Figure 7. NOS activity as measured by calcium-dependent conversion of L-arginine to L-citrulline in young (3 months) and aged (18 months) rat cavernosal tissue 7 days after transfection with vehicle, AdRSVßgal, and AdRSVeNOS. Aged cavernosal tissue had a significant reduction in constitutive NOS activity, which is primarily a measure of eNOS activity. After gene therapy with eNOS, constitutive NOS activity was restored to levels greater than those found in young rats. n indicates number of tissue samples; ^*, P < .05 when compared with young; ^**, P < .05 when compared with aged cavernosal tissue transfected with vehicle or Ad-RSVßgal.