AGT and chronic kidney disease: This correlation was recently confirmed in a large cohort study of CKD patients by Forman et al. They examined the relation between plasma 25-hydroxyvitamin D and elements of the RAS in 184 normotensive individuals in high sodium balance; these included circulating levels of plasma renin activity and Ang II, and the renal plasma flow response to infused Ang II, which is an indirect measure of the intrinsic RAS activity in the kidney.