Arteriolar Blood Research Articles

Real-time microcirculatory changes due to spreading depression under focal ischemia

Laser-scanning confocal fluorescence microscopy was used to investigate microcirculatory influences of spreading depression (SD)-like depolarizations elicited by occlusion of the rat middle cerebral artery (MCA). Six rats underwent halothane anesthesia and mechanical ventilation. A closed cranial window was implanted over their frontoparietal cortex. They were placed under a Biorad Viewscan confocal microscope and intravenously given fluorescein isothiocyanate (FITC)-Dextran and FITC-labeled erythrocytes. The capillaries were visualized down to 200 μm below the brain surface and the images were video recorded (50/s). The MCA was occluded under the microscope using an intraluminal remotely controlled method and the reperfusion was induced 2 h later. Furthermore, the brains were histologically examined 24 h later. Under ischemia, the erythrocyte velocity through the capillaries was depressed by 35% and venous blood became highly sluggish. The arteriole diameter did not change significantly, however, the direction of arteriolar blood flow was episodically and transiently reversed. During spontaneous SD-like depolarization, the arteriole diameter significantly increased (+19% vs. MCAO) while capillary erythrocyte velocity was further depressed by 15%. This decrease in velocity was more pronounced (25%) when depolarization were associated with transient reversal of arteriolar flow. Following reperfusion, microcirculatory variables rapidly returned to the baseline. All rats exhibited infarcts 24 h after the occlusion. These results indicate that SD-like depolarizations have an adverse influence on penumbral microcirculation, i.e., a reduction in capillary perfusion by erythrocytes, despite arteriolar dilatation.

Response to J. Schnermann: Adenosine mediates tubuloglomerular feedback

schnermann makes several strong points in his article “Adenosine mediates tubuloglomerular feedback responses” ([19][1]). We completely agree that the data provided by two independent laboratories demonstrating that tubuloglomerular feedback (TGF) responses to increases in distal perfusion rate

Early recovery of microvascular perfusion induced by t-PA in combination with abciximab or eptifibatide during postischemic reperfusion.

GPIIb/IIIa inhibitors abciximab and eptifibatide have been shown to inhibit platelet aggregation in ischemic heart disease. Our aim was to test the efficacy of abiciximab (Reo Pro) or eptifibatide (Integrilin) alone or in combination with plasminogen activator (t-PA) in an experimental model of ischemia reperfusion (I/R) in hamster cheek pouch microcirculation visualized by fluorescence microscopy. Hamsters were treated with saline, or abiciximab or eptifibatide or these drugs combined with t-PA infused intravenously 10 minutes before ischemia and through reperfusion. We measured the microvessel diameter changes, the arteriolar red blood cell (RBC) velocity, the increase in permeability, the perfused capillary length (PCL), and the platelet and leukocyte adhesion on microvessels. I/R elicited large increases in the platelet and leukocyte adhesion and a decrease in microvascular perfusion. These responses were significantly attenuated by abiciximab or eptifibatide (PCL:70 and 65% at 5-10 mins of reperfusion and 85 and 87% at 30 mins of reperfusion, respectively, p < 0.001) while t-PA combined with abiciximab or eptifibatide, was more effective and microvascular perfusion recovered immediately after postischemic reperfusion. Platelets are crucial in I/R injury, as shown by the treatment with abicixmab or eptifibatide, which decreased platelet aggregation in microvessels, and also decreased leukocyte adhesion in venules. Arterial vasoconstriction, decreased arterial RBC velocity and alterations in the endothelial barrier with increased permeability delayed the complete restoration of blood flow, while t-PA combined with inhibition of platelet aggregation speeded up the capillary perfusion after reperfusion.

Effects of experimental lower-limb ischaemia-reperfusion injury on the mesenteric microcirculation.

Ischaemia-reperfusion (I-R) of the leg is associated with functional and structural changes in the intestine. This study assessed whether acute hind-limb I-R in rats induced a reduction in perfusion and/or signs of an inflammatory response in the intestine. Rats were subjected to 2 h of unilateral hind-limb ischaemia followed by 2 h of reperfusion (I-R group, n = 9) or to a sham procedure (control group, n = 9). Mesenteric microvascular diameters, red blood cell velocity, blood flow and leucocyte-vessel wall interactions during reperfusion were measured using intravital microscopy. Blood pressure and heart rate decreased from 30 min of reperfusion onwards in the I-R group compared with controls. From 15 min after the start of reperfusion, mesenteric arteriolar and venular red blood cell velocity and blood flow decreased by 40-50 per cent. Microvascular diameters and leucocyte-vessel wall interactions did not change. Restoration of blood flow to an acutely ischaemic hind limb led to a significant decline in the splanchnic microcirculatory blood flow. There were, however, no signs of an early inflammatory response in the gut.

