Increased Renal Angiotensin II AT1 Receptor Function in Obese Zucker Rat

Angiotensin II (Ang II) via the activation of AT₁ receptors and subsequent stimulation of the tubular sodium transporters increases sodium and water reabsorption in the proximal tubule. An enhanced tubular action of Ang II is implicated in obesity related hypertension; however, the mechanism of such a phenomenon is unknown. Present study was designed to determine the AT₁ receptor numbers and function in the proximal tubule of obese and lean Zucker rats. Obese Zucker rats were hypertensive and hyperinsulinemic. The plasma renin activity was similar in the lean and obese rats. Angiotensin II stimulated the Na,H‐exchanger (NHE) activity in the proximal tubule, but the stimulatory response was markedly greater in obese than in lean rats. Similarly, Ang II caused greater inhibition in cAMP accumulation in the proximal tubule of obese compared to lean rats. The [¹²⁵I]sar‐Ang II binding revealed a 100% increase in the AT₁ receptor number in the brush border membrane (BBM) of obese compared to lean rats. The Western blot analysis revealed a 36–51% increase in the Giα₁ and Giα₃ in the BBM of obese compared to lean rats. We conclude that increases in the AT₁ receptor number and abundance of the Giα on BBM may be responsible for the enhanced signaling and subsequent greater stimulation of NHE by Ang II in proximal tubules of obese rats. The greater stimulation of NHE by Ang II may contribute to the increased tubular sodium reabsorption and to the hypertension in obese Zucker rats.     

Regional variations in action potential alternans in isolated murine Scn5a+/− hearts during dynamic pacing

Aim: Clinical observations suggest that alternans in action potential (AP) characteristics presages breakdown of normal ordered cardiac electrical activity culminating in ventricular arrhythmogenesis. We compared such temporal nonuniformities in monophasic action potential (MAP) waveforms in left (LV) and right ventricular (RV) epicardia and endocardia of Langendorff-perfused murine wild-type (WT), and Scn5a^+/− hearts modelling Brugada syndrome (BrS) for the first time. Methods: A dynamic pacing protocol imposed successively incremented steady pacing rates between 5.5 and 33 Hz. A signal analysis algorithm detected sequences of >10 beats showing alternans. Results were compared before and following the introduction of flecainide (10 μm ) and quinidine (5 μm ) known to exert pro- and anti-arrhythmic effects in BrS. Results: Sustained and transient amplitude and duration alternans were both frequently followed by ventricular ectopic beats and ventricular tachycardia or fibrillation. Diastolic intervals (DIs) that coincided with onsets of transient (tr) or sustained (ss) alternans in MAP duration (DI*) and amplitude (DI′) were determined. Kruskal–Wallis tests followed by Bonferroni-corrected Mann–Whitney U-tests were applied to these DI results sorted by recording site, pharmacological conditions or experimental populations. WT hearts showed no significant heterogeneities in any DI. Untreated Scn5a^+/− hearts showed earlier onsets of transient but not sustained duration alternans in LV endocardium compared with RV endocardium or LV epicardium. Flecainide administration caused earlier onsets of both transient and sustained duration alternans selectively in the RV epicardium in the Scn5a^+/− hearts. Conclusion: These findings in a genetic model thus implicate RV epicardial changes in the arrhythmogenicity produced by flecainide challenge in previously asymptomatic clinical BrS.     

Na+/H+ exchanger mediates TNF-α-induced hepatocyte apoptosis via the calpain-dependent degradation of Bcl-xL

