Figure 6.

Stimulators and sites of 1α,25(OH)₂D₃ synthesis in the kidney of normocalcemic and hypocalcemic rats. CT stimulates CYP27B1 in the proximal straight tubules (PST) of normocalcemic rats. In contrast, PTH increases CYP27B1 in the proximal convoluted tubules (PCT) of rats fed a vitamin D-deficient or a vitamin D-replete low-Ca diet, which show severe secondary hyperparathyroidism. Glm, glomeruli; cTAL, cortical thick ascending limb; DCT, distal convoluted tubules; CCD, cortical collecting duct.