Intermittent ischaemia maintains function after ischaemia reperfusion in steatotic livers

Background:

Ischaemic preconditioning (IPC) and intermittent ischaemia (INT) reduce liver injury after ischaemia reperfusion (IR). Steatotic livers are at a higher risk of IR injury, but the protection offered by IPC and INT is not well understood. The aim of the present study was to determine the effectiveness of IPC and INT in maintaining liver function in steatotic livers.

Material and methods:

A model of segmental hepatic ischaemia (45 min) and reperfusion (60 min) was employed using lean and obese Zucker rats. Bile flow recovery was measured to assess dynamic liver function, hepatocyte fat content quantified and blood electrolytes, metabolites and bile calcium measured to assess liver and whole body physiology. Liver marker enzymes and light and electron microscopy were employed to assess hepatocyte injury.

Results:

IPC was not effective in promoting bile flow recovery after IR in either lean or steatotic livers, whereas INT promoted good bile flow recovery in steatotic as well as lean livers. However, the bile flow recovery in steatotic livers was less than that in lean livers. In steatotic livers, ischaemia led to a rapid and substantial decrease in fat content. Steatotic livers were more susceptible to IR injury than lean livers, as indicated by increased blood ALT concentrations and major histological injury.

Conclusion:

INT is more effective than IPC in restoring liver function in the acute phase of IR in steatotic livers. In obese patients, INT may be useful in promoting better liver function after IR after liver resection.     

Baroreflex function in lifetime-captopril-treated spontaneously hypertensive rats

The effects of lifetime oral captopril treatment on baroreflex control of heart rate and lumbar sympathetic nerve activity were measured in 19-21-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). The sensitivity of baroreflex control of heart rate and lumbar sympathetic nerve activity were determined by the slopes of the relation between the change in mean arterial pressure (MAP) (mm Hg) versus the change in pulse interval (msec/beat) and the change in MAP versus the percent change in nerve activity, respectively. Untreated SHR had significantly higher MAP than WKY (157 +/- 3 vs. 115 +/- 3 mm Hg, p less than 0.001) and exhibited a decreased baroreflex control of heart rate. Lifetime treatment with captopril prevented the development of hypertension in SHR (MAP = 110 +/- 5 mm Hg) and increased the sensitivity of baroreflex function. The gains of the baroreflex control of heart rate for captopril-treated SHR and control SHR when MAP was raised or lowered by phenylephrine or nitroprusside were 2.38 +/- 0.49 vs. 1.10 +/- 0.33 msec/mm Hg (p less than 0.05) and 0.74 +/- 0.20 vs. 0.54 +/- 0.09 (NS) msec/mm Hg, respectively. The sensitivity of the baroreflex control of lumbar sympathetic nerve activity was greater in captopril-treated SHR than in control SHR when MAP was increased or decreased (-1.03 +/- 0.26 vs. -0.38 +/- 0.11, p less than 0.05; -0.84 +/- 0.2 vs. -0.04 +/- 0.58 (NS) mm Hg-1, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal function of conscious spontaneously hypertensive rats

Renal clearance studies were performed in conscious 13-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) before and during volume expansion by intravenous infusion of isotonic saline. Mean arterial pressure and filtration fraction were greater in SHR, whereas fractional and absolute excretion of sodium and water, glomerular filtration rate, and renal plasma flow in SHR and WKY were not statistically different. This was the case during hydropenia and volume expansion. We did not observe as exaggerated natriuresis after intravenous loading when unanesthetized SHR were compared with the response of WKY. These observations suggest that the kidneys of genetically hypertensive rats of the Okamoto-Aoki strain have adapted to an elevated renal perfusion pressure or that hypertension is required to normalize renal function so that excretion is appropriately matched with intake.     

Haemodynamic changes during tilt after autonomic blockade in spontaneously hypertensive rats

The haemodynamic shifts during head up and head down tilt were investigated in adult spontaneously hypertensive rats (SHR) and matched normotensive control rats (NCR) under nembutal anaesthesia and autonomic blockage. During head up tilt a greater fall in blood pressure and stroke volume was observed in SHR than in NCR, while the reverse was true when tilted in the opposite direction. This altered cardiac response to venous filling, also observed in patients with essential hypertension, is suggested to be caused by an altered Frank-Starling relationship of the hypertrophied heart in hypertensive individuals.     

