Changes in cardiovascular β-adrenoceptor responses during hypothermia

The purpose of this study was to determine cardiovascular β-adrenergic responses during hypothermia. In the present study, we used isoproterenol (Iso), a nonselective, potent β-adrenoceptor agonist, well known for its positive chronotropic and inotropic pharmacologic actions at normothermia. Rats were instrumented to measure mean arterial pressure (MAP) and left ventricular (LV) pressure–volume changes using a Millar pressure–volume conductance catheter. Core temperature was manipulated from 37 (normothermia) to 24 °C (hypothermia) and back to 37 °C (rewarming) using both internal and external heat exchangers. During cooling at each temperature (33, 30, 27, and 24 °C), central hemodynamic variables and MAP were measured while intravenously infusing Iso (doses of 1.7, 5, 10, and 20 ng/min). Seven animals underwent all phases of the protocol. At normothermia Iso infusion resulted in a significant, dose-dependent increase in heart rate (HR), stroke volume (SV), cardiac output (CO), LV dP/dt_max (left ventricular maximum derivative of systolic pressure over time) but no change in MAP. During cooling Iso infusion caused no dose-dependent change in any of the hemodynamic variables. After rewarming, baseline HR and LV dP/dt_max were increased, whereas SV was significantly reduced when compared with their pre-hypothermic baseline values. This study shows that physiological cardiovascular responses mediated by the β-adrenoceptor are significantly diminished during core hypothermia.     

Cardiovascular effects of levosimendan during rewarming from hypothermia in rat

BackgroundPrevious research aimed at ameliorating hypothermia-induced cardiac dysfunction has shown that inotropic drugs, that stimulate the cAMP, – PKA pathway via the sarcolemmal β-receptor, have a decreased inotropic effect during hypothermia. We therefore wanted to test whether levosimendan, a calcium sensitizer and dose-dependent phosphodiesterase 3 (PDE3) inhibitor, is able to elevate stroke volume during rewarming from experimental hypothermia.MethodsA rat model designed for circulatory studies during experimental hypothermia (4 h at 15 °C) and rewarming was used. The following three groups were included: (1) A normothermic group receiving levosimendan, (2) a hypothermic group receiving levosimendan the last hour of stable hypothermia and during rewarming, and (3) a hypothermic placebo control group. Hemodynamic variables were monitored using a Millar conductance catheter in the left ventricle (LV), and a pressure transducer connected to the left femoral artery. In order to investigate the level of PKA stimulation by PDE3 inhibition, myocardial Ser23/24-cTnI phosphorylation was measured using Western-blot.ResultsAfter rewarming, stroke volume (SV), cardiac output (CO) and preload recruitable stroke work (PRSW) were restored to within pre-hypothermic values in the levosimendan-treated animals. Compared to the placebo group after rewarming, SV, CO, PRSW, as well as levels of Ser23/24-cTnI phosphorylation, were significantly higher in the levosimendan-treated animals.ConclusionThe present data shows that levosimendan ameliorates hypothermia-induced systolic dysfunction by elevating SV during rewarming from 15 °C. Inotropic treatment during rewarming from hypothermia in the present rat model is therefore better achieved through calcium sensitizing and PDE3 inhibition, than β-receptor stimulation.     

Loss of heart phospholipid arachidonic acid without phospholipid peroxidation in anaesthetized rats rewarmed after prolonged deep hypothermia

