Species differences in histamine receptors in the vas deferens
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Histamine, specific H1-and H2-receptor agonists in conjunction with specific H1-and H2-receptor antagonists and other types of classical antagonists were used to characterize histamine receptors in the vasa deferentia of mice, rats and guinea pigs. The H1-receptor mediates contraction while the H2-receptor produces inhibition. There were marked qualitative and quantitative differences in the distribution of the two types of histamine receptors in the vas deferens of different species. Results indicate that mouse and rat vas deferens contain an inhibitory H2-receptor, but virtually no excitatory H1-receptor. In contrast, guinea pig vas deferens contained an excitatory H1-receptor but was essentially devoid of an inhibitory H2-receptor. The rank order of relative potencies of various agonists as well as the calculated pA2 values of cimetidine in the mouse and rat vas deferens suggest that the two species probably have the same H2-receptor. High concentrations of histamine and 2-methyl histamine have a stimulant action in the mouse and rat vas deferens which was secondary to release of endogenous noradrenaline rather than to the stimulation of an excitatory H1-receptor.
KeywordsHistamine Noradrenaline Cimetidine Rank Order Quantitative Difference
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