BACKGROUND: Prescribing incompetence is an important factor that contributes to prescribing error, and this is often due to inadequate training during medical schools. We therefore aimed to develop and validate an instrument to assess the prescribing readiness of medical students (PROMS) in Malaysia.
METHODS: The PROMS comprised of 26 items with four domains: undergraduate learning opportunities; hands-on clinical skills practice; information gathering behaviour; and factors affecting the learning of prescribing skills. The first three domains were adapted from an existing questionnaire, while items from the last domain were formulated based on findings from a nominal group discussion. Face and content validity was determined by an expert panel, pilot tested in a class of final year (Year 5) medical students, and assessed using the Flesch reading ease. To assess the reliability of the PROMS, the internal consistency and test-retest (at baseline and 2 weeks later) were assessed using the Wilcoxon Signed Ranks test and Spearman's rho. The discriminative validity of the PROMS was assessed using the Mann-Whitney U-test (to assess if the PROMS could discriminate between final year medical students from a public and a private university).
RESULTS: A total of 119 medical students were recruited. Flesch reading ease was 46.9, indicating that the instrument was suitable for use in participants undergoing tertiary education. The overall Cronbach alpha value of the PROMS was 0.695, which was satisfactory. Test-retest showed no difference for 25/26 items, indicating that our instrument was reliable. Responses from the public and private university final year medical students were significantly different in 10/26 items, indicating that the PROMS was able to discriminate between these two groups. Medical students from the private university reported fewer learning opportunities and hands-on practice compared to those from the public university. On the other hand, medical students from the private university reported more frequent use of both web based and non-web-based resources compared to their public university counterparts.
CONCLUSIONS: The PROMS instrument was found to be a reliable and valid tool for assessing medical students' readiness to prescribe in Malaysia. It may also inform on the adequacy of medical programmes in training prescribing skills.
Angiotensin II is known to act primarily on the angiotensin AT(1) receptors to mediate its physiological and pathological actions. Des-aspartate-angiotensin I (DAA-I) is a bioactive angiotensin peptide and have been shown to have contrasting vascular actions to angiotensin II. Previous work in this laboratory has demonstrated an overwhelming vasodepressor modulation on angiotensin II-induced vasoconstriction by DAA-I. The present study investigated the involvement of the AT(1) receptor in the actions of DAA-I on angiotensin II-induced vascular actions in the renal vasculature of normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and streptozotocin (STZ)-induced diabetic rats. The findings revealed that the angiotensin receptor in rat kidney homogenate was mainly of the AT(1) subtype. The AT(1) receptor density was significantly higher in the kidney of the SHR. The increase in AT(1) receptor density was also confirmed by RT-PCR and Western blot analysis. In contrast, AT(1) receptor density was significantly reduced in the kidney of the streptozotocin-induced diabetic rat. Perfusion with 10(-9)M DAA-I reduced the AT(1) receptor density in the kidneys of WKY and SHR rats suggesting that the previously observed vasodepressor modulation of the nonapeptide could be due to down-regulation or internalization of AT(1) receptors. RT-PCR and Western blot analysis showed no significant changes in the content of AT(1) receptor mRNA and protein. This supports the suggestion that DAA-I causes internalization of AT(1) receptors. In the streptozotocin-induced diabetic rat, no significant changes in renal AT(1) receptor density and expression were seen when its kidneys were similarly perfused with DAA-I.