Hypothermia–rewarming of the heart results in contractile dysfunction under in vitro as well as in vivo conditions. Increase in reactive oxygen species (ROS), lipid peroxidation and calcium overload are proposed mechanisms. In the first protocol of this study, the effect of putative phospholipase and calcium channel modulator mepacrine during deep hypothermia (4 h 14 °C) plus rewarming was tested in an isolated perfused rat heart model previously reported not to involve increase in lipid peroxides. Contractile function was measured under isovolumetric conditions using an intra-ventricular balloon connected to a transducer and recording system. Mepacrine completely reversed hypothermia–rewarming induced contractile failure in this model (LV dP/dt_max: 3236 ± 517 vs. 1058 ± 185 mm Hg/s in untreated hearts). In the second part of the study, lipid peroxidation of the heart was examined in vivo in anesthetized rats subjected to 4 h of deep hypothermia followed by rewarming. In this model recovery of heart function judged by cardiac output is decreased whereas blood pressure and heart rate recover fully. Peroxy conjugated diene isomers of unsaturated fatty acids were measured in heart phospholipids. The composition of the non-esterified fatty acids and the phospholipid fatty acid pool was examined in order to reveal signs of membrane remodeling. The results demonstrated no significant changes in phospholipid peroxidation after rewarming (91.07 ± 5.23 vs. 88.63 ± 7.73 nmol/g dry wt. in control). There was significant relative reduction in the content of arachidonic acid in the phospholipid fraction (29.55 ± 1.65 vs. 24.76 ± 1.48%). There was marked decrease in non-esterified fatty acids in myocardial tissue (1992 ± 291 vs. 1069 ± 189 nmol/g dry wt.), but a significant relative increase in arachidonic acid (20:4) in this fraction (3.46 ± 0.42 vs. 4.99 ± 0.30%). In conclusion, rewarming from deep hypothermia is not associated with increased phospholipid peroxidation. There is, however, a significant remodeling of the phospholipid fraction of myocardial lipids in vivo probably as a result of receptor or calcium stimulated phospholipase activity. Calcium or calcium stimulated phospholipase activity could contribute to posthypothermic contractile dysfunction.     

Effects of moderate hypothermia on in situ cardiac sympathetic nerve endings

Although hypothermia is known to alter neuronal control of circulation, it has been uncertain whether clinically used hypothermia (moderate hypothermia) affects in situ cardiac sympathetic nerve endings. We examined the effects of moderate hypothermia on cardiac sympathetic nerve ending function in anesthetized cats. By use of a cardiac dialysis technique, we implanted dialysis probes in the midwall of the left ventricle and monitored dialysate norepinephrine (NE) levels as an index of NE output from cardiac sympathetic nerve endings. Hypothermia (27.0+/-0.5 degrees C) induced decreases in dialysate NE levels. Dialysate NE levels did not return to the control level at normothermia after rewarming. Dialysate NE response to inferior vena cava occlusion was attenuated at hypothermia but restored at normothermia after rewarming. Dialysate NE response to high K(+) (100 mM) was attenuated at hypothermia and was not restored at normothermia after rewarming. Hypothermia induced increases in dialysate dihydroxyphenylglycol (DHPG) levels. There were no differences in desipramine (neuronal NE uptake blocker, 10 microM) induced increment in dialysate NE level among control, hypothermia, and normothermia after rewarming. However, hypothermia induced an increase in DHPG/NE ratio. These data suggest that hypothermia impairs vesicle NE mobilization rather than membrane NE uptake. We conclude that moderate hypothermia suppresses exocytotic NE release via central mediated reflex and regional depolarization.     

Myocardial mechanical dysfunction and calcium overload following rewarming from experimental hypothermia in vivo

Rewarming patients from accidental hypothermia are regularly complicated with cardiovascular instability ranging from minor depression of cardiac output to fatal circulatory collapse also termed “rewarming shock”. Since altered Ca²⁺ handling may play a role in hypothermia-induced heart failure, we studied changes in Ca²⁺ homeostasis in in situ hearts following hypothermia and rewarming. A rat model designed for studies of the intact heart in a non-arrested state during hypothermia and rewarming was used. Rats were core cooled to 15 °C, maintained at 15 °C for 4 h and thereafter rewarmed. As time-matched controls, one group of animals was kept at 37 °C for 5 h. Total intracellular myocardial Ca²⁺ content ([Ca²⁺]_i) was measured using ⁴⁵Ca²⁺. Following rewarming we found a significant reduction of stroke volume and cardiac output compared to prehypothermic control values as well as to time-matched controls. Likewise, we found that hypothermia and rewarming resulted in a more than six-fold increase in [Ca²⁺]_i to 3.01 ± 0.43 μmol/g dry weight compared to 0.44 ± 0.05 μmol/g dry weight in normothemia control. These findings indicate that hypothermia-induced alterations in the Ca²⁺-handling result in Ca²⁺ overload during hypothermia, which may contribute to myocardial failure during and after rewarming.     

