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Biomedical subjects

P Kreher

Publications and source records attributed to P Kreher.

At least 19 recordsLinked to original sources
PubMed2001

Ischemic tolerance of the heart by adaptation to chronic hypoxia is suppressed by high subchronic carbon monoxide exposure.

This study was designed to investigate whether exposure to carbon monoxide (CO) could alter the ischemic tolerance induced by chronic hypoxia. We aimed to determine whether chronic hypoxia-induced cardiovascular adaptation was modified during the return to normoxia or by subchronic CO exposure. The degree of resistance to an in vitro transient ischemia was measured, using the Langendorff method, in hearts from rats previously exposed to chronic hypoxic hypoxia and/or subchronic CO exposure to 600 ppm. Chronic hypoxia decreased ischemic contracture (15.6 +/- 04.9 vs. 60.8 +/- 07.7%) and improved both contractile recovery (59.6 +/- 07.3 vs. 21.8 +/- 06.8%) and ventricular arrhythmia during reperfusion (0 vs. 45%) compared to a control normoxic group. However, in our chronic hypoxia regression model many parameters returned near to control values except for the persistence of cardiomegaly, a significant decrease in both ischemic contracture (22.0 +/- 04.9 vs. 60.8 +/- 07.7%), and ventricular tachycardia (25 vs. 45%). CO exposure alone increased the coronary flow and improved both contractile recovery (42.6 +/- 7.2 vs. 21.8 +/- 6.8%) and ventricular arrhythmia (16.7 vs. 45%) without altering the action potential shape. These two models causing tissue hypoxia induced the same degree of polycythemia or cardiomegaly and provided similar ischemic tolerance. CO exposure after chronic hypoxia exacerbated ischemic contracture (69.3 +/- 10.5 vs. 22.0 +/- 14.5%) and ventricular tachycardia incidence (100 vs. 50%) but with significant alteration in contractile recovery (12.7 +/- 10.5%) compared to the chronic hypoxia or CO exposure. Thus, CO exposure completely suppressed the chronic hypoxia-induced ischemic tolerance.

Animals↗
PubMed2001

Acute ischemic preconditioning and high subchronic CO exposure independently increase myocardial tolerance to ischemia.

This study was designed to investigate whether exposure to carbon monoxide (CO) could alter or raise the ischemic tolerance induced by preconditioning. To this end, isolated rat hearts were aerobically perfused for 20 min. Hearts were then randomized to two groups: (1) a further 20-min aerobic perfusion, and (2) ischemic preconditioning (2 cycles of 5 min of ischemia followed by 5 min of reperfusion). Hearts were then subjected to 25 min of low-flow (0.3 ml/min.) global ischemia (37 degrees C) and 30 min of reperfusion. In parallel studies, the same protocols were performed in hearts from rats previously exposed to subchronic CO (600 ppm for 2 wk). Ischemic preconditioning accelerated the development of ischemic contracture (onset = 6.0 +/- 0.3 vs. 8.6 +/- 0.9 min), increased the preischemic coronary flow (19.0 +/- 1.0 vs. 11.6 +/- 0.6 ml/min/g), improved contractile recovery (73.7 +/- 8.9 vs. 30.8 +/- 7.5%), but was without effect on reactive hyperemia (151.2 +/- 4.7 vs. 149.2 +/- 5.1%) and incidence of ventricular arrhythmia during reperfusion (55.6 vs. 60.0%) compared to a control group. CO exposure alone increased the baseline coronary flow (20.1 +/- 1.5 vs. 12.8 +/- 0.6 ml/min/g) and the contracture magnitude (54.8 +/- 6.8 vs. 37.1 +/- 4.8%), improved both contractile recovery (66.1 +/- 6.3 vs. 30.8 +/- 7.5%) and ventricular arrhythmia incidence (22.2 vs. 60.0%), and increased the hyperemic coronary flow (26.7 +/- 1.5 vs. 19.1 +/- 0.7%). Preconditioning after CO exposure exacerbated ischemic contracture (shorter onset and higher magnitude), and increased the reactive hyperemia (29.8 +/- 1.4%), but raised the beneficial effects on contractile recovery (85.4 +/- 8.4%) without alteration of ventricular tachycardia prevention (22.2%). Thus, CO-exposed hearts could be preconditioned in the same way as normal myocardium.

Animals↗
PubMed2001

Beneficial effects of amiodarone and dronedarone (SR 33589b), when applied during low-flow ischemia, on arrhythmia and functional parameters asssessed during reperfusion in isolated rat hearts.

