Extracellular vesicles are carriers of adiponectin with insulin-sensitizing and anti-inflammatory properties

Recent evidence supporting that adipose tissue (AT)-derived extracellular vesicles (EVs) carry an important part of the AT secretome led us to characterize the EV-adipokine profile. In addition to evidencing a high AT-derived EV secretion ability that is further increased by obesity, we identify enrichment of oligomeric forms of adiponectin in small EVs (sEVs). This adipokine is mainly distributed at the EV external surface as a result of nonspecific adsorption of soluble adiponectin. EVs also constitute stable conveyors of adiponectin in the blood circulation. Adiponectin-enriched sEVs display in vitro insulin-sensitizing effects by binding to regular adiponectin receptors. Adoptive transfer of adiponectin-enriched sEVs in high-fat-diet-fed mice prevents animals from gaining weight and ameliorated insulin resistance and tissue inflammation, with major effects observed in the AT and liver. Our results therefore provide information regarding adiponectin-related metabolic responses by highlighting EVs as delivery platforms of metabolically active forms of adiponectin molecules.

Lipidomic analysis of adipose-derived extracellular vesicles reveals specific EV lipid sorting informative of the obesity metabolic state

Adipose extracellular vesicles (AdEVs) transport lipids that could participate in the development of obesity-related metabolic dysfunctions. This study aims to define mouse AdEV lipid signature by a targeted LC-MS/MS approach in either healthy or obesity context. Distinct clustering of AdEV and visceral adipose tissue (VAT) lipidomes by principal component analysis reveals specific AdEV lipid sorting when compared with secreting VAT. Comprehensive analysis identifies enrichment of ceramides, sphingomyelins, and phosphatidylglycerols species in AdEVs compared with source VAT whose lipid content closely relates to the obesity status and is influenced by the diet. Obesity moreover impacts AdEV lipidome, mirroring lipid alterations retrieved in plasma and VAT. Overall, our study identifies specific lipid fingerprints for plasma, VAT, and AdEVs that are informative of the metabolic status. Lipid species enriched in AdEVs in the obesity context may constitute biomarker candidates or mediators of the obesity-associated metabolic dysfunctions.

Faeces-derived extracellular vesicles participate in the onset of barrier dysfunction leading to liver diseases

The role of extracellular vesicles (EVs) from faeces (fEVs) and small circulating EVs (cEVs) in liver diseases such as non-alcoholic fatty diseases (NAFLD) and non-alcoholic steatohepatitis (NASH) has not been demonstrated. fEVs and cEVs of healthy donors, NAFLD and NASH patients were isolated and characterized. The effects of EVs were evaluated in intestinal, endothelial, Kupffer and stellate cells. Non-muscular myosin light chain kinase (nmMLCK) deficient mice were used in vivo. Bacterial origins of fEVs were analysed by 16s rDNA gene sequencing. fEVs and small cEVs were composed of prokaryotic and eukaryotic origins. Only NASH-fEVs exerted deleterious effects. NASH-fEVs increased intestinal permeability and reduced expression of tight junction proteins that were prevented by nmMLCK inhibition, increased endothelial cell permeability and inflammatory cytokines and chemokines requiring TLR4/lipopolysaccharide pathway. NASH-fEVs and NASH-cEVs activated profibrotic and proinflammatory proteins of hepatic stellate cells. Treatment with NASH-fEVs evoked an increase in intestinal permeability in wild type but not in nmMLCK deficient mice. Bacterial origins of fEVs were different between NAFLD and NASH patients and 16 amplicon sequence variants were differentially abundant. We demonstrate that fEVs actively participate in barrier dysfunctions leading to liver injuries underscoring the role of nmMLCK and lipopolysaccharide carried by fEVs.

Cross-linkage between bacterial taxonomy and gene functions: a study of metagenome-assembled genomes of gut microbiota in adult non-alcoholic fatty liver disease

BACKGROUND

The reconstruction of metagenome-assembled genomes (MAGs) has emerged as a powerful approach for combining the taxonomic and functional content of microbial populations.

