THE GERBIL: A MODEL FOR STUDIES OF BETA-CAROTENE AND MINERAL METABOLISM

Authors: House, William; Apgar, Barbara; Smith Jr, James

Submitted to: Nutrition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Zinc and vitamin A deficiencies are more likely to occur in people with low intakes of meat and dairy products. These food groups provide about 67% of zinc and 50% of the vitamin A in U.S. diets. Vitamin A can be obtained from carotenoids in fruits and vegetables, but the conversion is inefficient and may be affected by vitamin A stores in the liver. Zinc is required for release of vitamin A from the liver, but the role of zinc in conversion of carotenoids to vitamin A is not known. Humans absorb intact carotenoids much more efficiently than the laboratory animals most commonly used in nutrition studies, i.e., mice, rats, and guinea pigs. This lack of a subitable animal model has impeded research on dietary carotenoids. The recent finding that gerbils absorb intact beta-carotene prompted us to evaluate their suitability as models to study carotene metabolism and the metabolic interactions between zinc and vitamine A. We found that gerbils fed the AIN rodent diet grow normally, readily absorb beta-carotene and have tissue mineral concentrations similar to these in other laboratory animals. Therefore, the gerbil may be a more suitable model for studying the influence of zinc status on the metabolism of dietary carotenoids. Increased understanding of the interactions amongst zinc, vitamin A and carotenoids may help to ameliorate health problems associated with inadequate intakes of one or more of these nutrients.

Technical Abstract: Because the Mongolian gerbil (Meriones unguiculatus) absorbs B-carotene intact, it may be a good model for studying the metabolism of dietary carotenoids. Moreover, the ability of the gerbil to concentrate minerals suggests it also may be useful for studying mineral metabolism & toxicity. Since the nutritional requirements of gerbils are not well established, we: :1) investigated the suitability of the AIN-93G diet; 2) obtained informa- tion on the utilization of dietary B-carotene, iron & zinc; & 3) determined mineral concentrations in bone, liver & kidneys. Weanling gerbils (n=44) were fed either a pelleted cereal-based diet (PEL), the AIN-93G diet (CON), a modified AIN-93G diet with vitamin-free casein but no added vitamin A, iron, copper or zinc (DEP), or the latter diet with iron, copper & zinc but no vitamin A for 1 mo followed by the same diet with 1% B-carotene (CAR). Growth rates of gerbils fed the various diets did not differ during the study. As indicated by reduced hematocrit & iron concentrations in bone & liver, a mild iron deficiency occurred in animals fed the DEP diet. In the CAR-fed gerbils, hepatic concentrations of B-carotene were very high, but there were no apparent signs of toxicity. Compared to animals fed the other diets, gerbils fed the DEP diet had reduced liver vitamin A concentration but there were no signs of deficiency. Our study demonstrates that male gerbils: 1) grow normally when fed the AIN-93G rodent diet; 2) readily absorb large amounts of B-carotene; & 3) have tissue mineral concentrations similar to those of the rat.