Effects of Teucrium polium on blood pressure of hypertensive rat and its possible mechanism of action
Correspondence Address: DOI: 10.4103/2229-5119.102750
Objective: Previous study have been shown boiled leaf extract of Teucrium polium (T. polium) reduced blood pressure (BP) of normotensive rat. The present study was performed to investigate hydro-alcoholic and aqueous extract of T. polium effects on BP of hypertensive rats and its mechanism of action. Materials and Methods: Hypertension inducted by Goldblatt method in male Wistar rats (250-300 g). Hydroalcoholic or aqueous extract of T. polium (20 or 40 mg/kg, i.v.) or theirs vehicles injected in treatments or controls groups, respectively. To investigate the mechanism of extract effect on BP, L-NAME (5 mg/kg) or atropine (1 mg/kg) injected intraperitoneally and then T. polium (20 mg/kg, i.v.) administrated in hypertensive rats. Results: Hypertension induction increased BP significantly ( P <0.001). Hydroalcoholic extracts of T. polium have no significant effect on BP, but its aqueous extract reduced BP ( P <0.001) that follow by BP augmentation ( P <0.05). Intraperitoneal injection of L-NAME has no effect on basal BP and hypotensive action of T. polium. Atropine also has no effect on basal BP, but it's eliminating the hypotensive effect of T. polium. Conclusion: Our data showed that aqueous extract of T. polium reduced BP of hypertensive rats that seems mediated by muscasinic receptors. Keywords: Goldblatt hypertension, rat, Teucrium polium
Hypertension is a serious condition that increases the risk of heart disease and stroke. [1] Alternative medicine, including diet and herbal medicine present an effective way to control high blood pressure (BP). [2] As Teucrium polium (T. polium) has been used in traditional medicine as an antispasmodic, antidiabetic, anticonvulsant, etc. [3] Several studies also indicated T. polium have hypoglycemic [4] antiinflammatory, [5] anorexic, [6] hypolipidemic, [7] antinociceptive, [8] and hypotensive effects in normal rats. [9],[10] Moreover, it has been reported T. polium has positive inotropic effect on rabbits and Guinea pig heart, [11],[12] that seems slightly inconsistent with a hypotensive factor as reported by other studies. [9],[10] On the other hand, a hypotensive factor in normal subjects is not essentially effective in hypertensive ones. So this study was performed to evaluate the effect of hydro-alcoholic and aqueous extract of T. polium on high BP and its possible mechanism of action in a rat model of hypertension.
Animals and drugs Male Wistar rats were obtained from breeding colony of Semnan University of Medical Sciences, Semnan-Iran. Animals were housed in individual cages in a 12-h light/dark cycle at 22-24°C, with food and water ad libitum. All procedures on animals were performed in according to the National Institutes of Health Guide for Care and Use of Laboratory Animals. Drugs include ketamin and xylocine prepared from Woerdn-Holland. Also pentobarbital sodium, atropine and NG-nitro-L-arginine methyl ester (L-NAME) were obtained from Sigma and heparin from TRITTAU-Germany. Drugs and extract were dissolved in saline. Experimental procedure Eighty seven male Wistar rats (250-300 g) randomly have divided to 13 experimental groups, including normal (n=5), sham operated (n=5) and hypertensive groups (n=7*11). Hypertensive rats subdivided to treatment, control and mechanism evaluating groups. Hypertension induced by Goldblatt method (two kidney one clip) as described following. Animals anesthetized with ketamin-xylocine (60 and 8 mg/kg, i.p.), then left kidney exposed and a silver clip with an internal diameter of 0.2 mm placed on the kidney's artery and sutured surgery site. One month later hypertensive rats anesthetized with pentobarbital sodium (80 mg/kg, i.p.) and placed on a rat temperature unit (Narco Bio-system, USA) to maintain a constant rectal temperature of 36.5±0.5°C. Femoral vein was cannulated for extract injection. Femoral artery also was cannulated with a heparinized cannula that connected to a pressure transducer (P-1000B, Narco Bio-system, USA) for continuous measurements of arterial BP and heart rate. After stabilizing BP, extract injected intravenously. The mean of arterial blood pressure (MABP) was calculated as the 60% of diastolic pressure added to 40% of systolic pressure. [13] The effects of hydroalcoholic extract of T. polium (20 or 40 mg/kg i.v.) and its vehicle (saline + 20% or 30% alcohol) or aqueous extract of T. polium (20 or 40 mg/kg i.v.), and its vehicles (saline) on MABP were studied in seven hypertensive groups of rats (n=7). To assess the mechanism of T. polium action on BP, in another tree hypertensive groups (n=7), L-NAME (5 mg/kg) or atropine (1 mg/kg) or their vehicle (saline) administrated intraperitoneally and about 20 minutes later T. polium extract (20 mg/kg) injected intravenously. Plant and extract T. polium collection, identification and extract preparation doing by the organization of promotion, education and agricultural research, Semnan. The plant was collected from Semnan, Iran in the spring of 2009 and identified according to the FLORE of the Iran by Dr. Ghahraman, with a number of 1108 and codes of 114,039,018. Hydroalcoholic and aqueous extract of T. polium were made by soxhlet method. To calculate extract concentration, a small filter paper weighted accurately and 0.1 ml extract dropped on the paper surface. Paper weighted after completely dried with warm air and weight change used for the calculation of extract concentration. Statistical analysis The results presented as mean± SEM and a value of P<0.05 accepted as statistically significant different (SigmaStat 2.0; Jandel Scientific, Erkrath, Germany). Data were analyzed by one-way analysis of variance (ANOVA) followed by Holm-Sidak method as post hoc analysis. When the normality test failed, ANOVA on ranks (Kruskal-Wallis) was used followed by Dunn's test for multiple comparison.
