AGING AND VASOREACTIVITY - IN-VIVO RESPONSES IN THE BEAGLE HINDLIMB

The purpose of this investigation was to determine whether vasodilator responses are attenuated and whether vasoconstriction is augmented wi th age in resistance vessels in the hindlimb of the dog. We examined b lood flow (FAF) and pressure (FAP) responses in the femoral arterial s ystem in older (109 +/- 8-mo-old) and younger mature (31 +/- 3-mo-old) female beagles during pentobarbital anesthesia. Vasodilator responses were evaluated during the intra-arterial administration of acetylchol ine (ACh), which produces endothelium-dependent vasodilation, and albu terol, which mediates relaxation in vascular smooth muscle via beta-ad renoceptors. The vasoconstrictor response to phenylephrine (PE), an al pha-adrenergic agonist, was also examined. ACh and albuterol each indu ced dose-dependent vasodilation in the older and in the younger dogs. Resultant changes in neither FAF nor FAP were affected by age in respo nse to either of these vasodilator substances. Likewise, reductions in femoral vascular resistance (FVR) in response to ACh or to albuterol were not age dependent. Vasodilation following induced hindlimb ischem ia resulted in similar increases in FAF in both groups, but produced a greater reduction in FAP in older vs. younger dogs (P = 0.05). Simila rly, FVR decreased more in the older beagles (P = 0.02). Vasoconstrict ion mediated by PE resulted in similar reductions in FAF in both age g roups, but the increase in FAP was less at several PE doses in older v s. younger dogs (P < 0.05). However, increases in FVR in response to P E were not statistically different in the younger and older beagles. T hus dilator responses mediated by endothelium-dependent and beta-adren ergic agonists, as well as maximal vasodilation following induced hind limb ischemia, are maintained with age in femoral resistance vessels i n the dog. Moreover, vasoconstriction in response to an alpha-adrenerg ic agonist is not augmented with age in this vascular bed.