PHARMACOLOGICAL AND PHARMACOKINETIC CHARACTERISTICS OF YM435, A NOVELDOPAMINE DA(1)-RECEPTOR AGONIST, IN ANESTHETIZED DOGS

Time-course of plasma concentration of unchanged drug of the dopamine DA(1)-receptor agonist enyl)-7,8-dihydroxy-1,2,3,4-tetrahydroisoquinol ine hydrochloride hydrate (YM435), and its effects on blood pressure a nd renal blood flow were investigated in anaesthetized dogs. Continuou s intravenous infusion of YM435 (0.1-3 mu g kg(-1) min(-1)) rapidly in creased renal blood flow and lowered blood pressure in a dose-dependen t manner. These effects remained generally stable throughout the infus ion period. Following the start of infusion, plasma concentration of u nchanged drug also rose rapidly and dose-dependently and remained virt ually constant throughout the infusion period. A significant correlati on was observed between log YM435 plasma concentration and the increas e in renal blood flow (r = 0.93, P < 0.0001) and between the former an d the reduction in blood pressure (r = 0.93, P < 0.0001). The present results indicate that YM435 produces renal vasodilatation and lowering of blood pressure in a dose-dependent manner and with rapid onset fol lowing continuous intravenous infusion, and that these effects are gen erally stable throughout the period of infusion. These haemodynamic ef fects of YM435 were in good agreement with the time-course of plasma c oncentration of unchanged drug.