Lack of effect of thyroid hormone on diabetic rat heart function and biochemistry

Cardiac functional abnormalities are frequently seen in diabetics and diabetes is also known to produce a state of mild hypothyroidism. To study the degree of involvement of diabetes-induced hypothyroidism on altered myocardial function, thyroid replacement therapy was carried out in streptozotocin-diabetic rats. Triiodothyronine (T3) treatment was initiated 3 days after the rats were made diabetic and was carried out for 6 weeks thereafter. Isolated perfused hearts from diabetic rats exhibited a depression in left ventricular developed pressure and positive and negative dP/dt at higher filling pressures as compared with controls. The depression could not be prevented by thyroid treatment. Calcium uptake activity in the cardiac sarcoplasmic reticulum (SR) was also depressed as a result of diabetes and this depression also was not prevented by thyroid treatment. Long chain acyl carnitine levels were found to be elevated in diabetic cardiac SR and could not be lowered by T3 treatment. The results indicate that the myocardial dysfunction observed in diabetic rats is due to factors other than the induced hypothyroidism.     

Effects of insulin perfusion and altered glucose concentrations on heart function in 3-day and 6-week diabetic rats

Diabetes is known to result in depression of myocardial function, whereas hearts from insulin-treated diabetic rats exhibit functional characteristics similar to controls. In the present study, we have studied the effect of insulin perfusion on cardiac performance of 3-day and 6-week streptozotocin (STZ) diabetic rats. Three days of diabetes did not result in depressed cardiac performance when the hearts were isolated and perfused in the working heart mode. Increasing the concentration of glucose from 5 to 10 mM in the perfusion fluid did not alter the function in either control or in diabetic rat hearts. However, when regular insulin or glucagon-free insulin (Humulin) (5 mU/mL) was included in the perfusion medium, the ventricular function of hearts from control rats was significantly enhanced, while diabetic myocardial function remained unaffected. When the study was repeated on hearts from 6-week diabetic animals, cardiac function of diabetic rats was significantly depressed as compared with controls. As in the 3-day study, contractility was not affected in either group by increasing glucose concentration in the perfusion medium. Again, inclusion of insulin in the medium enhanced cardiac contractility only in control hearts. These results suggest that diabetes results in a loss of myocardial sensitivity to insulin which seems to occur as early as 3 days after induction of diabetes with STZ. The study also demonstrates that the beneficial effects of in vivo insulin treatment on myocardial alterations induced by diabetes are not due to its direct myocardial effects.     

The effect of chronic alloxan- and streptozotocin-induced diabetes on isolated rat heart performance

Cardiac disease is a common secondary complication appearing in chronic diabetics. Isolated perfused working hearts obtained from both acute and chronic diabetic rats have also been shown to exhibit cardiac functional abnormalities when exposed to high work loads. We studied cardiac performance at various time points after induction of diabetes in rats to determine exactly when functional alterations appeared and whether these alterations progressed with the disease state. Female Wistar rats were made diabetic by a single i.v. injection of either alloxan (65 mg/kg) or streptozotocin (STZ 60 mg/kg). Cardiac performance was assessed at 7, 30, 100, 180, 240, and 360 days after induction of diabetes using the isolated perfused working heart technique. No changes were observed in the positive and negative dP/dt development at various atrial filling pressures in the diabetic hearts 7 days after treatment. Alloxan diabetic rat hearts exhibited depressed left ventricular pressure and positive and negative dP/dt development when perfused at high atrial filling pressures, at 30, 100, and 240 days after treatment. STZ diabetic rat hearts exhibited depressed cardiac performance at high atrial filling pressures, at 100, 180, and 360 days after treatment, but not at 30 days after treatment. Control hearts exhibited slight but significant depressions in cardiac function with age. These results suggest that cardiac functional alterations appear in diabetic rats about 30 days after induction and progress with the disease. These alterations may indicate the development of a cardiomyopathy.     

