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What is The following statements regarding histamine are true, except: and explain in detail?
Histamine characteristically causes dilation of the finer blood vessels and tends to constrict the larger blood vessels, it is used as a positive control injection during allergy skin testing. It can stimulate various nerve endings and in the dermis it evokes pain and sometimes itching. Contraction of bronchial smooth muscles is due to activation of H1 receptors and relaxation is due to activation of H2 receptors. Hence, blockade of H2 receptors can potentiate histamine-induced bronchospasm.