Penumbral microcirculatory changes associated with peri-infarct depolarizations in the rat.

This study was designed to investigate the influence of peri-infarct depolarization elicited by occlusion of the middle cerebral artery on the dynamics of the microcirculation. The microcirculation in the frontoparietal cortex of 9 rats was visualized in real time through a closed cranial window with the use of laser-scanning confocal fluorescence microscopy combined with intravenous fluorescein isothiocyanate (FITC)-dextran and FITC-labeled erythrocytes. The direct current potential/electrocorticogram was continuously monitored. Intraluminal focal ischemia was induced for 2 hours in 6 rats anesthetized with halothane and mechanically ventilated. Reperfusion was monitored for 1 hour. Three rats underwent sham operation. Brains were removed 24 hours after occlusion and processed for histology. In control conditions, the velocity of fluorescent erythrocytes through capillaries was 0.51+/-0.19 mm/s (mean+/-SD), and the diameter of the arterioles studied was 33+/-12 microm. Under ischemia, erythrocyte velocity through capillaries was significantly decreased to 0.33+/-0.14 mm/s, while arteriole diameter did not change significantly. During spontaneous peri-infarct depolarizations, arteriole diameter was significantly increased (119+/-23% of baseline), while capillary erythrocyte velocity was further decreased by 14+/-34%. The direction of arteriolar blood flow episodically and transiently reversed during approximately half of the peri-infarct depolarizations. The decrease in capillary erythrocyte velocity was more pronounced (23+/-37%) in these cases. After reperfusion, the microcirculatory variables rapidly returned to baseline. All rats in the ischemic group had infarcts 24 hours after occlusion. Peri-infarct depolarization has an adverse influence on penumbral microcirculation, reducing capillary perfusion by erythrocytes, despite dilatation of arterioles. These findings suggest that a steal phenomenon contributes to the deleterious effect of these depolarizations.

Cerebral blood flow in hyperammonemia: heterogeneity and starling forces in capillaries.

In the brain hyperammonemia interferes with ion homeostasis, membrane potentials, neurotransmission, and neurotransmitter recycling and reduces metabolic rates for oxygen and glucose. Because, cerebral blood flow (CBF) is closely coupled to metabolism, CBF is most often reduced in diseases associated with hyperammonemia. However, in severe cases of hyperammonemia, as in patients with acute liver failure, Reye's syndrome, and inherited metabolic disorders of the urea cycle, the normal regulation of CBF is also impaired. One of the most prominent findings is a failure of CBF autoregulation that uncouples metabolism from CBF. Clinically failure of autoregulation may imply that both cerebral hypoxia and hyperaemia may develop in the patient depending on the driving pressure of the brain, i.e., cerebral perfusion pressure. In addition a gradual "nonreactive" dilatation of the cerebral arterioles often aggravates the mismatch between nutritive demands and delivery in the brain. The reason for arteriolar dilation and homogeneous capillary blood flow is not settled but seems not to be mediated by excessive release of nitro oxide. More likely the arachidonic acid cascade with increased synthesis of prostaglandins, cytochrome P450 metabolites, and potassium channel activation are implicated in this vasodilatation. The combination of cerebral hyperaemia, increased hydrostatic capillary blood pressure, and accumulation of organic and nonorganic osmolytes within the brain during hyperammonemia clearly will favor cerebral capillary water influx. This imbalance between colloid osmotic and hydrostatic pressures in patients with severe hyperammonemia means that simple interventions based on physiological principles may help ameliorate cerebral hyperaemia and water influx. Thus, it is suggested that not only monitoring of intracranial pressure (ICP) and cerebral perfusion are pivotal to help prevent high ICP but also basic clinical information, such as Tp, PaCO2, and plasma sodium/glucose concentrations, should be closely followed and corrected.

Cyclic variation of cerebral pial arteriolar diameter synchronized with positive-pressure inhalation.

