Arterial Strips Research Articles

Effect of amurinone on human pulmonary artery in vitro

We studied the effect of amurinone, a phosphodiesterase inhibitor, on human pulmonary arterial smooth muscle in vitro. Amurinone caused dose-dependent relaxation of pulmonary arterial strips precontracted with 60 mM KCl. Preincubation with either meclofenamate (31 microM), a cyclooxygenase inhibitor, or L-NG-nitroarginine (100 microM), an endothelium-derived relaxing factor (EDRF) production inhibitor, failed to inhibit amurinone-induced pulmonary vasodilation. The cyclic AMP (cAMP) levels in the supernatant of the lung vessel homogenates significantly increased after incubation with amurinone. These results indicate that amurinone causes relaxation of human pulmonary artery in vitro, and suggest a role for cAMP in the mechanisms of amurinone-induced pulmonary vasodilation.

Reactive oxygen species are involved in regulating α1-adrenoceptor-activated vascular smooth muscle contraction

BackgroundReactive oxygen species (ROS) were shown to mediate aberrant contractility in hypertension, yet the physiological roles of ROS in vascular smooth muscle contraction have remained elusive. This study aimed to examine whether ROS regulate α1-adrenoceptor-activated contraction by altering myosin phosphatase activities.MethodsUsing endothelium-denuded rat tail artery (RTA) strips, effects of anti-oxidants on isometric force, ROS production, phosphorylation of the 20-kDa myosin light chain (MLC20), and myosin phosphatase stimulated by α1-adrenoceptor agonist phenylephrine were examined.ResultsAn antioxidant, N-acetyl-L-cysteine (NAC), and two NADPH oxidase inhibitors, apocynin and VAS2870, dose-dependently inhibited contraction activated by phenylephrine. Phenylephrine stimulated superoxide anion production that was diminished by the pretreatment of apocynin, VAS2870, superoxide scavenger tiron or mitochondria inhibitor rotenone, but not by xanthine oxidase inhibitor allopurinol or cyclooxygenase inhibitor indomethacin. Concurrently, NADPH oxidase activity in RTA homogenates increased within 1 min upon phenylephrine stimulation, sustained for 10 min, and was abolished by the co-treatment with apocynin, but not allopurinol or rotenone. Phenylephrine-induced MLC20 phosphorylation was dose-dependently decreased by apocynin. Furthermore, apocynin inhibited phenylephrine-stimulated RhoA translocation to plasma membrane and phosphorylation of both myosin phosphatase regulatory subunit MYPT1Thr855 and myosin phosphatase inhibitor CPI-17Thr38.ConclusionsROS, probably derived from NADPH oxidase and mitochondria, partially regulate α1-adrenoceptor-activated smooth muscle contraction by altering myosin phosphatase-mediated MLC20 phosphorylation through both RhoA/Rho kinase- and CPI-17-dependent pathways.

Propagation Mechanisms of Calcium Waves Arising During Arterial Vasomotion

Vasomotion consists in cyclic arterial diameter variations induced by synchronous contractions and relaxations of smooth muscle cells (SMCs) present in the arterial wall. These contractions have been shown to be due to an increase in the intracellular cytosolic calcium concentration. However, the arteries do not contract simultaneously on macroscopic distances and a propagation of the diameter variations can be observed. Our aim was to investigate this propagation. We stimulated endothelium denuded rat mesenteric arterial strips with the vasoconstrictor, phenylephrine (PE) to obtain vasomotion and observed that the contraction waves are linked to intercellular calcium waves through the SMCs. A velocity of about 100 μm/s was measured for the two kinds of waves which could propagate either from the distal to the proximal side of the artery or in the opposite direction. To investigate the calcium wave propagation mechanisms, we used a method allowing a PE stimulation of a small area of the strip. No calcium propagation could be induced by this local stimulation when the strip was in its resting state. However, if a low PE concentration was added to the whole strip, local PE stimulations induced calcium waves spreading over finite distances. The calcium wave velocity induced by local stimulation was identical to the velocity observed during vasomotion. This suggests that the propagation mechanisms are similar in the two cases. Using inhibitors of gap junctions and of voltage operated calcium channels, we showed that the locally induced calcium propagation likely depends on the propagation of the SMCs depolarization. Finally, from the experimental data gathered, it is possible to propose a model of the mechanisms underlying the propagation.

