INHIBITORY EFFECTS OF HISTAMINE ON CONTRACTION INDUCED BY TRANSMURAL STIMULATION IN RAT VAS DEFERENS

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The effect of histamine on the contractions induced by neuromuscular transmission in the isolated rat vas deferens was investigated. Histamine, 10^-6-10-4M, showed a dose-dependent and reversible inhibition of the induced contractions. When the frequency of stimulation was altered(2.5-20Hz), the inhibitory effect tended to be marked at the lower frequencied. Contractions caused by norepinephrine, 10^-5M, were unaffected by histamine, indicating that the inhibitory effect of histamine was not due to a reduced sensitivity of the effector cells to the transmitter. Cimetidine, 7×10^-5M, diminished the response to histamine but chlorpheniramine, 10^-6M, did not. The results suggest that the inhibitory effect of histamine is mediated via H₂-receptors probably located at the adrenergic nerve terminal.