Laboratory observations have noted that during normocapnia and intact vascular tone, changes in the intracranial pressure (ICP) and arterial blood pressure (ABP) recordings are not similar. The purpose of the present study was to determine whether: 1) the diameter of cerebral pial arterioles synchronously increases during positive pressure inhalation and decreases during the expiration phase of ventilation; and 2) the variation in arteriolar diameter is greater when vascular tone is intact than when arterioles are maximally dilated. Severe hypercapnia was induced by prolonged ventilation with gas mixture of 20% O2, 10% CO2, and 70% N2 in 8 piglets. S-VHS recordings of 3600X magnification of nine pial arterioles were obtained during conditions of normal vascular tone and severe hypercapnia and digitally analyzed by an image-averaging method. Variation of the amplitude of arteriolar diameter over the ventilation cycle was computed and found to synchronously increase during positive pressure inhalation and to decrease to a steady state baseline during passive expiration. Mean amplitude of variation in diameter (+/- S.D.) during normal tone and hypercapnia was computed as 1.63 (+/- 0.693) microns and 1.012 (+/- 0.869) microns respectively and found to be significantly greater during the condition of normal vascular tone than during hypercapnia (p < .006). These results suggest that a cyclic variation of arteriolar blood volume is one causal factor related to the low frequency variation of the baseline of ICP associated with positive pressure ventilation.

Electroacupuncture at Hoku elicits dual effect on autonomic nervous system in anesthetized rats.

To address the effect of electroacupuncture (Ea) on the autonomic nerve activity, responses of arteriole blood pressure (BP), intragastric pressure (IGP) and parasympathetic vagal nerve activity (VNA) to Ea were investigated in alpha-chloralose anesthetized rats. The acupoint: Hoku (Li-4) was tested with two different stimulation frequencies (2 and 20 Hz). Decrease in VNA and basal IGP associated with elevation of BP were elicited during Ea at Hoku with stimulation intensity of 20 times of motor threshold. The pattern of response induced by the low frequency Ea (LFEa) was different from that by the high frequency Ea (HFEa), i.e. a tonic effect was elicited by the LFEa, while a phasic one was induced by the HFEa. All the results in this study implicated that: (1) Ea at Hoku may activate the sympathetic and simultaneously inhibit the gastric parasympathetic nerve; (2) Ea at Hoku with different stimulation frequencies may elicit distinct mechanism to induce therapeutic effect; (3) Ea at Hoku may ameliorate the hyperactive stomach in clinical therapy.

Influence of cell-free Hb on local tissue perfusion and oxygenation in acute anemia after isovolemic hemodilution.

Oxygen-carrying solutions are intended to eliminate the blood transfusion trigger. Their ability to maintain microvascular perfusion and to deliver oxygen to tissue when they replace the RBCs as oxygen carriers has not been directly measured. Microvascular response to exchange transfusion with a polymerized bovine cell-free Hb (PBH) solution after acute isovolemic hemodilution with a plasma expander was investigated by using the hamster window model. In vivo functional capillary density (FCD), blood flow, and high-resolution oxygen distribution in microvascular networks were measured by noninvasive methods. Exchange transfusion of PBH solution after a 60-percent isovolemic hemodilution with dextran 70 (MW, 70 kDa) resulted in a Hct of 11 percent and a Hb content of 6.7 g per dL. FCD was 0.37 of baseline. Interstitial pO2 was reduced from 21.0 mm Hg to 0.3 mmHg. Arteriolar and venular blood flows were ratios of 0.75 and 0.76 relative to baseline. In a previous study, tissue pO2 after hemodilution to 5.6 g of Hb per dL with dextran 70 was 23.0 mmHg. Hypervolemic injection of PBH solution increased blood pressure and caused vasoconstriction. Using PBH solution to replace RBC oxygen-carrying capacity during low Hb content conditions (<50%) causes abnormally low tissue oxygenation and FCD, while the same level of hemodilution with dextran maintains normal microvascular conditions.

