Effect of histamine and H1- and H2-agonists on the fractional outflow of radioactivity from the rat vas deferens preloaded with [3H]-noradrenaline

Histamine and relatively selective H₁- and H₂-receptor agonists caused a concentration-dependent increase in the fractional outflow of radioactivity from the rat isolated vas deferens preloaded with labelled noradrenaline. The evoked fractional outflow of radioactivity was not preferentially associated with either H₁- or H₂-selective agonists, nor was it related to the known potencies of the agonists within each group. The evoked fractional outflow caused by all compounds studied was independent of the extracellular Ca²⁺ concentration. The study cautions against ascribing all the effects of histamine analogs to their respective histamine receptor stimulation.