副甲状腺ホルモンとビタミンDのモルモット腎遠位曲尿細管における相互作用に関する定量細胞化学的研究
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概要
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The distal convoluted tubule of the mammlian kidney has been demonstrated to be a target organ for both parathyroid hormone (PTH) and 1,25-dihydroxycholecalciferol (1,25-(PH)_2D_3). In the present study, the interaction of PTH and 1,25-(OH)_2D_3 on glucose-6-phosphate dehydrogenase (G6PD) activity in the tubule was studied in vitro. The influence of vitamin D_3 depletion and repletion in guinea pigs in vivo on the cytochemicalbioassay for PTH was also examined. G6PD activity was measured by quantitative cytochemistry. G6PD activity decreased to the stable "basal" level 5 hours after the initiation of the maintenance culture of the kidney segments. The time-course study in vitamin D-depleted animals showed that the exposure of the kidney segments to bPTH-(1-84) induced cyclic changes of G6PD activity beginning with an increase from the "basal" level. The cycle lengths of the changes were shortened as the concentrations of PTH were increased from 0.001 to 10 pg/ml. When the kidney segments were incubated with 1,25-(OH)_2D_3 during the maintenance culture, the values of the "basal" activity were increased in proportion to the concentrations. In the presence of 1,25-(OH)_2D_3, the cycle lengths of the changes of G6PD activity elicited by PTH were shorter than those in the absence of the active vitamin D. Treating the kidney segments with cycloheximide inhibited the forementioned functions of 1,25-(OH)_2D_3. Chronic physiological repletion of vitamin D_3 or injection of large doses of vitamin D_3 50 hours before sacrifice increased the "basal" activity, similar to the effect of incubating the segments with 1,25-(OH)_2D_3 in vitro. These observations suggest that PTH and active vitamin D appear to be closely related in the regulation of G6PD activity in the distal covoluted tuble both in vitro and in vivo.
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