Jan Klimas

Heart rate correction of the QT duration in rats.

Duration of heart rate corrected QT interval (QTc) is a crucial and critical factor in the assessment of repolarization changes considering safety of drugs and cardiac disorders. In rats, a validated approach to QT correction is lacking. In this study, we tested the normalization of QTc using normalization factor according to rats cardiac cycle length (RR). Standard 12-lead ECG was measured in anesthetized rats at basal conditions and at various pharmacological conditions such as beta-adrenergic stimulation with isoproterenol or medication with clarithromycin (single- or repeated dosing for seven days), bisoprolol or ivabradine. For QT correction, standard Bazetts formula (QTc-B=QT/(RR)(1/2)) and Bazetts formula normalized to average rat RR (QTc(n)-B=QT/(RR/f)(1/2), f=150ms) were compared. Duration of QT showed a positive correlation with RR duration (Pearson r=0.7645, P<0.001). Calculated QTc-B gave 2-2.5 fold of values of uncorrected QT, whereas values of normalized QTc(n)-B were in the physiological range. QTc(n)-B was unrelated to RR (Pearson r=0.1122, not significant) but the relationship between QTc(n)-B and QT remained preserved (Pearson r=0.7216, P<0.001). Both single and repeated administration of clarithromycin prolonged QT as compared to the controls but a significant dose-dependent difference between clarithromycin applications was revealed only when QTc(n)-B was used. Beta-adrenergic stimulation with isoproterenol prolonged, while beta-blockade with bisoprolol shortened QTc(n)-B. Ivabradine dose-dependently induced bradycardia without altering QT. However, QTc(n)-B showed false positive shortening at sustained bradycardia. Therefore, adjusted formula for QTc(n)-B is suitable for QT correction in rats but its use should be considered carefully in case of very low heart rate.

Isoproterenol-induced heart failure in the rat is associated with nitric oxide-dependent functional alterations of cardiac function

The role of nitric oxide (NO) in heart failure (HF) is complex and remains controversial. We tested the hypothesis that the role of NO in isolated atria and cardiomyocytes is altered in isoproterenol‐induced HF.

Caffeine and cardiovascular diseases: critical review of current research

Abstract Caffeine is a most widely consumed physiological stimulant worldwide, which is consumed via natural sources, such as coffee and tea, and now marketed sources such as energy drinks and other dietary supplements. This wide use has led to concerns regarding the safety of caffeine and its proposed beneficial role in alertness, performance and energy expenditure and side effects in the cardiovascular system. The question remains “Which dose is safe?”, as the population does not appear to adhere to the strict guidelines listed on caffeine consumption. Studies in humans and animal models yield controversial results, which can be explained by population, type and dose of caffeine and low statistical power. This review will focus on comprehensive and critical review of the current literature and provide an avenue for further study.

Pycnogenol® efficiency on glycaemia, motor nerve conduction velocity and markers of oxidative stress in mild type diabetes in rats.

The aim of this study was to describe the effects of Pycnogenol® at various doses on preprandial and postprandial glucose levels, the levels of thiobarbituric acid reactive substances (TBARs) and N‐acetyl‐β‐d‐glucosaminidase (NAGA) and on motor nerve conduction velocity (MNCV) in streptozotocin (STZ)‐induced diabetic rats. Pycnogenol® treatment (10, 20, 50 mg/kg body weight (b.w.)/day) lasted for 8 weeks after induction of diabetes.

Discrepancy between increased left ventricular mass and “normal” QRS voltage is associated with decreased connexin 43 expression in early stage of left ventricular hypertrophy in spontaneously hypertensive rats

BACKGROUND AND PURPOSE On the basis of our previous results of animal and human studies, we assume that the discrepancies between increased left ventricular mass (LVM) and electrocardiographic (ECG) findings not exceeding the upper normal limits in left ventricular hypertrophy (LVH) are conditioned by the electrical remodeling of hypertrophied myocardium. We assumed that these discrepancies observed in the early stage of LVH in spontaneously hypertensive rats (SHR) are associated with a decreased expression of connexin 43. METHODS Standard 12-lead ECG was recorded in 20-week-old male SHR and age-matched and sex-matched normotensive Wistar rats (Institute of Experimental Pharmacology SAV, Dobra Voda, Slovakia). The approximated maximum QRS spatial vector magnitude (QRSmax) was calculated from leads V(2), aVF, and V(5). Left ventricular mass was weighed, and the specific potential (SP) of myocardium was calculated as the QRSmax-to-LVM ratio. Left ventricular protein levels of connexin 43 were analyzed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. RESULTS The LVM values were significantly higher in SHR than in normotensive controls (0.96 +/- 0.03 g and 0.680 +/- 0.07 g, respectively; P < .001). The QRSmax values in SHR did not follow the increase either in systolic blood pressure or in LVM. The SP values in SHR were significantly lower than those in control rats (0.92 +/- 0.11 mV/g and 1.358 +/- 0.06 mV/g, respectively; P < .01). A 37% decrease in connexin 43 level was observed in SHR. CONCLUSIONS The QRS voltage did not follow the increase in the LVM in 20-week-old SHR, and the values of connexin 43 were lower in SHR than in normotensive controls. We believe that the discrepant findings between ECG voltage and LVM can be caused by the electrical remodeling in the early stages of LVH.

