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ß-Carotene Absorption and Cleavage in Rats Is Affected by the Vitamin A Concentration of the Diet^1,2,

Trinette van Vliet^*,,3, Martje Fentener van Vlissingen, Frank van Schaik and Henk van den Berg^*

^* Department of Physiology and Kinetics Department of Analytical Sciences, TNO Nutrition and Food Research Institute, 3700 AJ Zeist, Netherlands Department of Experimental Zoology, Faculty of Biology, University of Amsterdam, 1098 SM Amsterdam, Netherlands

The purpose of this study was to examine whether intestinal ß-carotene cleavage activity, measured with the dioxygenase assay, is affected by vitamin A intake and whether this in vitro activity is a determinant of ß-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 ß-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 ß-carotene-supplemented rats intestinal dioxygenase activity was significantly lower than in unsupplemented rats. The molar ratio between retinyl esters and ß-carotene in lymph collected over 8 h after a single intestinal dose of ß-carotene (250 µg) to ß-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 ß-carotene-supplemented rats. Based on the difference in liver vitamin A contents between ß-carotene-supplemented and unsupplemented rats we estimated ß-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 ß-carotene cleavage activity is higher in vitamin A-deficient rats than in rats with a high intake of either vitamin A or ß-carotene. The intestinal dioxygenase activity as measured in vitro is an adequate indicator of in vivo ß-carotene cleavage activity.

KEY WORDS: • rats • ß-carotene metabolism • vitamin A • dioxygenase assay • lymph cannulation

¹ Published in part in abstract form: Vliet, T. van, Schaik, F. van, Berg, H. van den & Schreurs, W.H.P. (1993) Effect of vitamin A and ß-carotene intake on dioxygenase activity in rat intestine. Ann. N.Y. Acad. Sci. 691: 220–222.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 22 May 1995. Revision accepted 11 October 1995.

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