Background The volume overload of isolated mitral regurgitation (MR) in the dog results in left ventricular (LV) dilatation and interstitial collagen loss. To better understand the mechanism of collagen loss we performed a gene array and overlaid regulated genes into Ingenuity Pathway Analysis (IPA). Methods and Results Gene arrays from LV tissue were compared in 4 dogs prior to and 4 months after MR. Cine-magnetic resonance-derived LV end-diastolic volume increased 2-fold (p=0.005) and LV ejection fraction increased from 41 to 53% (p < 0.001). LV interstitial collagen decreased 40% (p<0.05) compared to controls and replacement collagen was in short strands and in disarray. IPA identified Marfan’s syndrome, aneurysm formation, LV dilatation, and myocardial infarction, all of which have extracellular matrix (ECM) protein defects and/or degradation. MMP-1 and -9 mRNA increased 5- (p=0.01) and 10-fold (0.003), while collagen I did not change and collagen III mRNA increased 1.5-fold (p=0.02). However, noncollagen genes important in ECM structure were significantly downregulated, including decorin, fibulin 1, and fibrillin 1. Decorin mRNA downregulation correlated with LV dilatation (r= 0.83 p<0.05). In addition, connective tissue growth factor and plasminogen activator inhibitor were downregulated, along with multiple genes in TGF-β signaling pathway, resulting decreased LV TGF-β1 activity (p=0.03). Conclusions LV collagen loss in isolated, compensated MR is chiefly due to post-translational processing and degradation. The downregulation of multiple noncollagen genes important in global ECM structure, coupled with decreased expression of multiple profibrotic factors, explain the failure to replace interstitial collagen in the MR heart.

A controlled, blind study was conducted to define the initial inflammatory response and lung damage associated with the death of precardiac stages of Dirofilaria immitis in cats as compared to adult heartworm infections and normal cats. Three groups of six cats each were used: UU: uninfected untreated controls; PreS I: infected with 100 D. immitis L3 by subcutaneous injection and treated topically with selamectin 32 and 2 days pre-infection and once monthly for 8 months); IU: infected with 100 D. immitis L3 and left untreated. Peripheral blood, serum, bronchial lavage, and thoracic radiographic images were collected from all cats on Days 0, 70, 110, 168, and 240. CT images were acquired on Days 0, 110, and 240. Cats were euthanized, and necropsies were conducted on Day 240 to determine the presence of heartworms. Bronchial rings were collected for in vitro reactivity. Lung, heart, brain, kidney, and liver tissues were collected for histopathology. Results were compared for changes within each group. Pearson and Spearman correlations were performed for association between histologic, radiographic, serologic, hematologic and bronchoalveolar lavage (BAL) results. Infected cats treated with selamectin did not develop radiographically evident changes throughout the study, were heartworm antibody negative, and were free of adult heartworms and worm fragments at necropsy. Histologic lung scores and CT analysis were not significantly different between PreS I cats and UU controls. Subtle alveolar myofibrosis was noted in isolated areas of several PreS I cats and an eosinophilic BAL cytology was noted on Days 75 and 120. Bronchial ring reactivity was blunted in IU cats but was normal in PreS I and UU cats. The IU cats became antibody positive, and five cats developed adult heartworms. All cats with heartworms were antigen positive at one time point; but one cat was antibody positive, antigen negative, with viable adult females at necropsy. The CT revealed early involvement of all pulmonary arteries and a random pattern of parenchymal disease with severe lesions immediately adjacent to normal areas. Analysis of CT 3D reconstruction and Hounsfield units demonstrated lung disease consistent with restrictive pulmonary fibrosis with an interstitial infiltrate, absence of air trapping, and decrease in total lung volume in Group IU as compared to Groups UU and PreS I. The clinical implications of this study are that cats pretreated with selamectin 1 month before D. immitis L3 infection did not become serologically positive and did not develop pulmonary arterial hypertrophy and myofibrosis.

