Acetate relaxation of isolated vascular smooth muscle

The Role of Gut Microbiota and Its Metabolites in Patients with Heart Failure

Heart failure (HF) is a significant health concern; early detection and prevention are crucial. Recent studies suggest that the gut microbiota and its metabolites may influence HF development and risk factors. We explored this relationship by examining changes in gut microbiota composition and metabolite levels in HF patients. HF patients often exhibit decreased alpha and beta diversity compared to controls, suggesting lower bacterial richness and community variation. Changes in specific bacterial phyla were observed, with decreases in Firmicutes (e.g., Ruminococcus) and Bacteroidetes (e.g., Prevotella) and increases in Proteobacteria (e.g., Escherichia, Shigella, and Klebsiella) and Actinobacteria. Gut-microbiota-related metabolites have been identified, potentially affecting various body systems, including the cardiovascular system. Among these are short-chain fatty acids (SCFAs), betaine, trimethylamine N-oxide (TMAO), phenylalanine, tryptophan-kynurenine, and phenylacetylgutamine (PAGIn). Although SCFAs positively affect our organisms, patients with HF have been observed to experience a decline in bacteria responsible for producing these chemical compounds. There have been indications of possible links between betaine, TMAO, phenylalanine, tryptophan-kynurenine, PAGIn, and heart failure. TMAO and phenylalanine, in particular, show promise as potential prognostic factors. However, their clinical significance has not yet been thoroughly evaluated and requires further investigation.

Recent Advances in Microbiota-Associated Metabolites in Heart Failure

Heart failure is a risk factor for adverse events such as sudden cardiac arrest, liver and kidney failure and death. The gut microbiota and its metabolites are directly linked to the pathogenesis of heart failure. As emerging studies have increased in the literature on the role of specific gut microbiota metabolites in heart failure development, this review highlights and summarizes the current evidence and underlying mechanisms associated with the pathogenesis of heart failure. We found that gut microbiota-derived metabolites such as short chain fatty acids, bile acids, branched-chain amino acids, tryptophan and indole derivatives as well as trimethylamine-derived metabolite, trimethylamine N-oxide, play critical roles in promoting heart failure through various mechanisms. Mainly, they modulate complex signaling pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells, Bcl-2 interacting protein 3, NLR Family Pyrin Domain Containing inflammasome, and Protein kinase RNA-like endoplasmic reticulum kinase. We have also highlighted the beneficial role of other gut metabolites in heart failure and other cardiovascular and metabolic diseases.

Short-Chain Fatty Acids in Gut-Heart Axis: Their Role in the Pathology of Heart Failure

Heart failure (HF) is a syndrome with global clinical and socioeconomic burden worldwide owing to its poor prognosis. Accumulating evidence has implicated the possible contribution of gut microbiota-derived metabolites, short-chain fatty acids (SCFAs), on the pathology of a variety of diseases. The changes of SCFA concentration were reported to be observed in various cardiovascular diseases including HF in experimental animals and humans. HF causes hypoperfusion and/or congestion in the gut, which may lead to lowered production of SCFAs, possibly through the pathological changes of the gut microenvironment including microbiota composition. Recent studies suggest that SCFAs may play a significant role in the pathology of HF, possibly through an agonistic effect on G-protein-coupled receptors, histone deacetylases (HDACs) inhibition, restoration of mitochondrial function, amelioration of cardiac inflammatory response, its utilization as an energy source, and remote effect attributable to a protective effect on the other organs. Collectively, in the pathology of HF, SCFAs might play a significant role as a key mediator in the gut-heart axis. However, these possible mechanisms have not been entirely clarified and need further investigation.

