Parathyroid hormone (PTH) is an 84-amino acid polypeptide hormone produced by the chief cells of the parathyroid glands. As the principal regulator of calcium homeostasis, PTH maintains extracellular calcium concentrations through coordinated actions on bone, kidney, and intestine. The hormone is synthesized as a 115-amino acid preprohormone that undergoes proteolytic processing to generate the biologically active peptide. PTH secretion is tightly controlled by extracellular calcium through the calcium-sensing receptor, ensuring precise regulation via a negative feedback mechanism.
Key Functions and Regulatory Mechanisms
PTH mediates its physiological effects through the PTH/PTHrP receptor, a class B G-protein-coupled receptor expressed predominantly in bone and kidney. Continuous elevation of PTH stimulates osteoclast-mediated bone resorption, releasing calcium and phosphate into the bloodstream. In the kidney, PTH promotes calcium reabsorption while reducing phosphate reabsorption and enhances the synthesis of active vitamin D, thereby increasing intestinal calcium absorption. PTH secretion is regulated by circulating calcium, phosphate, and vitamin D levels.
Research Applications and Clinical Significance
- Research applications: PTH expression and localization are commonly investigated using immunohistochemistry, immunofluorescence, Western blotting, ELISA, and fluorophore-conjugated antibodies.
- Clinical relevance: PTH measurement plays a central role in diagnosing hyperparathyroidism, characterized by elevated PTH and hypercalcemia, and hypoparathyroidism, which results in PTH deficiency and hypocalcemia.
- Therapeutic importance: Understanding PTH physiology supports the development and clinical application of treatments including parathyroidectomy, calcimimetics, and PTH-based anabolic therapies for osteoporosis.