Oxygen-enriched air reduces breathing gas consumption over air.

Owing to the unfamiliar environment, recreational and professional diving is confronted with several challenges. Usage of self-contained under-water breathing apparatuses during the dive provides the indispensable breathing gas supply for the diver. Instead of air, oxygen-enriched breathing gases (EANx or nitrox) are used with increasing frequency. Unfortunately, their usage implies negative effects because the elevated oxygen partial pressure (pO2) increases oxidative stress. As a result, the increased formation of reactive oxygen species exerts negative effects on the central nervous system, lungs, vasculature and eyes. However, these disadvantages can be avoided if appropriate rules are followed, e.g. a pO2<1.4 bar. EANx breathing gases have, on the other hand, major advantages as they help reducing narcotic nitrogen effects and bubble formation. Several land-based studies had proven a reduced ventilation of exercising subjects if EANx was used instead of air. As breathing gas is the most valuable under-water good, we wanted to translate the on-land results into under-water results. Appropriate studies now demonstrate a novel EANx property as under-water ventilation is also reduced with EANx. In this short communication, we present this additional advantage of EANx-breathing. This benefit seems to be of particular importance as it delays unforeseen running-out-of-gas and thus, contributes to further improving diving safety.

The characterisation of overweight and obese women who are under reporting energy intake during pregnancy.

BACKGROUND: Misreporting of energy intake is common and can contribute to biased estimates of the relationship between diet and disease. Energy intake misreporting is poorly understood in pregnancy and there is limited research assessing characteristics of women who misreport energy intake or changes in misreporting of energy intake across pregnancy. METHODS: An observational study in n = 945 overweight or obese pregnant women receiving standard antenatal care who participated in the LIMIT randomised trial. Diet, physical activity, psychological factors, body image satisfaction and dieting behaviour were assessed at trial entry (10-20 weeks gestation) and 36 weeks gestation. Energy misreporting status was assessed through the ratio of daily energy intake over basal metabolic rate. Logistic regression analyses were conducted with the dependent variable of under reporting of energy intake at study entry or 36 weeks in separate analysis. RESULTS: At study entry and 36 weeks, women were classified as under reporters (38 vs 49.4%), adequate reporters (59.7 vs 49.8%) or over reporters of energy intake (2.3 vs 0.8%) respectively. The prevalence of under reporting energy intake at 36 weeks was higher than at study entry (early pregnancy). Body mass index (BMI) at study entry and 36 weeks and socioeconomic status, dieting behaviour and risk of depression at 36 weeks were independent predictors of under reporting of energy intake. CONCLUSIONS: Under reporting of energy intake was present in over a third of overweight and obese pregnant women and was higher in late compared to early pregnancy. Characteristics such as BMI, socioeconomic status, past dieting behaviour and risk of depression may aid in identifying women who either require support in accurate recording of food intake or attention for improving diet quality. Results were unable to distinguish whether under reporting reflects misreporting or a true restriction of dietary intake. TRIAL REGISTRATION: Australian and New Zealand Clinical Trials Registry ACTRN12607000161426 , registered 9/3/2007.

The mediating effects of gestational diabetes on fetal growth and adiposity in women who are overweight and obese: secondary analysis of the LIMIT randomised trial.