Nandrolone-pretreatment enhances cardiac beta(2)-adrenoceptor expression and reverses heart contractile down-regulation in the post-stress period of acute-stressed rats

To investigate whether nandrolone decanoate (ND)-pretreatment can modulate (1) beta-adrenoceptor expression and (2) myocardial contractility in response to beta-adrenoceptors stimulation with isoproterenol (ISO), in hearts of both normal and stressed rats. Rats were treated with 15 mg/(kgday) of Deca-Durabolin (ND, 1 ml i.m.) or with vehicle (oil) for 14 days. The day after the last injection, the dose-response to ISO (1 x 10(-8), 5 x 10(-8) and 10(-7)M), was studied in isolated rat hearts harvested from unstressed animals (unstressed+vehicle (control) or unstressed+ND) or from stressed animals (stressed+vehicle or stressed+ND): acute stress protocol consisted in restrain for 1h immediately before sacrifice. ND-pretreatment increased beta(2)-adrenoceptor expression. In baseline conditions all hearts had a similar left ventricular developed pressure (LVDP) and maximum rate of increase of LVDP (dP/dt(max)). In hearts of unstressed+vehicle or unstressed+ND, ISO caused a similar increase in LVDP (+90-100%) and dP/dt(max) (+120-150%). However, hearts of stressed+vehicle animals showed a marked depression of inotropic response to ISO (i.e. for ISO 1 x 10(-8),-55% in LVDP response versus unstressed). Yet, in hearts of stressed+ND-animals the effect of stress was reversed, showing the highest response to ISO (i.e. for ISO 1 x 10(-7), +30% LVDP response versus unstressed). The ND-induced beta(2)-adrenoceptor overexpression does not affect ISO-response in unstressed animals. However, acute stress induces a down-regulation of ISO-response, which is reversed by ND-pretreatment. Since the physiological post-stress down-regulation of adrenergic-response is absent after nandrolone treatment, the heart may be exposed to a sympathetic over-stimulation. This might represent a risk for cardiovascular incidents in anabolic steroid addicts under stressing conditions.     

Impaired in vivo myocardial reactivity to norepinephrine in diabetic rats

The effects of long-term diabetes with and without insulin treatment on in vivo myocardial contractile activity were studied under basal conditions and as a function of intravenously infused norepinephrine. Diabetes was induced by iv injection of streptozotocin (50 mg/kg). Insulin-treated diabetic rats received 5 units per day of isophane insulin suspension. The duration of the study was 8 weeks. In vivo myocardial contractility measurements were performed in ketamine-xylazine-anesthetized rats using a miniature catheter-tip pressure transducer advanced through the right carotid artery into the left ventricle. Peak positive dP/dt and intraventricular developed pressure were comparable among the groups when measured under basal conditions; however, the magnitude of the response to variable doses of norepinephrine (6 X 10(-12) to 6 X 10(-8) mole/kg body wt) were significantly diminished in diabetic rats, but the sensitivity was unchanged. Negative dP/dt was decreased under basal conditions and in response to norepinephrine in diabetic rats. Insulin treatment to diabetic rats prevented these changes, but heart rate was elevated. These results demonstrate that the in vivo cardiovascular reactivity of diabetic rats to norepinephrine is significantly attenuated.     

Defective sarcolemmal phospholipase C signaling in diabetic cardiomyopathy

Phospholipase C (PLC) activity is known to influence cardiac function. This study was undertaken to examine the status of PLC beta3 in the cardiac cell plasma membrane (sarcolemma, SL) in an experimental model of chronic diabetes. SL membrane was isolated from diabetic rat hearts at 8 weeks after a single i.v. injection of streptozotocin (65 mg/kg body weight). The total SL PLC was decreased in diabetes and was associated with a decrease in SL PLC beta3 activity, which immunofluorescence in frozen diabetic left ventricular tissue sections revealed to be due to a decrease in PLC beta3 protein abundance. In contrast, the SL abundance of Gqalpha was significantly increased during diabetes. These changes were associated with a loss of contractile function (+/- dP/dt). A 2-week insulin treatment of 6-week diabetic animals partially normalized all of these parameters. These findings suggest a defect in PLC beta3-mediated signaling processes may contribute to the cardiac dysfunction seen during diabetes.     

