The Effects of Aqueous Extract of Vaccinium Arctostaphylos Leaves on Blood Pressure in Renal Hypertensive Rats

Archive of SID Iranian Red Crescent Medical Journal

ORIGINAL ARTICLE The Effects of Aqueous Extract of Vaccinium Arctostaphylos Leaves on Blood Pressure in Renal Hypertensive Rats

A Khalili1, MB Khosravi2,3, AA Nekooeian1,2*

1Department of Pharmacology, 2Cardiovascular Pharmacology Research Center, 3Department of Anesthesiology, Medical School, Shiraz University of Medical Sciences, Shiraz, Iran

Abstract

Background: The leaves of Vaccinium arctostaphylos (Qare qat) is advocated for the treatment of hypertension in Iran' folk medicine. The objective of was to examine the possible hypotensive activity of aqueous extract of Vaccinium arctostaphylos leaves in rat model of two-kidney, one-clip hypertension.

Methods: Rats were subjected to sham operation of the placement of Plexiglass clip on left renal arteries. Four weeks later, renal artery clipped rats were given intravenous injection of normal saline or the extract at 10, 25, or 75 mg/kg, and mean blood pressure and heart rate were measured before and 20, 40 and 60 minutes after vehicle or drug administration.

Results: Compared to sham group, renal artery clipped groups had a significantly higher mean blood pressure, heart and right kidney weights, lower left kidney weight and significantly indifferent heart rate. Compared to vehicle treatment, the extract at 75 mg/kg, but not at 10 or 25 mg/kg, did reduce the mean blood pressure at 20, 40 and 60 minutes after administration without changing the heart rate.

Conclusion: The findings showed that at a higher dose the extract did have hypotensive activity without changing the heart rate. The exact hypotensive mechanism remains to be investigated.

Keywords: Vaccinium arctostaphylos; Rat; Blood pressure; Hypertension

Introduction reperfusion3,4 apoptosis,3 serum glucose5-7 and serum lipids8,9 as well as antioxidant10,11 and urinary antisep- The Vaccinium genus, from Ericacea family, includes tic activities.10,12 nearly 450 species such as Vaccinium myrtillus (Bil- Vaccinium arctostaphylos (Qare qat in Persian) is berry), Vaccinium macrocarpon (Cranberry), Vaccin- the only species that grows in Iran.13 The berries and ium angustifolium (Lowbush blueberry), Vaccinium leaves of Vaccinium arctostaphylos have been re- erythrocarpum (Bearberry), Vaccinium ashei (Rab- ported to have serum glucose and lipid lowering ac- biteye Blueberry), Vaccinium pallidum (Blue ridge tivities.14 In Iran's folk medicine, the berries of the blueberry), and Vaccinium arctostaphylos (Whortle- plant are used for the treatment of diabetes and hyper- berry). Such species have been reported to have bene- tension.13-15 A recent analysis of the constituents of ficial pharmacological effects including reducing Vaccinium arctostaphylos ripped berries indicated 1-3 blood pressure, infarct size following ischemia and that it had 3 major anthocyanins including delphinidin 3-O-b-glucoside, petunidin 3-O-b-glucoside and 13,16,17

malvidin 3-O-b-glucoside. Consistent with

*Correspondence: Ali Akbar Nekooeian, PhD, Department of Iran's folk believe, delphinidin 3-O-b-glucoside was Pharmacology, Medical School, Shiraz University of Medical Sci- shown to have vasorelaxing activities.18 However, no ences, Shiraz, Iran. Tel: +98-711-2307591, Fax: +98-711-2307591, e-mail: [email protected], [email protected] such an analysis has been performed on the constitu- Received: April 10, 2010 Accepted: August 2, 2010 ents of the plant leaves.

Iran Red Crescent Med J 2011; 13(2):123-127 ©Iranian Red Crescent Medical Journawww.SID.irl Archive of SID Khalili et al.

