Vascular adrenergic neuroeffector function does not decline in aged rats.

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Abstract
To investigate adrenergic control of blood vessels during aging, rats aged 6, 12, 20, and 27 months were studied using in vitro techniques. Accumulation of [3H]norepinephrine, one index of adrenergic nerve density, did not alter with age in the femoral or renal arteries or renal vein. In the femoral vein [3H]norepinephrine accumulation was greater at 6 and 27 months of age. Norepinephrine sensitivity was determined in both an innervated vessel, the femoral artery, and a non-innervated vessel, the carotid artery. In both cases, sensitivity to norepinephrine did not alter with age. In the renal and femoral arteries and veins, no significant changes in maximum responses to norepinephrine (10(-5) M), potassium chloride, or transmural nerve stimulation were seen with advancing age. Furthermore, frequency response curves (2-16 Hz, 200 pulses) did not differ with age for any of the four vessels studied, with one exception. The response to stimulation at 4 Hz of the femoral vein from 6-month-old rats was significantly larger than responses at other ages. During nerve stimulation, the renal vein exhibited rapid contractions superimposed upon the maintained contractile response. This type of rapid contraction occurred only rarely (1 out of 5) in the renal vein from 27-month-old rats. In summary, neither adrenergic nerve density as reflected by [3H]norepinephrine accumulation nor norepinephrine sensitivity decline with age. As the net effect of various components, the ability of vascular smooth muscle to respond to adrenergic nerve stimulation is also maintained during advancing age.