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Biomedical subjects

A Simon

Publications and source records attributed to A Simon.

At least 235 records · Page 13Linked to original sources
PubMed1995

Role of blood pressure, uric acid, and hemorheological parameters on plasma homocyst(e)ine concentration.

Elevated concentration of plasma homocyst(e)ine is an independent risk factor for clinical atherosclerosis. In this study, the concentration of plasma homocyst(e)ine in men who lacked a history of atherosclerotic disease was correlated with hemodynamic, rheological and biochemical parameters. Hypertensive subjects had higher concentrations of plasma homocyst(e)ine than normotensive subjects. Positive correlations were found between concentrations of plasma homocyst(e)ine and several risk factors, but some of these correlations disappeared when they were adjusted for other variables. However, multivariate analyses demonstrated that systolic blood pressure, plasma uric acid, and hematocrit were predictors of concentrations of plasma homocyst(e)ine, after adjusting for certain risk factors. The possible significance of these interrelationships in atherogenesis require further study.

Blood Flow Velocity↗
PubMed1995

The retinal pigment epithelial-specific 11-cis retinol dehydrogenase belongs to the family of short chain alcohol dehydrogenases.

We have isolated and partially characterized a 32-kDa membrane-associated protein (p32), which forms a complex with p63, an abundant membrane protein in bovine retinal pigment epithelium. The sequence of a cDNA clone for p32 revealed an open reading frame encoding 318 amino acid residues. Several hydrophobic regions could be identified, suggesting that p32 is an integral membrane protein. A search of data bases identified p32 as a member of the superfamily of short chain alcohol dehydrogenases. Transcripts for p32 were specifically expressed in retinal pigment epithelium. Overexpression of p32 in Cos cells produced a membrane-bound stereospecific 11-cis retinol dehydrogenase, active in the presence of NAD+ as cofactor but not in the presence of NADP. We propose that p32 is the stereospecific 11-cis retinol dehydrogenase, which catalyzes the final step in the biosynthesis of 11-cis retinaldehyde, the universal chromophore of visual pigments.

Alcohol Oxidoreductases↗
PubMed1995

High-density lipoprotein subfractions as markers of early atherosclerosis. PCVMETRA Group. Prévention Cardio-Vasculaire en Medecene du Travail.

Although the inverse relation between high-density lipoprotein (HDL) cholesterol concentration and the risk of ischemic heart disease is well established, little is known about the relation of HDL subfractions HDL2 and HDL3 or lipoprotein A-I and A-I-A-II to extracoronary disease, particularly at its silent phase before the appearance of clinical lesions. We investigated the potential influence of HDL subfractions as risk markers, among the other main lipid and nonlipid risk factors, by assessing early atherosclerotic plaques detected by 3 ultrasound imaging sites in 181 hypercholesterolemic symptom-free men. No plaques were found in 36% of the patients, but plaques were found at carotid, aortic, and femoral sites in 24%, 40%, and 46% of subjects, respectively. Data were analyzed using univariate comparisons and multiple logistic regression. According to the logistic analysis, plaques were associated (1) with blood pressure (p = 0.008) and low-density lipoprotein (LDL) cholesterol (p = 0.02) in the carotid arteries; (2) with age (p = 0.0005), triglycerides (p = 0.002), and cigarette smoking (p = 0.02) at the aortic site; and (3) inversely with HDL3 cholesterol (p = 0.0008) and positively with cigarette smoking (p = 0.004), and age (p = 0.04) in the femoral site. The number of arterial sites affected (0, 1, 2, and 3) by plaques was inversely associated with HDL3 cholesterol (p = 0.001), and positively associated with smoking (p = 0.002), blood pressure (p = 0.002), LDL cholesterol (p = 0.003), and age (p = 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Wall thickening of carotid and femoral arteries in male subjects with isolated hypercholesterolemia. PCVMETRA Group. Prevention Cardio-Vasculaire en Medecine du Travail.

