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 s pontaneously 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 Wista r Kyoto (WKY) rats. The distribution densities of NA nerve fibres were measured by quantitative image analysis using the Interactive Bildana lyse System. The densities of NA nerve fibres of the left coronary art ery of SHRSP were significantly higher than those of WKY rats at all a ges 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 show ed 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 ag e, but was slightly modified by more invaginations and projections tha n that in WKY rats at 180 days of age. No necrotic cells, however, wer e found in SHRSP. By transmission electron microscopy the smooth muscl e cells in SHRSP were shown to be irregular in profile with deep inden tations of the plasma membrane and surrounded by many layers of basal lamina-like material, but no necrotic cells were found. We suggest tha t NA hyperinnervation protects the vascular smooth muscle cells from n ecrosis in the coronary artery of SHRSP by a trophic effect mediated b y NA nerve fibres.