Investigation of the Innervation of the Canine Mitral Valve by Immunohistochemical Staining
Sympathetic, parasympathetic and sensory nerve fibres have been identified in mitral valves from many species but not from dogs. This innervation suggests valvular movement and tone are not entirely passive.
The aims of this study were to use immunohistochemistry to confirm, map and characterise innervation within mitral valves from dogs of different ages.
Anterior mitral valve leaflets were collected from 11 healthy dogs. Four dogs were less than one year of age, 4 dogs were 5 years of age and 3 dogs were estimated as 9-10 years of age. Innervation was assessed qualitatively and semi-quantitatively.
Innervation was confirmed in leaflets in all 3 groups but it was markedly reduced in the aged group. Myxomatous valve disease (MVD) was present in the valves of dogs 5 years of age and older. Innervation was densest proximally and mainly associated with the epimysial, perimysial and endomysial layers of the muscle within the valve and with blood vessels. Innervation was reduced within the middle zone of the valve and absent distally. Chordal innervation was not identified. Nerve fibres were mostly sympathetic, some were parasympathetic and some sensory.
This study confirms that the canine mitral valve is innervated. Innervation is mainly sympathetic and within muscle and around blood vessels proximally suggesting a role in valvular function and health. Zonal distribution of innervation is similar to that in other species. Density of innervation reduces with age or MVD. Further investigation of the role of innervation in the pathophysiology of MVD is required.