AIM

To use this new approach to highlight mechanisms linking gut microbiota to NAFLD severity METHODS: Stool samples were collected from 96 NAFLD patients on the day of liver biopsy. Shotgun DNA sequencing of the gut microbiota was performed on an Illumina HiSeq3000 system. Contigs were binned into MAGs according to their co-abundances and tetranucleotide frequencies using Metabat v.0.32.4. Predicted protein-coding genes were clustered in orthologous groups (OGs) with DIAMOND against the EggNOG v4.5 database. Liver biopsies were read in accordance with the NASH CRN classification.

RESULTS

Fifty-four patients had NASH and 44 had significant fibrosis (F ≥ 2). Sequencing of DNA extracted from stools resulted in 13.8 + 3.2 million paired-end reads per sample. Of the 4,000 reconstructed MAGs, 220 in NASH patients, 192 in non-NASH patients, 203 in F ≥ 2 patients and 230 in F0-1 patients had > 70% completeness and < 5% contamination. Within these MAGs, 28 OGs were associated with NASH, 33 with significant fibrosis, and seven with both NASH and significant fibrosis. The study of MAGs showed associations between NAFLD severity and some gut bacteria with microbiota functions related to hydrogen sulfide production, citrate transport, hemicellulose degradation, aldehyde production and vitamin B12 synthesis.

CONCLUSION

Using new metagenomics methods, our study unveils potential mechanisms by which certain bacteria from the gut microbiota could protect or contribute to the development of NASH and liver fibrosis in NAFLD.

GNS561 acts as a potent anti-fibrotic and pro-fibrolytic agent in liver fibrosis through TGF-β1 inhibition

Background:

Hepatic fibrosis is the result of chronic liver injury that can progress to cirrhosis and lead to liver failure. Nevertheless, there are no anti-fibrotic drugs licensed for human use. Here, we investigated the anti-fibrotic activity of GNS561, a new lysosomotropic molecule with high liver tropism.

Methods:

The anti-fibrotic effect of GNS561 was determined in vitro using LX-2 hepatic stellate cells (HSCs) and primary human HSCs by studying cell viability, activity of caspases 3/7, autophagic flux, cathepsin maturation and activity, HSC activation and transforming growth factor-β1 (TGF-β1) maturation and signaling. The contribution of GNS561 lysosomotropism to its anti-fibrotic activity was assessed by increasing lysosomal pH. The potency of GNS561 on fibrosis was evaluated in vivo in a rat model of diethylnitrosamine-induced liver fibrosis.

Results:

GNS561 significantly decreased cell viability and promoted apoptosis. Disrupting the lysosomal pH gradient impaired its pharmacological effects, suggesting that GNS561 lysosomotropism mediated cell death. GNS561 impaired cathepsin activity, leading to defective TGF-β1 maturation and autophagic processes. Moreover, GNS561 decreased HSC activation and extracellular matrix deposition by downregulating TGF-β1/Smad and mitogen-activated proteine kinase signaling and inducing fibrolysis. Finally, oral administration of GNS561 (15 mg/kg per day) was well tolerated and attenuated diethylnitrosamine-induced liver fibrosis in this rat model (decrease of collagen deposition and of pro-fibrotic markers and increase of fibrolysis).

Conclusion:

GNS561 is a new potent lysosomotropic compound that could represent a valid medicinal option for hepatic fibrosis treatment through both its anti-fibrotic and its pro-fibrolytic effects. In addition, this study provides a rationale for targeting lysosomes as a promising therapeutic strategy in liver fibrosis.

The combination of everolimus and zoledronic acid increase the efficacy of gemcitabine in a mouse model of pancreatic adenocarcinoma

Background

Gemcitabine is a standard treatment for pancreatic adenocarcinoma. Many mechanisms are involved in gemcitabine resistance, such as reduced expression of the human equilibrative nucleoside transporter 1 (hENT1) membrane transporter, deoxycytidine kinase deficiency, and changes in the signal transmission of mitogen-activity protein kinase (MAPK) and the phosphoinositide 3-kinase (PI3K) pathways.

