Regulation Of Microvascular Blood Flow Research Articles

The combined effects of temperature and posture on regional blood flow and haemodynamics

Under simultaneous ambient temperature and postural stressors, integrated regional blood flow responses are required to maintain blood pressure and thermoregulatory homeostasis. The aim of the present study was to assess the effect of ambient temperature and body posture on regional regulation of microvascular blood flow, specifically in the arms and legs.Participants (N = 11) attended two sessions in which they experienced transient ambient conditions, in a climatic chamber. During each 60-min trial, ambient temperature increased from 15.7 (0.6) °C to 38.9 (0.6) °C followed by a linear decrease, and the participants were either standing or in a supine position throughout the trial; relative humidity in the chamber was maintained at 25.9 (6.6) %. Laser doppler flowmetry of the forearm (SkBFarm) and calf (SkBFcalf), and haemodynamic responses (heart rate, HR; stroke volume, SV; cardiac output, CO; blood pressure, BP), were measured continuously. Analyses of heart rate variability and wavelet transform were also conducted.SkBFarm increased significantly at higher ambient temperatures (p = 0.003), but not SkBFcalf. The standing posture caused lower overall SkBF in both regions throughout the protocol, regardless of temperature (p < 0.001). HR and BP were significantly elevated, and SV significantly lowered, in response to separate and combined effects of higher ambient temperatures and a standing position (all p < 0.05); CO remained unchanged. Mechanistic analyses identified greater sympathetic nerve activation, and higher calf myogenic activation at peak temperatures, in the standing condition.Mechanistically and functionally, arm vasculature responds to modulation from both thermoregulation and baroreceptor activity. The legs, meanwhile, are more sensitive to baroreflex regulatory mechanisms.

The Importance of Intra-Islet Communication in the Function and Plasticity of the Islets of Langerhans during Health and Diabetes.

Islets of Langerhans are anatomically dispersed within the pancreas and exhibit regulatory coordination between islets in response to nutritional and inflammatory stimuli. However, within individual islets, there is also multi-faceted coordination of function between individual beta-cells, and between beta-cells and other endocrine and vascular cell types. This is mediated partly through circulatory feedback of the major secreted hormones, insulin and glucagon, but also by autocrine and paracrine actions within the islet by a range of other secreted products, including somatostatin, urocortin 3, serotonin, glucagon-like peptide-1, acetylcholine, and ghrelin. Their availability can be modulated within the islet by pericyte-mediated regulation of microvascular blood flow. Within the islet, both endocrine progenitor cells and the ability of endocrine cells to trans-differentiate between phenotypes can alter endocrine cell mass to adapt to changed metabolic circumstances, regulated by the within-islet trophic environment. Optimal islet function is precariously balanced due to the high metabolic rate required by beta-cells to synthesize and secrete insulin, and they are susceptible to oxidative and endoplasmic reticular stress in the face of high metabolic demand. Resulting changes in paracrine dynamics within the islets can contribute to the emergence of Types 1, 2 and gestational diabetes.

Pericytes Within A Pulmonary Neurovascular Unit in Coronavirus Disease 2019 Elicited Pathological Changes.

A pericyte-centered theory suggesting that embolisms occurring within the microvasculature of a neurovascular unit that can result in either parenchymal hemorrhage or intravascular congestion is presented here. Dysfunctional microvascular pericytes are characterized by their location in the neurovascular unit, either on the arteriole or venule side. Pathophysiological and pathological changes caused by coronavirus disease 2019 (COVID-19) include pulmonary hypertension, edema, focal hemorrhage, microvascular congestion, and thrombosis. In this paper, the application of the pericytes-centered hypothesis to COVID-19 has been presented by proposing the concept of a pulmonary neurovascular unit (pNVU). The application of this concept implies that human lungs contain approximately 300 million pNVUs. This concept of existing local regulation of microvascular blood flow is supported by the observation of pathophysiology in pulmonary embolism and in acute high-altitude illness. The autonomic control seen in these three disease states matches blood flow with oxygen supply in each pNVU to maintain physiological blood oxygen saturation level. This paper illustrates how the malfunction of microvascular pericytes may cause focal hemorrhage, edema or microvascular congestion and thrombosis. A bypass existing in each pNVU would autonomically deviate blood flow from a COVID-19-affected pNVU to other healthy pNVUs. This action would prevent systemically applied medicines from reaching the therapeutic threshold in COVID-19-affected pNVUs. While testing this hypothesis with experimental evidence is urgently needed, supporting therapy aimed at improving microcirculation or rebuilding the physiological function of microvascular pericytes is recommended as a potentially effective treatment of COVID 19.