Angiotensin 1-7, a heptapeptide derived from metabolism of either angiotensin I or angiotensin II, is a biologically active peptide of the renin-angiotensin system. The present study investigated the effect of angiotensin 1-7 on the vasopressor action of angiotensin II in the renal and mesenteric vasculature of Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR) and streptozotocin-induced diabetic rats. Angiotensin II-induced dose-dependent vasoconstrictions in the renal vasculature. The pressor response was enhanced in the SHR and reduced in the streptozotocin-diabetic rat compared to WKY rats. Angiotensin 1-7 attenuated the angiotensin II pressor responses in the renal vasculature of WKY and SHR rats. However, the ability to reduce angiotensin II response was diminished in diabetic-induced rat kidneys. The effect of angiotensin 1-7 was not inhibited by 1-[(4-(Dimethylamino)-3-methylphenyl] methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate (PD123319), an angiotensin AT(2) receptor antagonist. (D-ALA(7))-Angiotensin I/II (1-7) (D-ALA) (an angiotensin 1-7 receptor antagonist), indomethacin (a cyclo-oxygenase inhibitor), and N(omega)-Nitro-L-Arginine Methyl Ester (L-NAME)(a nitric oxide synthetase inhibitor) abolished the attenuation by angiotensin 1-7 in both WKY rats and SHR, indicating that its action is mediated by angiotensin 1-7 receptor that is either coupled to the release of prostaglandins and/or nitric oxide. The vasopressor responses to angiotensin II in mesenteric vasculature bed was also dose-dependent but smaller in magnitude compared to the renal vasculature. The responses to angiotensin II were relatively smaller in SHR but no significant difference was observed between WKY and streptozotocin-induced diabetic rats. Angiotensin 1-7 attenuated the angiotensin II pressor responses in WKY, SHR and diabetic-induced mesenteric bed. The attenuation was observed at the lower concentrations of angiotensin II in WKY and diabetic-induced rats but at higher concentrations in SHR. Similar observation as in the renal vasculature was seen with PD123319, D-ALA, and L-NAME. Indomethacin reversed the attenuation by angiotensin 1-7 only in the SHR mesenteric vascular bed. The present findings support the regulatory role of angiotensin 1-7 in the renal and mesenteric vasculature, which is differentially altered in hypertension and diabetes.
The present study investigated the action of des-aspartate-angiotensin I (DAA-I) on the pressor action of angiotensin II in the renal and mesenteric vasculature of WKY, SHR and streptozotocin (STZ)-induced diabetic rats. Angiotensin II-induced a dose-dependent pressor response in the renal vasculature. Compared to the WKY, the pressor response was enhanced in the SHR and reduced in the STZ-induced diabetic rat. DAA-I attenuated the angiotensin II pressor action in renal vasculature of WKY and SHR. The attenuation was observed for DAA-I concentration as low as 10(-18) M and was more prominent in SHR. However, the ability of DAA-I to reduce angiotensin II response was lost in the STZ-induced diabetic kidney. Instead, enhancement of angiotensin II pressor response was seen at the lower doses of the octapeptide. The effect of DAA-I was not inhibited by PD123319, an AT2 receptor antagonist, and indomethacin, a cyclo-oxygenase inhibitor in both WKY and SHR, indicating that its action was not mediated by angiotensin AT2 receptor and prostaglandins. The pressor responses to angiotensin II in mesenteric vascular bed were also dose-dependent but smaller in magnitude compared to the renal vasculature. The responses were significantly smaller in SHR but no significant difference was observed between STZ-induced diabetic and WKY rat. Similarly, PD123319 and indomethacin had no effect on the action of DAA-I. The findings reiterate a regulatory role for DAA-I in vascular bed of the kidney and mesentery. By being active at circulating level, DAA-I subserves a physiological role. This function appears to be present in animals with diseased state of hypertension and diabetes. It is likely that DAA-I functions are modified to accommodate the ongoing vascular remodeling.
We assessed the effectiveness of an educational intervention in reducing antibiotic prescribing in public primary care clinics in Malaysia. Twenty-nine medical officers in nine clinics received an educational intervention consisting of academic detailing from the resident Family Medicine Specialist, as well as an information leaflet. The antibiotic prescribing rates were assessed for six months - three months before and three months after the intervention. A total of 28,562 prescriptions were analyzed. Among participating doctors, general antibiotic prescribing rates for pre- and post-intervention phases were 14.3% and 11.0% (post-intervention vs pre-intervention RR 0.77, 95% CI 0.72 to 0.83). The URTI-specific antibiotic prescribing rates for pre- and post-intervention phases were 27.7% and 16.6%, respectively (post-intervention vs pre-intervention RR 0.60, 95% CI 0.54 to 0.66). No significant change in antibiotic prescribing rates was observed among primary care practitioners who did not participate in the study. This low cost educational intervention using both active and passive strategies focusing on URTI produced a statistically significant (and clinically important) reduction in antibiotic prescribing.
