Rat Cerebral Arterioles Research Articles

Commonly used anesthetics modify alcohol and (-)-trans-delta9-tetrahydrocannabinol in vivo effects on rat cerebral arterioles

BackgroundEthyl alcohol and cannabis are widely used recreational substances with distinct effects on the brain. These drugs increase accidental injuries requiring treatment under anesthesia. Moreover, alcohol and cannabis are often used in anesthetized rodents for biomedical research. Here, we compared the influence of commonly used forms of anesthesia, injectable ketamine/xylazine (KX) versus inhalant isoflurane, on alcohol- and (-)-trans-delta9-tetrahydrocannabinol (THC) effects on cerebral arteriole diameter evaluated in vivo.MethodsStudies were performed on male and female Sprague–Dawley rats subjected to intracarotid catheter placement for drug infusion, and cranial window surgery for monitoring pial arteriole diameter. Depth of anesthesia was monitored every 10–15 min by toe-pinch. Under KX, the number of toe-pinch responders was maximal after the first dose of anesthesia and diminished over time in both males and females. In contrast, the number of toe-pinch responders under isoflurane slowly raised over time, leading to increase in isoflurane percentage until deep anesthesia was re-established. Rectal temperature under KX remained stable in males while dropping in females. As expected for gaseous anesthesia, both males and females exhibited rectal temperature drops under isoflurane.ResultsInfusion of 50 mM alcohol (ethanol, EtOH) into the cerebral circulation rendered robust constriction in males under KX anesthesia, this alcohol action being significantly smaller, but still present under isoflurane anesthesia. In females, EtOH did not cause measurable changes in pial arteriole diameter regardless of the anesthetic. These findings indicate a strong sex bias with regards to EtOH induced vasoconstriction.Infusion of 42 nM THC in males and females under isoflurane tended to constrict cerebral arterioles in both males and females when compared to isovolumic infusion of THC vehicle (dimethyl sulfoxide in saline). Moreover, THC-driven changes in arteriole diameter significantly differed in magnitude depending on the anesthetic used.Simultaneous administration of 50 mM alcohol and 42 nM THC to males constricted cerebral arterioles regardless of the anesthetic used. In females, constriction by the combined drugs was also observed, with limited influence by anesthetic presence.ConclusionsWe demonstrate that two commonly used anesthetic formulations differentially influence the level of vasoconstriction caused by alcohol and THC actions in cerebral arterioles.

3-Iodothyronamine, a trace amine-associated receptor agonist, regulates intracellular Ca2+ increases via CaMK II through Epac2 in rat cerebral arterioles.

Trace amines (TAs) in the nervous system bind to TA-associated receptors (TAARs) and are involved in the regulation of monoaminergic functions. Among TAAR subtypes, TAAR1 has been implicated in the development of neurological disorders, such as schizophrenia. The present study investigated the effects of the TAAR1 agonist, 3-iodothyronamine (T1AM) on cerebral arterioles using fluctuations in the intracellular concentration of Ca2+ ([Ca2+]i) as an index of contractile responses. In cerebral arterioles, most of the TAAR agonists did not increase [Ca2+]i, while only T1AM elevated [Ca2+]i in vascular smooth muscle cells. This increase involved extracellular Ca2+ influx through T-type Ca2+ channels and inositol trisphosphate- and ryanodine-receptor-mediated Ca2+ release from intracellular stores. The inhibition of the cAMP sensor, exchange protein directly activated by cAMP (Epac) 2, and calmodulin kinase (CaMK) II strongly inhibited Ca2+ elevations. The present study revealed that T1AM acted not only on the TAAR1 receptor as previously suggested, but also on other G-protein coupled receptors and/or signal transduction systems to increase intracellular Ca2+ in cerebral arteriole smooth muscle cells. These results suggest that when using T1AM in clinical practice, attention should be paid to the early rise in blood pressure.

