[Innervation of the mitral valve in normal and prolapsed mitral valves]

To evaluate the relationship between mitral valve prolapse (MVP) and autonomic nerve dysfunction, clinical and immunohistochemical studies were performed. I. Clinical study Autonomic function tests and supine bicycle exercise were performed in 60 patients with MVP, 41 under 35 years of age and 19 of 35 years and older, and the results were compared with those of 31 normal controls, 19 under 35 years of age and 12 of 35 years and older. Case with positive response on postural stress and cold pressor tests were more frequent in both MVP groups than those of controls. Plasma nor-adrenaline levels were higher in the MVP groups than in the control groups during exercise. Our clinical observation suggested that autonomic dysfunction, particularly sympathetic hyperactivity, probably is present in MVP irrespective of age. II. Immunohistochemical study In 23 mitral valves (15 of normal controls and eight of MVP), three normal tricuspid, three normal aortic and three normal pulmonic valves, immunohistochemical localizations of S-100 protein, glial fibrillary acidic protein (GFAP) and neurofilament protein (NFP) were examined to detect the distribution of all nerve endings, choline acetyltransferase (ChAT) to detect the distribution of cholinergic nerve fibers, and neuropeptide Y (NPY) and calcitonin gene related peptide (CGRP) to detect the distribution of afferent nerve fibers, using the avidin-biotin peroxidase complex (ABC) method. The distribution of adrenergic nerve fibers was examined by fluorescence with the glyoxylic acid method. In normal valves, S-100 protein was mainly demonstrated in the base and body of the valve cusp. It was very scanty in the tip, and was only found in the coaptation zone that is, the layer of the atrialis or along the boundary between the atrialis and the spongiosa in the atrioventricular valves. The distribution of S-100 protein in the prolapsed mitral valve was the same as that of the normal valve except for the lack of S-100 protein in the degenerated portion. The distribution of GFAP, NFP, ChAT, NPY, CGRP and adrenergic fluorescence were the same as that of S-100 protein in both the normal and prolapsed mitral valves. It is suggested that the above-mentioned anatomical distribution of the nerve in the mitral valve is closely related to the dysfunction of the autonomic nerve system in the condition of mitral valve prolapse, because the body of the mitral valve is rich in nerve endings and this area is most easily influenced by the mechanical stimulation due to abnormal coaptation.