Cardiac dysfunction subsequent to chronic ozone exposure in rats

A number of advancements have been made toward identifying the risk factors associated with cardiovascular disease (CVD) and have resulted in a decline in mortality. However, many patients with cardiac disease show no established previous risk. Thus, it appears that other unknown factors contribute to the pathophysiology of CVD. Out of 350,000 sudden cardiac deaths each year in the United States, 60,000 deaths have been linked to air pollution, suggesting a detrimental role of environmental pollutants in the development of CVD. This study tested the hypothesis that chronic ozone (O(3)) exposure diminishes myocardial function in healthy population. Male Sprague-Dawley rats were exposed 8 h/day for 28 and 56 days to filtered air or 0.8 ppm O(3). In vivo cardiac function was assessed by measuring LVDP, +dP/dt, -dP/dt, and LVEDP 24 h after termination of the O(3) exposure. Compared to rats exposed to filtered air, LVDP, +dP/dt, and -dP/dt were significantly decreased, and LVEDP was significantly increased in O(3) exposed animals. This attenuation of cardiac function was associated with increased myocardial TNF-alpha levels and lipid peroxidation as well as decreased myocardial activities of superoxidase dismutase and interleukin-10 levels. These novel findings suggest myocardial dysfunction subsequent to chronic O(3) exposure in normal adult rats may be associated with a decrease in antioxidant reserve and with an increased production of inflammatory mediators.     

Prevention of diabetes-induced myocardial dysfunction in rats by methyl palmoxirate and triiodothyronine treatment

Diabetes results in myocardial functional alterations which are accompanied by a depression of biochemical parameters such as myosin ATPase and calcium uptake in the sarcoplasmic reticulum. Methyl palmoxirate, a fatty acid analog, is reported to decrease circulating glucose levels by inhibiting fatty acid metabolism, thus forcing carbohydrate utilization. In the present study, we attempted to prevent streptozotocin diabetes-induced myocardial alterations in the rat. Using the isolated working heart preparation, we observed a depression of myocardial function in rats 6 weeks after the induction of diabetes, which was characterized by the inability of these hearts to develop left ventricular pressures and rates of ventricular contraction and relaxation as well as control hearts at higher left atrial filling pressures. Methyl palmoxirate treatment (25 mg kg-1 day-1 po daily) was unable to control diabetes-induced changes in plasma glucose, triglycerides, insulin, and total lipids. Also, the functional depression seen in diabetic rat hearts was present despite the treatment. However, depression of calcium uptake and elevation of long chain acyl carnitines seen in sarcoplasmic reticulum (SR) prepared from diabetic rat hearts could be prevented by the treatment. As triiodothyronine (T3) treatment has been shown to normalize depression of cardiac myosin ATPase in diabetic rats, we repeated the study using a combination of T3 (30 micrograms kg-1 day-1 sc daily) and methyl palmoxirate. While diabetic rats treated with T3 alone did not show significant improvement of myocardial function when compared with untreated diabetics, the function of those treated with both T3 and methyl palmoxirate was not significantly different from that in control rat hearts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Isolated hearts treated with skeletal muscle homogenates exhibit altered function