Mechanism Underlying Endothelium-Dependent Relaxation by 2-Methylthio-ADP in Monkey Cerebral Artery

We recently reported endothelium-dependent relaxation caused by nucleotides in the non-human primate cerebral artery. Here, we investigated the endothelium-dependent, nitric oxide- and prostanoid-independent relaxation induced by 2-methylthio-ADP (2MeSADP) in monkey cerebral artery. Mechanical responses of isolated monkey cerebral arteries to the agents were isometrically recorded. In endothelium-intact arterial strips treated with indomethacin plus NG-nitro-l-arginine and partially contracted with prostaglandin F2α, 2MeSADP (1 nM – 10 μM) induced concentration-dependent relaxation that was abolished by removal of endothelium but was not influenced by either carboxy PTIO or 18α-glycyrrhetinic acid. The 2MeSADP-induced relaxation was inhibited by MRS2179 and U73122. The relaxation was markedly suppressed by exposure of the strips to high K+ media, but was not affected by glibenclamide. Combination of charybdotoxin plus apamin markedly suppressed the relaxation, whereas iberiotoxin partially attenuated it. Relaxation induced by 2MeSADP was inhibited by arachidonyl trifluoromethyl ketone, ketoconazole, and 14,15-epoxyeicosa-5(Z)-enoic acid. The inhibitors that affected the 2MeSADP-induced relaxation did not influence relaxation caused by sodium nitroprusside or forskolin. These findings indicate that 2MeSADP elicits ‘endothelium-derived hyperpolarizing factor (EDHF)-type’ relaxation via stimulation of endothelial P2Y1 receptors in monkey cerebral artery. Furthermore, phospholipase A2, cytochrome P450–derived epoxyeicosatrienoic acids and Ca2+-activated K+ channels appear to be involved in the relaxation.

Differential sensitivities of pulmonary and coronary arteries to hemoglobin-based oxygen carriers and nitrovasodilators: Study in a bovine ex vivo model of vascular strips

Vasoconstriction is a major adverse effect of first and second generation hemoglobin-based oxygen carriers (HBOCs) that hinders their development as blood substitute. However, intravenous infusion of HBOC-201 (second generation) to patients induces significant pulmonary hypertension without significant coronary vasoconstriction. We compared contractile responses of isolated bovine pulmonary and coronary arterial strips to HBOC-201 and HBOC-205LL.LT.MW600 (third generation), polymerized bovine hemoglobins of different molecular weight, and their attenuation by nitroglycerin, sodium nitroprusside (SNP), and sodium nitrite. Pulmonary arteries developed negligible basal tone, but exhibited HBOC-dependent amplification of phenylephrine-induced contractions. In contrast, coronary arteries developed significant basal tone, and exhibited HBOC-dependent constant force increment to serotonin-induced contractions. Therefore, relative to basal tone, HBOC-induced contractions were greater in pulmonary than coronary arteries. Furthermore, HBOC-205LL.LT.MW600 appeared to be less vasoactive than HBOC-201. Unexpectedly, pulmonary and coronary arteries exhibited differential sensitivities to nitrovasodilators in parallel with their differential sensitivities to HBOC. However, SNP and sodium nitrite induced significant methemoglobin formation from HBOC, whereas nitroglycerin did not. These results suggest that phenotypic differences between pulmonary and coronary vascular smooth muscle cells could explain the differential hypertensive effects of HBOC on pulmonary and coronary circulation in patients. Among the three nitrovasodilators investigated, nitroglycerin appears to be the most promising candidate for attenuating HBOC-induced pulmonary hypertension in older HBOCs.