Comparison of microvascular pressures in normal and spontaneously hypertensive rats

The principal cardiovascular manifestations of essential hypertension are known to be an increase in peripheral vascular resistance and in systemic arterial blood pressure. However, it is not known if the increased vascular resistance is of appropriate location and magnitude to prevent an elevation of pressures in the microvasculature during hypertension. To examine this possibility, the pressures and diameters of microvessels in the cremasteric muscle were measured in normal (NR) and spontaneously hypertensive rats (SHR). The pressures and diameters in comparable orders of vessels in NR and SHR at their respective systemic arterial pressures of 88.5 ± 2.1 and 115.6 ± 1.8 mm Hg at age 7–8 weeks were measured by the servonull micropipet technique. Both the systemic pressure and the microvascular pressure in SHR are 30–35% higher than those measured in NR. The diameters of the arterioles and venules in SHR are as large or larger than comparable orders of vessels in NR. Therefore, the reported increase in vascular resistance during hypertension seems not to be caused by vasoconstriction of vessels in SHR as compared to NR, nor does the increased resistance prevent an increase in microvascular pressures.     

Abnormal thyroid function in spontaneously hypertensive rats.

Thyroid weight, thyroidal radioiodide uptake, and cyclic AMP-dependent protein kinase activity of a thyroid supernatant fraction were increased significantly in spontaneously hypertensive rats (SHR), apparently because of increased secretion of pituitary TSH. However, the thyroids of SHR did not make supernormal amounts of thyroxine (T4), and thyroidal radioiodine release was apparently impaired. In the SHR, proteolytic enzyme activity was less than normal and the thyroglobulin was more resistant to normal proteolytic enzyme than was control thyroglobulin. Presumably because of these abnormalities, plasma T4 was significantly lower than normal, but triiodothyronine (T4) was normal, as a result of compensatory processes occurring in T3 synthesis and hydrolysis of thyroglobulin. T4 and T3 were less effective in depressing pituitary TSH synthesis and secretion in SHR than in controls, possibly because of an abnormal setting of the "hormostat." Although the hypothalamic content of TRH was normal in SHR, the exact site of the abnormality in the "hormostat" is not delineated in the present study.     

Cardiovascular mass and ventricular function after celiprolol in Wistar-Kyoto and spontaneously hypertensive rats.

OBJECTIVE: The effects of a new beta 1 adrenergic receptor blocking agent with beta 2 receptor agonistic properties on cardiovascular mass, left ventricular function, and aortic distensibility were studied in Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. METHODS: 20 male SHR and 20 male WKY rats (10 treated and 10 untreated) aged 22 weeks were studied after three weeks of treatment. Cardiovascular mass was measured and left ventricular function was assessed using electromagnetic flowmetry while rapidly infusing whole blood at pharmacologically reduced mean arterial pressure and at pretreatment arterial pressure levels. Aortic distensibility was assessed by obtaining pressure-volume relationships in isolated aortic segments. RESULTS: Mean arterial pressure was reduced without changing cardiac output in SHR (p less than 0.01); it remained unchanged in WKY despite reduced cardiac output. Most noteworthy, and like no other agent studied to date, celiprolol significantly reduced both left and right ventricular as well as aortic mass in both WKY and SHR. Despite these similar mass reductions, celiprolol improved left ventricular function (p less than 0.01) and aortic distensibility (p less than 0.05) only in the SHR, a function maintained even when mean arterial pressure was increased abruptly to pretreatment levels. CONCLUSIONS: Unlike other beta receptor blockers (or any other agent studied in the SHR), celiprolol was effective in reducing mass of right and left ventricles and of aorta; decreasing mean arterial pressure through a fall in total peripheral resistance; and improving left ventricular function and aortic distensibility in the SHR. In contrast, while these structural changes were also produced in WKY, they were not associated with similar functional responses. These findings provide further support for the thesis of a structural and haemodynamic dissociation in antihypertensive therapy.     

Myocardial energy metabolism in the hypertrophied hearts of spontaneously hypertensive rats

Summary Age-related changes in the myocardial energy metabolism were studied in spontaneously hypertensive (SHR) rats of 5–25 weeks of age. Systolic blood pressure increased rapidly during 5 to 10 weeks of age (developing phase) and attained a plateau level at 10 to 15 weeks (sustained phase). Even during the developing phase, the heart was hypertrophic, as assessed by an increase in the ratio of the ventricular weight to body weight. However, myocardial contents of glycolytic intermediates and high energy phosphate compounds and thus, the myocardial energy state (phosphorylation potential) in SHR rats did not differ from those in age-matched normotensive Wistar-Kyoto (WKY) rats. The lactate/pyruvate ratio was significantly lower in SHR rats. On the other hand, during the sustained phase, cardiac hypertrophy progressed only gradually, and myocardial contents of creatine phosphate and ATP were lower, while the lactate content was higher than in WKY rats. The lactate/pyruvate ratio was elevated, while phosphorylation potential was lowered. These findings suggest that the energy state is normal during the developing phase of hypertension despite the presence of cardiac hypertrophy and the increased pressure load, whereas the energy state is at a lower level during the sustained phase of hypertension.

