Dalma Kellermayer

Rat model of exercise-induced cardiac hypertrophy: hemodynamic characterization using left ventricular pressure-volume analysis

Long-term exercise training is associated with characteristic structural and functional changes of the myocardium, termed athletes heart. Several research groups investigated exercise training-induced left ventricular (LV) hypertrophy in animal models; however, only sporadic data exist about detailed hemodynamics. We aimed to provide functional characterization of exercise-induced cardiac hypertrophy in a rat model using the in vivo method of LV pressure-volume (P-V) analysis. After inducing LV hypertrophy by swim training, we assessed LV morphometry by echocardiography and performed LV P-V analysis using a pressure-conductance microcatheter to investigate in vivo cardiac function. Echocardiography showed LV hypertrophy (LV mass index: 2.41 ± 0.09 vs. 2.03 ± 0.08 g/kg, P < 0.01), which was confirmed by heart weight data and histomorphometry. Invasive hemodynamic measurements showed unaltered heart rate, arterial pressure, and LV end-diastolic volume along with decreased LV end-systolic volume, thus increased stroke volume and ejection fraction (73.7 ± 0.8 vs. 64.1 ± 1.5%, P < 0.01) in trained versus untrained control rats. The P-V loop-derived sensitive, load-independent contractility indexes, such as slope of end-systolic P-V relationship or preload recruitable stroke work (77.0 ± 6.8 vs. 54.3 ± 4.8 mmHg, P = 0.01) were found to be significantly increased. The observed improvement of ventriculoarterial coupling (0.37 ± 0.02 vs. 0.65 ± 0.08, P < 0.01), along with increased LV stroke work and mechanical efficiency, reflects improved mechanoenergetics of exercise-induced cardiac hypertrophy. Despite the significant hypertrophy, we observed unaltered LV stiffness (slope of end-diastolic P-V relationship: 0.043 ± 0.007 vs. 0.040 ± 0.006 mmHg/μl) and improved LV active relaxation (τ: 10.1 ± 0.6 vs. 11.9 ± 0.2 ms, P < 0.01). According to our knowledge, this is the first study that provides characterization of functional changes and hemodynamic relations in exercise-induced cardiac hypertrophy.

Cardiac effects of acute exhaustive exercise in a rat model

BACKGROUND The role of physical exercise in the prevention and treatment of cardiovascular diseases has been well described, however, elevations in cardionecrotic biomarkers after prolonged exercise (i.e. ultramarathon running) were observed. We aimed at understanding the biochemical, molecular biological, structural and functional alterations in the heart after exhaustive exercise in a rat model. METHODS Rats of the exercise group were forced to swim for 3h with 5% body weight (workload) attached to the tail, control rats were taken into the water for 5min. After a 2-hour recovery period we performed left ventricular (LV) pressure-volume analysis to investigate LV function and mechanoenergetics. Additionally, blood and myocardium samples were harvested for biochemical and histological examinations. Gene expression changes were detected by qRT-PCR. RESULTS When compared to controls, elevated plasma levels of cardiac troponin T and creatine kinase were detected after exhaustive exercise. Histological analysis showed sporadic fragmentation of myocardial structure and leukocyte infiltration in the exercised group. We observed increased end-systolic volume, decreased ejection fraction, impaired contractility (preload recruitable stroke work) and mechanoenergetics (ventriculoarterial coupling, mechanical efficiency) of LV after exercise. Myocardial expression of major antioxidant enzymes was increased along with increased myocardial nitro-oxidative stress. Bax/Bcl-2 ratio and TUNEL staining showed enhanced apoptotic signaling. Exhaustive exercise also resulted in the dysregulation of the matrix metalloproteinase system. CONCLUSIONS Excessive physical activity has an adverse effect on the heart. The observed functional impairment is associated with increased nitro-oxidative stress, enhanced apoptotic signaling and dysregulation of the matrix metalloproteinase system after exhaustive exercise.

Prevention of the development of heart failure with preserved ejection fraction by the phosphodiesterase-5A inhibitor vardenafil in rats with type 2 diabetes.

