Ultrastructural morphologic evaluation of the phenotype of valvular interstitial cells in dogs with myxomatous degeneration of the mitral valve

OBJECTIVE: To evaluate morphologic changes in valvular interstitial cells of dogs and to find evidence for disease-associated phenotypic changes in these cells. ANIMALS: 5 clinically normal dogs and 5 dogs with severe mitral valve endocardiosis. PROCEDURE: Mitral valve leaflets were evaluated by use of transmission electron microscopy. Differences in cell type and cell location were identified. RESULTS: A change in cell type toward a myofibroblast or smooth muscle cell phenotype was detected, with the smooth muscle cell type being most common. These cells had long amorphous cytoplasmic extensions, fibrillar cytoplasm, incomplete basal lamina, few mitochondria, and eccentrically placed nuclei but lacked smooth endoplasmic reticulum or Golgi complexes. Remaining valvular interstitial cells had heterochromatic nuclei and produced only minimal quantities of collagen. Compared with normal valves, myxomatous valves ha many interstitial-like cells located adjacent to the endothelium. Deeper within the abnormal valves, cells with a heterogenous phenotype formed groupings that appeared to be anchored to adjacent collagen. CONCLUSIONS AND CLINICAL RELEVANCE: Myxomatous degeneration of the mitral valve in dogs is associated with phenotypic alteration, changing from an interstitial to a mixed myofibroblast or smooth muscle cell phenotype. A closer association between interstitial cells and the endothelium is evident in diseased valves. In response to the disease process, valvular interstitial cells of dogs appear to change toward a smooth muscle phenotype, possibly in an attempt to maintain valve tone and mechanical function.     

Oesophageal strictures in cats associated with doxycycline therapy

Four cases of oesophageal stricture subsequent to doxycycline administration are reported. All cases were young to middle age (median age 3 years; range 1-7 years), and either domestic shorthair or domestic longhair breed. In all cases the predominant clinical sign was regurgitation, which developed at variable times after doxycycline administration. In all cases the reason for doxycycline use was treatment or prophylaxis of suspected infections (Mycoplasma haemofelis, Chlamydophila felis or Bordetella bronchiseptica), and the duration of therapy was variable. In one case the stricture was definitively diagnosed at post mortem examination, in the three other cases, definitive diagnosis was by endoscopy. Balloon dilation was successful in the three cases that were treated. This is the largest case series, to date, of oesophageal disease in cats associated with doxycycline administration. Caution should be exercised when administering oral medication to cats, especially doxycycline, and should be accompanied either by a water or food swallow.     

Surface phosphatase activity of Sitka spruce mycorrhizas from a serpentine site

The p-nitrophenyl phosphatase activity of mycorrhizal roots of Sitka spruce from a phosphorus deficient site was inversely proportional to the concentrations of 0.5 n acetic acid-extractable phosphorus in the decaying organic matter from which the roots were removed. This is interpreted as the derepression of phosphatase synthesis under conditions of inorganic P deficiency and is discussed in relation to the possible roles of mycorrhizal surface phosphatase activity.     

Avian paramyxovirus type 1 infection of racing pigeons: 3 epizootiological considerations

During July to December 1983 birds in 192 racing pigeon lofts were confirmed as infected with paramyxovirus type 1 virus on the basis of disease signs alone when contact with infected cases was known (10) or with supporting serology (130), virus isolation (eight) or both (44). These outbreaks were mainly concentrated in south Wales (89) and Dorset (40). In all, 29 counties of Great Britain were involved. In the majority of outbreaks (69 per cent) activities associated with racing were strongly implicated in the spread of the disease but trade in birds, stray bird contact, loft visits and contact at shows were also possible methods of spread. Although considerable variation was seen in the pathogenicity of the viruses isolated from affected birds there were no apparent epizootiological links between isolates of similar virulence.