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Biomedical subjects

I Jacobs

Publications and source records attributed to I Jacobs.

156 records · Page 9Linked to original sources
PubMed1981

Muscle strength and fatigue after selective glycogen depletion in human skeletal muscle fibers.

Two groups of male subjects were studied to examine the effects of different exercise protocols on performance of an isokinetic, short-time strength test, the performance of which is related to fast twitch (FT) muscle fiber recruitment. The laboratory group (LG) (n = 10) cycled (30 min, 70% VO2 max), ran (75 min), and performed repeated bouts of "sprint" cycling and rapid, maximal contractions of the quadriceps. The marathon group (MG) (n = 7) participated in and completed Stockholm's Marathon 1979. A strength test was performed before and within 1-2 h after completion of the group exercise protocol. The m. vastus lateralis was biopsied and muscle fibers classified as slow twitch (ST) or FT. After periodic acid-Schiff staining fibers were qualitatively classified as to glycogen content. In LG significant glycogen depletion occurred in both fiber types and in MG predominantly ST fibers were exhausted of glycogen after the exercise protocol. The glycogen exhaustion from both fiber types in LG was associated with impaired maximal muscular strength produced during a single dynamic contraction, as well as with reduced muscle fatigue patterns. When glycogen exhaustion was induced in ST muscle fibers only in the MG, no impairment was observed for maximal muscular strength but fatigue during 50 consecutive contractions was significantly increased.

Adult↗
PubMed1981

Onset of blood lactate accumulation and marathon running performance.

This study was designed to examine the interrelationships among endurance running performance (marathon), the exercise intensity at which the "onset of blood lactate accumulation" (OBLA) occurs training volume, and muscle fiber characteristics. In conjunction with Stockholm's Marathon (1979), 18 male subjects underwent a test to determine the relationship between treadmill running velocity and blood lactate accumulation. The velocity at which a blood lactate accumulation of 4 mmol x l-1 occurred was referred to as the VOBLA. The m. vastus lateralis was biopsied and muscle fiber type distribution (% slow twitch, ST) and capillary density determined. With marathon running velocity (VM) as the dependent variable, multiple regression analysis showed that VOBLA accounted for 92% of the variation in VM, and VOBLA plus training volume prior to the marathon accounted for 96% of this variation. All performance variables were positively correlated to % ST muscle fiber distribution (r = 0.55-0.69) and capillary density (r = 052-0.63). Thus, marathon running performance was closely related to VOBLA and to the ability to run at a pace close to that velocity during the race. These properties were in turn related to % ST, capillary density, and training volume.

Adult↗
PubMed1981

Onset of blood lactate accumulation and enzyme activities in m. vastus lateralis in man.

In an earlier study, we reported close relationships between marathon running performance and the running velocity (V) at which the "onset of blood lactate accumulation" (VOBLA) occurs in a group of marathon runners. Using biopsy material from the m. vastus lateralis of the same subjects (n = 19), we have evaluated the relationship of VOBLA to different muscle enzyme activities together with muscle fiber composition and capillary density in the present study. The activities of lactate dehydrogenase (LDH EC 1.1.1.27), phosphofructokinase (PFK EC 2.7.1.11), and citrate synthase (CS EC 4.1.3.7) were determined. VOBLA was negatively correlated to LDH (r = -0.54) and PFK/CS (r = -0.68). Using multiple regression analysis, the PFK/CS ratio together with the capillary density accounted for 61% of the variation in VOBLA. Absolute training kilometrage was the most significant variable measured and accounted for 77% of the variation in VOBLA. Subjects were divided into elite runners (n = 6) and nonelite runners (n = 13) for an additional analysis of the relationship between VOBLA and the ratios of PFK/CS or LDH/CS. Significant relationships between VOBLA and the ratios were observed only in the nonelite runners (r = -0.77 and -0.66, respectively). The vertical distances between the regression lines for these two subject groups could not be explained only on the basis of the enzyme activity ratios. A greater adaptation to fat combustion in the elite runners might explain the disproportionally high VOBLA in relation to the PFK/CS or LDH/CS activity ratios.

Adult↗
PubMed1981

Lactate concentrations after short, maximal exercise at various glycogen levels.

The present study was designed to evaluate the effects of changes in glycogen concentrations on lactate accumulation in human skeletal muscle during a 1 min maximal muscle fatigue test (MFT). All subjects first performed the MFT during a control experiment. Four subjects then performed the MFT again 1 h after prolonged exercise. Seven other subjects performed the MFT again after a 3 day carbohydrate (CHO) poor diet and again after 4 additional days of a CHO rich diet. The m. vastus lateralis was biopsied prior to (for glycogen determinations) and immediately after (for lactate determinations) each performance of the MFT. High but similar lactate concentrations were observed (22.3 mmol x kg-1 w.w.) with normal and supernormal glycogen levels. Lactate was significantly reduced following both the prolonged exercise (to 7.0 mmol x kg-1 w.w.) and the CHO poor diet (to 16.8 mmol x kg-1 w.w.). Alterations in muscle strength and fatigue patterns were also observed from the dietary manipulations but they were neither commensurate with the changes in metabolite concentrations nor statistically significant.