Background and Aim:  It is well known that tumor necrosis factor-α (TNF-α) induces hepatocyte apoptosis and contributes to liver diseases. However, the exact mechanisms are not well understood.
Methods:  In the present study, we reported that Na⁺/H⁺ exchanger (NHE) is involved in TNF-α-induced hepatocyte apoptosis.
Results:  TNF-α time dependently induced an increase in NHE activity in hepatocytes, but cariporide, an NHE inhibitor, blocked the TNF-α-induced increase of NHE activity in a dose-dependent manner. Increased NHE activity induced by TNF-α was associated with increased intracellular calcium (Ca²⁺_i) concentration and calpain activity. Cariporide reversed these effects induced by TNF-α. In addition, TNF-α downregulated Bcl-xL, an anti-apoptotic protein, but not mRNA levels. The inhibition of either calpain or NHE blocked the TNF-α-induced decrease of the Bcl-xL protein. TNF-α did not change the pro-apoptotic Bax and Bak protein levels. Cariporide, calcium remover 1,2-bis (2-aminophenoxy) ethane-N,N,N0,N0–tetraacetic acid, or calpain inhibitor benzyloxycarbonyl-leucyl-leucinal attenuated TNF-α-induced hepatocyte apoptosis.
Conclusion:  TNF-α via NHE results in hepatocyte apoptosis through the calcium/calpain/Bcl-xL pathway.     

Neuropharmacological effects of lipoic acid and ubiquinone on δ‐aminolevulinic dehydratase,Na+, K+‐ATPase,and Mg2+‐ATPase activities in rat hippocampus after pilocarpine‐induced seizures

In this study, we investigated the effects of lipoic acid (LA) in the hippocampus oxidative stress caused by pilocarpine‐induced seizures in adult rats. Wistar rats were treated with 0.9% saline (i.p., control group), LA (10 mg/kg, i.p., LA group), ubiquinone [20 mg/kg, i.p., ubiquinone (UQ) group], pilocarpine (400 mg/kg, i.p., P400 group), and the association of LA (10 mg/kg, i.p.) plus pilocarpine (400 mg/kg, i.p.) or UQ (20 mg/kg, i.p.) plus pilocarpine (400 mg/kg, i.p.), 30 min before of administration of P400 (LA plus P400 group and UQ plus P400 group, respectively). After the treatments, all groups were observed for 1 h. The enzyme activities (δ‐aminolevulinic dehydratase (δ‐ALA‐D), Mg²⁺‐ATPase, and Na⁺, K⁺‐ATPase) were measured using spectrophotometric methods, and the results compared to values obtained from saline and pilocarpine‐treated animals. Protective effects of LA and UQ were also evaluated on the same parameters. We reported here for the first time that Na⁺, K⁺‐ATPase and δ‐ALA‐D activities inhibition and Mg²⁺‐ATPase stimulation in the pilocarpine model are probably attributed to the oxidative stress caused by seizures in the rat hippocampus. The addition of the antioxidants LA and UQ may reverses the previously mentioned Na⁺, K⁺‐ATPase and δ‐ALA‐D inhibitions and Mg²⁺‐ATPase stimulation. Conclusions: The oxidative stress plays an important signaling role in pilocarpine‐induced seizures, and antioxidant drugs might be considered as therapeutical tools in this pathology.     

Age-dependent changes in Na current magnitude and TTX-sensitivity in the canine sinoatrial node

In rabbit, sodium current (I_Na) contributes to newborn sinoatrial node (SAN) automaticity but is absent in adult SAN, where heart rate is slower. In contrast, heart rate is high and I_Na is functional in adult mouse SAN. Given the slower heart rates of large mammals, we asked if I_Na is functionally active in SAN of newborn or adult canine heart. SAN cells were isolated from newborn (6-10 days), young (40-43 days) and adult mongrels. I_Na was observed in > 80% of cells from each age. However, current density was markedly greater in newborn, decreasing with age. At all ages, I_Na was sensitive to nanomolar tetrodotoxin (TTX); 100 nmol/L inhibited I_Na by 46.7%, 59.9% and 90.7% in newborn, young and adult cells, respectively. While high TTX sensitivity suggested the presence of non-cardiac isoforms, steady-state inactivation was relatively negative (midpoints − 89.7 ± 0.7 mV, − 95.1 ± 1.2 mV and − 93.4 ± 1.9 mV from newborn to adult). Consequently, I_Na should be unavailable at physiological potentials under normal conditions, and 100 nmol/L TTX did not change cycle length or action potential parameters of spontaneous adult SAN cells. However, computer modeling predicts the large newborn I_Na protects against excess rate slowing from strong vagal stimulation. The results show that canine SAN cells have TTX-sensitive I_Na which decreases with post-natal age. The current does not contribute to normal automaticity in isolated adult cells but can be recruited to sustain excitability if nodal cells are hyperpolarized. This is particularly relevant in newborn, where I_Na is large and parasympathetic/sympathetic balance favors vagal tone.     

