Hematological and cardiac effects of excess zinc in rats

ABSTRACT

In this work administration of zinc sulphate at a dose of 20 mg/kg/day. 6 days/week for 4 successive weeks, resulted in significant decrease in RBCs count, hemoglobin content, hematocrit value and mean corpuscular hemoglobin concentration in zinc treated group compared to control group. Biochemical studies showed significant decrease in plasma triglyceride, and malondialdehyde levels in zinc treated group compared to control group. However, non significant difference was found between the two groups as regards plasma zinc level. ECG study demonstrated significant increase in heart rate [HR] in zinc treated group compared to control group. This was accompanied by shortening of QRS and prolongation in Q-Tc durations in zinc treated group compared to control group. In vitro study of isolated hearts perfused in a Langendorff preparation, significant increase in basal HR was shown in zinc treated group compared to control group. The maximal HR upon isoproterenol infusion [ISU], when expressed as percentage ratio from baseline values, showed significant decrease in zinc treated group compared to control group. As regards baseline peak tension [PT] and peak tension/left ventricular weight [PT/LV,], significant increase was found in zinc treated group compared to control group. Also, the PT maximal response upon ISU infusion, either absolute or upon correction of left ventricular weight, showed significant increase in zinc treated group. Significant shortening in baseline time to peak tension [TPT] and half relaxation time [l/2RT,] were noticed in zinc treated group compared to control group. However, basal myocardial flow rate [MFR] as well as MFR/L V showed non significant difference between the 2 studied groups. Post ischemic reperfusion responses showed non significant difference as regards HR between the 2 studied groups. The recovery of PT and PT/LV were significantly higher at 20, 25, and 30 minutes of reperfusion in zinc treated group compared to control group. As regard TPT reperfusion values, significant prolongation at 10 minute was noticed in zinc treated group compared to control group. However 1/2RT, MFR and MFR/LV reperfusion values, non significant differences were recorded between the two studied groups. From this study, it can be concluded that zinc administration at a dose of 20 mg/kg/day for 4 successive weeks, has a protective effect against the risk of atherosclerosis and oxidative stress in vivo. Also, zinc treatment maintained or even enhanced the intrinsic cardiac functions, both chronotropic and inotropic, and their responses to B-adrenergic stimulation. In addition, zinc proved to be a beneficial cardioprotective agent as it attenuated the detrimental effects of post-ischemia reperfusion on the myocardial contractility