Study site: Klinik Kesihatan, Negeri Sembilan, Malaysia
Medical students are usually drawn from the best of students, but it is not unusual to see these brilliant students fail their exams or even dismissed from medical school because of poor academic performance. Information overload has been recognized as one of the major contributing factors to this problem. The situation is expected to get worse, with the ever-present technology-induced exponential growth in information. In discussing this issue, the authors echo the concerns of several experts regarding the content overload of medical school curricula, particularly in pharmacology. It is the increasing awareness of this problem that led the Association of American Medical Colleges and the General Medical Council of Britain to promote the concept of a core curriculum for each of the principal disciplines in medicine. Several medical schools have adopted the concept and also the problem-based learning approach, which focuses on ameliorating the complex problems associated with information growth in medical education. Based on the authors' experience as medical students, medical practitioners, and pharmacology teachers, they discuss the factors that contribute to information overload, from psychological and nonpsychological perspectives. Issues such as the design and structure of the curriculum, the quality of training and effectiveness of the teachers (clinically qualified vs. nonclinically qualified teachers), and the psychological preparedness of the students are discussed. The authors make suggestions for improvement.
Since the introduction of problem-based learning (PBL) into medical education in the late 1960s, several new and old medical schools have adopted this approach the main attraction of which includes the promotion of student-centered and life-long learning, team spirit, communication skills and enquiry. With an ever-increasing information base and changing attitudes in the health sciences, these are highly desirable characteristics of the health worker of the future, who will be required to grapple with these phenomenal changes. From medical education, the PBL approach has inevitably spread to other disciplines, especially the health-related disciplines. In the Asia-pacific region (Malaysia in particular), PBL was introduced into medical education in the early 1970s, but the growth has been slow; the reasons are discussed. Only recently (in the 1990s) have more medical and non-medical schools started to adopt PBL. The management of the Pantai Institute of Health Science and Nursing decided to adopt PBL for the Nursing curriculum. A one-day introductory workshop was, therefore, organized to expedite the process. Post-workshop feedback obtained through a five-point Likert scale questionnaire indicated a successful outcome. The workshop process is, therefore, documented as reference especially for Nursing colleges in places where PBL expertise is in short supply.
Boldine, a major aporphine alkaloid found in Chilean boldo tree, is a potent antioxidant. Oxidative stress plays a detrimental role in the pathogenesis of endothelial dysfunction in hypertension. In the present study, we investigated the effects of boldine on endothelial dysfunction in hypertension using spontaneously hypertensive rats (SHR), the most studied animal model of hypertension. SHR and their age-matched normotensive Wistar-Kyoto (WKY) rats were treated with boldine (20 mg/kg per day) or its vehicle, which served as control, for seven days. Control SHR displayed higher systolic blood pressure (SBP), reduced endothelium-dependent aortic relaxation to acetylcholine (ACh), marginally attenuated endothelium-independent aortic relaxation to sodium nitroprusside (SNP), increased aortic superoxide and peroxynitrite production, and enhanced p47(phox) protein expression as compared with control WKY rats. Boldine treatment significantly lowered SBP in SHR but not in WKY. Boldine treatment enhanced the maximal relaxation to ACh in SHR, but had no effect in WKY, whereas the sensitivity to ACh was increased in both SHR and WKY aortas. Boldine treatment enhanced sensitivity, but was without effect on maximal aortic relaxation responses, to SNP in both WKY and SHR aortas. In addition, boldine treatment lowered aortic superoxide and peroxynitrite production and downregulated p47(phox) protein expression in SHR aortas, but had no effect in the WKY control. These results show that boldine treatment exerts endothelial protective effects in hypertension, achieved, at least in part, through the inhibition of NADPH-mediated superoxide production.
