All experimental procedures performed in accordance with the in-house guidelines Guide for the care and use of laboratory animals (National Institute of Health publication 86-23, Revised 1996) and occurs with the protocol approved by the Interinstitutional Animal Care and Use Committee of Tbilisi State Medical University, Ilia State University and International Centre of Introduction of New Biomedical Technology, Tbilisi, Georgia (No 11-819021). Experiments were carried out in 52 adult (35-42 days old) male Wistar rats weighing 220-260 g. Rats were kept under controlled conditions (temperature 21 ± 2 °C, humidity 60 ± 10%, 12 h inverted light cycle-light/dark) and fed ad libitum on the standard normal-protein diet and had free access to water. Seven days after acclimatization, animals were randomized in I control group - sham operated (SO, n=21) and II - hypertensive rats reproduced by 2 kidney -1 clip (2K-1C, n=32) model, created with a constricting silver clip (internal diameter - 0.2 mm) on the left renal artery for it s partial occlusion under (87 mg/kg Ketamine ( Zdorovye , Ukraine) + 13 mg/kg Xylazin Bio (Xylazin, 2%, Biovera ,Czech), as described early 3233. In control, SO rats, the same surgical procedures were performed with only kidney exposure without its removal or renal artery ligation. The rats were involved in experiments after 4 weeks of surgical intervention. Rats that had SBP > 140 mmHg defined as having hypertension. The development of RVH also confirmed by using non-invasive tail-cuff blood pressure methods. Three days before experiments in anesthetized rats, polyethylene catheter inserted in the right carotid artery and connected to a blood pressure transducer for measuring blood pressure (BP) with an electromanometer and heart period (HP) with a cardiotachometer. Catheter placed in the right jugular vein used for drug administration. To evaluate the parasympathetic (cardiochronotropic) and sympathetic components of baroreflex sensitivity (BRS), phenylephrine (PE) - 10 mcg/kg and sodium nitroprusside (SNP) -10 mcg/kg i.v. injections used, respectively. The animals from the II group in according with the received therapeutic treatment were secondly randomized into two group: positive control group - RVH rats received i.p. of 1,0 ml of phosphate buffer solution (PBS) containing 0.1% dimethyl sulphoxide (DMSO, Carl Roth, Germany) and main group - 3 mg/kg body weight of Luteolin, produced from plant Perilla Nankinensis Decne by the Department of Pharmacognosy and Pharmaceutical Botanic of Tbilisi State Medical University (quality analyzed by high-performance liquid chromatography, purity ³98%), during 2 weeks. Based on the literature data and our preliminary study Luteolin (3′,4′,5,7-tetrahydroxyflavone) was dissolved in sterile saline with 0.1%  DMSO in PBS, pH 7.4. No adverse effects or toxicity associated with luteolin administration observed in the present study at 24 h after injection. Among the selected compounds, luteolin showed higher inhibitory effect (IC50 μM) on sEH activity, providing vasodilatory action in rat isolated mesenteric resistance vessel preparation using myograph system (unpublished results). Luteolin dose 3 mg/kg i.p. has chosen after doses escalation experiments: 0.1, 0.3, 1.0, 3.0, 5.0 mg/kg. In all animals luteolin was administered i.p. 3 mg/kg during 2 weeks.

The body weight, heart and kidney weight were recorded. The cardiac and kidney hypertrophy index were expressed as heart weight/body weight (HW/BW), left kidney and right kidney weight and right kidney weight/body weight (RKW/BW).

Biochemical markers, endothelin -1 (ET-1), epoxyeicosatrienoic acids- EETs and prostaglandin - E2 (PGE2), levels were investigated in blood plasma taken from the carotid artery (placed in tubes with 1% heparin) and the animals were euthanized. The blood than immediately centrifuged (10 min at 845 × g and 4 oC temperatures) for plasma sample collection. The serum and plasma samples were stored at -80 oC until being analyzed. EETs plasma levels were analyzed using Elisa kits (cat. No: MBS9310869, Eagle Biosciences, USA), while PGE-2 (Cat. No: CSB-E07967r, Cusabio, USA) and ET-1 (Cat. No: CSB-E06979r, Cusabio, USA) plasma contents were measured by Elisa Kit (Cusabio, USA) in according with the manufacturer s instruction.

SPSS software is used for statistical analysis, measurement data to mean ± standard deviation (average ±SD), using t test and single factor analysis of variance for group comparison, P<0.05 indicates there was a significant difference, using Student s test.

In conscious freely moving rats, the analysis of hemodynamic parameters and BRS showed significant differences in baseline values of BP, HP and BRS in RVH and SO rats, however none of the rats died in any of the groups (Table 1). In RVH rats BP increased by 32%. Hypertension formation under 2K-1C model correlated with mean values of HP near 140±6 ms and reduction in parasympathetic (cardiochronotropic) component of BRS evaluated with PE vs. observed in SO rats. Assessment of sympathetic component of BRS with SNP in RVH rats significantly did not changes in comparison with hypertensive rats treated with vehicle and SO groups. However, treatment with luteolin reverse the ratio between Sympathetic/parasympathetic component of BRS from 1,12±0,08 ms mmHg-1 in chronic RVH to 0,92±0,06 ms mmHg-1 (p<0,01), the level observed in control animals. Thus, it will be suggested, that luteolin administration toward to the normal the balance of accentuated antagonism between sympathetic and parasympathetic nervous system.