Abstract P217: Direct Myosin-2 Inhibition Restores Cerebral Perfusion in Cortical and Subcortical Regions Resulting in Functional Improvement After Ischemic Stroke

Inefficient cerebral reperfusion is a major unresolved problem in ischemic stroke treatment because hypoxia-induced constriction of capillaries remains persistent even after recanalization by thrombolysis or thrombectomy. Capillary constriction is mediated by actomyosin contraction in precapillary smooth muscle cells (SMCs). We have developed and tested a formulation and administration technique to target the ischemic brain region and developed a promising small-molecule myosin-2 inhibitor (para-aminoblebbistatin (AmBleb) that mainly exerts its effect through direct inhibition of smooth muscle myosin-2 (SMM) in SMCs. The efficacy of SMM inhibition was tested in a rodent transient Middle Cerebral Artery Occlusion (tMCAO) stroke model. SMM was targeted by the direct administration of AmBleb into the ischemic region. AmBleb significantly accelerated the improvement of neurological deficits. Regional cerebral blood flow (rCBF) in the most important cortical and subcortical regions (e.g. motor- and somatosensory cortices, optic pathways, striatum, corpus callosum) showed drastic improvement in the AmBleb treated animals in line with the significant reduction of neurological deficits. We further optimized AmBleb and developed our lead compound MPH-222, which possesses significantly improved pharmacological properties than those of AmBleb. As observed with AmBleb, MPH-222 also fully relaxed isolated human and rat cerebral arterioles, and improved neurological functions of tMCAO operated rats characterized by significantly improved neurological deficits as well as enhanced locomotor symmetry. Moreover, as opposed to AmBleb, markedly lower MPH-222 dose was enough to achieve efficient concentrations in the ischemic region when catheter-based direct intra-arterial administration was applied. This result suggests that direct myosin inhibitor administration may be an optimal add-on therapy to thrombectomy. Funded by the Hungarian National Research, Development and Innovation Office (NVKP 16-1-2016-0051 and PIACI-KFI-2019-00488).

Influence of dual-specificity protein phosphatase 5 on mechanical properties of rat cerebral and renal arterioles.

We recently reported that KO of Dual‐specificity protein phosphatase 5 (Dusp5) enhances myogenic reactivity and blood flow autoregulation in the cerebral and renal circulations in association with increased levels of pPKC and pERK1/2 in the cerebral and renal arteries and arterioles. In the kidney, hypertension‐related renal damage was significantly attenuated in Dusp5 KO rats. Elevations in pPKC and pERK1/2 promote calcium influx in VSMC and facilitate vasoconstriction. However, whether DUSP5 plays a role in altering the passive mechanical properties of cerebral and renal arterioles has never been investigated. In this study, we found that KO of Dusp5 did not alter body weights, kidney and brain weights, plasma glucose, and HbA1C levels. The expression of pERK is higher in the nucleus of primary VSMC isolated from Dusp5 KO rats. Dusp5 KO rats exhibited eutrophic vascular hypotrophy with smaller intracerebral parenchymal arterioles and renal interlobular arterioles without changing the wall‐to‐lumen ratios. These arterioles from Dusp5 KO rats displayed higher myogenic tones, better distensibility, greater compliance, and less stiffness compared with arterioles from WT control rats. VSMC of Dusp5 KO rats exhibited a stronger contractile capability. These results demonstrate, for the first time, that DUSP5 contributes to the regulation of the passive mechanical properties of cerebral and renal arterioles and provide new insights into the role of DUSP5 in vascular function, cancer, stroke, and other cardiovascular diseases.

Propofol But Not Desflurane Maintains Rat Cerebral Arteriolar Responses to Acetylcholine During Acute Hyperglycemia.