The female gender reduces the risk, but succumbs more to cardiovascular disease. The hypothesis that short-term (8weeks) Streptozotocin-induced diabetes could produce greater female than male vascular tissue reactivity and the mechanistic basis were explored. Aortic ring responses to Phenylephrine were examined in age- and sex-matched normoglycaemic/diabetic rats. The normoglycaemic male tissue contracted significantly more than the normoglycaemic female and the male/female diabetic tissues. Endothelial-denudation, l-NAME or MB reversed these differences suggesting an EDNO-cGMP dependence. 17β-oestradiol exerted relaxant effect on all endothelium-denuded (and normoglycaemic endothelium-intact male) tissues, but not endothelium-intact normoglycaemic female. The greater male tissue contraction is attributable to absent 17β-oestradiol-modulated relaxation. Indomethacin blockade of COX attenuated male normoglycaemic and female diabetic tissue contraction (both reversed by l-NAME), but augmented diabetic male tissue contraction. These data are consistent with the raised contractile TXA(2) and PGE(2) in normoglycaemic male and diabetic female tissues, and the relaxant PGI(2) in diabetic male (and female). The higher levels of PGI(2) in the normoglycaemic and diabetic female perhaps explain their greater relaxant response to Acetylcholine compared to the respective male. In conclusion, there is an endothelium-dependent gender difference in the effect of short term diabetes on vascular tissue reactivity which is COX mediated.
The effect of acidosis on insulin-induced relaxation was studied in thoracic aortic rings (from Wistar-Kyoto (WKY) rats) with (+ED) or without (-ED) endothelium. The rings were mounted in normal (pH 7.4) or acidotic (pH 7.2) Krebs solution for isometric tension recording. Phenylephrine (PE, 3.0 microM)-contracted tissues were exposed to insulin in the presence or absence of various inhibitors. Insulin exerted similar concentration-dependent relaxation of +ED tissues in normal and acidotic pH. Endothelium denudation, significantly (p<0.05) reduced insulin effect in normal, but not acidotic pH. Under normal pH, treatment with L-NAME or methylene blue significantly (p<0.05) reduced insulin responses in the +ED (but not the -ED) tissues. The insulin effect was also significantly (p<0.05) inhibited by tetraethylammonium (TEA; BK(Ca) blocker), 4-Aminopyridine (4-AP; K(V) channel blocker), combined treatments (L-NAME+4-AP+TEA, in +ED tissues) or (4-AP+TEA, in -ED tissues). In either +ED or -ED tissues, indomethacin (cyclo-oxygenase inhibitor), glibenclamide (K(ATP) channel blocker), barium chloride (K(ir) channel blocker) or Ouabain (a Na(+)/K(+)-ATPase inhibitor) had no effect. Except for methylene blue (effect on +ED tissues), none of the drug treatments inhibited insulin vasodilator effect in acidosis (+ED or -ED tissues). These data indicate that insulin exerts an endothelium-dependent and -independent vasodilatation in rat aorta which in normal pH is mediated via BK(Ca) and K(v) channels, including the EDNO-cGMP cascade. Acidosis abolishes the endothelium-dependent relaxation mechanism unraveling a novel mechanism that is as efficacious and is cGMP-, but not EDNO-, BK(Ca)- or K(v)-mediated.
