Nobuo Suzuki

Calcitonin of the stingray: Comparison of the hypocalcemic activity with other calcitonins

Hypocalcemic potency of calcitonin isolated from the stingray (cartilaginous fish), Dasyatis akajei, was examined using the rat bioassay and compared with the activities of other calcitonins (human, pig, salmon, eel, and fowl). The potency of Dasyatis calcitonin (dCT) was estimated to be 1500-3800 IU/mg. However, when the duration of the hypocalcemic effect of dCT was taken into consideration, it was judged that dCT was approximately 2.4-6.2 times more potent than mammalian calcitonins, but about 2.3-3.5 times less active than other nonmammalian calcitonins.

The Relationship Between the Structure and Calcification of Dentin and the Role of Melatonin

The present study aimed to examine the relationship between the structure and composition of dentin and odontoblasts and the role of melatonin during the calcification process. The expression of MT1 and MT2 melatonin receptor was confirmed in the odontoblasts of the control group. In addition, the expression of MT1 was stronger than that of MT2. A strong expression of MT1 was detected in the odontoblasts in the melatonin-treated groups. MALDI-TOF MS analysis revealed that two peaks of 795 m/z and 818 m/z were found in dentin. These peaks increased commensurately with the amount of melatonin. The number and size of calcospherites in predentin increased in proportion to the concentration of melatonin. The degree of mineralization increased slightly in the melatonin-treated group using CMR analysis. Two peaks could be clearly detected in the melatonin-treated group at nighttime using X-ray diffraction analysis. Melatonin may participate in the dentin composition and the calcification mechanism of dentin.