Effect of chronic nNOS inhibition on blood pressure, vasoactivity, and arterial wall structure in Wistar rats.

While the unequivocal pattern of endothelial nitric oxide (NO) synthase (eNOS) inhibition in cardiovascular control has been recognised, the role of NO produced by neuronal NOS (nNOS) remains unclear. The purpose of the present study was to describe the cardiovascular effects of NO production interference by inhibition of nNOS with 7-nitroindazole (7-NI). Wistar rats (10 weeks old) were used: control and experimental rats were administered 7-NI 10 mg/kg b.w./day in drinking water for 6 weeks. Systolic blood pressure (BP) was measured by the tail-cuff plethysmographic method. Isolated thoracic aortas (TAs) were used to study vasomotor activity of the conduit artery in vitro. The BP response of anaesthetised animals was used to follow the cardiovascular-integrated response in vivo. Geometry of the TA was measured after perfusion fixation (120 mm Hg) by light microscopy. Expression of eNOS was measured in the TA by immunoblot analysis. Although 6 weeks of nNOS inhibition did not alter systolic BP, the heart/body weight ratio was decreased. Relaxation of the TA in response to acetylcholine (10(-9)-10(-5)mol/L) was moderately inhibited. However, no difference in the BP hypotensive response after acetylcholine (0.1, 1, 10 microg) was observed. The contraction of TA in response to noradrenaline (10(-10)-10(-5)mol/L), and the BP pressor response to noradrenaline (0.1, 1 microg) was attenuated. The inner diameter of the TA was increased, and the wall thickness, wall cross-sectional area, and wall thickness/inner diameter ratio were decreased. The expression of eNOS in the TA was increased. In summary, cardiac and TA wall hypotrophy, underlined by decreased contractile efficiency, were observed. The results suggested that two constitutive forms of NOS (nNOS, eNOS) likely participate in regulation of cardiovascular tone by different mechanisms.

Relation between QRS amplitude and left ventricular mass in the initial stage of exercise-induced left ventricular hypertrophy in rats.

The aim of the study was to analyze the relationship between QRS amplitude and left ventricular mass (LVM) in early stages of two different experimental models of left ventricular hypertrophy (LVH) in rats: in exercise-induced hypertrophy and pathological hypertrophy due to genetically conditioned pressure overload. Three groups of experimental animals were studied: healthy control Wistar-Kyoto rats (WKYs), spontaneously hypertensive rats (SHRs), and WKY rats exposed to training by intermittent swimming (SWIM). Orthogonal electrocardiograms were recorded in each group at the age of 12 and 20 weeks, and the maximum spatial QRS vector (QRSmax) was calculated. Then the animals were sacrificed and LVM was measured. The specific potential of myocardium (SP) was calculated as a ratio of QRSmax to LVM. The QRSmax values did not follow the changes in LVM. At the end of the follow-up period, the highest values of QRSmax were recorded in the control WKY rats (0.80 ± 0.05 mV). The QRSmax values in both groups with experimental LVH were significantly lower as compared with control animals (SHR 0.44 ± 0.02 mV, p < 0.001; SWIM 0.53 ± 0.04 mV, p < 0.001). Similarly, the SP values were significantly lower in both groups with experimental LVH as compared with control animals (SHR 0.42 ± 0.02 mV/g, p < 0.001; SWIM 0.55 ± 0.05 mV/g, p < 0.001). A decrease in QRSmax and SP was observed in both models of experimental LVH. We attributed these findings to the changes in electrogenetic properties of myocardium in the early stage of developing LVH. In other words, it is changes of nonspatial determinants that influence the resultant QRS voltage in terms of the solid angle theory.