Acute exposure to the flavonoid baicalein inhibited endothelium-dependent relaxation in physiological arteries, although the mechanisms are not fully understood. We investigated the effect of baicalein on vascular tone in Wistar-Kyoto (WKY) rat isolated aortic rings in the presence and absence of oxidative stress to further determine the underlying mechanisms. Exposure to baicalein (10 microM) completely abolished endothelium-dependent relaxation induced by acetylcholine and attenuated significantly the endothelium-independent relaxation induced by sodium nitroprusside. Baicalein, similar to Nomega-nitro-L-arginine methyl ester (L-NAME, 10 microM), potentiated significantly the contractile response of aortic rings to alpha1-adrenoceptor agonist phenylephrine. In the presence of L-NAME the baicalein effect on phenylphrine contraction or acetylcholine relaxation was unaltered, suggesting that these effects of baicalein are (like L-NAME effect) endothelial nitric oxide synthase (eNOS)/endothelium-derived nitric oxide-dependent. Inhibition of cyclooxygenase activity with indomethacin (10 microM) or scavenging of superoxide anions with superoxide dismutase (150 units/ml), but not scavenging of hydrogen peroxide with catalase (800 units/ml), enhanced significantly by an essentially similar extent the relaxation to acetylcholine in baicalein-pretreated aortic rings. Relaxant effect to acetylcholine was significantly attenuated in control aortic rings, but was completely abolished in baicalein-pretreated aortic rings in the presence of reduced form of beta-nicotinamide adenine di-nucleotide (beta-NADH, 300 microM). Baicalein blocked beta-NADH (300 microM)-induced transient contractions, suggesting that baicalein may have inhibited activity of NADH/NADPH-oxidase. Baicalein did not alter the failure of acetylcholine to induce relaxation in the presence of pyrogallol (300 microM). In summary, acute exposure to baicalein impairs eNOS/endothelium-derived nitric oxide-mediated vascular tone in rat aortas through the inhibition of endothelium-derived nitric oxide bioavailability coupled to reduced bioactivity of endothelium-derived nitric oxide and to cyclooxygenase-mediated release of superoxide anions.
In this study, we report the effects of a non-antioxidant flavonoid flavone on vascular reactivity in Wistar-Kyoto (WKY) rat isolated aortae. Whether flavone directly modulates vascular reactivity in spontaneously hypertensive rat (SHR) and streptozotocin-induced diabetic-WKY rat isolated aortae was also determined. Thoracic aortic rings were mounted in organ chambers and exposed to various drug treatments in the presence of flavone (10 microM) or its vehicle (DMSO), which served as control. Pretreatment with flavone enhanced relaxant effects to endothelium-dependent vasodilator acetylcholine (ACh) and attenuated contractile effects to alpha(1)-receptor agonist phenylephrine (PE) in WKY aortae compared to those observed in control aortic rings. Flavone had no effect on relaxations to ACh in WKY aortae incubated with either L-NAME or methylene blue, but enhanced relaxations to ACh in WKY aortae incubated with indomethacin or partially depolarized with KCl. Relaxations to ACh are totally abolished in both control or flavone pretreated endothelium-denuded WKY aortae. Flavone attenuated the inhibition by beta-NADH of ACh-induced relaxation in WKY aortae, but it had no significant effect on the transient contractions induced by beta-NADH nor the pyrogallol-induced abolishment of ACh-induced relaxation in WKY aortae. Flavone enhanced endothelium-independent relaxation to sodium nitroprusside (SNP) in both endothelium-intact and -denuded WKY aortae. Flavone enhanced relaxation to ACh and SNP as well as attenuated contractile effects to PE in SHR and diabetic aortae, a finding similar to that observed in normal WKY aortae. From these results, we conclude that flavone modulates vascular reactivity in normal as well as hypertensive and diabetic aortae. These effects of flavone results probably through enhanced bioactivity of nitric oxide released from the endothelium.
Des-aspartate angiotensin I (DAA-I), an endogenous nonapeptide, counteracts several effects of angiotensin II on vascular tone. The aim of this study was to investigate the acute protective effect of DAA-I on endothelial function in the spontaneously hypertensive rat (SHR) as well as its effect on angiotensin II-induced contractions and oxidative stress. Aortic rings were incubated with DAA-I (0.1μM) for 30min prior to the assessment of angiotensin II-induced contractions (0.1nM-10μM) in WKY and SHR aortas. Total nitrate and nitrite levels were assessed using a colorimetric method and reactive oxygen species (ROS) were measured by dihydroethidium (DHE) fluorescence and lucigenin-enhanced chemiluminescence. The effect of DAA-I was also assessed against endothelium-dependent and -independent relaxations to acetylcholine and sodium nitroprusside, respectively. Angiotensin II-induced contractions were significantly reduced by DAA-I, losartan and tempol. Incubation with ODQ (soluble guanylyl cyclase inhibitor) and removal of the endothelium prevented the reduction of angiotensin II-induced contractions by DAA-I. Total nitrate and nitrite levels were increased in DAA-I, losartan and tempol treated-SHR tissues while ROS level was reduced by DAA-I and the latter inhibitors. In addition, DAA-I significantly improved the impaired acetylcholine-induced relaxation in SHR aortas whilst sodium nitroprusside-induced endothelium-independent relaxation remained unaffected. The present findings indicate that improvement of endothelial function by DAA-I in the SHR aorta is mediated through endothelium-dependent release of nitric oxide and inhibition of angiotensin II-induced oxidative stress.