Intercellular calcium waves are associated with the propagation of vasomotion along arterial strips

Vasomotion consists of cyclic arterial diameter variations induced by synchronous contractions and relaxations of smooth muscle cells. However, the arteries do not contract simultaneously on macroscopic distances, and a propagation of the contraction can be observed. In the present study, our aim was to investigate this propagation. We stimulated endothelium-denuded rat mesenteric arterial strips with phenylephrine (PE) to obtain vasomotion and observed that the contraction waves are linked to intercellular calcium waves. A velocity of approximately 100 microm/s was measured for the two kinds of waves. To investigate the calcium wave propagation mechanisms, we used a method allowing a PE stimulation of a small area of the strip. No calcium propagation could be induced by this local stimulation when the strip was in its resting state. However, if a low PE concentration was added on the whole strip, local PE stimulations induced calcium waves, spreading over finite distances. The calcium wave velocity induced by local stimulation was identical to the velocity observed during vasomotion. This suggests that the propagation mechanisms are similar in the two cases. Using inhibitors of gap junctions and of voltage-operated calcium channels, we showed that the locally induced calcium propagation likely depends on the propagation of the smooth muscle cell depolarization. Finally, we proposed a model of the propagation mechanisms underlying these intercellular calcium waves.

Direct vasodilative effect of FK506 on porcine mesenteric artery in small bowel transplantation

Background Tacrolimus (FK506) is widely used as an immunosuppressive drug in small bowel transplantation. However, its precise effects on the vascular tone of the transplanted organ have not been studied. This study aimed to clarify the effects of FK506 on the porcine mesenteric artery. Methods The effects of FK506 on the changes in cytosolic Ca 2+ concentration ([Ca 2+]i) and force using fura-2 fluorometry were investigated in mesenteric arterial strips of the porcine small intestine. The effects of FK506 on the activity of voltage-dependent Ca 2+ channels and receptor-operated Ca 2+ channels using high K + (118 mmol/L K +) depolarization and thromboxane A 2 analog (U46619) stimulation were also examined. Results FK506 inhibited the force development induced by 118 mmol/L K + depolarization and 1 μmol/L U46619 stimulation in a concentration-dependent manner. The extent of inhibition of this contraction was greater than that of the K +-induced contraction, and its inhibitory potency was about 10-fold. FK506 (10 μmol/L) inhibited the increases in [Ca 2+]i (24.9% ± 7.4%) and the force development (52.0% ± 5.6%) induced by 1 μmol/L U46619, respectively. Conclusions FK506 induces arterial relaxation by decreasing [Ca 2+]i. Pretreatment of a graft with FK506 may reduce the risk of vasospasm, ischemia-reperfusion injury, and thrombosis in small bowel transplantation.

Impairment of α1-adrenoceptor-mediated contractile activity in caudal arterial smooth muscle from Type 2 diabetic Goto-Kakizaki rats

1. In the present study, we compared the responsiveness of de-endothelialized caudal artery smooth muscle strips, isolated from Type 2 diabetic Goto-Kakizaki (GK) and normal Wistar rats, to alpha(1)-adrenoceptor stimulation (cirazoline) and membrane depolarization (K(+)). 2. The contractile and myosin 20 kDa light chain (LC(20)) phosphorylation responses to 0.3 micromol/L cirazoline of caudal artery strips isolated from 12-week-old GK rats were significantly reduced compared with those of age-matched Wistar rats, whereas the contractile and LC(20) phosphorylation responses to 60 mmol/L K(+) were unaltered. 3. Stimulation of fura 2-AM-loaded strips from GK rats with 0.3 micromol/L cirazoline induced a significantly smaller rise in [Ca(2+)](i) (by approximately 20%) compared with that in strips from Wistar rats, whereas comparable Ca(2+) transients were evoked by K(+) in both. 4. Using quantitative polymerase chain reaction, no significant differences were detected in the mRNA expression of alpha(1A)-, alpha(1B)- and alpha(1D)-adrenoceptor subtypes between GK and Wistar rats. 5. Cirazoline (1 micromol/L)- and caffeine (20 mmol/L)-induced contractions in the absence of extracellular Ca(2+) were unaltered in GK rats, suggesting that the release of Ca(2+) from the sarcoplasmic reticulum in response to cirazoline does not differ between GK and Wistar rats. 6. The results of the present study suggest that Ca(2+) entry from the extracellular space via alpha(1)-adrenoceptor-activated, Ca(2+)-permeable channels, but not via membrane depolarization and voltage-gated L-type Ca(2+) channels, is impaired in caudal artery smooth muscle of GK rats.