Skeletal muscle fiber damage and necrosis can result in the release of intracellular molecules into the extracellular environment. These molecules, termed damage-associated molecular patterns (DAMPs), can act as signals capable of initiating immune and/or inflammatory responses through interactions with pattern recognition receptors. To investigate whether skeletal muscle DAMPs interact with the heart and alter cardiac function, isolated rat hearts were perfused for 75 min with buffer containing 1 μg/ml of either soleus (slow), white gastrocnemius (WG, fast), or heat-stressed white gastrocnemius (HSWG) skeletal muscle homogenates. Left ventricular developed pressure (LVDP) and rates of pressure increase/decrease (±dP/dt) were measured using the Langendorff technique. Compared to controls, no changes in LVDP or +dP/dt were observed over the 75-min perfusion when homogenates from the WG muscles were added. In contrast, at 30 min and thereafter, a decreased LVDP and +dP/dt was observed in the hearts treated with soleus muscle homogenates. The hearts treated with HSWG homogenates also showed a decrease in LVDP from 45 min until the end of perfusion. These results suggest that molecules present in slow muscle and heat-stressed muscle are capable of altering cardiac function. Thus, muscle fiber type and/or heat shock protein content of skeletal muscles may be factors that influence cardiac function following skeletal muscle damage.     

Acute insulin withdrawal contributes to ischemic heart failure in spontaneously diabetic BB Wistar rats

The contribution of poor metabolic control to myocardial ischemic failure was determined in isolated working hearts from insulin-dependent BB Wistar rats. Removal of insulin treatment 24 h prior to study (uncontrolled diabetic rats) resulted in significant increases in serum glucose, serum fatty acids, and myocardial triglyceride, compared with animals in which insulin treatment was not withheld (insulin-treated diabetic rats). Isolated working hearts obtained from these two groups were subjected to a 40% reduction in coronary flow in the presence of a maintained metabolic demand (hearts were paced at 200 beats/min and perfused at an 80 mmHg (1 mmHg = 133.3 Pa) left aortic afterload, 11.5 mmHg left atrial preload). Within 15 min of ischemia, a significant deterioration of mechanical function occurred in the uncontrolled diabetic rats, whereas function was maintained in the insulin-treated diabetic rats. Oxygen consumption by the two groups of hearts was similar prior to the onset of ischemia and decreased during ischemia in parallel with the work performed by the hearts. This suggests that the accelerated failure rate in uncontrolled diabetic rat hearts is unlikely a result of an increased oxygen requirement. These data are a direct demonstration that acute changes in metabolic control of the diabetic can contribute to the severity of myocardial ischemic injury.     

Short-term exercise improves myocardial tolerance to in vivo ischemia-reperfusion in the rat.

These experiments examined the independent effects of short-term exercise and heat stress on myocardial responses during in vivo ischemia-reperfusion (I/R). Female Sprague-Dawley rats (4 mo old) were randomly assigned to one of four experimental groups: 1) control, 2) 3 consecutive days of treadmill exercise [60 min/day at 60-70% maximal O2 uptake (VO2 max)], 3) 5 consecutive days of treadmill exercise (60 min/day at 60-70% VO2 max), and 4) whole body heat stress (15 min at 42 degrees C). Twenty-four hours after heat stress or exercise, animals were anesthetized and mechanically ventilated, and the chest was opened by thoracotomy. Coronary occlusion was maintained for 30-min followed by a 30-min period of reperfusion. Compared with control, both heat-stressed animals and exercised animals (3 and 5 days) maintained higher (P < 0.05) left ventricular developed pressure (LVDP), maximum rate of left ventricular pressure development (+dP/dt), and maximum rate of left ventricular pressure decline (-dP/dt) at all measurement periods during both ischemia and reperfusion. No differences existed between heat-stressed and exercise groups in LVDP, +dP/dt, and -dP/dt at any time during ischemia or reperfusion. Both heat stress and exercise resulted in an increase (P < 0.05) in the relative levels of left ventricular heat shock protein 72 (HSP72). Furthermore, exercise (3 and 5 days) increased (P < 0.05) myocardial glutathione levels and manganese superoxide dismutase activity. These data indicate that 3-5 consecutive days of exercise improves myocardial contractile performance during in vivo I/R and that this exercise-induced myocardial protection is associated with an increase in both myocardial HSP72 and cardiac antioxidant defenses.     

