SYMPATHETIC HYPERINNERVATION PROTECTS VASCULAR SMOOTH-MUSCLE CELLS FROM NECROSIS IN STRAKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

Sympathetic nerve fiber distribution and vascular smooth muscle morpho logy were investigated in the ophthalmic artery of stroke-prone sponta neously hypertensive rats (SHRSP) and were compared with those of norm otensive Wistar Kyoto (WKY) rats at the age of 120 days. The distribut ion of fluorescent noradrenergic (NA) nerve fibers was examined by the glyoxylic acid method. The ophthalmic artery was divided into two por tions according to the size of the outer diameter, that is into a prox imal portion (above 100 mu m) and a distal portion (30-70 mu m). The d istribution densities of noradrenergic nerve fibers were measured by q uantitative image analysis using the Interactive Bild-Analyse System ( IBAS). The distribution densities of NA nerve fibers in both portions of the ophthalmic artery were significantly higher (p<0.01) in SHRSP t han that in WKY rats. The difference in the density of NA fibers of th e ophthalmic arteries between SHRSP and WKY rats was 1.9 times in the proximal portion and 1.5 times in the distal portion. The vascular smo oth muscle cells of the ophthalmic arteries in SHRSP were observed by scanning electron microscope to examine the trophic effect of NA nerve fibers on the vascular smooth muscle cells. The smooth muscle cells o f both portions of the ophthalmic arteries in SHRSP showed a smooth su rface texture and no necrosis, and were very similar to those of WKY r ats. Taking into consideration previous papers stating that all smooth muscle cells from 6-month-old SHRSP were either structurally modified or necrotic in the proximal portion of middle cerebral arteries (Fuji wara et al. 1990), which were only innervated as densely as those in W KY rats (Kondo et al. 1991), the present findings suggest that the hyp erinnervation by NA fibers plays a protective role, due to their troph ic effect, against structural modifications and necrosis of vascular s mooth muscle cells in the ophthalmic artery of SHRSP.