Reduced intestinal butyrate availability is associated with the vascular remodeling in resistance arteries of hypertensive rats

During hypertension an unbalance of short-chain fatty acids (SCFAs) production by intestinal bacteria is described. However, no data evaluate the association of SCFAs and vascular remodeling in hypertension, which is an important hallmark of this disease. Thus, the present study aims to evaluate the correlations between SCFAs availability and the resistance arteries remodeling in hypertension, as well as to identify the possible pathway by which the SCFAs could exert a structural and mechanical influence. Hence, male spontaneously hypertensive rats (SHR) and normotensive Wistar rats had blood pressure measured by tail-cuff plethysmography; fecal SCFAs content assessed by gas chromatography; gene expression of SCFAs-transporters in gut epithelium and SCFAs-sensing receptors on mesenteric resistance arteries (MRA) quantified by PCR; and MRA structural and mechanical parameters analyzed by pressure myograph. Reduced butyrate fecal content was found in SHR, with no changes in propionate and acetate, as well as decreased mRNA levels of SCFAs-transporters (MCT1, MCT4, and SMCT1) in the intestinal epithelium. In addition, lower gene expression of SCFAs-sensing receptors (GPR41, GPR43, and GPR109a, but not Olfr78) was identified in MRAs of SHR, which also shows inward eutrophic remodeling with stiffness. Butyrate content presented a negative correlation with systolic blood pressure and with the structural alterations found on MRAs, while a positive correlation between butyrate content and mechanical parameters was detected. Altogether the present study suggests that lower butyrate content due to ineffective SCFA bioavailability, associated with lower SCFAs-sensing receptors expression, could favor MRA remodeling, increasing peripheral vascular resistance and worsening hypertension prognosis.

The Gut Microbiota and Vascular Aging: A State-of-the-Art and Systematic Review of the Literature

The gut microbiota is a critical regulator of human physiology, deleterious changes to its composition and function (dysbiosis) have been linked to the development and progression of cardiovascular diseases. Vascular ageing (VA) is a process of progressive stiffening of the arterial tree associated with arterial wall remodeling, which can precede hypertension and organ damage, and is associated with cardiovascular risk. Arterial stiffness has become the preferred marker of VA. In our systematic review, we found an association between gut microbiota composition and arterial stiffness, with two patterns, in most animal and human studies: a direct correlation between arterial stiffness and abundances of bacteria associated with altered gut permeability and inflammation; an inverse relationship between arterial stiffness, microbiota diversity, and abundances of bacteria associated with most fit microbiota composition. Interventional studies were able to show a stable link between microbiota modification and arterial stiffness only in animals. None of the human interventional trials was able to demonstrate this relationship, and very few adjusted the analyses for determinants of arterial stiffness. We observed a lack of large randomized interventional trials in humans that test the role of gut microbiota modifications on arterial stiffness, and take into account BP and hemodynamic alterations.

From salt to hypertension, what is missed?

Excess salt intake is viewed as a major contributor to hypertension and cardiovascular disease, and dietary salt restriction is broadly recommended by public health guidelines. However, individuals can have widely varying physiological responses to salt intake, and a tailored approach to evaluation and intervention may be needed. The traditional sodium related concepts are challenging to assess clinically for two reasons: (1) spot and 24-hour urine sodium are frequently used to evaluate salt intake, but are more suitable for population study, and (2) some adverse effects of salt may be blood pressure-independent. In recent years, previously unknown mechanisms of sodium absorption and storage have been discovered. This review will outline the limitations of current methods to assess sodium balance and discuss new potential evaluation methods and treatment targets.

Microbial Interventions to Control and Reduce Blood Pressure in Australia (MICRoBIA): rationale and design of a double-blinded randomised cross-over placebo controlled trial

Background

Hypertension is a prevalent chronic disease worldwide that remains poorly controlled. Recent studies support the concept that the gut microbiota is involved in the development of hypertension and that dietary fibre intake may act through the gut microbiota to lower blood pressure (BP). Resistant starch is a type of prebiotic fibre which is metabolised by commensal bacteria in the colon to produce short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate. Previous work in pre-clinical models provides strong evidence that both prebiotic fibre as well as SCFAs (i.e. postbiotics) can prevent the development of hypertension. The aim of this clinical trial is to determine if acetylated and butyrylated modified resistant starch can decrease BP of hypertensive individuals via the modulation of the gut microbiota and release of high levels of SCFAs.