Acute hyperglycemia causes vascular endothelial dysfunction in various organs including the cerebral vessels. It is associated with increased mortality and morbidity in the perioperative period. The impact of anesthetic agents on cerebral vasodilatory responses during hyperglycemia remains unclear. We investigated endothelial function in rat cerebral arterioles during acute hyperglycemia, under propofol or desflurane anesthesia. A closed cranial window preparation was used to measure changes in pial arteriole diameter induced by topical application of acetylcholine (ACh), an endothelium-dependent vasodilator, in rats anesthetized with propofol or desflurane. Pial arteriole responses to ACh were measured during normoglycemia and hyperglycemia. We then investigated whether the response of cerebral arterioles to acute hyperglycemia under propofol anesthesia were related to propofol or its vehicle, intralipid. ACh resulted in a dose-dependent dilation of cerebral arterioles during propofol and desflurane anesthesia under normoglycemic conditions. The vasodilatory effects of ACh were also maintained under hyperglycemic conditions during propofol anesthesia, but the vasodilator response to ACh was significantly impaired during hyperglycemia compared with normoglycemia with desflurane anesthesia. The vasodilatory effects of ACh were maintained during normoglycemia and hyperglycemia in rats receiving propofol or intralipid. Rat pial arteriole responses to ACh are maintained during conditions of acute hyperglycemia with propofol anesthesia but suppressed compared with normoglycemia with desflurane anesthesia.

Endothelium-dependent vasodilation in the cerebral arterioles of rats deteriorates during acute hyperglycemia and then is restored by reducing the glucose level.

Acute hyperglycemia in patients with traumatic brain injury correlates with a poor neurological outcome. We investigated the endothelium function of rat cerebral arterioles during acute hyperglycemia and after reducing the glucose levels using insulin. We also examined whether or not oxidative stress was involved in the cerebral arteriole response to acute hyperglycemia. In isoflurane-anesthetized, mechanically ventilated rats, we used closed cranial window preparation to measure the changes in the pial arteriolar diameter following the topical application of acetylcholine (ACh) or adenosine. We examined the pial arteriolar vasodilator response before hyperglycemia, during hyperglycemia, and after reducing the glucose level using insulin. After intravenous pretreatment with an NADPH oxidase inhibitor (apocynin or diphenylene iodonium), we reexamined the pial arteriolar vasodilator response following the topical application of ACh. Under control conditions, the topical application of ACh dose-dependently dilated the cerebral arterioles. The vasodilatory responses to topical ACh were impaired during hyperglycemia and improved after the administration of insulin. The vasodilatory responses to topical adenosine were not affected by the glucose levels. In the apocynin or diphenylene iodonium pretreatment group, the topical application of ACh dilated the cerebral arterioles during hyperglycemia. Acute hyperglycemia induces a dysfunction of the endothelium-dependent vasodilation of rat cerebral arterioles. The dysfunction can be reversed by improving the acute hyperglycemia and it can be prevented entirely by the administration of NADPH oxidase inhibitors. These results could suggest that controlling the glucose levels works protectivity to endothelium function of cerebral arterioles.

Vitamin D deficiency causes inward hypertrophic remodeling and alters vascular reactivity of rat cerebral arterioles.

Background and purposeVitamin D deficiency (VDD) is a global health problem, which can lead to several pathophysiological consequences including cardiovascular diseases. Its impact on the cerebrovascular system is not well understood. The goal of the present work was to examine the effects of VDD on the morphological, biomechanical and functional properties of cerebral arterioles.MethodsFour-week-old male Wistar rats (n = 11 per group) were either fed with vitamin D deficient diet or received conventional rat chow with per os vitamin D supplementation. Cardiovascular parameters and hormone levels (testosterone, androstenedione, progesterone and 25-hydroxyvitamin D) were measured during the study. After 8 weeks of treatment anterior cerebral artery segments were prepared and their morphological, biomechanical and functional properties were examined using pressure microangiometry. Resorcin-fuchsin and smooth muscle actin staining were used to detect elastic fiber density and smooth muscle cell counts in the vessel wall, respectively. Sections were immunostained for eNOS and COX-2 as well.ResultsVDD markedly increased the wall thickness, the wall-to-lumen ratio and the wall cross-sectional area of arterioles as well as the number of smooth muscle cells in the tunica media. As a consequence, tangential wall stress was significantly lower in the VDD group. In addition, VDD increased the myogenic as well as the uridine 5’-triphosphate-induced tone and impaired bradykinin-induced relaxation. Decreased eNOS and increased COX-2 expression were also observed in the endothelium of VDD animals.ConclusionsVDD causes inward hypertrophic remodeling due to vascular smooth muscle cell proliferation and enhances the vessel tone probably because of increased vasoconstrictor prostanoid levels in young adult rats. In addition, the decreased eNOS expression results in endothelial dysfunction. These morphological and functional alterations can potentially compromise the cerebral circulation and lead to cerebrovascular disorders in VDD.

