The vascular relaxing effects of sevoflurane and isoflurane are more important in hypertensive than in normotensive rats

Central Artery Hemodynamics in Angiotensin II-Induced Hypertension and Effects of Anesthesia

Systemic hypertension is a strong risk factor for cardiovascular, neurovascular, and renovascular diseases. Central artery stiffness is both an initiator and indicator of hypertension, thus revealing a critical relationship between the wall mechanics and hemodynamics. Mice have emerged as a critical animal model for studying effects of hypertension and much has been learned. Regardless of the specific mouse model, data on changes in cardiac function and hemodynamics are necessarily measured under anesthesia. Here, we present a new experimental-computational workflow to estimate awake cardiovascular conditions from anesthetized data, which was then used to quantify effects of chronic angiotensin II-induced hypertension relative to normotension in wild-type mice. We found that isoflurane anesthesia had a greater impact on depressing hemodynamics in angiotensin II-infused mice than in controls, which led to unexpected results when comparing anesthetized results between the two groups of mice. Through comparison of the awake simulations, however, in vivo relevant effects of angiotensin II-infusion on global and regional vascular structure, properties, and hemodynamics were found to be qualitatively consistent with expectations. Specifically, we found an increased in vivo vascular stiffness in the descending thoracic aorta and suprarenal abdominal aorta, leading to increases in pulse pressure in the distal aorta. These insights allow characterization of the impact of regionally varying vascular remodeling on hemodynamics and mouse-to-mouse variations due to induced hypertension.

Pregnancy hypertension-associated endothelial dysfunction is attenuated by isoflurane anesthesia: Evidence of protective effect related to increases in nitric oxide

AIMS

Pregnancy hypertension-induced endothelial dysfunction associated with impairment of nitric oxide (NO) bioavailability and hemodynamic derangements is a challenging for urgent procedures requiring maternal anesthesia. The volatile anesthetic isoflurane has demonstrated NO-associated protective effects. However, this isoflurane-induced effect is still unclear in pregnancy hypertension. Therefore, the present study examined the potential protective effects of isoflurane anesthesia on endothelial dysfunction and hemodynamic changes induced by hypertensive pregnancy associated with fetal and placental growth restrictions.

MATERIALS AND METHODS

Animals were distributed into four groups: normotensive pregnant rats (Preg), anesthetized pregnant rats (Preg+Iso), hypertensive pregnant rats (HTN-Preg), and anesthetized hypertensive pregnant rats (HTN-Preg+Iso). Systolic and diastolic pressures, mean arterial pressure (MAP), heart rate, fetal and placental weights, vascular contraction, endothelium-derived NO-dependent vasodilation, and NO levels were assessed. The vascular endothelial growth factor (VEGF) levels and endothelial NO synthase (eNOS) Serine (1177) phosphorylation (p-eNOS) expression were also examined.

KEY FINDINGS

Isoflurane produced more expressive hypotensive effects in the HTN-Preg+Iso versus Preg+Iso group, with respective reductions in MAP by 50 ± 13 versus 25 ± 4 mmHg (P < 0.05). Also, HTN-Preg+Iso compared to the HTN-Preg group showed (respectively) preventions against the weight loss of the fetuses (4.0 ± 0.6 versus 2.8 ± 0.6 g, P < 0.05) and placentas (0.37 ± 0.06 versus 0.30 ± 0.06 mg, P < 0.05), hyper-reactive vasocontraction response (1.8 ± 0.4 versus 2.8 ± 0.6 g, P < 0.05), impaired endothelium-derived NO-dependent vasodilation (84 ± 8 versus 50 ± 17 %, P < 0.05), reduced VEGF levels (147 ± 46 versus 25 ± 13 pg/mL, P < 0.05), and decreased p-eNOS expression (0.24 ± 0.07 versus 0.09 ± 0.05 arbitrary units, P < 0.05).

SIGNIFICANCE

Isoflurane anesthesia protects maternal endothelial function in pregnancy hypertension, and possibly endothelium-derived NO is involved.