Effect of hydro-alcoholic extract of T. polium on mean arterial blood pressure of hypertensive rats Hypertension induction increased mean arterial blood pressure (MABP) from 95 and 97 mmHg in normal and sham operated to 145 in the hypertensive group (P<0.001). Hydroalcoholic extracts of T. polium (20 or 40 mg/kg, i.v.) reduced MABP of hypertensive rats that compare to their controls (20% or 30% alcohol + saline) has no significant effect [Figure 1].
Effects of aqueous extract of T. polium on mean arterial blood pressure of hypertensive rats Intravenous injection of aqueous extracts of T. polium (20 or 40 mg/kg) reduced MABP of hypertensive rats significantly (P<0.001) that follow by an increase of BP, which was significant in the dose of 20 mg. Blood pressure returned to baseline later [Figure 2]. There is no significant different between two doses of T. polium in treatments groups.
Effects of L-NAME on hypotensive action of T. polium Intraperitoneal injection of L-NAME (5 mg/kg) has no significant effect on MABP of hypertensive rats. Following T. polium (20 mg/kg, i.v.) reduced BP significantly (P<0.001) that follow by an increase of BP [P<0.001, [Figure 3]].
Effects of atropine on hypotensive effect of F. persica Intraperitoneal injection of atropine (1 mg/kg) has no effect on MABP of hypertensive rats. Following T. polium (20 mg/kg, i.v.) injection increased BP significantly [Figure 4].
Our results showed that intravenous injection of hydroalcoholic extracts of T. polium has no significant effect on BP of hypertensive rats [Figure 1]. This result seems inconsistent with previous research that showed boiled leaf extract of T. polium reduced BP of normal rat. [9] This discrepancy may be related to the type of extract, model of study, alcohol effects of extract, etc. Acute alcohol causes a moderate fall in BP with increased cardiac output. [14] The amount of alcohol in our extract approximated to be 20-30%, according to the percent of alcohol of extract preparation and doses of T. polium. Different alcohol concentrations (10%, 20%, 30% and 40%) effect has been examined on BP that has a similar response to be hydroalcoholic extract of T. polium. Aqueous extract of T. polium has been used in following steps to get rid of this discrepancy. Aqueous extract reduced BP of hypertensive rats that follow by BP augmentation [Figure 2]. As repetitive saline injection intravenously has no effect on BP, physical effect of extract injection on BP has been rejected. Hypotensive effect of T. polium in our study is consistent with pervious research. [9] But T. polium showed a biphasic response in our work, reduction of BP that follows by an augmentation. This BP increment maybe resulted from extract effect on heart contractility as it has been reported T. polium has positive inotropic effect on rabbits and Guinea pig heart. [11],[12] Our extract probably was different from Suleiman's study, as the hypotensive effect of T. polium in that study was bigger than our work. The endothelial cells play a central role in the vascular tone regulation by the synthesis and release of vasoactive substances such as nitric oxide (NO), Prostacyclin (PGI2) and endothelium-derived hyperpolarizing factor (EDHF). [15],[16] To evaluate the mechanism of hypotensive effect of T. polium, L-NAME as a NO synthase inhibitor injected intraperitoneally that has no significant effect on BP and hypotensive effect of T. polium [Figure 3]. So it seems hypotensive effect of T. polium is independent of NO release. Also atropine injection intraperitoneally has no effect on basal BP, but it abolished the hypotensive effect of T. polium without affecting BP augmentation [Figure 4]. It appears muscarinics receptors participate in hypotensive effect of T. polium. Muscarinics M3 receptor's activation on the endothelium increase cytosolic calcium that causes NO, PGI2 and EDHF release. These vasoactive substances cause smooth muscles relaxation. [17] Since L-NAME has no effect in this study, hypotensive effect of T. polium possibly related to PGI2 or EDHF release. This reminds for more clarification. Other possibilities of hypotensive effect of T. polium may be related to its calcium antagonistic effect, as it has been reported in the rabbit intestine. [18] Different classes of compounds, including terpenoids and flavonoids have been isolated from T. polium. [19],[20],[21] Flavonoids inhibit the angiotensin-converting enzyme [22] that may be another possibility for hypotensive effect of T. polium in this study, but we didn't know the amount of flavonoids in our extract. In summary, present study provides evidence that aqueous extract of T. polium has the hypotensive effect that attributable to muscarinic receptor's activity. Further research is required to clarify the mechanism of this effect.
This work was financially supported (Grant No. 217) by Vice Chancellor for Research Centers of Semnan University of Medical Sciences, Semnan, Iran. The authors are most grateful to the head of department and research center of physiology of Semnan University of Medical Sciences for assistance in this study.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
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