Alarin alleviated cardiac fibrosis via attenuating oxidative stress in heart failure rats

The present study was to explore whether alarin could alleviate heart failure (HF) and attenuate cardia fibrosis via inhibiting oxidative stress. The fibrosis of cardiac fibroblasts (CFs) was induced by angiotensin (Ang) II. HF models were induced by ligation of the left anterior descending artery to cause ischemia myocardial infarction (MI) in Sprague–Dawley rats. Alarin (1.0 nM/kg/d) was administrated by intraperitoneal injection for 28 days. The decreases of left ventricular (LV) ejection fraction (EF), fractional shortening (FS), the maximum of the first differentiation of LV pressure (LV ± dp/dt_max) and LV systolic pressure (LVSP), and the increases of LV volume in systole (LVVS), LV volume in diastole (LVVD), LV end-systolic diameter (LVESD) and LV end-diastolic diameter (LVEDD) in MI rats were improved by alarin treatment. The increases in the expression levels of collagen I, collagen III, and transforming growth factor (TGF)-β were inhibited by alarin treatment in CFs and in the hearts of MI rats. The levels of NADPH oxidase (Nox) activity, superoxide anions and malondialdehyde (MDA) levels were increased, and the level of superoxide dismutase (SOD) activity was reduced in Ang II-treated CFs, which were reversed by alarin. Nox1 overexpression reversed the effects of alarin on attenuating the increases of collagen I, collagen III and TGF-β expression levels induced by Ang II in CFs. These results indicated that alarin improved HF and cardiac fibrosis via inhibiting oxidative stress in HF rats. Nox1 played important roles in the regulation of alarin effects on attenuating CFs fibrosis induced by Ang II.

     

Effects of anesthetics on systemic hemodynamics in mice

The aim of this study was to compare the systemic hemodynamic effects of four commonly used anesthetic regimens in mice that were chronically instrumented for direct and continuous measurements of cardiac output (CO). Mice (CD-1, Swiss, and C57BL6 strains) were instrumented with a transit-time flow probe placed around the ascending aorta for CO measurement. An arterial catheter was inserted into the aorta 4 or 5 days later for blood pressure measurements. After full recovery, hemodynamic parameters including stroke volume, heart rate, CO, mean arterial pressure (MAP), and total peripheral resistance were measured with animals in the conscious state. General anesthesia was then induced in these mice using isoflurane (Iso), urethane, pentobarbital sodium, or ketamine-xylazine (K-X). The doses and routes of administration of these agents were given as required for general surgical procedures in these animals. Compared with the values obtained for animals in the conscious resting state, MAP and CO decreased during all anesthetic interventions, and hemodynamic effects were smallest for Iso (MAP, -24 +/- 3%; CO, -5 +/- 7%; n = 15 mice) and greatest for K-X (MAP, -51 +/- 6%; CO, -37 +/- 9%; n = 8 mice), respectively. The hemodynamic effects of K-X were fully antagonized by administration of the alpha(2)-receptor antagonist atipamezole (n = 8 mice). These results indicate that the anesthetic Iso has fewer systemic hemodynamic effects in mice than the nonvolatile anesthetics.     

Mild hypothermia protects against postischemic hepatic endothelial injury and decreases the formation of reactive oxygen species

Abstract

The ability of mild hypothermia (MH; 34°C) to protect against postischemic endothelial injury and decrease reactive oxygen species' (ROS) formation was studied using lucigenin and luminol enhanced chemiluminescence (CL). Lucigenin CL is largely specific for superoxide, while luminol reacts with many ROS.

