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Biomedical subjects

S Laurent

Publications and source records attributed to S Laurent.

At least 19 recordsLinked to original sources
PubMed1992

[Do converting enzyme inhibitors differ from each other in the treatment of hypertension?].

Novel angiotensin converting enzyme inhibitors (ACE inhibitors) have recently been commercialized and the question arises whether differences in pharmacodynamic and pharmacokinetic properties should lead to specific therapeutic choices. To our knowledge there is no data which allows the physician to conclude to any different antihypertensive efficacy when ACE inhibitors are used at adequate dosage. Their pharmacokinetic characteristics may differ at every level: absorption, distribution, metabolism and excretion. Differences in chemical structure may also influence their diffusion in various tissues, therefrom the amplitude and duration of inhibition of angiotensin II at these sites. The duration of maximum blockade of ACE and the amplitude of residual blockade may theoretically influence the duration of the hypotensive effect and the number of daily dosages. Once-daily administered long acting ACE inhibitors keep their antihypertensive action through the whole 24-hour period, during chronic treatment. The theoretical advantage of such a property is an improved control of 24-hour blood pressure. However, no study, to our knowledge, concluded to any difference between long acting ACE inhibitors as far as this parameter was concerned. In addition, except captopril which has been reported to induce major untoward effects at the time high dosages were introduced, ACE inhibitors do not seem to bear different undesirable effects.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

[Effects of aging on arterial function in man].

The structure of arteries changes with age. Gradual disappearance of elastic fibres facilitates dilatation of the arterial lumen and increase in length of the vessels. Simultaneously, the arterial wall becomes thicker, but it is often difficult to distinguish the changes due to ageing from those caused by atherosclerosis. These structural alterations result in a greater rigidity of the arteries, which can now be evaluated by non-invasive segmental methods. This shows that ageing does not have the same functional effects on wide-caliber elastic arteries and on middle-sized muscular arteries. The increase of systolic arterial pressure observed in the elderly is a consequence of structural and functional changes in the arterial system.

Aged↗
PubMed1992

Acute changes in forearm haemodynamics produced by cigarette smoking in healthy normotensive non-smokers are not influenced by propranolol or pindolol.

The aim of the present study was to examine the effect of cigarette smoking in healthy non-smokers on blood pressure and forearm haemodynamics after acute oral administration of non-selective beta-adrenoceptor blockers with and without intrinsic sympathomimetic activity, viz. pindolol 15 mg and propranolol 80 mg. A preliminary study was done to compare cigarette smoking and sham smoking to evaluate the time-course of the haemodynamic effects of cigarette smoking. The second experiment was then carried out in the same six volunteers, according to a double-blind randomized placebo-controlled crossover design, to evaluate the possible effect of pre-treatment with beta-adrenoceptor blockers on blood pressure, heart rate and forearm haemodynamics (forearm blood flow, brachial artery diameter and brachio-radial pulse-wave velocity) measured at baseline, during smoking and every five minutes up to 1 h afterwards. No major difference from placebo in blood pressure or forearm haemodynamics was found and pre-treatment with beta-blockers did not prevent the acute vascular effects of cigarette smoking.

Adult↗
PubMed1992

Carotid arterial haemodynamics after mild degrees of lower-body negative pressure in man.

1. Pulsatile changes in the diameter of the common carotid artery were studied transcutaneously using an echo-tracking technique in 15 normal subjects: eight subjects before and during application of graded lower-body negative pressure from -5 to -15 mmHg, and seven subjects before and during weight-bearing head-up tilt at 30 and 60 degrees. 2. In concomitant studies of changes in forearm vascular resistance, it was seen that mild lower-body negative pressure produced deactivation of cardiopulmonary receptors without changes in systemic blood pressure or heart rate. 3. After lower-body negative pressure, a significant decrease in carotid arterial diastolic diameter [from 0.662 +/- 0.028 to 0.624 +/- 0.033 cm (lower-body negative pressure -10 mmHg) and 0.640 +/- 0.030 cm lower-body negative pressure -15 mmHg), P < 0.001 and < 0.05] was observed. 4. After head-up tilt, carotid arterial diameter was also significantly decreased at 30 and 60 degrees, whereas a significant increase in heart rate occurred only at 60 degrees and mean blood pressure did not change. 5. The study provides evidence that the geometry of the arterial wall is substantially modified by non-invasive manoeuvres such as head-up tilting and lower-body negative pressure. The latter is assumed to selectively deactivate human cardiopulmonary receptors, but the present data suggest that local changes may also influence carotid baroreceptors.

