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Biomedical subjects

D Laurent

Publications and source records attributed to D Laurent.

At least 55 records · Page 3Linked to original sources
PubMed1996

A method for simultaneous determination of plasma and erythrocyte antioxidant status. Evaluation of the antioxidant activity of vitamin E in healthy volunteers.

1. Since oxygen free radicals are directly involved in a variety of pathologies such as atherosclerosis, diabetes mellitus, inflammation and/or when a deficit of defences of the organism against radicals occurs, we developed a suitable and simple method to determine both the erythrocyte sensitivity to an oxidative stress and plasma antioxidant protective capacity. 2. This test is based on the introduction at 37 degrees C of a radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH), within an erythrocyte suspension leading to a membrane alteration and ultimately to haemolysis. The latter can be quantified by determining the lacticodeshydrogenase activity released in the medium. The erythrocyte sensitivity to haemolysis and the volume of plasma inhibiting 50% of the haemolysis were determined. 3. Intra-assay CVs were 1.9% for erythrocyte sensitivity to oxidative stress and 3.4% for inhibitory 50% plasma volume. Inter-assay CVs for both erythrocyte sensitivity and inhibitory 50% plasma volume were 4%. 4. The reliability of this method was assessed and applied to test the protective effect of vitamin E, a well known antioxidant agent, in six healthy volunteers. Two weeks after daily administration of 500 mg of vitamin E, the mean plasma vitamin E concentration increased by 41% from 10.7 +/- 2.0 mg l-1 before treatment (P < 0.05). As the vitamin E concentration increased, the mean inhibitory 50% plasma volume and the percentage of haemolysed erythrocytes decreased respectively by 29% from 3.35 +/- 0.5 microliter (P < 0.05) and 18% from 71.5 +/- 3.8% (P < 0.05). No significative variation of these parameters was observed in six adult men without vitamin E supplementation. 5. Thus, this global and simple test permits an antioxidant status evaluation of a patient. It can be applied to various pathologies and allows the potency of new antioxidant molecules to be evaluated.

Adult↗
PubMed1995

Longitudinal patterns of heart rate and fighting behavior in 9- through 12-year-old boys.

OBJECTIVE: To assess the temporal stability of heart rate and to examine its relationship with fighting behavior. METHOD: Heart rate at ages 9 through 12 was compared to a composite measure of fighting behavior in three cohorts of low socioeconomic status boys (n = 138; two cohorts of boys who had been rated as having disruptive behavior problems in kindergarten and one normative cohort) while controlling for body size, pubertal status, and level of family adversity. RESULTS: Heart rate showed moderate stability at 1- and 2-year intervals in two of the three cohorts. The composite fighting score was related to heart rate for 11-year-old boys in the normative cohort and 12-year-old boys in one of the disruptive cohorts. CONCLUSION: These data support the conclusion that there is a relationship between heart rate and aggression even within a low socioeconomic status sample.

Aggression↗
PubMed1995

Different left ventricular remodelling and function in two models of pressure overload as assessed in vivo by magnetic resonance imaging.

OBJECTIVES: To follow the development of left ventricular structure and function in vivo in two different models of pressure-overload hypertrophy. DESIGN: From age 6 weeks, left ventricular structure and function changes in spontaneously hypertensive (SHR) and renal hypertensive (RHR) rats were followed in vivo by magnetic resonance imaging over 7 months. Wistar-Kyoto rats served as controls. METHODS: Systolic blood pressure (SBP) was measured once a week by the tail-cuff method. Transverse left ventricular sections were obtained at end-diastole and end-systole by electrocardiogram-gated magnetic resonance imaging, allowing the determination of left ventricular mass, wall thickness and volume. Angiotensin II (Ang II) plasma levels were determined at 2 and 4 weeks into the study. At the end of the study functional parameters were obtained by left ventricular catheterization. RESULTS: After 4 weeks both SHR and RHR showed a similar degree of hypertension. At 4 weeks Ang II levels were significantly elevated in RHR and suppressed in SHR relative to controls. The extent of left ventricular hypertrophy was essentially the same in SHR and RHR, but the diastolic left ventricular wall thickness: volume ratio was substantially increased in RHR only. During the first 11 weeks of the study, a small end-systolic volume and an increased end-systolic wall thickness allowed the systolic wall stress in RHR to be maintained near control values. Thereafter a discrete deterioration of left ventricular function was observed, as demonstrated by the steady increase in end-systolic volume. In contrast, SHR did not show an increase in end-systolic wall thickness at any time, resulting in an elevated systolic wall stress. However, left ventricular function was stable during the observed period. CONCLUSION: Despite similar SBP and left ventricular mass, left ventricular remodelling and function were different in RHR and SHR. SHR appeared to be stable during the 30-week observation period, whereas RHR exhibited a progressive functional impairment after week 11. The distinct involvement of the renin-angiotensin system in the pathogenesis of hypertension in these models may account for these differences.

