Which of the following correctly describes the mechanism by which somatostatin inhibits GH release from the anterior pituitary?

• A Activates Gq protein increasing IP3 and causing Ca2+ release from ER
• B Directly antagonizes GHRH at the GHRH receptor on somatotrophs
• C Stimulates somatostatin receptors on hypothalamic neurons to reduce GHRH synthesis
• D Blocks Gs protein, reducing cAMP and inhibiting voltage-gated Ca2+ channels in somatotrophs ✓

Explanation

Somatostatin (SRIF) acts on SSTR2 and SSTR5 receptors coupled to Gi proteins, which inhibit adenylyl cyclase (reducing cAMP) and also reduce intracellular Ca2+ by activating K+ channels and inhibiting voltage-gated Ca2+ channels — together suppressing GH exocytosis. It does not directly block GHRH receptors but acts through a separate Gi-mediated pathway. This dual mechanism of reducing cAMP and Ca2+ makes somatostatin a potent GH inhibitor.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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