In vivo receptor binding of novel α₁-adrenoceptor antagonists for treatment of benign prostatic hyperplasia

New types of α₁-adrenoceptor antagonists (tamsulosin, KMD-3213 and JTH-601) are currently receiving a great deal of attention, especially in terms of developing effective therapeutic agents to treat bladder outlet obstruction with less side effects, such as postural hypotension, in patients with benign prostatic hyperplasia (BPH). In vivo α₁-adrenoceptor binding properties of these antagonists in prostate and other tissues of rats were examined. In, venous injections of tamsulosin, KMD-3213 and JTH-601 inhibited dose-dependently in vivo specific [³H]tamsulosin binding in various tissues. Ratios of ID₅₀(aorta) to ID₅₀(prostate) of KMD-3213 and JTH-601 were greater than those of tamsulosin and prazosin. Further, the ratios of ID₅₀(spleen) to ID₅₀(submaxillary gland) of these drags were greater than that of prazosin. Following intravenous injections of [³H]KMD-3213 in rats, the amount of specific binding in prostate was significantly greater than that of [³H]prazosin, but that in aorta or spleen was much smaller. Interestingly, [³H]JTH-601 showed little in vivo specific binding in aorta. These data suggest that KMD-3213 and JTH-601 exhibit higher affinity to α₁- adrenoceptors in prostate and submaxillary gland than in vascular tissues in vivo.