Since author was fascinated by the important functions of calcium (Ca) for the regulation of intracellular metabolism, author has focused the studies on Ca metabolism. A parameter which evaluates bone strength is essential for the study of Ca/bone metabolism and the prevention of osteoporosis. Therefore, a machine for measurement of bone strength was developed. Dual-energy X-ray absorptiometry (DXA: bone densitometer) is used very widely in human studies, and has proved to be safer and more accurate than other techniques. Author carried out DXA to determine whether it is suitable for the measurement of low bone mineral density (BMD) in small animals. The estrogen-deficient model rat produced by ovariectomy and the estrogen- and Ca-deficient model rat produced by ovariectomy and a low Ca diet were also evaluated to clarify whether these animal models were useful as osteoporotic models. For prevention of osteoporosis, it is necessary to take enough Ca and to carry out moderate physical activity. However, Ca intake has never been sufficient in Japan. Therefore, the effects of different Ca sources, other nutrients which affect Ca metabolism and physical activity on bone metabolism were examined. It is well known that a reaching a high peak bone mass at a young age and minimizing bone loss with aging and/or the menopause are also important for prevention of osteoporosis. Therefore, the effects of diet and daily physical activity on the BMD of pre/post menopausal women were investigated using DXA from the viewpoint of osteoporosis prevention.

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Branched chain fatty acids (BCFAs) of the iso and anteiso series are synthesized from branched-chain amino acids (BCAAs) in many bacteria and in animal skin. This communication describes the biosynthesis of BCFA in Bacillus subtilis and rat skin. BCFAs of Bacillus subtilis are synthesized from the α-keto acids of BCAAs. Two distinct decarboxylases were present in the crude BCFA synthetase of Bacillus subtilis: branched chain α-keto acid (BCKA) decarbaxylase and pyruvate decarboxylase. BCFA synthetase activity was completely lost upon immunoprecipitation of BCKA decarboxylase, suggesting that this enzyme is essential for BCFA biosynthesis by Bacillus subtilis. A BCKA decarboxylase-mediated mechanism was postulated for BCFA biosynthesis. Supplementation of the diet with valine and isoleucine increased the levels of respective BCFAs in the skin surface lipids of rat. However, this was not the case for leucine. Serum levels of valine, isoleucine and their α-keto acids correlated well with the level of the respective BCFAs in the skin surface lipids. Incorporation in vivo of [14C] -BCAA and BCKA into the skin surface lipids revealed that valine and isoleucine rather than their α-keto acids were used mainly for BCFA biosynthesis by rat skin. BCFA synthesis by rat skin differed from that by bacteria in that the systems did not use leucine as a primer. Leucine was used for biosynthesis of straight-chain fatty acids rather than for BCFAs. Substrate specificity and stereoselectivity in vivo of animal BCFA synthesis was described.

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An experiment was designed to evaluate the bioavailability of yeast magnesium (Mg) in Fischer 344 male rats based on the serum Mg level, kidney calcification, and bone Mg content. Male rats four weeks of age were divided into three groups of six rats. The three groups were the control, 1/2MgY diet and-MgY diet groups. 1/2 MgY and-MgY diets were prepared to contain equal amounts of Mg to the control diet with yeast Mg as half or all of the Mg source. After a two-week experimental period, the rats were decapitated and blood serum, the right kidney and right femur were collected for determination of Mg, calcium (Ca) and phosphorus (P). Serum Mg, kidney Ca and Mg showed no significant differences between the control group and yeast-supplemented (1/2 MgY, -MgY) rat groups. Also femur Mg levels in the yeast-supplemented groups were higher than in the control group. These results indicate that yeast Mg can be used effectively as a Mg source.

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Male Wistar rats weighing about 130g were fed normal, magnesium-deficient, and mineral-deficient diets for seven days. At 0, 0.25, 0.5, 1, 2, 4, 6, and 8h after orally administering 10, 20, and 40mg Mg/rat via a stomach tube to animals deprived of food for 16h immediately before the end of feeding, blood was obtained from a tail vein, and then the intestines were removed immediately after decapitation 8h later. The magnesium levels in plasma and the intestines were the determined. With the administration of 10mg Mg, the plasma magnesium concentration increased with time, reached a maximum level about 2h after administration, and then reduced slowly in all dietary groups. At about 0.5h after administering 20mg Mg, the maximum level of plasma magnesium increased and the level was maintained nearly constant for more than 8h in all groups. The amounts of magnesium administered tended to be correlated with the time taken to attain the maximum level of plasma magnesium. With 40mg Mg, the most of rats died with in 2h after administration. The enhancement of the plasma magnesium concentration in the mineral-deficient group was the greatest among the three groups. Kinetic analyses of the results suggested that the absorption of magnesium was a first-order process, the absorption rate of magnesium was much greater than its distribution (disappearance) rate, and the apparent volume of distribution in the normal group was much higher than those in the magnesium-deficient and mineral-deficient groups. Especially, it was suggested that in rats fed the mineral-deficient diets, the distribution volume of magnesium was reduced by the supply of a great deal of magnesium, which caused the rats to die.

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