A 60-year-old man started on enalapril develops recurrent episodes of lip and laryngeal swelling without urticaria. Which property of bradykinin best explains this adverse effect?

• A It is synthesized exclusively by mast cells through the cyclooxygenase pathway
• B It is a terminal complement component that generates the membrane attack complex
• C It acts only on H1 receptors located on smooth muscle
• D It causes vasodilation and increased permeability and is normally degraded by ACE ✓

Explanation

Bradykinin, generated from high molecular weight kininogen by kallikrein after factor XII activation, increases vascular permeability, causes vasodilation and stimulates pain fibers. It is rapidly inactivated by angiotensin converting enzyme (kininase II), so ACE inhibitors raise bradykinin levels and produce angioedema. Kinins are unrelated to mast cell arachidonate products, histamine receptors or complement.

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.