Cardiac and vascular effects of diltiazem, dobutamine and amrinone, drugs used after myocardial revascularization

Evaluation of cardioprotection and bio-efficacy enhancement of stevioside and diltiazem in rats

Background

Cardiovascular diseases and resultant complications of cardio-therapeutic regimens are one of the leading causes of mortalities in developing countries. Diltiazem is a calcium channel blocker primarily used in treatment of supraventricular arrhythmias, systemic hypertension, and hypertrophic cardiomyopathy. Stevioside, the chief component of Stevia plant, is a natural sweetener that has significant therapeutic properties. Stevioside is a known bioenhancer that acts by synergizing pharmacological activities of other drugs. Present study was designed to evaluate cardioprotective activity of stevioside and possible bioenhancement upon co-administration with diltiazem. Standard cardiotoxicity models—isoproterenol-induced myocardial infarction and ischemia-reperfusion injury (IRI) through modified Langendorff setup was used to test this hypothesis. Rats were randomly divided into control groups (normal—physiological saline and toxic—isoproterenol, 150 mg/kg, s.c., and IRI induced in normal control animals) and treatment groups (diltiazem—17.5 mg/kg, p.o., stevioside—100 and 200 mg/kg, p.o. and combination groups). At the end of the treatment period, animals were sacrificed and biochemical, electrocardiographic, and histopathological changes were measured.

Results

Pre-treatment with stevioside prevented leakage of biomarkers and normalized serum and perfusate levels of CK-MB, CK-NAC, LDH, AST, and ALT enzymes. It displayed lipid-lowering effect on TC and TG levels dose dependently. STV also showed protective action on levels of tissue antioxidant enzymes (SOD and Catalase), electrocardiographic parameters (HR, RR, QRS, QT, PR), and heart tissue histopathology when compared to concurrent toxic control groups. Combination of stevioside (200 mg/kg) and diltiazem (17.5 mg/kg) exerted a more significant pharmacodynamic response, significantly restored biomarkers, antioxidants levels, and myocardial histology, and normalized electrocardiographic parameters.

Conclusion

Stevioside and diltiazem both displayed cardioprotective effect when given alone. Co-administration displayed improved restorative action on antioxidant status, biomarkers, electrocardiographic parameters, and histology.

Magnesium and diltiazem relaxes phenylephrine-precontracted rat aortic rings

Perioperative vasospasm during cardiovascular surgery is a challenging problem. Several vasodilator agents are frequently utilized for its prevention in surgical practice. Magnesium and diltiazem both have known potential vasorelaxant effects. We planned to compare the efficacy of diltiazem and magnesium in relieving phenylephrine-precontracted rat aortic rings. Ten young adult female Wistar albino rats weighing 230-260 g were used in this study. The aortic rings in the organ bath equilibrated and reached their baseline tension. Precontraction was induced by 0.001 mmol/l phenylephrine and cumulative concentration-relaxation curves were obtained by consecutively increasing the addition of either diltiazem (10(-6)-0.1 mmol/l) or magnesium (0.1-10 mmol/l). The mean maximal relaxation responses observed by diltiazem and magnesium on separate aortic rings were 90 ± 3 and 53 ± 2%, respectively. The calculated EC50 of diltiazem was 0.01035 mmol/l, whereas the EC50 of magnesium was 4.064 mmol/l (P < 0.05). Both magnesium and diltiazem produced vasorelaxation on phenylephrine-precontracted rat aortic rings in this study, but the potency of diltiazem regarding the EC50 value was significantly higher than that of magnesium. Magnesium could be a candidate together with diltiazem to inhibit vasospasm on arterial grafts during coronary bypass surgery.

Vasorelaxant effect of iloprost on isolated human internal mammary artery

In this study, vasodilator effect of iloprost on KCl-induced contraction in human internal mammary artery (IMA) was studied and compared with other vasodilators papaverin and diltiazem. Ring segments of IMA were studied in organ baths for measurement of isometric tension. After the tissues has reached their baseline tension, precontraction was induced by 100 mm KCl and cumulative concentration-relaxation was measured by the application of iloprost (10(-9)-10(-6) m), papaverine (10(-5)-10(-4) m), diltiazem (10(-9)-10(-4) m) or ethanol; a solvent for iloprost; alone. The maximal relaxation of IMA segments to iloprost was 13.5 +/- 2.2%. Iloprost caused significantly limited relaxation when compared with papaverin (106.0 +/- 2.9%) and diltiazem (93.6 +/- 2.5%) (P < 0.001). Papaverin produced the greatest maximal relaxation to KCl-induced contraction of IMA. The potency of iloprost (-log EC(50) = 6.59 +/- 0.19) was significantly higher than those of papaverine (-log EC(50) = 4.21 +/- 0.11) and diltiazem (-log EC(50) = 5.63 +/- 0.06) (P < 0.001). In addition, -log EC(50) of diltiazem was significantly greater than papaverin (P < 0.001). Iloprost appears to be more potent than those of papaverine and diltiazem but it was inefficient in maximal inhibition on KCl-induced contraction. Iloprost may have little benefit in KCl-related vasoconstriction on human IMA segments.