Protective effects of choline against hypoxia-induced injuries of vessels and endothelial cells.

The current study aimed to lay a theoretical foundation for further development of choline as an anti-hypoxia damage drug. Wild-type, 3- to 5-month-old male Sprague-Dawley rats, weighing 180–220 g, were used in this study. The rats were randomly divided into a normoxic control group (n=16) and a chronic intermittent hypoxia (CIH) group (n=16). The effects of CIH on acetylcholine (ACh)-mediated endothelium-dependent vasodilatation in the rat cerebral basilar arterioles and mesenteric arterioles, as well as the protective effects of choline on the arterioles damaged by hypoxia were observed. Moreover, the effects of choline on endothelial cell proliferation during hypoxia were observed, and choline's functional mechanism further explored. The ACh-mediated vasodilatation of rat cerebral basilar and mesenteric arterioles significantly reduced during hypoxia (P<0.01). Choline significantly increased dilation in the rat cerebral basilar (P<0.01) and mesenteric arterioles (P<0.05) damaged by CIH compared with those in the control group. In addition, under hypoxic conditions, choline significantly promoted the proliferation of rat aortic endothelial cells (P<0.05) and significantly reduced lactate dehydrogenase activity in the cell culture supernatant in vitro (P<0.05). Furthermore, the effect of choline could be related to its ability to significantly increase the secretion of vascular endothelial growth factor (P<0.01) and activation of α7 non-neuronal nicotinic acetylcholine receptors under hypoxia (P<0.01). This study demonstrated that choline could have protective effects against hypoxic injuries.

Effect of a novel stobadine derivative on isolated rat arteries

The antioxidant and reactive-oxygen-species-scavenging activity of stobadine has been demonstrated in previous studies. Recently, chemical modification of this leading structure led to the synthesis of other pyridoindole derivatives with significantly increased intrinsic antioxidant efficacy. Further structural modifications of stobadine provided the opportunity to increase bioavailability and attenuate unwanted side effects, such as α-adrenolytic activity. The aim of the work was to evaluate the direct effect of a novel pyridoindole, SMe1EC2, on the vascular wall ex vivo. The vasomotor effect of SMe1EC2 (1×10–8–1×10–4 mol/l) was measured on isolated and pressurized rat cerebral and coronary arterioles using video-microscopy. The effect of SMe1EC2 (1×10–6 and 1×10–5 mol/l) on high potassium-, phenylephrine- or serotonin-induced contraction or acetylcholine-induced relaxation was also determined in aortic rings. We found that SMe1EC2 (1×10–8–1×10–4 mol/l) elicited significant dilatations in both cerebral and coronary arterioles (max dilatation: 25±8% and 18±5% respectively). Yet, SMe1EC2 (1×10–6 and 1×10–5 mol/l) did not influence the tone of aortic rings nor did it affect high potassium-, phenylephrine- or serotonin -induced contractions and acetylcholine-induced relaxation. Thus SMe1EC2 was able to dilate resistance arteries but did not affect aortic contractility. It is likely that SMe1EC2 does not possess α1-adrenolytic and anti-serotoninergic activity in the vascular wall.

G Protein–Coupled Estrogen Receptor Agonist Improves Cerebral Microvascular Function After Hypoxia/Reoxygenation Injury in Male and Female Rats