OBJECTIVE: To describe the mediating effect of maternal gestational diabetes on fetal biometry and adiposity measures among overweight or obese pregnant women. DESIGN: Secondary analysis of the LIMIT randomised trial. SETTING: Public hospitals, metropolitan Adelaide, South Australia. POPULATION: Pregnant women with body mass index (BMI) ≥25 kg/m2 and singleton gestation. METHODS: Fetal ultrasound measures at 36 weeks of gestation and baseline BMI from women randomised to the LIMIT trial Standard Care group (n = 912 women) were used to conduct causal mediation analyses using regression-based methods. MAIN OUTCOMES MEASURES: Ultrasound measures of fetal biometry and adiposity at 36 weeks of gestation. RESULTS: Increased maternal BMI was associated with increased measures of fetal head circumference [direct (unmediated) effect 0.18 (95% CI: 0.05-0.31), P = 0.005; total effect 0.17 (95% CI: 0.02-0.31), P = 0.018], abdominal circumference [direct effect 0.26 (95% CI: 0.11-0.41), P = 0.001; total effect 0.26 (95% CI: 0.11-0.42), P = 0.001] and estimated fetal weight [direct effect 0.22 (95% CI: 0.08-0.35), P = 0.002; total effect 0.22 (95% CI: 0.08-0.35), P = 0.002], with no evidence of mediation by treated gestational diabetes. There was no apparent association between maternal BMI and fetal adiposity measures, or mediation by treated gestational diabetes. CONCLUSIONS: We show an important association between increased maternal BMI and fetal growth, not mediated by treated gestational diabetes. There was no association between increased maternal BMI and fetal adiposity measures, or mediation by treated gestational diabetes. Whether these findings represent 'saturation' in the effect of maternal BMI on fetal growth or the effect of treatment of GDM is unclear. FUNDING: This project was funded by a 4-year project grant from the National Health and Medical Research Council (NHMRC), Australia (ID 519240); The Channel 7 Children's Research Foundation, South Australia; and the US National Institutes of Health (R01 HL094235-01). TWEETABLE ABSTRACT: Increased fetal growth associated with maternal obesity is not mediated by gestational diabetes.

Fetal middle cerebral artery Doppler to time intrauterine transfusion in red-cell alloimmunization: a randomized trial.

OBJECTIVES: To evaluate whether Doppler measurement of middle cerebral artery peak systolic velocity (MCA-PSV) for timing subsequent intrauterine transfusions (IUTs) in fetuses that had undergone one IUT for anemia secondary to red-cell alloimmunization is non-inferior to timing based on expected decrease in fetal hematocrit (Hct) or fetal hemoglobin level, without compromising infant hemoglobin at birth. METHODS: This was an international, pragmatic multicenter randomized controlled trial. Women with a pregnancy complicated by fetal anemia secondary to red-cell alloimmunization (due to any antibody alone or in combination), as indicated by the need to undergo a single IUT, were eligible for inclusion. Women were randomized to the determination of timing of further transfusion(s) by Doppler measurement of MCA-PSV (MCA-PSV Group), with a serial upward trend of values >1.5 multiples of the median considered indicative of the need for another IUT, or timing of transfusion by a decrease in fetal Hct (fetal Hct Group), with subsequent IUTs timed according to an estimated fall in fetal Hct of 1% per day or fetal hemoglobin of 0.3 g/dL per day, to maintain fetal hemoglobin level between 7 and 10 g/dL. The primary outcome was infant hemoglobin level measured at birth. RESULTS: A total of 71 women were randomized, 36 to the MCA-PSV Group and 35 to the fetal Hct Group. Median gestational age at randomization was 30.3 weeks, the majority of women were Caucasian and non-smokers, 9.9% of women had Kell alloimmunization, and 14% of fetuses were hydropic at their first IUT. No statistically significant differences between the two treatment groups were observed with regard to mean hemoglobin levels at birth (MCA-PSV Group, 10.36 ± 3.82 g/dL vs fetal Hct Group, 12.03 ± 3.14 g/dL; adjusted mean difference -1.56 g/dL (95% CI, -3.24 to 0.13 g/dL); P = 0.070), or the number of IUTs performed after randomization (MCA-PSV Group, 1.75 ± 1.79 vs fetal Hct Group 1.80 ± 1.32; adjusted relative risk 0.88 (95% CI, 0.61-1.26); P = 0.474). There was no statistically significant difference between the two groups with respect to the risk of adverse infant outcomes related to alloimmunization or procedure-related complications. CONCLUSION: Both Doppler measurement of MCA-PSV and estimation of the decrease in fetal Hct or hemoglobin can be used to determine the timing of second and subsequent IUTs in fetuses with red-cell alloimmunization. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Antenatal dietary and lifestyle advice for women who are overweight or obese and the effect on fetal growth and adiposity: the LIMIT randomised trial.

