A 40-year-old man with primary adrenal insufficiency presents in shock with a systolic BP of 70 mm Hg unresponsive to repeated fluid boluses. Norepinephrine infusion produces a minimal pressor response. After hydrocortisone is given, the same dose of norepinephrine restores blood pressure. Which physiologic principle explains this?
- A Cortisol directly activates vascular adrenergic receptors
- B Hydrocortisone increases circulating catecholamine half-life
- C Cortisol is permissive for the vascular actions of catecholamines ✓
- D Cortisol stimulates renin release, restoring volume acutely
Correct answer: C. Cortisol is permissive for the vascular actions of catecholamines
Explanation
Glucocorticoids exert a permissive effect on catecholamine action. They maintain expression of adrenergic receptors and permit downstream signaling such that alpha-mediated vasoconstriction works normally. Without cortisol, catecholamines fail to raise vascular tone adequately, which is why refractory shock in adrenal crisis responds dramatically once hydrocortisone is given. Cortisol does not bind adrenergic receptors itself, and neither altered catecholamine clearance nor acute renin effects explain the immediate restoration of pressor sensitivity.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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