Garlic induced vasorelaxation: role of endothelium and nitric oxide

Garlic is a remarkable plant that has various beneficial effects and seems to function by multiple mechanisms that may be affected by its way of handling. The aim of the present study was to investigate the possible modification in activity of fresh garlic on vascular reactivity due to extraction in different organic and inorganic solvents or after microfiltration through specific molecular sieving devices. The possible roles of vascular endothelium and nitric oxide [NO] in mediating garlic extract-induced vasodilatation were also investigated. In addition, the interaction between garlic and other endothelium-dependent and endothelim-independent vasorelaxant agents was studied. Experiments were performed on ring preparations, with intact or denuded endothelium, isolated from rat pulmonary artery [PA] and thoracic aorta [TA]. Isolated vascular rings were precountracted with phenylephrine prior to testing possible vasorelaxation responses to different fresh garlic extracts. In all endothelium-intact ring preparation precontracted with phenylephrine, the addition of either water, 5% polyethylene glycol [PEG] or 5% ethanol extracts of whole fresh micro /ml] resulted in a slow developing dose-depndent relaxation reaching an average maximum of -82 +/- 5,-86+/7% and -88 +/- 6, respectively, in case of pulmonary artery, and -87 +/- 6.-90 +/- 7, respectively, in case of thoracic aorta. Extracts of either absolute [100%] ethanol or pure polyethylene glycol [PEG] of garlic failed to produce a significant fascular response [E[max]=10 +/- 2 and -8 +/- 1%, respectively, with the PA, and -13 +/- 2 and -10 +/- 1%, respectively, with the TA]. Microfiltration of the water extracts of fresh garlic with either a 10 000 or 1000 molecular weight sieving device did not alter the observed relaxation responses of either the PA or the TA. Mechanical disruption of intimal endothelium significantly attenuated garlic extract-induced vasorelaxation by 52-80% in case of PA, and by 56-72% in case of TA compared with the control endothelium-intact vessels. Pretreatment with the NO synthase inhibitor, N[G]-intero-L-arginine methyl ester [L-NAME] significantly reduced garlic extract-induced vasorelaxation by 26-71% in case of PA, and by 36-58% in case of TA. Pretreatment with L-cysteine almost abolished garlic-induced relaxations and decreased E[max] values by 91% and 89% in casse of the PA and the TA, respectively. On the other hand, pre-incubation of the tissues with superoxide dismutase [SOD] significantly potentiated garlic-induced relaxations and increased relaxation values by 14-40% in case of the PA, and by 12-42% in case of the TA, resectivley. Pretreatment with garlic [500] micro g/ml] significantly potentiated acetylcholine-induced relaxation in endothelium-intact vessels, obtained from either the PA or the TA, by shifting the dose-response curve to the left. On the other hand, in endothelium disrupted vessels, same garlic pre-treatment did not alter-s-nitroso-N-acetylpenicilamine [SNAP]-induced relaxations of the PA, while reduced mild potentiationin case of TA with no significant change of E[max]. It is concluded that: 1] Garlic has potent vasorelaxant properties on both the pulmonary and systemic vasculature, 2] The active vasorelaxant ingredient[s] contained in fresh garlic extracts have molecular weight[s] less than 100, 3] To obtain the best vasorelaxant effects of fresh garlic, it should be extracted either in water or very dilute concentrations of organic solvents as ethanol and PEG, 4] Fresh garlic extracts can produce both endothelium-dependent and -independent vasodilatation-dependent and -independent vasodilatation; however, the endothelium-dependent component appears to play a greater role, 5] Endothelium-dependent relaxations of garlic are mediated mainly through increasing production and or/basal release of NO rather than stabilizing it

Pulmonary and systemic vasorelaxation by garlic extracts: role of allicin

Garlic has been advocated for a variety of therapeutic applications in management of various ailments. The possible vasorelaxant effects of water extracts of commercially available garlic were tested on ring preparations [with intact endothelium of isolated rat pulmonary artery [PA] and thoracic aorta [TA].Isolated vascular rings were precontracted with phenylephrine[PE] [0.1-1.0] micro M/L] prior to testing. Extracts from freeze dried powder [Quintessence], aged garlic powder [Kyolic], and garlic oil macerate [Sofigel] resulted in relaxant responses with E[max] values of [-65 +/- 3%, -21 +/- 3%, -21 +/- 4% and -5 +/- 0.9%, respectively, in case of PA, and -78 +/- 5%, -34 +/- 2% and -7 +/- 2% respectively, in case of TA. Differences in vasorelaxant potency were suggested to relate to the concentrations of the garlic active ingredient, allicin, in different garlic preparations. To investigate the role of allicin in garlic-induced vasorelaxation, the effects of water extracts from custom-prepared garlic powders with either no allicin or with specific concentration of allicin yield, were assessed. The average E[max] values obained with water extracts prepared form garlic powders of allicin yields of 0, 0.15, 0.825 and 4.1 micro g/ml were -5 +/- 0.9%, -34 +/- 2%, -61 +/- 3% and -87 +/- 3% in case of PA, and -7 +/- 2%, -43 +/- 2%, -74 +/- 5% and -98 +/- 2% in case of TA, respectively. On the other hand, pre-exposure to water extracts of the same garlic powders reduced E[max] of PE-induced contractions by 3%, 23%, 35% and 89% respectively, in case of PA, and by 7%, 20%, 36% and 56% respectively, in case of TA. Thus the vasodepressor effects of garlic correlated with the allicin content of different powders. In all experiments, the differences in garlic-induced relaxations, of water extracts of different powders, obtained with the thoracic aorta vs. the pulmonary artery were statistically significant if results were compared at the same concentration. The results of the present study indicate hat: 1] Allicin is the most responsible among garlic-derived active ingredients for pulmonary and systemic vasorelaxation, 2] Freeze dried garlic preparations, known for their high allicin content, are recommended as the best choice amongst commercial garlic forms to lower pathologically elevated vascular tone, 3] Allicin may serve as a promising candidate in the management of cases of pulmonary and systemic hypertension