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Zusammenfassung Die altersabhängigen Änderungen des myokardialen Energieumsatzes wurden bei spontanhypertensiven, 5 bis 25 Wochen alten Ratten (SHR) untersucht. Der systolische Blutdruck stieg zwischen der 5. und 10. Lebenswoche rasch an (Entwicklungsphase) und erreichte nach 10 bis 15 Wochen ein Plateau (Dauerphase). Auch während der Entwicklungsphase war das Herz hypertrophiert, gemessen an einem Anstieg des Verhältnisses Ventrikelgewicht: Körpergewicht. Jedoch unterschied sich der Gehalt des Myokards an Intermediärprodukten der Glykolyse und energiereichen Phosphaten und damit bezüglich des energetischen Status (Phosphorylierungspotential) bei SHR-Ratten nicht von gleichaltrigen normotensiven Wistar-Kyoto-Ratten (WKY). Das Lactat-Pyruvat-Verhältnis war bei SHR-Ratten signifikant vermindert. Andererseits nahm die Herzhypertrophie während der Dauerphase nur allmählich zu; der Gehalt an Kreatinphosphat und ATP war geringer, während der Lactatgehalt höher war als bei WKY-Ratten. Das Lactat-Pyruvat-Verhältnis war gesteigert, während das Phosphorylierungspotential vermindert war. Diese Befunde lassen vermuten, daß der energetische Status während der Entwicklungsphase der Hypertension normal ist trotz des Vorliegens einer Herzhypertrophie und gesteigerter Druckbelastung, während der energetische Status während der Dauerphase herabgesetzt ist.

     

Impaired mammary function and parathyroid hormone-related protein during lactation in growth-restricted spontaneously hypertensive rats

Evidence implicates pivotal roles for parathyroid hormone-related protein (PTHrP) during lactation, including stimulation of mammary and pup growth. As spontaneously hypertensive rat (SHR) pups are growth restricted compared with the control Wistar Kyoto (WKY), we examined the relative roles of pup suckling and maternal lactational environment on pup growth, mammary PTHrP, and milk PTHrP and calcium concentrations. SHR pups were lighter compared with the control from 6 days. SHR mammary PTHrP content and milk PTHrP were lower but maternal plasma PTHrP was raised compared with WKY. SHR mammary morphological development was also impaired compared with control. Cross fostering growth-restricted pups onto WKY mothers increased pup weight in association with normal mammary function and higher milk PTHrP and calcium. Control pups suckling on an SHR mother had reduced body weight. Both cross fostering groups were associated with increased maternal and milk PTHrP concentrations, indicating the importance of suckling, together with a functional mammary gland. The results suggested that impaired SHR mammary function and milk PTHrP are associated with a reduced SHR postnatal growth. Our data also indicated that milk and mammary PTHrP are regulated by different mechanisms but that they are influenced by the maternal lactational environment and the suckling pup.     

幼龄自发性高血压大鼠血管内皮功能研究

目的　本研究选取幼龄自发性高血压大鼠(SHR)作为研究对象 ,观察其尚未出现高血压时血浆一氧化氮 (NO)、血管壁一氧化氮合酶 (NOS)的情况及负荷运动对它的影响 ,从而进一步了解内皮功能在遗传性高血压发病中的地位。方法　 5～ 6wSHR、WKY各 2 8只随机分为静态组、运动组 ,静态组行有创血压测定、血浆NO及血管壁NOS测定 ,运动组行游泳负荷运动后行上述指标测定 ,分别比较静态组WKY、SHR 6min内的平均血压、峰血压、达峰时间、血浆NO的均数和运动组WHY、SHR的上述指标的均数 ,比较各组NOS免疫组化染色。结果　 (1)静态组WKY、SHR6min内的平均血压、峰血压、达峰时间有显著差异 (P <0 0 5 ) ;运动组WKY、SHR的平均血压、峰血压、达峰时间没有显著差异 (P >0 .0 5 ) ;(2 )静态组WKY、SHR的血浆NO无显著差异 (P <0 .0 5 ) ,运动组WKY、SHR的NO有显著差异(P <0 .0 5 ) ;无论是SHR还是SKY ,其运动组血浆NO均高于静态组 ,但WKY鼠运动组比静态组增高更明显 ;(3)各组血管壁NOS免疫组化染色范围未见明显不同。结论　SHR在高血压期前已存在内皮舒血管储备功能的不足。推测内皮舒血管功能的障碍可能参与了遗传性高血压的发病。     