Heart failure with preserved ejection fraction (HFpEF) has a great epidemiological burden. The pathophysiological role of cyclic guanosine monophosphate (cGMP) signalling has been intensively investigated in HFpEF. Elevated levels of cGMP have been shown to exert cardioprotective effects in various cardiovascular diseases, including diabetic cardiomyopathy. We investigated the effect of long‐term preventive application of the phosphodiesterase‐5A (PDE5A) inhibitor vardenafil in diabetic cardiomyopathy‐associated HFpEF.

Strain and strain rate by speckle-tracking echocardiography correlate with pressure-volume loop-derived contractility indices in a rat model of athlete's heart

Contractile function is considered to be precisely measurable only by invasive hemodynamics. We aimed to correlate strain values measured by speckle-tracking echocardiography (STE) with sensitive contractility parameters of pressure-volume (P-V) analysis in a rat model of exercise-induced left ventricular (LV) hypertrophy. LV hypertrophy was induced in rats by swim training and was compared with untrained controls. Echocardiography was performed using a 13-MHz linear transducer to obtain LV long- and short-axis recordings for STE analysis (GE EchoPAC). Global longitudinal (GLS) and circumferential strain (GCS) and longitudinal (LSr) and circumferential systolic strain rate (CSr) were measured. LV P-V analysis was performed using a pressure-conductance microcatheter, and load-independent contractility indices [slope of the end-systolic P-V relationship (ESPVR), preload recruitable stroke work (PRSW), and maximal dP/dt-end-diastolic volume relationship (dP/dtmax-EDV)] were calculated. Trained rats had increased LV mass index (trained vs. control; 2.76 ± 0.07 vs. 2.14 ± 0.05 g/kg, P < 0.001). P-V loop-derived contractility parameters were significantly improved in the trained group (ESPVR: 3.58 ± 0.22 vs. 2.51 ± 0.11 mmHg/μl; PRSW: 131 ± 4 vs. 104 ± 2 mmHg, P < 0.01). Strain and strain rate parameters were also supernormal in trained rats (GLS: -18.8 ± 0.3 vs. -15.8 ± 0.4%; LSr: -5.0 ± 0.2 vs. -4.1 ± 0.1 Hz; GCS: -18.9 ± 0.8 vs. -14.9 ± 0.6%; CSr: -4.9 ± 0.2 vs. -3.8 ± 0.2 Hz, P < 0.01). ESPVR correlated with GLS (r = -0.71) and LSr (r = -0.53) and robustly with GCS (r = -0.83) and CSr (r = -0.75, all P < 0.05). PRSW was strongly related to GLS (r = -0.64) and LSr (r = -0.71, both P < 0.01). STE can be a feasible and useful method for animal experiments. In our rat model, strain and strain rate parameters closely reflected the improvement in intrinsic contractile function induced by exercise training.

Physiological and pathological left ventricular hypertrophy of comparable degree is associated with characteristic differences of in vivo hemodynamics.

Left ventricular (LV) hypertrophy is a physiological or pathological response of LV myocardium to increased cardiac load. We aimed at investigating and comparing hemodynamic alterations in well-established rat models of physiological hypertrophy (PhyH) and pathological hypertrophy (PaH) by using LV pressure-volume (P-V) analysis. PhyH and PaH were induced in rats by swim training and by abdominal aortic banding, respectively. Morphology of the heart was investigated by echocardiography. Characterization of cardiac function was completed by LV P-V analysis. In addition, histological and molecular biological measurements were performed. Echocardiography revealed myocardial hypertrophy of similar degree in both models, which was confirmed by post-mortem heart weight data. In aortic-banded rats we detected subendocardial fibrosis. Reactivation of fetal gene program could be observed only in the PaH model. PhyH was associated with increased stroke volume, whereas unaltered stroke volume was detected in PaH along with markedly elevated end-systolic pressure values. Sensitive indexes of LV contractility were increased in both models, in parallel with the degree of hypertrophy. Active relaxation was ameliorated in athletes heart, whereas it showed marked impairment in PaH. Mechanical efficiency and ventriculo-arterial coupling were improved in PhyH, whereas they remained unchanged in PaH. Myocardial gene expression of mitochondrial regulators showed marked differences between PaH and PhyH. We provided the first comparative hemodynamic characterization of PhyH and PaH in relevant rodent models. Increased LV contractility could be observed in both types of LV hypertrophy; characteristic distinction was detected in diastolic function (active relaxation) and mechanoenergetics (mechanical efficiency), which might be explained by mitochondrial differences.

