Effects Of Dimethylamiloride And Amiloride On Cardiac Function And Myocardium Inotropism In Mature And Immature Rat Isolated Hearts And Its Primary Mechanism

AIM: To study effects of DMA and AM on cardiac function in mature and immature rat isolated hearts and myocardial contractility in mature and immature rat papillary muscle of left ventricular and search for the probable mechanism of DMA.METHODS: With Langendorff perfusion, we observed DMA and AM induced changes of the indexes reflecting cardiac function in immature rat hearts and compared with mature rat hearts. With isolated papillary muscle perfusion, developed tension was measured to estimated the inotropic action of DMA and AM on immature cardiac tissue and compared with mature cardiac tissue. By using calcium channel blocker and sodium calcium exchanger (NCX) blocker, we explore the probable mechanism of effects of DMA on immature rat cardiac function and myocardiac contractility of papillary muscle.RESULTS: (1) 1. With Langendorff-perfused immature rat hearts, DMA(1⁵μmol·L^-1)enhances cardiac function and exerts positive effects on LVSP-LVDP,+dp/dtmax,-dp/dtmax. In them, the effects of 2μmol·L^-1's DMA is most significant. 2. DMA(1²Î¼mol·L^-1)can improve developed tension of isolated immature isolated rat papillary muscle. 3. In mature rat hearts and myocardium, DMA shows similar pharmacologic profile but less sensitive than in immature rat hearts and myocardium. (2) 1. AM(0.05¹mmol·L^-1) can decline cardiac function of isolated immature rat hearts. 2. AM(0.05¹mmol·L^-1)can decline developed tension of isolated immature isolated rat papillary muscle. 3. In mature rat hearts and myocardium, AM show similar pharmacologic profile, but less sensitive than in mature rat. (3). Probable mechanism: The effects of DMA on cardiac function in immature rat isolated hearts and myocardium inotropism in immature rat isolated papillary muscle of left ventricle cannot be blocked by nicardipine --one of calcium channel blocker,but can be blocked by NiCl₂--one of sodium calcium exchanger (NCX) blockers.CONCLUSION: 1. DMA can enhances cardiac function in immature(1⁵μmol·L^-1) and...