This study was performed to determine whether hypercholesterolemic men had increased large artery intima-media thickness (IMT), a potential surrogate measure of atherosclerosis, compared to normocholesterolemic controls. The measurements were performed in the far walls of common carotid and femoral arteries with non-invasive automatic computerized ultrasonic technique in 101 asymptomatic men (28-60 years) of whom 40 were normocholesterolemic (total cholesterol < 5.2 mmol/l, controls), 25 had borderline hypercholesterolemia (5.2 < or = total cholesterol < 6.2 mmol/l, group 1) and 36 had hypercholesterolemia (total cholesterol > or = 6.2 mmol/l, group 2). All the subjects had no other traditional risk factors, except smoking. Carotid and femoral IMT were significantly increased in group 2 (P < 0.01) but not in group 1 compared to controls. When all subjects were pooled for analysis, carotid and femoral IMT were correlated (r = 0.47, P < 0.001) and increased with total cholesterol (r = 0.35, P < 0.001) and LDL cholesterol (r = 0.33, r = 0.34, respectively; P < 0.001). Carotid and femoral IMT increased with age in each group: controls, r = 0.46, P < 0.01 and r = 0.50, P < 0.001, respectively; group 1, r = 0.42, P < 0.05; group 2, r = 0.48, P < 0.01, and r = 0.59, P < 0.001, respectively. At the carotid and femoral sites, the regression slopes between age and IMT were steeper in group 2 than in controls (P < 0.01). Thus, hypercholesterolemia was associated with diffuse large artery wall thickening, whose presence might be useful in the identification of those hypercholesterolemic individuals most prone to developing atheromatous changes, in the decision to treat, and in the monitoring of lipid-lowering treatment.

Adult↗
PubMed1995

Are there dopaminergic ganglion cells in the mammalian retina?

New improvements of the tyrosine hydroxylase immunocytochemical labelling in wholemounts allowed us to visualize tyrosine hydroxylase-immunoreactive fibres in the nerve fibre layer of the mouse, rat and macaque monkey retinas. These fibres could not be related to labelled somata in the retina. Their possible origin from ganglion cells or brain nuclei is discussed.

Aging↗
PubMed1995

Stratification of vascular risk in hypertension and therapeutic perspective.

Hypertension is a major risk factor for cardiovascular disease and atherosclerosis is the cause of most hypertensive complications. Therefore the detection of preclinical atherosclerosis may contribute to the better identification of hypertensive subjects at high risk of complications. Three main alterations are currently able to be diagnosed noninvasively: calcification, thickening, and stiffening of the arterial walls. Calcification of epicardial coronary arteries can be seen noninvasively by ultrafast computed tomography thanks to its rapid acquisition of image. Coronary calcification of epicardial coronary arteries can be seen noninvasively by ultrafast computed tomography thanks to its rapid acquisition of image. Coronary calcification is typical of atherosclerosis but not of stenosis. Conversely, the absence of calcification eliminates, practically, coronary artery disease as a diagnosis. Coronary calcification is present in only 63% of asymptomatic hypertensive men, suggesting that the degree of coronary atherosclerosis associated with high blood pressure varies among individuals. Wall thickening can be quantified in vivo by automated computerized analysis of ultrasonic images of the far wall intima-media complex of extracoronary vessels. Carotid and femoral wall thickening was observed in hypertensive subjects who had never been treated for hypertension compared to normotensive controls of similar age. Such vascular hypertrophy was not found in all patients, attesting to the disparity of the structural arterial changes within hypertensive subjects. Recent evidence from studies of essential hypertension suggests the lack of association between diffuse wall thickening of carotid or femoral arteries and the presence of atherosclerotic plaque (focal echogenic encroachment) in the same vessel. However, other studies in at-risk subjects suggest that extracoronary wall thickening could be related to the presence of coronary atherosclerosis, and to the incidence of coronary events. Wall stiffening is the third arterial alteration related to the sclerotic component of atherosclerosis. Its evaluation is based on the velocity of pulse wave propagation within the arterial tree or on the ultrasonic (echotracking) assessment of arterial wall distension during the cardiac cycle. Arterial stiffening is increased in the presence of hypertension, and such an increase is potentiated by the presence of other risk factors, such as smoking or hypercholesterolemia. Finally, the detection of early atherosclerosis with the above techniques optimizes the stratification of atherosclerotic risk, and may provide relevant information on comparative effectiveness of various classes of antihypertensive agents.

