Which of the following mediate Lewis triple response?: (A) Axon reflex, (B) Histamine release from mast cells, (C) Injury to endothelium, (D) None of the above
Answer is B. Lewis triple response illustrates the effect of histamine on vascular smooth muscle, vascular endothelium and sensory nerve endings. Intradermal injection of histamine produces 3 distinct effects: Dilatation of capillaries in the immediate vicinity of injection resulting in a flush. Dilatation of aerioles resulting in an irregular red flare over an area wider than due to capillary dilatation. Wheal appearing in the area of capillary dilatation. In addition to wheal, flush and flare, transient pain and itching result from effect of histamine on sensory nerve endings.