Intracellular pH in thymocytes at the early stages of apoptosis and necrosis

Dynamics of intracellular pH during apoptotic and necrotic death of lymphocytes was studied with the help of fluorescent pH-sensitive probe BCECF. Change in intracellular pH is an early differential marker of apoptotic and necrotic types of death in thymus lymphocytes. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 10, pp. 387–390, October, 1999     

Toxicological assessment of a particulate yeast (1,3/1,6)-beta-D-glucan in rats.

This study investigates the toxicity of WGP 3-6, a yeast-derived beta-glucan ingredient, during single-dose acute and sub-chronic toxicity studies in rats. For the acute study, Fisher-344 rats were administered WGP 3-6 via gavage at a dose of 2000 mg/kg body weight, and any evidence of toxicity was monitored over a 14-day period. WGP 3-6 was well tolerated, indicating that the LD(50) value is greater than 2000 mg/kg body weight. For the sub-chronic study, Fisher-344 rats (10/sex/group) were randomly allocated to receive daily gavage treatment with WGP 3-6 at doses of 0, 2, 33.3, or 100 mg/kg body weight. Control and high-dose satellite recovery groups of each sex also were included. Full toxicological monitoring and endpoint investigations were performed throughout and upon completion of the study. No negative effects on animal weights or food consumption attributable to WGP 3-6 were evident at any dose. In addition, no mortality, clinical pathology, functional/behavioral, microscopic, or gross observations indicating toxicity were observed. Sporadic changes in some biochemical and hematological parameters were observed; however, since the effects were within the physiological ranges in historical controls, were not dose-responsive, or were not observed in both sexes, they were determined to be of no toxicological significance. In conclusion, no adverse or toxic effects were observed after subchronic oral administration of 2, 33.3, or 100mg/kg body weight/day of WGP 3-6 in Fisher-344 rats, and therefore, a no observed adverse effect level (NOAEL) of 100 mg/kg body weight/day, the highest dose tested, was determined.     

大鼠心肌缺血再灌注损伤对心肌细胞膜钠泵表达的影响

目的：观察心肌缺血再灌注（MIR）损伤大鼠心肌组织内洋地黄素水平、ATP酶活性、线粒体Ca^2＋浓度以及Na^＋-K^＋-ATP酶各亚基基因表达的改变，并观察钙通道阻滞剂维拉帕米对其影响，探讨内洋地黄素在MIR损伤细胞内钙超载中的可能作用及其机制。方法：24只雄性SD大鼠随机分成3组，每组8只。假手术组：丝线穿过左冠状动脉前降支，但不结扎：缺血再灌注组（MIR组）：结扎左冠状动脉前降支30min，再灌注45min；维拉帕米组：MIR模型＋5mg／kg维拉帕米，维拉帕米于再灌注前5min经股静脉注射。取缺血区左室心肌检测心肌匀浆内洋地黄素水平、心肌细胞膜Na^＋-K^＋-ATP酶和Ca^2＋-Mg^2＋-ATP酶活性、线粒体Ca^2＋浓度；免疫组化方法检测心肌Na^＋-K^＋-ATP酶α1、α2、α3和β1亚基蛋白水平表达的改变。结果：MIR损伤时，心肌组织内洋地黄素水平明显升高，心肌细胞膜Na^＋-K^＋-ATP酶和Ca^2＋-Mg^2＋-ATP酶活性显著下降，线粒体Ca^2＋浓度升高，Na^＋-K^＋-ATP酶α1、α2、α3和β1亚基蛋白水平表达均明显下降；维拉帕米除具有降低线粒体Ca^2＋浓度外，对缺血再灌注引起的其它各项异常指标无明显改善作用。结论：MIR促进机体内洋地黄素分泌增加，后者可能通过影响心肌细胞膜上的Na^＋-K^＋-ATP酶α1、α2、α3和β1亚基基因表达，抑制Na^＋-K^＋-ATP酶活性，导致线粒体内Ca^2＋超载。     