The body weights at the beginning of the experiment, 4 weeks after the surgical intervention, and 2 weeks after i.p. administration of the low doses of luteolin of two 2K-1C experimental model of RVH groups were not significantly different (Table 2). The cardiac mass of the RVH group was increased in comparison to the SO group, did not changes under treatment with vehicle and decreased in luteolin treated group up to control level. The mean weight of left clipped kidneys was significantly decreased while the right non-clipped kidneys weight was significantly increased in both 2K-1C groups compared to the SO group. Such alteration of body weights in RVH animals accompanied by marked increase of heart weight/body weight and right kidney weight/body weight ratio in SO rats that indicates for cardiac and renal hypertrophy development. Two weeks treatment with luteolin significantly attenuates cardiac and renal remodeling.

Plasma vasodilators and vasoconstrictors substances alterations in chronic 2K-1C experimental model of renovascular hypertension. Action of low doses of luteolin

Progression of RVH in this experimental model of arterial hypertension characterized with decreasing circulating in plasma vasodilators component such as total trans-EETs up to 4.3±0.1ng/ml from the 7.7±0.2ng/ml in SO group and PGE-2 up to 2.4±0.2 ng/ml from the 4.3±0.1 ng/ml. This accompanied with increased in circulated cytokine, ET-1, levels for about three folds (Table 3).

Intraperitonially administration of Luteolin during 2 weeks at the end of treatment associated with improvement of blunted cardiochronotropic component of BRS and increased plasma level of total trans EETs by 58% and did not significantly difference from control (SO) level, PGE-2 increased by 50%, but remained lower than in control group by 27% and markedly reduced ET-1 plasma levels, by 40%, however its exceeds control by 80% (Table 3).

Investigation conducted in last decade have provided evidence regarding valuability of epoxyeicosatrienoic acids (EETs) as a new target for the treatment of cardiovascular diseases 1034 being the most frequent causing factor of morbidity and fatal outcome 12. A number of experiments showed EETs beneficial effects in different model of arterial hypertension 5111418 by improving vascular homeostasis, increased Na+ elimination and reduction of inflammation. EETs vasodilatory action is decreased by an enzyme soluble epoxide hydrolase (sEH) converting EETs to less active dihydroxyeicosatrienoic acids (DHETs) limiting EETS pharmacological activity 1023. Currently a great interest is directed to compounds revealing sEH inhibitory properties with ability to prolong and enhance EETs cardioprotective potential 212326. According our experiments performed in 2K-1C 4 weeks hypertensive rats (HR) phenolic compound flavonoid luteolin with sEH inhibitory properties during 2 weeks of treatment significantly reduced blood pressure (BP), cardiac rhythm and improved blunted baroreflex cardiochronotropic component sensitivity without marked changes in baroreflex sympathetic component sensitivity. Our results are consistent with findings of other authors 335 demonstrated in SHR hypotensive effect of flavonoid quercetin with improving sensitivity of vagal component of baroreflex without marked influence on it s sympathetic component. Reduction in BP regarding luteolin and quercetin may be associated with induces NO production and arterial relaxation 3536, including reduction in blood pressure by endothelium dependent and independent mechanisms. Positive influence of abovementioned antioxidants in hypertensive states on baroreflex function by authors opinion is caused by improved autonomic function, endothelin dysfunction and baroreflex impulses from the carotid artery 35. Luteolin in our experiments significantly increased EETs plasma level in HR vs. SO animals resulting in it s vasodilatory effect which is in agreement with data obtained by other authors showing reduction in blood pressure of SHR in increased level of trans-EETs 18. Diminished endothelial function characterized with reduction in release of vasodilatory agents and increased production of vasoconstrictive substances 73537383940. Thus, observed increased of ET-1 plasma levels in RVH vs. SO rats consistent with elevation plasma level of ET-1 in experimental and clinical hypertension 839404142, which can be considered as a marker and predisposing factor for the development of RVH. Luteolin significantly decreased ET-1 plasma concentration in RVH which confirm the suggestion that luteolin directly inhibits the secretion and gene expression of ET-1, for example, in porcine aortic endothelial cells. Its ED50 was about 10 microM. In addition, the inhibition of ET-1 by a glycoside compound of luteolin (luteolin-6-C-glucoside) was weak 39. Not less important, that luteolin increase endothelium-dependent relaxation in rat aortic rings, which may be mediated by reducing reactive oxygen production, enhancing activity in the NOS-NO pathway and reducing levels of tumor necrosis factor -α and thus occurs anti-inflammatory action and reduced vascular inflammation in endothelial cells via preventing the activation of nuclear factor (NF)-kappa B 42. Regarding PGE-2 there are controversial data concerning PGE-2 plasma content in hypertensive states. Our results showed that plasma level of PGE-2 in RVH elevated after treatment with luteolin. This data are in agreement with results of other authors considering this potent lipid mediator as a vasodepressor and modulator of blood pressure homeostasis 9. In contrast to this and our data a group of authors suggest about increased activity of prostanoid system maintaining the hypertension 43. Such differences in obtained data can be explained by fact that PGE-2 reveals multiple actions throughout 4 distinct E-prostanoid (EP) receptor isoforms: EP-1 to EP-4. Among them EP-4 receptor facilitates to PGE-2-dependent vasodilation, but its role in the development of arterial hypertension is not fully elucidated. Multiple functioning role of EP4R in regulation of BP and in arterial hypertension based on the possible implication of the EP4R in different tissues beyond vascular smooth muscle cells 38. Epoxyeicosatrienoic acids provide improved myocardial and other tissues remodeling by revealing antioxidant, antiinflammatory and antifibrotic action 3443444546. Increased right kidney weight/body weight ratio simultaneously with diminished the same ratio in the left kidney of hypertensive rats in comparison with SO animals, indicate on the renal remodeling. 2 weeks treatment with luteolin significantly decreased such alteration in kidney weight. The same directions in alteration in heart and kidney weight/body weight ratio early found in 2K-1C hypertensive rats under influence of flavonoid nobiletin 47, which gave ground to suggested that this is intrinsic pathophysiological molecular mechanism of natural flavonoids.