Nutritional status affects intestinal carotene cleavage activity and carotene conversion to vitamin A in rats

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 beta-carotene to that after a dose of vitamin A, with the in vitro intestinal supernatant beta-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 microgram beta-carotene or 25-150 microgram vitamin A and four rats in each of the PD, PR and PA groups received only 100 microg beta-carotene or vitamin A. The plasma vitamin A AUC(0-12h) with beta-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 beta-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 beta-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.