1. There is a growing interest in the anti-oxidant characteristics and use of flavonoids in the management of cardiovascular diseases. The cardiovascular mechanism of action of these plant derivatives remains controversial. This study compared the effects of the flavonoid quercetin with those of the anti-oxidant vitamin ascorbic acid (vitamin C) on the reactivity of aortic rings from spontaneously hypertensive rats (SHR). 2. The phenylephrine (PE)-induced contractile and the endothelium-dependent and independent relaxant responses of aortic rings from 21 to 22 week old SHR and age-matched normotensive Wistar (WKY) rats were observed in the presence of quercetin or ascorbic acid. All the experiments were performed in the presence of the cyclooxygenase inhibitor, indomethacin (10 micromol/L). 3. The endothelium-dependent and independent relaxations to acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly lesser in the SHR compared to the WKY tissues whereas the contractile responses to PE were similar in both tissues. Pretreatment of WKY rings with quercetin or ascorbic acid had no effect on the responses to ACh or PE. In the SHR tissues, however, quercetin or ascorbic acid significantly improved the relaxation responses to ACh and reduced the contractions to PE with greater potency for quercetin. Both compounds lacked any effects on the responses to SNP in either aortic ring types. N(omega)-nitro-L-arginine methyl ester (l-NAME, 10 micromol/L) significantly attenuated the vasodepressor effects of quercetin and ascorbic acid, raising the responses to PE to a level similar to that observed in the control SHR tissues. In l-NAME pretreated aortic rings, quercetin and ascorbic acid inhibited the contractile responses to PE with the same magnitude in WKY and SHR tissues. 4. The present results suggest that acute exposure to quercetin improves endothelium-dependent relaxation and reduces the contractile responses of hypertensive aortae with a greater potency than ascorbic acid. This suggests a better vascular protection with this flavonoid than ascorbic acid in the SHR model of hypertension and possibly in human cardiovascular diseases.
Increased oxidative stress is involved in the pathogenesis and progression of diabetes. Antioxidants are therapeutically beneficial for oxidative stress-associated diseases. Boldine ([s]-2,9-dihydroxy-1,10-dimethoxyaporphine) is a major alkaloid present in the leaves and bark of the boldo tree (Peumus boldus Molina), with known an antioxidant activity. This study examined the protective effects of boldine against high glucose-induced oxidative stress in rat aortic endothelial cells (RAEC) and its mechanisms of vasoprotection related to diabetic endothelial dysfunction. In RAEC exposed to high glucose (30 mM) for 48 h, pre-treatment with boldine reduced the elevated ROS and nitrotyrosine formation, and preserved nitric oxide (NO) production. Pre-incubation with β-NAPDH reduced the acetylcholine-induced endothelium-dependent relaxation; this attenuation was reversed by boldine. Compared with control, endothelium-dependent relaxation in the aortas of streptozotocin (STZ)-treated diabetic rats was significantly improved by both acute (1 μM, 30 min) and chronic (20mg/kg/daily, i.p., 7 days) treatment with boldine. Intracellular superoxide and peroxynitrite formation measured by DHE fluorescence or chemiluminescence assay were higher in sections of aortic rings from diabetic rats compared with control. Chronic boldine treatment normalized ROS over-production in the diabetic group and this correlated with reduction of NAD(P)H oxidase subunits, NOX2 and p47(phox). The present study shows that boldine reversed the increased ROS formation in high glucose-treated endothelial cells and restored endothelial function in STZ-induced diabetes by inhibiting oxidative stress and thus increasing NO bioavailability.
