The unsettled science of nonrenal calcitriol production and its clinical relevance
J. Wesley Pike, Mark B. Meyer
Abstract
The primary function of vitamin D in higher vertebrates is to regulate mineral homeostasis through direct actions on intestinal calcium and phosphate absorption, bone mineral resorption, and renal mineral reabsorption Vitamin D itself is inactive and must undergo sequential modification via two specific chemical reactions, first in the liver to 25(OH)D3 by the enzyme CYP2R1, and then in the kidney to 1,25-dihydroxyvitamin D3 by the tightly regulated enzyme CYP27B1 Calcitriol, whose level is also modulated via renal CYP24A1-mediated degradation, is then secreted into the blood as an active endocrine hormone and delivered to distant target tissues Here, Pike and Meyer discuss the importance of adequate blood levels of vitamin D and the models for characterizing features of NRTC calcitriol production