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.