Reduced risk and severity of stroke in adult females are thought to depend on normal levels of endogenous estrogen, which is a known neuro- and vasoprotective agent in experimental cerebral ischemia. Recently, a novel G protein-coupled estrogen receptor (GPER, formerly GPR30) has been identified and may mediate the vasomotor and -protective effects of estrogen. However, the signaling mechanisms associated with GPER in the cerebral microcirculation remain unclear. We investigated the mechanism of GPER-mediated vasoreactivity and also its vasoprotective effect after hypoxia/reoxygenation (H/RO) injury. Rat cerebral penetrating arterioles from both sexes were isolated, cannulated, and pressurized. Vessel diameters were recorded by computer-aided videomicroscopy. To investigate vasomotor mechanism of the GPER agonist (G-1), several inhibitors with or without endothelial impairment were tested. Ischemia/reperfusion injury was simulated using H/RO. Vasomotor responses to adenosine triphophate after H/RO were measured with or without G-1 and compared with controls. G-1 produced a vasodilatory response, which was partially dependent on endothelium-derived nitric oxide (NO) but not arachidonic acid cascades and endothelial hyperpolarization factor. Attenuation of G-1-vasodilation by the NO synthase inhibitor and endothelium-impairment were greater in vessels from female than male animals. G-1 treatment after H/RO injury fully restored arteriolar dilation to adenosine triphophate compared with controls. GPER agonist elicited dilation, which was partially caused by endothelial NO pathway and induced by direct relaxation of smooth muscle cells. Further, GPER agonist restored vessel function of arterioles after H/RO injury and may play an important role in the ability of estrogen to protect the cerebrovasculature against ischemia/reperfusion injury.

Organ culture as an in vitro model for the study of dual‐specificity phosphatase‐5 (DUSP‐5) and myogenic response in rat cerebral arterioles

Increase in intravascular pressure causes depolarization and constriction of cerebral arteries. The molecular mechanism of pressure‐induced myogenic response remains obscure. Our goal was to provide an optimal time window and preserved vascular function for an organ culture of cerebral arteries for the study of mechanisms involved in the regulation of cerebral arterial function. We initiated a comparative study of cultured and freshly isolated cerebral arteries in response to elevated intravascular pressure, vasodilator and vasoconstrictor stimuli, activity of Ca2+‐activated K+ (KCa) single‐channel current and protein expression of CYP 4 and DUSP‐5 enzymes. The results indicate that 72 h time frame of organ culture of cerebral arteries maintains cellular integrity, pressure dependent constriction, CYP4A2 and 4F protein expression, endothelium‐dependent and independent dilations, KCa channel current activity and vasoconstrictor response to serotonin. Furthermore, using a permeabilization, transfection technique the 72 h cultured arteries elicited a gene specific siRNA induced knockdown of DUSP‐5 protein expression. Subsequent pressure myograph studies and inhibitor studies revealed role of DUSP‐5 in regulation of myogenic tone. We propose a possible mechanism by which DUSP‐5 and ERK regulate myogenic response in cerebral arterioles. RO1 HL033833, RO1 HL092105, T32 HL007792.

Effects of H&lt;sub&gt;2&lt;/sub&gt;S on Myogenic Responses in Rat Cerebral Arterioles

The potential biological significance of hydrogen sulfide (H₂S) has attracted growing interests in recent years, but its role in the myogenic response of rat cerebral arterioles has not been explored. Rats were injected with NaHS (an H₂S donor, 2-200 µmol·kg⁻¹·day⁻¹, i.p.) or saline for 3 weeks. MBP was measured with a tail-cuff method. Cerebral arterioles were isolated and cannulated in an organ bath system, and vessel diameters were measured with an image-shearing device. Changes in diameter in response to stepwise increases in intravascular pressure (20-120 mmHg) were investigated under no-flow conditions. After the treatments, plasma H₂S increased and MBP decreased significantly. NaHS reduced the myogenic response in a dose-dependent manner. This effect was markedly attenuated by glibenclamide, a K(ATP) channel blocker. Blockade of nitric oxide (NO) production with NG-nitro-L-arginine methyl ester (L-NAME, a NO synthase inhibitor) enhanced, whereas removal of the endothelium abolished the inhibitory role of NaHS on the myogenic response. For the first time it has been demonstrated that H₂S decreases the myogenic response of cerebral arterioles in vivo, and this effect is endothelium-dependent and partially mediated by K(ATP) channels.