Effects of exercise training combined with insulin treatment on cardiac NOS1 signaling pathways in type 1 diabetic rats

This study examined the effects of a dual treatment combining insulin treatment and exercise training on basal cardiac function and signaling pathways involving β3-AR, NOS1, and RyR2 in type 1 diabetic rats. Male Wistar rats were assigned into a diabetic group receiving no treatment (D), an insulin-treated diabetic (Ins), a trained diabetic (TD), and a trained insulin-treated diabetic (TIns) group. Control group (C) was included in order to confirm the deleterious effects of diabetes. Insulin treatment and/or treadmill exercise training were conducted for 8 weeks. Basal cardiac function was evaluated by Langendorff technique. Cardiac protein expression of β3-AR, NOS1, and RyR2 was assessed using Western blots. Diabetes induced a decrease of both basal diastolic and systolic (±dP/dt) cardiac function (P < 0.05). Moreover, diabetes was associated with an increase of β3-AR and NOS1 and a decrease of RyR2 expression (P < 0.05). Although combined treatment was not able to normalize -dP/dt, it succeeded to normalize +dP/dt of diabetic rats. Combined treatment led to an overexpression of RyR2. Effects of this combined treatment on +dP/dt and RyR2 were greater than the effects of insulin and exercise training, applied solely. Treatments, applied solely or in combination, resulted in a complete normalization of β3-AR and in a down-regulation of NOS1 because this protein expression in all treated diabetic rats became lower than control values (P < 0.01). Our study shows that unlike single treatments, dual treatment combining insulin treatment and exercise training was able to normalize basal systolic function of diabetic rats by a specific regulation of β3-AR-NOS1-RyR2 signaling pathways.     

Substrate-dependent functional defects and altered mitochondrial respiratory capacity in hearts from guinea pigs with iron deficiency anemia

Iron deficiency anemia was induced by dietary means in weanling guinea pigs. A 25% higher ventricular wall mass per 100 g body mass was seen after 6 weeks of feeding. Myocardial performance was determined in isolated perfused hearts using an isovolumic Langendorff preparation. All hearts exhibited a 25% decrease in left ventricular developed pressure (LVDP) and decreased dP/dt when substrate was switched from 10 mM pyruvate to 16.6 mM glucose. The glucose reduction in LVDP resulted from decreased systolic pressure, which completely reversed when hearts again metabolized pyruvate. With glucose as substrate, left ventricular developed pressure-end diastolic volume relationships were indistinguishable. However, with pyruvate, iron-deficient hearts appeared to be less responsive to the increased energy demands required by elevated diastolic volumes. Rates of state 3 respiration were 18% below control with glutamate + malate as substrate, and 38% lower with pyruvate + malate in mitochondria isolated from anemic animals. No differences in respiration were noted with succinate. Cytochrome a + a3 content, cytochrome oxidase activity and total mitochondrial protein content appeared to be unchanged. In contrast, cytochromes b, c + c1, and the flavoproteins were significantly decreased. The data suggest that iron deficiency anemia induces cardiac hypertrophy with a fixed but defective mitochondrial population, potentially placing the heart in an energetic imbalance. These differences in mitochondrial function were expressed by decreased myocardial performance when the heart metabolizes pyruvate, an exclusively aerobic substrate.     