Adult↗
PubMed1992

Rilmenidine: a novel approach to first-line treatment of hypertension.

Rilmenidine (RIL) is a novel antihypertensive drug selectively acting at the sites of imidazoline receptors. Compared with diuretics, beta-blockers, Ca2+ antagonists and angiotensin converting enzyme inhibitors, the four major groups recommended by the US Joint National Committee as first-line antihypertensive drugs, RIL appears to meet the same criteria of efficacy, safety, and acceptability. Rilmenidine dose-dependently decreases blood pressure (BP), acting as a vasodilator by decreasing vascular resistance through inhibition of the adrenergic nervous system, even while the BP changes due to standing and exercise. In comparison with placebo, RIL significantly decreased BP. In double-blind comparative trials versus first-line diuretics and beta-blockers, RIL normalized BP in approximately 60% patients, showing a similar efficacy to other drugs. In contrast with hydrochlorothiazide, RIL decreased total cholesterol and did not change plasma potassium levels. No tachyphylaxis was observed during long-term treatment. Central side effects, which have contributed to the limitation of the use of alpha 2-agonists as second- or third-line therapy for hypertension, were significantly less frequent with RIL than with clonidine or methyldopa. Indeed, the incidence of dry mouth and drowsiness during double-blind comparative trials versus clonidine and methyldopa was significantly lower with RIL. This absence of central side-effects was confirmed in double-blind comparative trials versus hydrochlorothiazide and atenolol. In contrast with clonidine, no sodium retention or weight gain were observed during chronic treatment with RIL.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1992

Mechanism of nitrate-induced improvement on arterial compliance depends on vascular territory.

The link between arterial caliber and distensibility has been studied extensively, with conflicting results. As have other researchers, we previously showed evidence of an increase in arterial diameter and a decrease in arterial stiffness with use of nitrates at the site of the brachial artery (BA) and the aorta. Whether these results would apply to other large superficial arteries remained to be established. In the present study, by means of an original pulsed ultrasound echo-tracking system based on Doppler shift, we measured internal diastolic diameter and stroke change in diameter of the common carotid artery (CCA), the femoral artery, and the BA in patients with essential hypertension and determined the acute effects of administration of isosorbide dinitrate (ISDN 20 mg). Twenty untreated hypertensive patients entered this randomized, placebo-controlled, double-blind, parallel study. No significant change occurred during placebo. During ISDN therapy, blood pressure (BP) decreased significantly; cross-sectional compliance increased at the site of the CCA, the BA, and the common femoral artery (CFA). The increase in cross-sectional compliance was mainly due to an increase in internal diameter for CCA and to an increase in distensibility coefficient (DC) for BA. The pattern of cross-sectional compliance was intermediate for CFA. During ISDN therapy, the augmentation index of the CCA distension waveform was significantly reduced, whereas no change occurred during placebo, suggesting a reduction in wave reflection by nitrates.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

An indirect evaluation of the effect of the autonomic nervous system following converting enzyme inhibition in hypertension.