Methods

This is a phase IIa double-blinded, randomised, cross-over, placebo controlled trial. Participants are randomly allocated to receive either a diet containing 40 g/day of the modified resistant starch or placebo (corn starch or regular flour) for 3 weeks on each diet, with a 3-week washout period between the two diets. BP is measured in the office, at home, and using a 24-h ambulatory device. Arterial stiffness is measured using carotid-to-femoral pulse wave velocity. Our primary endpoint is a reduction in ambulatory daytime systolic BP. Secondary endpoints include changes to circulating cytokines, immune markers, and modulation to the gut microbiome.

Discussion

The findings of this study will provide the first evidence for the use of a combination of pre- and postbiotics to lower BP in humans. The results are expected at the end of 2021.

Trial registration

Australia and New Zealand Clinical Trial Registry ACTRN12619000916145. Registered on 1 July 2019.

Acetate, a Short-Chain Fatty Acid, Acutely Lowers Heart Rate and Cardiac Contractility Along with Blood Pressure

Short-chain fatty acids (SCFAs) are metabolites produced almost exclusively by the gut microbiota and are an essential mechanism by which gut microbes influence host physiology. Given that SCFAs induce vasodilation, we hypothesized that they might have additional cardiovascular effects. In this study, novel mechanisms of SCFA action were uncovered by examining the acute effects of SCFAs on cardiovascular physiology in vivo and ex vivo. Acute delivery of SCFAs in conscious radiotelemetry-implanted mice results in a simultaneous decrease in both mean arterial pressure and heart rate (HR). Inhibition of sympathetic tone by the selective β-1 adrenergic receptor antagonist atenolol blocks the acute drop in HR seen with acetate administration, yet the decrease in mean arterial pressure persists. Treatment with tyramine, an indirect sympathomimetic, also blocks the acetate-induced acute drop in HR. Langendorff preparations show that acetate lowers HR only after long-term exposure and at a smaller magnitude than seen in vivo. Pressure-volume loops after acetate injection show a decrease in load-independent measures of cardiac contractility. Isolated trabecular muscle preparations also show a reduction in force generation upon SCFA treatment, though only at supraphysiological concentrations. These experiments demonstrate a direct cardiac component of the SCFA cardiovascular response. These data show that acetate affects blood pressure and cardiac function through parallel mechanisms and establish a role for SCFAs in modulating sympathetic tone and cardiac contractility, further advancing our understanding of the role of SCFAs in blood pressure regulation. SIGNIFICANCE STATEMENT: Acetate, a short-chain fatty acid, acutely lowers heart rate (HR) as well as mean arterial pressure in vivo in radiotelemetry-implanted mice. Acetate is acting in a sympatholytic manner on HR and exerts negative inotropic effects in vivo. This work has implications for potential short-chain fatty acid therapeutics as well as gut dysbiosis-related disease states.

Deficiency of Prebiotic Fiber and Insufficient Signaling Through Gut Metabolite-Sensing Receptors Leads to Cardiovascular Disease

BACKGROUND

High blood pressure (BP) continues to be a major, poorly controlled but modifiable risk factor for cardiovascular death. Among key Western lifestyle factors, a diet poor in fiber is associated with prevalence of high BP. The impact of lack of prebiotic fiber and the associated mechanisms that lead to higher BP are unknown. Here we show that lack of prebiotic dietary fiber leads to the development of a hypertensinogenic gut microbiota, hypertension and its complications, and demonstrate a role for G-protein coupled-receptors (GPCRs) that sense gut metabolites.