Antihypertensive Agents↗
PubMed1995

Porcine valves are reendothelialized by human recipient endothelium in vivo.

The degeneration of human allogeneic and porcine xenogeneic heart valves has not been clearly understood. The question is whether the observed loss of function and calcification is primarily an immunologic process or a mechanical process or is influenced by both factors. In the current study, we looked at explanted xenogeneic heart valves for the presence of recipient endothelium. Explanted valves were shock frozen and stored at -80 degrees C before use. They were subsequently examined by immunohistochemical staining with a variety of monoclonal antibodies. Xenogeneic valves showed clearly positive results for the human major histocompatibility complex class I and class II antigens and morphologically showed a thin layer of viable endothelium restricted to the annular region of the valve. Additionally, they were also positive for intercellular adhesion molecule-1 and the H-Y antigen. Although the xenogeneic valves were significantly degenerated, the endothelium was clearly defined and could be identified immunohistochemically as being of recipient origin. The grafts remained negative for endothelial cell-leukocyte adhesion molecule-1 and factor VIII. These data allow speculation on whether reendothelialization of valvular grafts with recipient endothelium is a normal repair mechanism in vivo.

Animals↗
PubMed1995

[Methodical investigations on the metabolism oriented determination of methionine requirement of broiler chickens. 3. Degradation of 14C-(CH3)- and 35S-methionine after feeding of synthetic diets].

In a chicken experiment was investigated, whether the kind of applied isotope and labelling site influence the results of the metabolism oriented estimation of the methionine requirement. Furthermore it was studied, if this method can give additional informations to weight gain and N-retention data concerning methionine requirement. 48 male broiler chickens received synthetic diets with a complete amino acid mixture from day 7 posthatching. The methionine content of the 8 experimental diets varied from 2.25 to 7.5 g methionine/kg DM (1.17 to 3.87 g/16 g N). The low weight gain (13 to 22 g/d) and N-retention (0.55 to 0.87 g/d; from day 13 to 17 posthatching) was due to the inferior intake of the synthetic diets. Methionine supplementation increased weight gain and N-retention only up to 3 g methionine/kg DM. The metabolic methionine requirement was measured after i.v. injection of 14C-(CH3)- and 35S-methionine by 14CO2-excretion with breath and 35S-excretion with excrements. Both parameters gave similar results and showed an increased methionine degradation at methionine contents exceeding 4.5 g methionine/kg DM. Because there was no increase in methionine degradation up to 4.5 g/kg DM, an increased reutilization of methionine within the range between 3 and 4.5 g methionine/kg DM was supposed, which may act as a spare-mechanism. For practical feeding applications, also in case of low feed intake, a minimal methionine content of 4.5 g/kg DM is recommended.

Amino Acids↗
PubMed1995

Reactive hyperemia unmasks reduced compliance of cutaneous arteries in essential hypertension.

