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The distribution of vasoactive intestinal polypeptide-, neuropeptide Y-, and calcitonin gene-related peptide-immunoreactive nerve fibres was investigated in the atrioventricular valves of the rat. These nerve fibres were visualized by immunostaining of whole-mount preparations by the avidin-biotin-peroxidase complex method. Vasoactive intestinal polypeptide-immunoreactive nerve fibres were observed mainly in the anterior cusp of the mitral valve and, to a lesser extent, in the medial cusp of the tricuspid valve. Numerous neuropeptide Y-immunoreactive nerve fibres were found covering all of the cusps. Both types of peptidergic nerve fibre formed dense networks that consisted of interlacing and anastomosing nerve fibres. Calcitonin gene-related peptide-immunoreactive nerve fibres were seen in every cusp, but did not form a fine network. These results provide detailed anatomical information for evaluation of the possible roles of each type of peptide-containing nerve fibre in the function of atrioventricular valves.

Dense distribution of varicose fibres containing neuropeptide Y-like immunoreactivity (NPY-LI) was found in the atrioventricular valves of the Japanese monkey, and moderately in the rat. The immunoelectron microscopy using immunogolds resulted in the localization of NPY-LI within the dense-cored vesicles which existed with the small clear vesicles in the unmyelinated axons near the endocardium. These NPY-LI-containing fibres may participate in regulation of vasomotor role or other functions of the atrioventricular valves.