PTH and secondary hyperparathyroidism: Independent of the VDR KO mouse strain, some data indicated that it is possible to prevent secondary hyperparathyroidism by feeding the RD (Li et al., 1998; Kaneko et al., 2011), while other and own data showed that VDR KO mice fed the RD had extremely high concentrations of circulating PTH when compared with WT mice (Song et al., 2003; Shiizaki et al., 2009; Kühne et al., 2016).