Abstract 14228: Pericytes Within a Pulmonary Neurovascular Unit in Covid-19-elicited Pathologic Changes

A pericyte-centered hypothesis suggests that embolisms occurring within microvasculature of a neurovascular unit can result in either parenchymal hemorrhage or intravascular congestion. Dysfunctional microvascular pericytes are featured depending on their location in the neurovascular unit. I extend the hypothesis by proposing a concept of pulmonary neurovascular unit (pNVU). In simulating pathophysiology in pulmonary embolisms, acute high-altitude illness and COVID-19, an existing local regulation of microvascular blood flow is believable. This control balances blood flow with oxygen supply to maintain physiological blood oxygen saturation level. We have reported a working module for the neurovascular unit in the sexually dimorphic nucleus of the preoptic area. Pericytes, labeled with alpha-smooth muscle actin immunoreactivity, are significantly denser within the microvasculature of the neurovascular unit in males, signifying their biological functions or potential pathophysiological role in diseases. Noticeably, an illustration provides an explanation of how malfunction of microvascular pericytes causes pulmonary focal hemorrhage, edema or microvascular congestion and thrombi [Fig. 1]. A bypass existing in the pNVU would autonomically deviate blood flow from COVID-19-affected pNVU to other healthy pNVU. Consequentially, systematically applied medicines including chloroquine and/or hydroxychloroquine became valueless due to low concentration of the medicine in the COVID-19-affected regions. Alternatively, a preventive, early antiviral therapy may be efficacious because dysfunctional blood-air exchange precedents and malfunction of pulmonary microcirculation follows. While testing the hypothesis with experimental evidence is urgently needed, supporting therapy aimed at improvement of microcirculation or rebuilding of microvascular pericytes’ physiological function may be recommended during the COVID pandemic.

Inonotus obliquus attenuates histamine-induced microvascular inflammation.

Cell-to-cell communication is a key element of microvascular blood flow control, including rapidly carrying signals through the vascular endothelium in response to local stimuli. This cell-to-cell communication is negatively impacted during inflammation through the disruption of junctional integrity. Such disruption is associated with promoting the onset of cardiovascular diseases as a result of altered microvascular blood flow regulation. Therefore, understanding the mechanisms how inflammation drives microvascular dysfunction and compounds that mitigate such inflammation and dysfunction are of great interest for development. As such we aimed to investigate extracts of mushrooms as potential novel compounds. Using intravital microscopy, the medicinal mushroom, Inonotus obliquus was observed, to attenuate histamine-induced inflammation conducted vasodilation in second-order arterioles in the gluteus maximus muscle of C57BL/6 mice. Mast cell activation by C48/80 similarly disrupted endothelial junctions and conducted vasodilation but only histamine was blocked by the histamine antagonist, pyrilamine not C48/80 suggesting the importance of mast cell activation. Data presented here supports that histamine induced inflammation is a major disruptor of junctional integrity, and highlights the important anti-inflammatory properties of Inonotus obliquus focusing future assessment of mast cells as putative target for Inonotus obliquus.

Murine Live Bladder Tissue Model to Study the Microvasculature Properties and Function In Situ