Prolonged lifespan in a spontaneously hypertensive rat (stroke prone) model following intravenous infusion of mesenchymal stem cells

Intravenous infusion of mesenchymal stem cells (MSCs) has been reported to provide therapeutic efficacy via microvascular remodeling in a spontaneously hypertensive rat. In this study, we demonstrate that intravenous infusion of MSCs increased the survival rate in a spontaneously hypertensive (stroke prone) rat model in which organs including kidney, brain, heart and liver are damaged during aging due to spontaneous hypertension. Gene expression analysis indicated that infused MSCs activates transforming growth factor-β1-smad3/forkhead box O1 signaling pathway. Renal dysfunction was recovered after MSC infusion. Collectively, intravenous infusion of MSC may extend lifespan in this model system.

Cardiac adaptation to hypertension in adult female Dahl salt-sensitive rats is dependent on ovarian function, but loss of ovarian function does not predict early maladaptation

Aim of study was to examine experimentally the adult female hypertensive heart in order to determine the role of ovary function in the response of the heart to salt-dependent hypertension. Dahl salt-sensitive rats, age 12 weeks, with/without ovariectomy were fed a standard (0.3% NaCl) or high-salt diet (8%) for 16 weeks. Mean arterial blood pressure monitored noninvasively in conscious state increased significantly by high salt. Echocardiography was performed at baseline and endpoint. Heart function and molecular changes were evaluated at endpoint by left ventricle catheterization, by sirius red staining for collagen and by gene expression using quantitative RT-PCR for selected genes. At endpoint, significant concentric hypertrophy was present with high salt. Increase in relative wall thickening with high salt compared to normal diet was more pronounced with intact ovaries (0.33 ± 0.02 and 0.57 ± 0.04 vs. 0.29 ± 0.00 and 0.46 ± 0.03) as was the reduction in midwall fractional shortening (20 ± 0.6 and 14 ± 2 vs. 19 ± 0.9 and 18 ± 1). Ovariectomy increased stroke volume and decreased the ratio of mitral peak velocity of early filling (E) to early diastolic mitral annular velocity (E') (E/E' ratio) when compared to hearts from intact rats. High salt increased expression of collagen I and III genes and perivascular collagen in the heart slightly, but % interstitial collagen by sirius red staining remained unchanged in intact rats and decreased significantly by ovariectomy. Added volume load but not deterioration of function or structure characterized the nonfailing hypertensive heart of salt-sensitive females ovariectomized at mature age when compared to corresponding intact females.

Desflurane inhibits endothelium-dependent vasodilation more than sevoflurane with inhibition of endothelial nitric oxide synthase by different mechanisms

The effects of desflurane on endothelium-dependent vasodilation remain uncertain, whereas sevoflurane is known to inhibit it. Endothelium-dependent vasodilation is mainly mediated by endothelial nitric oxide synthase. The effects of desflurane on endothelium-dependent vasodilation were compared with those of sevoflurane, and inhibition mechanisms, including phosphorylation of endothelial nitric oxide synthase and the calcium pathway, were evaluated for the two anesthetics. We hypothesized that desflurane would inhibit endothelium-dependent vasodilation in a concentration-dependent manner more than sevoflurane, with inhibition of a calcium pathway. Isolated rat aortic rings were randomly assigned to treatment with desflurane or sevoflurane for measurements of the vasodilation ratio. To determine NO production with desflurane and sevoflurane, an in vitro assay was performed with cultured bovine aortic endothelial cells. These cells were also used for measurement of intracellular calcium or Western blotting. For endothelium-dependent vasodilation, the ratio of vasodilation was more significantly inhibited by 11.4% desflurane than by 4.8% sevoflurane. Inhibition did not between 5.7% desflurane and 2.4% sevoflurane. No inhibitory effect of desflurane or sevoflurane was observed in endothelium-denuded aorta. Desflurane inhibited nitric oxide production caused by stimulation of bradykinin significantly more than sevoflurane. Desflurane had a greater suppressive effect on the bradykinin-induced increase in intracellular calcium concentration than did sevoflurane. Sevoflurane, but not desflurane, inhibited phosphorylation of the serine 1177 residue by bradykinin stimulation. Desflurane inhibited endothelium-dependent vasodilation more than sevoflurane through inhibition of a calcium pathway. Sevoflurane inhibited endothelium-dependent vasodilation by inhibition of phosphorylation of the serine 1177 residue of endothelial nitric oxide synthase.