How We Learned to Say NO

What seest thou else In the dark backward and abysm of time — —William Shakespeare First, there was Robert Furchgott.1 He simply and brilliantly demonstrated that endothelial cells play a pivotal role in relaxations evoked by acetylcholine in isolated arteries, and do so by activating muscarinic receptors of these cells. Actually, the quest for the understanding of the mechanism(s) underlying the vasodilator effect of acetylcholine in vivo (in contrast with the vasoconstrictor effect that the cholinergic transmitter almost always had in vitro) had started many years before that and led to the earlier interpretation that this could be explained best by a prejunctional (presynaptic) muscarinic effect resulting in the local inhibition of adrenergic neurotransmission in the blood vessel wall.2 To be honest, I am still convinced that if acetylcholine released from cholinergic nerves (the most likely, if not the only, source of acetylcholine in our body) contributes to the control of vasomotor tone, it does so by inhibiting the release of norepinephrine in the adventitia rather than by diffusing through the media to the endothelial cells. When asked the role is of muscarinic receptors on endothelial cells, I usually respond by saying that they have been placed there to make sure that Robert Furchgott, who already had contributed immensely to pharmacology before discovering endothelium-dependent relaxations, would make the trip to Stockholm! Yet his simple pharmacological experiments had opened a totally new avenue not only in vascular pharmacology and physiology but in science in general as they set the stage for the discovery of the role of nitric oxide (NO) in biology. In his seminal paper, Robert Furchgott elegantly demonstrated (using what he called “sandwich” preparations: a layering of strips of arteries with and without endothelium whereby the contractile responses are measured only in the strip without endothelium) that …

N-Methyl-D-Aspartate (NMDA) Antagonists—S(+)-ketamine, Dextrorphan, and Dextromethorphan—Act as Calcium Antagonists on Bovine Cerebral Arteries

Ketamine, an intravenous anesthetic and a major drug of abuse, is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. Ketamine's enantiomer, S(+)-ketamine, acts stereoselectively on neuronal NMDA receptors. The purpose of this in vitro study was to compare the direct effects of S(+)-ketamine, 2 other noncompetitive NMDA receptor antagonists (dextrorphan and dextromethorphan), and the calcium entry blocker nimodipine on the cerebral vasculature, using bovine middle cerebral arteries as an experimental model. Arterial rings were mounted in isolated tissue chambers equipped with isometric tension transducers to obtain pharmacologic dose-response curves. In the absence of exogenous vasoconstrictors, the NMDA antagonists or nimodipine had negligible effects on cerebral arterial tone. When rings were preconstricted with either potassium or the stable thromboxane A2 mimetic U46619, the NMDA antagonists and nimodipine each produced dose-dependent relaxation. Prior endothelial stripping had no effect on subsequent drug-induced relaxation of K+-constricted rings. In Ca2+-deficient media containing either potassium or U46619, the NMDA antagonists and nimodipine each produced competitive inhibition of subsequent Cainduced constriction. In additional experiments, arterial strips were mounted in isolated tissue chambers to directly measure calcium uptake, using 45calcium (45Ca) as a radioactive tracer. The NMDA antagonists and nimodipine each blocked potassium-stimulated or U46619-stimulated Ca2+ uptake into arterial strips. These results indicate that S(+)-ketamine, dextrorphan, and dextromethorphan, like nimodipine, directly dilate cerebral arteries by acting as calcium antagonists; they all inhibit 45Ca uptake through both potential-operated (potassium) and receptor-operated (U46619) channels in cerebrovascular smooth muscle.