Regulation of microvascular blood flow in the bladder has historically been associated with regulation by pre‐capillary arterioles and more recently to post‐capillary venules. Although pericytes are known to regulate capillary vessel diameter in various capillary beds (e.g. brain, retina, heart and kidney), their role in regulating bladder capillary diameter remains controversial.We have developed a mouse full‐thickness live bladder tissue model in which the microvasculature of the mucosa can be visualised in situ, enabling the regulation of suburothelial capillary diameter to be investigated. Bladder tissue viability was first investigated by fluorescence imaging of tissue labelled with Hoechst and propidium iodide to determine the live to dead cell ratio. Data indicated that tissue was viable in situ for up to 5 hours (&gt;60%; P&gt;0.05; n = 3 per time point). Real time DIC images of live tissue sections were collected for all experiments in which live tissue was exposed to vasoactive agents to investigate the pericyte‐mediated regulation of capillary diameter. Images were analysed off line and vessel diameter was measured at both pericyte and non‐pericyte sites along a capillary for each experiment. Angiotensin II (100 nM) and endothelin I (1 nM) evoked a pericyte‐mediated vasoconstriction of suburothelial capillaries at pericyte sites (13.3 ± 5.8%, 22.0 ± 9.7%) that was significantly greater (p&lt;0.05, n = 6 per drug) than that measured at non‐pericyte sites (3.2 ± 2.7%, 6.0 ± 3.4%). Prostaglandin E2 (30 μM) evoked a pericyte‐mediated dilation of capillaries (12.1 ± 2.6%) that was significantly greater than that measured at non‐pericyte sites (2.3 ± 2.3%, p = 0.03, n = 3).In this study we therefore demonstrate that suburothelial capillary pericytes act to regulate capillary diameter in response to agents previously reported to regulate capillary beds of other organs. This indicates that in addition to smooth muscle‐mediated regulation of upstream vessels in the bladder, spatial regulation of capillary diameter downstream of these vessels also occurs in the bladder.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Application of a Novel Microfluidic Device for Studying Microvascular Blood Flow Regulation In Vivo

ObjectiveValidate the efficacy of a novel liquid microfluidic device (LMFD) to manipulate microvascular blood flow by maintaining a fixed solute concentration, temperature, and physiologic gas conditions in a microscale region of tissue while simultaneously allowing for visualization and quantification of vascular geometry and hemodynamics.MethodsLMFD flow channels were moulded in polydimethylsiloxane (PDMS) using soft lithography techniques. A diffusive exchange window was created by patterning a 600×300 μm laser cut micro‐outlet into a glass coverslip. Cured PDMS flow channels were plasma bound to both the coverslip containing the micro‐outlet, and a glass slide to produce a complete LMFD.Ten Sprague‐Dawley rats (149–197g) were anesthetized with sodium pentobarbital; indwelling cannulas were placed into the left common carotid and right jugular vein for systemic monitoring, anaesthetic administration and fluid resuscitation; animals were then tracheotomized and mechanically ventilated. The extensor digitorum longus muscle of the lower hind‐limb was carefully dissected, externalized, and reflected across the LMFD secured in the stage of an inverted Olympus IX73 microscope. The muscle was allowed to equilibrate for 30 minutes while the LMFD was perfused with buffered Krebs solution at 37□.Logarithmic doses (10−8 M to 10−3 M) of adenosine triphosphate (ATP), acetylcholine (Ach), and phenylephrine (PE) were sequentially administered to the muscle via perfusion through the LMFD. The LMFD was perfused with each drug concentration for 5 minutes prior to data collection. Video of microvascular blood flow was recorded from multiple focal planes within the volume directly overlying the micro‐outlet. Recordings were analyzed offline to measure velocity, hematocrit, and supply rate. All animal protocols were approved by Memorial University's Institutional Animal Care Committee.ResultsATP significantly increased red blood cell supply rate (RBC SR) to 36.1 and 36.5 cell/s at concentrations of 10−4 and 10−3 M respectively (p &lt; 0.01) compared to the baseline level of 14.4 cell/s. Increasing concentrations of PE caused a graded change in RBC SR with significant decreases to 9.1, 3.5, and 0.8 cells/s at 10−5, 10−4, 10−3 M respectively (p &lt; 0.02). Changes in perfusion were observed only in areas directly overlying the micro‐outlet and within 200–300 μm of the window. Functional images generated at the highest drug concentrations showed that microvascular perfusion was unaffected in regions at greater distances from the micro‐outlet. Evan's Blue dye was used to confirm there were no leaks around the exchange window and that only tissue overlying the micro‐outlet was directly exposed to solutions perfusing the LMFD.ConclusionsOur novel LMFD allows for a controlled, continuous delivery of dissolved substances to highly constrained regions of microvasculature while simultaneously allowing visualization and measurement of blood flow within discrete vessels and networks. Blood flow changes can be directly observed in the region of interest while the surrounding vasculature is unaffected thus preserving integrated regulation to the tissue as a whole.Support or Funding InformationProject funded through a NSERC Discovery grant to GM Fraser.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Two-photon microscopic imaging of capillary red blood cell flux in mouse brain reveals vulnerability of cerebral white matter to hypoperfusion

