Vasoactive substances in the interstitium of contracting skeletal muscle examined by microdialysis

Chronic widespread pain: increased glutamate and lactate concentrations in the trapezius muscle and plasma

BACKGROUND

Chronic widespread pain (CWP), including fibromyalgia syndrome (FM), is associated with prominent negative consequences. CWP has been associated with alterations in the central processing of nociception. Whereas some researchers consider CWP/FM as a central hyperexcitability pain condition, others suggest that the central alterations are maintained by peripheral nociceptive input. Microdialysis can be used in vivo to study muscle alterations in chronic myalgia.

AIM

: The aim of the study was to investigate the plasma and interstitial concentrations of metabolites and algesics in the trapezius muscle of women with CWP and in pain-free women (CON).

MATERIALS AND METHODS

Seventeen women with CWP and 24 CON went through a clinical examination and completed a questionnaire; the pressure pain thresholds in the upper and lower extremities were registered. Microdialysis was conducted in the trapezius muscle, and a blood sample was drawn. Muscle blood flow, interstitial muscle concentrations, and plasma concentrations of lactate, pyruvate, glutamate, glucose, and glycerol (not in the plasma) were determined.

RESULTS

CWP patients had significantly increased interstitial muscle (P=0.02 to 0.001) and plasma (P=0.026 to 0.017) concentrations of lactate and glutamate. No significant differences existed in blood flow between CWP and CON. The interstitial concentrations-but not the plasma levels-of glutamate and lactate correlated significantly with aspects of pain such as pressure pain thresholds of the trapezius (R=0.22) and tibialis anterior (R=0.18) and the mean pain intensity (R=0.10) in CWP but not in CON.

CONCLUSIONS

The present study supports the suggestion that aspects of pain and central alterations in CWP/FM are influenced by peripheral tissue alterations.

Algogenic substances and metabolic status in work-related Trapezius Myalgia: a multivariate explorative study

BACKGROUND

This study compares the levels of algesic substances between subjects with trapezius myalgia (TM) and healthy controls (CON) and explores the multivariate correlation pattern between these substances, pain, and metabolic status together with relative blood flow changes reported in our previous paper (Eur J Appl Physiol 108:657-669, 2010).

METHODS

43 female workers with (TM) and 19 females without (CON) trapezius myalgia were - using microdialysis - compared for differences in interstitial concentrations of interleukin-6 (IL-6), bradykinin (BKN), serotonin (5-HT), lactate dehydrogenas (LDH), substance P, and N-terminal propeptide of procollagen type I (PINP) in the trapezius muscle at rest and during repetitive/stressful work. These data were also used in multivariate analyses together with previously presented data (Eur J Appl Physiol 108:657-669, 2010): trapezius muscle blood flow, metabolite accumulation, oxygenation, and pain development and sensitivity.

RESULTS

Substance P was significantly elevated in TM (p=0.0068). No significant differences were found in the classical algesic substances (p: 0.432-0.926). The multivariate analysis showed that blood flow related variables, interstitial concentrations of metabolic (pyruvate), and algesic (BKN and K+) substances were important for the discrimination of the subjects to one of the two groups (R2: 0.19-0.31, p<0.05). Pain intensity was positively associated with levels of 5-HT and K+ and negatively associated with oxygenation indicators and IL-6 in TM (R2: 0.24, p<0.05). A negative correlation existed in TM between mechanical pain sensitivity of trapezius and BKN and IL-6 (R2: 0.26-0.39, p<0.05).

CONCLUSION

The present study increased understanding alterations in the myalgic muscle. When considering the system-wide aspects, increased concentrations of lactate, pyruvate and K+ and decreased oxygenation characterized TM compared to CON. There are three major possible explanations for this finding: the workers with pain had relatively low severity of myalgia, metabolic alterations preceded detectable alterations in levels of algesics, or peripheral sensitization and other muscle alterations existed in TM. Only SP of the investigated algesic substances was elevated in TM. Several of the algesics were of importance for the levels of pain intensity and mechanical pain sensitivity in TM. These results indicate peripheral contribution to maintenance of central nociceptive and pain mechanisms and may be important to consider when designing treatments.