Cinaciguat prevents the development of pathologic hypertrophy in a rat model of left ventricular pressure overload.

Pathologic myocardial hypertrophy develops when the heart is chronically pressure-overloaded. Elevated intracellular cGMP-levels have been reported to prevent the development of pathologic myocardial hypertrophy, therefore we investigated the effects of chronic activation of the cGMP producing enzyme, soluble guanylate cyclase by Cinaciguat in a rat model of pressure overload-induced cardiac hypertrophy. Abdominal aortic banding (AAB) was used to evoke pressure overload-induced cardiac hypertrophy in male Wistar rats. Sham operated animals served as controls. Experimental and control groups were treated with 10 mg/kg/day Cinaciguat (Cin) or placebo (Co) p.o. for six weeks, respectively. Pathologic myocardial hypertrophy was present in the AABCo group following 6 weeks of pressure overload of the heart, evidenced by increased relative heart weight, average cardiomyocyte diameter, collagen content and apoptosis. Cinaciguat did not significantly alter blood pressure, but effectively attenuated all features of pathologic myocardial hypertrophy, and normalized functional changes, such as the increase in contractility following AAB. Our results demonstrate that chronic enhancement of cGMP signalling by pharmacological activation of sGC might be a novel therapeutic approach in the prevention of pathologic myocardial hypertrophy.

A hasonló fokú fiziológiás és patológiás balkamra-hipertrófia különböző in vivo hemodinamikai következményekhez vezet

Célkitűzés: A balkamra (BK)-hipertrófia a szívizom válasza a megnövekedett terhelésre, amely lehet fiziológiás (FH) vagy patológiás (PH) természetű. E két állapot funkcionális következményeinek direkt összehasonlításáról még nem született tanulmány. Célunk az FH és PH kisállat-modelljeinek részletes összehasonlító hemodinamikai jellemzése BK-i nyomás-térfogat (P-V) analízis segítségével. Módszerek: Patkányainkban FH kialakulását úszóedzéssel (sportszív), PH-t a hasi aorta műtéti szűkítésével (aortic banding, AB) idéztük elő. A szív morfológiai változásait echokardiográfiával követtük. A szívműködés részletes jellemzésére BK-i P-V analízist végeztünk. In vivo méréseinket hisztológiai és molekuláris biológiai módszerekkel egészítettük ki. Adatainkat az adott modell kontrollcsoportjára normalizáltuk. Eredmények: Szívultrahanggal hasonló mértékű hipertrófia volt kimutatható fiziológiás és patológiás hipertrófiában. Az AB-állatoknál fokozott szubendokardiális fibrózis volt jellemző, míg sportszívben fibrotikus átépülést nem találtunk a myocardiumban. A fötális génprogram reaktiválódása csak PH-ban volt megfigyelhető. FH-ban magasabb verőtérfogatot találtunk, ezzel szemben PH-ban emelkedett végszisztolés nyomás mellett változatlan verőtérfogatot mértünk. A diasztolés funkciót jellemző aktív relaxáció javult sportszívben, azonban nagyfokú romlást mutatott az AB-állatoknál. Az érzékeny BK-i kontraktilitás-indexek mindkét csoportban a hipertrófiával arányosan emelkedtek. Míg a BK mechanikus hatásfoka FH-ban javult, PH-ban változatlan maradt. A mitokondriális markerek génexpressziója csökkent PH-ban. Következtetések: Munkánkkal elsőként adtunk részletes funkcionális összehasonlítást a fiziológiás és patológiás BK-hipertrófia állatmodelljeiben. Mindkét típusú hipertrófiában fokozódik a szívizom kontraktilitása. A karakterisztikus különbségek a diasztolés funkcióban és a BK mechanoenergetikai állapotában mutatkoznak, amelynek hátterében mitokondriális különbségek állhatnak.

