1 Increased renal vascular resistance is one renal functional abnormality that contributes to hypertension, and alpha(1)-adrenoceptors play a pivotal role in modulating this renal vascular resistance. This study investigates the functional contribution of alpha(1)-adrenoceptor subtypes in the renal cortical vasculature of Wistar-Kyoto rats on a normal sodium diet (WKYNNa) compared with those given saline to drink for 6 weeks (WKYHNa). 2 The renal cortical vascular responses to the adrenergic agonists noradrenaline (NA), methoxamine (ME) and phenylephrine (PE) were measured in WKYHNa and WKYNNa rats either in the absence (the control phase) or presence of chloroethylclonidine (CEC), an alpha(1B)-adrenoceptor antagonist, 5-methylurapidil (5-MeU), an alpha(1A) antagonist, or BMY7378, an alpha(1D) antagonist. 3 Results showed a greater renal cortical vascular sensitivity to NA, PE and ME in the WKYHNa compared with WKYNNa rats (P < 0.05). Moreover, 5-MeU and BMY7378 attenuated adrenergically induced renal cortical vasoconstriction in WKYHNa and WKYNNa rats; this response was largely blunted in CEC-treated WKYHNa rats (all P < 0.05) but not in CEC-treated WKYNNa rats. 4 The data suggest that irrespective of dietary sodium content, in Wistar-Kyoto rats alpha(1A)- and alpha(1D)-subtypes are the major alpha(1)-adrenoceptors in renal cortical vasculature; however, there appears to be a functional involvement of alpha(1B)-adrenoceptors in the WKYHNa rats.
1 The present study investigated the effect of streptozotocin-induced diabetes on alpha(1)-adrenoceptor subtypes in rat renal resistance vessels. 2 Studies on renal haemodynamics were carried out 7 days after the last streptozotocin. Changes in renal blood flow were recorded in response to electrical stimulation of the renal nerve (RNS) and a range of adrenergic agonists; noradrenaline (NA), phenylephrine (PE) and methoxamine (MTX), either in the absence or the presence of nitrendipine (Nit), 5-methylurapidil (MEU), chlorethylclonidine (CEC) or BMY 7378. 3 In non-diabetic animals, Nit, MEU and BMY 7378 significantly attenuated renal vasoconstriction induced by adrenergic agonists, while CEC showed a significant accentuation in RNS-induced responses without having a significant effect on responses to adrenergic agonists. In diabetic rats, renal vasoconstriction was also significantly reduced in Nit-, MEU- and BMY 7378-treated groups and CEC potentiated RNS-induced contractions caused a change similar to that observed in non-diabetic rats. BMY 7378 significantly (P < 0.05) attenuated the PE- and MTX-induced vasoconstrictions but did not cause any significant (P > 0.05) alteration in the RNS- and NA-induced responses. 4 The results showed functional co-existence of alpha(1A)- and alpha(1D)-adrenoceptors in the renal vasculature of SD rats irrespective of the presence of diabetes. A possible minor contribution of prejunctional alpha-adrenoceptor subtype has also been suggested in either experimental group, particularly possible functional involvement of alpha(1B)-adrenoceptor subtypes in non-diabetic SD rats.
1 This study was undertaken to characterize the renal responses to acute unilateral renal denervation in anaesthetized spontaneously hypertensive rats (SHR) by examining the effect of acute unilateral renal denervation on the renal hemodynamic responses to a set of vasoactive agents and renal nerve stimulation. 2 Twenty-four male SHR rats underwent acute unilateral renal denervation and the denervation was confirmed by significant drop (P < 0.05) in renal vasoconstrictor response to renal nerve stimulation along with marked diuresis and natriuresis following denervation. After 7 days treatment with losartan, the overnight fasted rats were anaesthetized (sodium pentobarbitone, 60 mg kg(-1) i.p.) and renal vasoconstrictor experiments were performed. The changes in the renal vasoconstrictor responses were determined in terms of reductions in renal blood flow caused by renal nerve stimulation or intrarenal administration of noradrenaline, phenylephrine, methoxamine and angiotensin II. 3 The data showed that there was significantly (all P < 0.05) increased renal vascular responsiveness to the vasoactive agents in denervated rats compared to those with intact renal nerves. In losartan-treated denervated SHR rats, there were significant (all P < 0.05) reductions in the renal vasoconstrictor responses to neural stimuli and vasoactive agents as compared with that of untreated denervated SHR rats. 4 The data obtained in denervated rats suggested an enhanced sensitivity of the alpha(1)-adrenoceptors to adrenergic agonists and possible increase of AT(1) receptors functionality in the renal vasculature of these rats. These data also suggested a possible interaction between sympathetic nervous system and renin-angiotensin system in terms of a crosstalk relationship between renal AT(1) and alpha(1)-adrenoceptor subtypes.