Time-dependent changes in the vasoconstrictor responses in diabetic rats

Disturbed vascular reactivity is one of the cardinal complications of diabetes mellitus [DM]. Several mechanisms have been postulated to explain changes in vascular responses associated with DM such as altered intracellular calcium levels responses to the alpha -adrenergic stimulant, methoxamine [MTX] and the calcium pump inhibitor, cyclopiazonic acid [CPA] were tested on the aorta of streptozotocin [STZ] diabetic rats 2, 8 and 16 weeks after induction of diabetes. Neither MTX-nor CPA-evoked vasoconstrictor responses were changed in the 2-weeks-diabetic rats. In contrast, both MTX and CPA-induced contractions were significantly [P < 0.05] increased in the 8-weeks diabetic tissues. Conversely, the maximal vasoconstrictor responses to both MTX and CPA were significantly [P <0.05] reduced in the 16-weeks diabetic tissues [P < 0.05]. The increased MTX-induced contractions 8-wekks after induction of diabetes, and the reduction of responses in corresponding tissues 16-weeks after diabetes induction were reversed in the presence of the voltage-dependent calcium channel blocker, nifedipine. Changes in MTX-evoked responses in the 16-week diabetic tissues were unaffected in the Ca[++] -free medium or by endothelial denudation. The data of the current study suggest that: 1] Contractile responses to MTX and CPA change with the development of diabetes. 2] Middle stages of diabetes may be associated with enhanced contractile responses to the alpha-adrenergic agonists and calcium pump inhibitors, whereas in late stages of diabetes attenuation of responses to the same vasoconstrictor agents may develop, 3] Changes of functional Ca[++] store size in the endoplasmic reticulum, and Ca[++] influx, mainly through voltage-dependent Ca[++] channels, may account for altered contractile responses to MTX and CPA in diabetic rats

Comparison between morning and evening single dose administration of simvastatin on endothelium-dependent relaxation and superoxide dismutase enzyme level as an antioxident marker in cholesterol-fed rabbits

Statins are widely used hypocholesterolemic drugs that act through reversible competitive inhibition of the hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase [HMGCOA] enzyme. At first, morning use of statins was recommended but now it is known that choesterogenesis follows a circadian rhythm as it occurs at a higher rate during the evening time. Accordingly, accurate timing of statin administration should be re-evaluated in order to obtain the best therapeutic effect. As simvastatin is one of the widely prescribed HMG-CoA reductase inhibitors, it was chosen in this study to test and compare its effectiveness when administered as single dose in the morning and in the evening. The experiments were performed on Newzealand rabbits divided into four equal groups, each composed of 8 animals: control normocholesterolemic, hypercholesterolemic nontreated, hypercholesterolemic treated with morning simvastatin, and hypercholesterolemic treated with evening simvastatin. Animals of control group received a cholesterol-free diet for 16 weeks, while animals of the other three groups were maintained on a high cholesterol diet for an equal duration of time. Treated groups received simvastatin in a single oral daily dose of 10 mg/kg for 8 weeks starting at the beginning of the 9[th] week, administered either in the morning or in the evening. Blood cholesterol level was checked for all animals at the end of the 4[th], 8[th], l2[th] and 16[th] weeks. At the end of the 16[th] week, the level of the anti-oxidant superoxide dismutase [SOD] enzyme was determined in erythrocyte [RBC] lysates obtained from animals of all groups. The animals were then slaughtered and vascular reactivity to acetvlcholine [ACh] was tested on ring preparations obtained from their isolated aortae [ring preparations]. Both morning and evening treatment with simvastatin significantly reduced blood cholesterol level, augmented relaxation induced by [ACh] and increased SOD level in RBCs lysates, in comparison with non-treated hypercholestero!emic group. However, results obtained with the evening dosing regimen were much more significant when compared with the morning dosing schedule. It is concluded that therapeutic efficiency of simvastatin is best obtained when the drug is administered in the evening rather than in the morning. This most likely occurs due to the circadian rhythm of cholesterol biosynthesis that tends to occur at a much greater rate during night as a result of increased availability of cholesterol precursors. This chronotherapeutic pattern of simvastatin recommends its night administration to ensure introduction of the drug at the correct timing thus achieving the best therapeutic effect

