Negligible potency of acetylcholine in increasing vascular permeability

As acetylcholine (ACh) is claimed to be a possible mediator of cholinergic urticaria, the potency of acetylcholine (ACh) in increasing vascular permeability was tested by skin perfusion technique in rats and by dye extraction method from the skin of rabbits. The potency of vascular permeability increase of ACh was much lower than that of histamine (Hist) and bradykinin (BK) in rats and rabbits. The higher dose of ACh (10 mg in 0.1 ml of saline), however, produced slight increase of vascular permeability in rabbits, which was inhibited by the antihistamine, pyrilamine maleate. Furthermore, ACh did not potentiate the responses to BK or Hist, when injected simultaneously. It seems unlikely that ACh did increase or potentiate vascular permeabilitay in physiological doses.