This study investigated whether the alpha(1)-adrenoceptor subtype(s) mediating the vasoconstrictor actions of the renal sympathetic nerves were altered in rats with cisplatin-induced renal failure. Male Wistar Kyoto rats were used and half received cisplatin (5 mg/kg i.p.) to induce renal failure and were taken for study 7 days later. The renal blood flow reductions caused by electrical renal nerve stimulation and close intra-renal administration of noradrenaline, phenylephrine and methoxamine were determined before and after amlodopine (AMP), 5-methylurapidil (MeU), chloroethylclonidine (CEC) or BMY 7378. Water intake and creatinine clearance were decreased (P<0.05) by 40-50% while fractional excretion of sodium was increased two-fold in the cisplatin treated rats. Mean arterial pressure was higher, 110+/-2 versus 102+/-3 mmHg and renal blood flow was lower, 10.7+/-0.9 versus 18.9+/-0.1 ml/min/kg in the renal failure rats (both P<0.05). AMP, MeU and BMY 7378 decreased (all P<0.05) the adrenergically induced renal vasoconstrictor responses in the renal failure groups by 30 to 50% and in normal rats by 20 to 40%. In the presence of CEC, renal nerve stimulation and noradrenaline and methoxamine induced renal vasoconstrictor responses were enhanced (all P<0.05) in the renal failure but not in the normal rats. These data showed that alpha(1A)- and alpha(1D)-adrenoceptors were the major subtypes in mediating adrenergically induced renal vasoconstriction but there was no substantial shift in subtype in renal failure. The contribution of alpha(1B)-adrenoceptor subtypes either pre- or post-synaptic appeared to be raised in the renal failure rats.
Diabetes is associated with endothelial dysfunction, which is characterized by impaired endothelium-dependent relaxations. The present study aimed to examine the role of nitric oxide (NO), prostacyclin and endothelium-dependent hyperpolarization (EDH), in the relaxation of ventral tail arteries of rats under diabetic conditions. Relaxations of tail arteries of control and diabetic rats were studied in wire myograph. Western blotting and immunostaining were used to determine the presence of proteins. Acetylcholine-induced relaxations were significantly smaller in arteries of diabetic compared to control rats (Rmax; 70.81 ± 2.48% versus 85.05 ± 3.15%). Incubation with the combination of non-selective cyclooxygenase (COX) inhibitor, indomethacin and potassium channel blockers, TRAM 34 and UCL 1684, demonstrated that NO-mediated relaxation was attenuated significantly in diabetic compared to control rats (Rmax; 48.47 ± 5.84% versus 68.39 ± 6.34%). EDH-type (in the presence of indomethacin and NO synthase inhibitor, LNAME) and prostacyclin-mediated (in the presence of LNAME plus TRAM 34 and UCL 1684) relaxations were not significantly reduced in arteries of diabetic compared to control rats [Rmax: (EDH; 17.81 ± 6.74% versus 34.16 ± 4.59%) (prostacyclin; 15.85 ± 3.27% versus 17.23 ± 3.75%)]. Endothelium-independent relaxations to sodium nitroprusside, salbutamol and prostacyclin were comparable in the two types of preparations. Western blotting and immunostaining indicated that diabetes diminished the expression of endothelial NO synthase (eNOS), while increasing those of COX-1 and COX-2. Thus, since acetylcholine-induced NO-mediated relaxation was impaired in diabetes because of reduced eNOS protein expression, pharmacological intervention improving NO bioavailability could be useful in the management of diabetic endothelial dysfunction.
