Pharmacognosy Magazine

: 2011  |  Volume : 7  |  Issue : 25  |  Page : 14--18

The relaxant effect induced by Allium sativum L. bulb aqueous extract on rat isolated trachea

Badreddine Fehri1, KK Mueen Ahmed2, Jean-Marc Aiache3,  
1 Department of Pharmacology and Toxicology, Tunisia Pharmaceutical Industries Company (SIPHAT), Fondouk Choucha-Radès, 2013 Ben Arous, Tunisia
2 Department of Pharmaceutical Sciences, College of Clinical Pharmacy, King Faisal University, P. O. Box 400, Al-Ahsa-31982, Kingdom of Saudi Arabia
3 Department of Biopharmaceutics, Faculty of Pharmacy, Auvergne University, 28, Place Henri Dunant - BP 38, 63001 Clermont-Ferrand, France

Correspondence Address:
Badreddine Fehri
B.P. 181, 2040 Radès


Background: Garlic plays an important role in complementary and alternative medicine. Most people believe in and use herbal products even when they have not been as thoroughly researched as garlic. Garlic is also known for its beneficial effects on the cardiovascular system. Materials and Methods: The relaxant effect of Allium sativum L. bulb aqueous extract (ASBAE) containing 0.06%-0.10% of allicin was studied on isolated smooth muscle of trachea of rats precontracted using acetylcholine (10−5 M). Results: It was found that ASBAE induced a dose-dependent relaxation with recorded EC 50 values of 71.87 ± 5.90 μg/mL (n = 7). Pretreatments with mepyramine (10−7 M), methysergide (10−7 M), caffeine (10−6 M), theophylline (10−6 M), nifedipine (10−6 M), and dipyridamole (10−6 M) did not alter ASBAE concentration-response curves. In turn, concentration-response curves to ASBAE were significantly shifted toward right in the presence of aspirin (3.10−3 M), indomethacin (10−6 M), prazosin (10−6 M), and propranolol (10−7 M). Conclusion: It is suggested that the recorded relaxation results are due to the release of prostaglandins E 1 and E 2 consecutively to a- and b-adrenoreceptor stimulation.

How to cite this article:
Fehri B, Mueen Ahmed K K, Aiache JM. The relaxant effect induced by Allium sativum L. bulb aqueous extract on rat isolated trachea.Phcog Mag 2011;7:14-18

How to cite this URL:
Fehri B, Mueen Ahmed K K, Aiache JM. The relaxant effect induced by Allium sativum L. bulb aqueous extract on rat isolated trachea. Phcog Mag [serial online] 2011 [cited 2019 Dec 10 ];7:14-18
Available from:

Full Text


Allium sativum , commonly known as garlic, is one of the species belonging the onion family Alliaceae. Garlic is largely used around the world for its pungent flavor as a seasoning or condiment. [1] It is a fundamental component in many or most dishes of various regions, including eastern Asia, south Asia, Southeast Asia, the Middle East, northern Africa, southern Europe, and parts of South and Central America. [2] It contains the sulfur-containing compounds alliin, ajoene, diallylsulfide, dithiin, S-allyl cysteine and also enzymes, vitamin B, proteins, minerals, saponins, flavonoids, and maillard reaction products, which are non-sulfur-containing compounds. Furthermore, a phytoalexin called allixin (3-hydroxy-5-methoxy-6-methyl-2-penthyl-4H-pyran-4-one) was found, a nonsulfur compound with a γ-pyrone skeleton structure with antioxidative effects, antimicrobial effects, antitumor promoting effects, inhibition of aflatoxin B2 DNA binding, and neurotrophic effects. [3],[4],[5],[6],[7],[8]

A. sativum L. was also demonstrated to reduce cardiovascular risk factors, especially blood pressure, [9],[10],[11] hyperlipidema, and atherosclerosis. [12] Garlic is also shown to have significant relaxant effects on the airway smooth muscles. In this regard, it has been observed that administering garlic prevented the occurrence of high altitude breathing symptoms. [13] In 1998, Fallon et al.[14] demonstrated that active substances that are found in garlic caused vasorelaxation in the pulmonary arterial segments. Recently, a report indicated that a mixture of herbs containing A. sativum L. reduced an elevated respiratory rate in horses with recurrent airway obstruction. [15] In contrast, the mechanism of action of A. sativum L. in airway smooth muscle remains unclear. Hence, the present study is to investigate and identify the possible mechanism for the relaxant effects caused by A. sativum L. extracts.