Vascular smooth muscle dysfunction induced by monomethylarsonous acid (MMA III): A contributing factor to arsenic-associated cardiovascular diseases

While arsenic in drinking water is known to cause various cardiovascular diseases in human, exact mechanism still remains elusive. Recently, trivalent-methylated arsenicals, the metabolites of inorganic arsenic, were shown to have higher cytotoxic potential than inorganic arsenic. To study the role of these metabolites in arsenic-induced cardiovascular diseases, we investigated the effect of monomethylarsonous acid (MMA III), a major trivalent-methylated arsenical, on vasomotor tone of blood vessels. In isolated rat thoracic aorta and small mesenteric arteries, MMA III irreversibly suppressed normal vasoconstriction induced by three distinct agonists of phenylephrine (PE), serotonin and endothelin-1. Inhibition of vasoconstriction was retained in aortic rings without endothelium, suggesting that MMA III directly impaired the contractile function of vascular smooth muscle. The effect of MMA III was mediated by inhibition of PE-induced Ca 2+ increase as found in confocal microscopy and fluorimeter in-lined organ chamber technique. The attenuation of Ca 2+ increase was from concomitant inhibition of release from intracellular store and extracellular Ca 2+ influx via L-type Ca 2+ channel, which was blocked by MMA III as shown in voltage-clamp assay in Xenopus oocytes. MMA III did not affect downstream process of Ca 2+, as shown in permeabilized arterial strips. In in vivo rat model, MMA III attenuated PE-induced blood pressure increase indeed, supporting the clinical relevance of these in vitro findings. In conclusion, MMA III-induced smooth muscle dysfunction through disturbance of Ca 2+ regulation, which results in impaired vasoconstriction and aberrant blood pressure change. This study will provide a new insight into the role of trivalent-methylated arsenicals in arsenic-associated cardiovascular diseases.

The existence of a local 5-hydroxytryptaminergic system in peripheral arteries.

5-HT is a vasoconstrictor exhibiting enhanced effects in systemic arteries from subjects with cardiovascular disease. The effect of endogenous 5-HT on arteries is controversial, because the concentration of free circulating 5-HT is low and a 5-hydroxytryptaminergic system has not been identified in peripheral arteries. We hypothesized that a local 5-hydroxytryptaminergic system (including 5-HT synthesis, metabolism, uptake and release) with physiological function exists in peripheral arteries. The presence of key components of a 5-hydroxytryptaminergic system in rat aorta and superior mesenteric artery was examined using western blot analyses, immunohistochemistry and immunocytochemistry. The function of the rate-limiting enzyme in 5-HT biosynthesis, tryptophan hydroxylase (TPH), and 5-HT transporter was tested by measuring enzyme activity and 5-HT uptake, respectively. Isometric contraction of arterial strips was used to demonstrate the function of released endogenous 5-HT in arterial tissues. mRNA for TPH-1 was present in arteries, with low levels of TPH protein and TPH activity. Expression and function of MAO A (5-HT metabolizing enzyme) was supported by immunohistochemistry, western analyses and the elevation of concentrations of 5-hydroxyindoleacetic acid (5-HT metabolite) after exposure to exogenous 5-HT. The 5-HT transporter was localized to the plasma membrane of freshly isolated aortic smooth muscle cells. Peripheral arteries actively took up 5-HT in a time-dependent and 5-HT transporter-dependent manner. The 5-HT transporter substrate, (+)-fenfluramine, released endogenous 5-HT from peripheral arteries, which potentiated noradrenaline-induced arterial contraction. This study revealed the existence of a local 5-hydroxytryptaminergic system in peripheral arteries.

Sivelestat Relaxes Porcine Coronary Artery via Inhibition of Ca2+ Sensitization Induced by a Receptor Agonist

Sivelestat sodium hydrate (sivelestat) is a novel synthetic drug and specific inhibitor of neutrophil elastase that has been approved in Japan as a treatment for acute lung injury associated with systemic inflammatory response syndrome. There are no reports on the effects of sivelestat on the contractile regulation of vascular smooth muscle. The purpose of the present study was to assess the effects of sivelestat on porcine coronary artery. Sivelestat induced concentration-dependent (3 x 10 to 3 x 10 M) vasorelaxation in U46619 (100 nM)-precontracted porcine coronary artery with or without endothelium. Simultaneous measurements of tension and the cytosolic Ca concentration ([Ca]i) revealed that sivelestat shifted the [Ca]i-tension curve to the right and downward during stimulation with 118 mM K and 100 nM U46619. In beta-escin-permeabilized arterial strips, sivelestat abolished GTP plus U46619-induced contractions at constant [Ca]i, whereas it had no effect on Ca-induced contractions. Thus, sivelestat relaxes porcine coronary artery smooth muscle via the selective inhibition of Ca sensitization induced by a receptor agonist, without affecting Ca-induced contraction.