To evaluate changes in distal cutaneous arteries during hypertension, we used a noninvasive method to assess the compliance and vascular resistance of the hand radial arteries, mainly distributed to the skin, in 10 normotensive and 10 hypertensive (HT) men. Radial artery diameter and blood velocity were measured by means of pulsed Doppler concomitantly with measurements of finger arterial pressure by photoplethysmography. Hand radial vascular resistance was calculated as the ratio of mean arterial pressure to mean radial blood flow. A simple resistive-capacitive model of large and small arteries of the hand allowed us to evaluate arterial compliance from the exponential slope of finger diastolic pressure decay and vascular resistance. Measurements were made at baseline and during reactive hyperemia after 5 min of complete occlusion of the brachial artery with a pneumatic cuff. Except for pressure, there were no baseline differences between the groups. In normotensive and HT subjects, hyperemia increased radial artery diameter and blood velocity (P < 0.001) and compliance (P < 0.01 and P < 0.05, respectively) and decreased mean pressure (P < 0.01 and P < 0.001, respectively) and resistance (P < 0.001). During hyperemia, the only difference between the groups, except for pressure, was lower compliance in HT subjects (P < 0.01). Moreover, compliance during hyperemia negatively correlated with baseline mean pressure (P = 0.001). Thus hyperemia unmasked reduced compliance in the HT patients but did not show abnormal resistance, suggesting that the elastic properties of the hand skin radial arteries might be more sensitive than their resistive properties to high blood pressure.

Adult↗
PubMed1995

Evaluation of the sialic acid content of LDL as a marker of coronary calcification and extracoronary atherosclerosis in asymptomatic hypercholesterolemic subjects. PCVMETRA Group.

Recent studies have shown that the sialic acid content of LDL isolated from patients with angiographically demonstrated advanced coronary atherosclerosis is lower than that of LDL isolated from healthy subjects. These observations raise the question as to whether LDL sialic acid content could be used as an early marker of atherosclerosis. We screened for carotid, aortic, and femoral plaques by ultrasonography and for coronary calcifications by ultrafast computed tomography in 160 hypercholesterolemic subjects free of cardiovascular disease to investigate the relation between LDL sialic acid content and the prevalence of these early atherosclerotic lesions. LDL sialic acid values varied from 19.6 to 46.6 nmol/mg LDL protein (33.9 +/- 4.4, mean +/- SD) in the whole population, but the distribution was very similar: (1) in subjects with no plaque (34.1 +/- 4.9) relative to those with one or several plaques at one (34.2 +/- 4.4), two (33.0 +/- 3.6), or three (34.8 +/- 3.4) different arterial sites; (2) in subjects with (33.9 +/- 3.7) and without (34.1 +/- 4.8) coronary calcification; and (3) in subjects with both extracoronary and coronary lesions (33.8 +/- 3.9) relative to those with no arterial lesions (34.2 +/- 4.5). LDL sialic acid content was not related to sex, age, body mass index, smoking, blood pressure, or serum total cholesterol and lipoprotein(a) levels but correlated negatively with serum triglyceride levels (P < .001). These results suggest that LDL sialic acid content is not a discriminant marker of early atherosclerosis in asymptomatic hypercholesterolemic subjects.

Adult↗
PubMed1995

Platelet cytosolic Ca2+ and membrane dynamics in patients with primary hypercholesterolemia. Effects of pravastatin.

This study was designed to evaluate the relationships between platelet cytosolic Ca2+ concentration ([Ca2+]i) and plasma lipids in patients with primary hypercholesterolemia. In a double-blind, placebo-controlled trial, we determined platelet [Ca2+]i in the presence and virtual absence of extracellular Ca2+ and the effects of prolonged treatment with pravastatin, a selective inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. Platelet [Ca2+]i and membrane microviscosity were determined in 22 normotensive hypercholesterolemic men. Platelet [Ca2+]i was observed to vary with in vivo plasma lipid characteristics: in untreated patients, [Ca2+]i determined at low extracellular Ca2+ concentration was significantly associated with plasma triacylglycerols (P = .008) and with the total cholesterol to HDL cholesterol ratio (P = .044). Triacylglycerol levels also correlated inversely with the external Ca(2+)-dependent [Ca2+]i rise. Pravastatin treatment reduced plasma total cholesterol (-20 +/- 3%), LDL cholesterol (-30 +/- 3%), triacylglycerols (-17 +/- 6%), and apoB levels (-25 +/- 4%) and simultaneously decreased platelet [Ca2+]i measured in a low-Ca2+ medium by 14 +/- 6% (P = .03). However, [Ca2+]i values remained positively correlated with the total cholesterol to HDL cholesterol ratio (P = .04). Prvastatin treatment did not induce marked changes in membrane microviscosity, although the changes in trimethylaminodiphenylhexatriene anisotropy were inversely correlated with those of HDL cholesterol. These results indicate that plasma lipids can modulate cytosolic Ca2+ in platelets by affecting Ca2+ transport pathways that are dependent and independent of Ca2+ influx.

