PubMed Health⌕ Search

Biomedical subjects

M Ramaekers

Publications and source records attributed to M Ramaekers.

8 recordsLinked to original sources
PubMed2006

Fiber type-specific muscle glycogen sparing due to carbohydrate intake before and during exercise.

The effect of carbohydrate intake before and during exercise on muscle glycogen content was investigated. According to a randomized crossover study design, eight young healthy volunteers (n = 8) participated in two experimental sessions with an interval of 3 wk. In each session subjects performed 2 h of constant-load bicycle exercise ( approximately 75% maximal oxygen uptake). On one occasion (CHO), they received carbohydrates before ( approximately 150 g) and during (1 g.kg body weight(-1).h(-1)) exercise. On the other occasion they exercised after an overnight fast (F). Fiber type-specific relative glycogen content was determined by periodic acid Schiff staining combined with immunofluorescence in needle biopsies from the vastus lateralis muscle before and immediately after exercise. Preexercise glycogen content was higher in type IIa fibers [9.1 +/- 1 x 10(-2) optical density (OD)/microm(2)] than in type I fibers (8.0 +/- 1 x 10(-2) OD/microm(2); P < 0.0001). Type IIa fiber glycogen content decreased during F from 9.6 +/- 1 x 10(-2) OD/microm(2) to 4.5 +/- 1 x 10(-2) OD/microm(2) (P = 0.001), but it did not significantly change during CHO (P = 0.29). Conversely, in type I fibers during CHO and F the exercise bout decreased glycogen content to the same degree. We conclude that the combination of carbohydrate intake both before and during moderate- to high-intensity endurance exercise results in glycogen sparing in type IIa muscle fibers.

Adult↗
PubMed2005

Exercise in the fasted state facilitates fibre type-specific intramyocellular lipid breakdown and stimulates glycogen resynthesis in humans.

The effects were compared of exercise in the fasted state and exercise with a high rate of carbohydrate intake on intramyocellular triglyceride (IMTG) and glycogen content of human muscle. Using a randomized crossover study design, nine young healthy volunteers participated in two experimental sessions with an interval of 3 weeks. In each session subjects performed 2 h of constant-load bicycle exercise ( approximately 75% ), followed by 4 h of controlled recovery. On one occasion they exercised after an overnight fast (F), and on the other (CHO) they received carbohydrates before ( approximately 150 g) and during (1 g (kg bw)(-1) h(-1)) exercise. In both conditions, subjects ingested 5 g carbohydrates per kg body weight during recovery. Fibre type-specific relative IMTG content was determined by Oil red O staining in needle biopsies from m. vastus lateralis before, immediately after and 4 h after exercise. During F but not during CHO, the exercise bout decreased IMTG content in type I fibres from 18 +/- 2% to 6 +/- 2% (P = 0.007) area lipid staining. Conversely, during recovery, IMTG in type I fibres decreased from 15 +/- 2% to 10 +/- 2% in CHO, but did not change in F. Neither exercise nor recovery changed IMTG in type IIa fibres in any experimental condition. Exercise-induced net glycogen breakdown was similar in F and CHO. However, compared with CHO (11.0 +/- 7.8 mmol kg(-1) h(-1)), mean rate of postexercise muscle glycogen resynthesis was 3-fold greater in F (32.9 +/- 2.7 mmol kg(-1) h(-1), P = 0.01). Furthermore, oral glucose loading during recovery increased plasma insulin markedly more in F (+46.80 microU ml(-1)) than in CHO (+14.63 microU ml(-1), P = 0.02). We conclude that IMTG breakdown during prolonged submaximal exercise in the fasted state takes place predominantly in type I fibres and that this breakdown is prevented in the CHO-fed state. Furthermore, facilitated glucose-induced insulin secretion may contribute to enhanced muscle glycogen resynthesis following exercise in the fasted state.

Adult↗
PubMed2001

Constitutive equations for an elastic material with anisotropic rigid particles.

In this paper we have derived constitutive equations for an elastic material with anisotropic rigid particles. We have included a dependence on the Finger tensor B and the orientation tensor Q in the expression for the free energy of the system. With this expression for the free energy we have derived an expression for the stress tensor up to second order in both these variables. We have shown that the elastic modulus in this expression depends on Q, and this dependence leads to an effective elastic modulus that depends on the strain. We have calculated the explicit form of the equation for the stress tensor for a deformation in the xy plane with a strain equal to -gamma. For fully isotropic materials with Q=0 this expression reduces to an equation containing only odd powers of gamma. The inclusion of a non-zero value for the orientation tensor leads to an additional set of terms in the equation, all proportional to Qxy (the xy component of the tensor Q), and all proportional to even powers of gamma. We have qualitatively compared these expressions with Fourier transform (FT) rheological measurements of xanthan gels, at concentrations above and below the order-disorder transition. In FT rheometry an oscillatory deformation is applied in the nonlinear regime, and the resulting stress response is analyzed in Fourier space. In the 2% (w/w) xanthan system (disordered state) only odd harmonics were found in the stress response, whereas in the 4% (w/w) xanthan gel (ordered state) even harmonics could be detected. As predicted by our theory, the intensity of these even harmonics first increased with increasing gamma, until a maximum value was reached. Beyond this maximum the intensity decreased continuously with increasing gamma.