Exogenous and endogenous angiotensin-II decrease renal cortical oxygen tension in conscious rats by limiting renal blood flow

KEY POINTS

Our understanding of the mechanisms underlying the role of hypoxia in the initiation and progression of renal disease remains rudimentary. We have developed a method that allows wireless measurement of renal tissue oxygen tension in unrestrained rats. This method provides stable and continuous measurements of cortical tissue oxygen tension (PO2) for more than 2 weeks and can reproducibly detect acute changes in cortical oxygenation. Exogenous angiotensin-II reduced renal cortical tissue PO2 more than equi-pressor doses of phenylephrine, probably because it reduced renal oxygen delivery more than did phenylephrine. Activation of the endogenous renin-angiotensin system in transgenic Cyp1a1Ren2 rats reduced cortical tissue PO2; in this model renal hypoxia precedes the development of structural pathology and can be reversed acutely by an angiotensin-II receptor type 1 antagonist. Angiotensin-II promotes renal hypoxia, which may in turn contribute to its pathological effects during development of chronic kidney disease.

ABSTRACT

We hypothesised that both exogenous and endogenous angiotensin-II (AngII) can decrease the partial pressure of oxygen (PO2) in the renal cortex of unrestrained rats, which might in turn contribute to the progression of chronic kidney disease. Rats were instrumented with telemeters equipped with a carbon paste electrode for continuous measurement of renal cortical tissue PO2. The method reproducibly detected acute changes in cortical oxygenation induced by systemic hyperoxia and hypoxia. In conscious rats, renal cortical PO2 was dose-dependently reduced by intravenous AngII. Reductions in PO2 were significantly greater than those induced by equi-pressor doses of phenylephrine. In anaesthetised rats, renal oxygen consumption was not affected, and filtration fraction was increased only in the AngII infused animals. Oxygen delivery decreased by 50% after infusion of AngII and renal blood flow (RBF) fell by 3.3 ml min^-1 . Equi-pressor infusion of phenylephrine did not significantly reduce RBF or renal oxygen delivery. Activation of the endogenous renin-angiotensin system in Cyp1a1Ren2 transgenic rats reduced cortical tissue PO2. This could be reversed within minutes by pharmacological angiotensin-II receptor type 1 (AT₁ R) blockade. Thus AngII is an important modulator of renal cortical oxygenation via AT₁ receptors. AngII had a greater influence on cortical oxygenation than did phenylephrine. This phenomenon appears to be attributable to the profound impact of AngII on renal oxygen delivery. We conclude that the ability of AngII to promote renal cortical hypoxia may contribute to its influence on initiation and progression of chronic kidney disease.

Des-aspartate angiotensin I (DAA-I) reduces endothelial dysfunction in the aorta of the spontaneously hypertensive rat through inhibition of angiotensin II-induced oxidative stress

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.

Effects of propofol and sevoflurane on isolated human umbilical arteries pre-contracted with dopamine, adrenaline and noradrenaline

AIM

To assess the effects of propofol and sevoflurane on the contraction elicited by dopamine, adrenaline and noradrenaline on isolated human umbilical arteries.

METHODS

Umbilical arteries were cut into endothelium-denuded spiral strips and suspended in organ baths containing Krebs-Henseleit solution bubbled with O2 +CO2 mixture. Control contraction to phenylephrine (10(-5)  M) was recorded. Response curves were obtained to 10(-5)  M dopamine, 10(-5)  M adrenaline or 10(-5)  M noradrenaline. Afterwards, either cumulative propofol (10(-6)  M, 10(-5)  M and 10(-4)  M) or cumulative sevoflurane (1.2%, 2.4% and 3.6%) was added to the organ bath, and the responses were recorded. Responses are expressed percentage of phenylephrine-induced contraction (mean ± standard deviation) (P < 0.05 = significance).