Isolated rat livers perfused under constant flow in a non-recirculating system were exposed to 2.5 h of ischemia after 0.5 h perfusion with Krebs-Henseleit buffer at either normothermia (38°C) or mild hypothermia (34°C) (n = 5, all groups). CL (cps), vascular resistance (Woods units), O₂ consumption, and potassium efflux were measured at the end of perfusion, and at 0 min reperfusion, and every 30 min during reperfusion.

For both the lucigenin and luminol groups, CL and vascular resistance increased significantly (repeat measures ANOVA, P <0.05) for normothermia (NT, 38°C) but not mild hypothermia. Potassium efflux did not change significantly for the mild hypothermia groups. In the luminol enhanced group, oxygen consumption was greater in the mildly hypothermic group at 1 h and 1.5 h of reperfusion.

Mild hypothermia decreased postischemic ROS production. Increased vascular resistance in the normothermia group may indicate an endothelial injury. Mild hypothermia appears to protect against this injury.     

Left ventricular dysfunction following rewarming from experimental hypothermia

This study was aimed at elucidating whetherventricular hypothermia-induced dysfunction persisting after rewarmingthe unsupported in situ dog heart could be characterized as a systolic,diastolic, or combined disturbance. Core temperature of 8 mongrel dogswas gradually lowered to 25°C and returned to 37°C over aperiod of 328 min. Systolic function was described by maximum rate ofincrease in left ventricular (LV) pressure(dP/dt_max),relative segment shortening (SS%), stroke volume (SV), and theload-independent contractility index, preload recruitable stroke work(PRSW). Diastolic function was described by the isovolumic relaxationconstant () and the LV wall stiffness constant(K_p). Comparedwith prehypothermic control, a significant decrease in LV functionalvariables was measured at 25°C:dP/dt_max 2,180 ± 158 vs. 760 ± 78 mmHg/s, SS% 20.1 ± 1.2 vs.13.3 ± 1.0%, SV 11.7 ± 0.7 vs. 8.5 ± 0.7 ml, PRSW 90.5 ± 7.7 vs. 29.1 ± 5.9 J/m · 10²,K_p 0.78 ± 0.10 vs. 0.28 ± 0.03 mm¹, and  78.5 ± 3.7 vs. 25.8 ± 1.6 ms. After rewarming, the significant depression ofLV systolic variables observed at 25°C persisted: dP/dt_max 1,241 ± 108 mmHg/s, SS% 10.2 ± 0.8 J, SV 7.3 ± 0.4 ml, and PRSW52.1 ± 3.6 m · 10², whereasthe diastolic values ofK_p and  returned to control. Thus hypothermia induced a significant depressionof both systolic and diastolic LV variables. After rewarming, diastolicLV function was restored, in contrast to the persistently depressed LVsystolic function. These observations indicate that cooling inducesmore long-lasting effects on the excitation-contraction coupling and the actin-myosin interaction than on sarcoplasmicreticulum Ca²⁺trapping dysfunction or interstitial fluid content, makingposthypothermic LV dysfunction a systolic perturbation.

     

Cardiovascular effects of epinephrine during rewarming from hypothermia in an intact animal model.

