Norepinephrine kinetics in the rat with tail-suspension-induced central hypervolemia, as a model of cardio-vascular deconditioning.

Tail-suspension (TS) in the rat represents an interesting experimental condition to mimic, on Earth, the microgravity-induced cardiovascular deconditioning although the rat's profile of response is partially different from human's. To investigate underlying pathophysiological mechanisms, we have speculated on a decreased activity of the sympathetic system, (sigma S) triggered by the increase of the central venous pressure (CVP) induced by TS. Thus a decreased activity of the sigma S could account, at least partly, for the deconditioning of the cardiovascular system.

Adrenaline hypothesis: effect of formoterol on noradrenaline release.

1 Originally, the so-called 'adrenaline hypothesis' related the release of noradrenaline (NA) to stimulation of presynaptic beta2-receptors in nerve endings; now it confers a possible role to adrenaline taken up then released by nerves endings. It represents a potentially useful therapeutic pathway. The present study aims to investigate the effects of formoterol, a highly selective beta2-adrenoceptor agonist.

Norepinephrine kinetics in freely moving rats.

Norepinephrine (NE) kinetics were investigated in freely moving (FM) and minimally stressed (MS) rats with the isotope dilution technique. 1) The mean NE spillover rate (NE-SOR) was 79 +/- 6 ng. kg(-1).

Sympathetic activity in the rat: effects of anaesthesia on noradrenaline kinetics.

Noradrenaline (NA) kinetics represent an effective tool for evaluating the activity of the sympathetic system: thus plasma NA concentration, spillover rate (SOR) and metabolic clearance rate (MC) were measured in the rat. The dilution technique was adapted and validated: pithing that caused mechanical destruction of the spinal cord was shown to reduce drastically NA-SOR and plasma NA concentration with no effect on NA-MC. NA-SOR and plasma NA concentration were restored within their normal limits when 2.

Further study on the carotid baroreflex system in the cardiovascular deconditioning induced by head-down tilt.

Hypothesis: The responses of the carotid baroreflex and of the peripheral sympathetic system to stimulations induced by either lower body negative pressure (LBNP -40 mmHg) or cold pressor test were investigated in eight volunteers before and after 48 h in the -6 degrees head-down tilt (HDT).

Methods: Geometry (diastolic diameter and pulsatile distention) and dynamics (cross-sectional compliance and tangential tension) of the bulb and the common carotid artery were investigated using ultrasonic devices, echotracking and aplanation tonometry. The activity of the sympathetic system was evaluated through measurements of plasma concentrations of catecholamines (CAs) and 3,4-dihydroxyphenyl glycol (DHPG).

Mechanisms of the cardiovascular deconditioning induced by tail suspension in the rat.

The aim of the present work was to obtain insights into the pathophysiology of cardiovascular deconditioning (CVD) induced by tail suspension (TS) in the rat: during TS, when central venous pressure (CVP) has been normalized (E. Martel, P. Champéroux, P.

Venous and arterial behavior during normal pregnancy.

To assess the contribution of the arterial and venous systems in the hemodynamic changes of normal pregnancy, we studied blood flow, vascular resistance, venous tone, and the viscoelastic properties ("creep") of the upper and lower limbs (using plethysmography), aortic distensibility (using pulse wave velocity measurements), and cardiac dimensions (using echocardiography) in nine healthy women. Studies were longitudinally performed at the first (10-13 wk) and third (33-38 wk) trimesters of pregnancy in comparison with the period between the third and sixth month after delivery. From the first trimester, heart rate significantly increased while systemic blood pressure and limb vascular resistances did not change significantly and aortic distensibility increased (P < 0.

Red blood cells participate in the metabolic clearance of catecholamines in the rat.

The aim of the present study was to investigate the possible role of erythrocytes in the metabolic clearance of catecholamines (CAs) in the rat. Intravenous infusion of exogenous CAs (dopamine -DA-, norepinephrine -NE-, or epinephrine -Epi-) was carried out at increasing doses to cover a range of plasma concentrations from the lower to the upper physiological and to pharmacological levels. Whatever the mechanism(s) underlying the CAs erythrocyte/plasma balance: 1.

Antihypertensive effects and arterial haemodynamic alterations during angiotensin converting enzyme inhibition.

Objective: To assess the respective roles of the anti-hypertensive and blood pressure-independent effects of angiotensin converting enzyme (ACE) inhibition in the changed arterial haemodynamics observed in hypertensive patients with end-stage renal disease (ESRD) treated by haemodialysis.