Traditional acupuncture triggers a local increase in adenosine in human subjects

Acupuncture is a form of Eastern medicine that has been practiced for centuries. Despite its long history and worldwide application, the biological mechanisms of acupuncture in relieving pain have been poorly defined. Recent studies in mice, however, demonstrate that acupuncture triggers increases in interstitial adenosine, which reduces the severity of chronic pain through adenosine A1 receptors, suggesting that adenosine-mediated antinociception contributes to the clinical benefits of acupuncture. We asked here whether acupuncture in human subjects is also linked to a local increase in interstitial adenosine concentration. We collected microdialysis samples of interstitial fluid before, during, and after delivering 30 minutes of conventional acupuncture in the Zusanli point in human subjects. The interstitial adenosine concentration increased significantly during acupuncture and remained elevated for 30 minutes after the acupuncture. Acupuncture-mediated adenosine release was not observed if acupuncture was not delivered in the Zusanli point or if the acupuncture needle was inserted, but not rotated. This study strengthens the role of adenosine in acupuncture-mediated antinociception by directly providing such evidence in humans.

PERSPECTIVE

This article presents further evidence of the role of adenosine in acupuncture-mediated antinociception by demonstrating that local adenosine concentrations increase in the acupoint in human subjects receiving traditional acupuncture.

Relative recovery over time - an in vivo microdialysis study of human skeletal muscle

BACKGROUND

The microdialysis technique is a method for sampling endogenous molecules from the interstitial compartments of varying tissues and relies on diffusion of molecules between the tissue and a perfusate via a membrane. Such samples do not allow determination of the true interstitial concentration but only a certain percentage. This gives rise to one of the most crucial parameter that needs to be considered for a dependable microdialysis; the relative recovery. Relative recovery states the efficiency of which an analyte is extracted from its external medium. Aim. To investigate the relative recovery of small molecules (< 20 kDa) such as lactate, fluid recovery and the reproducibility of the relative recovery at group and individual level of the microdialysis technique applied in muscle.

MATERIALS AND METHODS

Using in vivo microdialysis of the trapezius muscle of 65 women from two separate occasions 4-6 months apart. Relative recovery of small molecules was measured from samples collected every 20 min during a period of 220 min.

RESULTS

Good reproducibility at group level of catheters with cut-offs 100 and 20kDa were found. Furthermore, there was a high and steady relative recovery with an overall good fluid recovery. Poor reproducibility was found at the individual level for both catheters.

CONCLUSIONS

This study demonstrates that when using microdialysis in skeletal muscle relative recovery is stable over time and is not affected by low-force exercise. Although there is a good reproducibility at group level this is not the case at the individual level. Thus in vivo, the relative recovery should be determined for each test subject and at each test occasion.

Forearm vasoconstrictor response in uncomplicated type 1 diabetes mellitus

BACKGROUND

According to the 'haemodynamic hypothesis', increased tissue perfusion predisposes to microangiopathy in diabetic patients. We hypothesized that the typical haemodynamic changes underlying the increased tissue perfusion can be explained by a decreased sympathetic nerve activity caused by chronic hyperglycaemia. In this study we investigated sympathetic activity in patients with uncomplicated type 1 diabetes mellitus (DM).

MATERIALS AND METHODS

In 15 DM patients (DM duration 6.3 +/- 3.8 year; HbA1c 7.9 +/- 1.3%) and 16 age- and sex-matched healthy volunteers (Control), sympathetic nervous system activity was measured at rest (baseline) and during sympathoneural stimulation (lower body negative pressure (LBNP)) by means of interstitial and plasma noradrenaline (NA) sampling and power spectral analysis. Muscle sympathetic nerve activity (MSNA) was measured before (baseline) and during a cold pressure test. Forearm blood flow was measured during forearm vascular alpha- and beta-adrenergic receptor blockade.

RESULTS

At baseline, forearm vascular resistance (FVR), plasma NA concentrations, MSNA and heart rate variability were similar in both groups. LBNP-induced vasoconstriction was significantly attenuated in the DM group compared with the Control group (DeltaFVR: 12 +/- 4 vs. 19 +/- 3 arbitrary units, P < 0.05). The responses of plasma NA and heart rate variability did not differ.

CONCLUSIONS

Baseline FVR and sympathetic nerve activity are normal in patients with uncomplicated type 1 diabetes. However, the forearm vasoconstrictor response to sympathetic stimulation is attenuated, which cannot be attributed to an impaired sympathetic responsiveness.

Calcitonin gene related peptide and neuropeptide Y in skeletal muscle after eccentric exercise: a microdialysis study

OBJECTIVES

To detect neuropeptides in human skeletal muscle at rest and after eccentric exercise.

METHOD

Eight healthy subjects participated in the study. Microdialysis of the distal part of the vastus lateralis of the quadriceps muscle and pain evaluation were performed immediately after eccentric exercise, after two days, and at rest. Calcitonin gene related peptide (CGRP) and neuropeptide Y (NPY), representatives of the sensory and autonomic nervous system, were analysed by radioimmunoassay.

RESULTS

Overall, the measured concentrations were low, some even below the limit of detection. At rest, CGRP was detected in two of seven samples, but after eccentric exercise it was detected in 27 of 30 samples. At rest, all NPY concentrations were below the limit of detection, but after exercise it was found in six of 30 samples.