Complete Reversion of Cardiac Functional Adaptation Induced by Exercise Training

Purpose Long-term exercise training is associated with characteristic cardiac adaptation, termed athletes heart. Our research group previously characterized in vivo left ventricular (LV) function of exercise-induced cardiac hypertrophy in detail in a rat model; however, the effect of detraining on LV function is still unclear. We aimed at evaluating the reversibility of functional alterations of athletes heart after detraining. Methods Rats (n = 16) were divided into detrained exercised (DEx) and detrained control (DCo) groups. Trained rats swam 200 min·d−1 for 12 wk, and control rats were taken into water for 5 min·d−1. After the training period, both groups remained sedentary for 8 wk. We performed echocardiography at weeks 12 and 20 to investigate the development and regression of exercise-induced structural changes. LV pressure–volume analysis was performed to calculate cardiac functional parameters. LV samples were harvested for histological examination. Results Echocardiography showed robust LV hypertrophy after completing the training protocol (LV mass index = 2.61 ± 0.08 DEx vs 2.04 ± 0.04 g·kg−1 DCo, P < 0.05). This adaptation regressed after detraining (LV mass index = 2.01 ± 0.03 vs 1.97 ± 0.05 g·kg−1, n.s.), which was confirmed by postmortem measured heart weight and histological morphometry. After the 8-wk-long detraining period, a regression of the previously described exercise-induced cardiac functional alterations was observed (DEx vs DCo): stroke volume (SV; 144.8 ± 9.0 vs 143.9 ± 9.6 &mgr;L, P = 0.949), active relaxation (&tgr; = 11.5 ± 0.3 vs 11.3 ± 0.4 ms, P = 0.760), contractility (preload recruitable stroke work = 69.5 ± 2.7 vs 70.9 ± 2.4 mm Hg, P = 0.709), and mechanoenergetic (mechanical efficiency = 68.7 ± 1.2 vs 69.4 ± 1.8, P = 0.742) enhancement reverted completely to control values. Myocardial stiffness remained unchanged; moreover, no fibrosis was observed after the detraining period. Conclusion Functional consequences of exercise-induced physiological LV hypertrophy completely regressed after 8 wk of deconditioning.

A cinaciguat megelőzi a patológiás szívizom-hipertrófia kialakulását bal kamrai nyomás-túlterhelés patkánymodelljén

A szív krónikus nyomásterhelése patológiás miokardiális hipertrófi a kifejlődéséhez vezet, amelynek kialakulását szakirodalmi adatok alapján a cGMP intracelluláris szintjének emelkedése sikeresen képes megakadályozni. Jelen kísérleteink során ezért a cGMP termeléséért felelős enzimet, a szolubilis guanilát-ciklázt aktiváló cinaciguat krónikus adagolásának hatásait vizsgáltuk nyomásindukált patológiás szívizom-hipertrófi a patkánymodelljén. A hasi aorta műtéti beszűkítésének (abdominális aortic banding, AAB) alkalmazásával hoztuk létre a bal kamra nyomásterhelését fi atal, hím Wistar-patkányokban; kontrollként sham operált állatokat használtunk. A kísérleti és kontrollcsoportok p.o. 10 mg/ kg/nap cinaciguat (Cin) vagy placebo (Co) kezelést kaptak hat héten keresztül. Nyomásterhelés hatására az AABCo-csoport állataiban a 6. hét végére szignifi káns mértékű patológiás miokardiális hipertrófi a fejlődött ki, amelyet emelkedett relatív szívtömeg, átlagos szívizomsejt-átmérő, kollagéntartalom és apoptózis jelenléte jellemzett. Cinaciguat alkalmazásával a vérnyomás szignifi káns változtatása nélkül csökkenthető volt e hipertrófi ára jellemző valamennyi morfológiai elváltozás, továbbá az AAB hatására a kardiális funkcióban, így a kontraktilitásban megfi gyelhető eltérések kialakulása is elmaradt a kezelt csoportban. Eredményeink alapján az sGC krónikus aktiválásával felerősített cGMP-jelátvitel hatékony, új stratégia lehet a patológiás miokardiális hipertrófi a kifejlődésének prevenciójában.