD rats was significantly lower (3.6 ± 1.30) compared to PR (13.7 ± 0.92) and PA groups (13.8 ± 1.6). Thus the results validate the methodology and confirm the role of nutritional factors in carotene conversion to vitamin A.

KEY WORDS: • vitamin A deficiency • protein deficiency • ß-carotene dioxygenase • rats

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