In vivo study of microvascular wall characteristics and resting control in young and mature spontaneously hypertensive rats.

This study was designed to determine if vessel wall hypertrophy and increased expression of sympathetic activity occur in the microcirculation during the development of hypertension. The cremaster muscle microvasculature of normal Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats was observed at age 5--7 weeks and 16--18 weeks. For age-matched WKY and SHR rats, the diameters, wall thicknesses and vessel wall cross-sectional areas for the majority of comparable types of arterioles were not significantly (p greater than 0.05) different. After denervation of the cremasteric muscle, the large and intermediate diameter arterioles of young WKY rats dilated significantly (p less than 0.05) more than did comparable vessels of SHR rats. In contrast, the dilation of comparable types of arterioles in mature WKY and SHR rats following denervation was not significantly (p greater than 0.05) different. The results do not support either abnormal vessel wall hypertrophy, vasoconstriction or increased expression of sympathetic activity in SHR rats compared to WKY rats up to age 16--18 weeks.