Stiffness of the thoracic aorta and individual VSMCs increase with hypertension and aging. Excised aortic rings from young (16 weeks old) and old (64 weeks old) WKY and SHR were mechanically stretched, and stiffness was determined from the stress-strain relationship, as shown for representative rings (A) (SHR = dashed; WKY = solid; Old = filled symbols: Young = open symbols). Stiffness was increased in the SHR at the young age, and further augmented with age (B). The stiffness of VSMCs derived from the thoracic aorta was determined by AFM nanoindentation. Each cell was individually probed with a microcantilever, and the force response was determined from the laser deflection of the microcantilever as it touched the cell surface, as shown for representative approach (blue) and retraction (red) curves (C). The stiffness was increased in SHR at both young and old ages (D). Data are shown as mean ± SEM. Post-hoc comparisons, parisons among the four groups were determined * p < 0.05, ** p < 0.01, compared to WKY; # p < 0.05, ## p < 0.01, compared to young.