Arteriovenous Sampling Research Articles

Retained Metabolic Flexibility of the Failing Human Heart.

The failing heart is traditionally described as metabolically inflexible and oxygen starved, causing energetic deficit and contractile dysfunction. Current metabolic modulator therapies aim to increase glucose oxidation to increase oxygen efficiency of adenosine triphosphate production, with mixed results. To investigate metabolic flexibility and oxygen delivery in the failing heart, 20 patients with nonischemic heart failure with reduced ejection fraction (left ventricular ejection fraction 34.9±9.1) underwent separate infusions of insulin+glucose infusion (I+G) or Intralipid infusion. We used cardiovascular magnetic resonance to assess cardiac function and measured energetics using phosphorus-31 magnetic resonance spectroscopy. To investigate the effects of these infusions on cardiac substrate use, function, and myocardial oxygen uptake (MVo2), invasive arteriovenous sampling and pressure-volume loops were performed (n=9). At rest, we found that the heart had considerable metabolic flexibility. During I+G, cardiac glucose uptake and oxidation were predominant (70±14% total energy substrate for adenosine triphosphate production versus 17±16% for Intralipid; P=0.002); however, no change in cardiac function was seen relative to basal conditions. In contrast, during Intralipid infusion, cardiac long-chain fatty acid (LCFA) delivery, uptake, LCFA acylcarnitine production, and fatty acid oxidation were all increased (LCFA 73±17% of total substrate versus 19±26% total during I+G; P=0.009). Myocardial energetics were better with Intralipid compared with I+G (phosphocreatine/adenosine triphosphate 1.86±0.25 versus 2.01±0.33; P=0.02), and systolic and diastolic function were improved (LVEF 34.9±9.1 baseline, 33.7±8.2 I+G, 39.9±9.3 Intralipid; P<0.001). During increased cardiac workload, LCFA uptake and oxidation were again increased during both infusions. There was no evidence of systolic dysfunction or lactate efflux at 65% maximal heart rate, suggesting that a metabolic switch to fat did not cause clinically meaningful ischemic metabolism. Our findings show that even in nonischemic heart failure with reduced ejection fraction with severely impaired systolic function, significant cardiac metabolic flexibility is retained, including the ability to alter substrate use to match both arterial supply and changes in workload. Increasing LCFA uptake and oxidation is associated with improved myocardial energetics and contractility. Together, these findings challenge aspects of the rationale underlying existing metabolic therapies for heart failure and suggest that strategies promoting fatty acid oxidation may form the basis for future therapies.

Surgical approach to patients with primary aldosteronism.

Primary hyperaldosteronism (PA) is one of the most common causes of hypertension that is amenable to surgical cure. Once a patient has a biochemical diagnosis of PA, workup should proceed with tumor lateralization to determine whether the patient has unilateral or bilateral disease. Tumor lateralization can be done with noninvasive imaging such as a CT or MRI. However, in older patients or in patients with non-lateralizing imaging, arteriovenous sampling (AVS) should be considered. If the patient has confirmed unilateral disease, options for surgical intervention include laparoscopic or, less commonly, open. Laparoscopic adrenalectomy for PA has been shown to be a safe and effective procedure that is associated with less morbidity compared to open adrenalectomy. Patients can either undergo a laparoscopic transabdominal adrenalectomy via a lateral (most common) or anterior approach or a retroperitoneoscopic adrenalectomy via a posterior approach. The majority of patients have complete biochemical success, defined as normalization of plasma aldosterone, renin and potassium levels and appropriate suppression with stimulation tests. Less than half of patients have complete clinical success, defined as normotensive with no antihypertensive medications. However, the majority of patients who do not have complete clinical success will have some improvement in their blood pressure and/or are able to decrease the number of antihypertensive medications that they require.

