Respiratory motion compensation by model-based catheter tracking during EP procedures

In many cases, radio-frequency catheter ablation of the pulmonary veins attached to the left atrium still involves fluoroscopic image guidance. Two-dimensional X-ray navigation may also take advantage of overlay images derived from static pre-operative 3D volumetric data to add anatomical details otherwise not visible under X-ray. Unfortunately, respiratory motion may impair the utility of static overlay images for catheter navigation. We developed a novel approach for image-based 3D motion estimation and compensation as a solution to this problem. It is based on 3D catheter tracking which, in turn, relies on 2D/3D registration. To this end, a bi-plane C-arm system is used to take X-ray images of a special circumferential mapping catheter from two directions. In the first step of the method, a 3D model of the device is reconstructed. Three-dimensional respiratory motion at the site of ablation is then estimated by tracking the reconstructed catheter model in 3D based on bi-plane fluoroscopy. Phantom data and clinical data were used to assess model-based catheter tracking. Our phantom experiments yielded an average 2D tracking error of 1.4mm and an average 3D tracking error of 1.1mm. Our evaluation of clinical data sets comprised 469 bi-plane fluoroscopy frames (938 monoplane fluoroscopy frames). We observed an average 2D tracking error of 1.0 + or - 0.4mm and an average 3D tracking error of 0.8 + or - 0.5mm. These results demonstrate that model-based motion-compensation based on 2D/3D registration is both feasible and accurate.

Genetic evolution of EGFR and the clonal origin of adenocarcinomas exhibiting various degrees of bronchioloalveolar carcinoma

e22050

Background: EGFR mutations may accumulate during multistage progression of bronchioloalveolar carcinoma (BAC), leading to heterogeneity within the tumor. Moreover, intrapulmonary emersions are the predominant sites of BAC progression in the absence of other distant metastases. In cases of emerging bilateral lung lesions during the follow-up to complete resection, the issue of how to differentiate between lesions originating from multifocal BACs or distant metastases/local recurrence is an important and unresolved issue. This study was performed to determine whether sequential adenocarcinoma with BAC features emerges in the lung field arises from a single clone or multiple clones in the same individual. Methods: Samples of adenocarcinomas exhibiting various degrees of BAC were obtained by thoracotomy. Sequential specimens were obtained on detection of novel lesions in the lung field. Genomic DNA was extracted from the specimens, and the presence of activating mutations in EGFR was analyzed by direct sequencing. Our pathological findings, sequential imaging, and EGFR sequence data were compared to monitor evidence of cancer evolution. Results: Based on an analysis of EGFR in tumor specimens from 428 lung cancer patients, fifteen cases of sequential BAC-related adenocarcinoma obtained by thoracotomy were identified. Together with alterations in BAC/adenocarcinoma components, the EGFR-TKI untreated series with at least one episode of EGFR-activating mutations represented three typical models: no significant EGFR evolution for a single clone, genetic alterations from mutant to wild-type EGFR for multifocal lesions, and a switch from wild-type to mutant EGFR, which might exhibit uncertain circumstances of cancer progression. Conclusions: Genetic analysis in conjunction with pathological and radiological diagnoses can be used to explore the origin of multifocal BAC. The single clone model indicates subsequent disease progression, whereas genetic alterations from mutations to wild-type EGFR are suggestive of secondary primary carcinoma. When additional lesions emerge after radical resection of BAC-related lung cancer, sequential tumor samples should be obtained for further evaluation.

No significant financial relationships to disclose.

Cell therapy for cardiac repair

Cardiovascular diseases remain the leading cause of morbidity and mortality in Western society. Among these diseases, congestive heart failure continues to be a significant health care burden. Recent medical and surgical advances in therapy have improved the quality and quantity of life for patients with heart failure. However, none of these therapies address the fundamental problem of loss of functional cardiomyocytes. Cell regeneration therapies have become an exciting potential treatment for heart failure and other cardiovascular diseases. This emerging therapeutic field has been pursued experimentally with both embryonic-derived stem cells and adult-derived progenitor cells. The identification of resident cardiac progenitor cells has propelled the field of cardiac regenerative biology forward at astonishing rates. This review will examine current findings of various stem and progenitor cells that have been proposed as potential sources for cardiac regeneration, and the recent therapeutic findings from preliminary clinical trials using some of these cell types for cardiovascular repair.

Albumin is not present in the murine interphotoreceptor matrix, or in that of transgenic mice lacking IRBP

PURPOSE

The interphotoreceptor matrix mediates interactions between the retinal pigment epithelium, photoreceptors, and Muller cells. Each of these cells contributes to specific proteoglycans, proteins, and growth factors in the interphotoreceptor matrix. Some components, such as interphotoreceptor retinoid binding protein (IRBP), are virtually unique to the interphotoreceptor matrix. It has been proposed that serum albumin, thought to be present in the interphotoreceptor matrix, could act as a surrogate retinoid binding protein within the subretinal space of transgenic mice lacking interphotoreceptor retinoid binding protein. To address this question, we sought to determine whether albumin is present in the interphotoreceptor matrix of IRBP+/+ mice or IRBP-/- mice.

METHODS

We examined the distribution of albumin in IRBP-/- mice and IRBP+/+ mice using immunofluorescence and immunoperoxidase histochemistry.

RESULTS

The distribution of albumin within the corneal stroma, sclera, and capillaries is consistent with previous work. Serum albumin could not be detected in the interphotoreceptor matrix. The distribution of albumin in IRBP-/- mice was similar to that of their wildtype counterparts.

CONCLUSIONS

Serum albumin is not a component of the interphotoreceptor matrix of IRBP+/+ mice or IRBP-/- mice.

Bilateral central retinal vein occlusions in a Chinese patient with HIV-infection

PURPOSE

To report a case of bilateral nonischemic central retinal vein occlusions as the initial presentation in a Chinese patient with HIV-infection.

METHODS

Complete ophthalmological examination and fundus fluorescein angiography were performed in the eyes of this patient.

RESULTS

Ophthalmic examination and fundus fluorescein angiography revealed bilateral nonischemic central retinal vein occlusions and optic disc edema in a 22-year-old man who was HIV-positive. The findings of fundus examination and fluorescein angiography were similar in both eyes.

CONCLUSION

This case provides additional evidence that central retinal vein occlusion is probably part of the spectrum of HIV retinopathy.

Infusion of light chains from patients with cardiac amyloidosis causes diastolic dysfunction in isolated mouse hearts

BACKGROUND

Primary (AL) amyloidosis is a plasma cell dyscrasia characterized by clonal production of immunoglobulin light chains (LC) resulting in the subsequent systemic deposition of extracellular amyloid fibrils. Cardiac involvement is marked by the hemodynamic pattern of impaired diastolic filling and restrictive cardiomyopathy. Although cardiac death in patients with AL amyloidosis is usually associated with extensive myocardial infiltration, the infiltration alone does not correlated with the degree of heart failure or survival. We hypothesized that circulating monoclonal LC may directly impair cardiac function, in addition to any mechanical effects of amyloid fibril deposition. Therefore, we examined the effects of amyloid LC proteins on diastolic and systolic cardiac function, as measured in an isolated mouse heart model.

METHODS AND RESULTS

LC were obtained from patients with nonamyloid disease or from those with noncardiac, mild cardiac, and severe cardiac involved AL amyloidosis. Saline or LC (100 microgram/mL) was infused into a Langendorff-perfused, isovolumically contracting mouse heart. Saline and control, noncardiac, and mild-cardiac LC infusions did not alter ex vivo cardiac function. In contrast, infusion of sever cardiac LC resulted in marked impairment of ventricular relaxation with preservation of contractile function.

