Specific 1,25-dihydroxyvitamin D₃ binding sites in choroid plexus

Quantitative autoradiographic analysis of [³H]1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) binding in vitamin D deficient mice provided evidence for high levels of specific binding in choroid plexus and, to a lesser extent, ventral hippocampus. Sucrose gradient analysis yielded a 3-4S peak of specific [³H]1,25(OH)₂D₃ binding in bovine choroid plexus, but not amygdala or hippocampus. Scatchard analysis of [³H]1,25(OH)₂D₃ binding in bovine choroid plexus yielded K_D = 0.23 ± 0.06 nM and N_max = 43.5 ± 0 fmol/g tissue (n = 5). This result indicates the presence of significant receptor-like [³]H]1,25(OH)₂D₃ binding sites in the choroid plexus and, thus suggests roles for this hormone in regulating the entry of calcium into the brain and/or in the central regulation of calcium homeostatis.