beta-Carotene absorption and cleavage in rats is affected by the vitamin A concentration of the diet.
The purpose of this study was to examine whether intestinal beta-carotene cleavage activity, measured with the dioxygenase assay, is affected by vitamin A intake and whether this in vitro activity is a determinant of beta-carotene cleavage in vivo, measured in lymph-cannulated rats. Six groups of 10-20 rats were fed a diet with a low, normal or high retinyl palmitate concentration (120 RE, 1200 RE and 12,000 RE per kg, respectively) for 14 to 18 wk, either supplemented or not with 50 mg beta-carotene/kg in the last 6 wk. Intestinal dioxygenase activity was 90% higher (P < 0.05) in the animals fed the unsupplemented low vitamin A diet than in the animals fed the unsupplemented high vitamin A diet, whereas in beta-carotene-supplemented rats intestinal dioxygenase activity was significantly lower than in unsupplemented rats. The molar ratio between retinyl esters and beta-carotene in lymph collected over 8 h after a single intestinal dose of beta-carotene (250 micrograms) to beta-carotene-unsupplemented rats fed the three levels of vitamin A was correlated with intestinal dioxygenase activity (r = 0.66, P = 0.003). Dioxygenase activity in the liver was not affected by the vitamin A concentration of the diet but was 70% higher in the beta-carotene-supplemented rats. Based on the difference in liver vitamin A contents between beta-carotene-supplemented and unsupplemented rats we estimated beta-carotene conversion factors of 9:1 for the rats fed the high vitamin A diet and 4:1 for the rats fed the normal and low vitamin A diets. Intestinal beta-carotene cleavage activity is higher in vitamin A-deficient rats than in rats with a high intake of either vitamin A or beta-carotene. The intestinal dioxygenase activity as measured in vitro is an adequate indicator of in vivo beta-carotene cleavage activity.
van Vliet
T
T
Department of Physiology and Kinetics, TNO Nutrition and Food Research Institute, Zeist, Netherlands.
van Vlissingen
M F
MF
van Schaik
F
F
van den Berg
H
H
D000818:Animals; D002338:Carotenoids / Q000032:analysis / Q000378:metabolism* / Q000493:pharmacokinetics*; D004224:Diterpenes; D004305:Dose-Response Relationship, Drug; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology*; D007422:Intestines / Q000201:enzymology; D008099:Liver / Q000737:chemistry; D008168:Lung / Q000737:chemistry; D008196:Lymph / Q000737:chemistry; D008297:Male; D010105:Oxygenases / Q000032:analysis; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D000084562:Retinyl Esters; D013997:Time Factors; D014801:Vitamin A / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000494:pharmacology; D019207:beta Carotene
D004224:Diterpenes; D000084562:Retinyl Esters; D019207:beta Carotene; D014801:Vitamin A; C014794:retinol palmitate; D002338:Carotenoids; D010105:Oxygenases