CONCLUSION

These results demonstrate that infusion of LC from patients with AL amyloidosis result in diastolic dysfunction similar to that observed in patients with cardiac involved AL amyloidosis, and they suggest that amyloid LC proteins may contribute directly to the pathogenesis and the rapid progression of amyloid cardiomyopathy, independent of extracellular fibril deposition.

Inhibition of telomerase is related to the life span and tumorigenicity of human prostate cancer cells

PURPOSE

Telomerase, the enzyme that catalyzes the elongation of telomeres, is illegitimately activated in the majority of cancers, including that of the prostate, where it may greatly extend the life span of malignant cells. The inhibition of telomerase by molecular intervention has been shown to lead eventually to cell death in several tumor or in vitro immortalized cell lines and in 1 case prevent tumor growth in vivo. Therefore, we tested whether a similar strategy may be used to limit the tumorigenic potential of late stage prostate cancer cells.

MATERIALS AND METHODS

PC-3, LNCaP and DU-145 human prostate cancer cells were infected with a retrovirus encoding a dominant-negative version of the catalytic subunit of telomerase (DN-hTERT). Subclones or polyclonal populations were assayed for DN-hTERT expression, telomerase activity, telomere length, cell life span and in most cases tumorigenicity in nude mice.

RESULTS

DN-hTERT expression levels directly correlated with cell life span and tumorigenic growth. PC-3 cells expressing high levels of DN-hTERT died rapidly and failed to form tumors in nude mice, whereas cells expressing the lowest levels proliferated the longest and generated tumors that later spontaneously regressed. Similarly the inhibition of telomerase activity in LNCaP cells was greater than in DU-145 cells and correspondingly LNCaP cells had a shorter life span.

CONCLUSIONS

DN-hTERT expression limits the life span and tumorigenic potential of human prostate cancer cells, although the onset of these effects appears to be dictated by the expression level of DN-hTERT. Therefore, telomerase represents an attractive target for potentially managing prostate cancer. Nevertheless, effective means of inhibiting the enzyme may be required for a therapeutically useful outcome.

High-throughput assessment of calcium sensitivity in skinned cardiac myocytes

Isolated permeabilized cardiac myocytes have been used in the study of myofilament calcium sensitivity through measurement of the isometric force-pCa curve. Determining this force-pCa relationship in skinned myocytes is relatively expensive and carries a high degree of variability. We therefore attempted to establish an alternative high-throughput method to measure calcium sensitivity in cardiac myocytes. With the use of commercially available software that allows for precise measurement of sarcomere spacing, we measured sarcomere length changes in unloaded skinned cardiac myocytes over a range of calcium concentrations. With the use of this technique, we were able to accurately detect acute increases or decreases in myofilament calcium sensitivity after exposure to 10 mM caffeine or 5 mM 2,3-butanedione monoxime, respectively. This technique allows for the simple and rapid determination of myofilament calcium sensitivity in cardiac myocytes in a reproducible and inexpensive manner and could be used for high-throughput screening of pharmacological agents and/or transgenic mouse models for changes in myofilament calcium sensitivity.

Regulation of the Mycobacterium tuberculosis hypoxic response gene encoding alpha -crystallin

Unlike many pathogens that are overtly toxic to their hosts, the primary virulence determinant of Mycobacterium tuberculosis appears to be its ability to persist for years or decades within humans in a clinically latent state. Since early in the 20th century latency has been linked to hypoxic conditions within the host, but the response of M. tuberculosis to a hypoxic signal remains poorly characterized. The M. tuberculosis alpha-crystallin (acr) gene is powerfully and rapidly induced at reduced oxygen tensions, providing us with a means to identify regulators of the hypoxic response. Using a whole genome microarray, we identified >100 genes whose expression is rapidly altered by defined hypoxic conditions. Numerous genes involved in biosynthesis and aerobic metabolism are repressed, whereas a high proportion of the induced genes have no known function. Among the induced genes is an apparent operon that includes the putative two-component response regulator pair Rv3133c/Rv3132c. When we interrupted expression of this operon by targeted disruption of the upstream gene Rv3134c, the hypoxic regulation of acr was eliminated. These results suggest a possible role for Rv3132c/3133c/3134c in mycobacterial latency.

Cell therapy attenuates deleterious ventricular remodeling and improves cardiac performance after myocardial infarction

BACKGROUND

Myocardial infarction (MI) promotes deleterious remodeling of the myocardium, resulting in ventricular dilation and pump dysfunction. We examined whether supplementing infarcted myocardium with skeletal myoblasts would (1) result in viable myoblast implants, (2) attenuate deleterious remodeling, and (3) enhance in vivo and ex vivo contractile performance.

METHODS AND RESULTS

Experimental MI was induced by 1-hour coronary ligation followed by reperfusion in adult male Lewis rats. One week after MI, 10(6) myoblasts were injected directly into the infarct region. Three groups of animals were studied at 3 and 6 weeks after cell therapy: noninfarcted control (control), MI plus sham injection (MI), and MI plus cell injection (MI+cell). In vivo cardiac function was assessed by maximum exercise capacity testing and ex vivo function was determined by pressure-volume curves obtained from isolated, red cell-perfused, balloon-in-left ventricle (LV) hearts. MI and MI+cell hearts had indistinguishable infarct sizes of approximately 30% of the LV. At 3 and 6 weeks after cell therapy, 92% (13 of 14) of MI+cell hearts showed evidence of myoblast graft survival. MI+cell hearts exhibited attenuation of global ventricular dilation and reduced septum-to-free wall diameter compared with MI hearts not receiving cell therapy. Furthermore, cell therapy improved both post-MI in vivo exercise capacity and ex vivo LV systolic pressures.

CONCLUSIONS

Implanted skeletal myoblasts form viable grafts in infarcted myocardium, resulting in enhanced post-MI exercise capacity and contractile function and attenuated ventricular dilation. These data illustrate that syngeneic myoblast implantation after MI improves both in vivo and ex vivo indexes of global ventricular dysfunction and deleterious remodeling and suggests that cellular implantation may be beneficial after MI.

Optimization of multiple-isocenter treatment planning for linac-based stereotactic radiosurgery

OBJECTIVE

Computer-assisted treatment planning for linac-based radiosurgery is still an open research problem, especially for multiple-isocenter procedures, primarily due to its high complexity and computational requirements. This paper focuses on the optimization of multiple-isocenter treatment planning for linac systems, and addresses several important issues associated with multiple isocenters, such as dose conformality, homogeneity, and optimization of isocenter position and dose.

METHODS

The key idea behind our approach is that the desired dose distribution can be decomposed into a number of fundamental components. In the current paper, an analytical form, the so-called Ellipsoidal Dose Distribution Estimation (EDDE) model, represents each component. We establish ways (arc configurations) to achieve such ellipsoidal doses of arbitrary position, orientation, and size. Since the EDDE model is described by relatively few parameters, it allows very quick estimation of the dose distribution corresponding to a particular isocenter and thus makes the optimization of isocenter position very efficient. It is further used in a framework for optimal treatment planning, in which a number of ellipsoidal dose distributions, each corresponding to a different isocenter, are optimally placed to cover the target while sparing healthy tissue.