OBJECTIVE: To report the influence of maternal overweight and obesity on fetal growth and adiposity and effects of an antenatal dietary and lifestyle intervention among these women on measures of fetal growth and adiposity as secondary outcomes of the LIMIT Trial. DESIGN: Randomised controlled trial. SETTING: Public maternity hospitals in metropolitan Adelaide, South Australia. POPULATION: Pregnant women with a body mass index ≥ 25 kg/m(2), and singleton gestation between 10(+0) and 20(+0) weeks. METHODS: Women were randomised to Lifestyle Advice or continued Standard Care and offered two research ultrasound scans at 28 and 36 weeks of gestation. MAIN OUTCOME MEASURES: Ultrasound measures of fetal growth and adiposity. RESULTS: For each fetal body composition parameter, mean Z-scores were substantially higher when compared with population standards. Fetuses of women receiving Lifestyle Advice demonstrated significantly greater mean mid-thigh fat mass, when compared with fetuses of women receiving Standard Care (adjusted difference in means 0.17; 95% CI 0.02-0.32; P = 0.0245). While subscapular fat mass increased between 28 and 36 weeks of gestation in fetuses in both treatment groups, the rate of adipose tissue deposition slowed among fetuses of women receiving Lifestyle Advice, when compared with fetuses of women receiving Standard Care (P = 0.0160). No other significant differences were observed. CONCLUSIONS: These findings provide the first evidence of changes to fetal growth following an antenatal dietary and lifestyle intervention among women who are overweight or obese.

The effect of antenatal lifestyle advice for women who are overweight or obese on secondary measures of neonatal body composition: the LIMIT randomised trial.

OBJECTIVE: To evaluate the effect of providing antenatal dietary and lifestyle advice on neonatal anthropometry, and to determine the inter-observer variability in obtaining anthropometric measurements. DESIGN: Randomised controlled trial. SETTING: Public maternity hospitals across metropolitan Adelaide, South Australia. POPULATION: Pregnant women with a singleton gestation between 10(+0) and 20(+0) weeks, and body mass index (BMI) ≥25 kg/m(2). METHODS: Women were randomised to either Lifestyle Advice (comprehensive dietary and lifestyle intervention over the course of pregnancy including dietary, exercise and behavioural strategies, delivered by a research dietician and research assistants) or continued Standard Care. Analyses were conducted using intention-to-treat principles. MAIN OUTCOME MEASURES: Secondary outcome measures for the trial included assessment of infant body composition using body circumference and skinfold thickness measurements (SFTM), percentage body fat, and bio-impedance analysis of fat-free mass. RESULTS: Anthropometric measurements were obtained from 970 neonates (488 Lifestyle Advice Group, and 482 Standard Care Group). In 394 of these neonates (215 Lifestyle Advice Group, and 179 Standard Care Group) bio-impedance analysis was also obtained. There were no statistically significant differences identified between those neonates born to women receiving Lifestyle Advice and those receiving Standard Care, in terms of body circumference measures, SFTM, percentage body fat, fat mass, or fat-free mass. The intra-class correlation coefficient for SFTM was moderate to excellent (0.55-0.88). CONCLUSIONS: Among neonates born to women who are overweight or obese, anthropometric measures of body composition were not modified by an antenatal dietary and lifestyle intervention.

Antihypertensive and cardioprotective effects of the dipeptide isoleucine-tryptophan and whey protein hydrolysate.

