Yoshito Wakao

Cardiac involvement in Beagle-based canine X-linked muscular dystrophy in Japan (CXMDJ): electrocardiographic, echocardiographic, and morphologic studies

BackgroundCardiac mortality in Duchenne muscular dystrophy (DMD) has recently become important, because risk of respiratory failure has been reduced due to widespread use of the respirator. The cardiac involvement is characterized by distinctive electrocardiographic abnormalities or dilated cardiomyopathy, but the pathogenesis has remained obscure. In research on DMD, Golden retriever-based muscular dystrophy (GRMD) has attracted much attention as an animal model because it resembles DMD, but GRMD is very difficult to maintain because of their severe phenotypes. We therefore established a line of dogs with Beagle-based canine X-linked muscular dystrophy in Japan (CXMDJ) and examined the cardiac involvement.MethodsThe cardiac phenotypes of eight CXMDJ and four normal male dogs 2 to 21 months of age were evaluated using electrocardiography, echocardiography, and histopathological examinations.ResultsIncreases in the heart rate and decreases in PQ interval compared to a normal littermate were detected in two littermate CXMDJ dogs at 15 months of age or older. Distinct deep Q-waves and increase in Q/R ratios in leads II, III, and aVF were detected by 6–7 months of age in all CXMDJ dogs. In the echocardiogram, one of eight of CXMDJ dogs showed a hyperechoic lesion in the left ventricular posterior wall at 5 months of age, but the rest had not by 6–7 months of age. The left ventricular function in the echocardiogram indicated no abnormality in all CXMDJ dogs by 6–7 months of age. Histopathology revealed myocardial fibrosis, especially in the left ventricular posterobasal wall, in three of eight CXMDJ dogs by 21 months of age.ConclusionCardiac involvement in CXMDJ dogs is milder and has slower progression than that described in GRMD dogs. The distinct deep Q-waves have been ascribed to myocardial fibrosis in the posterobasal region of the left ventricle, but our data showed that they precede the lesion on echocardiogram and histopathology. These findings imply that studies of CXMDJ may reveal not only another causative mechanism of the deep Q-waves but also more information on the pathogenesis in the dystrophin-deficient heart.

Diurnal Variations of Blood Pressure in Cats

Blood pressure (BP) was analyzed invasively using the telemetry system in unanesthetized, unrestrained healthy adult mongrel cats. After surgical implantation of a telemetry transmitter, BP was transiently elevated due to the invasive nature of the surgery, but it was gradually decreased. BP was largely stabilized seven to ten days postsurgery. Once BP was settled, systolic, diastolic and mean BPs(2) were obtained at 5-min intervals in individual cats. Hourly averages of these BP values revealed a diurnal variation with two peaks at 8:00 and 19:00. We also found that BP was significantly higher when cats were active compared to when they were sleeping or at rest (p<0.05). The average 24-hr BP in 20 healthy cats was 118.4+/-11.0 (systolic), 78.0+/-8.7 (diastolic) and 94.8+/-9.5 mmHg (mean) by the telemetry system.

Selective Vacuolar Degeneration in Dystrophin-Deficient Canine Purkinje Fibers Despite Preservation of Dystrophin-Associated Proteins With Overexpression of Dp71

Background— Respiratory support therapy significantly improves life span in patients with Duchenne muscular dystrophy; cardiac-related fatalities, including lethal arrhythmias, then become a crucial issue. It is therefore important to more thoroughly understand cardiac involvement, especially pathology of the conduction system, in the larger Duchenne muscular dystrophy animal models such as dystrophic dogs. Methods and Results— When 10 dogs with canine X-linked muscular dystrophy in Japan (CXMDJ) were examined at the age of 1 to 13 months, dystrophic changes of the ventricular myocardium were not evident; however, Purkinje fibers showed remarkable vacuolar degeneration as early as 4 months of age. The degeneration of CXMDJ Purkinje fibers was coincident with overexpression of Dp71 at the sarcolemma and translocation of μ-calpain to the cell periphery near the sarcolemma or in the vacuoles. Immunoblotting of the microdissected fraction showed that μ-calpain–sensitive proteins such as desmin and cardiac troponin-I or -T were selectively degraded in the CXMDJ Purkinje fibers. Utrophin was highly upregulated in the earlier stage of CXMDJ Purkinje fibers, but the expression was dislocated when vacuolar degeneration was recognized at 4 months of age. Nevertheless, the expression of dystrophin-associated proteins α-, β-, γ-, and Δ-sarcoglycans and β-dystroglycan was well maintained at the sarcolemma of Purkinje fibers. Conclusions— Selective vacuolar degeneration of Purkinje fibers was found in the early stages of dystrophin deficiency. Dislocation of utrophin besides upregulation of Dp71 can be involved with this pathology. The degeneration of Purkinje fibers can be associated with the distinct deep Q waves in ECG and fatal arrhythmia seen in dystrophin deficiency.