Pre‐clinical identification of potential molecular diagnostic biomarkers of secondary ischemia in microvascular fasciocutaneous flaps

Compromise of surgical microvascular flaps due to acute or late post‐operative circulatory complications remains a significant clinical problem worldwide. Timely detection of vessel occlusion may salvage a flap from necrosis, but monitoring of physical flap appearance is not always feasible and the etiology of compromise is hard to identify. Here we used a translational laboratory animal model of abdominal wall repair and Affymetrix gene expression microarray platform to reveal the molecular tissue and wound fluid markers of the arterial (AO), venous (VO) or mixed arterio‐venous (AVO) thrombosis of the pedicled flap in vivo. Bilateral 7×2.5cm epigastric flaps were raised in ~12 month old male and female Sprague‐Dawley retired breeder rats. Baseline fasciocutaneous tissue sample biopsies were obtained from the upper abdominal quadrants of sixteen sex‐matched rats prior to flap elevation. All flaps were then subjected to primary ischemia (PI), which was induced for 4 h by temporary clamping of superficial inferior epigastric artery (SIEA) and vein (SIEV) vessels to mimic free tissue transfer and anastomosis. Normoxic control (NC) samples were obtained from flaps after 24 h of non‐obstructed reperfusion. AO, VO or AVO samples were retrieved from paired flaps undergoing secondary ischemia (SI), in which SIEA, SIEV or both vessels were ligated for 4 h following 20 h of reperfusion. Total RNA was isolated from individual animal samples (n=8/gender group) and then pooled at equal concentrations prior to assessment of RNA quality. We observed 5011 (in males) and 4457 (in females) differentially expressed genes (DEGs) that demonstrated more than 2‐fold change in NC versus baseline conditions. There were 1403, 1643 and 2351 DEGs in male AO, VO and AVO flaps when compared to NC. In females, AO, VO and AVO‐associated DEG numbers were smaller (1074, 828 and 1518, respectively). Independently of gender, downregulation of keratinocyte‐specific small proline‐rich protein 4 (Sprr4) and upregulation of ankyrin repeat domain 37 (Ankrd37), previously identified as a target of hypoxia inducible factor‐1 (HIF‐1) gene, was significantly associated with the arterial SI. Venous SI was characterized by overexpression of major hematopoietic cell proteins (Gypa, Slc4a1, Lgals5, Hbq1b, Hemgn, Add2, Alas2), anti‐inflammatory bioactive lipid mediator arachidonate 15‐lipoxygenase (Alox15), CDK‐activating dual specificity phosphatase Cdc25B and Neuropeptide Y (Npy) ‐ an important neurotransmitter in skin vascular conductance. Upregulation of the latter genes distinguished VO not only from AO, but also from AVO. Finally, we identified 58 “master” DEGs shared by both genders that were present in SI regardless of its type (AO, VO, and AVO). Of these, “first‐tier” proteins included leukemia inhibitory factor (LIF), Depp1 autophagy regulator, adrenomedullin (Adm), growth arrest and DNA‐damage‐inducible, gamma (Gadd45g) and DNA‐damage‐inducible transcript 4 (Ddit4). Change in selected gene expression was further confirmed at protein or mRNA level by Western blotting or RT‐PCR analyses. In summary, our data revealed several SI‐associated diagnostic biomarkers that merit further investigation and, ultimately, validation in the human clinical trial setting.Support or Funding InformationThis work has been funded and supported by the Department of Otolaryngology ‐ Head &amp; Neck Surgery, Thomas Jefferson UniversityThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Dietary Fructose Metabolism By Splanchnic Organs: Size Matters

The initial metabolism of fructose is thought to primarily take place in the liver. Using stable isotope labeling combined with tissue and arterio-venous sampling, Jang etal. (2018) demonstrate that in mice, the small intestine is the primary site of fructose metabolism. This raises important questions about fructose handling in humans.

Metabolomics of Chronic Kidney Disease Progression: A Case-Control Analysis in the Chronic Renal Insufficiency Cohort Study

Background: Whereas several longitudinal metabolomics studies have been conducted in individuals with normal estimated glomerular filtration rate (eGFR) at baseline, disease progression among individuals with established chronic kidney disease (CKD) has not been rigorously examined. Methods: We performed a nested case-control study of rapid CKD progression in the Chronic Renal Insufficiency Cohort Study, profiling baseline plasma from 200 individuals each with eGFR slope <-3 ml/min/1.73 m²/year (cases) or between -1 and +1 ml/min/1.73 m²/year (controls), matched on baseline eGFR and proteinuria. To directly assess how the kidney modulates circulating metabolites, we profiled plasma from the aorta and renal vein of 25 hospital-based individuals. Results: At baseline, cases and controls had a mean eGFR of 41.7 ± 13.3 and 45.0 ± 14.5 ml/min/1.73 m², respectively. Ten plasma metabolites were nominally associated with CKD progression in logistic regression models adjusted for age, sex, race/ethnicity, hypertension, systolic and diastolic blood pressure, diabetes, eGFR and proteinuria; no metabolite achieved the Bonferroni-adjusted significance threshold (p < 0.0003). In a cross-sectional analysis, all 6 of the metabolites that were higher in cases than controls were significantly associated with eGFR at baseline. By contrast, threonine, methionine and arginine were lower in cases than in controls and had no association with baseline eGFR. Furthermore, in the hospital-based cohort that underwent renal arteriovenous sampling, these 3 metabolites were net released from the kidney. Combining these metabolites into a panel of markers further strengthened their association with CKD progression. Conclusion: Our results motivate interest in arginine, methionine and threonine as potential indicators of renal metabolic function and markers of renal prognosis.