To the authors' knowledge, the traditional belief that venous injection of normal saline (0.2 ml) as vehicle, Vaccinium arctostaphylos leaves might reduce the or aqueous extract of Vaccinium arctostaphylos blood pressure has not been examined using up-to- leaves at 10, 25 or 75 mg/kg in identical volumes. date experimental techniques. Therefore, the present The blood pressure and heart rate were measured 20, study aims at examining such a belief using rat model 40 and 60 minutes afterwards. At the end of experi- of two-kidney, one-clip hypertension. ments, the animals were sacrificed and weights of kidneys and hearts were determined. Mean arterial blood pressure was calculated as Materials and Methods diastolic pressure plus one third of pluse pressure. The weights of heart and left and right kidneys were Twenty five grams of dried leaves of Vaccinium arc- normalized to body weight. Data are presented as tostaphylos, obtained from Gol-Chay company (Te- mean±SEM. Mean arterial blood pressure and heart hran, Iran), were ground to powder, and soaked in 50 rate were analyzed using Kruskall Wallis test fol- ml distilled water for 48 hours in room temperature. lowed by Dunn's test for pair wise comparisons. The Afterwards, the product was filtered, concentrated in body, heart or kidney weights were compared using a rotary, and dried in a vacuum desicator. The yield one way analysis of variance (ANOVA) followed by was about 25-30%. Duncan's Multiple Range test for pair wise compari- Male Sprague-Dawley rats (200-250 g), obtained sons. A p value of ≤ 0.05 was considered statistically from Animal Breeding Center of Shiraz University of significant. Data analysis was performed using Sig- Medical Sciences were subjected to sham operation mastat statistical software. (n=6) or placement of a plexiglass clip around left renal arteries (n=23) as described previously.15 Briefly, under ketamine (60 mg/kg) and xylazine (8 mg/kg) Results anesthesia, a left flank incision was made, and left renal artery was exposed. The arteries were then dis- Four weeks after the operation, left renal artery sected free of surrounding connective tissues, and solid clipped rats had a significantly higher mean arterial plexiglass clips were placed around them. Antibiotic pressure than that of sham-operated rats (Figure 1). (penicillin G) powder (Jaber Ebne Hayyan, Tehran, However, there was no significant difference between Iran) was applied to the site of incision, and the ab- heart rate from sham-operated and left renal artery dominal wall and the skin were sutured using catgut clipped rats (Figure 2). Moreover, the heart and right and silk suture materials, respectively. Sham-operated kidney weights of renal artery clipped rats were sig- rats were subjected to a similar procedure, but no clips nificantly higher than those of sham-operated rats, were placed around renal arteries. The animals were respectively. However, the weight of left kidney from then recovered from anesthesia, and were kept for 4 renal artery clipped rats was significantly lower than weeks under standard condition (temperature; 22±2º C, that of sham-operated ones (Table 1). relative humidity; 50% and 12 hours light/dark cycle) There was no significant difference between base- with food (standard rat pellet) and water ad libitum. line mean blood pressure of renal artery clipped Four weeks later, animal were anesthetised with group receiving vehicle, or the extract at 10, 25 or 75 an intraperitoneal injection of sodium thiopenthal (80 mg/kg. Moreover, there was no significant difference mg/kg). The animals were then tracheotomized to between mean blood pressure of groups receiving the facilitate breathing during the experiment. The right extract at 10 or 25 mg/kg and that of group receiving carotid arteries were cannulated using PE-50 poly- vehicle at 20, 40 or 60 minutes after administration. ethylen catheters connected to a pressure transducer However, the mean blood pressure of group receiving (ADInstrument, Australia) for the measurement of the extract at 75 mg/kg was significantly lower than arterial pressure. Left jugular veins were cannulated that of vehicle-treated group at 20, 40 and 60 minutes for vehicle or extract administrations. The animals after administration. were allowed 30 minutes to recuperate from surgical There was no significant difference between the stress. Afterwards, a baseline measurement of arterial heart rates of sham-operated groups or renal artery blood pressure and heart rate was performed. Left clipped groups receiving vehicle or the extract at 10, renal artery clipped rats were then divided into 4 25 or 75 mg/kg at 20, 40 or 60 minutes after admini- groups (n=5-6 each), and assigned to receive an intra- stration (Figure 2).

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*Denotes significant difference (P≤0.05) from sham-operated group O Denotes significant difference (P≤0.05) from renal artery clipped rats receiving vehicle.

Fig. 1: Blood pressure (mmHg) of sham-operated and renal artery clipped groups receiving vehicle (0.2 ml normal saline) or aqueous extract of arctostaphylos berries at 10, 25 or 75 mg/kg at the baseline and 20, 40 and 60 minutes after drug or vehicle administration.

Fig. 2: Heart rate (beats/min) of sham-operated and renal artery clipped groups receiving vehicle (0.2 ml normal saline) or aqueous extract of arctostaphylos berries at 10, 25 or 75 mg/kg at the baseline and 20, 40 and 60 minutes after drug or vehicle administration.