Despite the importance of understanding the regulation of microvascular blood flow in white matter, no data on subcortical capillary blood flow parameters are available, largely due to the lack of appropriate imaging methods. To address this knowledge gap, we employed two-photon microscopy using a far-red fluorophore Alexa680 and photon-counting detection to measure capillary red blood cell (RBC) flux in both cerebral gray and white matter, in isoflurane-anesthetized mice. We have found that in control animals, baseline capillary RBC flux in the white matter was significantly higher than in the adjacent cerebral gray matter. In response to mild hypercapnia, RBC flux in the white matter exhibited significantly smaller fractional increase than in the gray matter. Finally, during global cerebral hypoperfusion, RBC flux in the white matter was reduced significantly in comparison to the controls, while RBC flux in the gray matter was preserved. Our results suggest that blood flow in the white matter may be less efficiently regulated when challenged by physiological perturbations as compared to the gray matter. Importantly, the blood flow in the white matter may be more susceptible to hypoperfusion than in the gray matter, potentially exacerbating the white matter deterioration in brain conditions involving global cerebral hypoperfusion.

The role of cyclo-oxygenase-1 in high-salt diet-induced microvascular dysfunction in humans.

Recent studies have shown that some of the deleterious effects of a high-salt (HS) diet are independent of elevated blood pressure and are associated with impaired endothelial function. Increased generation of cyclo-oxygenase (COX-1 and COX-2)-derived vasoconstrictor factors and endothelial activation may contribute to impaired vascular relaxation during HS loading. The present study aimed to assess the regulation of microvascular reactivity and to clarify the role of COX-1 and COX-2 in normotensive subjects on a short-term HS diet. The present study demonstrates the important role of COX-1 derived vasoconstrictor metabolites in regulation of microvascular blood flow during a HS diet. These results help to explain how even short-term HS diets may impact upon microvascular reactivity without changes in blood pressure and suggest that a vasoconstrictor metabolite of COX-1 could play a role in this impaired tissue blood flow. The present study aimed to assess the effect of a 1-week high-salt (HS) diet on the role of cyclo-oxygenases (COX-1 and COX-2) and the vasoconstrictor prostaglandins, thromboxane A2 (TXA2 ) and prostaglandin F2α (PGF2α ), on skin microcirculatory blood flow, as well as to detect its effect on markers of endothelial activation such as soluble cell adhesion molecules. Young women (n=54) were assigned to either the HS diet group (N=30) (∼14gday(-1) NaCl) or low-salt (LS) diet group (N=24) (<2.3gday(-1) NaCl) for 7 days. Post-occlusive reactive hyperaemia (PORH) in the skin microcirculation was assessed by laser Doppler flowmetry. Plasma renin activity, plasma aldosterone, plasma and 24h urine sodium and potassium, plasma concentrations of TXB2 (stable TXA2 metabolite) and PGF2α , soluble cell adhesion molecules and blood pressure were measured before and after the diet protocols. One HS diet group subset received 100mg of indomethacin (non-selective COX-1 and COX-2 inhibitor), and another HS group subset received 200mg of celecoxib (selective COX-2 inhibitor) before repeating laser Doppler flowmetry measurements. Blood pressure was unchanged after the HS diet, although it significantly reduced after the LS diet. Twenty-four hour urinary sodium was increased, and plasma renin activity and plasma aldosterone levels were decreased after the HS diet. The HS diet significantly impaired PORH and increased TXA2 but did not change PGF2α levels. Indomethacin restored microcirculatory blood flow and reduced TXA2 . By contrast, celecoxib decreased TXA2 levels but had no significant effects on blood flow. Restoration of of PORH by indomethacin during a HS diet suggests an important role of COX-1 derived vasoconstrictor metabolites in the regulation of microvascular blood flow during HS intake.

