Effects of garlic on myocardial dysfunction and plasma levels of nitric oxide, C-reactive protein and leptin hormone in diabetic rats

ABSTRACT

It is now accepted that allocin, the main biologically active compound in garlic, exhibits antioxidant activity. As well, garlic has been well known for its protective effects against cardiovascular disease. Diabetes mellitus is reported to be accompanied by severe oxidative stress. Since heart disease is the leading cause of death in diabetes, this study was carried out to determine the effect of garlic supplementation on cardiac performance as well as. on the cardiac responses to Badrenergic stimulation and on plasma levels of nitric oxide [NO], C-reactive protein [CRP] and leptin hormone in streptozotocin [STZ] diabetic rats. The study was carried out on 58 adult male albino rats, allocated into 4 groups Group 1 included non-diabetic control rats [n = 12] that received a single i.p. injection of citrate buffer, in a volume equal to that used as solvent for STZ used to induce diabetes in the test groups. Group 2 included nondiabetic garlic-treated rats [n = 14], which were injected i.p. with garlic in a dose of 200 mg/kg/day, 6 days/week, for 1 month. Group 3 included diabetic rats [n = 15], diabetes being induced by a single i.p. injection of STZ in a dose of 40 mg/kg. Group 4 included diabetic garlic-treated rats [n = 17], that received a single dose of STZ as in group and then treated with garlic in a dose of 200 mg/kg/day, given i.p., 6 days/week for 1 month. On the day of sacrifice, blood samples were taken from the aorta for estimation of plasma glucose, nitrate, CRP and leptin levels. Thereafter, the hearts were excised and subjected to in vitro cardiac studies to demonstrate the response of isolated hearts to isoproterenol [ISU] infusion. Hearts isolated from diabetic rats showed impairment of both intrinsic chronotropic and inotropic functions as shown by the diminished spontaneous beating rate [BR], peak developed tension [PT] and myocardial flow rate [MFR] together with prolonged time to peak tension [TPT]. Their response to the different doses of ISU stimulation was also diminished. Further, diabetes was found to be associated with increased plasma glucose, nitrate and CRP, with non significant change in plasma leptin level. Garlic administration to diabetic rats enhanced chronotropy, evidenced by increased BR, as well as inotropy as shown by the shortening of TPT. Garlic also caused significant reduction in blood glucose levels indicating its hypoglycemic effect, together with reduction of the elevated nitrate and CRP levels, yet no effect on leptin was detected. It can be concluded from the present study that diabetes caused impairment of cardiac functions, both basal and in response to ISU infusion. Moreover, the inflammatory effect of diabetes was manifested by the increase in CRP, whereas the high level of NO could be attributed to the oxidative stress induced iNOS activation. Garlic supplementation antagonized the diabetic adverse effects on cardiac functions through its cardioprotective, hypoglycemic, anti-inflammatory and antioxidant effects