Myxomatous mitral valve disease (MMVD) is the most common acquired heart disease in dogs whose progression is associated with progressive dysfunction within the vasculature. Endothelial dysfunction occurs when the endothelium can no longer release vasoactive factors, but little is known about its link with MMVD.

Part of this master’s project explored the potential of isometric myography to quantify the mechanical components of vascular function in dogs with MMVD. This technique involves the mounting of a section of blood vessel on wires or pins and immersing it in a physiological salt solution before stretching it to measure constrictive and relaxation responses to vasoactive substances.

Arteries were collected from a total of nine dogs euthanised for welfare or medical reasons, and the extent of their myxomatous degeneration was graded before isometric myography was performed. Vasoconstriction to phenylephrine and vasodilation to acetylcholine (endothelial-dependent) and sodium nitroprusside (endothelial-independent) were assessed by cumulative dose-response curves.

Responses to phenylephrine were similar between dogs, but a reduced response to acetylcholine compared with sodium nitroprusside was identified in 15 arteries, suggesting endothelial dysfunction. This suggests that the technique of isometric myography is feasible to be used on arteries from pet dogs with MMVD to identify loss of endothelial-dependent relaxation. Its use in further research could help understand the pathophysiology mechanisms of this disease.

This work was published open access in the American Journal of Veterinary Research, and can be read here.