Adrenergic regulation of carbohydrate metabolism during exercise

1. This series of studies was undertaken to examine the adrenergic regulation of carbohydrate metabolism during exercise. Recreationally active males were tested during moderate to intense exercise on a stationary cycle ergometer. Venous and arterial plasma obtained from indwelling catheters was analysed for hormonal and metabolite responses, and hepatic glucose production and glucose uptake were measured using the tracer-dilution method with stable isotopes. Muscle samples were obtained by the needle biopsy technique to examine muscle glycogen utilisation and the flux of related muscle metabolites using enzymatic, fluorometric and radioisotopic techniques. 2. During moderate exercise adrenaline infusion induced a marked hyperglycemia and this was due to reduced glucose uptake rather than enhanced hepatic glucose production. The reduction in glucose uptake was most likely mediated by a decrease in glucose phosphorylation, as indicated by the accumulation of glucose 6-phosphate with adrenaline infusion. 3. The hyperglycemic response to intense exercise was prevented by the administration of α- and β-adrenergic antagonists. Adrenergic blockade was without effect on hepatic glucose production whereas glucose uptake was enhanced when compared with control subjects. These data support the notion that adrenergic mechanisms are more important in restraining glucose uptake than enhancing hepatic glucose production during intense exercise. Other glucoregulatory factors are responsible for the increase in glucose production during intense exercise. 4. Elevated plasma adrenaline levels during moderate exercise in untrained men increases skeletal muscle glycogen breakdown and PDH activation which results

Reduced glycogen availability is associated with increased AMPKα2 activity, nuclear AMPKα2 protein abundance, and GLUT4 mRNA expression in contracting human skeletal muscle

Glycogen availability can influence glucose transporter 4 (GLUT4) expression in skeletal muscle through unknown mechanisms. The multisubstrate enzyme AMP-activated protein kinase (AMPK) has also been shown to play an important role in the regulation of GLUT4 expression in skeletal muscle. During contraction, AMPK [alpha]2 translocates to the nucleus and the activity of this AMPK isoform is enhanced when skeletal muscle glycogen is low. In this study, we investigated if decreased pre-exercise muscle glycogen levels and increased AMPK [alpha]2 activity reduced the association of AMPK with glycogen and increased AMPK [alpha]2 translocation to the nucleus and GLUT4 mRNA expression following exercise. Seven males performed 60 min of exercise at ~70% [VO.sub.2] peak on 2 occasions: either with normal (control) or low (LG) carbohydrate pre-exercise muscle glycogen content. Muscle samples were obtained by needle biopsy before and after exercise. Low muscle glycogen was associated with elevated AMPK [alpha]2 activity and acetyl-CoA carboxylase [beta] phosphorylation, increased translocation of AMPK [alpha]2 to the nucleus, and increased GLUT4 mRNA. Transfection of primary human myotubes with a constitutively active AMPK adenovirus also stimulated GLUT4 mRNA, providing direct evidence of a role of AMPK in regulating GLUT4 expression. We suggest that increased activation of AMPK [alpha]2 under conditions of low muscle glycogen enhances AMPK [alpha]2 nuclear translocation and increases GLUT4 mRNA expression in response to exercise in human skeletal muscle.

Haptically simulating soft tissue using spherical voxel and reactive agents

This thesis describes technology developed by the author enabling trainee surgeons to perform needle insertion procedures with force feedback (haptics) on a virtual patient. Addition of the sense of touch to medical simulation is arguably the most important step forward in the evolution of haptic technology to this day.

