Ex Vivo and in Vivo α_1-Adrenoceptor Binding Characteristics of a Novel α_<1L>-Adrenoceptor Antagonist, JTH-601,in Rat Tissues

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In vitro, ex vivo and in vito α_1-adrenoceptor binding of JTH-601 (3{N-[2-(4-hydroxy-2-isopropyl-5-methylphenoxy)ethyl]-N-methylaminomethyl}-4-methoxy-2,5,6-trimethyl-phenol hemifumarate), a novel α_<1L>-adrenoceptor antagonist, in rat tissues was investigated. JTH-601 competed in a concentration-dependent manner with [^3H]prazosin for binding sites in the prostate, submaxillary gland and spleen of rats in vitro, and the inhibitory effect was not largely different among these tissues, as shown by the K_i values of 2-3nM. At 0.25,0.5 and 3 h after oral administration of JTH-601 (6.5 μmol/kg) in rats, there was a significant (57,64 and 28%, respectively) increase in the apparent dissociation constant (K_d) for prostatic [^3H]prazosin binding, compared to the control value. The administration of a higher dose (21.8 μmol/kg) of this agent produced greater (67-99%) increase in K_d values for prostatic [^3H]prazosin binding at 0.5-12 h later. Similar significant increases in K_d values, as with the prostate, were seen in the submaxillary gland and heart 0.25-12 h after the oral administration of JTH-601 (6.5 and 21.8 μmol/kg), but significant increases in the spleen and cerebral cortex were seen only at 0.25-3 h and 0.5 h, respectively. At 10 min of i.v. injection of [^3H]JTH-601 in rats, in vivo specific binding was observed in the prostate, cerebral cortex, submaxillary gland, spleen and heart but not in the aorta. The binding in the prostate, submaxillary gland and heart, but not in the cerebral cortex and spleen, lasted until 120 min. It is concluded that JTH-601 may exert a considerably sustained blockade of α_1-adrenoceptors in the prostate of rats. This finding may be important in characterizing the therapeutic effect of JTH-601 for bladder outlet obstruction in patients with benign prostatic hyperplasia.
公益社団法人日本薬学会の論文
1999-07-15

Ex Vivo and in Vivo α_1-Adrenoceptor Binding Characteristics of a Novel α_<1L>-Adrenoceptor Antagonist, JTH-601,in Rat Tissues

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