胰岛素保护缺血/再灌注心脏:PI3-K/Akt和JNKs信号通路间的交互作用

我们前期研究表明胰岛素可激活细胞内信号转导机制如磷脂酰肌醇3．激酶．蛋白激酶B．内皮型一氧化氮合酶．一氧化氮（P13-K-Akt-eNOS-NO）信号通路,减轻心肌缺血／再灌注（ischemia／reperfusion,I／R）损伤,改善缺血后心肌功能恢复。然而c-Jun氨基末端激酶（c-JunNH2-terminal kinase,JNK）信号通路在胰岛素保护I／R心肌中的作用尚不清楚,本研究旨在探讨JNK信号通路在胰岛素保护I／R心肌中的作用及其与P13．K／Akt信号通路间的相互关系。离体Sprague-Dawley大鼠心脏缺血30min后施行2h或4h的再灌注,缺血前用LY294002（15mmol／L）和SP600125（10mmol／L）灌注15min,分别阻断P13．K／Akt和磷酸化JNK（phosphorylated．JNK,p-JNK）活化,观测心脏功能、心肌梗死、细胞凋亡和蛋白磷酸化水平。与对照组相比,胰岛素再灌注2h后,心率、左心室发展压和左心室收缩／舒张最大速率均明显增加,梗死面积减少约16．1％[（28．9±2．0）％vs（45．0±4．0）％,n=6,P〈O．01],细胞凋亡指数从（27．6±113）％减少到（16．0±0．7）％（n=6,P〈O．01）,Akt的活性增加1．7倍（n=6,P〈0．05）,同时JNK活性增加1．5倍铆=6,P〈O．05）。用LY294002处理后,胰岛素对I／R心肌的保护作用消失;而用SP600125处理可增强胰岛素的保护作用,且可部分逆转LY294002的抑制作用。进一步观察发现SP600125减弱了Akt的磷酸化m=6,P〈0．05）。上述结果表明,在I／R心肌中,胰岛素可同时激活P13．K／Akt及JNK信号通路,且通过后者进一步增加Akt活化,从而减轻I／R损伤,改善心肌功能。这种P13．K／Akt与JNK信号通路交互机制对胰岛素保护I／R心肌有重要意义。     

17beta-estradiol attenuates cardiac dysfunction and decreases NF-kappaB binding activity in mechanically stretched rat hearts

This study was to examine the effect of estrogen on mechanical stretching-induced cardiac dysfunction in an isolated heart model. The isolated rat hearts were perfused via the Langendorff system and exposed to left ventricular stretching. One group hearts (n=6) were perfused with 17beta-estradiol (100nM) and the other group hearts (n=6) were perfused with estrogen plus its receptor antagonist ICI182,780 (1microM) before myocardial stretching was performed. Control hearts (n=6) were perfused with perfusion buffer. Cardiac functions were recorded. At the end of perfusion, the hearts were harvested and the levels of tumor necrosis factor-alpha (TNF-alpha), phospho-p38 mitogen-activated protein kinase (MAPK) and nuclear factor-kappaB (NF-kappaB) binding activity were examined. Acute ventricular stretching resulted in significantly decrease in left ventricular developed pressure (LVDP) by 42.7%, maximal positive and negative values of the first derivative of pressure (+dP/dt and -dP/dt) by 43.2%, and 43.5%, respectively. The levels of TNF-alpha, phospho-p38 MAPK and NF-kappaB DNA binding activity were significantly increased following myocardial stretching. In 17beta-estradiol treated hearts, the myocardial functions were significantly improved. The levels of TNF-alpha, phospho-p38 MAPK, and NF-kappaB binding activity in myocardium were also significantly reduced by 35.7%, 56.9%, and 50%, respectively, compared with untreated stretched hearts. The beneficial effects of 17beta-estradiol on the stretched hearts were abolished by ICI182,780. The results suggest that pharmacological dose of 17beta-estradiol will attenuate stretching-induced cardiac dysfunction in an isolated heart model. The mechanisms could involve in blunting p38 MAPK and NF-kappaB signaling.     

