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)-p ositive nerve fibres with those of acetylcholinesterase-stained nerves in t he atrioventricular valves of guinea pigs. The occurrence and distribution of SP - positive nerve fibres in the bicuspid and tricuspid valves was stud ied using a modified indirect enzymatic immunohistochemical method. Interes tingly, an accumulation of SP-positive fibres was detected in the marginal zone between the atrioventricular ring and the bicuspidal valve. SP-positiv e immunoreactive nerve fibres run along the entire valve. A lower density o f SP-immunoreactive nerve fibres was observed in the intermediary zone. The distal zone contained peptidergic nerve fibres extending from the intermed iary 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 g uinea pig. Our findings allow us to assume that the SP-positive and acetylc holinesterase-posit ive nerve fibres are involved in the functions of the v alves. They most likely contribute to the regulation of valve cusp tonus by means of contractile elements or to the transmission of local pressure per ception or it is possible that they release/contract the valve during the d iastole and systole via afferent and efferent nerve fibres.