Rewarming from accidental hypothermia is often complicated by "rewarming shock," characterized by low cardiac output (CO) and a sudden fall in peripheral arterial pressure. In this study, we tested whether epinephrine (Epi) is able to prevent rewarming shock when given intravenously during rewarming from experimental hypothermia in doses tested to elevate CO and induce vasodilation, or lack of vasodilation, during normothermia. A rat model designed for circulatory studies during experimental hypothermia and rewarming was used. A total of six groups of animals were used: normothermic groups 1, 2, and 3 for dose-finding studies, and hypothermic groups 4, 5, and 6. At 20 and 24 degrees C during rewarming, group 4 (low-dose Epi) and group 5 (high-dose Epi) received bolus injections of 0.1 and 1.0 microg Epi, respectively. At 28 degrees C, Epi infusion was started in groups 4 and 5 with 0.125 and 1.25 microg/min, respectively. Group 6 served as saline control. After rewarming, both CO and stroke volume were restored in group 4, in contrast to groups 5 and 6, in which both CO and stroke volume remained significantly reduced (30%). Total peripheral resistance was significantly higher in group 5 during rewarming from 24 to 34 degrees C, compared with groups 4 and 6. This study shows that, in contrast to normothermic conditions, Epi infused during hypothermia induces vasoconstriction rather than vasodilation combined with lack of CO elevation. The apparent dissociation between myocardial and vascular responses to Epi at low temperatures may be related to hypothermia-induced myocardial failure and changes in temperature-dependent adrenoreceptor affinity.     

Allosteric effects of atropine and carbachol on the activity of α<Subscript>2</Subscript>-adrenoceptors in rat brain cortex membranes

Activation and inhibition of muscarinic cholinoceptors by atropine and carbachol are shown to exert allosteric effects on the binding of specific nonselective α₂-adrenoceptor antagonist [³H]RX821002 in rat brain cortex membranes. The ligand-receptor interaction for α₂-adrenoceptors corresponded to the model suggesting the presence of one homogeneous pool of receptors with two specific binding sites. The parameters of the [³H]RX821002 binding were as follows: [³H]RX821002 -K _d = 1.94 ± 0.08 nM, B _max = 13.4 ± 1.8 fmol/mg protein, n = 2. The inhibition of muscarinic cholinoceptors by atropine induced an increase of affinity (K _d = 1.36 ± 0.12 nM) and a decrease of the α2-adrenoceptor density (B _max = 10.18 ± 0.48 fmol/mg protein). The muscarinic cholinoceptor agonist carbachol induced an increase of the affinity (K _d = 1.56 ± 0.05 nM) and quantity of binding sites (B _max = 16.61 ± 0.29 fmol/mg protein). As a result, under the influence of atropine and carbachol, the efficiency of binding (E = B _max/2K _d) increased from 3.50 ± 0.40 to 5.60 ± 0.79 and 6.86 ± 0.20 fmol/mg protein/nM, respectively. The data suggest that α₂-adrenoceptors exist in rat brain cortex as homodimers.     

Effect of Mild Hypothermia on the Coagulation-Fibrinolysis System and Physiological Anticoagulants after Cardiopulmonary Resuscitation in a Porcine Model

The aim of this study was to evaluate the effect of mild hypothermia on the coagulation-fibrinolysis system and physiological anticoagulants after cardiopulmonary resuscitation (CPR). A total of 20 male Wuzhishan miniature pigs underwent 8 min of untreated ventricular fibrillation and CPR. Of these, 16 were successfully resuscitated and were randomized into the mild hypothermia group (MH, n = 8) or the control normothermia group (CN, n = 8). Mild hypothermia (33°C) was induced intravascularly, and this temperature was maintained for 12 h before pigs were actively rewarmed. The CN group received normothermic post-cardiac arrest (CA) care for 72 h. Four animals were in the sham operation group (SO). Blood samples were taken at baseline, and 0.5, 6, 12, 24, and 72 h after ROSC. Whole-body mild hypothermia impaired blood coagulation during cooling, but attenuated blood coagulation impairment at 72 h after ROSC. Mild hypothermia also increased serum levels of physiological anticoagulants, such as PRO C and AT-III during cooling and after rewarming, decreased EPCR and TFPI levels during cooling but not after rewarming, and inhibited fibrinolysis and platelet activation during cooling and after rewarming. Finally, mild hypothermia did not affect coagulation-fibrinolysis, physiological anticoagulants, or platelet activation during rewarming. Thus, our findings indicate that mild hypothermia exerted an anticoagulant effect during cooling, which may have inhibitory effects on microthrombus formation. Furthermore, mild hypothermia inhibited fibrinolysis and platelet activation during cooling and attenuated blood coagulation impairment after rewarming. Slow rewarming had no obvious adverse effects on blood coagulation.     