Sex differences in the myocardial inflammatory response to ischemia-reperfusion injury

The myocardium generates inflammatory mediators during ischemia-reperfusion (I/R), and these mediators contribute to cardiac functional depression and apoptosis. The great majority of these data have been derived from male animals and humans. Sex has a profound effect over many inflammatory responses; however, it is unknown whether sex affects the cardiac inflammatory response to acute myocardial I/R. We hypothesized the existence of inherent sex differences in myocardial function, expression of inflammatory cytokines, and activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway after I/R. Isolated rat hearts from age-matched adult males and females were perfused (Langendorff), and myocardial contractile function was continuously recorded. After I/R, myocardium was assessed for expression of TNF-alpha, IL-1beta, and IL-6 (RT-PCR, ELISA); IL-1alpha and IL-10 mRNA (RT-PCR); and activation of p38 MAPK (Western blot). All indexes of postischemic myocardial function [left ventricular developed pressure, left ventricular end-diastolic pressure, and maximal positive (+dP/dt) and negative (-dP/dt) values of the first derivative of pressure] were significantly improved in females compared with males. Compared with males, females had decreased myocardial TNF-alpha, IL-1beta, and IL-6 (mRNA, protein) and decreased activation of p38 MAPK pathway. These data demonstrate that hearts from age-matched adult females are relatively protected against I/R injury, possibly due to a diminished inflammatory response.     

Ketamine-induced cardiac depression is associated with increase in [Mg2+]i and activation of p38 MAP kinase and ERK 1/2 in guinea pig

This study investigated the signaling pathways responsible for ketamine-induced cardiac depression in guinea pigs. The left ventricular development pressure (LVDP), velocity of the change in pressure (dP/dt), and heart rate (HR) accompanied with the total magnesium efflux ([Mg]e) were measured simultaneously in perfused hearts. The level of activation of the extracellular signal-regulated kinases 1/2 (ERK 1/2) and p38 mitogen-activated protein (MAP) kinase. The intracellular ionized magnesium concentration ([Mg2+]i) was measured using Mag-fura 2 AM in a single cardiomyocyte. Ketamine produced reversible decreases in the LVDP, dP/dt, and HR accompanied by increases in the [Mg]e. Ketamine also produced significant activation of p38 MAP kinase and ERK 1/2, and produced a dose-dependent increase in the [Mg2+]i, which was inhibited SB203580 and PD98059. These results suggest that ketamine-induced cardiac depression can be partly responsible for the increase in [Mg2+]i and [Mg]e, accompanied by the activation of p38 MAP kinase and ERK 1/2 in guinea pigs.     

Effects of insulin resistance on geranylgeranylacetone-induced expression of heat shock protein 72 and cardioprotection in high-fat diet rats

We investigated the effects of insulin resistance on the expression of heat-shock proteins (HSPs) and myocardial protection against ischemia/reperfusion injury. Male Sprague-Dawley rats received normal chow (CNT) or high-fat (HiF) diet. HiF diet for 6 weeks resulted in the development of insulin resistance, which was evaluated by oral glucose test and insulin tolerance test. Twenty-four hour after oral administration of geranylgeranylacetone (GGA) (200 mg/kg), the heart was isolated and perfused retrogradely with two different doses of insulin (0.1 or 1 mU/ml). Myocardial expression of HSP72 was examined using Western blot analysis. In the HiF group, the expression of HSP72 in response to GGA was decreased. The recovery of left ventricular developed pressure (LVDP) 30 min after reperfusion was tended to be lower in HiF group than in CNT group. Although GGA improved the recovery of LVDP in both CNT and HiF rats, LVDP during reperfusion period was significantly lower in HiF group than in CNT group. High-dose insulin perfusion caused deterioration of post-ischemic functional recovery and LVDP was not different between the two groups, but GGA-induced cardioprotection was preserved irrespective of the dose of insulin both in the CNT and HiF rats. This is the first demonstration that expression of HSP72 was depressed in the heart and that reduced HSP72 was related with less cardioprotection against ischemic insult in high-fat diet-induced insulin resistance rats.     

