Normotensive Control Wistar Rats Research Articles

Differences in mitochondrial efficiency and heart function after different modes of exercise training in hypertension

Abstract Physical exercise is often used for the cardioprotective purpose in hypertension. However, it's not clear whether the mitochondrial efficacy will depend on the intensity and mode of physical exercise. The aim of the work is to investigate the effect of different modes of exercise training on mitochondria function and cardyohemodynamic in hypertension. All experimental procedures were performed in accordance with the European Communities Council Directive of 24 November 1986 (86/609 /EEC). Six-month-old spontaneously hypertensive rats (SHR) and normotensive control–Wistar rats were randomly assigned to 2 different training modes: moderate (20 min) and enhanced (45 min). Swimming training was done five times per week for 5–6 weeks. The functional cardiohemodynamic indicators were registered via microcatheter and Millar Pressure-Volume System. Mitochondrial oxygen consumption registered by Oxygraph. Moderate exercise training mode in SHR had a positive effect on the respiratory chain of mitochondria, respiratory control increased by 25,3%, the mitochondrial membrane potential increased by 47,8%. Moderate exercise training mode protected mitochondrial permeability transition pore (MPTP) formation. The threshold of MPTP opening increased by 1.4 times and the sensitivity of MPTP to inductor Ca2+ decreased. It was shown that end-systolic and end-diastolic pressure of SHR was decreased by 23,8% and 32,7% respectively. Moderate exercise improves end-diastolic heart function in SHR by increasing dP/dtmin and reducing the end-diastolic myocardial stiffness in 8,3 times. Stroke volume increased in 3,3 times, stroke work decreased by 17.2%, which may indicate the heart work efficiency increased after moderate exercise training. The Frank-Starling mechanism efficiency after moderate exercise was increased by 3,7 times. After enhanced exercise mode we didn't observe a protected effect on heart mitochondria and heart function in SHR. The mitochondrial membrane potential didn't increase, mitochondrial respiration in states V2, V3, V4 were significantly decreased. In conclusion, we showed that a moderate mode of exercise in SHR rats increased mitochondrial efficiency and improved heart function. The enhanced mode of exercise was excessive for SHR which was confirmed by suppressing the mitochondrial respiration and end-diastolic function of the heart. Funding Acknowledgement Type of funding sources: None.

Angiotensin II induces cyclooxygenase 2 expression in rat astrocytes via the angiotensin type 1 receptor

We previously showed that Angiotensin (Ang) II stimulated pro-inflammatory and mitogenic actions in astrocytes suggesting that astrocytes are emerging as key players in neuroinflammation. Evidence suggests that neuroinflammation may contribute to central sympathetic overactivity and elevated blood pressure. Further, cyclooxygenase (Cox)-derived prostanoids were implicated in Ang II-dependent hypertension. Cox2 is one of two Cox isoenzymes that is responsible for the formation of prostanoids from arachidonic acid. Constitutively expressed Cox2 has a protective and homeostatic role in the cardiovascular and renal systems. Inducible Cox2 has been associated with pathogenic stimuli resulting in inflammatory conditions and cancers. In this study, we investigated the effect of Ang II on Cox2 protein and mRNA expression in brainstem and cerebellum astrocytes, and determined whether any differences in Cox2 expression exist in spontaneously hypertensive rat (SHR) astrocytes compared to their normotensive control Wistar rats. We demonstrated that Ang II increased Cox2 protein and mRNA levels relative to untreated controls in a time-dependent manner, in Wistar and SHR brainstem and cerebellum astrocytes. Increases in Cox2 protein expression were evident within 4 h, with subsequent sustained elevation for several hours followed by a decline at 48 h. Ang II-induced Cox2 protein levels were higher in Wistar compared to SHRs in both brainstem and cerebellum astrocytes for the majority of time points examined. The Ang II-induced Cox2 mRNA levels increased within 8 h followed by a rapid decline to almost basal levels at later time points. At the earlier time points, Cox2 mRNA elevation were higher in SHR compared to Wistar rat astrocytes. These Ang II actions were mediated by the Ang type I receptor. Our results corroborate previous reports of Ang II's ability to stimulate neuroinflammatory mediators in astrocytes. Cox2-derived prostaglandins might play a role in brain-renin angiotensin system associated hypertension, and astrocytes could be significant players.