Adult↗
PubMed1995

Fibrinogen and silent atherosclerosis in subjects with cardiovascular risk factors.

Fibrinogen may play an active role in the development and progression of atherosclerotic plaques. We assessed the association between fibrinogen levels and atherosclerotic plaques over three different arterial sites in an asymptomatic never-treated male population with increased cardiovascular risk. We included 652 men aged 40 to 60 years old with at least one of the following cardiovascular risk factors: cholesterol > 6.2 mmol/L and/or systolic blood pressure > or = 160 mm Hg and/or diastolic blood pressure > or = 95 mm Hg, and/or because they smoked. Carotid and femoral arteries and the abdominal aorta were assessed by using ultrasonographic methods for the presence of plaque, and subjects were categorized according to the presence (or absence) and extent (one versus two or three sites) of plaque. Plasma fibrinogen was measured according to the thrombin-time method of Clauss. While the presence of atherosclerosis was significantly related to age, current smoking, systolic pressure, LDL cholesterol, and fibrinogen levels, the extent of atherosclerosis was related to age and triglyceride and fibrinogen levels. Multiple regression analysis indicated independent associations between fibrinogen and the presence and extent of atherosclerosis. Plaque prevalence was significantly more pronounced with increasing tertile of fibrinogen levels. The odds ratio of the upper to lower fibrinogen tertiles for the presence of plaque was 1.6 (95% confidence interval, 1.4 to 1.8) and 1.4 (95% confidence interval, 1.2 to 1.7) for its extent. Adjustment for other risk factors slightly reduced the association between fibrinogen and atherosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Effects of hypertension on viscoelasticity of carotid and femoral arteries in humans.

We compared the properties of common carotid and femoral arteries of 16 normotensive and 14 hypertensive men. Arterial pressure and diameter were recorded noninvasively in each vessel by tonometric and echotracking devices. The x-y composition of pressure and diameter waves provided the diameter-pressure hysteresis loop. The elastic diameter-pressure curve and wall viscosity index were deduced after hysteresis elimination. The compliance-pressure and distensibility-pressure curves were derived from the diameter-pressure curve, allowing the calculation of effective compliance and distensibility at the prevailing pressure of each subject and isobaric compliance and distensibility at the same standard pressure in all subjects. Systolic, diastolic, mean, and pulse pressures and diameters in each vessel were higher in the hypertensive than the normotensive group, except carotid pulse diameter, which did not differ. The carotid diameter-pressure, compliance-pressure, and distensibility-pressure curves did not differ between groups. In the carotid artery hypertensive patients had isobaric compliance and distensibility values similar to those of normotensive subjects, despite lower effective compliance (P < .05) and distensibility (P < .01). The femoral diameter-pressure curve was higher (P < .05) and the femoral compliance-pressure and distensibility-pressure curves were lower (P < .01) in the hypertensive than the normotensive group. Hypertensive patients had effective and isobaric femoral compliance and distensibility values lower than to those of normotensive subjects (P < .001). In both arteries, viscosity index was higher in the hypertensive than the normotensive group (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Arterial wall mechanics in conscious dogs. Assessment of viscous, inertial, and elastic moduli to characterize aortic wall behavior.