Mass spectrometry and its evolving role in assessing tissue specific steroid metabolism.

Glucocorticoid hormones play vital roles in regulating diverse biological processes in health and disease. Tissue levels are regulated by enzymes which activate and inactivate hormones. The enzyme, 11β-hydroxysteroid dehydrogenase type1 (11βHSD1), in particular, has been identified as a potential drug target; inhibiting this enzyme attenuates glucocorticoid action by lowering local levels of active hormone. A variety of mass spectrometric approaches have been developed to characterize this enzymeinvivo Endogenous glucocorticoids and their metabolites can be profiled in urine by GC-MS and circulating steroids are now more commonly quantified by liquid chromatography tandem mass spectrometry. Tracer dilution studies have allowed rates of generation of glucocorticoids by the enzyme to be distinguished from hormone generated directly by the adrenal glands and, in combination with arterio-venous (AV) sampling, rates of production by specific tissues have been quantified. This has allowed the contribution of liver, adipose, muscle and brain to cortisol production in metabolic disease and hence prioritized drug targets. Most recently MS imaging in combination with on-tissue derivatization has been developed to profile oxo-steroids in tissue sections, allowing molecular maps to be generated across complex tissues, where regional functions are important. The review provides a synopsis of how measurement of steroids by MS has evolved with technological advances and this has provided insight into the dynamic turnover of glucocorticoidsinvivo, highlighting the milestones that have advanced the field and identifying the remaining challenges for researchers, in terms of analytical chemistry and endocrine physiology and biochemistry.

Central venous blood gas and acid-base status in conscious dogs and cats.

To determine the reference level of central venous oxygen saturation (ScvO2) and clinical efficacy of central venous blood gas analysis, partial pressures of oxygen and carbon dioxide, pH, oxygen saturation, base excess (B.E.) and HCO3 concentration were compared between simultaneously obtained central venous and arterial blood samples from conscious healthy 6 dogs and 5 cats. Comparisons between arteriovenous samples were performed by a paired t-test and Bland-Altman analysis. Between arteriovenous samples, B.E. showed good agreement, but there were significant differences in other parameters in the dogs, and no good agreement was detected in cats. The ScvO2 in dogs and cats were 82.3 ± 3.5 and 62.4 ± 13.5%, respectively. Central venous blood gas analysis is indispensable, especially in cats.

11β-Hydroxysteroid dehydrogenase activity in the brain does not contribute to systemic interconversion of cortisol and cortisone in healthy men.

Context and Objective:11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) catalyses regeneration of cortisol in liver, adipose tissue, and skeletal muscle, making a substantial contribution to circulating cortisol as demonstrated in humans by combining stable isotope tracer infusion with arteriovenous sampling. In the brain, 11βHSD1 is a potential therapeutic target implicated in age-associated cognitive dysfunction. We aimed to quantify brain 11βHSD1 activity, both to assess its contribution to systemic cortisol/cortisone turnover and to develop a tool for measuring 11βHSD1 in dementia and following administration of 11βHSD1 inhibitors.Design, Setting, and Participants:With ethical approval and informed consent, 8 healthy men aged 38.1 years (sd 16.5) underwent an ECG-gated phase-contrast magnetic resonance scan to quantify internal jugular vein blood flow and were infused with 1,2 [2H]2-cortisone and 9,11,12,12 [2H]4-cortisol for 3 h before samples were obtained from the internal jugular vein and an arterialized hand vein. Steroids were quantified by liquid chromatography-tandem mass spectrometry.Main Outcome Measures and Results:Steady state tracer enrichments were achieved and systemic indices of cortisol/cortisone interconversion were consistent with previous studies in healthy men. However, there was no measurable release or production of cortisol, 9,12,12 [2H]3-cortisol or cortisone into the internal jugular vein.Conclusions:Although cerebral 11βHSD1 reductase activity may be greater in cognitively impaired patients, in healthy men any contribution of 11βHSD1 in the brain to systemic cortisol/cortisone turnover is negligible. The influence of 11βHSD1 in the brain is likely confined to subregions, notably the hippocampus. Alternative approaches are required to quantify pharmacodynamics effects of 11βHSD1 inhibitors in the human brain.