 Materials and Methods

Plant material

The drug studied was a A. sativum L. bulb aqueous extract (ASBAE) obtained from Finzelberg Laboratories (Germany), which answered the following parameters:

Ratio of dried plant/extract: 6:1Allicin content was determined using gas chromatography: 0.10%

Drugs used

ASBAE (Finzelberg), acetylcholine HCl, propranolol HCl, dipyridamole were purchased from Sigma, St. Louis, MO, USA, nifedipine from Dolder, Basel, Switzerland, aspirin DL-lysine (DL-lysine acetylsalicylate) from Sanofi-aventis Paris, France, prazosin HCl from Pfizer Kalamazoo, USA, caffeine, theophylline sodium anisate, methysergide maleate, indomethacin, and mepyramine maleate from Siphat, Fondouk Choucha-Radès, Tunisia.

Prior to their dilution in Tyrode's solution, indomethacin, dipyridamole, and nifedipine were dissolved in absolute ethanol and then diluted in Tyrode's solution. Theophylline and aspirin were used from ampoules for injection (Siphat, Fondouk Choucha-Radès, Tunisia and Sanofi-aventis, Paris, France). The other substances were directly dissolved in Tyrode's solution. The required concentrations of the compounds were added to the organ bath so that the volume of ethanol never exceeded 0.05 mL (0.4% by volume). Such quantity of ethanol had no effect on acetylcholine and ASBAE responses on isolated rat trachea.

Rat trachea in vitro

Male rats weighing 300-400 g were selected in a homogeneous breeding center (Central Animal House, Tunisia Pharmaceutical Industries Company, Fondouk Choucha-Radès, Tunisia). They were sacrificed by a blow and exsanguinated. The trachea was removed immediately and cut into small segments of 3-4 rings, which were equilibrated under a resting tension of 1.5 g and suspended in 10 mL baths containing Tyrode's solution at 37°C ± 0.5°C and the tissue was aerated continuously with 95% O 2 and 5% CO 2 . The composition of the Tyrode's solution was (mM): [NaCl: 139.2; KCl: 2.7; CaCl 2 : 1.8; MgCl 2 : 0.49; NaHCO 3 : 11.3; Na 2 HPO 4 : 0.4; glucose: 5.5]. Tension was measured isometrically with Ugo Basil strain gauges displayed on Geminy Ugo Basile recorders (Italy).

Experimental procedure

The tracheal rings (3 to 4) were placed in organ bath for 85 min and washed with Tyrode solution at every 15-min time interval. The tissue was contracted using acetylcholine (ACh 3.10−3 M) until maximal contraction was achieved. During that stage, the tissue was subjected to relaxation using with theophylline (THEO 3.10−3 M), further washed repeatedly and allowed to rest until it returned to baseline tension. When baseline tension was reached, it was again contracted with ACh 10−5 M, and maximal tension was obtained, during this time, it was studied to establish concentration-response curves to ASBAE by the method of cumulative addition. The final addition was followed by addition of THEO 3.10−3 M to obtain complete relaxation. Pretreatments with drugs were performed 30 min before ACh 10−5 M contractions. The relaxations induced by ASBAE were expressed as a percentage of relaxation vs complete relaxation (E MAX ). The −log EC 50 (pD 2 ) values, defined as the negative log concentration-effect curves, were evaluated graphically from each experiment.