RESULTS

The general ellipsoidal dose distribution of linac-based radiosurgery is summarized as a mathematical model with the aid of supporting experiments. Comparisons between the EDDE-optimized and clinically implemented plans are made, revealing the superior performance of the former. In addition, a dramatic reduction in planning time is achieved using the EDDE model.

CONCLUSION

The proposed EDDE model is a useful and effective dose model in multiple-isocenter treatment planning for linac-based radiosurgery.

Targeted inactivation of Galpha(i) does not alter cardiac function or beta-adrenergic sensitivity

Inhibitory Galpha(i) protein increases in the myocardium during hypertrophy and has been associated with beta-adrenergic receptor (beta-AR) desensitization, contractile dysfunction, and progression of cardiac disease. The role of Galpha(i) proteins in mediating basal cardiac function and beta-AR response in nonpathological myocardium, however, is uncertain. Transgenic mice with targeted inactivation of Galpha(i2) or Galpha(i3) were examined for in vivo cardiac function with the use of conscious echocardiography and for ex vivo cardiac response to inotropic stimulation with the use of Langendorff blood-perfused isolated hearts and adult ventricular cardiomyocytes. Echocardiography revealed that percent fractional shortening and heart rate were similar among wild-type, Galpha(i2)-null, and Galpha(i3)-null mice. Comparable baseline diastolic and contractile performance was also observed in isolated hearts and isolated ventricular myocytes from wild-type mice and mice lacking Galpha(i) proteins. Isoproterenol infusion enhanced diastolic and contractile performance to a similar degree in wild-type, Galpha(i2)-null, and Galpha(i3)-null mice. These data demonstrate no observable role for inhibitory G proteins in mediating basal cardiac function or sensitivity to beta-AR stimulation in nonpathological myocardium.

Galpha(i2) but not Galpha(i3) is required for muscarinic inhibition of contractility and calcium currents in adult cardiomyocytes

Parasympathetic stimulation of the heart acts through M(2)-muscarinic acetylcholine receptors to regulate ion channel activity and subsequent inotropic status. Although muscarinic signal transduction is mediated via pertussis toxin-sensitive G proteins Galpha(i/o), the specific signal transduction requirements of Galpha(i2) and Galpha(i3) in mediating muscarinic regulated L-type calcium currents (I(Ca, L)), intracellular calcium, and cell contractility remain to be determined. Adult ventricular myocytes were isolated from Galpha(i2)-null mice, Galpha(i3)-null mice, and their wild-type littermates. Cell shortening, intracellular calcium levels, and I(Ca, L) were all measured in response to isoproterenol, a beta-adrenergic receptor agonist, and carbachol, a cholinergic receptor agonist. With isoproterenol stimulation, myocytes from all groups demonstrated a marked increase in calcium currents, correlating with augmented intracellular calcium transient amplitude and cell shortening. Carbachol significantly attenuated the isoproterenol response in wild-type and Galpha(i3)-null cells but had no effect in Galpha(i2)-null cells. This study demonstrates that Galpha(i2), but not Galpha(i3), is required for muscarinic inhibition of the beta-adrenergic response in adult murine ventricular myocytes.

Altered beta-adrenergic signal transduction in nonfailing hypertrophied myocytes from Dahl salt-sensitive rats

Desensitization of the beta-adrenergic receptor (beta-AR) response is well documented in hypertrophied hearts. We investigated whether beta-AR desensitization is also present at the cellular level in hypertrophied myocardium, as well as the physiological role of inhibitory G (G(i)) proteins and the L-type Ca(2+) channel in mediating beta-AR desensitization. Left ventricular (LV) myocytes were isolated from hypertrophied hearts of hypertensive Dahl salt-sensitive (DS) rats and nonhypertrophied hearts of normotensive salt-resistant (DR) rats. Cells were paced at a rate of 300 beats/min at 37 degrees C, and myocyte contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) were simultaneously measured. In response to increasing concentrations of isoproterenol, DR myocytes displayed a dose-dependent augmentation of cell shortening and the [Ca(2+)](i) transient amplitude, whereas hypertrophied DS myocytes had a blunted response of both cell shortening and the [Ca(2+)](i) transient amplitude. Interestingly, inhibition of G(i) proteins did not restore beta-AR desensitization in DS myocytes. The responses to increases in extracellular Ca(2+) and an L-type Ca(2+) channel agonist were also similar in both DS and DR myocytes. Isoproterenol-stimulated adenylyl cyclase activity, however, was blunted in hypertrophied myocytes. We concluded that compensated ventricular hypertrophy results in a blunted contractile response to beta-AR stimulation, which is present at the cellular level and independent of alterations in inhibitory G proteins and the L-type Ca(2+) channel.

Impaired cell shortening and relengthening with increased pacing frequency are intrinsic to the senescent mouse cardiomyocyte

Increased heart rate enhances cardiac contractility and accelerates relaxation. Both the force- and relaxation-frequency relationships are critical to myocardial function, especially during stress, and have been shown to be impaired in senescent myocardium. While senescent myocardium is characterized by decreased sarcoplasmic reticulum calcium ATPase activity, it is unclear if altered calcium regulation is directly responsible for the attenuated contractility and relaxation observed with increasing pacing frequency in aged myocardium. We examined this issue using freshly dissociated left ventricular myocytes, isolated from young adult and senescent mouse hearts. Myocytes were paced from 2 to 9 Hz at 37 degrees C, and cell shortening and [Ca(2+)](i)were simultaneously measured using video edge-detection and fura-2 fluorescence, respectively. In adult myocytes, increasing the pacing rate resulted in a progressive increase in percent cell shortening (CS) (P<0.01). This positive CS-frequency relationship was paralleled by an increase in [Ca(2+)](i)transient amplitude (P<0.05). In contrast, the CS-frequency relationship was blunted in senescent myocytes with no increase in percent CS or [Ca(2+)](i)transient amplitude with increasing pacing rate. With increased pacing, the decreases in time constants (tau) of cell relengthening and Ca(2+)transient decay were much steeper in adult compared to senescent myocytes (P<0.05). This study demonstrates that adult mouse myocytes exhibit augmented intracellular Ca(2+)transient amplitude and enhanced intracellular Ca(2+)removal with increasing pacing frequency, resulting in increased cell shortening and enhanced relengthening with frequency. In contrast, senescent mouse myocytes exhibit impaired calcium handling with increasing pacing frequency, which correlated with impairment of both cell shortening and relengthening.

Chronic alpha-adrenergic receptor stimulation modulates the contractile phenotype of cardiac myocytes in vitro

BACKGROUND

Heart failure is characterized by contractile dysfunction of the myocardium and elevated sympathetic activity. We tested the hypothesis that chronic alpha-adrenergic (alpha-ADR) stimulation modifies the molecular and contractile phenotype of cardiac myocytes.

METHODS AND RESULTS

Adult rat ventricular myocytes in culture were exposed to alpha-ADR stimulation (norepinephrine + propranolol) for 48 hours. alpha-ADR stimulation decreased the mRNAs for sarcoplasmic reticulum Ca(2+)-ATPase and Ca(2+) release channel by 56% and 52%, respectively, and increased mRNA and protein for the Na(+)-Ca(2+) exchanger by 70% and 39%, respectively. After washout of the alpha-ADR agonist, simultaneous measurement of [Ca(2+)](i) transients with fura 2 and myocyte shortening by video edge-detection showed that [Ca(2+)](i) amplitude and myocyte shortening were decreased in alpha-ADR-treated myocytes, and the time to peak and time from peak to 80% decline of both [Ca(2+)](i) and myocyte shortening were increased. The concentration-response curve for myocyte shortening by the Na(+) channel activator veratridine was shifted leftward in alpha-ADR-stimulated myocytes (EC(50), 21.6+/-4.6 versus 105.8+/-10.5 nmol/L, P:<0.001).

