Abstract
The relationship between α<sub>1</sub>-adrenoceptor binding in rat tissues and pharmacodynamic effects of continuous infusion of KMD-3213 was examined. In vivo specific binding of [<sup>3</sup>H]KMD-3213 after continuous intravenous infusion of the ligand (100 pmol/kg/min for 10 min, followed by 30 pmol/kg/min for 60 or 90 min) differed largely among the tissues examined. Specific binding of [<sup>3</sup>H]KMD-3213 in aorta, heart, lung, and kidney was not different in terms of infusion time in the case of continuous infusion for 10, 70 and 100 min, whereas the binding in prostate, vas deferens, and submaxillary gland by 70- and/or 100-min infusion was significantly greater than that by the 10-min infusion. A similar extent of specific binding in the prostate was observed by the infusion (100 min) of a three-fold higher dose of [<sup>3</sup>H]KMD- 3213. Continuous intravenous infusion of KMD-3213 (100 pmol/kg/min for 10 min, followed by 30 pmol/kg/min) for 70 or 100 min significantly reduced the phenylephrine-induced increase in the mean blood pressure and that in the intraurethral pressure of anesthetized rats. Extent and time course of the KMD-3213 effect reduction in the phenylephrine-induced increase in intraurethral pressure were closely associated with those in prostatic [<sup>3</sup>H]KMD-3213 binding after continuous infusion of the corresponding dosage of the radioligand. The reduction in the phenylephrine-induced increase by the infusion of a three-fold higher dose of KMD-3213 was significantly greater in the case of the intraurethral pressure than in that of the mean blood pressure, thereby suggesting a greater selectivity for the α<sub>1</sub>-adrenoceptor in the lower urinary tract than for that in the vascular tissue. In conclusion, the present study has shown that specific binding of [<sup>3</sup>H]KMD-3213 in the rat prostate after the continuous intravenous infusion of the radioligand may be closely associated with the pharmacological effect of this drug on the lower urinary tract.
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