Distribution of NADPH-diaphorase activity in the tricuspid valve of the rat

A histochemical technique was used to investigate the neuronal structures t hat show NADPH-diaphorase activity in the valva tricuspidalis in the heart. This technique involved whole-mount stretch preparations of the valves, en abling the study of their innervation pattern by means of light microscopy. Wholemount valves provide an extremely useful means to study the occurrenc e of nerve fibres, their distribution and their interrelationships in the t ricuspid valve. The highest concentrations of NADPH-diaphorase positive ner ve fibres and fibres in the tunica adventitia of the arterial wall were fou nd in the basal zone of the tricuspid Valve adjacent to the fibromuscular a trioventricular ring. In the intermediate zone of the valve, very few nerve fibres were found. These nerve fibres had a vertical course and they ended directly as free nerve endings. In the distal parts of the valve short ner ve fibres were found, again in the vertical course. The fibres did not reac h either the free margin of the valve cusps or the chordae tendineae.