Melatonin and N-acetylserotonin inhibit leukocyte rolling and adhesion to rat microcirculation

The hormone melatonin produced by the pineal gland during the daily dark phase regulates a variety of biological processes in mammals. The aim of this study was to determine the effect of melatonin and its precursor N-acetylserotonin on the microcirculation during acute inflammation. Arteriolar diameter, blood flow rate, leukocyte rolling and adhesion were measured in the rat microcirculation in situ by intravital microscopy. Melatonin alone or together with noradrenaline did not affect the arteriolar diameter or blood flow rate. Melatonin inhibited both leukocyte rolling and leukotriene B 4 induced adhesion while its precursor N-acetylserotonin inhibits only leukocyte adhesion. The rank order of potency of agonists and antagonist receptor selective ligands suggested that the activation of MT 2 and MT 3 melatonin binding sites receptors modulate leukocyte rolling and adhesion, respectively. The effect of melatonin and N-acetylserotonin herein described were observed with concentrations in the range of the nocturnal surge, providing the first evidence for a possible physiological role of these hormones in acute inflammation.

Canines as Sentinel Species for Assessing Chronic Exposures to Air Pollutants: Part 2. Cardiac Pathology

The principal objective of this study is to evaluate by light and electron microscopy (LM, EM) the heart tissues in stray southwest and northeast metropolitan Mexico City (SWMMC, NEMMC) dogs and compare their findings to those from 3 less polluted cities (Cuernavaca, Tlaxcala, and Tuxpam). Clinically healthy mongrel dogs, including 109 from highly polluted SWMMC and NEMMC, and 43 dogs from less polluted cities were studied. Dogs residing in cities with lower levels of pollutants showed little or no cardiac abnormalities. Mexico City and Cuernavaca dogs exhibited LM myocardial alterations including apoptotic myocytes, endothelial and immune effector cells, degranulated mast cells associated with scattered foci of mononuclear cells in left and right ventricles and interventricular septum, and clusters of adipocytes interspersed with mononuclear cells. Vascular changes included scattered polymorphonuclear leukocytes (PMN) margination and microthrombi in capillaries, and small venous and arteriolar blood vessels. Small veins exhibited smooth muscle cell hyperplasia, and arteriolar blood vessels showed deposition of particulate matter (PM) in the media and adventitia. Unmyelinated nerve fibers showed endoneural and epineural degranulated mast cells. EM examination of myocardial mast cells showed distended and abundant rough endoplasmic reticulum with few secretory granules. Myocardial capillaries exhibited fibrin deposition and their endothelial cells displayed increased luminal and abluminal pinocytic activity and the formation of anemone-like protrusions of the endothelium into the lumen. A close association between myocardial findings, lung epithelial and endothelial pathology, and chronic inflammatory lung changes was noted. The myocardial changes described in dogs exposed to ambient air pollutants may form the basis for developing hypothesis-driven mechanistic studies that might explain the epidemiological data of increased cardiovascular morbidity and mortality in people exposed to air pollutants.

Effects of the interaction between carbogen and nicotinamide on R3230 Ac tumor blood flow in Fischer 344 rats.

Braun, R. D., Lanzen, J. L., Turnage, J. A., Rosner, G. and Dewhirst, M. W. Effects of the Interaction between Carbogen and Nicotinamide on R3230 Ac Tumor Blood Flow in Fischer 344 Rats. Radiat. Res. 155, 724-733 (2001). The purpose of this study was to determine whether there are interactions between carbogen breathing and various doses of nicotinamide at the level of the tumor arteriole that might contribute to the improvement in tumor blood flow and pO(2) that is often seen with this combination treatment. R3230 adenocarcinomas were implanted and grown to 4-5 mm in dorsal skin flap window chambers in F344 rats. Saline or 65, 200 or 500 mg/kg nicotinamide was injected i.p. while the rat breathed air through a face mask. After 20 min, either the breathing gas was switched to carbogen for 60 min or the animal remained on air. Measured end points included diameter of tumor arterioles, tumor perfusion, mean arterial blood pressure, and heart rate. None of the measured parameters were affected by injection of saline or nicotinamide, except at the highest nicotinamide dose (500 mg/kg). Mean arterial blood pressure showed a median decrease of 25% when 500 mg/kg nicotinamide was given. Diameter of tumor arterioles decreased significantly from 5-15 min after 500 mg/kg nicotinamide was given but was back to baseline by 20 min. Blood flow decreased significantly 5-20 min after administration of 500 mg/kg nicotinamide compared to the baseline prior to injection. Carbogen breathing resulted in a small increase in mean arterial blood pressure in all groups. There was a transient decrease in the diameter of tumor arterioles and blood flow during the first 5 min of carbogen breathing that was statistically significant in several groups. In the group injected with 500 mg/kg nicotinamide, the diameter of tumor arterioles increased by about 10% during the first 25 min of carbogen breathing, and blood flow increased by a median of 75% over the level prior to carbogen breathing up to 40 min after carbogen breathing. The increase in flow in this group was most likely caused by the concomitant arteriolar vasodilation. Thus there was direct evidence for an interaction between carbogen breathing and nicotinamide, but only at the dose of 500 mg/kg nicotinamide. Since this dose yields plasma levels of nicotinamide that are higher than can be tolerated clinically, it is uncertain whether these changes in arteriolar diameter and blood flow would occur in human tumors.