Mechanism of alkalosis-induced constriction of rat cerebral penetrating arterioles

Cerebral arterioles are in close contact with the supplied tissue and are strong regulators of cerebrovascular tone. Transient ischemia can cause brain intracellular alkalosis producing vasoconstriction. However, the mechanisms of alkalosis-induced cerebral arteriolar constriction are poorly understood. Here, we determined the vascular responses to alkalosis under different conditions by monitoring the internal diameter of pressurized penetrating arterioles isolated from the rat cerebrum with an operating microscope. The roles of Na +/H + exchanger (NHE), Na +/Ca 2+ exchanger (NCX), Na +/K +-adenosine triphosphatase (NKA), and potassium (K +) channels during alkalosis were examined using specific inhibitors. Our results indicated that the extent of constriction of the penetrating arterioles was dependent on alkaline pH. Moreover, the alkalosis-induced vasoconstriction was significantly attenuated by inhibitors of NHE, NCX, and NKA, but not K + channel inhibitors. Therefore, we concluded that NHE, NKA, and NCX are important regulators involved in alkalosis-induced vasoconstriction of rat cerebral penetrating arterioles.

Time-dependent action of carbon monoxide on the newborn cerebrovascular circulation

Carbon monoxide (CO) causes cerebral arteriolar dilation in newborn pigs by the activation of large-conductance Ca(2+)-activated K(+) channels. In adult rat cerebral and skeletal muscle arterioles, CO has been reported to produce constriction caused by the inhibition of nitric oxide (NO) synthase (NOS). We hypothesized that, in contrast to dilation to acute CO, more prolonged exposure of newborn cerebral arterioles to elevated CO produces constriction by reducing NO. In piglets with closed cranial windows, pial arteriolar responses to isoproterenol (10(-6) M), sodium nitroprusside (SNP; 10(-7) and 3 x 10(-7) M), and L-arginine ethyl ester (L-Arg; 10(-5) and 10(-4) M) were determined before and after 2 h of treatment with CO. CO (10(-7) M) caused transient dilation and had no further effects. CO (2 x 10(-7) and 10(-6) M) initially caused vasodilation, but over the 2-h exposure, pial arterioles constricted and removal of the CO caused dilation. Exposure to elevated CO (2 h) did not alter dilation to SNP or isoproterenol. Conversely, the NOS substrate L-Arg caused dilation before CO that was progressively lost over 90 min of elevated CO. If NO was held constant, CO caused dilation that was sustained for 2 h. We conclude that in neonates, cerebral arteriole responses to CO are biphasic: dilation to acute elevation with subsequent constriction from NOS inhibition after more prolonged exposure. As a result, short episodic production of CO allows function as a dilator gasotransmitter, whereas prolonged elevation can reduce NO to elevate cerebrovascular tone. The interaction between heme oxygenase/CO and NOS/NO could form a negative feedback system in the control of cerebral vascular tone.

Mechanism of ATP-Induced Local and Conducted Vasomotor Responses in Isolated Rat Cerebral Penetrating Arterioles

Background: Adenosine triphosphate (ATP), a potent vascular regulator in the cerebral circulation, initiates conducted vasomotor responses which may be impaired after pathological insults. We analyzed the mechanism of ATP-induced local vasomotor responses and their effect on conducted vasomotor responses in rat cerebral penetrating arterioles. Methods: Arterioles were cannulated and their internal diameter monitored. Vasomotor responses to ATP were observed in the presence or absence of inhibitors, or after endothelial impairment. Smooth muscle membrane potentials were measured in some vessels. Results: Microapplication of ATP produced a biphasic response (constriction followed by dilation), which resulted in conducted dilation preceded by a membrane hyperpolarization. α,β-methylene-ATP or pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS) blunted the ATP-mediated constriction and enhanced local and conducted dilation. N^ω-monomethyl-L-arginine, endothelial impairment and N-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide (MS-PPOH) reduced the local dilation caused by ATP. The conducted dilation was attenuated by MS-PPOH and endothelial impairment, but not N^ω-monomethyl-L-arginine or indomethacin. Conclusion: ATP-induced conducted dilation is preceded by membrane hyperpolarization. Local ATP induces initial local constriction via smooth-muscle P_2X1 and subsequent dilation via endothelial P_2Y receptors. Nitric oxide, cytochrome P450 metabolites, and intermediate and large conductance K_Ca channels mediate dilation caused by ATP. ATP-induced conducted dilation is dependent upon both the endothelium and cytochrome P450 metabolites.