A comparative study of cardiac function in transgenic hypertensive rats, in spontaneously hypertensive rats and in normotensive rats

Left ventricular hypertrophy (LVH) entails numerous functional and molecular changes that ultimately lead to cardiac insufficiency. The renin-angiotensin system and adrenergic receptor signalling pathway have both been implicated in LVH progression and interactions between these factors may precipitate contractile dysfunction. We therefore investigated cardiac function in hypertensive rats transgenic for the human renin and angiotensinogen genes (TGR) having a genetic activation of the renin-angiotensin system, stroke-prone spontaneously hypertensive rats (SHR) and normotensive controls (CTR) aged 6 weeks. The isolated perfused heart model was used and the effect of isoproterenol (0.1-1000 nmol/L on cardiac function was studied. Cardiac protein and gene expression was studied by Western blot and RNase protection assay. TGR had 75 mmHg higher blood pressure and a 24% higher cardiac/body weight ratio than CTR; blood pressure in SHR was 17 mmHg higher without heart weight difference (p < 0.05). Basal Pmax, +dP/dt and -dP/dt were higher in TGR and SHR compared with CTR hearts. Isoproterenol stimulated these parameters by a maximum factor 6-8 in CTR and SHR but had almost no effect in TGR (p < 0.05). Basal CF per g heart weight was similar in all experimental groups. Isoproterenol produced a significantly smaller vasodilation in TGR compared with CTR or SHR. beta 1 and beta 2 receptor and Gs alpha proteins were similar in TGR, SHR and CTR. Gi alpha was increased in TGR hearts (p < 0.05). Converting enzyme and atrial natriuretic factor mRNA expression was increased (p < 0.01) while beta 1 receptor, adenylyl-cyclase V, SERCA2a and phospholamban mRNA expression was unchanged in TGR compared with CTR. Thus, LVH in TGR is characterised by early adrenergic dysfunction and beta 1 receptor signalling abnormalities indicating progressive functional deterioration. The data may serve as support for an early preventive intervention in angiotensin-II dependent cardiac hypertrophy and may have also implications for patients with genetic alterations of the renin-angiotensin system.     

Brain angiotensin II and baroreceptor reflex function in spontaneously hypertensive rats

We examined whether the increase in baroreceptor reflex function previously reported in lifetime - captopril-treated spontaneously hypertensive rats (SHR) was due to an inhibition of brain angiotensin II mechanisms. Pregnant and lactating SHR were given oral captopril (100 mg/kg/day). After weaning, pups were maintained on captopril (50 mg/kg/day) until the study (19-21 weeks). Control rats received tap water. One week before study captopril-treated and control SHR were given an intracerebroventricular infusion of angiotensin II (7.5 ng/hr, osmotic pump) or vehicle (artificial cerebrospinal fluid). Baroreceptor reflex control of heart rate was assessed by the slope of the relation between the change in mean arterial pressure (mm Hg) versus the change in pulse interval (msec beat-1). Arterial pressure was raised or lowered by intravenous bolus injections of phenylephrine or nitroprusside, respectively. Central infusion of angiotensin II had no significant effect on mean arterial pressure in captopril or control SHR (captopril-angiotensin II 125 +/- 4 vs. captopril-vehicle 121 +/- 2; control-angiotensin II 169 +/- 5 vs. control-vehicle 173 +/- 7 mm Hg), but it produced a significant rise in basal heart rate (captopril-angiotensin II 371 +/- 10 vs. captopril-vehicle 323 +/- 8, p less than 0.0002; control-angiotensin II 338 +/- 7 vs. control-vehicle 312 +/- 8 beats/min, p less than 0.0183) and in daily water intake (captopril-angiotensin II 20.7 +/- 2.2 vs. captopril-vehicle 9.8 +/- 0.7, p less than 0.0426; control-angiotensin II 33.1 +/- 3.8 vs. control-vehicle 9.0 +/- 0.6 ml/100 g body wt, p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)     

盐酸埃他卡林对脑卒中易感型自发性高血压大鼠心功能的影响

目的研究盐酸埃他卡林（Ipt）对大鼠无创心功能参数的影响。方法利用清醒无创心功能血流动力学计算机监测系统,对比研究Ipt对正常血压大鼠和脑卒中易感型自发性高血压大鼠（SHRsp）心率、心脏收缩、舒张和泵血功能的影响。结果Ipt0.5mg/kg静注可降低SHRsp心率、室缩波、抑制心肌收缩力指数,延长左室射血期和心肌电机械收缩时间,降低心输出量,延长左室舒张期。Ipt相同剂量对正常血压大鼠心功能参数却无明显影响。结论Ipt可抑制SHRsp大鼠心脏收缩和泵血功能,延长左室舒张期时间,但不影响正常血压大鼠心脏功能,提示Ipt对心功能的影响与血压状态密切相关。     