METHODS

One hundred seventy-nine mice including C57BL/6J, gnotobiotic C57BL/6J, and knockout strains for GPR41, GPR43, GPR109A, and GPR43/109A were included. C57BL/6J mice were implanted with minipumps containing saline or a slow-pressor dose of angiotensin II (0.25 mg·kg^-1·d^-1). Mice were fed diets lacking prebiotic fiber with or without addition of gut metabolites called short-chain fatty acids ([SCFA)] produced during fermentation of prebiotic fiber in the large intestine), or high prebiotic fiber diets. Cardiac histology and function, BP, sodium and potassium excretion, gut microbiome, flow cytometry, catecholamines and methylation-wide changes were determined.

RESULTS

Lack of prebiotic fiber predisposed mice to hypertension in the presence of a mild hypertensive stimulus, with resultant pathological cardiac remodeling. Transfer of a hypertensinogenic microbiota to gnotobiotic mice recapitulated the prebiotic-deprived hypertensive phenotype, including cardiac manifestations. Reintroduction of SCFAs to fiber-depleted mice had protective effects on the development of hypertension, cardiac hypertrophy, and fibrosis. The cardioprotective effect of SCFAs were mediated via the cognate SCFA receptors GPR43/GPR109A, and modulated L-3,4-dihydroxyphenylalanine levels and the abundance of T regulatory cells regulated by DNA methylation.

CONCLUSIONS

The detrimental effects of low fiber Westernized diets may underlie hypertension, through deficient SCFA production and GPR43/109A signaling. Maintaining a healthy, SCFA-producing microbiota is important for cardiovascular health.

Short chain fatty acids and methylamines produced by gut microbiota as mediators and markers in the circulatory system

Ample evidence suggests that gut microbiota-derived products affect the circulatory system functions. For instance, short chain fatty acids, that are the products of dietary fiber bacterial fermentation, have been found to dilate blood vessels and lower blood pressure. Trimethylamine, a gut bacteria metabolite of carnitine and choline, has recently emerged as a potentially toxic molecule for the circulatory system. To enter the bloodstream, microbiota products cross the gut–blood barrier, a multilayer system of the intestinal wall. Notably, experimental and clinical studies show that cardiovascular diseases may compromise function of the gut–blood barrier and increase gut-to-blood penetration of microbiota-derived molecules. Hence, the bacteria products and the gut–blood barrier may be potential diagnostic and therapeutic targets in cardiovascular diseases. In this paper, we review research on the cardiovascular effects of microbiota-produced short chain fatty acids and methylamines.

Intradialytic hypotension and splanchnic shifting: Integrating an overlooked mechanism with the detection of ischemia-related signals during hemodialysis

In the most simple analysis, a patient's hematocrit during hemodialysis will rise when the rate of ultrafiltration exceeds the rate at which the fluid is mobilized from extravascular spaces; the greater the rise in hematocrit, the lower blood volume is and the more likely intradialytic hypotension (IDH) is to occur. A secondary mechanism of IDH may be due to sudden shift of blood volume away from the heart under conditions of borderline cardiac filling. A substantial portion of blood volume resides in the splanchnic venous system. During the early part of dialysis, a centripetal shift of red cells from this anatomical region to the central circulation has been documented to occur. The magnitude of this shift is unpredictable, and it may depend on the level of splanchnic vasoconstriction predialysis. The amount of splanchnic shift may also be reduced in patients with autonomic dysfunction. Once this central shift in blood volume has occurred, it can be reversed during further ultrafiltration due to ischemia-induced release of vasodilatory molecules that cause dilation of upstream splanchnic arterioles; this causes increased transmission of arterial pressure to the splanchnic veins, acutely increasing their capacity. The increased splanchnic venous capacity may cause a sudden shift of blood away from the central circulation to fill these veins under conditions where cardiac filling has already been reduced. The result can be severe IDH due to insufficient cardiac filling and cardiac output. One fruitful preventive approach might be to continuously monitor the blood or dialysate for the sudden appearance of such ischemia-related molecules or other signals which may herald not only dialysis hypotension but tissue stunning, warning that the fluid removal rate should be immediately reduced.

