The distribution of substance P-like immunoreactive nerves in the atrioventricular valves of the guinea pig

The aim of this study was to compare the distribution of substance P (SP)-positive nerve fibres with those of acetylcholinesterase-stained nerves in the atrioventricular valves of guinea pigs. The occurrence and distribution of SP - positive nerve fibres in the bicuspid and tricuspid valves was studied using a modified indirect enzymatic immunohistochemical method. Interestingly, an accumulation of SP-positive fibres was detected in the marginal zone between the atrioventricular ring and the bicuspidal valve. SP-positive immunoreactive nerve fibres run along the entire valve. A lower density of SP-immunoreactive nerve fibres was observed in the intermediary zone. The distal zone contained peptidergic nerve fibres extending from the intermediary zone and continuing to the free edge of the valve, some of them ending in chorda tendinea. The acetylcholinesterase-positive innervation density of the bicuspid valve was greater than that of the tricuspid valve of the guinea pig. Our findings allow us to assume that the SP-positive and acetylcholinesterase-posit ive nerve fibres are involved in the functions of the valves. They most likely contribute to the regulation of valve cusp tonus by means of contractile elements or to the transmission of local pressure perception or it is possible that they release/contract the valve during the diastole and systole via afferent and efferent nerve fibres.