CONCLUSIONS

Chronic alpha-ADR stimulation of cardiac myocytes causes decreases in the expression of sarcoplasmic reticulum Ca(2+)-ATPase and the Ca(2+) release channel that are associated with decreases in [Ca(2+)](i) and contractility. alpha-ADR stimulation simultaneously increases Na(+)-Ca(2+) exchanger expression, thereby increasing sensitivity to intracellular Na(+).

ATP synthesis during low-flow ischemia: influence of increased glycolytic substrate

BACKGROUND

Our goals were to (1) simulate the degree of low-flow ischemia and mixed anaerobic and aerobic metabolism of an acutely infarcting region; (2) define changes in anaerobic glycolysis, oxidative phosphorylation, and the creatine kinase (CK) reaction velocity; and (3) determine whether and how increased glycolytic substrate alters the energetic profile, function, and recovery of the ischemic myocardium in the isolated blood-perfused rat heart.

METHODS AND RESULTS

Hearts had 60 minutes of low-flow ischemia (10% of baseline coronary flow) and 30 minutes of reperfusion with either control or high glucose and insulin (G+I) as substrate. In controls, during ischemia, rate-pressure product and oxygen consumption decreased by 84%. CK velocity decreased by 64%; ATP and phosphocreatine (PCr) concentrations decreased by 51% and 63%, respectively; inorganic phosphate (P(i)) concentration increased by 300%; and free [ADP] did not increase. During ischemia, relative to controls, the G+I group had similar CK velocity, oxygen consumption, and tissue acidosis but increased glycolysis, higher [ATP] and [PCr], and lower [P(i)] and therefore had a greater free energy yield from ATP hydrolysis. Ischemic systolic and diastolic function and postischemic recovery were better.

CONCLUSIONS

During low-flow ischemia simulating an acute myocardial infarction region, oxidative phosphorylation accounted for 90% of ATP synthesis. The CK velocity fell by 66%, and CK did not completely use available PCr to slow ATP depletion. G+I, by increasing glycolysis, slowed ATP depletion, maintained lower [P(i)], and maintained a higher free energy from ATP hydrolysis. This improved energetic profile resulted in better systolic and diastolic function during ischemia and reperfusion. These results support the clinical use of G+I in acute MI.

Branch retinal artery occlusion after thyroid artery interventional embolization

PURPOSE

To report a case of branch retinal artery occlusion after thyroid artery interventional embolization.

METHODS

A 33-year-old man with hyperthyroidism complained of visual loss and scotoma in the left eye after thyroid artery interventional embolization. He underwent a full ophthalmologic examination, including fluorescein angiography.

RESULTS

Visual acuity was 20/25, with inferior and superior scotomas present in the left eye. Fluorescein angiography of the left eye revealed delayed filling of a superotemporal branch retinal artery and nonfilling of an inferotemporal branch retinal artery.

CONCLUSION

A small, but definite risk of retinal artery occlusion after thyroid artery interventional embolization should be considered.

Angiotensin II receptor blockade attenuates the deleterious effects of exercise training on post-MI ventricular remodelling in rats

OBJECTIVES

The effects of exercise training on LV remodelling following large anterior myocardial infarction (MI) remains controversial. Blockade of the renin-angiotensin system has been shown to prevent ventricular dilation and deleterious remodeling. We therefore tested, in a rat model of chronic MI, whether any potentially deleterious effects of exercise on post-MI remodelling could be ameliorated by angiotensin II receptor blockade.

METHODS

Male Wistar rats underwent coronary ligation or sham operation. Treatment with losartan (10 mg/kg/day) began 1 week post-MI and moderate treadmill exercise (25 m/min, 60 min/day, 5 days/week) was initiated 2 weeks post-MI. Systolic and diastolic pressure-volume relationships were measured in isolated, red-cell perfused, isovolumically beating hearts 8 weeks post-MI. Morphometric measurements were performed in trichrome stained cross sections of the heart. Five groups of animals were compared: sham (n=13), control MI (MI; n=11), MI plus losartan (MI-Los; n=13), MI plus exercise (MI-Ex; n=10) and MI plus exercise and losartan (MI-Ex-Los; n=12).

RESULTS

Infarct size (% of left ventricle, LV) was similar among the infarcted groups [MI=43+/-4%, MI-Los=49+/-2%, MI-Ex=45+/-1%, MI-Ex-Los=48+/-2% (NS)]. Exercise, losartan and exercise+losartan treatments all attenuated LV dilation post-MI to a similar degree. Exercise training increased LV developed pressure in both untreated and losartan treated hearts (P<0.05 vs. other MI groups). In addition, exercise resulted in additional scar thinning in untreated hearts, while no additional scar thinning was seen in post-infarct hearts receiving both losartan and exercise.

CONCLUSIONS

Following large anterior MI, losartan attenuated LV dilation and scar thinning. In untreated animals, exercise decreased dilation, but also contributed to scar thinning. Therefore, exercise concurrent with blockade of the renin-angiotensin system may provide optimal therapeutic benefit following large anterior MI.

Impaired lusitropy-frequency in the aging mouse: role of Ca(2+)-handling proteins and effects of isoproterenol

We examined the relationship between age-associated lusitropic impairment, heart rate, and Ca(2+)-handling proteins and assessed the efficacy of increasing left ventricular (LV) relaxation via beta-adrenergic stimulation in adult and aging mouse hearts. LV function was measured in isolated, isovolumic blood-perfused hearts from adult (5 mo), old (24 mo), and senescent (34 mo) mice. Hearts were paced from 5 to 10 Hz, returned to 7 Hz, exposed to 10(-6) M isoproterenol, and paced again from 7 to 10 Hz. Age-related alterations in Na(+)/Ca(2+) exchanger (NCX), sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a), and phospholamban (PLB) levels were assessed by immunoblot. Despite preserved contractile performance, aging caused impaired lusitropy. Increased pacing caused an elevation in end-diastolic pressure that progressively worsened with age. The time constant of isovolumic pressure decay (tau) was significantly prolonged in old and senescent hearts compared with adults. Relative to adult hearts, the SERCA2a-to-PLB ratios were reduced 68 and 69%, and NCX were reduced 37 and 58% in old and senescent hearts, respectively. Isoproterenol completely reversed the age-associated lusitropic impairments. These data suggest that impaired lusitropy in aging mouse hearts is related to a decreased rate of cytosolic Ca(2+) removal and that accelerating SR Ca(2+) resequestration via beta-adrenergic stimulation can reverse this impairment.

Elasticity and fracture strain of whole blood clots

The measurement of clot elasticity and fracture strain is carried out using a rotational rheometer with a controlled stress system. The elasticity is quantified by a shear elastic modulus and fracture strain by a critical strain (deformation) when the clot begins to break up. The results indicate a decrease of elasticity and increase of fracture strain of the clot with increasing hematocrit. Moreover, the elastic modulus of the clot is not constant but increasing with deformation.