The benefits of endurance training in cardiomyocyte function in hypertensive rats are reversed within four weeks of detraining

The aim of the present study was to verify the effects of low-intensity endurance training and detraining on the mechanical and molecular properties of cardiomyocytes from spontaneously hypertensive rats (SHRs). Male SHRs and normotensive control Wistar rats at 16-weeks of age were randomly divided into eight groups of eight animals: NC8 and HC8 (normotensive and hypertensive control for 8weeks); NT8 and HT8 (normotensive and hypertensive trained at 50–60% of maximal exercise capacity for 8weeks); NC12 and HC12 (normotensive and hypertensive control for 12weeks); NDT and HDT (normotensive and hypertensive trained for 8weeks and detrained for 4weeks). The total exercise time until fatigue (TTF) was determined by a maximal exercise capacity test. Resting heart rate (RHR) and systolic arterial pressure (SAP) were measured. After the treatments, animals were killed by cervical dislocation and left ventricular myocytes were isolated by enzymatic dispersion. Isolated cells were used to determine intracellular global Ca2+ ([Ca2+]i) transient and cardiomyocyte contractility (1Hz; ~25°C). [Ca2+]i regulatory proteins were measured by Western blot, and the markers of pathologic cardiac hypertrophy by quantitative real-time polymerase chain reaction (q-RT-PCR). Exercise training augmented the TTF (NC8, 11.4±1.5min vs. NT8, 22.5±1.4min; HC8, 11.7±1.4min vs. HT8, 24.5±1.3min; P<0.05), reduced RHR (NT8initial, 340±8bpm vs. NT8final, 322±10bpm; HT8initial, 369±8bpm vs. HT8final, 344±10bpm; P<0.05), and SBP in SHR animals (HC8, 178±3mmHg vs. HT8, 161±4mmHg; P<0.05). HC8 rats showed a slower [Ca2+]i transient (Tpeak, 83.7±1.8ms vs. 71.7±2.4ms; T50%decay, 284.0±4.3ms vs. 264.0±4.1ms; P<0.05) and cell contractility (Vshortening, 86.1±6.7μm/s vs. 118.6±6.7μm/s; Vrelengthening, 57.5±7.4μm/s vs. 101.3±7.4μm/s; P<0.05), and higher expression of ANF (300%; P<0.05), skeletal α-actin (250%; P<0.05) and a decreased α/β-MHC ratio (70%; P<0.05) compared to NC8. Exercise training increased [Ca2+]i transient (NC8, 2.39±0.06F/F0 vs. NT8, 2.72±0.06F/F0; HC8, 2.28±0.05F/F0 vs. HT8, 2.82±0.05F/F0; P<0.05), and cell contractility (NC8, 7.4±0.3% vs. NT8, 8.4±0.3%; HC8, 6.8±0.3% vs. HT8, 7.8±0.3%; P<0.05). Furthermore, exercise normalized the expression of ANF, skeletal α-actin, and the α/β-MHC ratio in HT8 rats, augmented the expression of SERCA2a (NC8, 0.93±0.15 vs. NT8, 1.49±0.14; HC8, 0.83±0.13 vs. HT8, 1.32±0.14; P<0.05) and PLBser16 (NC8, 0.89±0.18 vs. NT8, 1.23±0.17; HC8, 0.77±0.17 vs. HT8, 1.32±0.16; P<0.05), and reduced PLBt/SERCA2a (NC8, 1.21±0.19 vs. NT8, 0.50±0.21; HC8, 1.38±0.17 vs. HT8, 0.66±0.21; P<0.05). However, all these adaptations returned to control values within 4weeks of detraining in both SHR and normotensive control animals. In conclusion, low-intensity endurance training induces positive benefits to left ventricular myocyte mechanical and molecular properties, which are reversed within 4weeks of detraining.