Aim

To evaluate the anti-tumor efficiency of blocking signaling pathways using combined action of gemcitabine, everolimus and zoledronic acid versus gemcitabine alone in a mouse subcutaneous xenograft.

Methods

Implantations of two human pancreatic adenocarcinoma cells lines (PANC1, K-ras mutated and gemcitabine-resistant; and BxPc3, wild-type K-ras and gemcitabine-sensitive) were performed on male athymic nude mice. The mice received different treatments: gemcitabine, gemcitabine plus everolimus, everolimus, gemcitabine plus zoledronic acid, everolimus plus zoledronic acid, or gemcitabine plus everolimus and zoledronic acid, for 28 days. We measured the tumor volume and researched the expression of the biomarkers involved in the signaling pathways or in gemcitabine resistance.

Results

In wild-type K-ras tumors, the combinations of gemcitabine plus everolimus; zoledronic acid plus everolimus; and gemcitabine plus zoledronic acid and everolimus slowed tumor growth, probably due to caspase-3 overexpression and reduced Annexin II expression. In mutated K-ras tumors, gemcitabine plus everolimus and zoledronic acid, and the combination of zoledronic acid and everolimus, decreased tumor volume as compared to gemcitabine alone, inhibiting the ERK feedback loop induced by everolimus.

Conclusion

The combination of zoledronic acid and everolimus has an antitumor effect and could increase gemcitabine efficacy.

Relationship Between the Expression of O6-Methylguanine-DNA Methyltransferase (MGMT) and p53, and the Clinical Response in Metastatic Pancreatic Adenocarcinoma Treated with FOLFIRINOX

BACKGROUND

To date, no predictive biomarker for the efficacy of FOLFIRINOX in metastatic pancreatic adenocarcinoma has been demonstrated. Deficiency in O6-methylguanine-DNA methyltransferase (MGMT) has been associated with a therapeutic response in endocrine tumors of the pancreas and the lack of expression of protein 53 (p53) could interfere with the action of MGMT.

OBJECTIVE

The aim of our study was to assess the prevalence of MGMT and p53 in patients with metastatic pancreatic adenocarcinoma treated with FOLFIRINOX as a first-line treatment and to investigate their association with therapeutic response and survival.

PATIENTS AND METHODS

The immunohistochemical expression of MGMT was recorded as present or absent and the expression of p53 was semi-quantitatively scored in 30 patients with metastatic pancreatic adenocarcinoma, at Angers Hospital in France between September 2011 and June 2015. Clinical and radiologic data were collected retrospectively.

RESULTS

The presence or absence of MGMT expression entailed no significant differences in response rate. Median values of progression-free survival (PFS) and overall survival (OS) were lower in patients with MGMT expression, but sample size is too small to conclude that there is a statistically significant difference. No significant relationship for response rate and PFS was observed in relation with p53 expression. By contrast, patients with a strong tumor expression of p53 had a significantly lower OS compared to patients with no or weak expression of the protein (p = 0.027). There was a positive correlation between the expression of p53 and MGMT (p = 0.08).

CONCLUSIONS

These preliminary findings suggest that for patients treated with FOLFIRINOX as a first-line treatment for metastatic pancreatic adenocarcinoma, the immunohistochemical evaluation of MGMT could not predict the clinical outcome; however, the survival was not significant probably because of the under-powered study (due to small sample size). A strong tumor expression of p53 is associated with a poor prognosis of OS.