Needle and syringe provision and disposal in an Australian regional centre

The aim of this study was to investigate the provision and disposal of needles and syringes in Geelong, Victoria, supplying a comparison of needles provided to needles returned through needle and syringe programmes (NSPs), needles disposed of in 'Sharpsafe' bins and needles discarded. This study combined quantitative data obtained from a number of sources and qualitative data obtained from 60 interviews. An average of 18,337 (SD = 2796) per month were dispensed from NSPs and an average of 5576 needles are returned to NSP sites in Geelong per month. For the current year, 450 needles and syringes per month were placed in publicly located disposal bins. On average there were 19 callouts to discarded needles per month in the Geelong region and these needles constituted 0.38% of the monthly average of needles provided through NSPs. It was concluded that, while discarded needles are of major community concern, the vast majority of needles and syringes provided in this regional centre are not discarded. Findings are discussed in relation to the current laws surrounding the possession of injecting equipment.

3D haptic needle insertion simulator utilising an agent based spherical voxel model

This paper describes a technique for the real-time modeling of deformable tissue. Specifically geared towards needle insertion simulation, the low computational requirements of the model enable highly accurate haptic feedback to a user without introducing noticeable time delay or buzzing generally associated with haptic surgery simulation. Using a spherical voxel array combined with aspects of computational geometry and agent communication and interaction principals, the model is capable of providing haptic update rates of over 1000Hz with real-time visual feedback. Iterating through over 1000 voxels per millisecond to determine collision and haptic response while making use of Vieta’s Theorem for extraneous force culling.

Variations in vascular access flows in haemodialysis can depend on needle orientation

Introduction: While using the Transonic Qc[TM] machine to assess access flow in arteriovenous fistulae (AVF), we observed that when compared to antegrade arterial needle insertion, retrograde arterial needle insertion could regularly produce lower access flow measurements. This study sought to explore this phenomenon.

Method: 23 patients entered and 20 finished the study. Patient selection criteria included: functioning AVF and an adequate AVF length for either retrograde or antegrade arterial needle insertion. After ensuring stable and similar blood pressures, 3 flow measurements were taken during the first 2 hours on the same dialysis day of 3 consecutive weeks using antegrade needle insertion then were repeated on 3 further consecutive weeks using retrograde insertion.

Results: Overall, access flows measured with retrograde insertion were significantly lower by a mean difference of 107.15 ml/min (57-484 ml/min) than the flows measured with antegrade needle placement. In 5/20, 3 recorded minimal difference and 2 had a higher access flows during retrograde insertion. No recirculation was observed during either antegrade or retrograde needle insertion. The paired t-test showed that there was significant difference between the antegrade versus retrograde mean measurements (p = 0.005).

Conclusion: Although the sample size is small and the number of measurements limited, we conclude that access flows may be greater with an antegrade arterial orientation compared to flows recorded with a retrograde orientation. The phenomenon behind this conclusion is yet to be investigated. We suggest that when using the Transonic Qc[TM] access measurement device the arterial needle should always be in the same direction for each measurement for each individual patient.

A systematic review of the quality of liver biopsy specimens

Characteristics for an optimal liver biopsy specimen were recently defined as 20 to 25 mm long and/or containing more than 11 complete portal tracts (CPTs). A systematic review of percutaneous liver biopsy (PLB) and transjugular liver biopsy (TJLB) series yielded only 32 PLB studies in which these characteristics were evaluated: mean ± SD length, 17.7 ± 5.8 mm and number of CPTs, 7.5 ± 3.4; and 15 TJLB studies: mean ± SD length, 13.5 ± 4.5 mm and number of CPTs, 6.8 ± 2.3. Studies of sampling heterogeneity and intraobserver and interobserver variability also used inadequate specimens by present standards. Only 11 (5.3%) of 207 therapeutic studies for chronic hepatitis B and C documented length and/or number of CPTs. Of the current 12 studies evaluating noninvasive fibrosis tests, only 8 documented length or number of CPTs, and only 1 documented length and number of CPTs. New studies are needed based on adequate liver biopsy samples to provide reliable estimation of grading and staging in chronic liver disease.

