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Background and Objective: Hypothyroidism decreases cardiac contractility and heart rate. Since cardiac function is also modulated by diazepam, the aim of this study was to investigate the direct effect of diazepam on the isolated hypothyroid rat heart. Materials and Methods: This experimental study was conducted on 30 rats in four groups (control, hypothyroid, control diazepam and hypotyroid+diazepam). According to Langendorff method, isolated hearts were retrogradly perfused with Krebs solution and passed 3 stages of baseline, ischemia and reperfusion. Cardiac parameters including left ventricular developed pressure, Heart Rate (HR) and Rate Pressure Product (RPP) were calculated. Results: At baseline, heart function significantly decreased in hypothyroid group compared with control and control diazepam groups (P=0.01 & P=0.001 respectively). Percentage decline of HR and RPP at baseline stage after diazepam administration, was significantly different in the control diazepam and hypothyroid+diazepam groups (P=0.001 & P=0.002 respectively). Recovery percentage of RPP in reperfusion stage significantly increased in hypothyroid group (% 60±5) compared with control (% 38±5) and in hypotyroid+diazepam group (% 87±8) compared with hypothyroid group (%60±5), (P<0.0001 & P=0.02, respectively). Conclusion: Administration of diazepam exacerbates the effect of hypothyroidism at baseline and reperfusion stages in rats. In other words, diazepam perfusion leads to greater decline of hypothyroid rat heart function at baseline and higher recovery percentage at the reperfusion stage. These effects can be due to the common effects of hypothyroidism and diazepam on the L-type calcium channels or the amount of oxygen consumption in rats.

Keywords: Hypothyroidism, Isolated heart, Diazepm, Ischemia- reperfusion, Rat, Langendorff

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