Histamine H_1 Receptor-induced Contraction in Rat Blood Vessels

Rat blood vessels were reported not to constrict to histamine, and histamine-induced contraction at high concentration was mediated through α_1-adrenoceptors. In the present study, it was shown that rat arteries and veins constricted to histamine at low concentration (0.1-100μM) in a non-cumulative manner and that this contraction immediately desensitized. A histamine H_1 receptor antagonist, mepyramine, abolished this transient contraction completely, whereas cimetidine, phentolamine, reserpine and tetrodotoxin failed to inhibit the contraction, indicating that the contraction is mediated directly through H_1 receptor. H_1 receptor mRNA expression level detected by RT-PCR was quite parallel to H_1 receptor-mediated contraction in the vessels