Synergisms of cardiovascular effects between iptakalim and amlodipine, hydrochlorothiazide or propranolol in anesthetized rats

The primary object of this fundamental research was to survey the synergistic cardiovascular effects of iptakalim, a novel ATP–sensitive potassium channel(KATP) opener, and clinical first-line antihypertensive drugs, such as calcium antagonists, thiazide diuretics and β receptor blockers by a 2×2 factorial-design experiment. It would provide a theoretical basis for the development of new combined antihypertensive therapy program after iptakalim is applied to the clinic. Amlodipine besylate, hydrochlorothiazide and propranolol were chosen as clinical first-line antihypertensive drugs. Blood pressure, heart rate(HR) and cardiac functions were observed in anesthetized normal rats by an eightchannel physiological recorder. The results showed that iptakalim monotherapy in a low dose could produce significant antihypertensive effect. There was no interaction between iptakalim and amlodipine on the maximal changes of systolic blood pressure(SBP), diastolic blood pressure(DBP), mean arterial blood pressure(MABP), the left ventricular systolic pressure(LVSP), and the left ventricular end-diastolic pressure(LVEDP)(P>0.05). However, the effects of combination iptakalim/amlodipine on the maximal changes of SBP, DBP, MABP, LVSP and LVEDP were more obvious than those of iptakalim or amlodipine monotherapy. And there was strong positive interaction between iptakalim and amlodipine on the maximal changes of HR(P>0.05). According to the maximal changes of DBP, MABP, LVSP and LVEDP(P<0.05) of combination iptakalim with hydrochlorothiazide, there was strong positive interaction between them. But there was no interaction between iptakalim and hydrochlorothiazide on the maximal drop of SBP and HR(P>0.05). According to the maximal drops of DBP, MABP of combination iptakalim with propranolol, there was strong positive interaction between them(P<0.05). But there was no interaction between iptakalim and propranolol on the maximal changes of SBP, LVSP,LVEDP and HR(P>0.05). In conclusion, it was the first time to study the effects of amlodipine, hydrochlorothiazide or propranolol, which had different mechanisms of action from iptakalim, on cardiovascular effects of iptakalim in anesthetized normal rats. This study proved that the combination of iptakalim with hydrochlorothiazide or propranolol respectively had significant synergism on lowering blood pressure, while the combination of iptakalim/amlodipine had additive action on lowering blood pressure. Meanwhile the antihypertensive effect was explicit, stable and long-lasting. Iptakalim thus appears suitable for the clinical treatment of hypertensive people who need two or more kinds of antihypertensive agents.