Fig. 2. Role of renal calcium leak in essential hypertension. Hypertensives exhibit an increase in urinary calcium losses, which is exacerbated on high salt diets. This results in a transient decrease in serum ionized Ca²⁺. The parathyroid gland responds to this decrease with the release of parathyroid hormone (PTH), which activates the renal 1--hydroxylase, resulting in increased 1,25-(OH)₂-D production. 1,25-(OH)₂-D serves as a stimulus to increase vascular smooth muscle intracellular Ca²⁺.