Histochemical analysis of capillary and fiber-type distributions in skeletal muscles of spontaneously hypertensive rats

Various studies have suggested that hypertension causes a closure and eventual loss of microvessels. In muscle tissue that purported pattern of vascular rarification has been associated with a simultaneous loss of slow twitch fibers. The present study uses histochemical techniques to examine both the capillarization and distribution of fast (FOG) and slow (SO) twitch oxidative fibers, the most vascularized of the fiber types, in five muscles of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats: adductor magnus (AM), biceps femoris (BF), spinotrapezius (SP), medial gastrocnemius (MG), and soleus (SOL). The results show that FOG and SO tend to be slightly smaller in cross-sectional area in SHR, but that the percentage of those fibers in the total population is not decreased in any of the SHR muscles examined. Capillary/fiber ( C F ) ratios for most fiber categories were not significantly different in the two strains but tended toward slightly higher values in SHR. Since capillary density ( C/mm 2) is related to both fiber size and C F ratio, density values tended to be higher, rather than lower, in SHR. The data indicate that there is neither an anatomical rarification of capillaries, nor a loss of FOG or SO fibers in spontaneous hypertension.