Beyond gut feelings: how the gut microbiota regulates blood pressure

Hypertension is the leading risk factor for heart disease and stroke, and is estimated to cause 9.4 million deaths globally every year. The pathogenesis of hypertension is complex, but lifestyle factors such as diet are important contributors to the disease. High dietary intake of fruit and vegetables is associated with reduced blood pressure and lower cardiovascular mortality. A critical relationship between dietary intake and the composition of the gut microbiota has been described in the literature, and a growing body of evidence supports the role of the gut microbiota in the regulation of blood pressure. In this Review, we describe the mechanisms by which the gut microbiota and its metabolites, including short-chain fatty acids, trimethylamine N-oxide, and lipopolysaccharides, act on downstream cellular targets to prevent or contribute to the pathogenesis of hypertension. These effects have a direct influence on tissues such as the kidney, the endothelium, and the heart. Finally, we consider the role of the gut microbiota in resistant hypertension, the possible intergenerational effect of the gut microbiota on blood pressure regulation, and the promising therapeutic potential of gut microbiota modification to improve health and prevent disease.

Intracellular pH changes in human aortic smooth muscle cells in response to fluid shear stress

The smooth muscle cell (SMC) layers of human arteries may be exposed to blood flow after endothelium denudation, for example, following balloon angioplasty treatment. These SMCs are also constantly subjected to pressure driven transmural fluid flow. Flow-induced shear stress can alter SMC growth and metabolism. Signal transduction mechanisms involved in these flow effects on SMCs are still poorly understood. In this work, the hypothesis that shear stress alters the intracellular pH (pHi) of SMC is examined. When exposed to venous and arterial levels of shear stress, human aortic smooth muscle cells (hASMC) undergo alkalinization. The alkalinization plateau persisted even after 20 min of cell exposure to flow. Addition of amiloride (10 micromoles) or its 5-(N-ethyl-N-isopropyl) analog (EIPA, 10 micromoles), both Na+/H+ exchanger inhibitors, attenuated intracellular alkalinization, suggesting the involvement of the Na+/H+ exchanger in this response. The same concentrations of these inhibitors did not show an effect on pHi of hASMCs in static culture. 4-Acetamido-4'-isothio-cyanatostilbene-2,2'-disulfonic acid (SITS, 1 mM), a Cl-/HCO3- exchange inhibitor, affected the pHi of hASMCs both in static and flow conditions. Our results suggest that flow may perturb the Na+/H+ exchanger leading to an alkalinization of hASMCs, a different response from the flow-induced acidification seen with endothelial cells at the same levels of shear stress. Understanding the flow-induced signal transduction pathways in the vascular cells is of great importance in the tissue engineering of vascular grafts. In the case of SMCs, the involvement of pHi changes in nitric oxide production and proliferation regulation highlights further the significance of such studies.

Cardiovascular response to hemodialysis: the effects of uremia and dialysate buffer

Cardiovascular instability continues to be one of the primary clinical problems in hemodialysis. Acetate buffer in dialysate is one of the factors that may induce hypotension. Since uremia may have a direct effect on the regulation of the cardiovascular system, the present study was designed to investigate the separate effects of uremia and acetate hemodialysis on blood pressure in anesthesized dogs, as well as the hemodynamic parameters determined by invasive cardiovascular monitoring. Animals were separated into four groups: (1) group I, hemodialysis with acetate in controls; (2) group II, hemodialysis with acetate in uremic dogs; (3) group III, hemodialysis with bicarbonate in controls; and (4) group IV, hemodialysis with bicarbonate in uremic dogs. Acute uremia was induced by bilateral ureteral ligation and a 90-minute hemodialysis (acetate or bicarbonate) procedure was performed 72 hours later. The results obtained in this study show that, compared with dogs with normal renal function, acute uremia resulted in an elevation in mean arterial pressure (MAP; 178 +/- 13 vs. 115 +/- 23 mm Hg, P < 0.01), which was associated with an increase in cardiac index (CI) and left ventricular stroke work index (LVSWI). In these dogs, the pulmonary capillary wedge pressure (PCWP; preload) and the systemic vascular resistance index (SVRI; afterload) were not different than controls. In uremic dogs, hemodialysis with acetate, but not with bicarbonate, decreased the MAP to values similar to controls. The decrease in MAP induced by acetate hemodialysis in uremic dogs was associated with a decrease in SVRI and PCWP. These results suggest that in dogs with acute uremia, acetate hemodialysis (HD) decreases myocardial contractility that was previously increased by a direct effect of uremia. In controls, acetate produced a moderate decrease in MAP that was the result of a mild decrease in CI and SVR. Since PCWP was not significantly decreased after acetate HD, the decrease in CI can be attributed to a mild decrease in myocardial performance. In conclusion, this study in dogs suggests that uremia enhances myocardial contractility directly. Acetate hemodialysis reduces this elevated myocardial contractility to normal values.