The severity of nonalcoholic fatty liver disease is associated with gut dysbiosis and shift in the metabolic function of the gut microbiota

Several animal studies have emphasized the role of gut microbiota in nonalcoholic fatty liver disease (NAFLD). However, data about gut dysbiosis in human NAFLD remain scarce in the literature, especially studies including the whole spectrum of NAFLD lesions. We aimed to evaluate the association between gut dysbiosis and severe NAFLD lesions, that is, nonalcoholic steatohepatitis (NASH) and fibrosis, in a well-characterized population of adult NAFLD. Fifty-seven patients with biopsy-proven NAFLD were enrolled. Taxonomic composition of gut microbiota was determined using 16S ribosomal RNA gene sequencing of stool samples. Thirty patients had F0/F1 fibrosis stage at liver biopsy (10 with NASH), and 27 patients had significant F≥2 fibrosis (25 with NASH). Bacteroides abundance was significantly increased in NASH and F≥2 patients, whereas Prevotella abundance was decreased. Ruminococcus abundance was significantly higher in F≥2 patients. By multivariate analysis, Bacteroides abundance was independently associated with NASH and Ruminococcus with F≥2 fibrosis. Stratification according to the abundance of these two bacteria generated three patient subgroups with increasing severity of NAFLD lesions. Based on imputed metagenomic profiles, Kyoto Encyclopedia of Genes and Genomes pathways significantly related to NASH and fibrosis F≥2 were mostly related to carbohydrate, lipid, and amino acid metabolism.

CONCLUSION

NAFLD severity associates with gut dysbiosis and a shift in metabolic function of the gut microbiota. We identified Bacteroides as independently associated with NASH and Ruminococcus with significant fibrosis. Thus, gut microbiota analysis adds information to classical predictors of NAFLD severity and suggests novel metabolic targets for pre-/probiotics therapies.

The severity of nonalcoholic fatty liver disease is associated with gut dysbiosis and shift in the metabolic function of the gut microbiota

Several animal studies have emphasized the role of gut microbiota in nonalcoholic fatty liver disease (NAFLD). However, data about gut dysbiosis in human NAFLD remain scarce in the literature, especially studies including the whole spectrum of NAFLD lesions. We aimed to evaluate the association between gut dysbiosis and severe NAFLD lesions, that is, nonalcoholic steatohepatitis (NASH) and fibrosis, in a well-characterized population of adult NAFLD. Fifty-seven patients with biopsy-proven NAFLD were enrolled. Taxonomic composition of gut microbiota was determined using 16S ribosomal RNA gene sequencing of stool samples. Thirty patients had F0/F1 fibrosis stage at liver biopsy (10 with NASH), and 27 patients had significant F≥2 fibrosis (25 with NASH). Bacteroides abundance was significantly increased in NASH and F≥2 patients, whereas Prevotella abundance was decreased. Ruminococcus abundance was significantly higher in F≥2 patients. By multivariate analysis, Bacteroides abundance was independently associated with NASH and Ruminococcus with F≥2 fibrosis. Stratification according to the abundance of these two bacteria generated three patient subgroups with increasing severity of NAFLD lesions. Based on imputed metagenomic profiles, Kyoto Encyclopedia of Genes and Genomes pathways significantly related to NASH and fibrosis F≥2 were mostly related to carbohydrate, lipid, and amino acid metabolism.

CONCLUSION

NAFLD severity associates with gut dysbiosis and a shift in metabolic function of the gut microbiota. We identified Bacteroides as independently associated with NASH and Ruminococcus with significant fibrosis. Thus, gut microbiota analysis adds information to classical predictors of NAFLD severity and suggests novel metabolic targets for pre-/probiotics therapies.

Effects of hydrogen sulfide on hemodynamics, inflammatory response and oxidative stress during resuscitated hemorrhagic shock in rats

Introduction

Hydrogen sulfide (H₂S) has been shown to improve survival in rodent models of lethal hemorrhage. Conversely, other authors have reported that inhibition of endogenous H₂S production improves hemodynamics and reduces organ injury after hemorrhagic shock. Since all of these data originate from unresuscitated models and/or the use of a pre-treatment design, we therefore tested the hypothesis that the H₂S donor, sodium hydrosulfide (NaHS), may improve hemodynamics in resuscitated hemorrhagic shock and attenuate oxidative and nitrosative stresses.