Four alkaloids comprising two vallesamine, one strychnan, and one pyranopyridine alkaloid, in addition to 32 other known alkaloids were isolated from two Malayan Alstonia species, Alstonia pneumatophora and Alstonia rostrata. The structures of these alkaloids were determined using NMR and MS analyses, and in one instance, confirmed by X-ray diffraction analysis. The nor-6,7-secovallesamine alkaloid, pneumatophorine, is notable for an unusual incorporation of a 3-ethylpyridine moiety in a monoterpenoid indole. The rhazinilam-type alkaloids (rhazinicine, nor-rhazinicine, rhazinal, and rhazinilam) showed strong cytotoxicity toward human KB, HCT-116, MDA-MB-231, and MRC-5 cells, while pneumatophorine, the uleine alkaloid undulifoline, and the strychnan alkaloids, N4-demethylalstogustine and echitamidine, induced concentration dependent relaxation in phenylephrine-precontracted rat aortic rings.
The potency, structure-activity relationship, and mechanism of vasorelaxation of a series of flavonoids, representing different subclasses (flavonols: fisetin, rutin, quercetin; flavones: chrysin, flavone, baicalein; flavanones: naringenin, naringin; isoflavones: diadzein and flavanes: epigallo catechin gallate), were examined in the isolated rat aorta. Most of the flavonoids tested showed concentration dependent relaxant effects against K+ (80 mM) and phenylephrine (PE, 0.1 microM)-induced contractions with a greater inhibition of the responses to the alpha1-adrenoceptor agonist. The relaxant effects of most of the flavonoids involve in part the release of nitric oxide and prostaglandins from the endothelium as pretreatment with L-NAME and indomethacin attenuated the responses. In addition, the relaxant action of the flavonoids includes inhibition of Ca+2 influx and release of Ca+2 from intracellular stores. A structure-activity relationship amongst the flavonoids was suggested.
Adiponectin exerts vasodilatory effects. Irbesartan, an angiotensin receptor blocker, possesses partial peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist activity and increases circulating adiponectin. This study explored the effect of irbesartan alone and in combination with adiponectin on blood pressure, renal hemodynamic excretory function, and vasoactive responses to angiotensin II and adrenergic agonists in spontaneously hypertensive rat (SHR). Irbesartan was given orally (30 mg/kg/day) for 28 days and adiponectin intraperitoneally (2.5 μg/kg/day) for last 7 days. Groups of SHR received either irbesartan or adiponectin or in combination. A group of Wistar Kyoto rats (WKY) served as controls. Metabolic data and plasma samples were taken on days 0, 21, and 28. In acute studies, the renal vasoconstrictor actions of angiotensin II (ANGII), noradrenaline (NA), phenylephrine (PE), and methoxamine (ME) were determined. SHR control rats had a higher mean blood pressure than the WKY (132 ± 7 vs. 98 ± 2 mmHg), lower plasma and urinary adiponectin, creatinine clearance, urine flow rate and sodium excretion, and oxidative stress markers compared to WKY (all P
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.
This study investigates the subtypes of the alpha1-adrenoceptor mediating the adrenergically-induced renal vasoconstrictor responses in streptozotocin-induced diabetic and non-diabetic 2-kidney one clip (2K1C) Goldblatt hypertensive rats.
