# Introduction atechins are one group of natural polyphenols found in many plants, especially in green tea (leaves of Camellia sinensis) (1)(2)(3). The four main catechin derivatives mainly find in green tea include the isomers epicatechin, (-)-epicatechingallate (ECG), (-)epigallocatechin (EGC), and (-)-epigallocatechin gallate (EGCG) (3). EGC is a flavan-3-ol containing a benzopyran-3,5,7-triol linked to a 3,4,5-hydroxyphenyl moiety. Thus, EGC is considered to be a flavonoid lipid molecule (4) (Figure 1). The health benefits associated with the consumption of green tea are due to the activity of EGCG and EGC which are both present at higher amounts (5). EGC has many beneficial cardiovascular properties. However, most of these effects are nonspecific, such as antioxidant (1-2, 6-7), antiinflammatory (1,5,7), and antiatherogenic activities (8). Another remarkable property attributed to tea catechins is the cholesterol-lowering action, involving the upregulation of the LDL receptor, the reduction of cholesterol absorption, and the modulation of both synthetic and metabolic pathways (see for review 9). # Further investigations of the cellular mechanisms are needed to investigate the cardiovascular effects of this flavonoid. Other flavonoids such as naringenin, quercetin, and genistein have direct actions on rat cardiac and vascular smooth muscles (10). The present work evaluated the possible direct effects of EGC on electrical and contractile activities of rat isolated rat hearts. # II. # Materials and Methods # a) Animals Male adult (7-8 weeks) Wistar rats were brought from the National Center for Laboratory Animal Reproduction (CENPALAB; La Habana). Before the experiments, animals were for seven days adapted to laboratory conditions (controlled temperature 25 ± 2°C, relative humidity 60 ± 10%, and 12 h light/dark cycles). Tap water and standard diet for rodents supplied by CENPALAB were freely provided. All procedures fulfilled with the European Commission for the use and care of laboratory animals. The Committee for Animal Care in Research of the Center (No. 08-2012, folio 73, book 01, 2012) approved the present study. # b) Isolated hearts As previously reported (11), under pentobarbital anesthesia rat hearts were removed and placed in cold Tyrode (see below). Hearts were carefully dissected, mounted on a Langendorff column and perfused at constant flow (10 mL/min) with a Tyrode solution of the following composition (mmol/L): 140 NaCl, 2.5 KCl, 0.5 MgCl2, 2 CaCl2, 10 Tris-hydroxymethyl amino methane, 10 Glucose (pH =7.4, gassed with O2; T = 35°C). On the ventricular epicardium was placed a bipolar platinum recording electrode to record the surface electrocardiogram. Another bipolar platinum electrode was placed near the atrioventricular ring and was connected to an electronic stimulator. To record the force of contraction (FC), the cardiac apex was fixed to a force-displacement transducer with a surgical 6-0 silk thread. Surface electrocardiogram and FC values were recorded at the heart rate and a fixed stimulus rate (500ms RR interval). # c) ECG and chemicals Stock solutions of ECG were prepared in ethanol, and diluted in the bathing solution on the day of the experiment. All chemicals were from Sigma Aldrich. Means and standard errors of means expressed the results. Student's t-test evaluated the statistical significance for paired samples, previously checked that the data complied with the premise of normality. Differences were considered statistically significant for p < 0.05. The graphics and the statistical processing were done using the software OriginPro 8 SRO v8.0724 (MA, USA). # Results and Discussion The corrected QT (QTc) interval of the surface electrocardiogram (QTc = QT/?RR) was not significantly affected by EGC at concentrations from 0.001 to 3 µM (Table 1). These results should be possible because this flavonoid could exert multiple actions on different ionic channels, resulting in an apparent absence of effects on QT interval of the cardiac surface electrogram. As a fat, catechins modulate several ionic channels (12)(13)(14)(15). EGC showed a tendency to increase QRS interval of the surface electrocardiogram, but only at the highest concentration studied (3 µM) this increase was statistically significant (p < 0.05) (Table 1). EGCG, catechin structurally related to EGC, at 30 µM prolonged QRS interval in isolated spontaneously beating guinea pig hearts (15). The QRS wave is dependent