Noradrenergic hyperinnervation may inhibit necrosis of coronary arterial smooth muscle cells in stroke-prone spontaneously hypertensive rats.

Noradrenergic (NA) nerve fibre distribution and vascular smooth muscle morphology were investigated in the coronary artery of stroke-prone spontaneously hypertensive rats (SHRSP). Fluorescent NA nerve fibres of SHRSP aged 10, 30, 60, 90 and 180 days were examined by the glyoxylic acid method and compared with those of age-matched normotensive Wistar Kyoto (WKY) rats. The distribution densities of NA nerve fibres were measured by quantitative image analysis using the Interactive Bildanalyse System. The densities of NA nerve fibres of the left coronary artery of SHRSP were significantly higher than those of WKY rats at all ages examined. NA hyperinnervation in the coronary artery of SHRSP may be caused by the hyperfunction of the stellate ganglia which innervate the coronary arteries. Scanning electron microscopy observations showed that the surface of smooth muscle cells of the left coronary artery in SHRSP was smooth and similar to that of WKY rats at 120 days of age, but was slightly modified by more invaginations and projections than that in WKY rats at 180 days of age. No necrotic cells, however, were found in SHRSP. By transmission electron microscopy the smooth muscle cells in SHRSP were shown to be irregular in profile with deep indentations of the plasma membrane and surrounded by many layers of basal laminalike material, but no necrotic cells were found. We suggest that NA hyperinnervation protects the vascular smooth muscle cells from necrosis in the coronary artery of SHRSP by a trophic effect mediated by NA nerve fibres.