Reduced skin hyperemia during tap water iontophoresis after intake of acetylsalicylic acid

Skin microcirculation and skin temperature of 10 healthy subjects (6 men and 4 women, 20-44 yr of age) without any vascular diseases were registered when a thermoindifferent tap water iontophoresis was applied. The aim of this controlled study was to evaluate the development of skin hyperemia after the intake of 500 mg of acetylsalicylic acid (ASA). The measurement was conducted by laser-Doppler flowmetry on the proximal forearm. The skin temperature was measured before and after the treatment by an infrared thermometer. In all persons there was an intense erythema on the side of the cathode and only a modest one on the side of the anode. Without ASA preliminary treatment, the cutaneous flow showed an increase of 106% at the anodal side and that of 834% at the cathodal side (P < 0.001). After ending tap water iontophoresis, the skin temperature increased more on the cathode side than on the anode side (P < 0.001). After the intake of 500 mg ASA, the increase of the flow was 78% at the anode and 88% at the cathode. The comparison of the skin microcirculation did not show any differences at the anodal side when acetylsalicylic acid was taken before, but a strong suppression of the galvanic erythema at the cathodal side was observed after the intake of ASA. There is a direct influence of acetylsalicylic acid on the induction of the neurogenic inflammation caused by a galvanic erythema. The intensity of the induced erythema correlates with the analgesic effects of constant current treatment. An attenuation of the electrotherapeutic analgesia is possible.

Skin microcirculation during tapwater iontophoresis in humans: cathode stimulates more than anode

The aim of this controlled study was to evaluate the influence of anode and cathode on skin blood flow by using direct current. Skin microcirculation and skin temperature of 26 healthy subjects (17 men and 9 women, 20-64 years of age) without any vascular diseases were registered when a tapwater iontophoresis was applied. Thermoindifferent water temperature was used to prevent thermic effects on microcirculation. The blood flow measurement was conducted by laser-Doppler flowmetry on the proximal forearm and on the back of the wrist. The skin temperature was measured before and after treatment by an infrared thermometer. In 19 persons there was an intense erythema on the side of the cathode and an only modest one on the side of the anode, while 7 persons showed meager reactions on both sides. The erythema rose strongly from the distal (back of the hand) to the proximal forearm. The comparison of the microcirculation of the arms showed an increase of 120% at the anode and of 700% at the cathode. The differences between the two sides were significant (P < 0.001). After the end of tapwater iontophoresis the skin temperature increased more on the side of the cathode than on the anode side (P < 0.001). The frequency of vasomotion did not change. The vasomotion amplitude increased 67% at the anode (P < 0.05) and 175% at the cathode (P < 0.001). The increased blood flow effect was not age or sex dependent. Although the increased blood flow effect was six times larger on the cathode side, the subjects did not perceive any subjective difference.