AIMS: Angiotensin-converting enzyme inhibitors are treatment of choice in hypertensive patients. Clinically used inhibitors exhibit a structural similarity to naturally occurring peptides. This study evaluated antihypertensive and cardioprotective effects of ACE-inhibiting peptides derived from food proteins in spontaneously hypertensive rats. METHODS AND RESULTS: Isoleucine-tryptophan (in vitro IC50 for ACE = 0.7 µm), a whey protein hydrolysate containing an augmented fraction of isoleucine-tryptophan, or captopril was given to spontaneously hypertensive rats (n = 60) over 14 weeks. Two further groups, receiving either no supplement (Placebo) or intact whey protein, served as controls. Systolic blood pressure age-dependently increased in the Placebo group, whereas the blood pressure rise was effectively blunted by isoleucine-tryptophan, whey protein hydrolysate and captopril (-42 ± 3, -38 ± 5, -55 ± 4 mm Hg vs. Placebo). At study end, myocardial mass was lower in isoleucine-tryptophan and captopril groups but only partially in the hydrolysate group. Coronary flow reserve (1 µm adenosine) was improved in isoleucine-tryptophan and captopril groups. Plasma ACE activity was significantly decreased in isoleucine-tryptophan, hydrolysate and captopril groups, but in aortic tissue only after isoleucine-tryptophan or captopril treatment. This was associated with lowered expression and activity of matrix metalloproteinase-2. Following isoleucine-tryptophan and captopril treatments, gene expression of renin was significantly increased indicating an active feedback within renin-angiotensin system. CONCLUSION: Whey protein hydrolysate and isoleucine-tryptophan powerfully inhibit plasma ACE resulting in antihypertensive effects. Moreover, isoleucine-tryptophan blunts tissue ACE activity, reduces matrix metalloproteinase-2 activity and improves coronary flow reserve. Thus, whey protein hydrolysate and particularly isoleucine-tryptophan may serve as innovative food additives with the goal of attenuating hypertension.

Experimental hyperhomocysteinaemia: differences in tissue metabolites between homocystine and methionine feeding in a rat model.

AIM: Hyperhomocysteinaemia, diagnosed by serum levels, is regarded as an independent risk indicator for cardiovascular events and is associated with various diseases. The pathomechanisms seem to be partly due to concentrations of homocysteine metabolites and their effect on the cellular transmethylation processes. METHODS: We compared two common models for experimental hyperhomocysteinaemia - high methionine diet and homocystine-enriched diet - regarding their effects on tissue concentrations of homocysteine metabolites. RESULTS: Both diets induced hyperhomocysteinaemia without affecting renal function or vitamine status. However, the tissue contents of homocysteine and its precursors S-adenosyl-homocysteine (SAH) and S-adenosyl-methionine exhibited major differences between both models. Transmethylation potential was elevated 1.7-fold in liver of rats fed the methionine diet, whereas it was unaltered after homocystine-enriched diet. Kidneys of rats fed the methionine diet did not show any alterations in tissue content of homocysteine and its precursors, whereas in the homocystine group homocysteine and the transmethylation inhibitor SAH were elevated from 23.1 +/- 10.4 to 78.0 +/- 26.0 nmol g(-1) and from 106 +/- 4 to 170 +/- 22 nmol g(-1) respectively. Homocysteine tissue content was elevated in the homocystine, but not in the methionine group. CONCLUSIONS: Alterations to homocysteine metabolism are distinct in both models. These findings may explain divergent results, which have been published for these models of hyperhomocysteinaemia and which have resulted in controversial discussions in the past.

Measurement of the endogenous adenosine concentration in humans in vivo: methodological considerations.

The endogenous nucleoside adenosine has profound tissue protective effects in situations of ischaemia or inflammation. Animal studies have shown that various drugs can activate this protective mechanism by interfering with the metabolism of adenosine. Translation of this concept to the clinical arena is hampered by the difficulties encountered in measuring the adenosine concentration, due to the rapid cellular uptake and degradation of adenosine, which continues unabated after blood sampling, and due to the metabolically active endothelial barrier for adenosine. In the current paper, we critically discuss the various methods to measure the adenosine concentration in humans in vivo. For the measurement of circulating adenosine, we conclude that the use of a pharmacological blocker solution (containing inhibitors of the enzymes ecto-5'-nucleotidase, adenosine deaminase, and adenosine kinase, and of the equilibrative nucleoside transporter) and a purpose-built syringe which mixes the blood with this solution immediately at the tip of the needle, seems to be the most sensitive technique. However, for the measurement of adenosine concentrations in interstitial tissue, microdialysis is a suitable method, when used with an appropriate method to determine the recovery of adenosine across the semipermeable membrane to calculate the absolute adenosine concentration. Consistent use of these methods could help in the comparison of the various studies focussed on endogenous adenosine and could help to facilitate the use of drugs that modulate the adenosine concentration to protect tissues in the clinical arena.