Methods

Thirty-two rats were mechanically ventilated and instrumented to measure mean arterial pressure (MAP) and carotid blood flow (CBF). Animals were bled during 60 minutes in order to maintain MAP at 40 ± 2 mm Hg. Ten minutes prior to retransfusion of shed blood, rats randomly received either an intravenous bolus of NaHS (0.2 mg/kg) or vehicle (0.9% NaCl). At the end of the experiment (T = 300 minutes), blood, aorta and heart were harvested for Western blot (inductible Nitric Oxyde Synthase (iNOS), Nuclear factor-κB (NF-κB), phosphorylated Inhibitor κB (P-IκB), Inter-Cellular Adhesion Molecule (I-CAM), Heme oxygenase 1(HO-1), Heme oxygenase 2(HO-2), as well as nuclear respiratory factor 2 (Nrf2)). Nitric oxide (NO) and superoxide anion (O₂^-) were also measured by electron paramagnetic resonance.

Results

At the end of the experiment, control rats exhibited a decrease in MAP which was attenuated by NaHS (65 ± 32 versus 101 ± 17 mmHg, P < 0.05). CBF was better maintained in NaHS-treated rats (1.9 ± 1.6 versus 4.4 ± 1.9 ml/minute P < 0.05). NaHS significantly limited shock-induced metabolic acidosis. NaHS also prevented iNOS expression and NO production in the heart and aorta while significantly reducing NF-kB, P-IκB and I-CAM in the aorta. Compared to the control group, NaHS significantly increased Nrf2, HO-1 and HO-2 and limited O₂^- release in both aorta and heart (P < 0.05).

Conclusions

NaHS is protective against the effects of ischemia reperfusion induced by controlled hemorrhage in rats. NaHS also improves hemodynamics in the early resuscitation phase after hemorrhagic shock, most likely as a result of attenuated oxidative stress. The use of NaHS hence appears promising in limiting the consequences of ischemia reperfusion (IR).

Hemodynamic effects of the early and long-term administration of propranolol in rats with intrahepatic portal hypertension

Background and aims The aims of this study were to evaluate a preventive effect on collateral venous circulation of long-term administration of propranolol in intrahepatic portal hypertensive rats. Methods Eighty-six Sprague-Dawley rats were allocated to two models of hepatic fibrosis, bile duct-ligated (BDL) induced and carbon tetrachloride (CCl(4)) induced. Each model was divided into two groups: one receiving placebo and the other propranolol (75 mg kg(-1) d(-1)). Mean arterial pressure (MAP), heart rate (HR), portal pressure (PP), cardiac index (CI), vascular systemic resistance, and splenorenal shunt blood flow (SRS-BF) were measured in anesthetized rats. Results In the BDL model, no significant hemodynamic changes were observed in the propranolol group compared with the placebo group. In CCl(4)-induced rats, HR (390 +/- 50 vs. 329 +/- 51 beats/min, P = .001), CI (44 +/- 11 vs. 34 +/- 10 ml/min, P = .004), PP (15.4 +/- 3.0 vs. 13.4 +/- 1.9 mmHg, P = .045), and SRS-BF (1.4 +/- 1.1 vs. 1.0 +/- 1.0 ml/min, P = .047) were significantly lower in the propranolol group. Conclusions This study showed that propranolol has a significant hemodynamic effect only in the CCl(4) model and suggested a model-dependent effect of propranolol.

Hemodynamic and antifibrotic effects of a selective liver nitric oxide donor V-PYRRO/NO in bile duct ligated rats

AIM: To assess whether a liver specific nitric oxide (NO) donor (V-PYRRO/NO) would prevent the development of portal hypertension and liver fibrosis in rats with bile duct ligation (BDL).

METHODS: Treatment (placebo or V-PYRRO/NO 0.53 μmol/kg per hour) was administered i.v. to rats 2 d before BDL (D-2) and maintained until the day of hemodynamic measurement (D26). Intra-hepatic NO level was estimated by measuring liver cGMP level. Effects of V-PYRRO/NO on liver fibrosis and lipid peroxidation were also assessed.