Peritubular membrane potential in kidney proximal tubular cells of spontaneously hypertensive rats

Peritubular membrane potential in kidney proximal tubular cells of spontaneously hypertensive rats (SHR-Okamoto strain adult rats) was measured with conventional 3 mol KCl microelectrodes, in vivo. Peritubular cell membrane potential was not different in SHR (-66.5 ± 0.7 mV) as compared with normotensive control Wistar rats (-67.5 ± 1.2 mV). To test the effects of possible altered sodium membrane transport in SHR on proximal tubule peritubular membrane potential, we allowed SHR and control rats to drink 1% NaCl for two weeks. Again, proximal tubule peritubular membrane potential was not different in SHR on 1% NaCl (-67.0 ± 1.0 mV) as compared with control rats on 1% NaCl (-64.7 ± 1.3 mV). From these results we concluded that peritubular membrane potential in kidney proximal tubular cells of SHR was not different from normotensive Wistar control rats, and if some alteration of sodium transport in kidney proximal tubular cells of SHR could exist, that was not possible to evaluate from the measurements of peritubular membrane potential in kidney proximal tubular cells.

Are sodium-dependent V1 receptors and sympathetic nerve activations involved in regulation of blood pressure in borderline-hypertensive Hiroshima rats?

Sympathetic nerve activity (SNA) was estimated by the magnitude of depressor response after ganglionic blockade with hexamethonium bromide (C6; 25 mg/kg weight). The depressor effects of C6 were significantly less in borderline-hypertensive Hiroshima rats (BHR) than in deoxycorticosterone acetate (DOCA)-salt hypertensive rats (DOCA rats) or in spontaneously hypertensive rats (SHR), but they were not different in BHR and normotensive control Wistar rats (NCR). After sympatho-inhibition, the depressor effects of a selective vasopressin V1 receptor antagonist (V1A; 10 microg/kg: [d(CH2)5(1), O-Me-Tyr2, Arg8]-vasopressin) were significantly greater in BHR than in DOCA rats, SHR or NCR. In a previous study, we reported that the depressor effects of C6 were significantly less in BHR than in SHR, but after sympatho-inhibition, the depressor effects of V1A were significantly greater in BHR than in SHR (Hypertens Res 2002; 25: 241-248). After high-salt diet loading in the present study (8% salt-containing diet for 10 weeks), the magnitudes of increase in mean arterial pressure in BHR and NCR were almost the same. There was almost no difference in the depressor effects of V1A after sympatho-inhibition between BHR with high-salt intake and BHR without high-salt intake. The depressor effects of an angiotensin-converting enzyme inhibitor, captopril (1 mg/kg), were almost the same between BHR and NCR both before and after sympatho-inhibition. However, these effects were completely inhibited after the high-salt diet. The results show that SNA was within the normal range in BHR and that no further accelerated responsiveness of endogenous vasopressin was observed in BHR after high-salt intake.

Membrane microviscosity and plasma triacylglycerols in the rat.

1. Multiple cell membrane alterations have been described in humans and animals with various genetic forms of hypertension and/or dyslipidaemia. The aim of our study was to characterize membrane microviscosity, using two different fluorescent probes exploring either the outer membrane leaflet [trimethylamino-diphenylhexatriene (TMA-DPH)] or the lipid membrane core [diphenylhexatriene (DPH)], in platelets and erythrocytes of genetically hypertensive rats of the Prague hereditary hypertriglyceridaemic (HTG) strain. The relationships of membrane microviscosity to hypertension, hypertriglyceridaemia and cell calcium handling were also investigated. 2. Membrane microviscosity was similar in HTG and normotensive control Wistar rats when measured in platelets or erythrocyte ghosts incubated in Na(+)-containing medium. On the contrary, TMA-DPH fluorescence anisotropy was significantly reduced in HTG platelets incubated in Na(+)-free medium because external Na+ removal elicited a larger rise of TMA-DPH anisotropy in Wistar platelets. 3. Plasma triacylglycerols were associated positively with platelet TMA-DPH anisotropy and negatively with DPH anisotropy in both strains. The slopes of these relationships were reduced in HTG compared with Wistar rats. Platelet TMA-DPH anisotropy correlated positively and DPH anisotropy negatively with the cytosolic calcium concentration in unstimulated platelets, the slopes being almost identical in both strains. 4. Pulse pressure correlated negatively with TMA-DPH anisotropy and positively with DPH anisotropy found in erythrocyte ghosts. 5. The present results suggest that plasma triacylglycerols and cytosolic calcium are capable of modulating the membrane microviscosity in this new animal model of genetic hypertension associated with hypertriglyceridaemia.