Common carotid blood flow and cold pressor test were evaluated in 16 patients with sustained essential hypertension before and after 30 days treatment with the converting enzyme inhibitor Enalapril (20 mg). Enalapril decreased blood pressure and carotid vascular resistance with no significant change in heart rate. After treatment, despite a wide range of the responses, the changes in systolic blood pressure to cold test were significantly attenuated, whereas the heart rate responses were not. Acute random and double blind administration of either Cadralazine or Nitrendipine, two vasodilating drugs which are known to cause an activation of the autonomic nervous system, were performed before and after long term treatment by Enalapril. Whereas the blood pressure and heart rate responses to cold test was unmodified by these compounds before Enalapril treatment, significant changes were observed after converting enzyme inhibition: Cadralazine reduced the heart rate response whereas Nitrendipine increased it significantly. The study provides evidence that converting enzyme inhibition causes sympatho-inhibitory influences which are principally observed in stress conditions, with heterogeneous responses depending on the nature and the type of stimulation.

Adult↗
PubMed1992

Incompressibility of the human arterial wall: an in vitro ultrasound study.

AIM: The assumption that the arterial wall behaves like incompressible material simplifies the analysis of arterial wall elasticity. Experimental evidence for the incompressibility assumption has been obtained directly by volume-displacement and radiological methods. Recent developments in ultrasound technology have made it possible to take direct, high-resolution measurements of the internal diameter and wall thickness of an artery and thus calculate the cross-sectional area of the arterial wall. The objective of this study was to determine the cross-sectional area of the arterial wall in vitro at different levels of strain in order to demonstrate the incompressibility assumption. METHODS: Two different types of fresh, human, medium-sized arteries were studied, the internal mammary artery, and a less elastic and more muscular artery, the radial artery. The internal diameter and wall thickness were measured with an ultrasonic echo-tracking device (NIUS 1; Asulab, Neuchâtel, Switzerland) over 1-min steps of increasing intra-arterial pressure (0, 50, 100, 150 and 175 mmHg). RESULTS: The cross-sectional area of the arterial wall of the radial and internal mammary artery remained unchanged under different levels of strain. CONCLUSION: Since the artery length remained constant during the pressure increases, the lack of change in the cross-sectional area of the arterial wall suggests that the arterial wall of human medium-sized arteries is essentially incompressible.

Arteries↗
PubMed1992

Opposing effects of ageing on distal and proximal large arteries in hypertensives.

AIM: Hypertension has been reported to accelerate the alterations in large arteries induced by ageing. Distal large arteries have been poorly investigated in contrast to proximal large arteries. The objectives of this cross-sectional study were (1) to compare the storage capacity of different arterial sites in normotensive subjects or hypertensive patients; and (2) to compare the different arterial sites with respect to the effects of ageing on storage capacity, in normotensives and in hypertensives. METHODS: Two recently developed ultrasonic echo-tracking devices, offering a high resolution for the assessment of internal arterial diameter and its systolo-diastolic variations, were used to measure end-diastolic diameter, absolute (change at end-systole minus change at end-diastole) and relative (absolute change divided by change at end-diastole) changes in diameter with stroke and the absolute change in cross-sectional area (3.14 x the end-diastolic diameter x half the absolute stroke change in diameter) at the site of the common carotid artery, the abdominal aorta, the common femoral artery, the brachial artery and the radial artery in 50 untreated essential hypertensive patients and 32 normotensive subjects. RESULTS: In both groups, the end-diastolic diameter increased with age for the common carotid artery and the abdominal aorta but not for the common femoral, brachial or radial arteries. In the normotensives, the relative stroke change in diameter was negatively correlated with age for the common carotid artery (P < 0.001) and the abdominal aorta (P < 0.001), and not correlated for the common femoral, brachial and radial arteries. In hypertensives, the relative stroke change in diameter was negatively correlated with age for the common carotid artery (P < 0.05) and the abdominal aorta (P < 0.05), positively correlated with age for the common femoral (P < 0.05) and the radial arteries (P < 0.05) and not correlated for the brachial artery. Similar results were observed for the relationships between the absolute change in cross-sectional area and age. CONCLUSIONS: In hypertensives, enlargement of the proximal large arteries offsets the decrease in the relative stroke change in diameter and maintains an adequate storage capacity. It thus appears that ageing exerts opposing effects on central elastic large arteries and distal muscular medium-sized arteries.

Adult↗
PubMed1992

[Absence of labetalol interference on urine metanephrine determination in hypertensive patients].