Efficacy of increased resistant starch consumption in human type 2 diabetes

Resistant starch (RS) has been shown to beneficially affect insulin sensitivity in healthy individuals and those with metabolic syndrome, but its effects on human type 2 diabetes (T2DM) are unknown. This study aimed to determine the effects of increased RS consumption on insulin sensitivity and glucose control and changes in postprandial metabolites and body fat in T2DM. Seventeen individuals with well-controlled T2DM (HbA1c 46.6±2 mmol/mol) consumed, in a random order, either 40 g of type 2 RS (HAM-RS2) or a placebo, daily for 12 weeks with a 12-week washout period in between. At the end of each intervention period, participants attended for three metabolic investigations: a two-step euglycemic–hyperinsulinemic clamp combined with an infusion of [6,6-2H2] glucose, a meal tolerance test (MTT) with arterio-venous sampling across the forearm, and whole-body imaging. HAM-RS2 resulted in significantly lower postprandial glucose concentrations (P=0.045) and a trend for greater glucose uptake across the forearm muscle (P=0.077); however, there was no effect of HAM-RS2 on hepatic or peripheral insulin sensitivity, or on HbA1c. Fasting non-esterified fatty acid (NEFA) concentrations were significantly lower (P=0.004) and NEFA suppression was greater during the clamp with HAM-RS2 (P=0.001). Fasting triglyceride (TG) concentrations and soleus intramuscular TG concentrations were significantly higher following the consumption of HAM-RS2 (P=0.039 and P=0.027 respectively). Although fasting GLP1 concentrations were significantly lower following HAM-RS2 consumption (P=0.049), postprandial GLP1 excursions during the MTT were significantly greater (P=0.009). HAM-RS2 did not improve tissue insulin sensitivity in well-controlled T2DM, but demonstrated beneficial effects on meal handling, possibly due to higher postprandial GLP1.

Increased net muscle protein balance in response to simultaneous and separate ingestion of carbohydrate and essential amino acids following resistance exercise

Relative to essential amino acids (EAAs), carbohydrate (CHO) ingestion stimulates a delayed response of net muscle protein balance (NBAL). We investigated if staggered ingestion of CHO and EAA would superimpose the response of NBAL following resistance exercise, thus resulting in maximal anabolic stimulation. Eight recreationally trained subjects completed 2 trials: combined (COMB - drink 1, CHO+EAA; drink 2, placebo) and separated (SEP - drink 1, CHO; drink 2, EAA) post-exercise ingestion of CHO and EAA. Drink 1 was administered 1 h following an acute exercise bout and was followed 1 h later by drink 2. A primed, continuous infusion of l-[ring-(13)C6]-phenylalanine was combined with femoral arteriovenous sampling and muscle biopsies for the determination of muscle protein kinetics. Arterial amino acid concentrations increased following ingestion of EAA in both conditions. No difference between conditions was observed for phenylalanine delivery to the leg (COMB: 167 ± 23 μmol·min(-1)·(100 mL leg vol)(-1) × 6 h; SEP: 167 ± 21 μmol·min(-1)·(100 mL leg vol)(-1) × 6 h, P > 0.05). In the first hour following ingestion of the drink containing EAA, phenylalanine uptake was 50% greater for the SEP trial than the COMB trial. However, phenylalanine uptake was similar for COMB (110 ± 19 mg) and SEP (117 ± 24 mg) over the 6 h period. These data suggest that whereas separation of CHO and EAA ingestion following exercise may have a transient physiological impact on NBAL, this response is not reflected over a longer period. Thus, separation of CHO and EAA ingestion is unnecessary to optimize post-exercise muscle protein metabolism.

Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise

Timing of nutrient ingestion has been demonstrated to influence the anabolic response of muscle following exercise. Previously, we demonstrated that net amino acid uptake was greater when free essential amino acids plus carbohydrates were ingested before resistance exercise rather than following exercise. However, it is unclear if ingestion of whole proteins before exercise would stimulate a superior response compared with following exercise. This study was designed to examine the response of muscle protein balance to ingestion of whey proteins both before and following resistance exercise. Healthy volunteers were randomly assigned to one of two groups. A solution of whey proteins was consumed either immediately before exercise (PRE; n = 8) or immediately following exercise (POST; n = 9). Each subject performed 10 sets of 8 repetitions of leg extension exercise. Phenylalanine concentrations were measured in femoral arteriovenous samples to determine balance across the leg. Arterial amino acid concentrations were elevated by approximately 50%, and net amino acid balance switched from negative to positive following ingestion of proteins at either time. Amino acid uptake was not significantly different between PRE and POST when calculated from the beginning of exercise (67 +/- 22 and 27 +/- 10 for PRE and POST, respectively) or from the ingestion of each drink (60 +/- 17 and 63 +/- 15 for PRE and POST, respectively). Thus the response of net muscle protein balance to timing of intact protein ingestion does not respond as does that of the combination of free amino acids and carbohydrate.

Contributions of working muscle to whole body lipid metabolism are altered by exercise intensity and training

To evaluate the contribution of working muscle to whole body lipid oxidation, we examined the effects of exercise intensity and endurance training (9 wk, 5 days/wk, 1 h, 75% Vo(2 peak)) on whole body and leg free fatty acid (FFA) kinetics in eight male subjects (26 +/- 1 yr, means +/- SE). Two pretraining trials [45 and 65% Vo(2 max) (45UT, 65UT)] and two posttraining trials [65% of pretraining Vo(2 peak) (ABT), and 65% of posttraining Vo(2 peak) (RLT)] were performed using [1-(13)C]palmitate infusion and femoral arteriovenous sampling. Training increased Vo(2 peak) by 15% (45.2 +/- 1.2 to 52.0 +/- 1.8 ml.kg(-1).min(-1), P < 0.05). Muscle FFA fractional extraction was lower during exercise (EX) compared with rest regardless of workload or training status ( approximately 20 vs. 48%, P < 0.05). Two-leg net FFA balance increased from net release at rest ( approximately -36 micromol/min) to net uptake during EX for 45UT (179 +/- 75), ABT (236 +/- 63), and RLT (136 +/- 110) (P < 0.05), but not 65UT (51 +/- 127). Leg FFA tracer measured uptake was higher during EX than rest for all trials and greater during posttraining in RLT (716 +/- 173 micromol/min) compared with pretraining (45UT 450 +/- 80, 65UT 461 +/- 72, P < 0.05). Leg muscle lipid oxidation increased with training in ABT (730 +/- 163 micromol/min) vs. 65UT (187 +/- 94, P < 0.05). Leg muscle lipid oxidation represented approximately 62 and 30% of whole body lipid oxidation at lower and higher relative intensities, respectively. In summary, training can increase working muscle tracer measured FFA uptake and lipid oxidation for a given power output, but both before and after training the association between whole body and leg lipid metabolism is reduced as exercise intensity increases.

Skeletal Muscle Protein Anabolic Response to Increased Energy and Insulin Is Preserved in Poorly Controlled Type 2 Diabetes

Type 2 diabetes (T2DM) subjects failing diet treatment are characterized by hyperinsulinemia and insulin resistance leading to fasting and postprandial hyperglycemia and hyperlipidemia. Energy is essential for allowing the process of protein synthesis to proceed. Additionally, insulin can stimulate protein synthesis in human muscle. The aims of this study were to determine if poorly controlled T2DM affects postabsorptive muscle protein anabolism, and if the muscle anabolic response to hyperinsulinemia with high energy availability is maintained. Control (n = 6) and T2DM subjects (n = 6) were studied in the postabsorptive state and during an isoenergetic high nutritional energy clamp (relative to postabsorptive state). Muscle protein synthesis and breakdown (nmol . min(-1) . 100 g leg muscle(-1)) were assessed using stable isotope methodology, femoral arterio-venous sampling, muscle biopsies, and a three-pool model to calculate protein turnover. Postabsorptive phenylalanine net balance and whole body rate of appearance (Ra) were not different between groups; however, basal muscle protein breakdown was higher in T2DM (94 +/- 9) than in controls (58 +/- 12) (P < 0.05) and muscle protein synthesis tended (P = 0.07) to be elevated in T2DM (66 +/- 14) compared with controls (39 +/- 6). During the clamp, net balance increased, whole body Ra and muscle protein breakdown decreased (P < 0.05), and muscle protein synthesis tended to decrease (P = 0.08) to a similar extent in both groups. We conclude that postabsorptive muscle protein turnover is elevated in poorly controlled T2DM, however, there is no excessive loss of muscle protein because net balance is not different from controls. Moreover, the anabolic response to increased insulin and energy availability is maintained in T2DM.