To evaluate arterial physiopathology, complete arterial wall mechanical characterization is necessary. This study presents a model for determining the elastic response of elastin (sigma E, where sigma is stress), collagen (sigma C), and smooth muscle (sigma SM) fibers and viscous (sigma eta) and inertial (sigma M) aortic wall behaviors. Our work assumes that the total stress developed by the wall to resist stretching is governed by the elastic modulus of elastin fibers (EE), the elastic modulus of collagen (EC) affected by the fraction of collagen fibers (fC) recruited to support wall stress, and the elastic modulus of the maximally contracted vascular smooth muscle (ESM) affected by an activation function (fA). We constructed the constitutive equation of the aortic wall on the basis of three different hookean materials and two nonlinear functions, fA and fC: sigma = sigma E + sigma C + sigma SM + sigma eta + sigma M = EE. (epsilon - epsilon 0E) + EC.fC.epsilon + ESM.fA.epsilon + eta. [equation: see text] + M.[equation: see text] where epsilon is strain and epsilon 0E is strain at zero stress. Stress-strain relations in the control state and during activation of smooth muscle (phenylephrine, 5 micrograms.kg-1.min-1 IV) were obtained by transient occlusions of the descending aorta and the inferior vena cava in 15 conscious dogs by using descending thoracic aortic pressure (microtransducer) and diameter (sonomicrometry) measurements. The fC was not linear with strain, and at the onset of significant collagen participation in the elastic response (break point of the stress-strain relation), 6.02 +/- 2.6% collagen fibers were recruited at 23% of stretching of the unstressed diameter. The fA exhibited a skewed unimodal curve with a maximum level of activation at 28.3 +/- 7.9% of stretching. The aortic wall dynamic behavior was modified by activation increasing viscous (eta) and inertial (M) moduli from the control to active state (viscous, 3.8 +/- 1.3 x 10(4) to 7.8 +/- 1.1 x 10(4) dyne.s.cm-2, P < .0005; inertial, 61 +/- 42 to 91 +/- 23 dyne.s2.cm-2, P < .05). Finally, the purely elastic stress-strain relation was assessed by subtracting the viscous and inertial behaviors.

Animals↗
PubMed1995

Some correlates of individuals' attitudes toward lesbians.

The relationship between individuals' attitudes toward lesbians and other attitudes and personal characteristics was investigated. A total of 564 participants completed the Attitudes Toward Lesbians (ATL) scale (Herek, 1988) along with items assessing interactions with lesbians. Additionally, smaller portions of the sample received some combination of other questionnaires. Most predictions were supported: attitudes were generally not related to respondent sex and gender role self-concept, and positive attitudes were associated with having positive contact with lesbians, lesbian friends, and contemporary attitudes toward women. Predictions involving the relationship between attitudes and social desirability, sexual permissiveness, and love style received mixed support. The two-fold purpose of the investigation, to provide information about correlates and to replicate past trends, was accomplished.

Adolescent↗
PubMed1995

Sex ratio in triplets.

Since the introduction of different ovulation induction regimens the incidence of triplet pregnancies increased from a spontaneous rate of about 1:10,000 to the frequency of nearly 1:1000. Sex ratio of trigemini and male/female proportion of the three newborns within the same triplet set is the amazing issue that we attempted to elucidate in the present study. Data on 36 women with triplet pregnancies delivered in our hospital and information regarding 2717 triplet pregnancies reported by 16 relevant papers were included in this study. 36 women delivered 63 (58%) male and 45 (42%) female babies. Triplet sets of same gender comprised 33% of all trigemini. Sex ratios (male/female) for the spontaneous, menotropin and clomiphene group were 2.00, 1.57 and 0.94 respectively. Homogenous male/female set ratio was 5.0, 2.0 and 0.5 in menotropin, spontaneous and clomiphene groups respectively. As the percentage of ovulation induction triplet pregnancies increased constantly from 0% to 100%, a decline in the fraction of homogenous gender triplet sets was observed--from 73% to 23%. It may be concluded that sex ratio in triplet newborns is divergent according to different publications with most of the authors reporting a male/female ratio of less than 1.00. Ovulation induction results in a lower proportion of homogenous sex triplets sets. Superovulation by menotropins cause a higher percentage of male triplet newborns when compared to ovulation induction by clomiphene.

Clomiphene↗