Functional hyperemia is reduced in skeletal muscle of aged rats.

Objective: To test the hypothesis that active hyperemia is reduced in skeletal muscle of old rats due to a decreased bioavailability of prostanoids, which in turn is due to increased oxidative stress.

Methods: The microvasculature of the spinotrapezius muscle of 3-, 12-, and 24-month male Sprague-Dawley rats was examined using in vivo videomicroscopy. Arteriolar diameter and centerline red cell velocity were measured in resting and contracting muscle. The effect of prostanoids was examined using indomethacin (10 microM), and passive resting arteriolar diameters were determined using adenosine (100 microM). Lipid peroxidation was assessed ex vivo by measuring tissue levels of malondialdehyde.

Results: Arteriolar diameters and blood flow in resting muscle did not differ among the age groups, but increases in diameter and flow during muscle contraction in young rats were greater than in the two older age groups. Indomethacin did not affect resting arteriolar diameters and blood flow in 3- and 12-month rats, but significantly decreased both parameters in 24-month rats. Indomethacin had no effect on arteriolar diameter and blood flow responses during muscle contraction in any age group. Passive resting diameters of arterioles were significantly smaller in 12- and 24-month rats than in 3-month rats. Tissue levels of TBARS were not different among the three age groups.

Conclusions: Arteriolar tone and blood flow in resting skeletal muscle of rats is not altered with age, whereas the increases in these variables that normally accompany muscle contraction are markedly impaired during aging. Neither cyclooxygenase metabolites nor lipid peroxidation appear to be involved in this impairment.