Red Wine Polyphenols Improve Endothelium-dependent Dilation in Rat Cerebral Arterioles

Moderate consumption of red wine is associated with a lower incidence of cardiovascular disease. Red wine polyphenols (RWP) have been proposed to be beneficial, but there is lack of evidence concerning the cerebrovascular effects of RWP. We studied the effect of local administration of a RWP extract (10(-2) mg/mL) on the diameter of rat cerebral arterioles using an open cranial window technique in vivo. We measured cerebral arteriolar diameter and systemic blood pressure. Cerebral arterioles reacted concentration-dependently to adenosine diphosphate [ADP, dilatation EC50 5.3 x 10(-5) M (95% confidence interval: 3.1 to 9.0 x 10 M(-5))], NG-nitro-L-arginine methyl ester [L-NAME, constriction EC50 5.8 x 10(-9) M (95% CI: 2.5 x 10(-9) to 1.4 x 10(-8) M)]. and sodium nitroprusside [SNP, dilatation EC50 1.0 x 10(-6) M (95% CI: 9.2 x 10(-7) to 1.1 x 10(-6) M)]. RWP enhanced vasodilation induced by ADP (10(-4) M) from 17 +/- 2% to 29 +/- 4% and reversed L-NAME-induced vasoconstriction but did not affect SNP-induced vasodilation. Systemic hypotension induced by hemorrhage caused myogenic arteriolar dilation. RWP further dilated cerebral arterioles (from -1 +/- 2% to 8 +/- 3%) with 1 mL of blood withdrawn. In summary, RWP improved endothelium-dependent and pressure-induced vasodilation in rat cerebral arterioles. This could be beneficial in improving cerebral blood flow under ischemic condition.

A BRIEF COMMUNICATION

In newborn pigs, carbon monoxide (CO) contributes to regulation of cerebrovascular circulation. Results from isolated adult cerebral arteries suggest CO may have less dilatory potential in mature animals. However, few data are available on the direct effects of CO on cerebrovascular circulation in vivo except for those from newborn pigs. Therefore, we tested the hypothesis that i) rat cerebral arterioles dilate to CO in vivo and ii) CO-induced cerebrovascular dilatory responses are age dependent in pigs. Also, we examined whether the permissive role of nitric oxide in CO-induced dilation observed in piglets is present in older pigs and rats. Experiments used anesthetized newborn, 7-week-old, and juvenile (3- to 4-month-old) pigs and 3- to 4-month-old rats with closed cranial windows and topical applications of CO and sodium nitroprusside (SNP). Dilations to SNP were not different at different ages in pigs or between pigs and rats. CO produced pial arteriolar dilations in all groups. Dilation to 10−5 M CO was reduced in juvenile pigs as compared to newborn and 7-week-old pigs, and tended to less at 10−6 M CO. Dilations of rat pial arterioles to all concentrations were less than those of newborn and 7-week-old pigs, but not different from those of juvenile pig pial arterioles. In newborn and 7-week-old pigs, l-nitro-arginine (LNA) inhibited the dilation to CO, an effect reversed by a constant background of SNP. In contrast, LNA did not reduce dilation to CO in juvenile pigs or rats. In conclusion, rat pial arterioles like those in piglets dilate to CO in vivo, but there are age and species differences with regard to reactivity and interaction with NO.