Does the Endothelium Abolish or Promote Arterial Vasomotion in Rat Mesenteric Arteries? Explanations for the Seemingly Contradictory Effects

Background and Aims: Vasomotion consists in cyclic oscillations of the arterial diameter induced by the synchronized activity of the smooth muscle cells. So far, contradictory results have emerged in the literature about the role of the endothelium in the onset and maintenance of vasomotion. Here our aim is to understand how the endothelium may either abolish or promote vasomotion. Methods and Results: We investigate rat mesenteric arterial strips stimulated with phenylephrine (PE). Our results show that the endothelium is not necessary for vasomotion. However, when the endothelium is removed, the PE concentration needed to induce vasomotion is lower and the rhythmic contractions occur for a narrower range of PE concentrations. We demonstrate that endothelium-derived relaxing products may either induce or abolish vasomotion. On the one hand, when the strip is tonically contracted in a nonoscillating state, an endothelium-derived relaxation may induce vasomotion. On the other hand, if the strip displays vasomotion with a medium mean contraction, a relaxation may induce a transition to a nonoscillating state with a small contraction. Conclusion: Our findings clarify the role of the endothelium on vasomotion and reconcile the seemingly contradictory observations reported in the literature.

Effect of hyperthermia on the function of thyroid gland

Hyperthermia may be a consequence of environmental conditions, bacterial or viral infections and/or thyroid storm. This study investigates the acute effect of body temperature elevation on thyroid function and on its scintigraphy studies. Thyroid scintigraphy was performed on New Zealand White rabbits weighing approximately 3-3.5 kg. Each rabbit was injected with 115 MBq (3.1 mCi) technetium-99 m pertechnetate ((99m)Tc pertechnetate). Studies were performed using Gamma camera equipped with a low energy, high resolution, pinhole collimator interfaced with a computer. Static images were acquired 20 min after administration of the radiotracer. Two days later the same protocol was repeated for the same rabbit after increasing the body temperature by 2 degrees C. The experiment was repeated again after a 2-day interval at 3 degrees C, and then after another 2-day interval at 4 degrees C. Plasma free thyroxine (FT(4)), free triiodothyronine (FT(3)) and thyroid stimulating hormone (TSH) were measured at control and at different hyperthermic temperatures (+2, 3, 4 degrees C). We recorded isometric tension of rabbit thyroid artery strips in organ baths during stepwise temperature elevation. During hyperthermia the decrease in thyroid function and thyroid scintigraphy studies was proportional to body temperature elevation. The recording of isometric tension in rabbit thyroid artery strips in organ baths showed vasoconstriction during hyperthermia which is proportional to the heating temperature. Plasma FT(4) and FT(3) level were decreased while TSH levels were not affected by acute fever. Our results indicate that hyperthermia causes a transient decrease in thyroid gland function and scintigraphic patterns on radionuclide studies. Thus, body temperatures must be measured before radionuclide studies in order to ensure that interpretation of data is not influenced by hyperthermia.

