A 30-year-old man with a craniopharyngioma compressing the hypothalamus presents with ACTH deficiency. He has normal cortisol response to exogenous ACTH stimulation. During a CRH stimulation test, his ACTH response is blunted. Which hypothalamic neuropeptide normally acts synergistically with CRH at the corticotroph to amplify ACTH release, and its deficiency contributes to this blunted response?

• A Growth hormone-releasing hormone (GHRH) acting via Gs-coupled receptors
• B Arginine vasopressin (AVP) acting via V1b receptors ✓
• C Somatostatin acting via Gi-coupled receptors
• D Gonadotrophin-releasing hormone (GnRH) acting via Gq-coupled receptors

Explanation

AVP from parvocellular PVN neurons potentiates CRH-induced ACTH secretion by acting on V1b receptors on corticotrophs, which are Gq-coupled and synergize with CRH-mediated cAMP signaling. In hypothalamic ACTH deficiency, chronic lack of both CRH and AVP leads to corticotroph atrophy, producing a blunted ACTH response to CRH alone. GHRH and GnRH do not regulate corticotrophs. Somatostatin inhibits rather than amplifies ACTH release.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.