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.