Design And Methods: Twelve hypertensive patients with ESRD were included in a double-blind, cross-over study comparing a single 20 mg dose of the ACE inhibitor quinapril versus placebo. Two study periods each of 172 h duration were separated by a 2-week placebo period.

A dopamine transporter in human erythrocytes: modulation by insulin.

Red blood cells are capable of transport and accumulation of catecholamines. The aim of this paper is to characterize the catecholamine transport system in the human red blood cell and in particular that of dopamine. Dopamine, noradrenaline and adrenaline enter the red blood cell by a similar process, which shows saturation kinetics with Vmax values of 0.

Central hypervolemia in the conscious rat: a model of cardiovascular deconditioning.

The aim of the present study as to investigate whether increased central hypervolemia induced by tail suspension (TS) in the rat is an appropriate model of cardiovascular deconditioning (CVD). First, the physiological relationship between central venous pressure (CVP) and extracellular fluid volume (ECFV) was studied. TS (20 degrees) increased CVP (5.

Segmental necrosis of ascending colon in haemodialysis patients.

A segmental necrosis of the ascending colon sometimes affecting the terminal ileum was observed 13 times in 12 end-stage renal disease patients over a 5400 patient-years observation period. In all but three cases the patient was operated within 24 h of onset of the abdominal pain. Three patients had a bowel perforation; nine had a limited intestinal necrosis.

Carotid arterial hemodynamics in response to LBNP in normal subjects: methodological aspects.

Pulsatile changes in blood pressure and arterial diameter were studied noninvasively with applanation tonometry and echo-tracking techniques at the sites of the common carotid artery (CCA) and the carotid arterial bulb (CAB) in 12 healthy volunteers. Determinations were performed before and during application of -10 and -40 mmHg lower body negative pressure (LBNP) to investigate noninvasively the tensile forces acting on the CAB. Together with significantly decreased mean arterial pressure, increased heart rate, forearm vascular resistance, and plasma norepinephrine, the -40 mmHg LBNP stimulus produced the following significant changes in CCA and CAB hemodynamics: 1) for the same decrease in mean arterial pressure, a greater decrease in carotid than in brachial pulse pressure was observed (P < 0.

Carotid artery pulsatility during parabolic flights.

In cardio-vascular hemodynamic, the arterial pulsatility, represented by the arterial pulse pressure (PP= systolic blood pressure-diastolic blood pressure), is different from one site to another, in opposite with the mean blood pressure almost identical in the whole body in supine position (or in microgravity). This is due to the arterial tree geometry and regional differences in the distensibility properties of the arterial wall. As the level of blood pressure opposed to the cardiac left ventricle work is the central pressure, on one hand and as the arterial pulsatility at the site of arterial baro-receptors (located on aortic arch and carotid arteries' bifurcation) regulates the sympathetic and vagal control of heart and peripheral resistances on the other hand, to determine the evolution of this central pulse pressure is of major importance in the knowledge of cardio-vascular hemodynamic during hyper or hypogravity as observed during parabolic flights.

Neuronal metabolism of catecholamines in pithed and electrically stimulated rats.

The aim of the present study was to investigate a possible physiological equilibrium, assessed by statistically significant correlations, between pre-junctional mechanisms that regulate both release and reuptake of norepinephrine (NE) and post-junctional mechanisms that participate in the regulation of the smooth muscle cell and thus in the regulation of blood pressure. This study was carried out in pithed and electrically stimulated (2.5 Hz) rats to obtain an experimentally controlled release of NE.

Cardiac hypertrophy, aortic compliance, peripheral resistance, and wave reflection in end-stage renal disease. Comparative effects of ACE inhibition and calcium channel blockade.

Background: We wished to assess the respective roles of the antihypertensive and blood pressure (BP)-independent effects of antihypertensive drugs on arterial hemodynamics and left ventricular hypertrophy (LVH) in end-stage renal disease (ESRD) patients.

Methods And Results: In a double-blind study, 24 ESRD patients with LVH were randomized to 12 months' administration of either the angiotensin-converting enzyme (ACE) inhibitor perindopril (n = 14) or the calcium channel blocker nitrendipine (n = 10). Repeated measurements of the following parameters were performed: BP (mercury sphygmomanometry), left ventricular mass (LVM, echocardiography), cardiac output (aortic cross-section and velocity integral), total peripheral resistance (cardiac output and mean BP), aortic and large-artery compliance (pulse wave velocity, Doppler flowmeter), and arterial wave reflections (augmentation index, applanation tonometry).