RESULTS

Propofol and sevoflurane elicited concentration-dependent relaxations in strips pre-contracted with dopamine, adrenaline and noradrenaline (P < 0.05). Highest (10(-4)  M) concentration of propofol caused significantly higher relaxation compared with the highest (3.6%) concentration of sevoflurane in the contraction elicited by dopamine. High (10(-5)  M) and highest concentrations of propofol caused significantly higher relaxation compared with the high (2.4%) and highest concentrations of sevoflurane on the contraction elicited by adrenaline. High and highest concentrations of sevoflurane caused significantly higher relaxation compared with the high and highest concentrations of propofol on the contraction elicited by noradrenaline.

CONCLUSION

Dopamine, adrenaline and noradrenaline elicit contractions in human umbilical arteries, and noradrenaline causes the highest contraction. Both propofol and sevoflurane inhibit these contractions in a dose-dependent manner. Propofol caused greater relaxation in the contractions elicited by dopamine and adrenaline while sevoflurane caused greater relaxation in the contraction elicited by noradrenaline.

In vivo assessment of arterial stiffness in the isoflurane anesthetized spontaneously hypertensive rat

Background

Rodent models are increasingly used to study the development and progression of arterial stiffness. Both the non-invasive Doppler derived Pulse Wave Velocity (PWV) and the invasively determined arterial elastance index (EaI) have been used to assess arterial stiffness in rats and mice, but the need for anesthetic agents to make these in vivo estimates may limit their utility. Thus, we sought to determine: 1) if known differences in arterial stiffness in spontaneously hypertensive rats (SHR) are detectable by PWV and EaI measurements when made under isoflurane anesthesia, and 2) if these two uniquely acquired assessments of arterial elasticity correlate.

Methods

We obtained PWV and EaI measurements in isoflurane anesthetized young and old SHRs, which are known to have significant differences in arterial stiffness. Doppler pulse waves were recorded from carotid and iliac arteries and the distance (D) between probe applantation sites was recorded. Simultaneously, an EKG was obtained, and the time intervals between the R-wave of the EKG to the foot of the Doppler waveforms were measured and averaged over three cardiac cycles. Pulse-transit time (T) of the carotid to iliac artery was determined, and PWV was calculated as Distance (D)/Time (T), where D = the distance from the carotid to the iliac notch and T = (R to iliac foot) - (R to carotid foot). EaI was subsequently determined from pressure volumes loops obtained via left ventricle catheterization.

Results

PWV and EaI were found to be significantly faster in the older rats (13.2 ± 2.0 vs. 8.0 ± 0.8 m/sec, p < 0.001; 120 ± 20 vs. 97 ± 16 mmHg/μl/g, p <0.05). Bland-Altman analyses of intra- and inter-observer measures demonstrate a statistically significant relationship between readings (p < 0.0001). PWV and EaI measurements were found to be significantly and positively correlated with a correlation coefficient of 0.53 (p < 0.05).

Conclusion

Our study suggests that isoflurane administration does not limit Doppler PWV or EaI measures in their ability to provide accurate, in vivo assessments of relative arterial stiffness in isoflurane anesthetised SHR rats. Furthermore, PWV data obtained in these rats correlate well with invasively determined EaI.

Occipital Artery Function during the Development of 2-Kidney, 1-Clip Hypertension in Rats

This study compared the contractile responses elicited by angiotensin II (AII), arginine vasopressin (AVP), and 5-hydroxytryptamine (5-HT) in isolated occipital arteries (OAs) from sham-operated (SHAM) and 2-kidney, 1-clip (2K-1C) hypertensive rats. OAs were isolated and bisected into proximal segments (closer to the common carotid artery) and distal segments (closer to the nodose ganglion) and mounted separately on myographs. On day 9, 2K-1C rats had higher mean arterial blood pressures, heart rates, and plasma renin concentrations than SHAM rats. The contractile responses to AII were markedly diminished in both proximal and distal segments of OAs from 2K-1C rats as compared to those from SHAM rats. The responses elicited by AVP were substantially greater in distal than in proximal segments of OAs from SHAM rats and that AVP elicited similar responses in OA segments from 2K-1C rats. The responses elicited by 5-HT were similar in proximal and distal segments from SHAM and 2K-1C rats. These results demonstrate that continued exposure to circulating AII and AVP in 2K-1C rats reduces the contractile efficacy of AII but not AVP or 5-HT. The diminished responsiveness to AII may alter the physiological status of OAs in vivo.