Table 1: The weights (% of body weight) of left kidneys (LKW), right kidneys (RKW), hearts (HW) and body (BW) of sham-operated rats (Sham) and renal artery-clipped (RAC) rats receiving vehicle (RAC-Veh; normal saline; 0.2 ml), or aqueous extract of Vaccinium arctostaphylos berries at 10 (RAC-AE10), 25 (RAC-AE25) or 75 (RAC- AE75) mg/kg body weight. Sham RAC-Vehicle RAC-AE RAC-AE RAC-AE 10 mg/kg 25 mg/kg 75 mg/kg RK 0.40±.01 0.49±0.01* 0.47±0.01* 0.48±0.02* 0.49±0.01* LK 0.38±0.01 0.19±0.02* 0.25±0.01* 0.20±0.02* 0.22±0.01* HW 0.33±0.01 0.44±0.02* 0.43±0.01* 0.420±0.01* 0.43±0.02* BW 240±7.3 249±9.3 244±0.6 240±5.7 245±15.6 *Denotes significant difference from sham-operated group

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Discussion oxide release enhancement.25,26 Whether or not, similar mechanisms do play a role needs to be investigated. The present study showed that placement of solid The hypotensive activity of Vaccinium arc- Plexiglass clips on left renal artery resulted in hyper- tostaphylos extract in the present study was not ac- tension characterized by increased mean arterial pres- companied by tachycardia reflex. Vasodilating agents 27 sure as well as the weights of the heart and right kid- including α1-antagonists and direct vasodilators, are ney, and reduced left kidneys weight. It also showed believed to induce reflex tachycardia, whereas angio- that aqueous extract of Vaccinium arctostaphylos at tensin converting enzyme inhibitors do not cause such 75, but not 10 or 25 mg/kg, did reduce mean arterial an effect,27 Judging the findings of the present study pressure without changing the heart rate. along with that of others', that the leaves of other Two-kidney, one-clip model of experimental hyper- Vaccinium genus had angiotensin converting enzyme tension is one the widely-used models for the study of inhibition activities23 might be suggestive of the in- antihypertensive effects of various drugs or medicinal volvement of a similar mechanism. plants. This model has been induced in laboratory rats From the findings of the present study, it is not using silver clips.20,21 However, we have induced this possible to speculate as to what constituent of the model using solid Plexiglass clips.19,22 plant leaves might be responsible for its antihyperten- The present study also showed that aqueous ex- sive effects and what the likely mechanisms would tract of Vaccinium arctostaphylos leaves reduced be. To the best of our knowledge, the chemical con- blood pressure at the highest dose used. To the au- stituents of the Vaccinium leaves have not been in- thors knowledge, this represents the first report on vestigated. However, previous publications on the antihypertensive effects of Vaccinium arctostaphylos Vaccinium genus might shed some light on the mat- leaves extract. In agreement with the findings of his ter. Vaccinium arctostaphylos berries were reported study, the berries of other species of Vaccinium were to include anthocyanins namely, delphinidin 3-O-β- shown to have antihypertensive effects. Feeding of glucoside, petunidin 3-O-β-glucoside and malvidin 3- spontaneously hypertensive rats with diets containing O- β-glucoside.13,17 Moreover, Delphinidin 3-O-b- 30% freeze-dried wild blueberry (Vaccinium angusti- glucoside was shown to possess vasorelaxing activ- folium) for 8 weeks was associated with a reduction ity.19 The chemical constituents of the plant leaves of blood pressure staring at 4 weeks of diet consump- and their possible involvements in the observed hy- tion.1 Moreover, diet containing 3% of blueberries potensive activity are in need of further investigation. (Vaccinium ashei reade) leaves resulted in the reduc- In conclusion, the findings of the present study tion of blood pressure in spontaneously hypertensive showed for the first time that aqueous extract of Vac- rats.23 In addition, the consumption of whole billber- cinium arctostaphylos leaves did have hypotensive ries (Vaccinium myrtillus) and crushed lingoberries activities without causing reflex tachycardia. The for 8 weeks in human subjects was associated with a findings can not speculate on the likely mechanisms significant reduction in blood pressure.24 Vaccinium involved. The exact hypotensive mechanism of the macrocarpon (American cranberries) was also re- extract needs to be investigated. ported to have antihypertensive activities in human.11 The findings of this study can not speculate on the likely mechanisms underlying the hypotensive activity Acknowledgement of the extract. However, the hypotensive activity of aqueous extract of blueberry (Vaccinium ashei reade) This study was supported by a research grant (84- leaves23 was attributed to angiotensin converting en- 2697) from the Vice-Presidency in Research, Shiraz zyme inhibition. In addition, other Vaccinium berries University of Medical Sciences. 24 were reported to act via α1-antagonism and angiotensin converting enzyme inhibition,2,5,23 and endothelial nitric Conflict of interest: None declared.

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