Noradrenergic hyperinnervation in the heart of stroke-prone spontaneously hypertensive rats (SHRSP)

Noradrenergic (NA) nerve fiber density was investigated in the subepicardium and myocardium of ventricles in stroke-prone spontaneously hypertensive rats (SHRSP) and was compared with that of normotensive Wistar Kyoto (WKY) rats. Fluorescent NA nerve fibers in the subepicardium of the right and left ventricles of both strains at the ages of 10, 30, 60, 90, and 180 days were examined by the glyoxylic acid method. NA nerve fibers in the myocardium of the right and left ventricles and the ventricular septum of both strains at the ages of 30, 90, and 180 days were also examined in a similar manner. The density of NA nerve fibers was measured by quantitative image analysis. The distribution pattern of NA nerve fibers in the entire subepicardium of ventricles of both strains showed a meshwork pattern throughout the examination period. In sections of the myocardium, NA nerve fibers were distributed between heart muscle cells and around blood vessels in both strains at all ages examined. The densities of NA nerve fibers in the subepicardium of the ventricles of SHRSP were significantly higher than those of WKY rats at all ages examined except for the subepicardium of the left ventricle at 90 days of age. The densities in the myocardium of the right ventricle in 30- and 90-day-old SHRSP were significantly higher than those in WKY rats. The ratios of NA nerve fiber density of SHRSP to that of WKY rats were greater in the subepicardium of the right and left ventricles, except at 90 days of age, and in the myocardium of the right ventricle of younger animals as compared with older ones. NA hyperinnervation in the subepicardium and myocardium of the ventricles of SHRSP may be a primary change of the heart before the onset of hypertension and may be caused by hyperfunction of the stellate ganglia.