Figure 5.

Renal Cyp27b1 gene expression and serum 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) level in response to long-term low dietary calcium (Ca) intake. Four-month-old control (Ctrl), whole-intestine Vdr knockout (WIK), and large-intestine Vdr knockout (LIK) mice received tamoxifen (0.05 mg/g BW, intraperitoneally, 5 days) to induce recombination of the floxed Vdr alleles. Afterward, mice were randomly assigned to an AIN93M diet with either 0.5% or 0.2% Ca. After 16 weeks, A, renal Cyp27b1 messenger RNA (mRNA) levels were assessed by real-time polymerase chain reaction and B, serum 1,25(OH)₂D₃ level by enzyme immunoassay. AU, arbitrary units. For Cyp27b1 mRNA, analysis of covariance (ANCOVA) was conducted on log10-transformed data without covariates. For PCo, ANCOVA was conducted on square-root–transformed data without covariates. Data derived from each genotype and diet group are presented as box plots (n = 10-12 per group) with individual data points represented by ▴ = males, ● = females, and the median represented by a line. Multiple comparisons were made by the Tukey-Kramer test with P values for the effect diet within each genotype group as indicated. The value for 0.2% Ca-fed WIK mice was higher than all other groups (P < .0001 for Kd Cyp27b1, P < .005 for serum 1,25(OH)₂D₃).