Modulation of plasma 1,25-dihydroxyvitamin D in man by stimulation and suppression tests

In normal volunteers infusion of parathyroid extract raised plasma 1,25-dihydroxyvitamin D (1,25-[OH]2D) levels by 80% (peak 8--40 h after infusion) without producing any significant change in plasma calcium, phosphate, or magnesium. An oral calcium load suppressed plasma 1,25-(OH)2D to 63% of control values within 48--72 h. These responses will be useful in the diagnosis and management of disturbances of calcium and mineral metabolism in which vitamin D metabolism is abnormal.