Pituitary response to TRH and LHRH in spontaneously hypertensive rats.

SummaryThe LH response to LHRH and the TSH and PRL response to TRH were examined in spontaneously hypertensive rats and normotensive control Wistar rats to determine if the pituitary response to these releasing hormones is altered in the hypertensive rats. Although basal levels of LH were similar in the two groups of rats, the LH response to LHRH was significantly less in the hypertensive rats than in the normotensive controls. The spontaneously hypertensive rats had higher basal levels of TSH and PRL and significantly greater TSH and PRL responses to TRH. The results of this study suggest that the hypothalamo-pituitary axis is altered in the spontaneously hypertensive rat.

Hemodynamics of experimentally hypertensive rats in conscious and anesthetized states.

Cardiac output was measured by a pulse contour method in reno-vascular hypertensive rats, deoxycorticosterone (DOC) hypertensive rats and normotensive control Wistar rats in the conscious state. All rats were male in sex and 12-13 weeks of age (2-3 weeks after operation in the hypertensive rats). Cardiac output per body weight was not significantly different among the groups. Therefore, the hypertension in the experimentally hypertensive rats in the conscious state was ascribable to an increased total peripheral resistance. After anesthesia with pentobarbital and thoracotomy, the DOC rats were no longer hypertensive. However, in the renovascular hypertensive rats, the hypertensive state due to an increase in vascular resistance persisted after anesthesia, thoracotomy, and even ganglion blockade with hexamethonium bromide, indicating the importance of non-neural factors in the renovascular hypertension. Aortic compliance measured in vivo under anesthesia was smaller in either the renovascular or DOC hypertensive rats than in the control rats before and after ganglion blockade, which suggests a non-neural hardening of elastic vessels in the experimental hypertensions.

Ontogenesis of the renin-angiotensin system in spontaneously hypertensive and normal Wistar rats.

Kidney renin activity was investigated in spontaneously hypertensive and normotensive control Wistar rats. Kidneys were obtained from fetal rats after 18 and 21 days of gestation and from neonatal rats 1, 7, 14, and 21 days old. Kidney renin activity was determined by a modification of the radioimmunoassay for angiotensin I developed in this laboratory, and tissue from each age group was stained for juxtaglomerular granules. Kidney renin activity progressively increased in both strains from day 18 of fetal life until day 1 of neonatal life when a plateau level developed. In 1-day-old neonatal rats, significant differences in the kidney renin activity of the spontaneously hypertensive and the normotensive strains were initially noted. Kidney renin activity was maintained at significantly higher levels in the spontaneously hypertensive strain under 21 days of age when, because of a rise in the kidney renin activity of the normotensive control strain and a fall in the kidney renin activity of the spontaneously hypertensive strain, the difference between the two strains became statistically insignificant. In both strains, juxtaglomerular granules were first noted in 1-day-old neonatal rats and in each age group thereafter.

Synthesis and turnover of norepinephrine in the heart of the spontaneously hypertensive rat.

The kinetics of norepinephrine (NE) metabolism in the heart was studied in genetically hypertensive and normotensive control Wistar rats. Concentrations of endogenous NE were similar in the two groups. However, rates of synthesis of NE were reduced in these hypertensive rats, whether calculated from the rate of decline (fractional turnover rate) of cardiac tritiated NE ( 3 H-NE) after intravenous injection, or estimated from levels of 14 C-NE in the heart after injection of the precursor 14 C-L-tyrosine. In experiments with 3 H-NE the synthesis rate of NE was 30.2 ng/hour/g heart in control and 18.2 ng/hour/g heart in hypertensive rats. The levels of 14 C-NE found in the heart of normotensive rats given 14 C-tyrosine were up to 1.4 times those found in hypertensive rats. These findings indicate a reduced rate of release of NE in this form of hypertension and, rather than implicating NE as a primary factor, suggest a secondary, compensatory mechanism.