Animals↗
PubMed1995

Conductance catheter measurement of left ventricular volume: evidence for nonlinearity within cardiac cycle.

The conductance catheter gain factor, alpha, is usually determined by an independent measure of stroke volume and, as such, is assumed to be constant. However, nonlinearity of the conductance-volume relation has been proposed on theoretical grounds. The present study was designed to establish the extent of nonlinearity, or variability of alpha, within the cardiac cycle using magnetic resonance imaging (MRI) as the reference method. Pentobarbital-anesthetized minipigs (n = 10, 10-13 kg) were instrumented with left ventricular (LV) conductance and Millar catheters. Conductance catheter signals were recorded, and volumes were corrected for parallel conductance using a saline-dilution technique. Animals were then placed in a 4.7-T magnet, and first time derivative of LV pressure-gated transverse MRI images (5-mm slices) acquired during isovolumic contraction (end diastole) and relaxation (end systole). LV cavity volumes were then determined using a third-order polynomial model. The gain alpha was computed three ways: by dividing conductance stroke volume by MRI stroke volume (alpha SV), by dividing conductance end-diastolic volume by MRI end-diastolic volume (alpha ED), and by dividing conductance end-systolic volume by MRI end-systolic volume (alpha ES). alpha SV was 0.62 +/- 0.15, with alpha ED (0.71 +/- 0.17) significantly lower than alpha ES (0.81 +/- 0.21; P < 0.001). Using alpha SV to adjust conductance gain (i.e., assuming constant gain) resulted in a significantly larger end-diastolic volume (25.8 +/- 4.6 ml) and smaller ejection fraction (46.8 +/- 7.2%) than those obtained with MRI (23.0 +/- 4.1 ml and 53.1 +/- 7.3%, respectively; P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Electromyogram spectrum changes during sustained contraction related to proton and diprotonated inorganic phosphate accumulation: a 31P nuclear magnetic resonance study on human calf muscles.

The calf muscles of five clinically healthy men were submitted to isometric exercise and examined by 31P nuclear magnetic resonance (NMR) spectroscopy and electromyography (EMG) to evaluate the influence of proton (H+) and diprotonated forms of inorganic phosphate (H2PO4-) accumulation on EMG spectrum changes. The experiments were performed in a supra-conducting magnet (2.35 Tesla, 35-cm effective diameter) using a surface coil (7-cm diameter) positioned against the calf muscles. The EMG surface electrodes were applied on the gastrocnemius medialis muscle and acquisition of both NMR and EMG signals was synchronized. The exercise consisted of a sustained isometric contraction at 70% of the maximal voluntary contraction until exhaustion. A continuous decrease in phosphocreatine content and a large concomitant increase in H2PO4- was observed in the calf muscles of each subject. A significant increase in H+ concentration was also found when considering the whole population but intracellular acidosis was low for two subjects. Moreover, a quasilinear decrease in mean power frequency (MPF) was found during the test. Changes in MPF were correlated with variations in H+ and H2PO4- concentration but a more significant relationship was found when MPF changes were correlated with H2PO4- concentration. An interpretation of EMG spectrum changes in terms of an accumulation of by-products of anaerobic metabolism and an increase in the relative number of activated slow fibres is proposed.

Adult↗
PubMed1993

Role of atrial natriuretic factor in impaired sodium excretion of normocapnic and hypercapnic patients with chronic obstructive lung disease.

To investigate the mechanisms of sodium retention in patients with chronic obstructive lung disease (COLD), we examined the renal and hormonal responses to volume expansion with isotonic saline and to infusion of atrial natriuretic factor (ANF) in 10 hypercapnic (PaCO2 52 +/- 2 mm Hg) and 12 normocapnic patients (PaCO2 39 +/- 1 mm Hg). Sodium excreted within 4 h of loading (expressed as % sodium load) was 23.5 +/- 2.5% (p < 0.05) in normocapnic and 8.5 +/- 1.5% (p < 0.001) in hypercapnic patients, compared with 32.5 +/- 3.0% in 11 age-matched control subjects. Sodium excretion and renal blood flow correlated negatively with arterial PCO2 and positively with FEV1. Basal plasma ANF concentrations were 72 +/- 5 pg/ml in controls, 100 +/- 14 pg/ml in normocapnic patients, and 230 +/- 52 pg/ml in hypercapnic patients (p < 0.001). Plasma renin activity and aldosterone did not differ between groups. In response to volume expansion, plasma ANF increased in both normocapnic and controls (with a greater increase in normocapnic patients) but remained unchanged in hypercapnic patients. Exogenous ANF increased glomerular filtration rate, renal plasma flow, natriuresis, and diuresis in both groups of patients. Patients with COLD have depressed renal function that appears unrelated to activation of the renin-angiotensin-aldosterone system. An increased secretory response of ANF to volume expansion may help to maintain volume homeostasis in normocapnic patients, while a blunted secretory response of ANF may contribute to sodium retention in hypercapnic patients.