The effects of short-term amiodarone and dronedarone treatments on action potential characteristics and arrhythmia (ventricular tachycardia ) induced by reperfusion after global low-flow ischemia were studied in rat hearts. The actions of amiodarone and SR on recovery of coronary flow and contractile function were also determined. Isolated hearts were stabilized for 40 min and were then submitted to 25-min global low-flow ischemia (constant coronary flow, 0.3 ml/min) followed by 30 min of reperfusion at constant pressure. Drugs were applied only during ischemia: consequently, action potential duration (APD) tended to widen. During reperfusion, APD tended to recover or shorten, and the more complete the recovery, the less the arrhythmia. Despite its ability to widen APD during ischemia, amiodarone facilitated APD recovery during reperfusion. Moreover, APD shortening and ventricular tachycardia suppression exhibit a bell-shaped concentration-response relation, implying that the drugs affect ventricular tachycardia by a class III-independent action. These results point to an anti-ischemic action supported by improvement in function and inhibition of reactive hyperemia.

Action Potentials↗
PubMed2000

[Prosthesis fitting after maxillectomy: an indispensable factor in acceptance and rehabilitation].

Surgical resection is often required for maxillary cancer, producing a communication between the oral cavity and the nose or paranasal sinuses. After maxillectomy, patients experience major dysfunction in speech and swallowing which have a very negative psychological effect. These problems can be overcome with an immediate prosthesis but to be fully successful, coordinated work is required between the surgeon and the maxillofacial prosthodontist before, during and after surgery. Ten days after surgery, an interim obturator is made with soft lining materials. This prosthesis will evolve as scar tissue forms, preparing space for the definitive obturator which will restore good quality of life for maxillectomy patients.

Dental Prosthesis Design↗
PubMed1999

Ciliary neurotrophic factor is a regulator of muscular strength in aging.

Ciliary neurotrophic factor (CNTF) participates in the survival of motor neurons and reduces the denervation-induced atrophy of skeletal muscles. Experiments performed in rats show a decrease in peripheral CNTF synthesis during aging, associated with an overexpression of its alpha-binding receptor component by skeletal muscles. Measurement of sciatic nerve CNTF production and of the muscular performance developed by the animals revealed a strong correlation between the two studied parameters (r = 0.8; p < 0.0003). Furthermore, the twitch and tetanic tensions measured in the isolated soleus skeletal muscle in 24-month-old animals increased 2. 5-fold by continuous in vivo administration of CNTF. Analyses of the activation level of leukemia inhibitory factor receptor beta- and signal transducer and activator of transcription 3-signaling molecules in response to exogenous CNTF revealed an increased tyrosine phosphorylation positively correlated with the twitch tension developed by the soleus muscle of the animals.

Aging↗
PubMed1997

Electrophysiological approach of the role of Na+/H+ exchange in low-flow global ischemia and in ischemic preconditioning.

We investigated, at first in low-flow global ischemia and then with ischemic preconditioning, the effects of a compound, (4-isopropyl-3-methylsulphonylbenzoyl)guanidine hydrochloride (HOE 642), known to inhibit the Na+/H+ exchange in rat cardiomyocytes. In rat isolated hearts, perfused on a Langendorff apparatus with Krebs-Henseleit carbonate buffer, the action potentials and the contractile function were measured during a 25-min period of global low-flow ischemia (coronary flow, 0.3 mL.min-1) followed by a 30-min reperfusion. In hearts previously preconditioned, two intermittent periods of total ischemia for 5 min each, separated by 5 min reflow, were performed before low-flow ischemia. Treated hearts received HOE 642 (3.0 x 10(-8) mol.min-1) exclusively during low-flow ischemia. Treatment with HOE 642 during low-flow ischemia improves cardiac performance and lowers the rise in diastolic tension during reperfusion. Concomitantly HOE 642 shortens the action potential, and has striking effects on ventricular arrhythmias during reperfusion as well. These results support the concept that Na+/H+ exchange activation is a contributing factor to low-flow ischemia-reperfusion injuries. HOE 642 exhibited minor effects when combined with the preconditioning protocol, but a lengthening in action potential was observed and ventricular arrhythmias were mostly affected. Preconditioned hearts demonstrated marked glycogen depletion compared with controls. These results support the hypothesis that preconditioning could decrease glycogenolysis and therefore subsequently limit acidification during low-flow ischemia.

Action Potentials↗
PubMed1996

Action potentials in right and left ventricles from chronic hypoxic rats: effect of almitrine.