The mechanism by which insulin causes vasodilatation remains unclear, so we explored this in aortic rings from normal Wistar Kyoto and streptozotocin-induced diabetic rats. Insulin-induced relaxation of phenylephrine-contracted [endothelium (ED) intact or denuded] aortic rings was recorded in the presence or absence of various drug probes. Insulin relaxant effect was more in ED-intact than in-denuded tissues from normal or diabetic rats. l-NAME or methylene blue partially inhibited insulin effect in ED-intact but not the ED-denuded tissues, whereas indomethacin (cyclooxygenase inhibitor) had no effect on any of the tissues, indicating that insulin induces relaxation by ED-dependent and -independent mechanisms, the former via the NOS-cyclic guanosine monophosphate but not the cyclooxygenase pathway. The voltage-dependent K channel (KV) blocker (4-aminopyridine) inhibited insulin action in all the tissues (normal or diabetic, with or without ED), whereas the selective BKCa blocker, tetraethylammonium, inhibited it in normal (ED intact or denuded) but not in diabetic tissues, indicating that KV mediates insulin action in normal and diabetic tissues, whereas the BKCa mediates it only in normal tissues, with possible pathophysiologic absence in diabetic tissues. The inward rectifier K channel (Kir) blocker (barium chloride) significantly inhibited insulin effect only in ED-intact or -denuded diabetic tissues, whereas the KATP channel blocker, glibenclamide, inhibited it only in the ED-denuded diabetic tissues, suggesting that Kir channels mediate insulin-induced relaxation in ED-intact or -denuded diabetic tissues, whereas the KATP channel mediates it in ED-denuded diabetic tissues. All the agents combined did not abolish insulin action, suggestive of a direct vasodilatory effect. In conclusion, insulin causes vasodilatation in normal and diabetic tissues via ED-dependent and -independent mechanisms differentially modulated by K channels, some of which functions are altered in diabetes and thus are potential therapeutic targets.
The present work examined the effect of chronic oral administration of quercetin, a flavonoid antioxidant, on blood glucose, vascular function and oxidative stress in STZ-induced diabetic rats. Male Wistar-Kyoto (WKY) rats were randomized into euglycemic, untreated diabetic, vehicle (1% w/v methylcellulose)-treated diabetic, which served as control, or quercetin (10mgkg(-1) body weight)-treated diabetic groups and treated orally for 6 weeks. Quercetin treatment reduced blood glucose level in diabetic rats. Impaired relaxations to endothelium-dependent vasodilator acetylcholine (ACh) and enhanced vasoconstriction responses to alpha(1)-adrenoceptor agonist phenylephrine (PE) in diabetic rat aortic rings were restored to euglycemic levels by quercetin treatment. Pretreatment with N(omega)-nitro-l-arginine methyl ester (l-NAME, 10microM) or methylene blue (10microM) completely blocked but indomethacin (10microM) did not affect relaxations to ACh in aortic rings from vehicle- or quercetin-treated diabetic rats. PE-induced vasoconstriction with an essentially similar magnitude in vehicle- or quercetin-treated diabetic rat aortic rings pretreated with l-NAME (10microM) plus indomethacin (10microM). Quercetin treatment reduced plasma malonaldehyde (MDA) plus 4-hydroxyalkenals (4-HNE) content as well as increased superoxide dismutase activity and total antioxidant capacity in diabetic rats. From the present study, it can be concluded that quercetin administration to diabetic rats restores vascular function, probably through enhancement in the bioavailability of endothelium-derived nitric oxide coupled to reduced blood glucose level and oxidative stress.
