A 50-year-old woman with primary hyperparathyroidism has serum calcium of 12.8 mg/dL and markedly elevated PTH. PTH activates Gs-coupled receptors on renal tubular cells. Which second messenger mediates the renal effects of PTH, including increased calcium reabsorption and decreased phosphate reabsorption?
- A cAMP ✓
- B IP3
- C cGMP
- D Calcium ions
Correct answer: A. cAMP
Explanation
PTH binds the PTH1R, a Gs-coupled GPCR. Activation of adenenylyl cyclase increases cAMP, which activates PKA. PKA phosphorylates downstream targets to increase calcium reabsorption in the distal tubule and decrease phosphate reabsorption in the proximal tubule. PTH can also activate Gq and the IP3/DAG pathway in some contexts, but cAMP is the principal second messenger for its renal tubular effects.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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