Distribution of NADPH-diaphorase and AChE activity in the anterior leaflet of rat mitral valve

Abstract

The mitral valve, as an active flap, forms the major part of the left ventricular inflow tract and therefore plays an important function in many aspects of left ventricular performance. The anterior leaflet of this valve is the largest and most ventrally placed of two leaflets that come together during ventricular systole to close the left atrioventricular orifice. Various neurotransmitters are responsible for different functions including controlling valve movement, inhibiting or causing the failure of impulse conduction in the valve and the sensation of pain. Nitric oxide acts as a gaseous free radical neurotransmitter, neuromediator and effective cardiovascular modulator. Acetyl-choline is known to function as a typical neurotransmitter. Histochemical methods for detection of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), as an indirect nitric oxide-synthase marker, and method for detection of acetylcholinesterase (AChE) were used. Both methods were performed on the same valve sample. A widespread distribution of nerve fibres was observed in the anterior leaflet of the mitral valve. The fine NADPH-d positive (nitrergic) nerve fibres were identified in all zones of valve leaflet. AChE positive (cholinergic) nerve fibres were identified forming dense network and fibres organized in stripes. Endocardial cells and vessels manifested heavy NADPH-d activity. Our observations suggest a different arrangement of nitrergic and cholinergic nerve fibres in the anterior leaflet of the mitral valve. The presence of nitrergic and cholinergic activity confirms the involvement of both neurotransmitters in nerve plexuses and other structures of mitral valve.

Figure 1

The mitral valve of the rat heart. The picture shows the zone adjacent to the fibromuscular ring (arrow on the left) and the free moving zone (arrow on the right), (original magnification × 5).

Figure 2

Scheme of the mitral valve. Drawing of the valve segment depicting the basal, intermediate and distal zones (arranged according to Ahmed et al.)

Figure 3

(A, B, C). The basal zone of the anterior mitral leaflet. NADPH-d positive arterioles and capillares are localized in the area of fibromuscular ring (3A: small arrow up; 3C: arrow on the left). The fine NADPH-d positive (nitrergic) nerve fibres running close to the vessels (3C: arrows on the right) and in tunica adventitia (arrow on the left). Blue stained endothelial cells are seen in different colour on the background (3A: small arrow down; 3C). AChE positive (cholinergic) nerve fibres are identified forming both a dense network and fibres organized in stripes (3A: big arrow; 3B). Calibration bars: 3A, B 20 µm, 3C 10 µm.

Figure 4

(A, B, C). The intermediate zone of the anterior mitral leaflet. The fine NADPH-d positive nerve fibres (4C: small arrows) and blue stained endothelial cells are seen in different colour on the background. AChE positive nerve fibres are in this area sparsely arranged (4A: arrow; 4B; 4C: big arrows). Calibration bars: 4A, B, C 20 µm.

Figure 5

(A, B). The distal zone of the anterior mitral leaflet. The fine NADPH-d positive nerve fibres were identified especially in this zone running along margins of endothelial (endocardial) cells or crossing them only in the direction of blood flow. In spite of the direct course of NADPH-d positive nerve fibres, AChE positive nerve fibres were seen running in various directions (5B: arrow; 5A). Calibration bars: 5A, B 20 µm.