Comparison between the effect of bosentan and perindopril on diabetic angiopathy and nephropathy in streptozotocin-induced diabetic rats

Angiopathy and nephropathy are serious problems encountered in the management of diabetes, mellitus. There is accumulating literatrues describing some sort of hystological interaction between angiotensin II [ALI] and endothelins [ETs] in addition to their possible contributing roles in the pathogenesis of diabetic complications. In the present study, the angiotensin converting enzyme inhibitor [ACEI] perindopril to prevent or minimize the development of angiopathy [endothelial dysfunction] and nephropathy in a strepozotocininduced model of diabetes type I in albino rats. Animals were classified into six groups: untreated healthy non diabetic [ND] control rats, healthy [ND] rats treated with perindopril [3 mg/kg/day], healthy [ND] rats treated with bosentan [100 mg/kg/day], untreated diabetic rats, and diabetic rats treated with either perindopril or bosentan in the same doses described before. Rats were rendered diabetic by a single injection, in the tail vein, of 55 mg/kg streptozotocin [STZ] after overnight fast. Treatment with bosentan and perindopril was continued for 16 weeks during which the 24[th] urine volume, urinary albumin content, urine and plasma levels of creatinine as well as systolic blood pressure [SBP] were assessed at the end of each 4 weeks. At the end of the 16[th] week rats were sacrificed and the kidneys were removed for examination of histopathological changes, while the thoracic aortae were removed for assessment of the vasorelaxant effect of acetylcholine [Ach]. Diabetic rats developed typical functional changes manifested by hyperglycemia, polyuria, albuminuria, elevated SBP, reduced response to vasorelaxant effect of ACh in addition to histopathological changes manifested by tubular dilatation, diffuse interstitial edema and decreased density of the brush border of epithelial cells. In the healthy [ND] animals, changes obtained in the different parameters studied were insignificant between the treated and non-treated groups. In diabetic animals, however; both perindopril and bosentan significantly reduced albuminuria and lowered elevated SBP. In addition both drugs improved creatinine clearance and relaxant response to ACh to a large extent. Perindopril was more potent with regard to the hypoalbuminuric effect and the effect on creatinine clearance, while bosentan-induced improvement of vascular reactivity to ACh was more significant. Different potencies of perindopril and bosentan in affecting certain studied parameters suggests that the two drugs work either through different mechanisms or through similar pathways but to different extents. The renoprotective and antiangiopathic effects of both drugs were independent of the blood glucose level because this parameter was not significantly altered by either treatment. In conclusion, it seems that both angiotensin II and endothelins play an important role in the pathogenesis of diabetic angiopathy and nephropathy with probable interaction between the two systems to augment the production of such pathological disorders. Therefore, ACELs and ET receptor antagonists are highly recommended in the management of diabetic and ET receptor antagonists are highly recommended in the management of diabetic complications

Novel vip analogues: relative potency, duration of action and antagonism to relaxant effect of natural vip on guinea pig trachea

This study was performed on two novel VIP analogues; namely, [N1e17, A1a24, A1a25, Va126]-VIP-[1-27]-NH2 [analogue 1] and [Ser [SO3H]3, Nle17-VIP [analogue 2], which were obtained by undergoing certain changes in the amino acid sequence of the VIP molecule in a trial to reach a novel more stable, but still active form of VIP. Relative potency as well as duration of action of the two analogues was tested versus that of native VIP on isolated guinea pig tracheal strips placed in organ baths. Changes in smooth muscle tension were measured by isometric force transducers and recorded continuously. Analogue 1 was significantly more potent and had a significantly longer duration of action than natural VIP as a tracheal relaxant at the lower concentration range of 5 x 10-9 M to 5 x 10-8 M and its maximal relaxing effect was 72% of that of native VIP. Analogue 2 was significantly much less potent than natural VIP at all concentrations tested with maximal potency of only 11% of that of native VIP and showed shorter duration of action. However, it significantly reduced VIP-induced tracheal relaxation. The encouraging results with analogue 1 suggest its clinical trial in therapy of bronchial asthma. As VIP antagonists may potently inhibit the basal growth of cancer cells in vitro and certain tumors in vivo, especially lung carcinoma, analogue 2 may serve as a useful candidate in this respect. The interesting findings with the two analogues suggest further investigation to enhance their potency, whether agonistic [for analogue 1] or antagonistic [for analogue 2], at VIP receptors by additional changes in their molecules to improve the chance of possible clinical applications