Blockade of 5-hydroxytryptamine-induced responses of rat seminal vesicle by lithium-possible mediation through calcium exchange.

Effect of lithium on the contractile responses of rat isolated seminal vesicle to 5-hydroxytryptamine (5-HT) were investigated by varying the Ca++ and Mg++ concentrations of the incubation medium in the absence and presence of EDTA. Preparations incubated in excess Ca++ (4.2 mM) or in Ca++-free Krebs solution showed decrease in sensitivity to 5-HT, whereas the responses to 5-HT were potentiated in Mg++-free incubation media and reduced in media containing excess Mg++. Rezerpinization failed to induce supersensitivity to 5-HT in any Mg++ concentration in the medium. However, reserpinized tissue in Mg++-free solution with EDTA showed increased sensitivity to 5-HT. Li+ inhibited responses to 5-HT. The inhibitory action of Li+ was augmented in medium lacking in Ca++ and was antagonized in media containing excess Ca++ (4.2mM). Li+ reduced the sensitivity and decreased maximum responses to 5-HT in any Mg++ concentration in the medium. In the presence of EDTA, the inhibition observed with Li+ in excess Mg++ (3.6 mM) medium was comparatively much less in both non-reserpinized and reserpinized preparations. Thus Li+ may be inhibiting responses to 5-Ht by block of influx of Ca++ or delayed efflux of Ca++ or inhibition of uptake of Ca++ or a combination of two or more of these effects.