Statistical analysis

All data were expressed as mean ± SEM. Data of relaxant effects of different concentrations of extracts were compared with the results of negative and positive control using Student t test. Significant differences with controls are shown as * p < 0.05 and *** p < 0.001.


ASBAE exhibited a dose-dependent relaxant effect on the rat isolated trachea precontracted with ACh 10−5 M [Figure 1]. On basal tone of isolated tissue, ASBAE showed mild contractile effects at lower doses ranging from 10−6 to 10−4 g/mL, followed by relaxant effects at higher doses (from 10−3 to 3.10−3 g/mL) (data not shown). {Figure 1}

Pretreatments with mepyramine 10−7 M and methysergide 10−7 M, ASBAE concentration-response curves were not significantly modified as observed by pD 2 values [Table 1]. Statistical analysis of pD 2 values also failed to detect any difference in the relaxant effect of ASBAE between control and tracheal rings treated with caffeine (10−6 M), theophylline (3.10−6 M), nifedipine (10−6 M), and dipyridamole (10−6 M) [Table 1]. In turn, pretreatments with aspirin (3.10−3 M) and indomethacin (10−6 M) caused right shift to ASBAE concentration-response curves, and pD 2 values significantly decreased [Table 1] and [Figure 2]. Prazosin (10−6 M) and propranolol (10−7 M) had the same effect (P < 0.05 and P < 0.001) [Table 1] and [Figure 3]. {Figure 2}{Figure 3}{Table 1}


The present work indicated that ASBAE induced multiple effects on rat isolated trachea according to the level on tone. On basal tone trachea, ASBAE induced contractile effects at low doses (10−6 to 10−4 g/mL), whereas at higher doses (10−3 to 3.10−3 g/mL), it induced relaxation effect.

Furthermore, it was also demonstrated through the present work that ASBAE induced a dose-dependent relaxation with EC 50 values of 71.87 ± 5.90 μg/mL (n = 7) on the rat isolated trachea precontracted with ACh 10−5 M. In the presence of both, mepyramine 10−7 M, an antagonist of H 1 receptors [16] and methysergide 10−7 M, an antagonist of serotonin (5-Hydroxytryptamine) receptors, [17] the induced relaxation of ASBAE was not significantly modified. The present study suggests that ASBAE-induced relaxation may not be resulting from interactions with histamine and serotonin receptors. In the other hand, caffeine (10−6 M) and theophylline (3.10−6 M), two phosphodiesterase (PDE) inhibitors, [18] and nifedipine (10−6 M) and dipyridamole (10−6 M), two compounds acting as calcium antagonists, [19] did not alter ASBAE-induced relaxation; hence, it is possible to suggest that the recorded relaxation does not involve inhibition of cyclic nucleotide phosphodiesterase or a calcium blocking influx phenomenon.

The prostaglandin synthetase inhibitors, aspirin (3.10−3 M) and indomethacin (10−6 M), [19] significantly antagonized ASBAE-induced relaxation. The present outcome may possibly suggest that the recorded relaxation could be mediated due to the release of the relaxant metabolites of arachidonic acid (AA) produced under the activation of cyclooxygenase. It has been shown that garlic prevents platelet aggregation by selectively inhibiting platelet thromboxane (TX) synthesis and reducing vascular prostacyclin (PGI 2 ). [20],[21]

The lungs of many animal species, including man, are rich in prostaglandins (PGs) that do influence the tone of tracheal and bronchial muscles. Many studies demonstrated that PGs of the E series and PGs of F series, respectively, induce a relaxation and a contraction of tracheal smooth muscle in vitro. Takano et al.[22] particularly studied the effects of PGs E 1 , E 2 , F2α, A 1 , A 2 , and B 2 on guinea pig-isolated trachea and showed that F2α, B 2 , and A 2 produced contraction, whereas PGs E 1 and E 2 produced relaxation. The same authors reported that PG A 1 produced no response. The same result was obtained by Coleman and Kennedy, [23] who studied the effect of 12 PGs on the guinea pig-isolated trachea. PGs of series E are considered to be bronchodilators not only in experimental animals but also in man. [24] Taking into consideration, based on these observations, it is now possible to suggest that active components contained in ASBAE induced the recorded relaxation by a stimulation of PGs E 1 and E 2 , and further, the effect was antagonized by aspirin and indomethacin pretreatments.

