In this paper, the author briefly summarizes the nutritional and physiological aspects of vitamin A metabolism and functions which we have investigated. Initially, I examined vitamin A's coenzyme-like function, as a water-soluble vitamin. It was revealed that mannosyl retinyl phosphate (Ret-P-Man) occurred in vivo in rat liver and intestinal mucosa, and that this may function as one of several lipid intermediates in the transfer of mannose to endogenous acceptors in rat liver membrane preparations. In the second investigation, the author demonstrated that there are some relationships between vitamin A status and protein metabolism in chick and rat. When newly-hached chicks were fed a high-protein diet without vitamin A, urate accumulated in the ureter and kidney, and growth stopped earlier than in chicks fed a standard protein diet. We then examined the relationship between nuclear retinoid receptor (RARs, RXRs) genes and expression of their target genes under varying vitamin A status. We found that the expression of nuclear receptors was very complex, and therefore it is quite difficult to summarize the regulation mechanisms of these genes systematically. Finally, we revealed that rapid in vivo isomerization of retinoic acid, e. g. all-trans-RA=9-cis-RA, occurred in rats. These results suggest that the apparent action of 9-cis- and all-trans-RAs or gene expression in vivo may be mediated to some extent by the converted stereoisomer.
Although tin and rubidium are essential trace elements for some bacteria and plants, their essentiality for higher animals is not fully established. This study examined the effects of low dietary levels of tin and rubidium on growth, tissue mineral concentrations and the selected plasma biochemical indices of growing rats. Compared to rats given 2μg tin/diet, rats fed a 17ng tin/g diet exhibited lower weight gain, decreased food efficiency, alopecia, altered mineral levels in some tissues and changes in plasma lipid concentrations. Compared to rats fed an 8μg rubidium/g diet, rats fed a 0.5μg rubidium/g diet showed decreased rubidium concentrations in all tissues examined, altered levels of other minerals in various tissues and an increased urea nitrogen level in plasma. These results suggest that tin and rubidium are essential for animals.