Diabetes mellitus is associated with endothelial dysfunction; it causes progressive vascular damage resulting from an impaired endothelium-dependent vasorelaxation. In the diabetes state, presence of hyperglycemia and insulin resistance predisposes to endothelial dysfunction. Clinacanthus nutans, widely used as a traditional medicine for diabetes is reported to have hypoglycemic, hypolipidemic, antioxidant, and anti-inflammatory properties. However, the possibility of C. nutans affecting the vascular endothelial function in diabetes remains unclear. This study was aimed at evaluating the effects of C. nutans methanolic leaves extract (CNME) on endothelial function in a type 2 diabetes (T2DM) rat model. Sixty male Sprague-Dawley rats were divided into five groups (n = 12 per group): nondiabetic control, nondiabetic treated with four weeks of CNME (500 mg/kg/daily), untreated diabetic rats, diabetic treated with metformin (300 mg/kg/daily), and diabetic treated with CNME (500 mg/kg/daily). T2DM was induced by a single intraperitoneal injection of low-dose streptozotocin (STZ) to rats fed with high-fat diet (HFD). Endothelial-dependent and endothelial-independent relaxations and contractions of the thoracic aorta were determined using the organ bath. Aortic endothelial nitric oxide synthase (eNOS) expression was determined using Western blotting. Endothelial-dependent relaxation was reduced in diabetic rats. Both diabetic groups treated with CNME or metformin significantly improved the impairment in endothelium-dependent vasorelaxation; this was associated with increased expression of aortic eNOS protein. CNME- and metformin-treated groups also reduced aortic endothelium-dependent and aortic endothelium-independent contractions in diabetics. Both of these diabetic-treated groups also reduced blood glucose levels and increased body weight compared to the untreated diabetic group. In conclusion, C. nutans improves endothelial-dependent vasodilatation and reduces endothelial-dependent contraction, thus ameliorating endothelial dysfunction in diabetic rats. This may occur due to its effect on increasing eNOS protein expression.
This study investigated the role of α1D-adrenoceptor in the modulation of renal haemodynamics in rats with left ventricular hypertrophy (LVH). LVH was established in Wistar-Kyoto (WKY) rats with isoprenaline (5.0 mg · (kg body mass)(-1), by subcutaneous injection every 72 h) and caffeine (62 mg · L(-1) in drinking water, daily for 14 days). Renal vasoconstrictor responses were measured for noradrenaline (NA), phenylephrine (PE), and methoxamine (ME) before and immediately after low or high dose intrarenal infusions of BMY 7378, a selective α1D-adrenoceptor blocker. The rats with LVH had higher mean arterial blood pressure and circulating NA levels, but lower renal cortical blood perfusion compared with the control group (all P < 0.05). In the LVH group, the magnitude of the renal vasoconstrictor response to ME was blunted, but not the response to NA or PE (P < 0.05), compared with the control group (LVH vs. C, 38% vs. 50%). The magnitude of the drop in the vasoconstrictor responses to NA, PE, and ME in the presence of a higher dose of BMY 7378 was significantly greater in the LVH group compared with the control group (LVH vs. C, 45% vs. 25% for NA, 52% vs. 33% for PE, 66% vs. 53% for ME, all P < 0.05). These findings indicate an impaired renal vasoconstrictor response to adrenergic agonists during LVH. In addition, the α1D-adrenoceptor subtype plays a key role in the modulation of vascular responses in this diseased state.
Vascular endothelial dysfunction (VED) plays an important role in the initiation of cardiovascular diseases. Roselle, enriched with antioxidants, demonstrates high potential in alleviating hypertension. This study was undertaken to investigate the effects of roselle supplementation of VED and remodelling in a rodent model with prolonged nicotine administration. Male Sprague-Dawley rats (n = 6 per group) were administered with 0.6 mg/kg nicotine for 28 days to induce VED. The rats were given either aqueous roselle (100 mg/kg) or normal saline orally 30 min prior to nicotine injection daily. One additional group of rats served as control. Thoracic aorta was isolated from rats to measure vascular reactivity, vascular remodelling and oxidative stress. Roselle significantly lowered aortic sensitivity to phenylephrine-induced vasoconstriction (Endo-(+) Cmax = 234.5 ± 3.9%, Endo-(-) Cmax = 247.6 ± 5.2%) compared with untreated nicotine group (Endo-(+) Cmax = 264.5 ± 6.9%, Endo-(-) Cmax = 276.5 ± 6.8%). Roselle also improved aortic response to endothelium-dependent vasodilator, acetylcholine (Endo-(+) Rmax = 73.2 ± 2.1%, Endo-(-) Rmax = 26.2 ± 0.8%) compared to nicotine group (Endo-(+) Rmax = 57.8 ± 1.7%, Endo-(-) Rmax = 20.9 ± 0.8%). In addition, roselle prevented an increase in intimal media thickness and elastic lamellae proliferation to preserve vascular architecture. Moreover, we also observed a significantly lowered degree of oxidative stress in parallel with increased antioxidant enzymes in aortic tissues of the roselle-treated group. This study demonstrated that roselle prevents VED and remodelling, and as such it has high nutraceutical value as supplement to prevent cardiovascular diseases.