C-alkylated spiro[benzofuran-3(2H),4'-1'-methyl-piperidine-7-ols] as potent opioids: a conformation-activity study

Among a series of C-alkylated analogs of the weak mu opioid ligand spiro[benzofuran-3(2H),4'-1'-methylpiperidine-7-ol] (1), the 2-methyl, 2-ethyl, and cis 3'-methyl analogs, namely compounds (+/-)2, (+/-)-3, and (+/-)-4, showed much enhanced mu-affinities, with (+/-)-4 being almost as potent as (-)-morphine; while the trans 3'-methyl analog (+/-)-5 remained a weak mu-binder. Energy calculations and nmr data indicated that compounds 2-4 favor phenyl-axial conformations, while compounds 1 and 5 favor phenyl-equatorial conformations.

Early changes in excitation-contraction coupling: transition from compensated hypertrophy to failure in Dahl salt-sensitive rat myocytes

OBJECTIVE

The aims were to (1) define the early changes in excitation-contraction coupling during the transition from cardiac hypertrophy to heart failure, and (2) to clarify the causal relationship between mechanical dysfunction and abnormal Ca2+ handling in the Dahl salt-sensitive rat model.

METHODS

Myocardial contractile function was assessed in whole heart perfusion studies. In separate experiments, isolated left ventricular myocytes from Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats were paced at a physiological rate of 5Hz and cell shortening (CS) and [Ca2+]i measured simulataneously by video-edge detection and fura-2 fluorescence.

RESULTS

DS hearts developed hypertrophy after 4 weeks of a high-salt diet (4WHSD), as indicated by a 26% increase (p < 0.01) in the heart to body weight ratio and a 21% increase (p < 0.01) in cell width. Heart failure developed after 12 weeks of a high-salt diet (12WHSD), as indicated by an 11% increase (p < 0.01) in the lung wet to dry weight ratio. Furthermore, in DS-12WHSD hearts, the diastolic pressure-volume relationship had shifted rightward. DR rats did not develop hypertension and seved as age-matched controls. A 31% (p < 0.05) increase in the %CS in DS-4WHSD myocytes compared to DR-4WHSD myocytes with a trend of a parallel increase in Ca2+ transient amplitude was found. There was no difference in the Ca2+ transient parameters between DR and DS at 12WHSD, but an 18% (p < 0.01) decrease occurred in peak [Ca2+]i in DS myocytes between 4WHSD and 12WHSD. In DS-12WHSD, the time to peak shortening and the time from peak shortening to 50% and 90% relaxation was significantly prolonged by 27%, 44%, and 38%, respectively, as compared to the age-matched DR myocytes.

CONCLUSION

Our results indicated that: (I) normal Ca2+ homeostasis is preserved at the stage of compensated hypertrophy; (2) the early signs of isolated myocyte dysfunction were a prolongation of the shortening and relaxation time course without an abnormal time course of the Ca2+ transient. Thus, in the hypertensive Dahl salt rat model, abnormal Ca2+ handling appears neither to precede nor initiate the transition to failure.

Animal models of cardiovascular disease for pharmacologic drug development and testing: appropriateness of comparison to the human disease state and pharmacotherapeutics

For proper drug development, targeting and testing the use of suitable animal models that are well controlled with regard to duration, degree, and stage of the disease are vitally needed. Furthermore reliable phenotyping and genotyping with regard to functional physiology as well as cellular biochemistry and molecular biology are vital to early decision making in drug discovery, development, and successful clinical development. The use of animal models allows the design of clinical trials without the complication of having to impose "accepted treatment modalities" on top of investigative agents. With the availability of human myocardium for study as a result of cardiac transplantation programs, experimental findings previously reported in several animal models of heart disease have been questioned with regard to suitability for comparison to the human condition. With the development and application of sophisticated techniques and biochemical assays to the study of heart tissue several adaptive changes have been identified and labeled "markers of heart failure." Several animal models share some of these adaptive changes in common with failing human myocardium, but not others. The goal of this report is to point out similarities and differences reported to date in failing and nonfailing human myocardium to that reported in animal models of human heart disease. This discussion indicates important dissimilarities found in several key animal models that have resulted in the development of cardioactive agents and therapeutic interventions for the treatment of human heart disease and the unexpected outcomes. Although focusing on heart failure, a vital goal of this report is to emphasize some key principles supporting the need for clear, comprehensive, and unbiased evaluation of animal models currently in use to study any disease condition, as well as the need for further model development and study in open collaborative efforts.

Decreased energy reserve in an animal model of dilated cardiomyopathy. Relationship to contractile performance

An animal model was used to test the hypothesis that in heart failure the decrease in the ability to resynthesize ATP through the creatine kinase (CK) reaction (which we call energy reserve) contributes to the inability of the heart to maintain its normal function and contractile reserve. One-week-old turkey poults were fed furazolidone for 14 days to induce dilated cardiomyopathy. Isolated Langendorff-perfused hearts from these myopathic animals showed a 73% decrease in baseline isovolumic contractile performance. Neither increasing [Ca2+]o nor electrical pacing rate increased isovolumic contractile performance. Measured by 31P nuclear magnetic resonance magnetization transfer and chemical assay, ATP concentration was decreased by 23%, phosphocreatine concentration by 42%, CK enzyme activity by 34%, and the pseudo first-order rate constant for the CK reaction by 50%. Measured CK reaction velocity decreased by 71%. The reduced ability to increase cardiac performance in response to increasing [Ca2+]o in hearts with lower CK reaction velocity was reproduced in part by feeding a separate group of turkey poults beta-guanidino-propionic acid to specifically reduce CK reaction velocity by decreasing guanidino substrate concentration. These hearts had normal baseline performance but blunted contractile reserve. These observations provide further support for the hypothesis that a decrease in energy reserve via the CK system contributes to reduced cardiac function in the failing heart.

Effect of a high omega-3 fatty acid diet on cardiac contractile performance in Oncorhynchus mykiss

OBJECTIVE

Omega-3 fatty acids have been implicated in the amelioration of cardiovascular disease in humans. Since these fatty acids are found in salmonid fish and are known to be essential for all salmonids, this study was undertaken to determine the effect of a high dietary intake of omega-3 fatty acids on the function of trout myocardium.

METHODS

Rainbow trout (Oncorhynchus mykiss) from a single stock population were divided into two groups and fed either a diet high in omega-3 fatty acids (i.e. 4.0%) or low in omega-3 fatty acids (i.e. 2.1%) for 3 months. Heart function was studied at the whole heart and isolated muscle level.

RESULTS

In whole heart preparations, peak developed pressures in freely ejecting hearts from salmonids fed the high omega-3 fatty acid diet were significantly greater than the hearts from salmonids fed the low omega-3 fatty acid diet (21 +/- 1.5 vs. 11.5 +/- 0.9 mmHg respectively, P < 0.05). These data correlated with results from isolated muscle preparations of myocardium from fish fed high and low omega-3 fatty acid diets (4.12 +/- 0.32 vs. 3.08 +/- 0.28 mN/mm2 respectively, P < 0.05). The calcium uptake rate of heart homogenates from fish fed the high omega-3 diet was slower and sarcoplasmic reticulum Ca2+ ATPase activity was lower. The myofilament force-calcium relationship in myocardium from trout fed the low omega-3 diet was shifted leftward on the calcium axis to lower intracellular calcium concentrations (delta 0.4 pCa units) compared to mammalian myocardium. This resulted in greater activation at lower intracellular calcium concentrations. However, trouts fed diets high in omega-3 fatty acids had [Ca2+] required for half maximal activation more similar to what has been reported for mammalian myocardium (delta 0.1 pCa unit). Furthermore, the myofilaments of trout hearts appear to show less cooperativity (Hill coefficient approximately 1) than has been found in mammalian myocardium (Hill coefficient > or = 2).