Quantitative evaluation of drug-induced microvascular constriction in mice kidney using a novel tool for 3D geometrical analysis of ex vivo organ vasculature

The analysis of organ vasculature, and more specifically organ microvasculature, carries special importance for toxicological sciences, and especially for evaluation of drug-induced vascular toxicity. This field presents a special challenge in nonclinical drug safety assessments since there are currently no reliable microvascular toxicity biomarkers. Therefore, we aimed to systematically investigate the use of microvascular 3D geometrical analysis of corrosion casts for evaluation of drug-induced vascular toxicity, utilizing a novel image investigation tool that allows full 3D-quantified geometrical analysis of the entire vascular tree structure. Vascular casts of kidneys from control and low- and high-dose ephedrine/caffeine-treated mice were scanned by a micro CT, and images were processed and analyzed using the Vasculomics™ platform. All evaluations were performed on the kidney cortex. Treatment resulted in a significant and dose-related reduction in overall microvessel density throughout the kidney cortex. This effect was most pronounced for vessels with diameters between 25 µm and 35 µm, and affected mostly vessels located in the superficial part of the kidney cortex. The use of 3D analysis tools in drug-induced vascular toxicity studies allows for very high resolution and characterization of drug effects on the microvasculature and can be used as a valuable tool in drug safety assessments.

Changes of dorsalis pedis artery flow pattern after caudal block in children: observational study using a duplex sonography

OBJECTIVE

To evaluate the changes of the flow velocity, the volume flow, and the diameter of dorsalis pedis artery using a duplex ultrasonography after caudal block with sevoflurane anesthesia in children.

AIM

To know the acute change in peripheral arterial flow patterns of sympathetically blocked lower limbs in anesthetized children.

BACKGROUND

Caudal analgesia in combination with general anesthesia may affect the circulatory hemodynamics due to sympatholytic vasodilating effects.

METHODS

After approval by the Ethics Committee, we evaluated the changes of peripheral hemodynamics using a duplex ultrasonography before and after a caudal block in sevoflurane-anesthetized children.

RESULTS

A caudal block using 0.15% ropivacaine 1.5 ml·kg(-1) significantly altered the arterial flow patterns; increased peak velocity (24%) and volume flow (76%), and the diameter of the dorsalis pedis artery (20%) in children. However, blood pressures and heart rates were not affected significantly by caudal block.

CONCLUSIONS

Duplex sonographic measurements indicate that a caudal block changes the flow patterns of the dorsalis pedis artery significantly in the anesthetized children.

The cellular mechanisms underlying the inhibitory effects of isoflurane and sevoflurane on arginine vasopressin-induced vasoconstriction

PURPOSE

Arginine vasopressin (AVP) is a potent vasoconstrictor that is sometimes used for the treatment of refractory vasodilatory shock. AVP constricts vascular smooth muscle by increasing both intracellular calcium concentration ([Ca(2+)](i)) and myofilament Ca(2+) sensitivity. However, the modulation of AVP-mediated vasoconstriction by volatile anesthetics remains to be determined. This study investigates the effects of isoflurane and sevoflurane on AVP-induced vasoconstriction and elucidates the underlying mechanisms, with an emphasis on the Ca(2+)-mediated pathways and Ca(2+) sensitization pathways of rat aortic smooth muscle.

METHODS

The effects of isoflurane and sevoflurane on AVP-induced vasoconstriction and on the AVP-induced increase in [Ca(2+)](i) and Rho activity in rat aorta were investigated by isometric force recording, by measuring [Ca(2+)](i) using fluorescence dye, and by Western blotting techniques.

RESULTS

Arginine vasopressin (10⁻⁷M) elicited a transient contractile response that was inhibited by isoflurane and sevoflurane in a concentration-dependent manner. AVP (10⁻⁷ M) induced a transient increase in intracellular Ca(2+) concentration ([Ca(2+)](i)). Isoflurane and sevoflurane also inhibited an AVP-induced increase in [Ca(2+)](i) in a concentration-dependent manner. AVP (10⁻⁷ M) increased the Rho activity that was attenuated by 2 minimum alveolar concentration of sevoflurane (P < 0.01), but not by an equipotent concentration of isoflurane.