Somatosensory nociceptive mechanical stimulation modulates systemic and mesenteric microvascular hemodynamics in anesthetized rats

The effects of somatosensory nociceptive pinch stimulation of the hindpaw on mesenteric microvascular hemodynamics and systemic circulatory parameters were investigated in anesthetized rats using an intravital microscope–television system. Blood flow velocity in the terminal (18–40 μm in diameter) or precapillary (10–20 μm in diameter) arterioles of the mesentery was monitored by the dual sensor method developed by the authors. In the proximal terminal arterioles, blood flow velocity decreased substantially along with arteriolar constriction induced by pinching of the hindpaw for 30 s. In the distal terminal arterioles and precapillary arterioles, blood flow velocity increased after pinching. In the proximal terminal arterioles, the decrease of velocity in response to reflex vasoconstriction was abolished by intravenous injection of an α-blocker (phentolamine, 10 mg/kg). The increase in mesenteric precapillary arteriolar blood flow velocity (43±9%, p<0.01) associated with the increase in mean arterial pressure (MAP) (22±1%, p<0.01) was observed within a few seconds after the onset of the stimulation, and then the response in blood flow velocity returned to the baseline ahead of MAP response recovery after the end of the stimulus. These responses were diminished by α-adrenergic receptor blockade. The heart rate (HR) increase (4±1%, p<0.01) induced by pinching was abolished by β-adrenergic receptor blockade (propranolol, 3 mg/kg, i.v.). There was a strong correlation between the increase in MAP and the decrease in renal blood flow measured by laser Doppler flowmeter ( r=0.87–0.98). Pinch stimulation of the rat hindpaw evoked changes in mesenteric arteriolar blood flow velocity that were mediated via the somato-sympathetic reflex vasoconstriction and the pressor response.

The juxtaglomerular apparatus in young type-1 diabetic patients with microalbuminuria. Effect of antihypertensive treatment.

Our goal was to investigate the effect of antihypertensive drugs on the juxtaglomerular apparatus (JGA) in young type-1 diabetic patients with microalbuminuria. Twelve patients were allocated to treatment with either an angiotensin-converting enzyme inhibitor (group 1, six subjects) or a beta-receptor blocker (group 2, six subjects). A comparable group of nine patients without antihypertensive treatment provided reference values (group 3, nine subjects). Renal biopsies were taken at baseline and after a median of 40 months (groups 1 and 2) and 30 months (group 3). Using light microscopy with 1microm serial sections of the plastic-embedded biopsies, volumes of the JGA and glomerulus and areas of the macula densa and lumina of the afferent and efferent arterioles were obtained. A significant decrease of the volume of the JGA (P=0.026) and of the volume of the JGA relative to that of its corresponding glomerulus (P=0.0005) was noted in the reference group only. Negative correlations existed between the increase in the luminal area of the afferent arteriole and mean diastolic blood pressure in the study period in group 1 (P=0.024) and group 2 (P=0.032). Our results showed that a decrease in the size of the JGA is offset by antihypertensives. The negative correlation between the change in the luminal area of the afferent arteriole and mean diastolic blood pressure in groups 1 and 2 suggest that renal protection in antihypertensive treatment may be through a better constriction of the afferent arteriole protecting the glomerulus from systemic blood pressure.

Dynamic interaction between myogenic and TGF mechanisms in afferent arteriolar blood flow autoregulation.

