Species differences in histamine receptors in the seminal vesicle

Histamine and specific H1- and H2-receptor agonists and antagonists in conjunction with phentolamine and (or) reserpine pretreatment were used to characterize histamine receptor(s) in the seminal vesicle of rat and guinea pig. Stimulation of H1 receptors produced a contraction whereas that of H2 receptors inhibited the contraction evoked by electrical field stimulation. The rat seminal vesicle was relatively refractory to the action of histamine and selective H1- or H2-receptor agonists. The evidence, however, does not preclude the presence of a small population of H2 receptors in this preparation. The guinea pig seminal vesicle contained both H1 and H2 receptors but the H1 receptors were dominant. The presence of H2 receptors in the guinea pig seminal vesicle could be demonstrated either with histamine after blockade of the dominant H1 receptor (mepyramine) or with dimaprit, a selective H2-receptor agonist. In a previous study, we reported that the mouse seminal vesicle contained an inhibitory H2 receptor but was virtually devoid of an excitatory H1 receptor. Data from that study and the present one indicate that there are marked qualitative and quantitative differences in the distribution of the two types of histamine receptors in the seminal vesicles of different species.