The effect of elevated prolactin levels on plasma 1,25-dihydroxyvitamin D and intestinal absorption of calcium.

Because of evidence in experimental animals that prolactin stimulates production of 1,25-dihydroxyvitamin D, we evaluated several indices of calcium metabolism in patients who had hyperprolactinemia due to functioning pituitary adenomas and in normal age-matched controls. Plasma levels of 1,25-dihydroxyvitamin D in hyperprolactinemic patients were in the normal range (15 to 24 pg/ml versus 15 5o 75 pg/ml in controls). Intestinal absorption of calcium, plasma levels of immunoreactive parathyroid hormone, and serum values for calcium, phosphorus, and alkaline phosphatase were similar in patients and controls. We conclude that prolactin probably has no effect on plasma 1,25-dihydroxyvitamin D levels or calcium metabolism in man.