CONCLUSION

Arginine vasopressin-induced vasoconstriction is mediated by an increase in [Ca(2+)](i) and by the activation of the Rho-Rho kinase pathway in rat aortic smooth muscle. Although both isoflurane and sevoflurane, at clinically relevant concentrations, attenuate AVP-induced contraction, the cellular mechanisms of their inhibitory effects appear to differ.

Sevoflurane does not alter norepinephrine-induced intracellular Ca²(+) changes in the diabetic rat aorta

PURPOSE

The effect of volatile anesthetics on the mechanism(s) of vascular contraction in diabetes mellitus (DM) has not been fully understood. The current study was designed to determine the effects of sevoflurane on the norepinephrine (NE)-induced changes in contractile state and intracellular Ca²(+) concentrations ([Ca²(+)](i)) in the spontaneously developing type 2 DM rat.

METHODS

The effects of sevoflurane on NE (10⁻⁶M)-induced vasoconstriction and increase in [Ca²(+)](i) in the aortas from Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 DM model, and from age-matched control Long-Evans Tokushima Otsuka (LETO) rats were investigated using an isometric force transducer and fluorometer with fura-2 as an indicator of [Ca²(+)](i).

RESULTS

Norepinephrine-induced increases in tension and [Ca²(+)](i) in OLETF rats were 54.8%, 95% confidence interval (CI) 36.9-72.6% and 58.8%, 95% CI 51.5-66.1%, respectively, and in LETO rats they were 46.4%, 95% CI 39.0-53.7% and 53.8%, 95% CI 46.9-60.7%, respectively, when expressed as the percentage relative to that induced by KCl 30 mM. In LETO rats, sevoflurane at a concentration of 3.4% inhibited the vascular contraction (9.4%, 95% CI 6.3-12.6%; P < 0.001) and the increase in [Ca²(+)](i) (33.3%, 95% CI 27.4-39.2%; P = 0.002). In OLETF rats, however, sevoflurane failed to affect either the NE-induced contraction (43.6%, 95% CI 28.3-58.9%; P = 0.68) or the elevation in [Ca²(+)](i) (60.5%, 95% CI 56.3-64.8%; P = 0.93).

CONCLUSION

Sevoflurane at clinically relevant concentrations inhibited the NE-induced increase in [Ca²(+)](i) in the aortic smooth muscle from normal rats but not in that from type 2 DM rats. Thus, a Ca²(+)- signalling pathway resistant to sevoflurane appears to exist in the type 2 DM rat aorta.

Intra- and extrarenal arteries exhibit different profiles of contractile responses in high glucose conditions

BACKGROUND AND PURPOSE

The renal artery (RA) has been extensively investigated for the assessment of renal vascular function/dysfunction; however, few studies have focused on the intrarenal vasculature.

EXPERIMENTAL APPROACH

We devised a microvascular force measurement system, which allowed us to measure contractions of interlobar arteries (ILA), isolated from within the mouse kidney and prepared without endothelium.

KEY RESULTS

KCl (50 mM) induced similar force development in the aorta and RA but responses in the ILA were about 50% lower. Treatment of RA with 10 microM phenylephrine (PE), 10 nM U46619 (thromboxane A(2) analogue) or 10 microM prostaglandin F(2 alpha) elicited a response greater than 150% of that induced by KCl. In ILA, 10 nM U46619 elicited a response that was 130% of the KCl-induced response; however, other agonists induced levels similar to that induced by KCl. High glucose conditions (22.2 mM glucose) significantly enhanced responses in RA and ILA to PE or U46619 stimulation. This enhancement was suppressed by rottlerin, a calcium-independent PKC inhibitor, indicating that glucose-dependent, enhanced small vessel contractility in the kidney was linked to the activation of calcium-independent PKC.

CONCLUSION AND IMPLICATIONS

Extra- and intrarenal arteries exhibit different profiles of agonist-induced contractions. In ILA, only U46619 enhanced small vessel contractility in the kidney, which might lead to renal dysfunction and nephropathy through reduced intrarenal blood flow rate. A model has been established, which will allow the assessment of contractile responses of intrarenal arteries from murine models of renal disease, including type 2 diabetes.