Evidence against nitric oxide-quenching effects of chemically defined Maillard reaction products.

Direct interaction between Maillard reaction products (MRPs) and nitric oxide (NO) has been suggested as a pathophysiological mechanism involved in enhanced diabetic arteriosclerosis. Only MRPs without structural characterization have been studied to date. Using chemically synthesized and analytically well defined individual MRPs, we investigated whether the native nitric oxide concentration is directly affected by the Amadori compound N-epsilon-fructosyllysine or the advanced glycation end product N-epsilon-carboxymethyllysine. MRPs were incubated with nitric oxide solution or NO donors (SNAP, spermine-NONOate). Changes in the nitrite (oxidative metabolite of NO) concentration served as indicator of NO availability. MRPs, either as free amino acids or covalently bound to bovine serum albumin (BSA), had no influence on nitrite concentration when using NO solution. In contrast, incubation of the respective NO donors with several covalently protein-bound MRPs as well as native BSA significantly reduced nitrite concentration. If SNAP was co-incubated with EDTA or with Fe (2+) ions, nitrite concentration was decreased or increased, respectively, suggesting a metal ion-dependent alteration of the NO liberation rate. Native NO concentration was not affected by the MRPs tested. Substitution of native NO by NO-releasing substances may be inadequate as a model of NO-MRP interaction, as metal ions or chelators present in compound preparations may affect the NO-liberating mechanism of the donor.

[Hyperthermia and hypothermia. Effects on the cardiovascular system]. / Hyperthermie und Hypothermie. Auswirkungen auf das Herz-Kreislauf-System.

Heat and cold are environmental factors which severely affect the cardiovascular system. An increase in the body core temperature (hyperthermia) from approximately 36.5 to 39 degrees C causes a doubling of the cardiac output. In connection with vasoconstriction in the splanchnic circulation and in skeletal muscle this results in large increases of skin blood flow. The underlying vasodilatation is evoked by reflex regulation of the efferent sympathetic system. While there is a reduction of alpha-adrenergic vasoconstriction, there is also evidence for active sympathetic cholinergic and nitric oxide-dependent vasodilatation. In the presence of risk factors, e.g. age and diabetes, the circulatory adaptation to heat stress may be compromised. During a reduction of the core temperature (hypothermia) there is a reflex adrenergic vasoconstriction (noradrenalin) of the skin. Cardiac output falls below a core temperature of 34 degrees C due to increasing bradycardia. The reflex vasoconstriction following cold exposure may be aggravated at higher ages, which may cause steeper increases of arterial blood pressure. Due to the reflex nature, the regulatory processes are severely compromised during anaesthesia.

Insulin effects on myocardial function and bioenergetics in L-bupivacaine toxicity in the isolated rat heart.

BACKGROUND AND OBJECTIVES: A positive effect of insulin-glucose-potassium infusion in severe bupivacaine-induced cardiovascular collapse has been described in vivo. It has been speculated that an antagonistic influence of insulin on sodium channel inhibition, transient outward potassium current, calcium-dependent adenosine triphosphatase or even improved myocardial energetics may be responsible for this effect. Using an isolated heart model, we therefore sought to further elucidate insulin effects in l-bupivacaine-induced myocardial depression. METHODS: An isolated rat heart constant-pressure perfused, non-recirculating Langendorff preparation was used. Hearts were exposed to l-bupivacaine 5 microg mL(-1) and insulin 10 mIU mL(-1). Heart rate, systolic pressure, the first derivative of left ventricular pressure (+dP/dt), coronary flow, double product, PR and QRS intervals were recorded. Hearts were freeze-clamped and high-performance liquid chromatography measurement of the total adenine nucleotide pool was performed. RESULTS: l-Bupivacaine led to a significant decrease in heart rate, +dP/dt, systolic pressure, coronary flow and double product, and to an increase in PR and QRS. Insulin exerted a positive inotropic effect, significantly augmenting +dP/dt and systolic pressure in both l-bupivacaine-treated and control hearts. Heart rate, coronary flow, total adenine nucleotides, PR and QRS were not significantly changed by the insulin intervention. CONCLUSION: Insulin did not have a significant effect on total adenine nucleotides in controls and in l-bupivacaine-treated hearts. However, it does exert a positive inotropic action in bupivacaine-induced myocardial depression. We conclude that the positive effect of insulin application lies in positive inotropic action and not in changes in total adenine nucleotides.