It is also reported that PGs E 1 and E 2 cause relaxation when tone is present and contraction when tone is absent. [19],[24],[25] This may explain the contractile effects induced at low doses (from 10−6 to 10−4 g/mL) by ASBAE on basal tone trachea. [26] This contraction phase could therefore be mediated by PGs E 1 and E 2 . When basal tone has reached a sufficient level, then a relaxation phase occurred (from 10−3 to 3.10−3 g/mL) probably due to the release of PGs E 1 and E 2 .

Pretreatments with the respective α- and β-adrenoreceptor blockers, prazosin 10−6 M [27],[28] and propranolol 10−7 M,caused right shift of ASBAE concentration-effect curves. The order of potency of the recorded antagonism was propranolol 10−7 M > prazosin 10−6 M [Table 1] and [Figure 3].

This result may suggest that active components present in ASBAE could stimulate both α- and β-adrenergic receptors with a higher affinity for β than for α receptors. The affinity of various Allium species for adrenergic (α1, α2, β1 , and β2 ) receptors has recently been studied. Nencini et al.[29] reported that A. sativum L. did not show high affinity for α1 and α2 receptors and showed a partial affinity for β1 receptors, whereas wild-type Allium species presented a greater affinity for these receptors, in particular for β2 receptors (Allium neapolitanum and Allium subhirsutum species).


Further investigations need to be undertaken to determine the affinity of A. sativum L. for adrenergic receptors on rat trachea. The link between PGs E 1 and E 2 and α- and β-adrenergic receptor stimulation by which active components contained in ASBAE relax the rat isolated trachea should also be clarified. In this respect, it has been suggested that PGs E2 exert their biologic actions via at least 4 receptor subtypes (EP 1 -EP 4 ) and that EP 1 could act as a modulator of β2 -adrenergic receptor. [30] Active components present in ASBAE could possibly relax the rat isolated trachea by such mechanism of action.