The adenosine system in skeletal muscle of individuals with essential hypertension and the effect of physical training

The study examined vascular function and the adenosine (ADO) system in skeletal muscle of individuals diagnosed with essential hypertension (EH; N=10) and normotensive (N; N=11) individuals, before and after a period of aerobic training. Before and after the training period, the subjects participated in two experiments in which a) leg blood flow was determined during arterial infusion of ADO, acetylcholine (ACh) or during exercise, and b) interstitial fluid was sampled from v. lateralis muscle during exercise and ADO infusion. Leg vascular conductance (LVC) in response to arterial ADO infusion was similar in the EH and N group. Interstitial ADO formation during exercise was lower in the EH than the N group. In EH, the period of training did not affect vasodilator responsiveness to arterially infused ADO but improved the formation of interstitial ADO and prostacyclin. In the N group, training resulted in a lower LVC in response to arterial ADO infusion, which was paralleled by a lower leg blood flow during submaximal exercise. In conclusion, whereas the responsiveness to circulating ADO in individuals with essential hypertension remained unaltered with training, the capacity to form ADO and prostacyclin at the microcirculatory level was enhanced, suggesting an improvement in microvascular blood flow regulation. In normotensive individuals, aerobic training reduced the vasodilatory response to intraluminal ADO.

Pharmacologically Augmented S -Nitrosylated Hemoglobin Improves Recovery From Murine Subarachnoid Hemorrhage

S-nitrosylated hemoglobin (S-nitrosohemoglobin) has been implicated in the delivery of O(2) to tissues through the regulation of microvascular blood flow. This study tested the hypothesis that enhancement of S-nitrosylated hemoglobin by ethyl nitrite inhalation improves outcome after experimental subarachnoid hemorrhage (SAH). A preliminary dosing study identified 20 ppm ethyl nitrite as a concentration that produced a 4-fold increase in S-nitrosylated hemoglobin concentration with no increase in methemoglobin. Mice were subjected to endovascular perforation of the right anterior cerebral artery and were treated with 20 ppm ethyl nitrite in air, or air alone for 72 hours, after which neurologic function, cerebral vessel diameter, brain water content, cortical tissue Po(2), and parenchymal red blood cell flow velocity were measured. At 72 hours after hemorrhage, air- and ethyl nitrite-exposed mice had similarly sized blood clots. Ethyl nitrite improved neurologic score and rotarod performance; abated SAH-induced constrictions in the ipsilateral anterior, middle cerebral, and internal carotid arteries; and prevented an increase in ipsilateral brain water content. Ethyl nitrite inhalation increased red blood cell flow velocity and cortical tissue Po(2) in the ipsilateral cortex with no effect on systemic blood pressure. Targeted S-nitrosylation of hemoglobin improved outcome parameters, including vessel diameter, tissue blood flow, cortical tissue Po(2), and neurologic function in a murine SAH model. Augmenting endogenous Po(2)-dependent delivery of NO bioactivity to selectively dilate the compromised cerebral vasculature has significant clinical potential in the treatment of SAH.

Simulation of metabolism‐perfusion matching in a heterogeneous microvascular network

Microvascular blood flow regulation involves multiple mechanisms designed to maintain adequate perfusion under conditions of varying metabolic demand. The impact of various regulatory factors on metabolism‐perfusion matching was assessed using a heterogeneous microvascular network model that accounted for myogenic, shear, and metabolic flow regulation. Estimates of oxygen extraction under control conditions were compared to an increase in tissue oxygen consumption in combination with a reduction in perfusion. For the values of parameters used, overall oxygen extraction was increased by a factor of 7.19 with a tenfold increase in consumption and a factor of 1.47 when perfusion was reduced by 50%. Combining increased consumption with decreased flow resulted in an increase in extraction by a factor of 9.20 compared to control, suggesting that network regulatory capacity remained intact under these conditions. This has significant implications for the optimization of metabolism‐perfusion matching, since impairment of flow regulation under conditions of increased consumption and decreased perfusion can lead to microvascular perfusion heterogeneity and cause organ failure in critically ill patients.

Mathematical modeling of metabolism‐perfusion matching in a microvascular network

Microvascular blood flow regulation has important implications for optimization of metabolism‐perfusion matching in physiological and pathophysiological conditions such as exercise and sepsis. The purpose of this theoretical study is to assess the impact of various regulatory factors on metabolism‐perfusion matching. A microvascular network model including myogenic, shear, and metabolic flow regulation was developed and utilized to obtain estimates of oxygen extraction under control conditions as compared to a 20% global increase in blood flow accompanied by a 50% increase in oxygen consumption. The exercise state was simulated with preserved flow regulation and sepsis was simulated with impaired metabolic flow regulation. For the values of parameters used, overall oxygen extraction was found to be 28% higher in exercise compared to control values as opposed to only 23% higher in sepsis. This study demonstrates the impact of impaired flow regulation on oxygen delivery and highlights microvascular perfusion abnormalities as a putative mechanism for organ failure in critically ill patients.