Metabolic coronary flow regulation--current concepts.

The concept of metabolic coronary flow control provides a rationale for the close relationship of coronary flow and myocardial metabolic rate of oxygen. The concept is based on the presence of an oxygen (metabolic) sensor coupled functionally to effector mechanisms, which control vascular tone. Four modes of metabolic control models have been proposed. 1) An oxygen sensor located in the wall of coronary vessels coupling to smooth muscle tension. Endothelial prostaglandin production may support this concept. 2) An oxygen sensing mechanism located in the myocardium and changing metabolism in response to changes of local pO(2). Adenosine is a metabolite produced at an accelerated rate when the supply-to-demand relationship for oxygen falls. 3) Sensing of oxygen turnover may be achieved by carbon dioxide production and, potentially, by mitochondrial production of reactive oxygen species. 4) The red blood cell might serve as an oxygen sensor in response to changes of haemoglobin oxygenation. A potential link to vessel relaxation may be red cell ATP release. A large body of experimental evidence supports the notion that K(ATP) channels play a significant role causing smooth muscle hyper-polarization. However, additional yet unknown effector mechanisms must exist, because block of K(ATP) channels does not lead to deterioration of coronary flow control under conditions of exercise. Thus, although several lines of evidence show that metabolic flow regulation is effective during hypoxic conditions,mechanisms mediating normoxic metabolic flow control still await further clarification.

The influence of downstream arterial perfusion parameters on doppler pulsatility index and resistance index in an in-vitro perfusion model.

BACKGROUND: To investigate in vitro how downstream perfusion parameters influence pulsatility index (PI), resistance index (RI) and their constituting Doppler velocities. MATERIALS AND METHODS: We analyzed the influence of resistance, compliance, reflection coefficient and input impedance on PI and RI in an in-vitro model of arterial flow. RESULTS: The nominators of PI and RI were determined by resistance. The numerators were determined by compliance and by the reflection coefficient. There were close relationships of PI and RI with resistance under the condition of constant compliance, but not when compliance was variable. CONCLUSION: PI and RI consist of velocity terms which are independently influenced by different parameters of impedance: compliance, reflection coefficient and resistance. These findings explain the contradictory results reported for the relationship between the indices and peripheral resistance in studies where compliance and reflection effects were not considered.

Myocardial ferritin content is closely related to the degree of ischaemia.