An estrogen‐induced decrease in voltage‐gated calcium channel expression attenuates coronary artery contractility

Estrogen (E2) can pharmacologically inhibit Ca2+ influx into vascular smooth muscle cells. However, little is known about the ability of E2 to alter vascular Ca2+ channel expression. The goal of our study was to determine if a physiological E2 concentration can decrease the expression of voltage‐gated calcium channels (VGCC) in small coronary arteries. Right coronary arteries were obtained from hearts of reproductively cycling sows. The distal end of the artery was cut into 4 mm rings or longitudinal strips and incubated for 24 hours in E2 (1 nM) or its ethanol solvent. Western blots using protein isolated from the arterial strips demonstrated a decreased expression of the pore‐forming α1C subunit of the VGCC in E2‐treated arteries. In parallel studies, isometric tension recording revealed that E2‐treated arterial rings contracted significantly less to 30 mM KCl. However, E2 and ethanol‐treated rings preconstricted with 60 mM KCl showed similar relaxation responses to E2 (1 nM to 1 μM). These findings suggest that physiological concentrations of E2 down‐regulate VGCC, thereby providing a potentially novel mechanism for limiting coronary vasoconstriction. In the same arteries, E2‐dependent relaxation is intact. By limiting the expression of VGCC, E2 may promote coronary blood flow and potentially lower the incidence of coronary events in pre‐menopausal women. Support: NCRR of the NIH, Grant #P20 RR‐16460

Characterization of mechanical behavior of a porcine pulmonary artery strip using a randomized uniaxial stretch and stretch-rate protocol

BackgroundMuch of the experimental work in soft tissue mechanics has been focused on fitting approximate relations for specific tissue types from aggregate data on multiple samples of the tissue. Such relations are needed for modeling applications and have reasonable predictability – especially given the natural variance in specimens. There is, however, much theoretical and experimental work to be done in determining constitutive behaviors for particular specimens and tissues. In so doing, it may be possible to exploit the natural variation in tissue ultrastructure – so to relate ultrastructure composition to tissue behavior. Thus, this study focuses on an experimental method for determining constitutive behaviors and illustrates the method with analysis of a porcine pulmonary artery strip. The method characterizes the elastic part of the response (implicitly in terms of stretch) and the inelastic part in terms of short term stretch history (i.e., stretch-rate) Ht2, longer term stretch history Ht1, and time since the start of testing T.MethodsA uniaxial testing protocol with a random stretch and random stretch-rate was developed. The average stress at a particular stretch was chosen as the hyperelastic stress response, and deviation from the mean at this particular stretch is chosen as the inelastic deviation. Multivariable Linear Regression Analysis (MLRA) was utilized to verify if Ht2, Ht1, and T are important factors for characterizing the inelastic deviation. For acquiring Ht2 and Ht1, an integral function type of stretch history was employed with time constants chosen from the relaxation spectrum of an identical size strip from the same tissue with the same orientation. Finally, statistical models that characterize the inelasticity were developed at various, nominal values of stretch, and their predictive capability was examined.ResultsInelastic deviation from hyperelasticity was high (31%) for low stretch and declined significantly with increasing stretch to a nadir of 3.6% for a stretch of 1.7. The inelastic deviation then increased with increasing stretch at the same point in the stress-strain curve where stiffness began to increase strikingly. MLRA showed that T is a major inelastic parameter at low deformation. For moderate and high deformations, Ht2 and Ht1 were dominant.DiscussionA randomized uniaxial testing protocol was applied to a strip of porcine pulmonary artery to characterize the elasticity and inelasticity of a soft tissue. We were successful in determining the elastic response and the factors that gave rise to the inelastic deviation. This investigation seeks methods to better define, phenomenologically, the elastic and inelastic behavior of soft tissues.

Influence of hyperthermia on carotid blood flow using 99mTc-HMPAO

Hyperthermia can be the result of many causes such as environmental conditions, brain tumors and infectious diseases. Since hyperthermia is very common, its role in causing stroke through a decrease in cerebral blood flow needed further emphasis. The aim of this study was to record cerebral blood flow in vitro by using isolated rabbit carotid artery strips and in-vivo using radioactive isotope scanning during temperature elevation. The recording of isometric tension in rabbit carotid artery strips in organ baths, and the scintigraphic cerebral imaging of technetium-99m-hexamethyl-propyleneamineoxime (99mTc-HMPAO) using Gamma camera, were acquired at control and higher body temperature by 4 degrees C. Blood pressure was measured through femoral artery and cerebral blood flow was measured through carotid artery. Elevating temperature by 4 degrees C induced reproducible contraction. During hyperthermia, the carotid artery contraction leads to a decrease in cerebral blood flow although the blood pressure did not decrease. The uptake of 99mTc-HMPAO in the brain was significantly reduced. This decrease in cerebral perfusion is regionally dependent, which is more in the frontal area, the cerebral hemispheres than the cerebellum. The decrease was 36+/-3, 37+/-2, 22+/-2%, respectively. Hyperthermia causes carotid artery contraction leading to decrease in cerebral blood flow, which was confirmed by 99mTc-HMPAO images. The decrease is regionally dependent. Since the blood pressure did not decrease by heating, the reduction in cerebral perfusion is mainly due to carotid contraction. The applied neck cooling may be considered as a promising therapeutic strategy for the hyperthermic patient to avoid brain damage. This can be achieved by external application of an ice-water-perfused neck collar.