Molecular Effects of C-Peptide in Microvascular Blood Flow Regulation

C-Peptide is produced in beta-cells in the pancreas, and secreted into the blood stream in equimolar amounts with insulin. For a long time, C-peptide was considered as an important component in the biosynthesis of insulin, but otherwise believed to possess minimal biological activity. In the recent years, numerous studies demonstrated that lacking C-peptide in type 1 diabetic patients might exert an important role in the development of microvascular complications such as nephropathy or neuropathy. There is increasing evidence that the biological effects of C-peptide are, at least in part, mediated through the modulation of endothelial function and microvascular blood flow. In several tissues, an increase in microvascular and nutritional blood flow could be observed during substitution of physiological amounts of C-peptide. Recent studies confirmed that C-peptide stimulates endothelial NO release by the activation of Ca2+ calmodulin-regulated endothelial NO synthase. A restoration of Na+/K+-ATPase activity during C-peptide supplementation could be observed in erythrocytes and renal tubular cells. The improvement of erythrocyte Na+/K+-ATPase is associated with an increase in erythrocyte deformability, and improved rheological properties. In this article, we consider the role of C-peptide in the context of endothelial function and microvascular blood flow as pathophysiologic components in the development of microvascular complications in patients with diabetes mellitus and loss of beta-cell function.

Role of C‐Peptide in the Regulation of Microvascular Blood Flow

During the recent years, the role of C-peptide, released from the pancreatic beta cell, in regulating microvascular blood flow, has received increasing attention. In type 1 diabetic patients, intravenous application of C-peptide in physiological concentrations was shown to increase microvascular blood flow, and to improve microvascular endothelial function and the endothelial release of NO. C-peptide was shown to impact microvascular blood flow by several interactive pathways, like stimulating Na+K+ATPase or the endothelial release of NO. There is increasing evidence, that in patients with declining beta cell function, the lack of C-peptide secretion might play a putative role in the development of microvascular blood flow abnormalities, which go beyond the effects of declining insulin secretion or increased blood glucose levels.

Coupling a change in intraluminal pressure to vascular smooth muscle depolarization: still stretching for an explanation

pressure-induced (myogenic) constriction of arterioles is believed to be a fundamental contributor to the local regulation of microvascular blood flow and pressure. Myogenic constriction provides a level of tone upon which vasodilators can act to lower resistance and match blood flow to metabolic

Evaluation of forearm microvascular blood flow regulation by laser Doppler flowmetry, iontophoresis, and curve analysis: contribution of axon reflex

The relative contribution of vasodilating factors to the control of blood flow in the forearm cutaneous microcirculation is not well defined. Therefore, a mathematical transformation is introduced to decompose the superimposed signal and to investigate the involved mechanisms separately. Transdermal iontophoresis was used for the delivery of acetylcholine (ACh) or sodium nitroprusside (SNP) into the forearm, and cutaneous perfusion was measured using a laser Doppler flowmeter (LDF). The curve fitting procedure used in this study indicates that the LDF signal in response to ACh iontophoresis can be described by the superposition of two independent hyperbolic response curves. Obviously, each component of LDF signal indicates the existence of a separate mechanism, with corresponding rate constant k, latency T, and the saturation level F max. Blockade of C-fiber function (axon reflex) with topical anesthesia removes one of the two components of this response and allows the precise quantification of its contribution. SNP-evoked response also has two components, but their parameters were different from those of ACh. Therefore, ACh and SNP cause vasodilation in the skin microcirculation through different pathways. These findings have implications for clinical studies that use the iontophoresis technique for assessing vascular function and comparing responses to ACh and SNP to evaluate endothelial dysfunction.

Significance of hepatic arterial responsiveness for adequate tissue oxygenation upon portal vein occlusion in cirrhotic livers.