Journal Article↗
PubMed2001

No effects of oral ribose supplementation on repeated maximal exercise and de novo ATP resynthesis.

A double-blind randomized study was performed to evaluate the effect of oral ribose supplementation on repeated maximal exercise and ATP recovery after intermittent maximal muscle contractions. Muscle power output was measured during dynamic knee extensions with the right leg on an isokinetic dynamometer before (pretest) and after (posttest) a 6-day training period in conjunction with ribose (R, 4 doses/day at 4 g/dose, n = 10) or placebo (P, n = 9) intake. The exercise protocol consisted of two bouts (A and B) of maximal contractions, separated by 15 s of rest. Bouts A and B consisted of 15 series of 12 contractions each, separated by a 60-min rest period. During the training period, the subjects performed the same exercise protocol twice per day, with 3-5 h of rest between exercise sessions. Blood samples were collected before and after bouts A and B and 24 h after bout B. Knee-extension power outputs were approximately 10% higher in the posttest than in the pretest but were similar between P and R for all contraction series. The exercise increased blood lactate and plasma ammonia concentrations (P < 0.05), with no significant differences between P and R at any time. After a 6-wk washout period, in a subgroup of subjects (n = 8), needle-biopsy samples were taken from the vastus lateralis before, immediately after, and 24 h after an exercise bout similar to the pretest. ATP and total adenine nucleotide content were decreased by approximately 25 and 20% immediately after and 24 h after exercise in P and R. Oral ribose supplementation with 4-g doses four times a day does not beneficially impact on postexercise muscle ATP recovery and maximal intermittent exercise performance.

Adenine Nucleotides↗
PubMed1996

Enrichment of tumor cells for cell kinetic analysis in human tumor biopsies using cytokeratin gating.

PURPOSE: To determine the feasibility of using cytokeratin antibodies to distinguish normal and malignant cells in human tumors using flow cytometry. The goal was ultimately to increase the accuracy of cell kinetic measurements on human tumor biopsies. MATERIAL AND METHODS: A panel of four antibodies was screened on a series of 48 tumors from two centres; 22 head and neck tumors (Amsterdam) and 26 esophagus carcinomas (Leuven). First, screening was carried out by immunohistochemistry on frozen sections to test intensity of staining and the fraction of cytokeratin-positive tumor cells. The antibody showing the most positive staining was then used for flow cytometry on the same tumor. RESULTS: The two broadest spectrum antibodies (AE1/AE3, E3/C4) showed overall the best results with immunohistochemical staining, being positive in over 95% of tumors. Good cell suspensions for DNA flow cytometry could be made from frozen material by a mechanical method, whereas enzymatic methods with trypsin or collagenase were judged failures in almost all cases. From fresh material, both collagenase and trypsin produced good suspensions for flow cytometry, although the fraction of tumor cells, judged by proportion aneuploid cells, was markedly higher for trypsin. Using the best cytokeratin antibody for each tumor, two parameter flow cytometry was done (cytokeratin versus DNA content). Enrichment of tumor cells was then tested by measuring the fraction of aneuploid cells (the presumed malignant population) of cytokeratin-positive cells versus all cells. An enrichment factor ranging between 0 (no enrichment) and 1 (perfect enrichment, tumor cells only) was then calculated. The average enrichment was 0.60 for head and neck tumors and 0.59 for esophagus tumors. CONCLUSIONS: We conclude that this method can substantially enrich the proportion of tumor cells in biopsies from carcinomas. Application of this method could significantly enhance accuracy of tumor cell kinetic measurements.

Aneuploidy↗
PubMed1995

Can measurements of potential doubling time (Tpot) be compared between laboratories? A quality control study.

The purpose of this study was to investigate the reproducibility of potential doubling time measurements of human tumors in different laboratories and to distinguish which steps in the measurement procedure were subject to the greatest variation. This was achieved by comparing measurements on the same source material in two different laboratories in which three aspects of the technique were separately studied, namely, preparation and staining of the nuclear suspensions, running the samples on the flow cytometer (FCM), and analyzing the two-parameter FCM data. This involved exchange between the two centers of fixed tumor material, stained nuclear suspensions, and FCM data on floppy disks. The analysis step was found to be the least variable step. For DNA synthesis time, Ts, and the labeling index, LI, the coefficients of determination (R2) ranged from 92% to 95.4%. A small systematic bias was observed, with one center measuring approximately 15% higher values for both LI and Ts. Different criteria for window placements were found to be a contributing factor. Variations in the FCM step were approximately equal to those for analysis, with no systematic deviations. Variations for the preparation and staining step were the largest (R2 = 60.5% and 38.1% for LI and Ts, respectively). However, this step was the only one subject to intratumoral variability, which was the largest contributing factor to the variations observed. In addition, however, LI was on average 41% higher in one center compared to the other, resulting in a systematic bias. Differences in the level of green fluorescence of the labeled cells implicated antibody differences as a possible cause. The variations found here for the three procedural aspects were significantly smaller than variations observed between tumors, a requirement for a predictive assay. Suggestions for implementation of quality control procedures include objective (computer-assisted) data analysis on two-parameter histograms and optimization of antibody combinations.

Carcinoma, Squamous Cell↗