CONCLUSION

The significant increase in detectability of CGRP after eccentric exercise may be related to the increased experience of pain. Therefore the occurrence of CGRP after heavy eccentric exercise may be associated with the regulation of delayed onset muscle soreness and possibly also the stimulation of tissue regeneration.

Effects of age and resistance exercise on skeletal muscle interstitial prostaglandin F(2alpha)

Prostaglandin (PG) F2alpha has been shown to contribute to the anabolic events in skeletal muscle. We measured the skeletal muscle interstitial concentration of PGF2alpha at rest and following a standard bout of resistance exercise in eight young (27+/-2 year) and eight old (75+/-4 year) men. Interstitial PGF2alpha concentration was determined from microdialysate samples obtained from two microdialysis probes placed in the vastus lateralis. Microdialysates were collected 1h pre- and 5-6, 8-9, and 24-25 h postexercise. The exercise bout consisted of 4 exercises (3 sets of 8 replications at 80% 1 RM per exercise) emphasizing the quadriceps. Interstitial PGF2alpha levels were not different (P>0.05) between young and old at rest (1.50+/-0.35 vs. 1.52+/-0.30 ng ml-1) or at any time point following the resistance exercise bout. For the young and old combined there was a change (P<0.05) in PGF2alpha levels at 5-6 h (93%) and 8-9 h (95%), which had returned to preexercise levels by 24-25 h. These results show that PGF2alpha is increased in skeletal muscle following a standard bout of resistance exercise and aging does not alter interstitial levels of this PG at rest or after exercise. These data, coupled with previous findings, suggest that the anabolic factor PGF2alpha should be considered when discussing the complex processes that regulate muscle mass in young and old individuals.

Methodological approaches to the study of metabolism across individual tissues in man

PURPOSE OF REVIEW

This article is intended to briefly overview available methodological approaches for the study of regional metabolism in man in vivo, and to summarize recent advances in this field of research.

RECENT FINDINGS

Several methods have been developed and currently allow for the qualitative and quantitative assessment of energy interconversions and substrate fluxes across individual tissues of man, including the measurement of arteriovenous concentration differences, microdialysis, and nuclear magnetic resonance spectroscopy of carbon, hydrogen, and phosphorus isotopes. Each method alone has been used rather extensively to examine certain aspects of organ and tissue metabolism under a variety of experimental conditions, and has contributed novel information in this regard. The most exciting development appears to be the combined use of more than one investigational technique, across one or more tissues simultaneously. A handful of recent studies have employed complex experimental designs or hybrid methodologies, ultimately demonstrating the potential for a more detailed assessment of metabolism at the local level.

SUMMARY

Clearly, advances in the use, performance, and applications of available methods are expected to provide improved and more powerful tools for the metabolic investigation of organs and tissues in humans in vivo.

Use of Microdialysis to Study Interstitial Nitric Oxide and Other Reactive Oxygen and Nitrogen Species in Skeletal Muscle

Microdialysis techniques can be used to sample the interstitial space of tissues such as skeletal muscle. Analytical developments have allowed adaptations of these techniques to permit continuous monitoring of nitric oxide and a number of other reactive oxygen and nitrogen species in skeletal muscle extracellular space. Methods are described for assessment of interstitial nitrate and nitrite content, superoxide anion content, hydroxyl radical activity, and the content of relatively stable lipid radicals detectable using spin trapping and electron spin resonance techniques in skeletal muscle of rodents at rest and during contractile activity.

Contraction-related factors affect the concentration of a kallidin-like peptide in rat muscle tissue

In order to study the effects of the manipulation of various factors related to muscular activity on the concentration of kinins in muscular tissue, a microdialysis probe was implanted in the adductor muscle of the hindlimb in anaesthetized rats. After collection of baseline samples, the perfusion fluid was changed to a Ringer solution containing sodium lactate (10 or 20 mM), adenosine (50 or 100 microM) or a lower pH (7.0 or 6.6). Whereas perfusion with lactate did not have any significant effect on the concentration of kinins in the dialysate, the perfusion with a lower pH or with adenosine dose-dependently increased the kinin content in the samples. In a second microdialysis experiment, by using specific radioimmunoassays (RIA) for bradykinin and kallidin, we observed that about 70 % of the total kinins dialysed from rat muscle are a kallidin-like peptide. Also, the simultaneous perfusion with 100 microM caffeine totally abolished the increase in kinin levels induced by the perfusion at pH 6.6. In a third experiment, soleus muscles from rat were stimulated in vitro during 30 min in the presence or absence of 77 microM caffeine. Electrically stimulated contraction, but not the addition of 10 mU ml(-1) insulin, induced an increase in the concentration of the kallidin-like peptide in the buffer. This effect was totally prevented by the addition of the adenosine antagonist caffeine. These results show that a kallidin-like peptide is released from rat muscle, and that its production is enhanced by muscle activity. Furthermore, the increase in kinin peptides during muscle contraction may be mediated by an increase in adenosine levels.

