Myocardial collagen deposition and inflammatory cell infiltration in cats with pre-clinical hypertrophic cardiomyopathy.

The histological features of feline hypertrophic cardiomyopathy (HCM) have been well documented, but there are no reports describing the histological features in mild pre-clinical disease, since cats are rarely screened for the disease in the early stages before clinical signs are apparent. Histological changes at the early stage of the disease in pre-clinical cats could contribute to an improved understanding of disease aetiology or progression. The aim of this study was to evaluate the histological features of HCM in the left ventricular (LV) myocardium of cats diagnosed with pre-clinical HCM. Clinically healthy cats with normal (n = 11) and pre-clinical HCM (n = 6) were identified on the basis of echocardiography; LV free wall dimensions (LVFWd) and/or interventricular septal wall (IVSd) dimensions during diastole of 6-7 mm were defined as HCM, while equivalent dimensions <5.5 mm were defined as normal. LV myocardial sections were assessed and collagen content and inflammatory cell infiltrates were quantified objectively. Multifocal areas of inflammatory cell infiltration, predominantly lymphocytes, were observed frequently in the left myocardium of cats with pre-clinical HCM. Tissue from cats with pre-clinical HCM also had a higher number of neutrophils and a greater collagen content than the myocardium of normal cats. The myocardium variably demonstrated other features characteristic of HCM, including arteriolar mural hypertrophy and interstitial fibrosis and, to a lesser extent, myocardial fibre disarray and cardiomyocyte hypertrophy. These results suggest that an inflammatory process could contribute to increased collagen content and the myocardial fibrosis known to be associated with HCM.

Comparative pharmacokinetics and pharmacodynamics of tablet, suspension and paste formulations of atenolol in cats.

This study compared the pharmacokinetic and pharmacodynamic profiles of an extemporaneously prepared (compounded) atenolol paste and suspension for oral administration, against the commercially available divided tablet in healthy cats. Eleven healthy cats (mean: age 4 ± 0.4 year, weight 5.0 ± 0.7 kg) were dosed twice-daily with 12.5 mg atenolol (tablet, paste or suspension) for 7 days in a randomized cross-over design with a 7-day wash-out period. On day 7, an electrocardiogram was performed before and immediately after stress provocation (jugular venipuncture) at prestudy screening, and at 2, 6 and 12 h after morning dosing. Systolic arterial blood pressure (BP) was assessed following the second electrocardiogram. Plasma was collected at prestudy screening, and at 1, 2, 6 and 12 h to measure atenolol plasma concentrations. Mean atenolol dose was 2.5 mg/kg (range: 2.1-3.3 mg/kg). Stress-induced rise in heart rate was attenuated (P < 0.05) at every time point compared to baseline for all formulations. Although the paste significantly attenuated stress-induced elevation in heart rate at all time points, the effect was not consistently equivalent to the tablet. The BP was not altered (P > 0.05) at any time point by any formulation. In conclusion, there were no significant differences (P > 0.05) in any of the pharmacokinetic parameters or pharmacodynamic profiles of the paste and suspension compared to the commercially available tablet.

Trauma-induced central diabetes insipidus in a cat.

A 1-year-old neutered male domestic shorthair cat presented with a 4-week history of polydipsia that began immediately after an 8 m fall. Trauma-induced central diabetes insipidus was suspected on the basis of the identification of hyposthenuria, normal haematology and serum biochemistry profile and unremarkable abdominal ultrasound examination. Failure to concentrate urine with water deprivation followed by production of hypersthenuric urine with administration of the synthetic antidiuretic hormone, Damino-8-D-arginine vasopressin (DDAVP), confirmed the diagnosis of central diabetes insipidus. Treatment via conjunctival administration of DDAVP failed to attenuate the polydipsia, however, resolution of polydipsia was achieved with subcutaneous administration of DDAVP and the cat remains eudipsic with twice daily subcutaneous DDAVP administration 17 months after diagnosis.

The effect of hydration status on the echocardiographic measurements of normal cats.

