Proximal renal tubular acidosis in vitamin D deficiency rickets.

A proximal renal tubular acidosis (RTA) is the mechanism underlying the systemic acidosis found in vitamin D deficiency rickets. Acidotic subjects have high levels of PTH. In non-acidotic subjects proximal bicarbonate wasting can be induced by exogenous PTH injection. Carbonic anhydrase activity is not involved in this process. Calcium infusion is able to suppress both the spontaneous and the PTH-induced bicarbonate leak. The development of RTA in vitamin D deficiency is related to a particular equilibrium between two antagonizing factors at tubular level, parathyroid hormone and calcium.