Similar 24h anabolic response to intact and hydrolysed whey protein ingested postexercise in elderly subjects

Since peptides are absorbed faster than intact proteins it was hypothesized that ingestion of protein hydrolysate after resistance exercise would cause a greater anabolic response than intact protein as timing is of significance in elderly. Muscle protein turnover was measured during a 27 h infusion of L-[1-13C]-leucine in 7 healthy (5M and 2F) aged 71(4) yr (mean(SEM)) who received on separate days carbohydrate with intact, IP or hydrolyzed whey protein, HP (0.25g/kg ~ 18g) over a 2h period after resistance exercise. Arteriovenous samples and muscle biopsies were obtained. Evaluated 1–1.5 h postexercise net balance of leucine was positive, although highest (p<0.05) in IP (0.38 ± 0.07 v 0.09 ± 0.08 mg*h−1*leg−1). Accordingly, was AUC of art-[leucine] higher in IP than HP (6.2 ± 0.5 v 5.4 ± 0.4 mmol/L). Subsequently, no difference was observed. Further, no differences were observed at any time point between IP and HP for protein synthesis, breakdown or oxidation. Muscle fractional synthetic rate was not different between IP an HP over 4 (0.07 ± 0.01 v 0.09 ± 0.01 %/h) or 24 hours post-exercise (0.08 ± 0.01 v 0.09 ± 0.01 %/h). These results suggest that protein ingested after resistance exercise in elderly results in a transient positive net protein synthesis, with no overall difference in the anabolic response between intact and hydrolysed whey.

Plasma urocortin 1 in sheep: Regional sampling and effects of experimental heart failure

Although urocortin 1 (Ucn-1) has been reported to circulate in human plasma and be raised in heart failure, little, if any, information is available regarding the source of circulating Ucn-1. Accordingly, we have performed trans-organ arteriovenous sampling for measurement of Ucn-1 concentration in anesthetized sheep before and after development of pacing-induced heart failure. Arterial plasma Ucn-1 levels measured 15.2 ± 0.5 pmol/L in normal sheep and increased significantly following development of heart failure to 19.1 ± 1.6 ( p < 0.05). Small but significant positive arteriovenous gradients were observed across the hepatic and renal tissue beds in both states, with rises across the hind limb significant in normal animals and across the head in heart failure. This is the first report identifying sources of circulating Ucn-1.

Methods for measuring tissue protein breakdown rate in vivo

To describe the latest innovations in measuring protein breakdown in vivo, particularly in muscle. The traditional method of using 3-methylhistidine excretion to measure muscle protein breakdown has been updated to include arteriovenous or microdialysis measurements, which address the concern that there are alternative sources of 3-methylhistidine in the body other than muscle. Several variations of a precursor-product method to measure fractional breakdown rate of tissues have been developed that are analogous to fractional synthesis rate of tissues. These methods are more generally applicable than the 3-methylhistidine methods and are less invasive than arteriovenous methods. The various precursor-product methods are distinguished by whether they require an isotopic steady state or multiple tracers and by how many biopsies are required. The new precursor-product methods have enabled assessment in clinical trials of protein breakdown for proteins other than myofibrillar proteins and in circumstances in which arteriovenous sampling is not feasible.

Regional sampling and the effects of experimental heart failure in sheep: Differential responses in A, B and C-type natriuretic peptides

While regional plasma concentrations of the endocrine hormones atrial and brain natriuretic peptide (ANP and BNP) have been studied, there are few reports of regional changes in the largely paracrine C-type natriuretic peptide (CNP) and its amino terminal fragment NT-CNP. Accordingly, we have performed trans-organ arteriovenous sampling for measurement of plasma ANP, BNP, CNP and NT-CNP in anesthetized sheep before and after induction of experimental heart failure. ANP and BNP plasma concentrations are sourced from a single organ (the heart) and are subject to substantial extraction across most tissue beds. In contrast, our data demonstrate that multiple tissues including liver, heart, hind limb and kidney contribute to circulating CNP. Given that arteriovenous gradients for NT-CNP were similar, this is likely to represent de novo secretion. Circulating levels of CNP and NT-CNP were raised in heart failure but to a much lesser degree than ANP and BNP. There was no evidence of net extraction of CNP or NT-CNP across any tissue bed.