Hypothermia protects H9c2 cardiomyocytes from H2O2 induced apoptosis

The purpose of our study was to investigate underlying basic mechanisms of hypothermia-induced cardioprotection during oxidative stress in a cardiomyocyte cell culture model. For hypothermic treatment we cooled H9c2 cardiomyocytes to 20 °C, maintained 20 min at 20 °C during which short-term oxidative damage was inflicted with 2 mM H₂O_2, followed by rewarming to 37 °C. Later on, we analyzed lactate dehydrogenase (LDH), caspase-3 cleavage, reactive oxygen species (ROS), mitochondrial activity, intracellular ATP production, cytoprotective signal molecules as well as DNA damage. Hypothermia decreased H₂O₂ damage in cardiomyocytes as demonstrated in a lower LDH release, less caspase-3 cleavage and less M30 CytoDeath staining. After rewarming H₂O₂ damaged cells demonstrated a significantly higher reduction rate of intracellular ROS compared to normothermic H₂O₂ damaged cardiomyocytes_. This was in line with a significantly greater mitochondrial dehydrogenase activity and higher intracellular ATP content in cooled and rewarmed cells. Moreover, hypothermia preserved cell viability by up-regulation of the anti-apoptotic protein Bcl-2 and a reduction of p53 phosphorylation. DNA damage, proven by PARP-1 cleavage and H2AX phosphorylation, was significantly reduced by hypothermia. In conclusion, we could demonstrate that hypothermia protects cardiomyocytes during oxidative stress by preventing apoptosis via inhibiting mitochondrial dysfunction and DNA damage.     

The respiratory chain of the facultative thermophile,Bacillus coagulans

Two oxidases were found to be present in membranes from the facultative thermophile Bacillus coagulans grown at 55°C, compared to one in cells grown at 37°C. Cytochrome spectra and inhibitors of the respiratory chain identified them as cytochrome oxidases aa ₃ and d. Both were present in membranes from 55°C grown cells, but only cytochrome oxidase aa ₃ was found in membranes from 37°C grown cells. The presence of cytochrome d in 55°C grown cultures was found to be due to decreased oxygen tension and not to the high growth temperature. This was confirmed by (a) induction of cytochrome d at 37°C under conditions of oxygen limitation and (b) its repression at 55°C under conditions of high aeration and its subsequent induction on lowering the dissolved oxygen concentration in chemostat cultures. Two cytochromes b (_max 558 and _max 562) were present in both 37°C and 55°C grown cells. Results from the inhibition of substrate oxidation by membranes suggested different pathways of electron transport by the respiratory chain.     

Short-term adaptation of five- to seven-year-old children to mental load

Tetrapolar rheography according to Kubicek has been used to estimate the adaptive capacity of the cardiovascular system in 150 five- to seven-year-old children at rest and during mental load. Mental load evokes two variants of stroke volume (SV) responses, one of them characterized by an increase in the SV, and the other, by a decrease in the SV and an increase in the diastolic blood pressure (BP_d). Irrespective of the direction of the change in the SV, short-term adaptation to mental load in most five- to seven-year-old children does not stress the mechanisms of the cardiovascular system control and is generally favorable. In 13–15% of the children examined, short-term adaptation to mental load considerably stressed the cardiovascular system control. This is expressed in increased systolic blood pressure (BP_s), BP_d, and heart rate (HR); decreased CV and cardiac output (Q); and a prolonged restoration period for most central hemodynamic parameters.     

Vector Selection of a Quadripolar Left Ventricular Pacing Lead Affects Acute Hemodynamic Response to Cardiac Resynchronization Therapy: A Randomized Cross-Over Trial

Background

A suboptimal left ventricular (LV) pacing site may account for non-responsiveness of patients to cardiac resynchronization therapy (CRT). The vector selection of a novel quadripolar LV pacing lead, which was mainly developed to overcome technical issues with stimulation thresholds and phrenic nerve capture, may affect hemodynamic response, and was therefore assessed in this study. (German Clinical Trials Register DRKS00000573).