BACKGROUND: Diagnosis of cardiomyopathy of cats is based on 2-dimensional (2D) echocardiography. However, circulating fluid volume largely determines diastolic cardiac chamber dimensions, and reduced diastolic volume in other species results in what has been called "pseudohypertrophy of the ventricular myocardium." HYPOTHESIS: Altered hydration produces changes on 2D echocardiography that may confound the diagnosis or severity assessment of cardiomyopathy of cats. ANIMALS: Ten normal colony-sourced mixed breed cats were included. METHODS: Cats were examined by echocardiography at baseline and at completion of 3 protocols (volume depletion and maintenance-rate and anesthetic-rate IV fluid administration) applied in randomized crossover design with a 6-7 day washout period. RESULTS: Volume depletion increased diastolic left ventricular interventricular septal (IVSd) and free wall diameter (4.5 +/- 0.4 to 5.8 +/- 0.6 mm; P < .001) with wall thickness exceeding 6 mm in 4 cats. Diastolic left ventricular internal diameter (LVIDd) decreased, and reduction in systolic left ventricular internal diameter (LVIDs) produced end-systolic cavity obliteration in 7 cats. Left-atrial-to-aortic-root ratio (LA: Ao, 1.4 +/- 0.2 to 1.2 +/- 0.1, P < .05) and left atrial area in diastole (LAAd) decreased with volume depletion. Maintenance-rate IV fluid administration increased LAAd and fractional shortening (FS%). Anesthetic-rate IV fluid administration increased LVIDd, FS%, LAAd, and LA:Ao ratios (to 1.7 +/- 0.1, P < .01), producing an LA: Ao ratio above normal limits in 6 cats. A systolic heart murmur developed with administration of fluid at maintenance (n = 1) and anesthetic rates (n = 6). CONCLUSIONS: Altered hydration status produces changes in the echocardiographic examination of normal cats that may lead to an erroneous diagnosis of cardiomyopathy or mask its presence. Hydration status should be considered during echocardiographic examination in cats.

Pulmonary arteriopathy and idiopathic pulmonary arterial hypertension in six dogs.

Pulmonary arteriopathy (PA) is the pathologic hallmark in human medicine of diffuse constrictive (medial and intimal remodeling) or multifocal complex (plexiform and dilatative lesions) arterial lesions, or both, that lead to irreversible obliteration of the arterial lumen. Clinically, PA leads to pulmonary arterial hypertension (PAH), of which idiopathic (IPAH) is one of the 5 subsets, and ultimately, to right-sided heart failure (RHF). Clinical and pathologic findings from 6 dogs with diagnosis of IPAH and PA were reviewed. These dogs were of various pure (5/6, 83%) and mixed (1/6, 17%) breeding, 5 months to 9 years (mean 5.2 years) old, and predominantly female (4/6, 67%) and reproductively intact (4/6, 67%). Doppler echocardiography (n = 5) indicated increased pulmonary arterial pressures during systole (70-135 mm Hg, mean 98 mm Hg) and diastole (35-80 mm Hg, mean 58 mm Hg). All 6 dogs had right ventricular pressure overload, right ventricular eccentric hypertrophy, and RHF. Histologic examination confirmed the clinical diagnosis of IPAH in all dogs, revealing PA characterized by 1 of the 4 main human histologic subsets: 1) isolated medial hypertrophy (1/6, 17%); 2) medial hypertrophy-intimal thickening without the plexiform lesion (1/6, 17%); 3) medial hypertrophy-intimal thickening concurrent with the plexiform lesion, which often was regionally clustered and situated near branching points of the respiratory artery, the poststenotic dilatation lesion, and vasculitis (4/6, 66%); and 4) isolated arteritis (1/6, 17%). Ancillary lesions similar to those in humans also complicated the PA (5/6, 83%). The complex lesions and ancillary exudative alveolitis seemed to be important indicators of severe, likely rapidly progressive and fatal, IPAH.

Immediate and late outcomes of transarterial coil occlusion of patent ductus arteriosus in dogs.