1Gardner CD, Messina M, Lawson LD, Farkuhar JW. Soy, garlic, and Ginko biloba: Their potential role in cardiovascular disease prevention and treatment. Curr Atheroscler Rep 2003;5:468-75.
2Khanum F, Anilalkumar KR, Viswanathan KR. Anticarcinogenic properties of garlic. A review. Crit Rev Food Sci Nutr 2004;44:479-88.
3Tattleman E. Health effects of garlic. Am Fam Phys 2005;72:103-6.
4Sharma A, Sharma V, Kansal L. Therapeutic Effects of Allium sativum on Lead-induced Biochemical changes in Soft tissues of Swiss Albino Mice. Phcog Mag 2009;5:364-71. Available from: [last cited on 2010 Oct 12].
5Navaneetha LK, Veerakumari L. Effect of Allium sativum on the phosphoenolpyruvate carboxykinase and pyruvate kinase activity of Haemonchus contortus in vitro. Phcog Mag 2009;5:430-2.
6Petrovska BB, Cekovska S. Extracts from the history and medical properties of garlic. Phcog Rev 2010;4:106-10.
7Afkhami-Ardekani M, Kamali-Ardekani A, Shojaoddiny-Ardekani A. Effects of garlic on serum lipids and blood glucose of type 2 diabetic patients. Int J Diab Dev Ctries 2006;26:86-8.
8Biren N Shah, Bhavesh S Nayak, Manish A Patel, Ashish D Mishra, Avinash K Seth. Aged garlic extract-a health benefit review. Phcog Mag 2006;2:90-5.
9Banerjee SK, Maulik SK. Effect of garlic on cardiovascular disorders: A review. Nutr J 2002;1:4-14.
10Dhawan V, Jain S. Effect of garlic supplementation on oxidized low density lipoproteins and lipid peroxidation in patients of essential hypertension. Mol Cell Biochem 2004;266:109-15.
11Turner B, Mølgaard C, Marckmann P. Effect of garlic (Allium sativum) powder tablets on serum lipids, blood pressure and arterial stiffness in normo-lipedaemic volunteers: A randomized, double blind, placebo-controlled trial. Br J Nutr 2004;92:701-6.
12WHO. Bulbus Allii Sativi. In: WHO monographs on selected medicinal plants. Vol 1. Geneva WHO; 1999. p. 16-32.
13Harris L. The book of Garlic. Reading, MA: Addison-Wesley; 1995.
14Fallon MB, Gary AA, Tarek TA, Jun D, Shi JC, Yiu FC, et al. Garlic prevents hypoxic pulmonary hypertension in rats. Am J Physiol Lung Cell Mol Physiol 1998;275:283-7.
15Pearson W, Charch A, Brewer D, Clarke AF. Pilot study investigating the ability of an herbal composite to alleviate clinical signs of respiratory dysfunction in horses with recurrent airway obstruction. Can J Vet Res 2007;78:145-51.
16Parsons ME, Ganellin CR. Histamine and its receptors. Br J Pharmac 2006;147:S127-35.
17Saxena PR, Lawang A. A comparison of cardiovascular and smooth muscle effects of 5-hydroxytryptamine and 8-carboxamidotryptamine, a selective agonist of HT 1 receptors. Arch Int Pharmacodyn Ther 1985;277:235-52.
18Weiss B, Hait WN. Selective cyclic nucleotide phosphodiesterase inhibitors as potential therapeutic agents. Ann Rev Pharmacol Toxicol 1977;17:441-77.
19Nayler WG, Poole-Wilson P. Calcium antagonists: definition and mode of action. Basic Res Cardiol 1981;76:1-15.
20Vane T, Booting R. Inflammation and mechanism of action of anti-inflammatory drugs. FASSEB J 1987;1:89-96.
21Ali M, Mohammed SY. Selective suppression of platelet thromboxane formation with sparing of vascular prostacyclin synthesis by aqueous extract of garlic in rabbits. Prostaglandins Leukot Med 1986;25:139-46.
22Takano S, Sawano A, Watanabe H, Suzuki T. A comparison of response of guinea-pig isolated trachea to six prostaglandins. Prostaglandins 1978;15:485-9.
23Coleman RA, Kennedy I. Contractile and relaxant actions of prostaglandins on guinea-pig isolated trachea. Br J Pharmacol 1980;68:533-9.
24Rosenthale ME. Prostaglandins as bronchodilators. N Y State J Med 1975;75:374-8.
25Puglish L. Opposite effects of prostaglandins E and F on tracheal smooth muscles and their interactions with calcium ions. Adv Biosci 1973;9:219-27.
26Lambley JE, Smith AP. The effects of arachidonic acid, indomethacin and SC-19220 on guinea-pig tracheal muscle tone. Eur J Pharmac 1975;30:148-53.
27Davey MJ. The pharmacology of prazosin, an alpha- adrenoreceptor antagonist and the basis for its use in the treatment of essential hypertension. Clin Exp Hypertens 1982;a4:1-2,47-59.
28Frishman WH, Cheng-Lai A. Nawarskas Current Cardiovascular Drugs. 4 th ed. Curr Med 2005. p. 152.
29Nencini C, Franchi GG, Micheli L. Cardiovascular receptor binding affinity of aqueous extracts from Allium species. Int J Food Sci Nutr 2010;61:433-9.
30McGraw DW, Mihibachler KA, Schwarb MR, Rahman FF, Small KM, Almoosa KF, et al. Airway smooth muscle prostaglandin-EP 1receptors directly modulate β2 -adrenergic receptors within a unique heterodimeric complex. J Clin Invest 2006;116:1400-9.