Methods and Results

Hemodynamic effects of a total of 145 LVPCs (9.1 per patient) of CRT devices with a quadripolar LV lead (Quartet™, St. Jude Medical) were assessed in 16/20 consecutive patients by invasive measurement of LV+dP/dt_max at an invasively optimized AV-interval in random order. Optimal (worst) LVPCs per patient were identified as those with maximal (minimal) %change in LV+dP/dt_max (%ΔLV+dP/dt_max) as compared to a preceding baseline. LV+dP/dt_max significantly increased in all 145 LVPCs (p<0.0001 compared to baseline) with significant intraindividual differences between LVPCs (p<0.0001). Overall, CRT acutely augmented %ΔLV+dP/dt_max by 31.3% (95% CI 24%–39%) in the optimal, by 21.3% (95% CI: 15%–27%) in the worst and by 28.2% (95% CI: 21%–36%) in a default distal LVPC. This resulted in an absolute additional acute increase in %ΔLV+dP/dt_max of 10.0% (95% CI: 7%–13%) of the optimal when compared to the worst (p<0.0001), and of 3.1% (95% CI: 1%–5%) of the optimal when compared to the default distal LVPC (p<0.001). Optimal LVPCs were not programmable with a standard bipolar lead in 44% (7/16) of patients.

Conclusion

The pacing configuration of a quadripolar LV lead determinates acute hemodynamic response. Pacing in the individually optimized configuration gives rise to an additional absolute 10% increase in %ΔLV+dP/dt_max when comparing optimal and worst vectors.     

Activated expression of cardiac adenylyl cyclase 6 reduces dilation and dysfunction of the pressure-overloaded heart

Background and objective

Cardiac-directed adenylyl cyclase 6 (AC6) expression attenuates left ventricular (LV) hypertrophy and dysfunction in cardiomyopathy, but its effects in the pressure-overloaded heart are unknown.

Methods

Mice with cardiac-directed and regulated expression of AC6 underwent transaortic constriction (TAC) to induce LV pressure overload. Ten days prior to TAC, and for the duration of the 4 week study, cardiac myocyte AC6 expression was activated in one group (AC-On) but not the other (AC-Off). Multiple measures of LV systolic and diastolic function were obtained 4 week after TAC, and LV samples assessed for alterations in Ca²⁺ signaling.

Results

LV contractility, as reflected in the end-systolic pressure–volume relationship (E_max), was increased (p = 0.01) by activation of AC6 expression. In addition, diastolic function was improved (p < 0.05) and LV dilation was reduced (p < 0.05). LV samples from AC-On mice showed reduced protein expression of sodium/calcium exchanger (NCX1) (p < 0.05), protein phosphatase 1 (PP1) (p < 0.01), and increased phosphorylation of phospholamban (PLN) at Ser16 (p < 0.05). Finally, sarcoplasmic reticulum (SR) Ca²⁺ content was increased in cardiac myocytes isolated from AC-On mice (p < 0.05).

Conclusions

Activation of cardiac AC6 expression improves function of the pressure-overloaded and failing heart. The predominant mechanism for this favorable adaptation is improved Ca²⁺ handling, a consequence of increased PLN phosphorylation, reduced NCX1, reduced PP1 expression, and increased SR Ca²⁺ content.     