Records from dogs (n = 125) that underwent attempted transarterial coil occlusion of patent ductus arteriosus (PDA) at the University of California, Davis, between 1998 and 2003, were reviewed, and a subset of these dogs (n = 31) in which the procedure was performed at least 12 months earlier were reexamined to determine long-term outcome. Coil implantation was achieved in 108 dogs (86%). Despite immediate complete ductal closure in only 34% of dogs, the procedure was hemodynamically successful as evidenced by a reduction in indexed left ventricular internal diameter in diastole (LVIDd; P < .0001), fractional shortening (P < .0001), and left atrial to aortic ratio (LA: Ao; P = .022) within 24 hours. Complete ductal closure was documented in 61% of dogs examined 12 to 63 months after coil occlusion. Long-standing residual ductal flow in the other 39% of dogs was not associated with increased indexed LVIDd or LA: Ao and was not hemodynamically relevant. Repeat intervention was deemed advisable in only 4 dogs with persistent (n = 1) or recurrent (n = 3) ductal flow. Complications included aberrant embolization (n = 27), death (n = 3), ductal reopening (n = 3), transient hemoglobinuria (n = 2), hemorrhage (n = 1), aberrant coil placement (n = 1), pulmonary hypertension (n = 1), and skin abscessation (n = 1). Serious infectious complications did not occur despite antibiotic administration to only 40% of these dogs. Transarterial coil occlusion was not possible in 14 dogs (11%) because of coil instability in the PDA and was associated with increased indexed minimum ductal diameter (P = .03), LVIDd (P = .0002), LVIDs (P = 0.001), and congestive left heart failure (P = .03) reflecting a relatively large shunt volume.

Trauma-induced central diabetes insipidus in a cat.

A 1-year-old neutered male domestic shorthair cat presented with a 4-week history of polydipsia that began immediately after an 8 metre fall. Trauma-induced central diabetes insipidus was suspected on the basis of the identification of hyposthenuria, normal haematology and serum biochemistry profile and unremarkable abdominal ultrasound examination. Failure to concentrate urine with water deprivation followed by production of hypersthenuric urine with administration of the synthetic antidiuretic hormone, Deamino-8-D-arginine vasopressin (DDAVP), confirmed the diagnosis of central diabetes insipidus. Treatment via conjunctival administration of DDAVP failed to attenuate the polydipsia, however, resolution of polydipsia was achieved with subcutaneous administration of DDAVP and the cat remains eudipsic with twice daily subcutaneous DDAVP administration 17 months after diagnosis.

Effects of the paralysis tick, Ixodes holocyclus, on the electrocardiogram of the Spectacled Flying Fox, Pteropus conspicillatus.

OBJECTIVE: To evaluate cardiac electrical function in the Spectacled Flying Fox (bat) infested with Ixodes holocyclus. DESIGN: Prospective clinical investigation of bats treated for naturally occurring tick toxicity. PROCEDURE: ECGs were performed on bats with tick toxicity (n = 33), bats that recovered slowly (n = 5) and normally (n = 5) following treatment for tick toxicity, and on normal bats with no history of tick toxicity (n = 9). RESULTS: Bats with tick toxicity had significantly prolonged corrected QT intervals, bradycardia and rhythm disturbances which included sinus bradydysrhythmia, atrial standstill, ventricular premature complexes, and idioventricular bradydysrhythmia. CONCLUSIONS: The QT prolongation observed on ECG traces of bats with tick toxicity reflected delayed ventricular repolarisation and predisposed to polymorphic ventricular tachycardia and sudden cardiac death in response to sympathetic stimulation. The inability to document ventricular tachycardia in bats shortly before death from tick toxicity may be explained by a lack of sympathetic responsiveness attributable to the unique parasympathetic innervation of the bat heart, or hypothermia-induced catecholamine receptor down-regulation. Bradycardia and rhythm disturbances may be attributable to hypothermia.

Long QT syndrome in dogs with tick toxicity (Ixodes holocyclus).

OBJECTIVE: To evaluate cardiac electrical function in dogs with tick toxicity. DESIGN: A prospective clinical investigation of 39 client-owned dogs treated for naturally occurring tick toxicity. PROCEDURE: An ECG was performed on each dog on several occasions; at admission to hospital with tick toxicity, 24 h later, at discharge from hospital when clinically normal and approximately 12 months later. RESULTS: The mean QT interval corrected for heart rate (QTc) was prolonged at admission, 24 h and at discharge compared to the QTc measured 12 months later. T wave morphology was altered in dogs at admission. All other parameters were within normal limits. CONCLUSIONS: The prolonged QTc interval and altered T wave morphology of dogs with tick toxicity reflects delayed cardiac repolarisation and is comparable with long QT syndrome (LQTS) in people who are predisposed to polymorphic ventricular tachycardia and sudden death. Resolution of ECG changes lagged behind clinical recovery.

