Within minutes of a mosquito bite, a wheal forms at the site. The vascular change responsible is increased permeability of postcapillary venules through retraction and contraction of endothelial cells opening intercellular gaps. Which mediator produces this response?
- A Leukotriene C4 acting on venules over several hours
- B Histamine binding to H1 receptors on venular endothelium ✓
- C Thrombin causing direct endothelial cell necrosis
- D VEGF-induced cytoskeletal rearrangement lasting days
Correct answer: B. Histamine binding to H1 receptors on venular endothelium
Explanation
Histamine released from mast cells binds H1 receptors on postcapillary venular endothelium and causes rapid actinomyosin-mediated contraction, producing the immediate transient response that peaks within 30 minutes and lasts up to an hour. Leukotrienes C4 and D4 also increase permeability but produce a prolonged (several hour) response rather than the immediate one described here.
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.