CONCLUSIONS

Our experimental results demonstrate for the first time that dietary omega-3 fatty acid content affects myocardial force of contraction by affecting calcium metabolism and myofilament calcium-activation.

Is contractility depressed in the failing human heart?

Is contractility depressed in the failing human heart? The question must be approached in a stringent manner. Myocardium from failing human hearts has been shown to generate normal physiological force under the ideal conditions of low stimulation and an adequate energy supply. Nevertheless, even when subjected to physiologically conducive conditions, failing myocardium experiences a slowed relaxation, adversely affecting the diastolic properties of the heart. In addition, experiments have shown that increasing the contraction rates of failing hearts clearly results in lowered force and pressure evolution. This information indicates a decrease in contractile reserve in both a systolic and diastolic sense. Not surprisingly, the term end-stage heart failure becomes questionable when applied to myocardium obtained from patients undergoing cardiac transplantation. A number of studies involve such myocardium from feasible regions of the heart perfused within ideal physiological conditions yielding, at times, nonfailing performance. Therefore, it becomes imperative to bear in mind the role of such myocardium within the framework of the entire diseased heart.

Comparison of twitch force and calcium handling in papillary muscles from right ventricular pressure overload hypertrophy in weanling and juvenile ferrets

OBJECTIVE

The aim was to compare differences in peak twitch force occurring despite similar degrees of right ventricular hypertrophy in ferrets with pulmonary artery banding at either weanling or juvenile age.

METHODS

After inducing pressure overload hypertrophy by banding the pulmonary artery of weanling and juvenile age ferrets, mechanical function (that is, isometric twitch force and passive stiffness), intracellular [Ca2+] using the calcium indicator aequorin, markers of myocardial energy supply, and quantified connective tissue content were studied.

RESULTS

It was previously found that there was a reduced peak isometric twitch force despite normal [Ca2+]i in juvenile banded ferrets age 10-12 weeks with right ventricular pressure overload hypertrophy (POHj). In the present study we report findings in banded weanling ferrets (POHw) age 7 weeks. POHw animals showed a similar degree of hypertrophy to that found in the POHj. However, there was a greater peak twitch force in hypertrophied muscles at higher [Ca2+]o. There was no difference in peak [Ca2+]i: -3.1(SEM 0.1) v -3.1(0.3) (log fractional luminescence) at 16 mM [Ca2+]o for control and POHw, respectively. Connective tissue content for control animals was 10(1)% versus 10(2)% in POHw. Despite a lack of quantitative change in connective tissue content or resting [Ca2+]i in POHw, passive stiffness in papillary muscles was increased. Retrospective analysis of tissue from POHj revealed a connective tissue content of 24(6.8)% (P << 0.001). Thus the decreased peak twitch force reported in POHj might in part be due to an increase in fibrous connective tissue. In this study, lactate dehydrogenase was significantly higher (38%) in POHw animals. In contradistinction, total creatine kinase activity and total creatine content were significantly less (22%) in hearts from POHj animals, indicating differences in myocyte remodelling despite similar degrees and durations of hypertrophy.

CONCLUSIONS

Comparison of POHw and POHj showed that, when there is restructuring of the extracellular space in terms of increased fibrosis, there is also molecular remodelling in the myocyte, as demonstrated by a decrease in the creatine kinase system.

Enalapril treatment increases cardiac performance and energy reserve via the creatine kinase reaction in myocardium of Syrian myopathic hamsters with advanced heart failure

BACKGROUND

Converting enzyme inhibitor treatment of congestive heart failure slows progression to failure and reduces mortality rate. It is known whether these benefits are due solely to improved hemodynamics or also to improved myocyte energetics. This study examines the effect of enalapril treatment on both isovolumic contractile performance and its biochemical correlate, flux through the creatine kinase (CK) system, in an animal model of severely failing myocardium.

METHODS AND RESULTS

Seven-month-old Syrian cardiomyopathic (TO-2 strain) and normal golden Syrian (FIB strain) hamsters were each randomly assigned to one of three groups supplied daily with either no, low (25 mg/kg body wt), or high (100 mg/kg body wt) doses of enalapril for 12 to 14 weeks. At 10 months of age, all substrates and products and flux through the CK reaction were measured in isolated perfused hearts by 31P magnetization transfer and chemical assay. Compared with normal hamsters, the myopathic hamsters exhibited significantly lower body weights and higher biventricular heart weights, which were partially reversed by drug treatment. The Langendorff-perfused hearts showed decreased isovolumic contractile performance with identical load conditions. This was partially reversed by drug treatment. In the failing hearts, the following substrate and product concentrations and enzyme activities were decreased compared with nonfailing hearts but were unchanged by drug treatment: ATP (-28%), phosphocreatine (-48%), free creatine (-64%), ADP (-51%), and CK (-34%, primarily MM isoenzyme). Flux through the CK reaction for the untreated cardiomyopathic hamster hearts was decreased by 67%, and this decrease was almost completely reversed by enalapril treatment. The increased CK flux is due to an increase in the rate constant for the reaction, since substrate concentrations are unchanged, and is not predicted by the rate equation. In enalapril-treated failing hearts, phosphoryl transfer via the CK reaction increased with contractile performance. This was not observed in the nonfailing hearts, in which energy reserve is adequate to support changes in contractile performance.

CONCLUSIONS

Decreased flux through CK reaction leads to decreased capacity for ATP synthesis and may contribute to decreased contractile performance in cardiomyopathic hamster hearts. Enalapril treatment results in increased phosphoryl transfer through the CK reaction in failing myocardium, and this increase is coupled to improved cardiac performance. Decreased CK flux in failing hearts is due to a combination of decreased Vmax and lower guanidino pool; this mechanism fails to explain changes in CK flux in enalapril-treated failing hearts.

The relation of the location of haptics of posterior chamber intraocular lenses and peripheral anterior synechia

PURPOSE

To investigate the occurrence, outcome and influencial factors of the peripheral anterior synechia (PAS) following implantation of posterior chamber intraocular lenses for finding a way to reduce the PAS.

SUBJECTS

40 eyes of 38 senile cataract patients with normal chamber angle and intraocular pressure (IOP) preoperatively were examined.

METHODS

Extracapsular cataract extraction was performed under microscope with insertion of a posterior chamber lens implant vaulted anteriorly by 10 degrees. Gonioscopy and slit-lamp examination and photography of the operated eyes were performed 3 to 6 months postoperatively.

RESULTS

PAS were found in 20 (50%) of the 40 eyes. Among the 20 eyes with PAS the locations of 23 haptics in 17 eyes corresponded with those of the PAS. PAS were seen more frequently with vertically sulcus-fixated haptics than with the horizontally capsular-fixated haptics, showing a significant difference (P < 0.05). 88% of the eyes with PAS had pupillary deformation, but their visual acuities and IOP were not affected.

CONCLUSIONS

PAS is more likely to occur with vertically sulcus-fixated IOL. Rotating the capsular-fixated haptics to the horizontal position may reduce the incidence of PAS. Gonioscopy should be a routine follow-up examination.

[Gonioscopic observation after posterior chamber intraocular lens implantation]

6 months after senile extra-capsular cataract extraction and posterior chamber intraocular lens (IOL) implantation, Goldmann gonioscopy was performed on 30 eyes having undertaken the surgery. Peripheral anterior synechiae (PAS) were found in 17 eyes (56%). PAS overlying the positions of 20 lens haptics were observed in 15 eyes. It is easier to develop PAS in eyes with vertically fixed haptics than in eyes with horizontally fixed ones. The causes and the consequences of PAS were discussed. It is suggested that during the follow-up, routine gonioscopic observation after posterior chamber IOL implantation be necessary.