N-oleoyldopamine, a novel endogenous capsaicin-like lipid, protects the heart against ischemia-reperfusion injury via activation of TRPV1

N-oleoyldopamine (OLDA), a bioactive lipid originally found in the mammalian brain, is an endovanilloid that selectively activates the transient receptor potential vanilloid type 1 (TRPV1) channel. This study tests the hypothesis that OLDA protects the heart against ischemia and reperfusion (I/R) injury via activation of the TRPV1 in wild-type (WT) but not in gene-targeted TRPV1-null mutant (TRPV1(-/-)) mice. Hearts of WT or TRPV1(-/-) mice were Langendorffly perfused with OLDA (2 x 10(-9) M) in the presence or absence of CGRP8-37 (1 x 10(-6) M), a selective calcitonin gene-related peptide (CGRP) receptor antagonist; RP-67580 (1 x 10(-6) M), a selective neurokinin-1 receptor antagonist; chelerythrine (5 x 10(-6) M), a selective protein kinase C (PKC) antagonist; or tetrabutylammonium (TBA, 5 x 10(-4) M), a nonselective K(+) channel antagonist, followed by 35 min of global ischemia and 40 min of reperfusion (I/R). Left ventricular end-diastolic pressure (LVEDP), left ventricular developed pressure (LVDP), coronary flow (CF), and left ventricular peak positive dP/dt (+dP/dt) were evaluated after I/R. OLDA improved recovery of cardiac function after I/R in WT but not TRPV1(-/-) hearts by increasing LVDP, CF, and +dP/dt and by decreasing LVEDP. CGRP8-37, RP-67580, chelerythrine, or TBA abolished the protective effect of OLDA in WT hearts. Radioimmunoassay showed that the release of substance P (SP) and CGRP after OLDA treatment was higher in WT than in TRPV1(-/-) hearts, which was blocked by chelerythrine or TBA. Thus OLDA exerts a cardiac protective effect during I/R injury in WT hearts via CGRP and SP release, which is abolished by PKC or K(+) channel antagonists. The protective effect of OLDA is void in TRPV1(-/-) hearts, supporting the notion that TRPV1 mediates OLDA-induced protection against cardiac I/R injury.     

C-peptide exerts cardioprotective effects in myocardial ischemia-reperfusion

Ischemia followed by reperfusion in the presence of polymorphonuclear leukocytes (PMNs) results in cardiac dysfunction. C-peptide, a cleavage product of proinsulin to insulin processing, induces nitric oxide (NO)-mediated vasodilation. NO is reported to attenuate cardiac dysfunction caused by PMNs after ischemia-reperfusion (I/R). Therefore, we hypothesized that C-peptide could attenuate PMN-induced cardiac dysfunction. We examined the effects of C-peptide in isolated ischemic (20 min) and reperfused (45 min) rat hearts perfused with PMNs. C-peptide (70 nmol/kg iv) given 4 or 24 h before I/R significantly improved coronary flow (P < 0.05), left ventricular developed pressure (LVDP) (P < 0.01), and the maximal rate of development of LVDP (+dP/dt(max)) compared with I/R hearts obtained from rats given 0.9% NaCl (P < 0.01). N(G)-nitro-L-arginine methyl ester (L-NAME) (50 micromol/l) blocked these cardioprotective effects. In addition, C-peptide significantly reduced cardiac PMN infiltration from 183 +/- 24 PMNs/mm(2) in untreated hearts to 44 +/- 10 and 58 +/- 25 PMNs/mm(2) in hearts from 4- and 24-h C-peptide-treated rats, respectively. Rat PMN adherence to rat superior mesenteric artery exposed to 2 U/ml thrombin was significantly reduced in rats given C-peptide compared with rats given 0.9% NaCl (P < 0.001). Moreover, C-peptide enhanced basal NO release from rat aortic segments. These results provide evidence that C-peptide can significantly attenuate PMN-induced cardiac contractile dysfunction in the isolated perfused rat heart subjected to I/R at least in part via enhanced NO release.