The dynamic activity of afferent arteriolar diameter (AAD) and blood flow (AABF) responses to a rapid step increase in renal arterial pressure (100-148 mmHg) was examined in the kidneys of normal Sprague-Dawley rats (n = 11) before [tubuloglomerular feedback (TGF)-intact] and after interruption of distal tubular flow (TGF-independent). Utilizing the in vitro blood-perfused juxtamedullary nephron preparation, fluctuations in AAD and erythrocyte velocity were sampled by using analog-to-digital computerized conversion, video microscopy, image shearing, and fast-frame, slow-frame techniques. These assessments enabled dynamic characterization of the autonomous actions and collective interactions between the myogenic and TGF mechanisms at the level of the afferent arteriole. The TGF-intact and TGF-independent systems exhibited common initial (0-24 vs. 0-13 s, respectively) response slope kinetics (-0.53 vs. -0.47% DeltaAAD/s; respectively) yet different maximum vasoconstrictive magnitude (-11.28 +/- 0.1 vs. -7. 02 +/- 0.9% DeltaAAD; P < 0.05, respectively). The initial AABF responses similarly exhibited similar kinetics but differing magnitudes. In contrast, during the sustained pressure input (13-97 s), the maximum vasoconstrictor magnitude (-7.02 +/- 0.9% DeltaAAD) and kinetics (-0.01% DeltaAAD/s) of the TGF-independent system were markedly blunted whereas the TGF-intact system exhibited continued vasoconstriction with slower kinetics (-0.20% DeltaAAD/s) until a steady-state plateau was reached (-25.9 +/- 0.4% DeltaAAD). Thus the TGF mechanism plays a role in both direct mediation of vasoconstriction and in modulation of the myogenic response.

Microvascular flow and tissue PO(2) in skeletal muscle of chronic reduced renal mass hypertensive rats.

This study determined whether arteriolar blood flow, capillary red blood cell (RBC) velocity, capillary hematocrit (Hct(cap)), and tissue PO(2) are altered in cremaster muscles of rats with chronic reduced renal mass hypertension (RRM-HT) relative to normotensive rats on high- or low-salt (NT-HS vs. NT-LS) diet. The blood flow in first- through third-order arterioles was not different between NT and HT rats, either at rest or during maximal relaxation of the vessels with 10(-4) M adenosine. Capillary RBC velocity was similar between the groups at rest but was elevated in RRM-HT and NT-HS rats during adenosine superfusion. Hct(cap) was reduced at rest in RRM-HT and NT-HS rats compared with NT-LS and was reduced in RRM-HT rats during adenosine-induced dilation. Tissue PO(2) was reduced in RRM-HT and NT-HS rats compared with NT-LS rats during control conditions and was lower in RRM-HT than in NT-LS rats during adenosine-induced dilation. These results indicate that both RRM-HT and chronic exposure of normotensive rats to a high-salt diet lead to reduced tissue oxygenation, despite the maintenance of normal arteriolar blood flow.

Thoracic epidural anesthesia increases mucosal perfusion in ileum of rats.

Previous studies reported that thoracic epidural anesthesia (TEA) protected against a decrease in gastric intramucosal pH, suggesting that TEA increased gut mucosal perfusion. The current study examines the effects of TEA on ileal mucosa using intravital microscopy in anesthetized rats. Nineteen rats were equipped with epidural catheters, with the tip placed at T7 through T9. Rats were anesthetized and mechanically ventilated. After midline abdominal incision, the ileum was prepared for intravital microscopy. Videomicroscopy on the ileal mucosa was performed before and after epidural infusion of 20 microliter of bupivacaine 0.4% (TEA group, n = 11 rats) or normal saline (control group, n = 8 rats). Microvascular blood flow in ileum mucosa was assessed offline using computerized image analysis. Control rats exhibited unchanged mean arterial pressure and microvascular perfusion. During TEA, mean arterial pressure was decreased compared with the control group (93 +/- 10 vs. 105 +/- 9 mmHg; P < 0.05). Epidural bupivacaine increased red cell velocity in terminal arterioles from 888 +/- 202 to 1,215 +/- 268 micrometer/s (control, 793 +/- 250 to 741 +/- 195 micrometer/s; P < 0.001 between groups). Because arteriolar diameter was not affected, this increase in red cell velocity may represent an increase in arteriolar blood flow. Total intercapillary area (inversely related to perfused capillary density) was unchanged, but for the TEA group the difference between total intercapillary area and the intercapillary area calculated for continuously perfused capillaries was decreased compared with the control group (16 +/- 12 vs. 40 +/- 19%; P < 0.001), indicating a decrease in intermittent (stop-and-go) blood flow in the villus microcirculation. Thoracic epidural anesthesia increased gut mucosal blood flow and reduced intermittent flow in the villus microcirculation in the presence of a decreased perfusion pressure.