Coupling of calcium to the interaction of troponin I with troponin C from cardiac muscle

The interaction of troponin I (CTnI) with troponin C (CTnC) from bovine cardiac muscle was studied using CTnC modified at Cys35 and Cys84 with the fluorescent probe 2-[(4'-iodoacetamido)-anilino]naphthalene-6-sulfonic acid (CTnCIAANS). The association constant for complex formation between the two proteins was determined at 20 degrees C in 0.4 M KCl, 1 mM DTT, 1 mM EGTA, and 25 mM MOPS, pH 7.2. In the presence of EGTA, Mg2+, and Ca2+ these constants were 1.46 x 10(7), 4.1 x 10(7), and 12.7 x 10(7) M-1, respectively, with corresponding free energy values of -9.62, -10.23, and -10.88 kcal mol-1. The CTnI-CTnCIAANS complex was stabilized by -0.61 kcal when the two Ca/Mg sites of CTnCIAANS were saturated with Mg2+ and by -1.26 kcal when all three Ca2+ sites were occupied by Ca2+. These results suggest that calcium activation in cardiac muscle may be accompanied by a coupling free energy of -0.65 kcal. This value is a factor of 4 smaller than the value previously determined, using a similar method, for the (troponin I).(troponin C) complex from skeletal muscle [Wang, C.-K., & Cheung, H.C. (1985) Biophys. J.48, 727-739]. Since CTnC has only one Ca(2+)-specific site and troponin C from skeletal muscle has two such sites, the present result is a factor of 2 smaller than that for the skeletal complex on the basis of a single specific site. Phosphorylation of CTnI by 3',5'-cyclic AMP-dependent protein kinase resulted in a decrease of the association constants by a factor of 2.5-3.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of MCI-154 and caffeine on Ca(++)-regulated interactions between troponin subunits from bovine heart

We studied the effects of MCI-154 (6-[4-(4-pyridyl)aminophenyl]-4,5- dihydro-3(2H)-pydridazinone hydrochloride) and caffeine on the regulation of Ca++ in the interaction between troponin subunits from bovine hearts by using fluorescence spectroscopy. The titration of MCI-154 to bovine cardiac troponin C (TnC) resulted in a concentration-dependent change in intrinsic fluorescence, indicating that MCI-154 may induce conformational changes and perturb the microenvironments of the intrinsic fluorophores. MCI-154-induced changes in the rotational correlation times obtained from fluorescently modified TnC and its complex with cardiac troponin I (TnI) indicate that the effect of MCI-154 may be highly correlated with a gross alteration in the overall molecular shape of TnC. A right shift in the-fluorescence curve with a significant decrease in maximal fluorescence intensity was observed in the presence of MCI-154 in isolated TnC, indicating a decrease in the affinity of TnC for Ca++. However, in the reconstituted binary (TnC.TnI) and ternary (TnC.TnI.TnT) complexes the pCa-curve was shifted to the left under similar conditions. These data indicate that the complexation of TnC with TnI and TnT resulted in an increase in the affinity of TnC for Ca++ in the presence of MCI-154. In the studies of caffeine effect, the results showed that the effect of caffeine on isolated TnC was similar to that of MCI-154. Caffeine (0.5 microM) shifted the pCa-fluorescence curve to the right by 0.4 U in the binary complex and to the left by 0.2 U in the ternary complex at pCa50% when compared to the curve in the absence of caffeine.(ABSTRACT TRUNCATED AT 250 WORDS)

[Ca2+]i in human heart failure: a review and discussion of current areas of controversy

Multiple abnormalities have been reported in the setting of human heart failure. It is unclear whether detected changes reflect adaptive alterations in myocardium subjected to increased and sustained hemodynamic overload or are pathogenic to the disease process. As a result of the observation that the primary defect in heart failure is decreased pump function, investigators have concentrated their efforts on determining systolic [Ca2+]i as a logical corollary and a causative mechanism for contractile dysfunction. A simple cause and effect relationship has therefore been proposed with regard to contractile dysfunction and [Ca2+]i. Yet some investigators have found no difference in peak systolic [Ca2+]i between failing and non-failing human myocardium, whereas others have found peak [Ca2+]i to be significantly reduced in failing hearts. Resting calcium concentrations have been reported either to be elevated in failing human myocardium or not different from non-failing human myocardium. Investigators should now appreciate that the force-calcium relationship is not a simple relationship. One must take into account the prolonged time course and slowed mobilization of [Ca2+]i as opposed to simply peak [Ca2+]i. When put in perspective of mechanisms and determinants of the Ca(2+)-force relationship, we begin to realize that failing human myocardium has the "potential" to generate normal levels of force. Only when stressed by [Ca2+]i overload and/or frequency perturbation does myocardium from patients with end-stage heart disease demonstrate contractile failure. Although [Ca2+]i availability and mobilization are likely to play a role in the systolic as well as diastolic dysfunction reported in human heart failure, it is likely that other mechanisms are involved as well (e.g., myocardial energetics). Myocardial energetics is directly related to [Ca2+]i and mobilization in failing human myocardium, because metabolites, e.g., ADP, inhibit pumps, such as sarcoplasmic reticulum Ca2+ ATPase activity. We therefore conclude that there is a role for intracellular calcium mobilization and myocardial energetics for systolic and diastolic dysfunction seen in human heart failure.

Pathophysiological and biochemical characterisation of an avian model of dilated cardiomyopathy: comparison to findings in human dilated cardiomyopathy

OBJECTIVE

With the recent availability of human myocardium, many animal models have been shown to be unsuitable as models of human heart failure. The aim of this study was to describe the pathophysiological changes in a model of dilated cardiomyopathy in turkey poults and to compare them to results obtained from failing human hearts.

METHODS

After receiving furazolidone for 2-3 weeks, animals developed cardiomyopathy (Fz-DCM) and were studied at the whole heart and isolated muscle level. Myofibrillar ATPase activity and noradrenaline turnover were determined in tissue homogenates in failing and non-failing control hearts.

RESULTS

Fz-DCM animals had greater heart weights, heart weight/body weight ratios, and end diastolic volumes. Fractional shortening of the left ventricle and systolic blood pressures were reduced (p < 0.01) in myopathic animals. Isolated perfused hearts had lower peak developed pressures (p < 0.01). Isolated muscle preparations showed no significant differences in peak twitch forces between control and Fz-DCM muscles at a 1 Hz stimulation rate. The relationship between force and frequency of stimulation was positive in control muscles up to 1.7 Hz, whereas in Fz-DCM muscles the relationship was sharply negative above 1 Hz. Time to 80% relaxation was markedly slower in the Fz-DCM muscles. Although [Ca2+]o responsiveness was similar for Fz-DCM and normal animals, responsiveness to isoprenaline was significantly reduced in Fz-DCM hearts. Cardiomyopathic animals displayed diminished noradrenaline content in the left ventricle. Fractional noradrenaline turnover was higher (p < 0.05) in the cardiomyopathic birds. In skinned fibre preparations from control and Fz-DCM hearts calcium activations were similar. Maximum myofibrillar ATPase activities were, however, significantly lower in myopathic animals and myofibrillar protein content was reduced by 25%.