Reactions to tick antitoxin serum and the role of atropine in treatment of dogs and cats with tick paralysis caused by Ixodes holocyclus: a pilot survey.

OBJECTIVE: To determine the incidence and nature of adverse reactions of dogs and cats to tick antitoxin serum and to re-evaluate the role of atropine in the treatment of tick paralysis. DESIGN: A retrospective questionnaire of veterinarians. PROCEDURE: Questionnaires were posted to 320 veterinarians in tick-endemic regions of Australia. Questions referred to dogs and cats treated for tick paralysis over a period of three years: the number treated, treatment protocols and adverse systemic reactions to tick antitoxin serum. Ninety completed questionnaires were returned and responses analysed. RESULTS: Veterinarians reported that approximately 3% of dogs exhibited adverse reactions immediately following treatment with tick antitoxin serum. Eighteen percent of these reactions were described as anaphylaxis, with the remaining 82% attributed to the Bezold-Jarisch reflex. Six percent of cats treated with tick antitoxin serum reacted adversely and the majority of reactions (63%) were ascribed to the Bezold-Jarisch reflex. Atropine was used routinely by 10% of responding veterinarians in the treatment of dogs and cats with tick paralysis. A similar number of veterinarians used atropine only in selected cases. Most veterinarians (76%) reported that they never used atropine in the treatment of tick paralysis in either dogs or cats. Within the survey population, premedication with atropine reduced the number of Bezold-Jarisch reactions following tick antitoxin administration approximately five-fold in dogs and four-fold in cats. CONCLUSIONS: Data from this pilot survey indicate that more cats than dogs have adverse systemic reactions to tick antitoxin serum and that the majority of these reactions in both dogs and cats could be related to the Bezold-Jarisch reflex. The number of reactions to tick antitoxin serum in dogs and cats could be significantly reduced by the routine use of atropine prior to administration of tick antitoxin serum.

Prospective survey of tick paralysis in dogs.

OBJECTIVE: To obtain information on tick paralysis in dogs, including the nature of disease, host signalment, tick-host relationship, treatment, disease progression and recovery, and preventive measures. DESIGN: A prospective survey of 577 dogs affected by tick paralysis was conducted during 1998. Forty-two veterinary clinics along the eastern coast of Australia were instructed to complete survey forms for the first 15 dogs that presented with tick paralysis during September to November. RESULTS: Five percent of dogs died from tick paralysis. Younger dogs were more likely to survive. Long coat length was associated with a greater tick burden but not greater tick size, whereas coat thickness had no bearing on either. Dogs with mild disease recovered more quickly from tick paralysis. Respiratory and gait scores reflected disease severity and were good prognostic indicators. The size of the tick did not reflect the severity of the clinical condition it induced in the host. No method of tick removal or in situ treatment improved recovery time or reduced mortality. However, the time spent in hospital was significantly less for dogs from which the live tick was manually removed. Inspiratory stridor, evident in some dogs with tick paralysis, was not related to tick attachment on the neck. The use of acepromazine maleate or dexamethasone did not reduce recovery time or mortality. Increasing the dose of tick antitoxin serum (TAS) above 0.1 mL/kg had no effect on mortality or recovery time. Dogs with severe disease that received an additional dose of TAS were significantly less likely to survive. Subcutaneous use of TAS at the site of tick attachment was of no benefit in reducing mortality or time to initial clinical improvement. A registered preventative product had not been used on the majority of dogs. Clipping the coat to search for ticks did not reduce mortality. CONCLUSIONS: Therapy needs to address cardiopulmonary dysfunction that may be due directly to the effect of tick toxin and not just respiratory compromise caused by progressive respiratory muscle failure.

Transcription termination by RNA polymerase III: uncoupling of polymerase release from termination signal recognition.