The Mechanism Behind the Inhibitory Effect of Isoflurane on Angiotensin II-Induced Vascular Contraction Is Different from That of Sevoflurane

BACKGROUND

Angiotensin II (Ang II)-induced vascular contraction is mediated both by a Ca(2+)-mediated signaling pathway and a Ca(2+) sensitization mechanism. We recently demonstrated that sevoflurane inhibits the contractile response to Ang II, mainly by inhibiting protein kinase C (PKC) phosphorylation that regulates myofilament Ca(2+) sensitivity, without significant alteration of intracellular Ca(2+) concentration ([Ca(2+)](i)) in rat aortic smooth muscle. The current study was designed to determine the mechanisms by which isoflurane inhibits Ang II-induced contraction of rat aortic smooth muscle.

METHODS

The effects of isoflurane on vasoconstriction, increase in [Ca(2+)](i), and phosphorylation of PKC in response to Ang II (10(-7) M) were investigated, using an isometric force transducer, a fluorometer, and Western blotting, respectively.

RESULTS

Ang II elicited a transient contraction of rat aortic smooth muscle that was associated with an increase in [Ca(2+)](i) and PKC phosphorylation. Isoflurane (1.2%-3.5%) inhibited Ang II-induced contraction of rat aortic smooth muscle in a concentration-dependent manner (P < 0.05 at 1.2%, P < 0.01 at 2.3% and 3.5% isoflurane, n = 6). Isoflurane also inhibited elevation of [Ca(2+)](i) in response to Ang II (P < 0.01 at 2.3% and 3.5% isoflurane, n = 6), but failed to affect Ang II-induced phosphorylation of PKC at concentrations up to 3.5% (n = 7).

CONCLUSION

These results suggest that, unlike sevoflurane, the inhibitory effect of isoflurane on Ang II-induced contraction is mainly mediated by attenuation of the Ca(2+)-mediated signaling pathway.

The Inhibitory Effects of Sevoflurane on Angiotensin II- Induced, p44/42 Mitogen-Activated Protein Kinase-Mediated Contraction of Rat Aortic Smooth Muscle

Sevoflurane dilates blood vessels and reduces arterial blood pressure in a dose-dependent manner. Angiotensin II (Ang II) is one of the primary regulators of vascular tension and arterial blood pressure, and the p44/42 mitogen-activated protein kinases (p44/42 MAPK) are involved in Ang II-mediated vascular smooth muscle contraction. We designed this study to examine the effects of sevoflurane on Ang II-induced, p44/42 MAPK-mediated contraction of rat aortic smooth muscle. The effects of the p44/42 MAPK kinase (MEK1/2) inhibitor, PD 098059 (10(-5) molar [M], 5 x 10(-5) M and 10(-4) M), and sevoflurane (1.7%, 3.4%, and 5.1%) on Ang II-induced contraction and p44/42 MAPK phosphorylation were tested in rat aortic smooth muscle, using isometric force measurement and Western blot analysis, respectively. Ang II induced both a transient contractile response and phosphorylation of p44/42 MAPK, which were significantly attenuated by PD 098059 (P < 0.05-0.01). Sevoflurane inhibited Ang II-induced contractile response in a dose-dependent manner (P < 0.05 and 0.01 in response to 3.4% and 5.1% sevoflurane, respectively). Sevoflurane also dose-dependently depressed Ang II-elicited p44/42 MAPK phosphorylation (P < 0.01 in response to 3.4% and 5.1% sevoflurane). These results suggest that the inhibitory effect of sevoflurane on Ang II-induced vasoconstriction is, at least in part, caused by the inhibition of the p44/42 MAPK-mediated signaling pathway.

IMPLICATIONS

The present study demonstrates that sevoflurane can dose-dependently inhibit both angiotensin II (Ang II)-induced contraction and p44/42 MAPK phosphorylation of rat aortic smooth muscle. These data suggest that sevoflurane-produced inhibition of Ang II-induced vasoconstriction is, at least in part, caused by depression of the p44/42 MAPK-mediated signaling pathway.