We investigated sinusoidal blood flow and hepatic tissue oxygenation during portal vein occlusion in cirrhotic rat livers to examine the effect of cirrhosis on the properties of hepatic microvascular blood flow regulation. After 8 weeks of CCl4/phenobarbital sodium treatment to induce cirrhosis Sprague-Dawley rats were prepared surgically to allow assessment of portal venous and hepatic arterial inflow using miniaturized flow probes with simultaneous analysis of hepatic microcirculation and tissue oxygenation by fluorescence microscopy and polarographic oxymetry. Age-matched noncirrhotic animals served as controls. Upon portal vein occlusion in cirrhotic livers (flow reduction to < 20%), hepatic arterial blood flow increased 1.5-fold (61 +/- 8 ml/min per 100 g liver) of baseline (40 +/- 7 ml/min per 100 g liver), reflecting an appropriate hepatic arterial buffer response (HABR), similarly as seen in control livers. The net result was a reduction in total liver inflow from 90 +/- 12 to 72 +/- 11 ml/min per 100 g liver, which was associated with a significant decrease in both sinusoidal red blood cell velocity and volumetric blood flow to approx. 71% and 76% of baseline values. However, portal vein occlusion did not cause a deterioration in hepatic tissue pO2 (11 +/- 3 vs. 10 +/- 3 mmHg at baseline). Sinusoidal diameters were found unchanged, disproving a major role of the sinusoidal tone in the regulation of HABR. Microvascular response of cirrhotic livers did not generally differ from that in noncirrhotic livers upon portal inflow restriction. We conclude that HABR in cirrhotic livers operates sufficiently to meet the liver tissue oxygen demand, most probably by an increased relative contribution of arterial perfusion of hepatic sinusoids.

Severe contusion of the femoral vessels in rats alters tissue oxygenation and microvascular blood flow regulation in the skeletal muscles of the limb.

Severe contusion of an artery often presents clinical problems in that it affects flow distal to the injury. However, the effect of a contusion on the microvascular flow regulation in the distal part of the limb is still largely unknown. A multipoint microelectrode technique was used to assess both tissue oxygenation (PtO2) and microflow (hydrogen clearance) on the skeletal muscle surface in a standard contusion injury to the femoral vessels in rats. A significant increase in and an altered distribution of (PtO2) as well as a reduction in and altered distribution of microflow on the muscle surface distal to the injury was found in all animals (n = 27) compared with the uninjured control leg. These findings could not be reproduced experimentally by sympathectomy or when the adjacent skeletal muscle alone was injured. The results suggest that the changes observed distal to the injury are of vascular origin, possibly as a result of endothelial damage at the site of the contusion.

The Trp64Arg amino acid polymorphism of the beta3-adrenergic receptor gene does not contribute to the genetic susceptibility of diabetic microvascular complications in Caucasian type 1 diabetic patients.

The beta3-adrenergic receptor is involved in regulation of microvascular blood flow. A missense mutation (Trp64Arg) in the beta3-adrenergic receptor gene has been suggested as a risk factor for proliferative retinopathy in Japanese type 2 diabetic patients. The aim of the present study was to evaluate the contribution of this polymorphism to the development of microangiopathic complications in Caucasian type 1 diabetic patients. We studied the relationship between the Trp64Arg polymorphism in type 1 diabetic patients with nephropathy (204 men/132 women, age 42.8 +/- 11.0 years, diabetes duration 28 +/- 9 years) and in type 1 diabetic patients with persistent normoalbuminuria (118 men/73 women, age 42.6 +/- 10.2 years, diabetes duration 27 +/- 8 years). Proliferative retinopathy was present in 254 patients (48%), while 66 patients (13%) had no diabetic retinopathy. There were no differences in Trp64Arg genotype distribution between type 1 diabetic patients with diabetic nephropathy and type 1 diabetic patients with normoalbuminuria: 295 (88%)/38 (11%)/3 (1%) vs 161 (84%)/30 (16%)/- had Trp/Trp, Trp/Arg or Arg/Arg genotype respectively. Odds ratio (95% CI) of nephropathy in carriers of the mutation was 0.75 (0.45-1.25). No associations between the Trp64Arg polymorphism and simplex or proliferative retinopathy were revealed either. The frequency of the Arg-allele was 0.069 in patients with proliferative retinopathy, 0.066 in patients with simplex retinopathy and 0.090 in patients with no signs of diabetic retinopathy, NS. The Trp64Arg polymorphism of the beta3-adrenergic receptor gene does not contribute to the genetic susceptibility to diabetic nephropathy in Caucasian type 1 diabetic patients. Nor does our study support previous findings of an association between this variant and proliferative retinopathy.