AIM: Ferritin acts as an iron scavenger and thereby may reduce iron catalysed oxygen radical production during reperfusion injury. We tested the hypothesis that the myocardial ferritin concentration is enhanced during ischaemia in proportion to the blood flow reduction. METHODS: In 10 anaesthetized, open chest Beagle dogs (six controls and four with 60 min coronary occlusion) regional myocardial blood flow (RMBF) was measured with the tracer microsphere technique and ferritin was determined in samples with an average mass of 125 mg (124-256 samples per heart). RESULTS: Under physiological conditions heart rate was 88 +/- 12 bpm, mean aortic pressure 98 +/- 8 mmHg, and RMBF 0.99 +/- 0.33 mL min-1 g-1. Data did not differ between experimental groups, P > 0.05. In the control group regional myocardial ferritin concentration averaged 11.76 +/- 3.54 ng mg-1 protein and exhibited a significant blood flow independent heterogeneity (CV(biol) = 0.27). However, between low and high flow areas (relative flow <0.5 and >1.5 times the average RMBF, respectively) no significant difference in ferritin was found, P > 0.05. In four experiments, in which regional blood flow was reduced by 40% to 0.60 +/- 0.23 mL min-1 g-1, regional ferritin content was significantly higher as compared with the control group 27.95 +/- 6.16 vs. 11.76 +/- 3.54 ng mg-1 protein, respectively. An inverse relationship was observed between ferritin and RMBF, r = -0.61, P < 0.001. Thus, a reduction of RMBF of >80% was associated with a 2.75-fold increase of the average ferritin content. Between subepicardium and subendocardium no significant difference in ferritin content was observed, neither in the control group nor in the group with induced ischaemia. Regions with control low and high flow responded similarly to the coronary constriction with regard to the local ferritin concentration: 27.88 +/- 15.22 vs. 30.10 +/- 14.91 ng mg-1, P > 0.05, respectively. A data analysis using Baye's theorem indicated that sensitivities were 0.28 and 0.94 for average flow reductions of 5 and 93%. In additional in vitro measurements (ischaemic incubation at 37 degrees C) myocardial ferritin content increased almost linearly within the first 60 min of incubation and thereafter remained unchanged. CONCLUSIONS: (1). Local physiological ferritin content in myocardium is heterogeneous and unrelated to control myocardial blood flow. (2). Ischaemia results in an enhanced ferritin content in relation to the degree of ischaemia. (3). The increase of myocardial ferritin requires a severe degree of ischaemia.

Plasma nitrite rather than nitrate reflects regional endothelial nitric oxide synthase activity but lacks intrinsic vasodilator action.

The plasma level of NO(x), i.e., the sum of NO(2)- and NO(3)-, is frequently used to assess NO bioavailability in vivo. However, little is known about the kinetics of NO conversion to these metabolites under physiological conditions. Moreover, plasma nitrite recently has been proposed to represent a delivery source for intravascular NO. We therefore sought to investigate in humans whether changes in NO(x) concentration are a reliable marker for endothelial NO production and whether physiological concentrations of nitrite are vasoactive. NO(2)- and NO(3)- concentrations were measured in blood sampled from the antecubital vein and brachial artery of 24 healthy volunteers. No significant arterial-venous gradient was observed for either NO(2)- or NO(3)-. Endothelial NO synthase (eNOS) stimulation with acetylcholine (1-10 microg/min) dose-dependently augmented venous NO(2)- levels by maximally 71%. This effect was paralleled by an almost 4-fold increase in forearm blood flow (FBF), whereas an equieffective dose of papaverine produced no change in venous NO(2)-. Intraarterial infusion of NO(2)- had no effect on FBF. NOS inhibition (N(G)-monomethyl-l-arginine; 4-12 micromol/min) dose-dependently reduced basal NO(2)- and FBF and blunted acetylcholine-induced vasodilation and NO release by more than 80% and 90%, respectively. In contrast, venous NO(3)- and total NO(x) remained unchanged as did systemic arterial NO(2)- and NO(3)- levels during all these interventions. FBF and NO release showed a positive association (r = 0.85; P < 0.001). These results contradict the current paradigm that plasma NO(3)- and/or total NO(x) are generally useful markers of endogenous NO production and demonstrate that only NO(2)- reflects acute changes in regional eNOS activity. Our results further demonstrate that physiological levels of nitrite are vasodilator-inactive.

Spatial heterogeneity of energy turnover in the heart.

Local myocardial blood flow varies substantially in spite of a rather homogeneous morphology. To further elucidate this paradox, the spatial heterogeneity of tricarboxylic acid cycle turnover (J(TCA), micromol min(-1) g(-1)) and coronary flow was assessed at a high spatial resolution (6x6x6 mm3) in the open chest dog. Local flow differed more than 2.5-fold between individual samples in each heart (n=7). Out of 1,500 myocardial samples, 1/10 received less than 60% and another 1/10 more than 138% of the normalized mean. In low- and high-flow samples, pyruvate uptake and metabolism were analyzed by 13C NMR spectroscopy. Following [3-13C]pyruvate infusion (2 mM, 12 min), glutamate [4-13C]/[3-13C] was significantly greater in low-flow (2.21+/-0.75, 40 samples) than in high-flow (1.64+/-0.49, 39 samples) areas. This suggests that there are major differences in J(TCA). Glutamate, citrate and lactate content positively correlated with flow. Anaplerotic pathways contributed a fraction similar to J(TCA) in low- and high-flow areas, as demonstrated by isotopomer analysis after 60 min of [3-13C]pyruvate application. Mathematical model analysis of NMR data and relevant pool sizes revealed that J(TCA) and thus myocardial oxygen consumption (MVO2) in high-flow areas exceed values in low-flow areas at least threefold. Thus low and high metabolic states normally coexist within the well perfused heart, suggesting that there is considerable spatial heterogeneity of cardiac energy generation and work.