Resuscitation of uncontrolled liver hemorrhage: effects on bleeding, oxygen delivery, and oxygen consumption

Using a standardized liver injury model of uncontrolled hemorrhage, we tested the effect of different fluid resuscitation regimens on hemodynamics, oxygen delivery, oxygen consumption, bleeding volume, and fluid resuscitation requirements. Rats were randomized into three bolus resuscitation groups 15 minutes after liver injury: lactated Ringer's solution (LR, n = 10), hypertonic saline (HS, n = 10), and hypertonic sodium acetate (HA, n = 10). In all resuscitation groups, a 4 mL/kg bolus was first infused at a rate of 0.4 mL/min. Continuous supplemental LR infusion was then given for 90 minutes to maintain a mean arterial pressure of 80 mm Hg. An initial bolus of LR led to minimal changes in hemodynamics. Initial resuscitation with HS markedly increased blood pressure and cardiac index. The bolus of HA increased cardiac index but did not increase blood pressure; systemic vascular resistance was significantly decreased and bleeding significantly increased. Resuscitation with HS did not increase bleeding compared with LR and resulted in the smallest total resuscitation volume requirement. Resuscitation with HS and HA both resulted in a rapid increase in oxygen consumption; LR did not increase oxygen consumption. Animals in the HS group had significantly higher oxygen extraction ratios at the conclusion of the experiment. The use of different bolus fluids for the resuscitation of uncontrolled hemorrhage resulted in significant differences in hemodynamics, oxygen metabolism, and blood loss even when subsequent resuscitation was the same in all groups. Results from large vessel injury animal models and clinical studies of patients with penetrating trauma may not apply to solid parenchymal injuries.

Liver injury as a model of uncontrolled hemorrhagic shock: resuscitation with different hypertonic regimens

Using a standardized liver injury model of uncontrolled hemorrhage, we tested the effect of different hypertonic solutions on mortality, blood pressure, intra-abdominal bleeding, and circulating blood volume. After liver injury, rats were randomized to 4 groups: lactated Ringer's (LR, n = 10), Isosal (ISO, n = 10), hypertonic saline (HS, n = 10), and hypertonic sodium acetate (HA, n = 10). In all resuscitation groups, 4 mL/kg was infused at a rate of 0.4 mL/min. Blood volume was evaluated both directly and by estimation. Mortality was highest after HA resuscitation (40%) and lowest after HS resuscitation (0%), but this difference was not significant. Blood pressure was significantly higher after HS resuscitation, and this difference was sustained for 4 hours. The HA resuscitation did not increase blood pressure compared with LR resuscitation. Intraperitoneal blood volume was significantly higher with HS (25.5 +/- 0.7 mL/kg) and HA (26.8 +/- 1.2 mL/kg) than with LR (22.5 +/- 0.4 mL/kg). The HA resuscitation led to a significantly larger drop from baseline values of estimated terminal circulating blood volume than LR resuscitation. Nonparametric analysis combining survival time and directly measured change in blood volume demonstrated a significant advantage to HS, compared with LR. HA and HS resuscitations increased bleeding from uncontrolled solid viscus injury. The HS resuscitation restored blood pressure better than the other hypertonic solutions and maintained circulating blood volume in spite of increased bleeding. The HA and ISO resuscitations did not exhibit any advantage over LR in resuscitation of solid viscus injury.

Hemodialysis with acetate, DL-lactate and bicarbonate: a hemodynamic and gasometric study

Using invasive techniques we have studied various hemodynamic and gasometric parameters in the course of hemodialysis (HD) with different buffers in an animal model. HD sessions of 180 minutes at zero ultrafiltration were carried out on three groups of eight uremic dogs each, under anesthesia and constant mechanical ventilation. The three groups differed only in the buffer used: acetate (Group AC), equal proportions of DL-lactate and acetate (Group AC+LA), and bicarbonate (Group BC). No hemodynamic changes were seen in Group BC. In the AC and AC+LA groups we observed on minute 1 a decrease of the mean blood pressure (MBP) and of the systemic vascular resistances (SVR). These parameters returned to baseline values within the first 30 minutes in Group AC+LA. In Group AC the SVR also returned to baseline values after the minute 30, but the MBP remained below baseline throughout the study period, together with cardiac index and left ventricular stroke work index decreases. Only in Group AC did we see a flattening of the ventricular function curves. Only in this Group was there a decrease of the arterial oxygen pressure (PaO2) with an associated increase of the alveolo-arterial and arterio-venous O2 differences. The O2 consumption was not modified in any of the groups. Acetate as a single buffer induces hemodynamic instability through peripheral vasodilation and reduction of myocardial contractility. The myocardial depression induced by acetate, in its turn, causes a reduction in PaO2. The mixed acetate+lactate buffer is hemodynamically better tolerated than acetate as single buffer, as it induces only vasodilation.