Metabolic adaptations to repeated periods of contraction with reduced blood flow in canine skeletal muscle

BackgroundPatients suffering from Intermittent Claudication (IC) experience repeated periods of muscle contraction with low blood flow, throughout the day and this may contribute to the hypothesised skeletal muscle abnormalities. However, no study has evaluated the consequences of intermittent contraction with low blood flow on skeletal muscle tissue. Our aim was to generate this basic physiological data, determining the 'normal' response of healthy skeletal muscle tissue. We specifically proposed that the metabolic responses to contraction would be modified under such circumstances, revealing endogenous strategies engaged to protect the muscle adenine nucleotide pool. Utilizing a canine gracilis model (n = 9), the muscle was stimulated to contract (5 Hz) for three 10 min periods (separated by 10 min rest) under low blood flow conditions (80% reduced), followed by 1 hr recovery and then a fourth period of 10 min stimulation. Muscle biopsies were obtained prior to and following the first and fourth contraction periods. Direct arterio-venous sampling allowed for the calculation of muscle metabolite efflux and oxygen consumption.ResultsDuring the first period of contraction, [ATP] was reduced by ~30%. During this period there was also a 10 fold increase in muscle lactate concentration and a substantial increase in muscle lactate and ammonia efflux. Subsequently, lactate efflux was similar during the first three periods, while ammonia efflux was reduced by the third period. Following 1 hr recovery, muscle lactate and phosphocreatine concentrations had returned to resting values, while muscle [ATP] remained 20% lower. During the fourth contraction period no ammonia efflux or change in muscle ATP content occured. Despite such contrasting metabolic responses, muscle tension and oxygen consumption were identical during all contraction periods from 3 to 10 min.Conclusionrepeated periods of muscle contraction, with low blood flow, results in cessation of muscle ammonia production which is suggestive of a dramatic reduction in flux through AMP deaminase.

Urotensin II: Evidence for cardiac, hepatic and renal production

Although urotensin II (UII) has been reported to circulate in human plasma and be raised in cardiovascular disorders, little, if any, information is available regarding the source of plasma UII. Accordingly, we have performed trans-organ arteriovenous sampling for measurement of UII concentration in anesthetized sheep. Plasma UII levels were measured in the low picomolar range in normal sheep and arterial plasma levels rose steadily with increasing time of anesthesia. Significant arteriovenous gradients were observed across the heart (36%), liver (40%) and kidney (44%). This is the first report to identify the heart, liver and kidney as sources of UII in the circulation.

Enhanced Metabolic Cycling in Subjects after Colonic Resection for Ulcerative Colitis

Colonic resection leads to insulin resistance, but the mechanisms are unknown. We used an integrated approach to examine adipose tissue and skeletal muscle metabolism in patients lacking a colon. Ten healthy colectomized patients having undergone surgery for ulcerative colitis and 10 matched control subjects were studied with a hyperinsulinemic-euglycemic clamp to measure insulin sensitivity, an arteriovenous sampling meal tolerance study to measure postprandial substrate flux across adipose tissue and skeletal muscle, and adipose tissue and skeletal muscle biopsies to quantify the expression of genes involved in glucose and lipid metabolism. Colectomized subjects exhibited lower insulin sensitivity (homeostatic model assessment model, 33% reduction, P = 0.03; minimal model, 29% reduction, P = 0.05), elevated aldosterone (9-fold, P = 0.003), leptin (2.2-fold, P = 0.03), and an increased rate of nonesterified fatty acid and glycerol release from adipose tissue (P = 0.02) especially in the late postprandial period. The uptake of fatty acids into muscle was also significantly increased (P = 0.007), as were muscle CD36 and LPL mRNA expression compared with controls. In adipose tissue, hormone-sensitive lipase mRNA expression was increased (P = 0.015), whereas peroxisome proliferator-activated receptor-gamma expression was decreased (P = 0.02), as was that of CD36 (P = 0.001). In this study, alterations in fatty acid metabolism after colonic resection altered may have contributed to the impairment of insulin sensitivity.