Beta-adrenergic receptor- (-AR) mediated vasorelaxation declines with age in humans and animal models. This is not caused by changes in expression of -AR, Gs, adenylyl cyclase, or protein kinase A, but is associated with decreased cAMP production. Expression and activity of G protein receptor kinase-2 (GRK-2), which phosphorylates and desensitizes the -AR, increases with age in rat aortic tissue. Caveolin scaffolds the -AR, GRK, and other proteins within "signaling pockets," and inhibits GRK activity when bound. We questioned the effect of age on caveolin-1 expression, and interaction between caveolin-1 and GRK-2 in vascular smooth muscle (VSM) isolated from 2-, 6-, 12-, and 24-month-old male Fischer 344 rat aorta. Western blotting found expression of caveolin-1 declined with age (6-, 12- and 24-month-old express 92%, 50%, and 42% of 2-month-old respectively). Results from density-buoyancy analysis showed a lower percentage of GRK in caveolin-1-specific fractions with age (6-, 12- and 24-month-old express 95%, 56%, and 12% of 2-month-old respectively). Coimmunoprecipitation confirmed this finding; density of GRK in caveolin-1 immunoprecipitates was 97%, 30%, and 21% of 2-month-old in aorta from 6-, 12- and 24-month-old animals respectively. Immunohistocytochemistry and confocal microscopy confirmed that GRK-2 and caveolin-1 colocalize in VSM. These results suggest that in non-overexpressed, intact tissue, the decline in - AR-mediated vasorelaxation may be caused by both a reduction in caveolin-1 expression, and a reduction in binding of GRK-2 by caveolin-1. This could lead to an increase in the fraction of free GRK-2, which could phosphorylate and desensitize the -AR.