Adult↗
PubMedDate not supplied

Simultaneous autoradiography and line immunoelectrophoresis (ARLIE): a novel combination to identify de novo protein synthesis by pregnancy tissues.

A novel combination of two conventional techniques (autoradiography, AR and line immunoelectrophoresis, LIE; ARLIE) for identification of specific proteins synthesized de novo by explants is described. The incorporation rate of [35S]-methionine was linear in proteins derived from cytosol fractions and supernatants of first trimester human trophoblast and gestational endometrium for up to 18 h. SDS-PAGE analysis of these fractions provided further evidence of the protein synthesis and secretion by the tissue explants. The ARLIE system was evaluated by investigating the synthesis and secretion of five test proteins (PP12, PP14, hPL, FA-1 and FA-2) by trophoblast and gestational endometrium. The synthesis P12 and PP14 could be demonstrated by gestational endometrium only. Similarly the synthesis of hPL could be demonstrated by the trophoblast alone. The synthesis of the fetal proteins (FA-1 and FA-2) could not be demonstrated by either tissue. The control procedure, Protein A assisted immunoprecipitation, yielded similar results for PP14 but not hPL. This novel combination (ARLIE) provides a simple technique with which to study the de novo synthesis of several proteins simultaneously which is independent of the subclass and species of origin of antibodies.

Amniotic Fluid↗
PubMedDate not supplied

New tumor markers: CA125 and beyond.

A variety of biomarkers have been developed to monitor growth of ovarian cancer and to detect disease at an early interval. CA125 (MUC16) has provided a useful serum tumor marker for monitoring response to chemotherapy, detecting disease recurrence, distinguishing malignant from benign pelvic masses, and potentially improving clinical trial design. A rapid fall in CA125 during chemotherapy predicts a favorable prognosis and could be used to redistribute patients on multiarmed randomized clinical trials. Several studies now document that CA125 can serve as a surrogate marker for response in phase II trials. Serial measurement of CA125 might also provide a useful marker for monitoring stabilization of disease with cytostatic targeted therapeutic agents. The greatest potential for serum markers may be in detecting ovarian cancer at an early stage. A rising CA125 can be used to trigger transvaginal sonography (TVS) in a small fraction of patients. An algorithm has been developed that calculates risk of ovarian cancer based on serial CA125 values and refers patients at highest risk for TVS. Use of the algorithm is currently being evaluated in a trial with 200,000 women in the UK that will test critically the ability of a two-stage screening strategy to improve survival in ovarian cancer. Whatever the outcome, as 20% of ovarian cancers have little or no expression of CA125, additional serum markers will be required to detect all patients in an initial phase of screening. More than 30 serum markers have been evaluated alone and in combination with CA125 by different investigators. Some of the most promising include: HE4, mesothelin, M-CSF, osteopontin, kallikrein(s), and soluble EGF receptor. Two proteomic approaches have been used: one examines the pattern of peaks on mass spectroscopy and the other uses proteomic analysis to identify a limited number of critical markers that can be assayed by more conventional methods. Both approaches are promising and require further development. Several groups are placing markers on multiplex platforms to permit simultaneous assay of multiple markers with very small volumes of serum. Mathematical techniques are being developed to analyze combinations of marker levels to improve sensitivity and specificity. In the future, serum markers should improve the sensitivity of detecting recurrent disease as well as facilitate earlier detection of ovarian cancer.

Biomarkers, Tumor↗
PubMedDate not supplied

Blood lactate. Implications for training and sports performance.

The blood lactate response to exercise has interested physiologists for over fifty years, but has more recently become as routine a variable to measure in many exercise laboratories as is heart rate. This rising popularity is probably due to: the ease of sampling and improved accuracy afforded by recently developed micro-assay methods and/or automated lactate analysers; and the predictive and evaluative power associated with the lactate response to exercise. Several studies suggest that the strong relationship between exercise performance and lactate-related variables can be attributed to a reflection by lactate during exercise of not only the functional capacity of the central circulatory apparati to transport oxygen to exercising muscles, but also the peripheral capacity of the musculature to utilise this oxygen. For example, several studies contrast the relationship between VO2max and endurance running performance with that between a lactate variable and the same running performance. In every study, the lactate variable is more highly correlated with performance. Similarly, prescribing training intensity as a function of the lactate concentration elicited by the training may prove to be a means of obtaining a more homogeneous adaptation to training in a group of athletes or subjects than is obtained by setting intensity as a function of maximal heart rate or % VO2max. A review of the recent literature shows that the lactate response to supramaximal exercise is a sensitive indicator of adaptation to 'sprint training' and is correlated with supramaximal exercise performance. This review also describes the possible applications of lactate measurements to enhance the rate of recovery from high intensity exercise. Although the lactate response to exercise is reproducible under standardised conditions it can be influenced by the site of blood sampling, ambient temperature, changes in the body's acid-base balance prior to exercise, prior exercise, dietary manipulations, or pharmacological interpretation.

Adolescent↗