Rabbits fed on β-carotene have higher serum levels of all-transretinoic acid than those receiving no β-carotene

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Abstract
The aim of the present work was to determine the effect of giving increasing doses of supplements of β-carotene on serum retinoic acid levels in rabbits. Four groups of 7-week-old female rabbits were fed for 9 weeks on a pelleted diet containing 1.72 mg vitamin A as retinyl acetate/kg and including control gelatin beadlets devoid of β-carotene or 1, 2 or 4 mg β-carotene/kg body-weight per d. Serum was collected at 3, 6 and 9 weeks after the beginning of the experiment and the concentration of all-transretinoic acid was determined by a gradient reverse-phase high-performance liquid chromatography system following a double-phase extraction. The average concentration of retinoic acid in serum of the combined control and 1 mg β-carotene/kg groups was 3.80, 3.06 and 2.40 nM at 3, 6 and 9 weeks respectively. The concentrations of retinoic acid in serum of the combined 2 and 4 mg β-carotene/kg groups were 4.80 nM (P< 0.05), 3.76 nM (not significant) and 4.90 nM (P< 0.005) at 3, 6 and 9 weeks respectively. A SAS (SAS Institute Inc., 1985) general linear model repeated-measures analysis of variance revealed that the effects of treatment (PP< 0.05) and treatment x time interaction (P< 0.05) were statistically significant. It is concluded that giving β-carotene is associated with higher concentrations of all-transretinoic acid in the serum of rabbits than in those receiving no β-carotene.