Hydrogen peroxide (H(2)O(2)) contributes in the regulation of vascular tone, especially in pathological states. The role of H(2)O(2) and superoxide anion free radicals in angiotensin II (Ang II)-induced contraction of diabetic tissues was examined with the aim of elucidating the underlying mechanisms. Isometric tension in response to various drug treatments was measured in isolated superior mesenteric arteries of streptozotocin (STZ)-induced diabetic WKY rats using the Mulvany wire myograph. Compared to the normal (euglycaemic) arteries, the Ang II-induced contraction was significantly reduced in diabetic arteries. Superoxide dismutase (SOD; converts superoxide to H(2)O(2)) significantly reduced the contraction in both types of arteries -- an effect abolished by catalase (H(2)O(2) scavenger), suggesting that the SOD effect was mediated by H(2)O(2). Treatment with catalase had no effect on the Ang II contraction in euglycaemic arteries, but it raised the contraction in diabetic arteries to euglycaemic levels. This increase was similar to that observed with diabetic arteries incubated with L-NAME. Combined catalase and L-NAME treatment further enhanced the contraction in diabetic arteries, suggesting that the catalase effect was not mediated by nitric oxide (NO). The catalase effect was abolished by indomethacin treatment. These results suggest that attenuation of Ang II-induced contraction in diabetic tissues is modulated by endogenous H(2)O(2), the scavenging of which unmasks an indomethacin-sensitive (and therefore cyclooxygenase product-mediated) Ang II-induced contraction.
The present work examined ex vivo the acute effect of quercetin on diabetic rat aortic ring reactivity in response to endothelium-dependent (acetylcholine, ACh) and endothelium-independent (sodium nitroprusside, SNP) relaxants, and to the alpha(1)-adrenergic agonist phenylephrine (PE). Responses were compared to those of aortic rings from age- and sex-matched euglycemic rats. Compared to euglycemic rat aortic rings, diabetic rings showed less relaxation in response to ACh and SNP, and greater contraction in response to PE. Pretreatment with quercetin (10microM, 20min) increased ACh-induced relaxation and decreased PE-induced contraction in diabetic, but did not affect euglycemic rat aortic ring responses. Following pretreatment with the nitric oxide synthase inhibitor Nomega-nitro-l-arginine methyl ester (l-NAME, 10microM), quercetin reduced PE-induced contractions in both aortic ring types, although l-NAME attenuated the reduction in the diabetic rings. Quercetin did not alter SNP vasodilatory effects in either ring type compared to their respective controls. These findings indicate that quercetin acutely improved vascular responsiveness in blood vessels from diabetic rats, and that these effects were mediated, at least in part, by enhanced endothelial nitric oxide bioavailability. These effects of quercetin suggest the possible beneficial effects of quercetin in vivo in experimental diabetes and possibly in other cardiovascular diseases.
Pioglitazone is an anti-diabetic drug with potential to cause adverse effects following prolonged use. This study, therefore, investigated the effects of combination treatment of a subliminal concentration of pioglitazone and quercetin, a potent antioxidant, on vascular reactivity of aorta isolated from fructose-streptozotocin (F-STZ)-induced diabetic rats. Relaxation to acetylcholine and sodium nitroprusside, and contraction to phenylephrine were tested in organ bath chambers following pre-incubation with vehicle (DMSO; 0.05%), quercetin (10-7 M), pioglitazone (10-7 M), or their combination (P+Q; 10-7 M each drug). Subliminal concentration of quercetin or pioglitazone did not alter the acetylcholine- induced relaxation nor the phenylephrine-induced contraction in both normal rat and diabetic F-STZ induced tissues. However, P+Q combination synergistically improved the impaired acetylcholine-induced relaxation and decreased the elevated phenylephrine-induced contraction in aortic rings from diabetic, but not in the normal rats. Neither mono nor combination treatment altered sodium nitroprusside-induced relaxation. The combination also synergistically decreased superoxide anion and increased nitric oxide production compared to the individual treatments in aorta from diabetic rats. Overall, these data demonstrated a synergistic effect, in which, a combination (P+Q; 10-7 M each drug) caused a significantly greater effect than 10-6 M of either agent in improving endothelial function of isolated diabetic aorta. In conclusion, a combination of subliminal concentrations of pioglitazone and quercetin is able to decrease oxidative stress and provide synergistic vascular protection in type 2 diabetes mellitus and thus the possibility of using quercetin as a supplement to pioglitazone in the treatment of diabetes with the goal of reducing pioglitazone toxicity.