Nutritive blood flow improves interstitial glucose and lactate exchange in perfused rat hindlimb

Microdialysis was used to assess the interstitial concentrations of glucose and lactate in the constant-flow-perfused rat hindlimb under varying levels of nutritive flow controlled by vasoconstrictors. Increased nutritive flow was achieved by norepinephrine (NE) or angiotensin II (ANG II) and decreased nutritive flow by serotonin (5-HT). NE and ANG II increased oxygen and glucose uptake as well as hindlimb lactate release by 50%. 5-HT decreased oxygen uptake by 15% but had no significant effect on glucose uptake or hindlimb lactate release. Microdialysis recovery of glucose and lactate was significantly elevated by NE and ANG II and decreased by 5-HT. The calculated interstitial concentration of glucose was increased by NE and ANG II but decreased by 5-HT. The interstitial concentration of lactate was decreased by NE and ANG II but increased by 5-HT. In all cases, nitroprusside reversed the effects of the vasoconstrictors. These data indicate that increased nutritive blood flow enhances the exchange of glucose and lactate by improving the supply of glucose to and the removal of lactate from the interstitium.

Microdialysis of skeletal muscle at rest

Techniques in human skeletal muscle research are by necessity predominantly 'descriptive'. Microdialysis has raised high expectations that it could meet the demand for a method that allows 'mechanistic' investigations to be performed in human skeletal muscle. In the present review, some views are given on how well the initial expectations on the use of the microdialysis technique in skeletal muscle have been fulfilled, and the areas in which additional work is needed in order to validate microdialysis as an important metabolic technique in this tissue. The microdialysis catheter has been equated to an artificial blood vessel, which is introduced into the tissue. By means of this 'vessel' the concentrations of compounds in the interstitial space can be monitored. The concentration of substances in the collected samples is dependent on the rate of perfusate flow. When perfusate flow is slow enough to allow complete equilibration between interstitial and perfusate fluids, the concentration in the perfusate is maximal and identical to the interstitial concentration. Microdialysis data may be influenced by changes in blood flow, especially in instances where the tissue diffusivity limits the recovery in vivo, i.e. when recovery in vitro is 100%, whereas the recovery in vivo is less than 100%. Microdialysis data indicate that a significant arterial-interstitial glucose concentration gradient exists in skeletal muscle but not in adipose tissue at rest. While the concentrations of glucose and lactate in the dialysate from skeletal muscle are close to the expected values, the glycerol values obtained for muscle are still puzzling. Ethanol added to the perfusate will be cleared by the tissue at a rate that is determined by the nutritive blood flow (the microdialysis ethanol technique). It is concluded that microdialysis of skeletal muscle has become an important technique for mechanistic studies in human metabolism and nutrition.

Macronutrient metabolism of adipose tissue at rest and during exercise: a methodological viewpoint

The metabolism of white adipose tissue is regulated by many factors, including hormones and substrates delivered in the blood, the activity of the autonomic nervous system and the rate of flow of blood through the tissue. An integrated view of adipose tissue metabolism can only be gained, therefore, from studies in vivo. Of the various techniques available for studying adipose tissue metabolism in vivo, the measurement of arterio-venous differences offers some unique possibilities. In human subjects this technique has been performed mostly by catheterization of the venous drainage of the subcutaneous abdominal depot. Studies using this technique indicate that adipose tissue has an active pattern of metabolism, responding rapidly to meal ingestion by suppressing the release of non-esterified fatty acids, or to exercise with an increase in fat mobilization. Adipose tissue blood flow may also change rapidly in these situations; for instance, it increases markedly after a meal, potentially increasing the delivery of triacylglycerol to the enzyme lipoprotein lipase (EC 3.1.1.34) for hydrolysis. During exercise, there is evidence that adipose tissue blood flow does not increase sufficiently to allow delivery of all the fatty acids released into the systemic circulation. The various adipose tissue depots have their own characteristic metabolic properties, although in human subjects these are difficult to study with the arterio-venous difference technique. A combination of tracer infusion with selective catheterization allows measurements of leg, splanchnic and non-splanchnic upper-body fat mobilization and triacylglycerol clearance. Development of such techniques may open up new possibilities in the future for obtaining an integrated picture of adipose tissue function and its depot-specific variations.