Xenopus RNA polymerase III specifically initiates transcription on poly(dC)-tailed DNA templates in the absence of other class III transcription factors normally required for transcription initiation. In experimental analyses of transcription termination using DNA fragments with a 5S rRNA gene positioned downstream of the tailed end, only 40% of the transcribing polymerase molecules terminate at the normally efficient Xenopus borealis somatic-type 5S rRNA terminators; the remaining 60% read through these signals and give rise to runoff transcripts. We find that the nascent RNA strand is inefficiently displaced from the DNA template during transcription elongation. Interestingly, only polymerases synthesizing a displaced RNA terminate at the 5S rRNA gene terminators; when the nascent RNA is not displaced from the template, read-through transcripts are synthesized. RNAs with 3' ends at the 5S rRNA gene terminators are judged to result from authentic termination events on the basis of multiple criteria, including kinetic properties, the precise 3' ends generated, release of transcripts from the template, and recycling of the polymerase. Even though only 40% of the polymerase molecules ultimately terminate at either of the tandem 5S rRNA gene terminators, virtually all polymerases pause there, demonstrating that termination signal recognition can be experimentally uncoupled from polymerase release. Thus, termination is dependent on RNA strand displacement during transcription elongation, whereas termination signal recognition is not. We interpret our results in terms of a two-step model for transcription termination in which polymerase release is dependent on the fate of the nascent RNA strand during transcription elongation.

Displacement of Xenopus transcription factor IIIA from a 5S rRNA gene by a transcribing RNA polymerase.

In the absence of other components of the RNA polymerase III transcription machinery, transcription factor IIIA (TFIIIA) can be displaced from both strands of its DNA-binding site (the internal control region) on the somatic-type 5S rRNA gene of Xenopus borealis during transcription elongation by bacteriophage T7 RNA polymerase, regardless of which DNA strand is transcribed. Furthermore, substantial displacement is observed after the template has been transcribed only once. Since the complete 5S rRNA transcription complex has previously been shown to remain stably bound to the gene during repeated rounds of transcription by either RNA polymerase III or bacteriophage SP6 RNA polymerase, these results indicate that a factor(s) in addition to TFIIIA is required to create a complex that will remain stably associated with the template during transcription. Thus, transcription complex stability during passage of RNA polymerase cannot be explained solely on the basis of the DNA-binding properties of TFIIIA.

Nuclear protein phosphorylation in isolated nuclei from HeLa cells. Evidence that 32P incorporation from [gamma-32P]GTP is catalyzed by nuclear kinase II.

A nuclear system for studying nuclear protein phosphorylation is characterized, using as phosphate donor either low levels of [gamma-32P]GTP, low levels of [gamma-32P]ATP, or low levels of labeled ATP plus excess unlabeled GTP. Since nuclear casein kinase II is the only described nuclear protein kinase to use GTP with high affinity, low levels of GTP should specifically assay this enzyme. ATP should measure all kinases, and ATP plus unlabeled GTP should measure all kinases except nuclear casein kinase II (ATP-specific kinases). The results are consistent with these predictions. In contrast with the ATP-specific activity, endogenous phosphorylation with GTP was enhanced by 100 mM NaCl, inhibited by heparin and quercetin, stimulated by polyamines, and did not use exogenous histone as substrate. The GTP- and ATP-specific kinases phosphorylated different subsets of about 20 endogenous polypeptides each. Addition of purified casein kinase II enhanced the GTP-supported phosphorylation of the identical proteins that were phosphorylated by endogenous kinase. These results support the hypothesis that activity measured with GTP is catalyzed by nuclear casein kinase II, though other minor kinases which can use GTP are not ruled out. Preliminary observations with this system suggest that the major nuclear kinases exist in an inhibited state in nuclei, and that the effects of polyamines on nuclear casein kinase II activity are substrate specific. This nuclear system is used to determine if the C-proteins of hnRNP particles, previously shown to be substrates for nuclear casein kinase II in isolated particles, is phosphorylated by GTP in intact nuclei. The results demonstrate that the C-proteins are effectively phosphorylated by GTP, but in addition they are phosphorylated by ATP-specific kinase activity.