Carnosine inhibits cataract formation and inactivation of Na+-K+ATPase induced by a glucocorticoid

To investigate whether carnosine can inhibit cataract formation and protect Na⁺-K⁺ATPase against inactivation induced by a glucocorticoid. METHODS: Two hundred and twenty clear lenses cultured in vitro were randomly divided into five groups: control group (DMEM), steroid group (DMEM+Dexamethason 10μmol/L), lower concentration carnosine-treated group (DMEM+Dexamethason 10μmol/L+Carnosine 2mmol/L), higher concentration carnosine-treated group (DMEM+Dexamethason 10μmol /L+ Carnosine 5mmol/L) and carnosine group (DMEM + Carnosine 5mmol/L). Progression of cataract formation was evaluated daily using a dissecting microscope. On 1, 3, 5 and 7 days, 10 lenses of every group were homogenized and the activity of Na^{+-K+ATPase was measured by using spectrophotometer. RESULTS: During the incubation, mistlike opacity was observed in the lenses of the control group and carnosine group, but in the steroid group appeared dense nuclear opacity, while both two carnosine-treated groups came out visible demarcation between nuclear and cortical regions on 7 days. A decrease in the activity of Na+-K+ATPase was found in the lens of the steroid group. On 3, 5, 7 days, Na+-K+ATPase activity decreased 22.34% (P =0.002), 47.98% (P <0.001), 75.37%(P <0.001) compared with that at 1 day, respectively. In the carnosine group, the activity of Na+-K+ATPase remained at the level of the control throughout the 7-day incubation, indicating that carnosine itself did not interfere with the original lens enzyme activity. In the lower concentration carnosine-treated group, on 3, 5, 7 days, the activity of Na+-K+ATPase increased 10.8% (P <0.05), 44.6% (P <0.01), 57.4% (P <0.01) of control activity, respectively. In the higher concentration carnosine-treated group, the activity of Na+-K+ ATPase increased 11.3% (P <0.05), 45.7% (P <0.01), 57.6% (P <0.01), respectively on 3, 5, 7 days. The activity of Na+-K+ATPase in both two carnosine-treated groups were only 6.7% and 6.5% lower than that of the control group after 7-day incubation. After the 7-day incubation, the Na+-K+ ATPase activity of the lenses in the steroid group decreased significantly compared with carnosine-treated groups(P ＜0.01). CONCLUSION: Carnosine prevents the cataract formation induced by a glucocorticoid, and significantly inhibits the inactivation of Na+-K+ATPase induced by a glucocorticoid.}     

One-year chronic toxicity of madder color in F344 rats – Induction of preneoplastic/neoplastic lesions in the kidney and liver

To evaluate chronic toxicity of madder color (MC), a natural food colorant extracted from the roots of Rubia tinctorum L., F344 rats were fed diet containing 0%, 0.2%, 1.0% or 5.0% MC for 53 weeks. Hematological changes including anemia and serum biochemical alterations indicating hepatotoxicity were demonstrated at 5.0% in both sexes. Relative weights of the liver were significantly increased from 1.0% in both sexes, and those of the kidney were significantly increased from 1.0% in males and from 0.2% in females. Histopathologically, atypical renal tubule hyperplasias were increased at 1.0% or higher in both sexes in association with increase of cell proliferative activity in the tubules. A renal cell adenoma was observed in a male rat receiving 5.0% MC. In addition, glutathione S-transferase placental form-positive liver cell foci were significantly increased at 5.0% in both sexes. These results indicate that MC has chronic toxicity targeting kidney, liver and blood cells. Moreover, the results strongly suggest that MC may have the carcinogenic potential in the kidney and the liver.