CONCLUSIONS

In this model of dilated cardiomyopathy: (1) relaxation is markedly prolonged; (2) the response to beta adrenergic stimulation is diminished; (3) Mg-ATPase activities and myofibrillar protein content are reduced; and (4) sympathetic activity in the heart is markedly increased with depletion of noradrenaline stores. Furthermore, a reduction in tissue noradrenaline content per se is a misleading index of the dynamic state of cardiac noradrenaline stores. With its similarities to human cardiomyopathy, this model promises to provide new insights into the pathophysiology and progression of dilated cardiomyopathy.

Differences in cardioprotective efficacy of adrenergic receptor antagonists and Ca2+ channel antagonists in an animal model of dilated cardiomyopathy. Effects on gross morphology, global cardiac function, and twitch force

Turkey poults fed furazolidone (Fz) in high concentrations (700 ppm) develop dilated cardiomyopathy (Fz-DCM). We tested whether five cardioactive agents were cardioprotective in this model of heart failure, ie, whether they prevented dilatation and wall thinning and improved contractile performance. We compared the effects of chronic administration of a beta 1-selective and a nonselective beta-receptor antagonist, an alpha-receptor antagonist, and two Ca2+ channel antagonists in the presence of Fz administration. The greatest cardioprotection was found with treatment with either propranolol or nifedipine. At the gross morphological level, the effect of propranolol (a nonselective beta-adrenergic antagonist) was greater than the effect of atenolol (a selective beta 1-adrenergic antagonist), and the effect of nifedipine was greater than that of verapamil (Ca2+ channel antagonists), with all agents more cardioprotective than phenoxybenzamine (an alpha 1-adrenergic > alpha 2-adrenergic antagonist). Differences in cardioprotective efficacy of each agent increased with increased concentration. These data indicate that the dose and choice of a specific type of Ca2+ channel antagonist or beta-receptor antagonist might be important in the treatment of dilated cardiomyopathy. All agents that were cardioprotective caused similar functional improvements at both the whole heart and isolated muscle levels. Compared with control animals, Fz-DCM animals showed a significant reduction in peak left ventricular (LV) developed pressure (92 +/- 17 versus 143 +/- 24 mm Hg, P < .05), +dP/dt (1151 +/- 219 versus 2454 +/- 549 mm Hg/s), and -dP/dt (1128 +/- 291 versus 1875 +/- 396 mm Hg/s), with a significant increase in LV end-diastolic volumes (2.8 +/- 0.7 versus 0.16 +/- 0.1 mL for control animals, P < .05). In contradistinction, LV + dP/dt and -dP/dt values for animals receiving Fz plus a cardioactive agent that demonstrated cardioprotection were not significantly different from control values. Peak LV developed pressures were also similar for Fz animals receiving an agent that demonstrated cardioprotection and control animals not receiving any pharmacologic agent. Isolated muscles from Fz-DCM animals as well as animals receiving Fz plus cardioprotective pharmacologic agents responded normally with regard to increasing extracellular Ca2+ concentrations. Peak twitch forces were greater for animals receiving cardioprotective agents plus Fz than control animals not receiving any pharmacologic agents or Fz alone. At higher stimulation rates, Fz-DCM muscles demonstrated a significantly reduced peak twitch force (4 +/- 0.5 versus 1.5 +/- 0.4 g/mm2 for control muscles versus Fz-DCM muscles, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Rotational dynamics of skeletal muscle troponin C

Upon excitation by 280 nm, the intensity decay of the 2 tyrosine residues (residues 10 and 109) of rabbit skeletal muscle troponin C is resolved into three components. The anisotropy decay in the absence of divalent cation is biphasic with a short correlation time of 0.67 ns and a long correlation time of 9.23 ns. The limiting anisotropy is 0.225, considerably lower than the value expected for immobilized tyrosine. Upon excitation by 290 nm, the anisotropy decay is also biphasic, and the limiting anisotropy increases to 0.274. The recovery of anisotropy by excitation at a wave-length near the red edge of the tyrosine absorption spectrum is evidence of fluorescence resonance energy transfer between the two tyrosines. For energy transfer to occur, the average separation between the 2 tyrosines is unlikely much larger than the Förster distance Ro, congruent to 10 A, and this close proximity of the residues would require a highly distorted dumbbell shape of troponin C in solution. These results are consistent with a flexible central helix, which either has a segmental flexibility with large amplitude or results in a spectrum of conformations including those in which the two globular domains are in a very close proximity.

Phosphocreatine T1 measurements with and without exchange in the heart

The intrinsic phosphocreatine (PCr) T1 values measured by time-dependent magnetization transfer in isolated perfused rat, hamster, and turkey hearts were indistinguishable. The value of 3.5 +/- 0.3 s for the rat heart is similar to values measured by other magnetization transfer methods. Irreversibly inhibiting the phosphoryl exchange between PCr and ATP in the rat heart using iodoacetamide changed the apparent T1 values of the two exchanging species when measured by inversion recovery: The apparent T1 of PCr increased from 1.92 +/- 0.06 s to 3.55 +/- 0.06 s, in excellent agreement with the intrinsic T1 measured by magnetization transfer. The apparent T1 of [gamma-P]ATP decreased from 0.92 +/- 0.07 s to 0.44 +/- 0.03 s. The value for the T1 of [gamma-P]ATP in hearts with inhibited phosphoryl exchange was similar to T1 values for [alpha-P]ATP and [beta-P]ATP, which remained unchanged. This illustrates that apparent T1 values for PCr and [gamma-P]ATP measured by inversion recovery in the presence of exchange are average T1 values in between the intrinsic values. The large differences between the intrinsic T1 measured by magnetization transfer and the T1 measured by inversion recovery makes the use of the appropriate value in different applications quantitatively important.

Time-resolved tryptophan emission study of cardiac troponin I

We have carried out a time-resolved fluorescence study of the single tryptophanyl residue (Trp-192) of bovine cardiac Tnl (CTnl). With excitation at 300 nm, the intensity decay was resolved into three components by a nonlinear least-squares analysis with lifetimes of 0.60, 2.22, and 4.75 ns. The corresponding fractional amplitudes were 0.27, 0.50, and 0.23, respectively. These decay parameters were not sensitive to complexation of CTnl with cardiac troponin C (CTnC), and magnesium and calcium had no significant effect on the decay parameters. After incubation with 3':5'-cyclic AMP-dependent protein kinase, the intensity decay of CTnl required a fourth exponential term for satisfactory fitting with lifetimes of 0.11, 0.81, 1.95, and 6.63 ns and fractional amplitudes of 0.06, 0.37, 0.27, and 0.29, respectively. When bound to CTnC, the intensity decay of phosphorylated CTnl (p-CTnl) also required four exponential terms for satisfactory fitting, but the longest lifetime increased by a factor of 1.7. The decay parameters obtained from the complex formed between p-CTnl and CTnC were not sensitive to either magnesium or calcium. The anisotropy decay was resolved into two components with rotational correlation times of 0.90 and 23.48 ns. Phosphorylation resulted in a decrease of the long correlation time to 14.61 ns. The anisotropy values recovered at zero time suggest that the side chain of the Trp-192 had considerable subnanosecond motional freedom not resolved in these experiments. Within the CTnl.CTnC complex, the unresolved fast motions appeared sensitive to calcium binding to the calcium-specific site of CTnC. The observed emission heterogeneity is discussed in terms of possible excited-state interactions in conjunction with the predicted secondary structure of CTnl. The loss of molecular asymmetry of cardiac troponin I induced by phosphorylation as demonstrated in this work may be related to the known physiological effect of beta-agonists on cardiac contractility.