The vasorelaxant effects of acetate: role of adenosine, glycolysis, lyotropism, and pHi and Cai2+

The mechanism of acetate vasorelaxation is unknown. In the rat caudal artery, acetate has a vasorelaxant effect and also increases cyclic AMP. Here we evaluate the role of adenosine, of possible glycolysis inhibition by acetate, of the lyotropic properties of acetate and other anions, and of intracellular calcium and pH. Adenosine per se did not relax the caudal artery in the range of 10(-8) to 10(-2) M. Preincubation with adenosine deaminase (ADA, 5.0 U/ml) or with 8-phenyltheophylline (8-PT, 10(-6) to 10(-4) M) increased, rather than blocked the vasorelaxant effect of acetate. Oxypurinol (10(-3) M) or the nucleoside transport inhibitor NBMPR (10(-4) M) had no effect on acetate relaxation. Whereas acetate increased tissue cyclic AMP content, 10(-3) M adenosine or 10(-6) M PIA had no effect. In strips studied under conditions of inhibited glycolysis (no glucose, with 11 mM 2-deoxyglucose, 1.0 mM pyruvate, and 0.5 mM 5-iodoacetate), acetate-induced relaxation, as well as acetate-induced cyclic AMP generation, tended to be reduced but not significantly so. Other anions relaxed vascular strips in relation to their lyotropic number, but only at higher doses, and they did not stimulate cyclic AMP formation. Acetate (10 mM) caused a transient fall in Ca2+i followed by a slight, sustained rise. A concomitant decrease in pHi was seen. DIDS, which blocks the relaxant and cyclic AMP effects of acetate, had no effect on the pHi decrease, but did decrease the rate of pHi recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

L-lactate high-efficiency hemodialysis: hemodynamics, blood gas changes, potassium/phosphorus, and symptoms

Hemodynamic changes were measured during high-efficiency hemodialysis (HEHD) using three dialysis solutions: L-lactate (46 mM), bicarbonate (35 mM + 4 mM acetate), and acetate (39 mM). Cardiac output was determined by changes in thoracic electrical bioimpedance. Although there appeared to be subtle differences in hemodynamic response to L-lactate versus bicarbonate, the blood pressure, cardiac output, and total peripheral resistance were affected less with either of these solutions than with acetate. In particular, neither L-lactate nor bicarbonate HEHD were associated with a change in cardiac output, whereas with acetate HEHD a marked (22%) increase in cardiac output was seen concurrently with a moderate fall in blood pressure and TPR. Both acetate and L-lactate HEHD were associated with hypoxemia, whereas with bicarbonate HEHD the PO2 did not change. With L-lactate HEHD, correction of pH and plasma HCO3 concentrations was delayed but these values were not significantly different from those obtained with bicarbonate HEHD by one hour after dialysis. Potassium removal was comparable with the three dialysis solutions. Phosphorus removal with L-lactate tended to be slightly less than with bicarbonate, but not less than with acetate. Our results suggest that L-lactate (46 mM) dialysis solution may be a suitable alternative to acetate for HEHD, being associated with a hemodynamic profile that is similar to that of bicarbonate and better than that of acetate. Our results further suggest that the hypoxemia associated with the use of acetate dialysis solution is not intrinsic to acetate, but is due either to a low dialysis solution PCO2 level or to accelerated consumption of oxygen during substrate metabolism.