The dosage of urinary catecholamines and their metabolites is a main element of diagnosis in the research of a pheochromocytoma in patients with high blood pressure. The literature reports high values of these compounds in patients treated with labetalol (an alpha/beta-blocker). An analytical interference has been evoked to explain these misleading results, which have not been observed with other beta-blockers. The goal of this work was to look for this eventual analytical interference in the dosage of urinary metanephrine by reversed phase liquid chromatography coupled with electrochemical detection, in patients with high blood pressure. Eighteen hypertensive patients, 52 +/- 14 years old, were included in the study. In 8 patients, a dosage of metanephrine, normetanephrine and creatinine on a 24 hours urine sample was performed before (D1) and 24 hours after (D3) the prescription of labetalol (200 mg twice a day). In the other group, labetalol was not prescribed but dosage was made in the same conditions. Urinary excretion of these compounds (metanephrine+normetanephrine) divided by urinary creatinine was not modified in the treated group (0.16 +/- 0.08 vs 0.14 +/- 0.04), nor in the reference group (0.17 +/- 0.08 vs 0.17 +/- 0.08). This study shows that administration of labetalol in patients with essential hypertension does not interfere with urinary metanephrine and normetanephrine determination after 48 hours of treatment. This implies that research for a pheochromocytoma is possible in patients with hypertension and receiving labetalol, by using reversed phase liquid chromatography coupled with an electrochemical detector for the dosage of urinary metanephrine and normetanephrine.

Adrenal Gland Neoplasms↗
PubMed1991

Arterial distensibility and left ventricular hypertrophy in patients with sustained essential hypertension.

Reduced aortic distensibility and compliance may participate in the genesis of cardiac hypertrophy in patients with hypertension. In these patients the increase in end-systolic stress, a determinant factor contributing to the development of cardiac hypertrophy, is influenced not only by the geometric properties of the ventricle but also by the level of systolic pressure. In patients with sustained essential hypertension, the degree of cardiac hypertrophy correlates significantly with the increase in aortic rigidity, which is assessed by the calculation of the characteristic impedance, by the measurement of carotid-femoral pulse-wave velocity, or by the calculation of the Peterson elastic modulus at the level of the aortic arch. Dihydralazine-like substances are unable to modify arterial stiffness, whereas calcium-entry blockers and converting-enzyme inhibitors improve arterial stiffness when achieving the same degree of blood pressure reduction. Modifications in the stiffness of the aorta and other large arteries must be considered to understand reversion of cardiac hypertrophy as a result of antihypertensive treatment.

Antihypertensive Agents↗
PubMed1991

Miniglucagon [glucagon-(19-29)] is a component of the positive inotropic effect of glucagon.

Glucagon is well known for its cardiotonic effect, but its mechanism of action remains undetermined. In the present study, we showed that glucagon, under minimal degradation conditions, had no effect on the amplitude of contractility of beating chick embryo ventricular cells. This raised the question of the contribution of the active metabolite of glucagon, glucagon-(19-29), referred to as miniglucagon, to the positive inotropic effect of glucagon. Incubation of glucagon with heart cells led to its rapid conversion into miniglucagon, as measured by radioimmunoassay. Accumulation of the metabolite was maximal after 8 min and remained stable until 15 min. reaching 6% of the initial glucagon concentration. Bacitracin inhibited this processing of glucagon into miniglucagon. Miniglucagon, from 0.1 pM to 1 nM, exerted a potent negative inotropic action. The most striking observation was a 45% increase in the amplitude of cell contractility elicited by the combination of 30 nM glucagon with 1 nM miniglucagon. A similar effect was obtained when glucagon was replaced by a low concentration (75 microM) of 8-bromoadenosine 3',5'-cyclic monophosphate. We conclude that glucagon processing into miniglucagon may be essential for the positive inotropic effect of glucagon on heart contraction.

Animals↗
PubMed1991

Central hypotensive effects of nicardipine in conscious freely moving spontaneously hypertensive rat.