Differential response of two models of genetically modified mice fed with high fat and cholesterol diets: relationship to the study of non-alcoholic steatohepatitis

Thyroid hormone deficiency has been reported to decrease expression and function of both β₁- and β₂-adrenoceptor in different tissues including heart. The purpose of this study was to examine the possible contribution of β₃-adrenoceptors to cardiac dysfunction in hypothyroidism. In addition, effect of this pathology on β₁- and β₂-adrenoceptor was investigated. Hypothyroidism was induced by adding methimazole (300 mg/l) to drinking water of rats for 8 weeks. Cardiac hemodynamic parameters were measured in anesthetised rats in vivo. Responses to β-adrenoceptor agonists were examined in rat papillary muscle in vitro. We also studied the effect of hypotyroidism on mRNA expression of β-adrenoceptors, Giα, GRK, and eNOS in rat heart. All of the hemodynamic parameters (systolic, diastolic and mean arterial pressure, left ventricular pressure, heart rate, +dp/dt, and ?dp/dt) were significantly reduced by the methimazole treatment. The negative inotropic effect elicited by BRL 37344 (a β₃-adrenoceptor preferential agonist) and positive inotropic effects produced by isoprenaline and noradrenaline, respectively, were significantly decreased in papillary muscle of hypothyroid rats as compared to those of controls. On the other hand, hypothyroidism resulted in increased cardiac β₂- and β₃-adrenoceptor, Giα₂, Giα₃, GRK3, and eNOS mRNA expressions. However, β₁-adrenoceptor and GRK2 mRNA expressions were not changed significantly in this pathology. These results show that mRNA expression of β₃-adrenoceptors as well as the signalling pathway components mediated through β₃-adrenoceptors are significantly increased in hypothyroid rat heart. Since we could not correlate these alternates with the decreased negative inotropic response mediated by this receptor subtype, it is not clear whether these changes are important for hypothyroid induced reduction in cardiac function.     

Salutary effects of moderate hypothermia on the circulatory and myocardial consequences of acute coronary occlusion in dogs

The efficacy of moderate hypothermia with rewarming in attenuating the myocardial and circulatory consequences of acute coronary ligation was studied in open-chest, anesthetized dogs. Thirty minutes after ligation of the proximal left anterior descending coronary artery, 14 dogs were surface-cooled to 27 degrees C, maintained at this temperature for 2 hr, rewarmed to normothermic levels, and monitored for an additional hour. Fifteen dogs were maintained for a corresponding time period after coronary ligation at normothermic levels. Dogs maintained normothermic demonstrated significant depression (from preligation values) of dP/dt, cardiac output (CO), stroke volume (SV), and left ventricular stroke work and power (LVSW, LVSP) at elevated levels of left ventricular end-diastolic pressure (LVEDP). Dogs subjected to the hypothermic procedure demonstrated decreased inotropic status during hypothermia, but with rewarming, exhibited significantly greater values of left ventricular pressure, dP/dt, CO, SV, LVSW, and LVSP at lower values of LVEDP than observed in dogs maintained normothermic. Increased dysrhythmic activity was not observed during hypothermia. Hearts from dogs subjected to the hypothermic protocol demonstrated qualitatively greater dehydrogenase activity both at the periphery and in the center of the nonperfused region. The results suggest that moderate hypothermia during evolving myocardial infarction may preserve left ventricular cardio- and hemodynamics and thus may be useful in delaying morphological and functional deterioration until definitive treatment can be instituted.     

Transplasmalemma electron transport is changed in simian virus 40 transformed liver cells

Transplasma membrane electron transport activity by fetal rat liver cells (RLA209-15) infected with a temperature-sensitive strain of SV40 has been measured with cells grown at the restrictive temperature (40°C) and permissive temperature (33°C). The transformed cells grown at 33°C had only one-half the rate of external ferricyanide reduction as the nontransformed cells held at 40°C. Both theK _m andV _max for ferricyanide reduction were changed in the transformed state. The change inV _max can be based on a decrease of NADH in the transformed cells. The change in rate with ferricyanide does not depend on change in surface charge. Reduction of external ferricyanide was accompanied by release of protons from the cells. The ratio of protons released to ferricyanide reduced was higher in the transformed cells than in the non-transformed cells. Since the transplasma membrane electron transport has been shown to stimulate cell growth under limiting serum, the changes in the plasma membrane electron transport and proton release in transformed cells may relate to modification of growth control.