ROLE OF ADRENERGIC TONE IN MECHANICAL AND FUNCTIONAL-PROPERTIES OF CAROTID-ARTERY DURING AGING

The present study was designed to assess the role of the adrenergic tone in the regulation of carotid arterial compliance during aging. An experimental model of in situ isolated carotid arteries has been used to evaluate the elastic properties of the arterial wall in young (3-mo-old) and older (18-mo-old) Wistar rats. Binding experiments were performed in the same strain of rats to evaluate alpha1- and beta-adrenoceptor affinity and density. In a third set of experiments, structural parameter of the carotid artery in younger and older rats was evaluated. Arterial distensibility (compliance per unit of volume) was significantly lower in older rats. This was associated with a significant thickness of the media (45.6 +/- 2.8 vs. 57.5 +/- 5.7 mum, P < 0.01) and increased collagen content in older rats (4,420 +/- 310 vs. 7,320 +/- 850 mum2/mm, P < 0.001). However, carotid arterial compliance was not altered in older rats because of the significant increase in cross-sectional area with aging. Aging did not affect alpha1-adrenoceptor affinity and density, whereas it decreased beta-density without changing their affinity. Pharmacological stimulation of alpha1-adrenoceptor with phenylephrine (10(-5)M) decreased compliance in older but not in younger animals. Blockade of these receptors with prazosin or labetalol increased compliance in younger and had no effect on older rats. Beta-receptor stimulation with isoproterenol or blockade with propranolol had no effect in any of the studied groups. We suggest that with aging there is an increased vasoconstricting effect of alpha-agonists and a decreased vasodilatative action of alpha-blockade. Our results were not associated with changes in alpha-adrenoceptor number or affinity and may be related to differences in basal adrenergic tone or to the alterations of the structure of the arterial wall, inducing modifications to the vasoconstriction/vasorelaxation mechanism.