Background-This study tested the hypothesis that ␤ 1 -adrenoreceptor blockade modulates the angiotensin II (Ang II)-evoked neural release of norepinephrine (NE) and epinephrine (Epi) into the cardiac interstitial fluid (ISF) space in experimentally induced mitral regurgitation (MR) in the dog. Methods and Results-Normal dogs (nϭ8) were compared with dogs with MR of 2 (nϭ8) and 4 (nϭ6) weeks' duration and with dogs with MR treated with ␤ 1 -receptor blockade (RB; extended-release metoprolol succinate, 100 mg QD; MRϩ␤ 1 -RB) that was started 24 hours after MR induction for 2 (nϭ6) and 4 weeks (nϭ8). Left ventricular end-diastolic dimension increased 20% as plasma Ang II levels increased Ͼ5-fold in both MR and MRϩ␤ 1 -RB dogs at 2 and 4 weeks. Ang II infusion into the left atrium produced increases in ISF NE and Epi in normal dogs, which were further increased in 2-and 4-week MR dogs but were restored to normal in 4-week MRϩ␤ 1 -RB dogs. Ang II infusion produced 4-fold increases in circulating NE and Epi in 2-and 4-week MR dogs that returned to normal in 4-weekϩ␤ 1 -RB dogs. Left ventricular angiotensin-converting enzyme activity and ISF Ang II were increased in 4-week MR dogs but were decreased in 4-week MRϩ␤ 1 -RB dogs. Conclusions-␤

Abstract. An 8-month-old female Great Pyrenees dog with chronic epistaxis and a history ofgingival bleeding during shedding of deciduous teeth was evaluated for platelet function. Platelet morphology was normal at both the light and electron microscopic level. Platelet number and mean platelet volume were also normal. Platelet aggregation responses to adenosine diphosphate, collagen, platelet activating factor, and thrombin were markedly reduced, although shape change responses were normal. Clot retraction was markedly impaired. Monoclonal protein electrophoresis. This is the first reported case of type I Glanzmann's thrombasthenia in the dog that closely resembles the clinical syndrome and the platelet morphology described in type I Glanzmann's thrombasthenia of human beings.

Pat B, Killingsworth C, Denney T, Zheng J, Powell P, Tillson M, Dillon AR, Dell'Italia LJ. Dissociation between cardiomyocyte function and remodeling with ␤-adrenergic receptor blockade in isolated canine mitral regurgitation. Am J Physiol Heart Circ Physiol 295: H2321-H2327, 2008. First published October 10, 2008 doi:10.1152/ajpheart.00746.2008.-The low-pressure volume overload of isolated mitral regurgitation (MR) is associated with increased adrenergic drive, left ventricular (LV) dilatation, and loss of interstitial collagen. We tested the hypothesis that ␤1-adrenergic receptor blockade (␤1-RB) would attenuate LV remodeling after 4 mo of MR in the dog. ␤1-RB did not attenuate collagen loss or the increase in LV mass in MR dogs. Using MRI and three-dimensional (3-D) analysis, there was a 70% increase in the LV end-diastolic (LVED) volumeto-LV mass ratio, a 23% decrease in LVED midwall circumferential curvature, and a Ͼ50% increase in LVED 3-D radius/wall thickness in MR dogs that was not attenuated by ␤1-RB. However, ␤1-RB caused a significant increase in LVED length from the base to apex compared with untreated MR dogs. This was associated with an increase in isolated cardiomyocyte length (171 Ϯ 5 m, P Ͻ 0.05) compared with normal (156 Ϯ 3 m) and MR (165 Ϯ 4 m) dogs. Isolated cardiomyocyte fractional shortening was significantly depressed in MR dogs compared with normal dogs (3.73 Ϯ 0.31 vs. 5.02 Ϯ 0.26%, P Ͻ 0.05) and normalized with ␤1-RB (4.73 Ϯ 0.48%). In addition, stimulation with the ␤-adrenergic receptor agonist isoproterenol (25 nM) increased cardiomyocyte fractional shortening by 215% (P Ͻ 0.05) in ␤1-RB dogs compared with normal (56%) and MR (50%) dogs. In summary, ␤1-RB improved LV cardiomyocyte function and ␤-adrenergic receptor responsiveness despite further cell elongation. The failure to attenuate LV remodeling associated with MR could be due to a failure to improve ultrastructural changes in extracellular matrix organization. heart failure; volume overload ISOLATED MITRAL REGURGITATION (MR) is characterized by initial left ventricular (LV) dilation and augmented stroke volume that is mediated by the Starling mechanism and facilitated by regurgitation into the low-pressure left atrium. Increased sympathetic drive follows the initial recruitment of preload reserve in the early phase of MR in the human (8) and dog (4, 9, 17). Using the microdialysis technique in healthy open-chest canines, we have shown that there is compartmentalized norepinephrine and epinephrine release into the LV interstitial fluid space during electrical stimulation of the stellate ganglion (4, 17). We have reported that catecholamine release into the cardiac interstitial fluid in response to ANG II and stellate ganglion stimulation is enhanced in 4-wk MR compared with normals and, moreover, that the interstitial fluid catecholamine release was normalized after chronic treatment with extended release metoprolol succinate (4), a relatively selective ␤ 1 -adrenergic receptor blocker (␤ 1 -RB) (17). In addition, ␤ 1 -RB with...