Endothelin-1-mediated retinal artery vasospasm and the rabbit electroretinogram.

Electroretinogram (ERG) changes invariably accompany the selective interruption of the retinal circulation that occurs in human central retinal artery occlusion. Since arteriolar ligation or ocular hypertension in the rabbit eye is occasionally used to model human central retinal artery occlusion, we conducted the present study to determine whether selective interruption of the retinal circulation of the rabbit eye alters retinal function as measured by the ERG. The vasoconstrictor, endothelin-1, was injected into the vitreous of rabbits' eyes to induce complete vasospasm and selective interruption of the retinal circulation. This procedure was compared to vascular ligation of the ophthalmic and ciliary arteries in which both the retinal and choroidal circulations were interrupted. A total of 8 rabbits was studied. Circulation was monitored angiographically in half of the eyes, and retinal function was monitored by the ERG in the remaining eyes. Endothelin-1 obliterated retinal arteriolar blood flow without affecting choroidal blood flow for at least 1 hr. Although ERG a-wave amplitude showed a small decline over 2 hr, b-wave and oscillatory potential amplitudes (measures of inner retinal function) showed no loss over this period. In contrast, ligation of the ophthalmic and ciliary arteries produced complete obliteration of both retinal arteriolar and choroidal blood flow and complete loss of the ERG after 2 min. Endothelin-1 induces acute, selective interruption of retinal arteriolar blood flow which has no significant physiologic effect on inner retinal function of the rabbit as monitored by the ERG. The avascular rabbit retina appears to be a poor choice for modeling human retinal artery occlusion.

Protective effects of leukopenia and tissue plasminogen activator in microvascular ischemia-reperfusion injury.

Ischemia shifts the anticoaugulant/procoagulant balance of the endothelium in favor of activation of coagulation. We studied whether cheek pouch microcirculation of leukopenic hamsters was protected by tissue plasminogen activator (tPA) (50 microg/100 g body wt) against ischemia-reperfusion injury. Adherent leukocytes, total perfused capillary length (PCL), permeability increase, and arteriolar and venular red blood cell (RBC) velocity were investigated by fluorescence microscopy. Measurements were made at control, 30 or 60 min of ischemia, and at 30 or 60 min of reperfusion. Hamsters were made leukopenic by treatment with cyclophosphamide (20 mg/100 g body wt ip, 4 days before the experiment), which decreased circulating leukocyte count by 85-90%. Leukopenic hamsters undergoing 30 min of ischemia followed by 30 min of reperfusion showed no significant decrease in PCL or increased permeability. Leukopenic hamsters undergoing 60 min of ischemia followed by 60 min of reperfusion presented a significant decrease in microvascular perfusion where PCL was 28 +/- 7% of baseline, low-flow conditions, and increased permeability. In leukopenic hamsters treated with tPA there was complete protection of capillary perfusion with no significant changes in permeability or arteriolar and venular RBC velocity. In conclusion, thrombus formation may be an additional and independent factor that with leukocyte-mediated mechanisms determines ischemia-reperfusion injury.

Effects of near-infrared low-level laser irradiation on microcirculation.

Recently, there has been an increase in the clinical application of low-level laser irradiation (LLLI) in various fields. The present study was conducted to explore the effects of LLLI on microcirculation. We investigated the effects of LLLI on rat mesenteric microcirculation in vivo, and on cytosolic calcium concentration ([Ca2+]i) in rat vascular smooth muscle cells (VSMCs) in vitro. LLLI caused potent dilation in the laser-irradiated arteriole, which led to marked increases in the arteriolar blood flow. The changes were partly attenuated in the initial phase by the superfusion of 15 microM L-NAME, but they were not affected by local denervation. Furthermore, LLLI caused a power-dependent decrease in [Ca2+]i in VSMCs. The circulatory changes observed seemed to be mediated largely by LLLI-induced reduction of [Ca2+]i in VSMCs, in addition to the involvement of NO in the initial phase.