RESULTS: Compared to placebo treatment, V-PYRRO/NO improved splanchnic hemodynamics in BDL rats: portal pressure was significantly reduced by 27% (P < 0.0001) and collateral circulation development was almost completely blocked (splenorenal shunt blood flow by 74%, P = 0.007). Moreover, V-PYRRO/NO significantly prevented liver fibrosis development in BDL rats (by 30% in hepatic hydroxyproline content and 31% in the area of fibrosis, P < 0.0001 respectively), this effect being probably due to a decrease in lipid peroxidation by 44% in the hepatic malondialdehyde level (P = 0.007). Interestingly, we observed a significant and expected increase in liver cGMP, without any systemic hemodynamic effects (mean arterial pressure, vascular systemic resistance and cardiac output) in both sham-operated and BDL rats treated with V-PYRRO/NO. This result is in accordance with studies on V-PYRRO/NO metabolism showing a specific release of NO in the liver.

CONCLUSION: Continuous administrations of V-PYRRO/NO in BDL rats improved liver fibrosis and splanchnic hemodynamics without any noxious systemic hemo-dynamic effects.

Low skin temperature impairs the cutaneous vasodilator response to local progressive pressure strain

A pressure-induced vasodilation (PIV) was recently reported as a putative protective response in human skin. Therefore, we examined the influence of skin temperatures on cutaneous blood flow responses to local progressive pressure strain. Ten healthy volunteers were studied at different ambient temperatures leading to low (29.0 +/- 0.3 degrees C), intermediate (32.6 +/- 0.1 degrees C), high (33.9 +/- 0.1 degrees C) and very high (36.0 +/- 0.1 degrees C) skin temperatures. We measured cutaneous blood flow using laser Doppler flowmetry on the foot in response to a local progressive pressure increase of 5.0 mm Hg min(-1). Progressive pressure strain led to an almost linear cutaneous laser Doppler flow decrease at both low and intermediate skin temperatures (-40.1 +/- 6.6% and -31.2 +/- 6.5% from baseline at 30 +/- 1.25 mm Hg), whereas at both high and very high skin temperatures, subjects responded with a transient cutaneous vasodilation (+33.6 +/- 10.6% and +50.6 +/- 15.4% from baseline at 30 +/- 1.25 mm Hg). These findings suggest that high skin temperatures are required for the PIV to develop.

Signal Processing Methodology to Study the Cutaneous Vasodilator Response to a Local External Pressure Application Detected by Laser Doppler Flowmetry

The existence of a cutaneous pressure-induced vasodilation (PIV) has recently been reported. This paper proposes a signal processing methodology to improve PIV knowledge. Temporal variations of laser Doppler signals rhythmic activities are first analyzed on anesthetized rats. The results lead to a method that provides a better PIV understanding.

Evidence for the involvement of VPAC1 and VPAC2 receptors in pressure-induced vasodilatation in rodents

A transient increase in skin blood flow in response to an innocuous local pressure application, defined as pressure-induced vasodilatation (PIV), delays the occurrence of ischaemia, suggesting a protective feature against applied pressure. The PIV response depends on capsaicin-sensitive nerve fibres and calcitonin gene-related peptide (CGRP) has been shown to be involved. In these fibres, CGRP coexists with pituitary adenylate cyclase-activating polypeptide (PACAP). Three distinct receptors mediate the biological effects of PACAP: VPAC1 and VPAC2 receptors binding with the same affinity for PACAP and vasoactive intestinal peptide and PAC1 receptors showing high selectivity for PACAP. Because the receptors are widely expressed in the nervous system and in the skin, we hypothesized that at least one of them is involved in PIV development. To verify this hypothesis, we used [D-p-Cl-Phe(6),Leu(17)]-VIP (nonspecific antagonist of VPAC1/VPAC2 receptors), PG 97-269 (antagonist of VPAC1 receptors), PACAP(6-38) (antagonist of VPAC2/PAC1 receptors) and Max.d.4 (antagonist of PAC1 receptors) in anaesthetized rodents. The blockade of VPAC1/VPAC2, VPAC1 or VPAC2/PAC1 receptors eliminated the PIV response, whereas PAC1 blockade had no effect, demonstrating an involvement of VPAC1/VPAC2 receptors in PIV development. Moreover, endothelium-independent and -dependent vasodilator responses were unchanged by the VPAC1/VPAC2 antagonist. Thus, the absence of a PIV response following VPAC1/VPAC2 blockade cannot be explained by any dysfunction of the vascular smooth muscle or endothelial vasodilator capacity. The involvement of VPAC1/VPAC2 receptors in the development of PIV seems to imply a series relationship in which each receptor type (CGRP, VPAC1, VPAC2) is necessary for the full transmission of the response.

