Background: Nitric oxide (NO) has been noted to produce ischemic preconditioning (IPC)-mediated cardioprotection. Caveolin is a negative regulator of NO, which inhibits endothelial nitric oxide synthase (eNOS) by making caveolin-eNOS complex. The expression of caveolin is increased during diabetes mellitus (DM). The present study was designed to investigate the involvement of caveolin in attenuation of the cardioprotective effect of IPC during DM in rat.Methods: Experimental DM was induced by single dose of streptozotocin (50 mg/Kg,i.p,) and animals were used for experiments four weeks later. Isolated heart was mounted on Langendorff's apparatus, and was subjected to 30 min of global ischemia and 120 min of reperfusion. IPC was given by four cycles of 5 min of ischemia and 5 min of reperfusion with Kreb's-Henseleit solution (K-H). Extent of injury was measured in terms of infarct size by triphenyltetrazolium chloride (TTC) staining, and release of lactate dehydrogenase (LDH) and creatin kinase-MB (CK-MB) in coronary effluent. The cardiac release of NO was noted by measuring the level of nitrite in coronary effluent.Results: IPC- induced cardioprotection and release of NO was significantly decreased in diabetic rat heart. Pre-treatment of diabetic rat with daidzein (DDZ) a caveolin inhibitor (0.2 mg/Kg/s.c), for one week, significantly increased the release of NO and restored the attenuated cardioprotective effect of IPC. Also perfusion of sodium nitrite (10 μM/L), a precursor of NO, significantly restored the lost effect of IPC, similar to daidzein in diabetic rat. Administration of 5-hydroxy deaconate (5-HD), a mito K_ATPchannel blocker, significantly abolished the observed IPC-induced cardioprotection in normal rat or daidzein and sodium nitrite perfused diabetic rat heart alone or in combination.Conclusions: Thus, it is suggested that attenuation of the cardioprotection in diabetic heart may be due to decrease the IPC mediated release of NO in the diabetic myocardium, which may be due to up -regulation of caveolin and subsequently decreased activity of eNOS.

Mercury generates free radicals and subsequently increases oxidative stress, which leads to renal injury. Tribulus terrestris (TT) has good anti-inflammatory and antioxidant properties. Hydroalcoholic extract of different dose of TT was evaluated against mercuric chloride-induced nephrotoxicity. Rats (n = 6) were treated with TT at doses of 100, 200, and 300 mg/kg. Drugs were administered orally for 7 days. Single dose of mercuric chloride (5 mg/kg, intraperitoneal) on the 5^th day caused significant elevation of blood urea nitrogen, serum creatinine, malondialdehyde, liver fatty acid binding protein, kidney injury molecule-1, and kidney mercury level and fall in glutathione, superoxide dismutase, glutathione peroxidase, and histopathological changes in disease control as compared to normal control group (P < 0.001). Dose of TT 200 and 300 mg/kg significantly (P < 0.001) prevented the renal injury, and mercury accumulation in kidney tissues significantly decreases in higher dose, i.e., 300 mg/kg as compared to control group. Our result indicates that the treatment of TT exerted significant protection against renal damage induced by mercuric chloride possibly due to its antioxidant and anti-inflammatory properties and by decreasing the renal accumulation of mercury.