Enalaprilat increases PPARβ/δ expression, without influence on PPARα and PPARγ, and modulate cardiac function in sub-acute model of daunorubicin-induced cardiomyopathy

Anthracycline therapy is limited by a cardiotoxicity that may eventually lead to chronic heart failure which is thought to be prevented by ACE inhibitors (ACEi). However, the protective effect of ACEi in early stages of this specific injury remains elusive. Activated nuclear transcription factors peroxisome proliferator-activated receptors (PPAR) regulate cellular metabolism, but their involvement in anthracycline cardiomyopathy has not been investigated yet. For this purpose, Wistar rats were administered with daunorubicin (i.p., 3 mg/kg, in 48 h intervals) or co-administered with daunorubicine and enalaprilat (i.p., 5 mg/kg in 12 h intervals). Control animals received vehicle. Left ventricular function was measured invasively under anesthesia. Cell-shortening was measured by videomicroscopy in isolated cardiomyocytes. Expression of PPARs mRNA in cardiac tissue was measured by Real-Time PCR. Although the hemodynamic parameters of daunorubicin-treated rats remained altered upon ACEi co-administration, ACEi normalized daunorubicin-induced QT prolongation. On cellular level, ACEi normalized altered basal and isoproterenol-stimulated cardiac cell shortening in daunorubicine-treated group. Moreover, anthracycline administration significantly up-regulated heart PPARα mRNA and its expression remained increased after ACEi co-administration. On the other hand, the expression of cardiac PPARβ/δ was not altered in anthracycline-treated animals, whereas co-administration of ACEi increased its expression. Conclusively, effect of ACEi can be already detected in sub-acute phase of anthracycline-induced cardiotoxicity. Altered expression of heart PPARs may suggest these nuclear receptors as a novel target in anthracycline cardiomyopathy.

Pycnogenol® improves left ventricular function in streptozotocin-induced diabetic cardiomyopathy in rats

We studied whether Pycnogenol® (PYC) may attenuate the development of experimental streptozotocin‐induced diabetic cardiomyopathy in rat. In addition, we aimed to study whether PYC affects cardiac oxidative stress and the protein expression of reactive oxygen species (ROS)‐producing molecules (gp91phox‐containing NADPH oxidase and NO‐signalling proteins). Experimental diabetes mellitus was manifested by hyperglycaemia and impaired cardiac function estimated using left ventricular catheterisation in vivo. PYC lowered fasting plasma glucose and normalized basal cardiac function. Excessive oxidative stress in streptozotocin (STZ) hearts, evidenced by 40% increase (P < 0.05) of thiobarbituric acid reactive substances (TBARS) concentration, was associated with increased expression of gp91phox (by 75%, P < 0.05), iNOS (by 40%, P < 0.05) and alpha‐tubulin (by 49%, P < 0.05), but unchanged expression of eNOS and its alosteric regulators, as compared to CON. PYC failed to affect these expression abnormalities. Our study shows that PYC corrects diabetic cardiac dysfunction, probably by its metabolic and direct radical scavenging activity without affecting the molecular maladaptations of ROS‐producing enzymes and cytoskeletal components. Copyright

The initial stage of left ventricular hypertrophy in spontaneously hypertensive rats is manifested by a decrease in the QRS amplitude/left ventricular mass ratio.

In this study we tested the hypothesis of the relative voltage deficit, i.e. the discrepancy between increased left ventricular mass (LVM) and QRS amplitudes, in an experimental model of spontaneously hypertensive rats (SHR) during the period of a moderate increase in blood pressure. To address this issue we recorded orthogonal electrocardiograms of male SHR at the age of 12 and 20 weeks. During this period the systolic blood pressure (sBP) increased from 165 ± 3 mmHg to 195 ± 1 mmHg (p < 0.001). Age and sex matched WKY rats were used as control groups. The sBP values in WKY normotensive control groups were within normal limits (122 ± 8 mmHg and 130 ± 4mmHg, respectively). The maximum QRS spatial vector magnitude (QRSmax) was calculated from X, Y, Z amplitudes of the orthogonal electrocardiograms. The animals were sacrificed and the left ventricular mass was weight. The specific potential of myocardium (SP) was calculated as a ratio of QRSmax to LVM. The LVM in SHR (0.86 ± 0.05 g and 1.05 ± 0.07 g, respectively) was significantly higher as compared to WKY (0.65 ± 0.07 g and 0.70 ± 0.02 g), and the increase of LVM closely correlated with the sBP increase. On the other hand, QRSmax in SHR did not follow either the increase of sBP, or LVM. The QRSmax values in SHR did not differ from those of WKY at the age of 12 weeks (0.59 ± 0.14 mV compared to 0.46 ± 0.05 mV), and they were even lower in SHR at the age of 20 weeks (0.74 ± 0.08 mV compared to 0.44 ± 0.05 mV, p < 0.001). The values of SP, quantifying the relative voltage deficit, were significantly lower in SHR as compared to the WKY control. The values decreased significantly in SHR with increasing age, sBP and LVM, i.e., with the progression of hypertrophic remodeling of the left ventricle. The results of this study support the hypothesis of the relative voltage deficit in LVH. These results are consistent with the finding of a high number of false negative ECG results in clinical ECG diagnostics of LVH, and could contribute to an understanding of the diagnostic importance of the false negative ECG results, their re‐evaluation and utilization for clinical diagnosis and prognosis.