Cerebral microvascular dilation during hypotension and decreased oxygen tension: a role for nNOS

Endothelial (eNOS) and neuronal nitric oxide synthase (nNOS) are implicated as important contributors to cerebral vascular regulation through nitric oxide (NO). However, direct in vivo measurements of NO in the brain have not been used to dissect their relative roles, particularly as related to oxygenation of brain tissue. We found that, in vivo, rat cerebral arterioles had increased NO concentration ([NO]) and diameter at reduced periarteriolar oxygen tension (Po(2)) when either bath oxygen tension or arterial pressure was decreased. Using these protocols with highly selective blockade of nNOS, we tested the hypothesis that brain tissue nNOS could donate NO to the arterioles at rest and during periods of reduced perivascular oxygen tension, such as during hypotension or reduced local availability of oxygen. The decline in periarteriolar Po(2) by bath manipulation increased [NO] and vessel diameter comparable with responses at similarly decreased Po(2) during hypotension. To determine whether the nNOS provided much of the vascular wall NO, nNOS was locally suppressed with the highly selective inhibitor N-(4S)-(4-amino-5-[aminoethyl]aminopentyl)-N'-nitroguanidine. After blockade, resting [NO], Po(2), and diameters decreased, and the increase in [NO] during reduced Po(2) or hypotension was completely absent. However, flow-mediated dilation during occlusion of a collateral arteriole did remain intact after nNOS blockade and the vessel wall [NO] increased to approximately 80% of normal. Therefore, nNOS predominantly increased NO during decreased periarteriolar oxygen tension, such as that during hypotension, but eNOS was the dominant source of NO for flow shear mechanisms.

Mechanism of hypoxia/reoxygenation damage in rat cerebral arterioles

Background: It is not known if Ischemia/Reperfusion (I/R) directly impairs cerebral microvascular regulation. Such impairment could contribute to regional hypoperfusion as observed after I/R. Methods: Cerebral arterioles were isolated, cannulated and their internal diameter monitored with a video microscope. Vasomotor responses to adenosine tri-phosphate (ATP) were obtained before and/or after 60 to 120 min. of hypoxia (PO2< 5 mmHg) with rapid normoxic reoxygenation (H/RO) in the presence or absence of inhibitors. Results: Arterioles significantly constricted during hypoxia. Reoxygenation resulted in a transient dilation followed by a significant vasoconstriction which lasted more than 120 min. Dilation to ATP was significantly decreased. Application of oxygen radial scavenger MnTBAP or calcium sensitive potassium channel activators restored dilation to ATP but not inhibition of nitric oxide synthase. Conclusions: H/RO directly impairs cerebral arteriolar regulation causing prolonged constriction and reduced dilation which could contribute to the hypoperfusion observed after ischemia/reperfusion and promote neuronal damage. possibly via production of reactive oxygen species (ROS) and subsequent inhibition of calcium activated potassium channels. ROS scavenging or potassium channel openers rescued the vessel response. NIH HL57540 (HHD) and NS30555 (RGD and HHD).

Effects of middle cerebral artery occlusion on the conduction of vasomotor responses along rat cerebral arterioles

Vascular communication mechanisms, such as conducted vasomotor responses, likely play an important role in cerebrovascular regulation, but it is unclear how these mechanisms may be affected by ischemia. In this study, we determined the effect of focal cerebral ischemia on the conducted vasomotor responses of intracerebral arterioles to ATP and to adenosine (Ado). After 2- hours of middle cerebral artery occlusion (MCAO) and a 24-hour reperfusion period in Sprague Dawley rats, intracerebral branches of the MCA were isolated and cannulated with a concentric micropipette system. Both ischemic (n=13) and sham-control (n=8) arterioles developed similar myogenic tone (~70% of passive diameter, 60 mmHg). Pressure-pulse application of Ado (10 mM) and ATP (5 mM) induced both a direct local response, and a secondary conducted response that spread longitudinally along the vessel. ATP caused a local biphasic response of constriction (17±2%) followed by dilation (7±3%), whereas Ado elicited only dilation (13±2%). In sham-control vessels, the constriction/dilation responses to ATP markedly decreased (71%/57%) over a 1 mm distance. Ado-induced dilation decayed even more rapidly and was undetectable at 1 mm. In ischemic vessels, the decay of ATP-induced constriction (70%) was similar to that in sham-controls. On the other hand, dilation responses to either ATP or Ado conducted with virtually no decay in ischemic arterioles over the same distance. We conclude that ischemia-reperfusion led to a specific upregulation of conducted vasodilaton in rat cerebral arterioles. Funded by AHA Grant 0255703N.