Parathyroid hormone PTH is secreted by chief cells of the parathyroid gland and results in increased calcium and decreased phosphate in serum. Secretion is stimulated by decreased ionized calcium, decreased calcitriol, magnesium, dopamine, PGE 2 .
Secretion is inhibited by increased ionized calcium and increased calcitriol.
Parathyroid hormone has 2 primary sites of action, the kidney and the bone. In the kidney, PTH enhances renal resorption of calcium in the distal tubules, collecting ducts and ascending limb of the loop of Henle and promotes excretion of phosphate in the proximal renal tubules. Parathyroid hormone can be measured by immunoassay. Interpretation of PTH levels should be done concurrently with knowledge of ionized calcium values, e.g. a normal PTH concentration in an animal with a high ionized calcium is inappropriate and compatible with a diagnosis of primary hyperparathyroidism. Parathyroid hormone related protein is produced by several different cell types including lymphocytes, squamous epithelium, endocrine glands, bone, skeletal and smooth muscle and the kidney.