This article consists of the following 3 parts. 1) Metabolism of 1,25-(OH)_2-D_3 and Its Binding Mechanism in Familial Hypophosphatemic Vitamin D Resistant Rickets It is known that serum calcium concentration is not readily increased by vitamin D metabolites such as 1,25-(OH)_2-D_3 or 1α-(OH)-D_3 in familial hypophosphatemic vitamin D resistant rickets (VDRR). It has been reported that the same phenomenon is observed in the VDRR mouse known as a VDRR model. This abnormal biological response may be ascribed to abnormal interaction between 1,25-(OH)_2-D_3 and its receptor. We investigated receptors of 1,25-(OH)_2-D_3. No difference was observed in cytosol receptors in the duodenum between the control and VDRR mouse, but a significant decrease was observed in the nuclear uptake of 1,25-(OH)_2-D_3 by duodenal mucosal cells of the mice. 2) Effects of vitamin D_3 on Secretion of Insulin The effects of vitamin D_3 on the secretion of insulin was examined in perfusion tests using isolated pancreas of D-deficient rats. These results suggest that the decreased insulin release in the D-deficient rats is due to a reduction of intracellular Ca^<++> storage in the B cell, which we believe is a result of long term low plasma Ca levels in the D-deficient rats. 3) Biological Characterization of 1,25-(OH)_2-D_3 receptors in Chick Embryonal Duodenal Cytosol The binding activity of 1,25-(OH)_2-D_3 receptor in chick duodenal cytosol was maximal at the state of hatching. In addition, 1,25-(OH)_2-D_3 receptor before hatching might be composed of different forms of proteins corresponding to "fetal form".

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Recently, much attention has been focused on the ubiquitous distribution of specific 1α,25-(OH)_2-D_3 receptors in normal and cancer cells. This suggests that the role of this vitamin in biology extends far beyond its classical role in mineral metabolism. Since 1981, we have been investigating the differentiating action of vitamin D compounds primarily in hematopoietic cells. 1α,25-(OH)_2-D_3 inhibits proliferation and induces differentiation of immature bone marrow cells and myeloid leukemia cells (M1, HL-60 and U937) preferentially into monocyte-macrophages. Furthermore, the vitamin promotes activation and fusion of mouse alveolar macrophages to form multinucleated giant cells. Of vitamin D_3 derivatives tested, 1α,25-(OH)_2-D_3 is the most potent in inhibiting cell growth and in promoting cell differentiation, activation and fusion. These results suggest the possibilities that 1α,25-(OH)_2-D_3 is involved in multinucleated osteoclast formation in bone and that the in vivo administration of vitamin D compounds to tumor-bearing animals decreases their tumorigenicity.

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Relationship between vitamin D_2 content in Shiitake (Lentinus edodes) and quantum of UV light in the environment of cultivation was investigated and the results suggested that vitamin D_2 (including pre-D_2) was photochemically produced from ergosterol by solar radiation during farming because of the following reasons: (1) The assayed values of vitamin D_2 (including pre-D_2) in various kinds of Shiitake were correlated with the quanta of UV light in solar radiation at the cultivation places. (2) Existence of pre-D_2 in raw Shiitake was identified by HPLC and GC-MS. (3) The weight ratio of pre-D_2 to vitamin D_2 in raw Shiitake was about 7:1, whereas that in dried Shiitake was about 1:10. The result suggested that pre-D_2 was photochemically produced from ergosterol during cultivation was thermally isomerized into vitamin D_2 during heat drying. (4) The assayed value of vitamin D_2 (including pre-D_2) in a sample of Shiitake increased about 2.3 times when exposed to direct sun light for 3 hrs. (5) The assayed values of vitamin D_2 (including pre-D_2) in the Shiitake cultured in abundant solar radiation were higher than those cultured in poor radiation.

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NAD in 9 organs as well as in blood of rats fed on various niacin contents of diets were measured. The results indicated that the blood NAD value varied depending on niacin contents in the diets. Fifteen μl of whole blood was required for the proposed method of NAD determination. The blood NAD value was decreased with statistically significant difference from the 6th day after the diet for rats was switched from the complete diet to tryptophan-limited and nicotinic acid-free diet (tryptophan content, 0.043%).

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