Rats were exposed to a 3-wk regimen of chronic normobaric hypoxia, with or without almitrine treatment. Chronic hypoxia led to a significant rise in the right ventricular mass and lengthened the action potential duration (APD) in right ventricle and in nonhypertrophied left ventricle. Hypertrophy and APD lengthening were significantly enhanced by almitrine. The classical acute hypoxia-induced shortening in APD was much larger in hypoxia-adapted hearts. In these hearts, almitrine treatment almost completely prevented such shortening, while the acute hypoxia-induced decrease in cardiac contraction was similar with or without almitrine. It is concluded that APD lengthening during chronic hypoxia can occur independently of ventricular hypertrophy. The similar directional effects of almitrine and chronic hypoxia on APD support the hypothesis of an energy-linked phenomenon. The dissociation of the almitrine effect on APD and contractility is in accordance with the view of a cellular energy compartmentation.

Action Potentials↗
PubMed1995

Effects of chronic angiotensin I-converting enzyme inhibition on the relations between ventricular action potential changes and myocardial hypertrophy in aging rats.

We studied the effect of aging on cardiac hypertrophy and action potential duration (APD) in normotensive male WAG/Rij rats and evaluated the role of the renin-angiotensin system (RAS) in these effects. Cardiac hypertrophy occurs in 30-month-old rats, as indicated by an increase in heart weight, and APD gradually increases with aging in the epicardial region of the right and the left ventricle. Short-term treatment (1 month) with the angiotensin-converting enzyme inhibitor (ACEI) perindopril prevented age-related increase in heart weight/body weight ratio independent of its antihypertensive effects, but did not prevent changes in APD in 30-month-old rats. Our results show a dissociation of changes in cardiac mass from changes in APD during aging. The effect of ACEI on hypertrophy may be due in part to a direct angiotensin effect on cellular growth. Changes in APD are not related to hypertrophy but rather to the process of aging.

Action Potentials↗
PubMed1995

Mechanical and electrophysiological effects of preconditioning in isolated ischemic/reperfused rat hearts.

Changes in action potential duration (APD) were studied during ischemic/reperfusion injury preceded or not by preconditioning in isolated rat hearts. Hearts were perfused on a Langendorff apparatus with Krebs-Henseleit carbonate buffer and submitted to 25-min global low-flow ischemia (coronary flow, 0.3 mol x min-1) followed by 30-min reperfusion. In hearts that had been preconditioned, two intermittent periods of total ischemia for 5 min each, separated by 5-min reflow, were performed before low-flow ischemia. At the end of the ischemic period, APs were significantly prolonged in nonpreconditioned hearts; this prolongation was abolished by preconditioning. Moreover, preconditioning increased the recovery of the contractile function. Therefore, ischemia can widen APD. The results also showed that in rats, preconditioning can be produced in a manner qualitatively similar to preconditioning in other species. Verapamil (3 x 10(-9) mol x min(-1)) or 4-aminopyridine (4-AP, 3 x 10(-6) mol x min(-1)) applied exclusively during low-flow ischemia significantly improved postischemic contractile function in nonpreconditioned hearts (25.9 +/- 4.4. and 37.9 +/- 2.4 vs. 12.9 +/- 5.3%, respectively) as well as in preconditioned hearts (61.8 +/- 4.2 and 55.5 +/- 4.7 vs. 36.0 +/- 1.4%, respectively). With verapamil, this protection was associated with a decrease in APD at 90% of repolarization in the nonpreconditioned hearts (APD90 32.2 +/- 0.1 vs. 71.1 +/- 6.7 ms at the end of ischemia). With 4-AP, this same protection was associated with an increase in APD in the preconditioned hearts (APD90 67.7 +/- 0.7 vs. 48.5 +/- 2.6 ms at the end of ischemia). Both agents given during a 25-min ischemic challenge improved myocardial recovery in nonpreconditioned and preconditioned hearts, despite discordant effects on the AP. Furthermore, the action of these agents was cumulative with the effect of preconditioning.

4-Aminopyridine↗
PubMed1989

Hypertrophy induced alteration of action potential and effects of the inhibition of angiotensin converting enzyme by perindopril in infarcted rat hearts.

Not much is known about alterations in electrical activity in the healthy part of a heart made hypertrophic as a result of local ischaemia, yet such an investigation might allow us to predict the stages leading to cardiac failure and so aid its prevention. We therefore studied the electrophysiological changes which occurred in rats in which ligation of the left coronary artery had produced hypertrophy of the non-infarcted myocardium. One month after the intervention the overall degree of hypertrophy of the ventricles reached 15.3%. This was accompanied in the healthy part of the left ventricle (septum) by altered electrical activity consisting of a lengthening of the action potentials at 25, 50, 75 and 90% of repolarisation. Myocardial hypertrophy was absent after chronic treatment of the animals with perindopril, an angiotensin converting enzyme inhibitor, given orally at 2 mg.kg-1 body weight, and the electrophysiological alterations induced by the infarct were partially eliminated: phase 2 of the myocardial action potential was shortened and phase 3 completely restored. We postulate that angiotensin may have a direct effect on the cardiac cell.