Arteriovenous shunts resembling patent ductus arteriosus in dogs: 3 cases

Three dogs presented for the evaluation of cardiac murmurs were diagnosed with aberrant arteriovenous shunts. All cases demonstrated the following findings: 1) relatively soft continuous murmur loudest at the left heart base resembling patent ductus arteriosus (PDA); 2) shunt flow signals in the pulmonary artery on echocardiography; and 3) no PDA on selective angiography, but evidence of anomalous shunting vessels from thoracic aorta to pulmonary vasculature. An aberrant arteriovenous shunt should be considered when a continuous murmur of relatively small intensity is heard.

Proximal Paraconal Interventricular Myocardial Bridge in Dog: Ultrastructural Characterization

The ultrastructure of the dog myocardial bridges (MB), named here the proximal paraconal interventricular-myocardial bridge (PPI-MB), was examined to determine if its structure is identical to that of ordinary cardiac muscle. This study is preparatory to the establishment of PPI-MB as a physical and physiological model system to examine the influence of MB on coronary flow in cardiac function. Five of 46 dog hearts examined possessed PPI-MB, the occurrence of which was independent of sex, age and breed. The dog PPI-MB was localized in a limited area in the proximal third of the paraconal interventricular groove. PPI-MB myocytes and myofibrils were arranged quite straight and smooth, with minimum branching. PPI-MB myocytes formed side-by-side cell junctions through the mediation of mitochondria. Connective tissue elements were involved in terminal cell adhesion to form the myomyous junction beside the intercalated disc. The excitation conductive system of sarcoplasmic reticulum-T tubule often showed a triad. Numerous nerve axons or nerve ending-like structures appeared. Many structural views deviated somewhat from common cardiac muscle structure. This paper represents the first detailed description of PPI-MB muscle.

Feasibility of radial and circumferential strain analysis using 2D speckle tracking echocardiography in cats

The purpose of the present study is to investigate the feasibility of strain analysis using speckle tracking echocardiography (STE) in cats and to evaluate STE variables in cats with hypertrophic cardiomyopathy (HCM). Sixteen clinically healthy cats and 17 cats with HCM were used. Radial and circumferential strain and strain rate variables in healthy cats were measured using STE to assess the feasibility. Comparisons of global strain and strain variables between healthy cats and cats with HCM were performed. Segmental assessments of left ventricle (LV) wall for strain and strain rate variables in cats with HCM were also performed. As a result, technically adequate images were obtained in 97.6% of the segments for STE analysis. Sedation using buprenorphine and acepromazine did not affect any global strain nor strain rate variable. In LV segments of cats with HCM, reduced segmental radial strain and strain rate variables had significantly related with segmental LV hypertrophy. It is concluded that STE analysis using short axis images of LV appeared to be clinically feasible in cats, having the possibility to be useful for detecting myocardial dysfunctions in cats with diseased heart.

The variation in excretory urinary glycyl-prolyl dipeptidyl aminopeptidase in dogs

We studied the excretory variation of urinary glycyl-prolyl dipeptidyl aminopeptidase (GP-DAP, EC 3.4.14.5) in dogs. Adult domestic mongrel dogs (seven males and nine females, 7.5 to 13 kg bodyweight) which were considered to be healthy by laboratory tests were used. Urine and blood samples were obtained every four hours. Urine volume was measured for each sample and urine GP-DAP activity, and creatinine levels were determined. Creatinine clearance, creatinine excretion, GP-DAP activity and GP-DAP index (GP-DAP/Cr ratio) did not show any significant variation between the time periods. However, urine volume and urinary GP-DAP excretion significantly increased from 8:00 am to 12:00 pm. The GP-DAP index in spot urine samples showed low correlation with 24 hour GP-DAP excretion. In addition, a sex difference was observed in GP-DAP excretion. In conclusion, urinary GP-DAP excretion showed a circadian variation and sex difference. Therefore, GP-DAP in spot urine is not of use for the detection of renal disorders, and the 24-hour excretion value of GP-DAP should be determined.