Epithelial cell folate is an accurate marker when compared with whole tissue biopsy folate for examining the role of folate status in colorectal cancer

Background – Epidemiological studies have shown low folate status is associated with colorectal cancer. Colonic tissue folate levels at different stages of cancer development should give important information, but different methodologies to extract the colonic tissue folates have been used. This has hampered progress in defining the relationship between systemic and tissue folate levels.
Objective – To evaluate two methods of colonic tissue preparation for estimation of total folate content.
Design – Whole tissue punch biopsy samples were obtained from the descending colon of 31individuals following a normal colonoscopy. Blood samples were obtained for the determination of plasma homocysteine (Hcy), red cell folate (RCF), methylenetetrahydrofolate reductase 677C>T genotype, and serum vitamin B12 and folate. Colonic tissue folate was measured both in washed whole tissue biopsies and in epithelial cells isolated from tissue biopsies.
Outcomes - Whole biopsy and epithelial cell folate concentrations were significantly correlated (R=.375; P=.038). Hcy was inversely correlated with both measures (R=-.365; P=.043 and R=-.364; P=.044 respectively). RCF was significantly correlated with isolated epithelial cell folate (R=.477; P=.007) but not with whole tissue biopsy folate (R=.264; P=.151). There were no significant associations between serum and colonic folate in this study.
Conclusion - Both methods are useful for comparing systemic and localised tissue folate status but epithelial cells may provide more reliable data.

The need to examine metastatic tissue at the time of progression of breast cancer : is re-biopsy a necessity or a luxury?

Knowledge of estrogen receptor (ER), progesterone receptor (PgR) and human epidermal growth factor receptor-2 (HER2) status is necessary for determining the optimal treatment of breast cancer patients. At the same time, the discordance between marker profiles (ER/PR and HER2) of primary and metastatic breast cancer is well documented. Whether discordant cases are secondary to “clonal selection” in the face of targeted anti-estrogen or anti-HER2 therapy or whether they are a laboratory artifact is still debated; both scenarios are likely. This article outlines current modalities for ER, PR, and HER2 testing in primary breast carcinoma and its metastases and reviews prospective and retrospective studies that have addressed these issues, as well as recent advances in the field.

Single cell stiffness measurement at various humidity conditions by nanomanipulation of a nano-needle

This paper presents a method for single cell stiffness measurement based on a nano-needle and nanomanipulation. The nano-needle with a buffering beam was fabricated from an atomic force microscope cantilever by the focused ion beam etching technique. Wild type yeast cells (W303) were prepared and placed on the sample stage inside an environmental scanning electron microscope (ESEM) chamber. The nanomanipulator actuated the nano-needle to press against a single yeast cell. As a result, the deformation of the cell and nano-needle was observed by the ESEM system in real-time. Finally, the stiffness of the single cell was determined based on this deformation information. To reveal the relationship between the cell stiffness and the environmental humidity conditions, the cell stiffness was measured at three different humidity conditions, i.e. 40, 70 and 100%, respectively. The results show that the stiffness of a single cell is reduced with increasing humidity.

The reliability of muscle biopsies taken from vastus lateralis

The purpose of this study was to examine whether a single biopsy sample of vastus lateralis could provide an accurate estimate of capillary density (CD) which is indicative of the entire muscle, or whether capillary density is distributed unevenly and varies with muscle depth. Whole muscle cross sections of vastus lateralis were excised post mortem (n=11) for analysis of capillary density at three muscle depths, (superficial, mid and deep regions). Muscle thickness varied widely (17–79mm) across subjects. The distribution of CD throughout the depth of the muscle was homogeneous in 8 subjects, but in 3 subjects it was heterogeneous (p<0.05). In 3 of these subjects there was a significant (p<0.05) effect of sample depth on CD. These data indicate that tissue from a single biopsy will not adequately represent the CD of the entire vastus lateralis in some individuals. Single biopsies from unspecified muscle depth, have routinely been used to estimate CD and fibre type in vastus lateralis. The present study indicates that a more reliable method of analysis would be to use the tissue from two needle biopsies taken at the superficial and deep portions of the muscle from a group of at least 10 subjects. Sampling theory analysis supported this conclusion.