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The mitral complex is a functional entity composed of the annulus, valve leaflets, chordae, and papillary muscles. The mechanical properties of the complex are dependent on the unique structural relations of the collagen in the leaflets and chordae. In the chordae the collagen is arranged in avascular columns. These columns interdigitate between muscle fibers in the papillary muscles, and the collagen is anchored to the myofiber membrane by microfibrils. In the leaflet the chordae are continuous with the dense fibrous tissue, forming a sheet of collagen which merges with the annulus. Within the leaflet there are cardiac muscle fibers in direct continuity with left atrial muscle. Contraction of isolated valve preparations can be initiated by electrical stimulation and is preceded by a propagated depolarization. Action potentials from cells in the middle third of the leaflet have a slow upstroke velocity, prominent plateau, and a characteristic positive afterpotential. Valve muscle electromechanical properties are markedly altered by 1 X 10~7M acetylcholine; this concentration has little effect on working left atrial muscle. In preparations containing portions of the left atrium and valve leaflet, the excitation wave spreads into the leaflet after electrical stimulation of the atrial muscle. This suggests that the accompanying contractile event may occur in situ before the initiation of systole.KEY WORDS acetylcholine mitral valve leaflet action potential comparative pathology papillary muscle length-force relation electrophysiology chordae tendineae left atrial muscle mitral excitation• The anatomical structures regulating the flow of blood at the mitral orifice have been termed the mitral complex (1). This is composed of the mitral annulus, valve leaflets, chordae tendineae, and papillary muscles. Mitral valvular fibrosis in man and dog is well known clinically and pathologically. In the dog, the abnormal physiological function resulting in mitral insufficiency may be related to structural alterations in one or more regions

This publication is the seventh in a series of safety evaluations performed by the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA). In 1993, the Panel initiated a comprehensive program to re-evaluate the safety of more than 1700 GRAS flavoring substances under conditions of intended use. Elements that are fundamental to the safety evaluation of flavor ingredients include exposure, structural analogy, metabolism, pharmacokinetics and toxicology. Flavor ingredients are evaluated individually and in the context of the available scientific information on the group of structurally related substances. Scientific data relevant to the safety evaluation of the use of cinnamyl derivatives as flavoring ingredients is evaluated.

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