Action Potentials↗
PubMed1989

Altered electrical response to caffeine exposure in hypertrophied rat myocardium.

We investigated the electrophysiological effects of cardiac hypertrophy induced by different experimental models. Comparison of the action potentials of hypertrophied and control rat hearts reveals a pronounced prolongation of the action potential for all types of hypertrophy. This prolongation affects the entire repolarization phase of the action potential 8 days after severe aortic constriction, after 8 days of isoproterenol treatment (5 mg/kg per day), and 3 months after an aortocaval fistula. The electrical changes associated with myocardial hypertrophy induced by pressure overload (aortic constriction) were compared with those resulting from volume overload (aortocaval fistula). Our results show that action potential alterations depend on the nature, duration, and severity of the work load. Thus, pressure overload is more potent to induce these modifications. In the hearts subjected to pressure overload, action potential alterations appear more rapidly and are more marked for the same degree of hypertrophy than those of the volume-hypertrophied myocardium. Furthermore, such data also demonstrate that the early alteration of the action potential during the development of compensatory hypertrophy is a prolongation of the later phase of repolarization (phase 3), without prolongation of the other repolarization phases (1 and 2). This change appears 3 days after aortic constriction, 1 month after coronary artery ligation (in the healthy part of the left ventricle), and 1 month after an aortocaval fistula.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1986

Role of ATP in the maintenance of action potential configuration of the isolated working rat heart.

The relation between action potential configuration and myocardial adenosine triphosphate (ATP) concentration was analysed in isolated low and high work rat heart preparations. Glucose used as sole substrate could not provide total energy production when the isolated hearts performed high work. This may explain the decrease in action potential duration and plateau amplitude (phases 2 and 3) that occurred concomitantly with a low total myocardial ATP concentration. When atrial perfusion was changed to the retrograde mode, however, the action potential configuration was restored without an increase in the global myocardial ATP concentration. Pyruvate used as substrate instead of glucose enhanced ATP production by mitochondrial oxidation and partly restored the action potential modifications (principally phase 2). Adenosine added to glucose in the perfusate or infused in situ (before heart isolation and perfusion) enhanced ATP production by the adenine nucleotide salvage pathway and provided a protective effect for phase 2 and 3 action potential variables. The results using glucose as perfusate showed that there was no correlation between global ATP concentration and myocardial electrical activity. An analysis of the other results suggests that the primary problem in the working heart preparation is that the myocardium is in a state of relative hypoxia or ischaemia and that adenosine merely acts as a coronary vasodilator to improve myocardial oxygen delivery.

Action Potentials↗
PubMed1985

[Absence, in the hypertrophied rat heart caused by aortocaval fistula, of several metabolic and electrophysiological changes seen in other models of hypertrophy].

In this work, we compared the electrophysiological and metabolic parameters of a volume overload model of cardiac hypertrophy (aorto-caval fistula) with those of two other models of hypertrophy (aortic stenosis and isoproterenol pretreatment). In these last models, a prolongation of action potential and a decrease of myocardial ATP content are observed. However, these alterations are not shown in the aorto-caval fistulated animals while their heart are well hypertrophied. The amplitude increase of phase 3 AP seemed to be a common factor of these models of cardiac hypertrophy.

Action Potentials↗
PubMed1978

Role of membrane permeabilities (calcium, chloride, and potassium) in the genesis of the notch observed on simian and prosimian cardiac action potentials.

The effect of temperature reduction on monkey ventricular action potentials has been studied. Under this condition the genesis of a notch separating the AP spike from the AP plateau has been related either to a conduction phenomenon or to a delay in the activation of the slow inward current. It is observed that the development of a notch at the beginning of the plateau depends both on the presence of a large outward, repolarising current, carried by chloride and/or potassium ions, and on the presence of a slow inward calcium current large enough to depolarise the membrane as the chloride current deactivates.

Action Potentials↗
PubMed1975

[Thymic ectopia and parathyroid tissue in the pangolin (Manis tricuspis Rafinesque)].

Thymic ectopies are under study in 45 Pangolin's thyroids (Manis tricuspis Rafinesque). Their frequency seems to be independent of the sex of the animal but this frequency also appears to be in relation to the age of the animal. The topographic and morphological studies suggest a close relationship between these inclusions made out of thymic tissue and the presence of parathyroid islets included into the thyroid capsule. Some pictures, showing a connection between parathyroid cells and thymis parenchym elements, plead in favour of a functional interelation between these different structures as the Mc Manus experiments suggest it.

Animals↗