Innervation of the mitral valve is strikingly depleted with age.

Previous reports demonstrated that mammalian atrioventricular (AV) valves possess a dense nerve plexus, consisting of nerve subpopulations which differ from each other in densities and patterns of distribution in the valves, and which may have sensory or motor roles in valve function. Although there is extensive evidence that age-related changes occur in autonomic nerves of animals and humans (Daly et al. J. Pharm. Exp. Ther., 1988;245(3):798-803; Ingall et al. Aust. NZ J. Med., 1990;20:570-577; Tumer et al. Exp. Gerontol., 1992;27:301-307), and that these changes contribute to changes in cardiac function (Klausner and Schwartz Clin. Geriat. Med., 1985;1(1):119-114), there is little information about age-related changes in heart valve innervation. In this study, we used acetylcholinesterase (AChE) histochemistry to localize and compare qualitative and quantitative changes in the innervation of the mitral valves in young adult and aged animals of three species. Young adult and aged guinea pigs, mice, and Wistar and Fischer 344 rats were anesthetized with Nembutal, the hearts removed, and the mitral valves dissected out and processed for AChE localization. Camera lucida drawings of the AChE-positive nerves in representative segments of valve cusps were made directly from slides; these drawings were digitized and subjected to computer-assisted image analysis to obtain quantitative information about nerve plexus density in the valves. All three animal species showed profuse AChE-positive innervation in the mitral valves of young adult animals, and decreases in the density of this innervation in aged animals. The most striking loss of innervation, compared to the young adult, occurred in the mitral valves of aged Fischer 344 rats, in which large regions of the valves appeared virtually devoid of nerves. Further studies are needed to investigate whether and to what extent age-related losses in heart valve innervation affect valvular structure and function.