Early disturbance of baroreflex control of heart rate after tail suspension in conscious rats.

Experiments were performed on conscious chronically instrumented rats maintained on tail suspension to determine the time course of changes in baroreceptor control of heart rate produced by this procedure. Pressor responses were elicited by bolus injections of graded doses of phenylephrine and sodium nitroprusside, permitting evaluation of the totality of the sigmoidal curve relating mean arterial pressure to heart rate. Compared with control rats maintained at 0 degrees, rats maintained at 20 degrees using tail suspension for 24 h showed a significant reduction in reflex gain (-3.

[Pressure-independent improvement of aortic distensibility in hypertensive hemodialysed patients].

Hypertensive patients undergoing hemodialysis (HPH) have a marked impairment of their large artery distensibility and an increased cardiovascular morbidity. We investigated twelve HPH (8 males, 4 females, 53 +/- 12 years of age, +/- SD) following a single dose of an ACE inhibitor (quinapril 20 mg) comparatively to a placebo in a randomised cross over study over a week (H0 to H172). We measured repeatedly blood pressure and aortic distensibility (carotid-femoral pulse wave velocity, PWV).

Plasma erythrocyte relationship of catecholamines in human blood.

The equilibrating process of catecholamines (CAs) between plasma and red blood cells (RBC) was studied by measuring their erythrocyte/plasma concentration gradient (E/P ratio); ratio of E/P > 1 for a given amine was considered the consequence of its accumulation in or on RBC. We studied in vitro human blood obtained from 9 polycythemic patients from whom blood was drawn in control condition and in response to loading with exogenous CAs. Preliminary study showed a lack of difference in results obtained in these patients from those in 9 healthy volunteers and confirmed that RBC accumulate dopamine (DA) and epinephrine (EPI) but not norepinephrine (NE).

Neuronal metabolism of catecholamines: plasma DHPG, DOMA and DOPAC.

Pre-synaptic endings of the sympathetic nervous fibers control the metabolism of catecholamines, particularly inactivating norepinephrine after its neuronal recapture. The present study was carried out to investigate this segment of the metabolism of catecholamines through measurements of DHPG, DOMA and DOPAC concentrations in plasma. A sensitive and specific radio-enzymatic assay was developed of which the major characteristic is to include the plasma sample in the incubation mixture without initial extraction of the deaminated metabolites.

Effects of clonidine on plasma catecholamines and neuropeptide Y in hypertensive patients at rest and during stress.

Neuropeptide Y (NPY), a potent vasoconstrictor agent reported to be released, in addition to norepinephrine (NE), by sympathetic nerve endings during stress, may contribute to the pressor response to various stimuli. The objectives of this study were to determine (a) whether plasma NPY concentrations are altered during different types of stress (cold pressor test, mental stress, and active orthostatism) and (b) whether clonidine, via its central sympatholytic effect, affects the stress-induced blood pressure, NPY, and/or catecholamine changes. Eighteen untreated patients with mild essential or borderline hypertension participated in an acute randomized, double-blind, parallel study.

Twenty four hours head-down tilt decreases arterial baroreflex function in conscious rat.

In human zero gravity induces a cardiovascular deconditioning. The transfer of blood from the periphery to the thoracic compartment, occuring immediately at the beginning of the exposure to microgravity seems to be involved in this phenomenon. We have previously shown that LBNP (-40 mm Hg) produced an exaggerated heart rate response at the end of 24 hours of bed rest without modification of the cardiopulmonary receptors in human.

Microgravity and orthostatic intolerance: carotid hemodynamics and peripheral responses.

A ground-based model [24 h of bed rest (BR) with head-down tilt (HDT)] was used to investigate the cardiovascular deconditioning responsible for orthostatic intolerance, frequently observed after weightlessness flights. This experimental deconditioning is shown to be distinguished by an increase of mean blood pressure (P < 0.05), with increased total peripheral resistances (TPRs).

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.

Potential role of the renal tubule in fixing the level of plasma sulfoconjugated catecholamines in the dog.

Plasma levels of sulfoconjugated catecholamines in human subjects and in dogs are usually much higher than those of native amines. Their origins and the mechanism(s) involved in fixing their plasma concentrations are not well known; however, several lines of clinical evidences indicate a major role for the kidney. Thus this study was undertaken to measure the renal fractional excretion--used as an overall index of kidney mechanisms involved in the handling of catecholamines and their sulfoconjugates in the dog--and to look for any possible relationships between plasma concentration and urinary excretion.