Effect of isoflurane on skin-pressure-induced vasodilation

Since general anesthesia has been shown to attenuate endothelium-dependent vasodilation, it was of interest to verify whether general anesthesia would modify skin vasodilation in response to local pressure application, which is endothelium dependent. To study the effect of general anesthesia on pressure-induced vasodilation development, we examined the effects of low- and high-dose isoflurane. Skin blood flow was measured by laser Doppler flowmetry during 11.1 Pa s(-1) increases in locally applied pressure in anesthetized rats treated with low or high doses of isoflurane. Following the administration of low doses of isoflurane, skin blood flow increased from baseline, with increasing local pressure application (+37 +/- 10% at 2.0 kPa). The increase in skin blood flow was absent in rats treated with high doses (-20 +/- 5% at 2.0 kPa), even when the anesthesia-induced hypotension was corrected by gelofusine infusion (-20 +/- 10% at 2.0 kPa). Whereas sodium-nitroprusside-induced vasodilation developed following low and high doses of isoflurane, acetylcholine-induced vasodilation was impaired with high doses compared to low doses. These data show that pressure-induced vasodilation is abolished with high doses of anesthetics. It is not the anesthesia-induced hypotension, but the depth of anesthesia, which can lead to the disappearance of pressure-induced vasodilation by an alteration in endothelial function.

Effect of head-upright tilt on the dynamic of cerebral autoregulation

The effect of head-upright tilting on the rate of cerebral autoregulation was studied in 12 healthy volunteers (nine men and three women; age range 20-36 years). The dynamics of cerebral autoregulation was determined from the rate of change in cerebral resistance (RoR) during a drop in arterial blood pressure induced by rapid deflation of a 3-min ischaemic thigh cuff and from the ratio of changes in cerebral blood flow and arterial blood pressure (CAI) during the recovery period after the drop in arterial blood pressure. The test was performed supine and with 40 degrees head-up tilt (40 degrees HUT). Middle cerebral artery mean blood flow velocity was measured by transcranial Doppler simultaneously with peripheral arterial blood pressure using Finapres. The thigh cuff deflation induced a larger drop in arterial pressure during 40 degrees HUT [median -28% (25 percentile -36, 75 percentile -19)] than in the supine position [-16% (-23, -15)] (P < 0.01) and in cerebral resistance [supine: -12% (-15, -6); 40 degrees HUT: -15% (-20, -12); P < 0.05]. There was no significant change in RoR [15% s-1 (12, 15)] and CAI [1.9 (1.5, 3.1)] measured supine and during 40 degrees HUT [RoR: 13% s-1 (12, 15); CAI: 1.3 (0.99, 1.9)]. During the drop in arterial pressure, the relationship between arterial blood pressure and systolic peak-to-peak interval exhibited an hysteresis loop, indicating a cardiopulmonary and/or baroreflex activation that was not observed with cerebral resistance. The rate of autoregulation is an intrinsic property of the cerebral vascular bed and is not affected by the vasodilator state in the range of arterial blood pressure changes induced by the tight cuff method.