Aged↗
PubMed1993

Discrimination between cross-country and downhill skiers by pulmonary and local 31PNMR evaluations.

The purpose of the present study was to correlate data on calf muscle metabolism using 31P nuclear magnetic resonance spectroscopy with measurements of whole body maximal oxygen consumption and maximal power output, and to determine whether the combination of these data could be used to predict athletic ability. Experiments were performed in a 2.35 Tesla, 35 cm diameter electromagnet on the leg muscle of sedentary human subjects (N = 6) and groups of athletes trained for endurance (cross-country skiers, N = 7) or strength performance (downhill skiers, N = 5). The exercise protocol consisted of successive plantar flexions performed at graded fractions of the maximal voluntary contraction (MVC). The results obtained from NMR investigation (changes in content of inorganic phosphate: Pi, phosphocreatine: PC and muscle ATP, and intracellular pH) were then compared with those of maximal O2 consumption (VO2max) and maximal power (MP). When the data on athletes were compared with those obtained on sedentary subjects, the curves illustrating the relationship between the imposed load and the Pi/PC ratio were significantly shifted toward high output power for a given Pi/PC value. It also appeared from this study that specific training in force development (downhill skiing) induced a slighter decrease in PC level than for endurance (cross-country skiers) despite improvement in physical performance. A slight but significant intracellular acidification was observed in the muscles of sedentary subjects and downhill skiers for contraction at, respectively, 50% and 80% of MVC, but not in the skeletal muscles of cross-country skiers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Traditional remedies used in the western Pacific for the treatment of ciguatera poisoning.

Ciguatera is a specific type of food poisoning associated with the ingestion of tropical fish, which, although normally safe for consumption, may at times contain high amounts of ciguatoxin, as well as other chemically related toxins. Widespread in tropical regions where coral reefs are present, ciguatera fish poisoning constitutes a major hindrance for local fishing industries, local economies and foreign trade. Because no symptomatic treatment has been totally satisfactory, folk remedies remain of great interest. In this paper, a list of plants used in treating ciguatera poisoning in the Western Pacific region is presented, with emphasis on species whose exact utilization (part of plant used, preparation, dosage) has been determined.

Animals↗
PubMed1992

Effect of training on the calf muscle energy metabolism. A 31P-NMR study on four elite downhill skiers challenged with a standardized exercise protocol.

This study evaluates the effects of a 6 months' training period on the bioenergetics of the calf muscle of elite athletes by means of phosphorus-31 Nuclear Magnetic Resonance Spectroscopy (31P-NMR). Four downhill skiers, belonging to the Spanish National Team, performed a standardized exercise protocol using their right leg inside a wide-bore 2.35 Tesla magnet. The inorganic phosphate/phosphocreatine (Pi/PC) ratio and intracellular pH (pHi) were measured at steady-state during an exercise protocol composed of 5 work levels between 20% and 80% of the maximum voluntary contraction (MVC), before and after the training period. The measured values, which were markedly scattered at the beginning, regrouped after training. This was caused by a shift towards lower Pi/PC ratios and by a lower pHi acidification in three of the four subjects. This result suggests that 31P-NMR is a good tool to evaluate changes in the muscle aerobic capacity of athletes induced by training.

Adenosine Diphosphate↗
PubMed1992

Muscle bioenergetics in skiers: studies using NMR spectroscopy.

Sedentary human subjects (n = 6) and two homogeneous groups of athletes, trained for down-hill skiing (n = 5) and cross-country skiing (n = 7), were subjected to cardiorespiratory testing and to evaluation of the bioenergetics of calf muscles by means of Phosphorus Nuclear Magnetic Resonance Spectroscopy. The exercise consisted of successive plantar flexions performed at graded fractions of the maximal voluntary contraction force. It appears from this study that the decrease in phosphocreatine level induced by exercise at 80% of maximal voluntary contraction, was smaller in the muscles of athletes who trained for cross-country skiing, than in the muscles of down-hill skiers and control subjects. Intracellular acidosis was virtually absent in cross-country athletes. The rate of restitution of phosphocreatine, after the exercise, was higher in both groups of skiers, compared to sedentary subjects. The maximal oxygen consumption and the maximal alactic power were higher in athletes than in sedentary subjects. NMR data and mechanical measurements are used in consideration with functional systemic indexes to characterize the capabilities of skiers.

Adult↗