Screening of plasma homocysteine in peripheral arterial disease.

BACKGROUND: Homocysteine (HCY) was recently established as an independent risk factor for atherosclerosis. The prevalence of an increased homocysteine plasma concentration was reported to be up to 6-fold higher in patients with different locations of arterial occlusive diseases. AIM: This study evaluated critically whether the total HCY plasma concentration can be used as a screening marker for peripheral arterial disease in the general population. METHODS: Study subjects were 40 patients (51.8 +/- 7.5 years) with symptomatic lower limb peripheral arterial disease (PAD) (stage II) and 40 healthy volunteers (45.6 +/- 6.8 years, P< 0.05 vs PAD). The percentage of women in both groups was 30%. The plasma HCY concentration was determined by using derivatization techniques and subsequent fluorescence high-performance liquid chromatography. RESULTS: Total plasma HCY concentration was significantly higher in the PAD group than in controls (14.90 +/- 5.78 microM vs 11.32 +/- 2.95 microM, respectively, P< 0.001). Also, the coefficient of variation of plasma HCY in PAD was significantly higher than that in the control group, 0.38 vs 0.25 (P< 0.001), respectively, reflecting greater interindividual differences. In addition to a PAD-specific effect, the plasma HCY concentration was also dependent on gender and age (both P< 0.05). Sensitivity and specificity of HCY as a marker of PAD were 0.3 and 0.95, respectively. Positive and negative predictive values were 0.85 and 0.42, respectively. CONCLUSIONS: From these data it is concluded that HCY metabolism may have an influence on the development of PAD in one-third of all patients with PAD, and that total plasma HCY concentration may not be suited as a screening test for PAD in the general population but rather serves as a monitoring marker in certain risk groups.

Heterogeneity of metabolic parameters in the left ventricular myocardium and its relation to local blood flow.

It is well established that myocardial blood flow is heterogeneous on the local level. During recent years comprehensive studies have been undertaken to assess the relation between myocardial metabolism and spatial blood flow heterogeneity. Based on the type of measurements two major groups of studies have been performed: enzyme activity and tissue metabolite level assessments. Enzyme activity measurements have provided only limited insight into the coupling of local metabolism and flow. This is probably due to the fact that, in addition to estimated Vmax values, local substrate affinity (Km values) and substrate concentrations affect the metabolite fluxes. However, the latter two variables remain normally unknown. In contrast, valuable insight has been obtained concerning flow-metabolism matching from tissue metabolite measurements, especially when connected with mathematical model analyses. The latter permitted the calculation of metabolic flux rates (e.g., production of oxidation water, citric acid cycle flux, glucose uptake, fatty acid uptake) or the translation of the metabolic indexes into physiologically meaningful local metabolite concentrations (e.g., free cytosolic adenosine). The bottom line of the studies reported to date is that the broad range of myocardial flows observed under resting control conditions correlates with local metabolism possibly affected by spatial differences in adrenergic stimulation. Thus, high flow samples exhibit a higher oxidative metabolism than low flow samples. As a result the flow threshold below which local myocardial ischemia ensues is higher in control high flow samples. The importance of these findings with respect to local flow-metabolism matching is underlined by the finding that the probability of developing an infarction following ischemia/reperfusion is related to the functional state of the myocardium under control conditions, i.e., the local level of flow-metabolism matching.