ROLE OF EUGENOL IN REVERSAL OF VASCULAR DYSFUNCTION INDUCED BY EXPERIMENTAL DIABETES AND HYPERTENSION
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2018-10
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517502. (A.P.) INDIA
Abstract
ABSTRACT :
Phenylpropanoids are a diverse group of phytochemicals with immense health benefits and found throughout the plant kingdom. Eugenol is a member of the phenylpropanoids and is remarkably versatile molecule which is present abundantly in clove, nutmeg, cinnamon, basil and bay leaf. Epidemiological evidence and clinical trial data indicates that due to presence of biologically active phytochemicals, the plant originated diets can reduce the risk of chronic disease conditions such as cardiovascular disease, hypertension, diabetes and cancer. Hypertension and diabetes are the lifestyle diseases which are considered to be main causes of mortality for decades in humans. Vascular dysfunction is the major change that is associated with diabetes and hypertension. It is well documented that both diabetes and hypertension occur together in most of the human beings that is an additive cause for increase in risk of vascular complications. Though there are standard treatments available at present for these complications, a look for an alternative approach that can better address the vascular problems is most wanted. Hence the present study was designed to know the effect of eugenol against vascular dysfunction associated with either diabetes or hypertension alone and diabetes with hypertension together. The study was carried out in rats that are divided into eight groups with ten rats in each. Group-I (normal control) received vehicle alone for eight weeks whereas group II (eugenol control) received eugenol orally and daily at the rate of 80 mg/kg for eight weeks. Group- III, IV and V constitute experimentally induced hypertension control, diabetic control and diabetic rats with hypertension. Hypertension was induced in rats with administration of L-NAME in drinking water (40 mg/kg/day). Whereas single dose of streptozotocin was injected intraperitoneally at 40 mg/kg for inducing diabetes in rats. Group V rats received both streptozotocin and L-NAME. Group- VI (eugenol treated hypertensive rats), VII (eugenol treated diabetic rats) and VIII (eugenol treated diabetic rats with hypertension) received eugenol 80 mg/kg orally from the day after the onset of diabetes, hypertension or both conditions experimentally. Development of hypertension and diabetes in rats was confirmed by decrease in total nitrate/nitrite levels in serum and high blood glucose levels (>300 mg/dl) respectively. At the end of the study, rats were sacrificed and thoracic aorta was collected for studying vascular reactivity and histopathology. In addition, effect of eugenol in ameliorating the oxidative stress induced by experimental diabetes, hypertension and diabetes associated hypertension was also studied. Moreover, liver and kidney function markers in plasma were estimated in different study groups to know the effect of eugenol on liver and kidney function. Total nitrate (NO3-) and nitrite (NO2-) levels in serum were significantly (P < 0.05) decreased in hypertension control, diabetic control and diabetes associated hypertensive rats. Eugenol treatment had no impact on reversing the nitrate and nitrite levels in diabetes and hypertension back to the normal values noticed in control rats. Hyperglycemia was observed both in diabetic and diabetic hypertensive rats. Eugenol treatment did not have any effect in restoring the blood glucose levels to normal. Eugenol treatment could not show any favorable effect on body weight that had reduced in diabetic and diabetic hypertensive rats. Eugenol treatment had no effect on increased oxidative stress noticed in diabetic, hypertensive and diabetic hypertensive rats. Levels of liver function markers were raised in diabetic and diabetic hypertensive rats indicating liver damage and eugenol had no protective effect on liver damage. But elevated plasma creatinine, blood urea nitrogen levels and reduced plasma total protein in diabetic and diabetic hypertensive rats were restored to normal by eugenol treatment indicating protective effect of eugenol on kidney. Vascular reactivity was studied in-vitro by taking myographic recordings of aorta as described here; 1. Contractile response to phenylephrine and 5-HT. 2. Ach relaxation on phenylephrine and 5-HT induced contraction. 3. Eugenol relaxation of phenylephrine and 5-HT induced contraction. The lower mean log EC50 values of phenylephrine (-7.856 M) and 5-HT (-6.967 M) in hypertensive control and diabetic hypertensive rats (Phe: -7.960 M and 5-HT: -7.035 M) demonstrates hyper responsiveness of aortic smooth muscle to phenylephrine and 5-HT in comparison with normal control (Phe: -6.588 M and 5-HT: -5.700 M), and hyper-responsiveness of aorta to phenylephrine was partially reversed by eugenol treatment. But aorta from diabetic control rats showed hyper-responsiveness to phenylephrine (-7.137 M) and hypo reactivity to 5-HT (-5.247 M) compared to normal control rats. Eugenol treatment showed no impact on hyper-reactivity to phenylephrine or hypo-reactivity to 5-HT in diabetic rats. Maximum relaxation (% Emax) by acetylcholine in aorta on phenylephrine and 5-HT induced contractions was significantly reduced in diabetic, hypertensive and diabetic hypertensive rats. The effect was complete in hypertension and diabetic hypertension. Eugenol treatment had no significant change on acetylcholine induced relaxation in diabetic rats but significantly (P<0.001) improved relaxation in hypertensive and diabetic hypertensive rats. Eugenol produced dose dependent relaxation on phenylephrine and 5-HT induced contraction in all experimental groups but its effect was less potent than acetylcholine. Emax of eugenol on phenylephrine induced contraction was reduced in hypertensive, diabetic and diabetic hypertensive rats. Eugenol treatment to diabetic and diabetic hypertensive rats significantly improved Emax of eugenol. Eugenol relaxation on 5-HT induced contraction in diabetic control, hypertensive control and diabetic hypertensive rats were similar to control rats. The pathological changes observed in aorta, heart and kidney due to hypertension, diabetes and diabetic hypertension were not reestablished to normal with eugenol treatment. In conclusion, eugenol partially reversed phenylephrine and 5-HT induced vascular hyper-responsiveness in aorta and augmented the relaxation to acetylcholine in hypertensive and diabetic hypertensive rats but failed to produce a similar response in diabetic rats. However, eugenol had no role in maintaining blood glucose and serum nitrate levels indicating its inability to alleviate diabetes and hypertension. Further, eugenol treatment could not modulate oxidative stress and histopathological changes induced by diabetes and hypertension in plasma, heart and kidney. Further studies are needed to know the molecular mechanism involved in partial reversal of vascular dysfunction by eugenol.
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