Morphometric analysis of skeletal muscle capillaries in early spontaneous hypertension

Capillary narrowing, elongation, and rarification have been described in various tissues in human and animal hypertension. The present study was undertaken to assess whether they are features of the skeletal muscle vascular bed during the developmental phase of the disease in spontaneously hypertensive rats. In neonatal (19 days old) and young adult (9-10 weeks old) rats of the hypertensive (SHR) and normotensive (WKY) strains, capillary diameter, length, and density were measured in spinotrapezius muscle by histological and intravital microscopic techniques. In neonates, capillary diameters (WKY = 3.98 +/- 0.13; SHR = 4.26 +/- 0.14 micron), lengths (WKY = 327 +/- 9; SHR = 334 +/- 6 microns), and densities (WKY = 1768 +/- 106; SHR = 1779 +/- 124 capillaries/mm2) were not significantly different in WKY and SHR. In young adults, capillary diameters (WKY = 4.28 +/- 0.09; SHR = 4.61 +/- 0.09 micron), lengths (WKY = 430 +/- 13; SHR = 443 +/- 12 microns), and densities (WKY = 1263 +/- 76; SHR = 1414 +/- 37 capillaries/mm2) were also not significantly changed in hypertension. Contrary to the findings of narrowing and decreased numbers of capillaries in human hypertensives, diameters and densities were slightly increased. The data suggest that those morphological changes at the capillary level do not occur in the developmental (period of rising arterial pressure) phase of spontaneous hypertension.