Myocardial catecholamine responsiveness of spontaneously hypertensive rats as influenced by swimming training

Summary Alterations of myocardial mechanical catecholamine responsiveness by swimming training (2×90 min/day, 4 weeks) were examined in 13-week-old spontaneously hypertensive male rats (SHR). The relationships between myocardial mechanical catecholamine responsiveness and ventricular -adrenoceptors as well as myosin isoenzyme pattern were also examined. Compared with sedentary controls, trained rats showed a greater responsiveness to isoproterenol (10^–6 mol/l) on isometric tension (T) and its first derivative (dT/dt) (T:0.45±0.55 vs. –0.15±0.11 10^–2 N/mm², p<0.01, dT/dt: 17.1±10.1 vs. 8.3±3.6 10^–2 N/mm²·s, p<0.05). In sedentary SHR, dT/dt_max increased significantly, whereas developed tension decreased slightly, coupled with a decrease of time to peak tension by high dose (10^–6 mol/l) isoproterenol. Therefore, it can be stated that dT/dt is a better indicator for catecholamine sensitivity than isometric tension. -adrenoceptor density ([³H]-dihydroalprenolol binding) decreased significantly in trained rats (68.7±7.62 vs. 102.4±4.37 fmol/mg protein, p<0.01) with no significant difference in K_D values (4.61±2.26 vs. 6.11±1.94 nM, ns). In addition, myosin isoenzyme pattern revealed by pyrophosphate gel electrophoresis shifted towards VM-1 after swimming training. The increased catecholamine sensitivity of fast contracting myocardium is, in principle, compatible with the assumption of cAMP-dependent regulation of myofibrillar ATPase activity (21) or cross bridge kinetics (9), although other postreceptor processes should also be taken into consideration for the increased catecholamine sensitivity.Supported by the Deutsche Forschungsgemeinschaft     

Erythrocytosis in spontaneously hypertensive rats

Spontaneously hypertensive rats (SH) with an increased number of red blood cells (RBC), microcytosis, and normal hemoglobin (Hb) concentration were used to study the effect of different manipulations of the erythron on erythropoietin production and on erythroid progenitor proliferation by bone marrow cells in order to gain insight regarding the regulation of erythropoiesis. The serum erythropoietin (Ep) level was increased in untreated SH rats. After stimulation by either bleeding, hemolysis, or acute hypoxia, both the erythropoietin level and erythroid colony-forming unit (CFU-E) proliferation by bone marrow cells increased in SH rats to levels that were similar to those of normotensive Wistar (W) rats. Exposure to chronic hypoxia induced an increase in Hb concentration in SH rats concomitantly with the increase in RBC. The results obtained in SH rats raise the possibility of a defect in nonEp stimulators of erythropoiesis that may alter Hb synthesis.     

Intestinal microvascular adaptation during maturation of spontaneously hypertensive rats

Adaptive microvascular changes in increased arterial pressure were investigated in the intestine of spontaneously hypertensive rats (SHR). In 4- to 5-week-old normal Wistar-Kyoto (WKY) and SHR ras, as well as in 18- to 21-week-old WKY rats, the number of arterioles of a given type per milligram of tissue were very similar. However, 18- to 21-week-old SHR had 30% to 35% fewer arterioles in the diameter range of 25--35 mu, as if intestinal vessels were lost or failed to grow during maturation. The largest and smallest arterioles in the intestine of adult SHR were constricted by 20% to 25%, but other vessels in the SHR had an equal or increased diameter relative to those in WKY rats. As a result of rarefaction and selective vasoconstriction in SHR, microvascular pressures in the intestinal muscle of SHR were near those in WKY rats, and those in villi of SHR were equal to those in WKY rats despite a 60% to 70% increase in mean arterial pressure in SHR. The percentage of small arterioles (less than 15 mu) that were intermittently closed to flow at rest was minimal, and the total number of small vessels per milligram of tissue was equal in WKY and SH rats. These data indicate that the adaptive changes in the intestinal vasculature of SHR do not include the loss of small arterioles as occurs in skeletal muscle but that the vascular branching pattern is disturbed, and the largest and smallest arterioles are constricted in the intestine of SHR.