The central cardiovascular effects of the calcium channel blocker nicardipine was studied in conscious freely moving normotensive Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Nicardipine was administered in a 1.5 microliters volume into the lateral ventricle of the brain (i.c.v.) or intravenously (i.v.). The injection of vehicle alone did not significantly change mean arterial pressure (MAP) or heart rate (HR). Nicardipine (10, 30, 100 and 300 micrograms/kg) intravenously administered, dose-dependently decreased MAP and increased HR in WKY and SHR. However, when administered i.c.v., nicardipine (10 micrograms/kg) increased MAP and HR in WKY and decreased MAP without any significant change in HR in SHR. These results are consistent with previous work reporting an exaggerated hypotensive response to i.c.v. administration of dihydropyridine calcium channel blockers in anesthetized SHR as compared to WKY. They suggest that a 1,4-dihydropyridine-sensitive pressor system is present in the SHR but not in the WKY.

Animals↗
PubMed1991

Stiffness of the common carotid artery in treated hypertensive patients.

Antihypertensive treatment, by lowering blood pressure and correcting functional and/or structural abnormalities of the arterial wall, may prevent the arterial damage due to the accelerated ageing process. The objective of the present study was to determine, using a cross-sectional approach, whether arterial distensibility of patients whose blood pressure had been normalized for several months by antihypertensive treatment, was significantly higher than that of untreated hypertensive patients. The properties of the vessel wall of the common carotid artery (CCA) were studied non-invasively, using an original pulsed ultrasound echo-tracking system based on Doppler shift, during a study comparing 46 normotensive subjects and 81 age-matched hypertensive patients. The latter group included 25 patients well controlled by antihypertensive treatment for at least 3 months and 56 untreated hypertensives. The three groups did not differ with respect to age, total and high-density lipoprotein cholesterol, blood glucose and smoking. In each group, there were significant relationships between age and CCA dimensional and functional data, including end-diastolic diameter, absolute and relative stroke changes in diameter and Peterson modulus, indicating a widening of the CCA with advancing age and a decrease in its buffering function. When compared with untreated hypertensives, well controlled hypertensives had significantly lower blood pressure and Peterson elastic modulus according to age. However, although blood pressure of well controlled hypertensives was not significantly different from that of normotensive subjects, their arterial distensibility remained altered compared with that of normotensive subjects (significant increase in Peterson elastic modulus). These results suggest that long-term antihypertensive treatment may not fully reverse arterial lesions due to the hypertensive disease.

Adult↗
PubMed1991

[Study of flow-dependent vasodilation of the femoral artery in hypertensive and normal subjects].

Flow dependent vasodilation of brachial artery is not significantly different in hypertensives as compared to normotensives. Since, in vitro, changes in vasomotor tone of large arteries in response to endothelial stimulation may differ depending on the territory, we re-examined phenomenon of flow-dependent vasodilation at the level of the femoral artery in 10 normotensives (NT) and 12 age matched (45 +/- 9 vs 43 +/- 4 yrs) hypertensives (HT). Systolo-diastolic variations of femoral artery diameter (D) were recorded using an original echo-tracking system based on doppler shift while blood flow velocity was measured at the same level using a bidimensional pulsed doppler system (V). A 10 min period of leg ischemia did not induce any significant change in D and V in each group but decreased foot skin blood flow (laser doppler). This decrease occurred to the same extent in NT and HT. During reactive hyperemia following release of the pneumatic cuff, V increased (from 2.1 +/- 0.3 to 12.5 +/- 2.4 cm/s in NT) and returned to control level at the 3rd min. Diastolic diameter (Dd) increased (max: 2nd min) in NT (9.3 +/- 0.8 vs 8.8 +/- 0.9 mm; p less than 0.001) and in HT (9.5 +/- 1.2 vs 8.4 +/- 1.2 mm; p less than 0.01). Dd increased to a greater extent in HT than in NT while reactive hyperemia (laser doppler) did not differ. Thus, a non-invasive method is able to demonstrate a flow-dependent vasodilation at the level of the femoral artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