The prolonged intake of diet containing repeatedly heated vegetable oil can cause hypertension in the long run. In this study, the effects of citrus leaf extract (CLE) supplementation on vascular reactivity, plasma nitrite, and aortic structure in hypertensive rats were investigated by the consumption of repeatedly heated vegetable oil [corrected]. Male Sprague Dawley rats (n = 56) were divided into 7 groups corresponding to the respective diets. For 16 weeks, 1 group was given standard rat chow (control) while other groups were given diets containing 15% w/w of palm oil, fresh palm oil (FPO), palm oil heated 5 times (5HPO), and palm oil heated 10 times (10HPO), with or without the incorporation of 0.15% w/w CLE (FPO+CLE, 5HPO+CLE, or 10HPO+CLE). Plasma nitrite levels were measured before and at 16 weeks of treatment. After 16 weeks, the rats were sacrificed and aortae were harvested for measuring vascular reactivity and for microscopic study. CLE supplementation had significantly reduced the loss of plasma nitrite and attenuated the vasoconstriction response to phenylephrine in the 5HPO group but not in the 10HPO group. However, CLE had no significant effect on the vasorelaxation response to acetylcholine and sodium nitroprusside. The elastic lamellae of tunica media in 5HPO, 10HPO, and 10HPO+CLE groups appeared disorganised and disrupted. Obtained findings suggested that CLE was able to enhance nitric oxide bioavailability that might dampen the vasoconstriction effect of phenylephrine.
Diabetes mellitus contributes to macro- and microvascular complications, leading to adverse cardiovascular events. This study examined the effects of vitamin D deficiency on the vascular function and tissue oxidative status in the microcirculation of diabetic rats and to determine whether these effects can be reversed with calcitriol (active vitamin D metabolite) supplementation. Streptozotocin-induced diabetic rats were fed for 10 weeks with control diet (DC) or vitamin D-deficient diet without (DD) or with oral calcitriol supplementation (0.15 μg/kg) in the last four weeks (DDS) (10 rats each group). A nondiabetic rat group that received control diet was also included (NR). After 10 weeks, rats were sacrificed; mesenteric arterial rings with and without endothelium were studied using wire myograph. Western blotting of the mesenteric arterial tissue was performed to determine the protein expression of endothelial nitric oxide synthase (eNOS) enzyme. Antioxidant enzyme superoxide dismutase (SOD) activity and oxidative stress marker malondialdehyde (MDA) levels in the mesenteric arterial tissue were also measured. The DC group had significantly lower acetylcholine-induced relaxation and augmented endothelium-dependent contraction, with reduced eNOS expression, compared to NR rats. In mesenteric arteries of DD, acetylcholine-induced endothelium-dependent and sodium nitroprusside-induced endothelium-independent relaxations were lower than those in DC. Calcitriol supplementation in DDS restored endothelium-dependent relaxation. Mesenteric artery endothelium-dependent contraction of DD was greater than DC; it was not affected by calcitriol supplementation. The eNOS protein expression and SOD activity were significantly lower while MDA levels were greater in DD compared to DC; these effects were not observed in DDS that received calcitriol supplementation. In conclusion, vitamin D deficiency causes eNOS downregulation and oxidative stress, thereby impairing the vascular function and posing an additional risk for microvascular complications in diabetes. Calcitriol supplementation to diabetics with vitamin D deficiency could potentially be useful in the management of or as an adjunct to diabetes-related cardiovascular complications.