Vasorelaxing effect of the Rho-kinase inhibitor, Y-27632, in isolated canine basilar arteries

Objectives: Increased calcium sensitization mediated by Rho/Rho-kinase may be important in the pathogenesis of cerebral vasospasm. The effects of a highly selective Rho-kinase inhibitor, Y-27632, were investigated on spasmogen-induced contractions of canine basilar artery.Methods: Typical spasmogenic substances present after subarachnoid hemorrhage (SAH), including prostaglandin F2a (PGF2a), 12-deoxyphorbol 13-isobutyrate (DPB), sphingosylpho-sphorylcholine (SPC) and high K+, were used in the study. Isometric tension was recorded in canine basilar artery rings in vitro. Intracellular calcium concentration ([Ca2+]i) and contraction force were measured simultaneously in fura-2-loaded canine basilar artery strips. The myosin light chain (MLC) phosphorylation levels were measured by glycerol gel electrophoresis followed by Western blotting.Results: Isometric tension recording revealed that the Rho-kinase inhibitor, Y-27632, dose-dependently inhibited vasocontraction induced by PGF2a and SPC, but not that induced by DPB. Simultaneous recordings of [Ca2+]i and tension revealed that the vasorelaxing effect of Y-27632 was not associated with changes in [Ca2+]i, suggesting that Y-27632 may inhibit calcium sensitization. Vasocontraction induced by DPB was not inhibited by Y-27632, but was inhibited by staurosporine. Phosphorylation of MLC was increased by PGF2a and SPC, and significantly inhibited by Y-27632, whereas such phosphorylation was increased by DPB, but not significantly inhibited by Y-27632.Discussion: Several spasmogenic mediators released after SAH may cause vasospasm through Rho-kinase-mediated increase in calcium sensitization. Rho-kinase inhibitors, including Y-27632, may be effective for the prevention of cerebral vasospasm after SAH.

Synergistic effects of ethanol and hyperthermia on carotid artery vasoconstriction

Heatstroke is a serious condition and clinical studies indicate that vascular stroke increases with excessive consumption of alcohol (ethanol). It was our objective to test the influence of ethanol on cerebral perfusion at normal and higher temperatures. Recording of isometric tension in rabbit carotid artery strips in organ baths with different concentrations of ethanol at 37 degrees C and during hyperthermia (39-43 degrees C) and scintigraphic cerebral imaging of a radioactive isotope in the control situation and during hyperthermia. Stepwise heating induced reproducible reversible graded contraction, proportional to temperature. At high concentrations (toxic levels), ethanol induced an increase in tension and heating potentiated these responses. Extracellular Mg(2+) potentiated both heat-induced contraction and ethanol-induced contraction while extracellular Ca(2+) had no effect on these responses. During hyperthermia and ethanol scintigraphic isotope uptake was reduced in cortical and cerebellar regions. Carotid artery vasomotor tone is temperature dependent and heating induces vasoconstriction. Alcohol (ethanol) at 37 degrees C elicited carotid artery contraction at high concentrations (toxic levels) but at any concentration during elevated temperature (39-43 degrees C). Ethanol potentiated the effect of hyperthermia-induced vasoconstriction and reduced cerebral perfusion as shown by radionuclide imaging. The synergistic effect of ethanol and hyperthermia may induce heat stroke and brain damage.