on sodium channel activity, Kang et al., 2010 showed that EGCG inhibited the cloned human cardiac sodium channel Nav1.5 in a dose-dependent manner with 45.7 ± 6.9 % inhibition at 100 µM (15). EGCG reduced the amplitude of voltage-gated sodium channel current in a concentration-depend manner in the range of 0.1 -400 µM in rat hippocampal CA1 neurons (13). On the other hand, EGC prolonged the RR interval of surface electrocardiogram and this increase was statistically significant (p < 0.05) since 0.03 µM (Table 1). EGCG at 30 µM did not affect heart rate of guinea pig hearts (15). Green tea extract used with dietary supplements did not alter heart rate (16). Other study concluded that Camellia sinensis has effect on heart rate, it decreases the heart rate in normotensive female individuals and increases the heart rate in the normotensive male individuals (17). In the present study in the concentration range from 0.001 to 3 µM, EGC significantly decreased the force of contraction (FC) in isolated rat hearts (Figure 2); concentrations as low as 0.001 µM of EGC decreased FC by 28.4 ± 8.7 %. Since EGC slightly changed RR interval, hearts were paced at 500-ms stimulus interval (over the spontaneous RR interval under control condition; 531.05 ± 18.9 ms) to avoid any frequencydependent change in FC. Experimental data were fitted to a Hill function (Figure 2), and the estimated IC50 for inhibition of contraction was 0.03 ± 7.8 µM for EGC. The action of EGC on FC was not reversible upon washout with the normal Tyrode solution. Although further studies are needed to see if EGC has any direct effect on calcium channels, the decrease of force of cardiac contraction by EGC should be at least partly due to an inhibition of calcium channels. The L-type calcium channel was inhibited by 20.8% at 30 µM by EGCG, reached a maximum of 37.1 ± 4.2% at a concentration of 100 µM (15). Tadano et al., 2010 reported that EGC had no significant effects on cardiac myofilament Ca2+-sensitivity. However ECG and EGCG were found to decrease Ca2+ sensitivity, they were Ca2+ desensitizers acting through binding to cardiac troponin C (18). At concentrations within the same range at which similar flavonoid EGCG have vasorelaxant effects related to the inhibition of Ca2+ influx in smooth muscle cells (19), in the present results, EGC concentrationdependently relaxed with almost equal effectiveness the contraction of rat hearts. On the strength of these results, the physiological relevance of the decrease of force of cardiac contraction by EGC can be asserted by considering the data available on the in vivo level of the related catechin EGCG ([EGCG] = 0.3-7.5 µM in the blood of green tea consumers (20). Three-month supplementation with green tea capsules decreased systolic (SBP) and diastolic blood pressure (DBP) by four mmHg in obese hypertensive (21) but not obese subjects (22). A recent metaanalysis which included eleven trials concluded that short-term consumption (>6 months) of black tea could decrease SBP and DBP by 1-2 mmHg and green tea by three mmHg (23). IV. # Conclusions The present study revealed that EGC has direct cardiac effects. The results presented here con firm the role of tea catechin EGC, as a precursor for the development of novel drugs for the treatment of cardiovascular disorders. 1![Figure 1: Chemical structure of (?)-Epigallocatechin III.](image-2.png "Figure 1 :") 2![Figure 2: Concentration-response curves for the inhibition of force of contraction by EGC. Experimental data (n = 6 for each point) were fitted to a Hill function](image-3.png "Figure 2 :") 1QTc (mseg)pQRS (mseg)pRR (mseg)pControl88.55 ± 7.211.80 ± 0.7531.05 ± 18.9EGC 0.001 ?M84.20 ± 4.70.7112.50 ± 0.10.36541.48 ± 20.20.72EGC 0.003 ?M98.01 ± 7.10.4612.65 ± 0.20.28552.20 ± 20.10.47EGC 0.01 ?M84.20 ± 11.20.7412.85 ± 0.30.22605.63 ± 41.40.15EGC 0.03 ?M98.70 ± 0.30.3913.20 ± 0.30.12639.13 ± 37.5 *0.04EGC 0.1 ?M90.02 ± 10.00.9113.30 ± 0.20.09669.50 ± 30.1 *0.008EGC 0.3 ?M86.50 ± 5.50.8613.40 ± 0.30.08676.50 ± 33.4 *0.009EGC 1 ?M87.40 ± 6.70.9113.60 ± 0.30.05682.78 ± 33.4 *0.008EGC 3 ?M95.10 ± 13.10.6513.78 ± 0.3 *0.04678.05 ± 34.8 *0.009* p < 0.05 vs. Control © 2018 Global Journals * Beneficial effects of green tea: A literature review SMChacko PTThambi RKuttan INishigaki 2010 13 * Theaflavins in black tea and catechins in green tea are equally effective antioxidants LLeung YSu RChen ZZhang YHuang ZYChen J. 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