Comparison of the effects of candesartan cilexetil and enalapril maleate on right ventricular myocardial remodeling in dogs with experimentally induced pulmonary stenosis

OBJECTIVE To compare the effects of candesartan cilexetil and enalapril maleate on right ventricular myocardial remodeling in dogs with experimentally induced pulmonary stenosis. ANIMALS 24 Beagles. PROCEDURES 18 dogs underwent pulmonary arterial banding (PAB) to induce right ventricular pressure overload, and 6 healthy dogs underwent sham operations (thoracotomy only [sham-operated group]). Dogs that underwent PAB were allocated to receive 1 of 3 treatments (6 dogs/group): candesartan (1 mg/kg, PO, q 24 h [PABC group]), enalapril (0.5 mg/kg, PO, q 24 h [PABE group]), or no treatment (PABNT group). Administration of treatments was commenced the day prior to surgery; control dogs received no cardiac medications. Sixty days after surgery, right ventricular wall thickness was assessed echocardiographically and plasma renin activity, angiotensin-converting enzyme activity, and angiotensin I and II concentrations were assessed; all dogs were euthanatized, and collagenous fiber area, cardiomyocyte diameter, and tissue angiotensin-converting enzyme and chymase-like activities in the right ventricle were evaluated. RESULTS After 60 days of treatment, right ventricular wall thickness, cardiomyocyte diameter, and collagenous fiber area in the PABNT and PABE groups were significantly increased, compared with values in the PABC and sham-operated groups. Chymase-like activity was markedly greater in the PABE group than in other groups. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that treatment with candesartan but not enalapril effectively prevented myocardial remodeling in dogs with experimentally induced subacute right ventricular pressure overload.

A semi-immobilization of a partial auricle induces hypertrophy and ultrastructural alteration of cardiomyocytes.

Semi-immobilization of a partial area of the ventral edge, lateral epicardium of the left auricle (ventrolateral of left auricle), by using quick adhesion glue induces moderate hypertrophy of myocytes with an average increase of 34% in cross-sectional area. Intercellular connective tissues increased, and cellular sizes varied markedly. The ultrastructure of immobilized (semi-immobilized) myocytes commonly exhibited degenerating features in myofibrils, various cytoplasmic organelles including mitochondrial cristae and sarcoplasmic reticulum (SR) were disrupted, and T-tubules disappeared. Z-line streaming and widening (hypertrophic Z-line, rod bodies) and increase of metabolic particle deposition are typical phenomena in addition to intercalated disc (Id) disorganization. The results suggest that semi-immobilization of the auricle induces hypertrophy of myocytes in association with degeneration and disruption of myofibrils and other cytoplasmic organelles, and an increase of intercellular connective tissues, rather than increase of myofibril mass. This is the first study to immobilize only a part of the heart rather than the whole animal. Our results using artificial immobilization of cardiac myocytes were extremely significant since the structural alterations obtained were similar to that observed in cardiomyopathies. This suggests that myocytes progressing to heart failure are also subjected to inhibition of movement. Therefore, this experiment may prove very useful as a model for studying the functional effect of heart failure observed in cardiomyopathy.

Pharmacokinetics of nicorandil in dogs with mild mitral regurgitation.

The aim of this study was to examine the pharmacokinetics of nicorandil, a hybrid of an adenosine triphosphate-sensitive potassium channel opener and a nitrate, and to estimate its clinical doses in dogs with mild mitral valve regurgitation (MR). Nicorandil (0.1, 0.3, and 1.0 mg/kg) was administered orally to normal dogs and those with experimentally-induced MR, and its plasma concentrations were analyzed using high-performance liquid chromatography. Plasma concentrations increased dose-dependently after the administration of nicorandil, and were not different between normal dogs and those with MR. Similar to the effective plasma values obtained in cardiac disease in humans, the findings of this pharmacokinetic study may indicate that a dose of 0.3-1.0 mg/kg has the same effectiveness in dogs with cardiac dysfunction.