Effect of age on the contractile response of the rat carotid artery in the presence of sympathetic drugs and L-NAME

Omar, N.M. and Abbas, A.M. and Abdel-Malek, Hala and Suddek, G.M. (2013) Effect of age on the contractile response of the rat carotid artery in the presence of sympathetic drugs and L-NAME. Acta Physiologica Hungarica, 100 (3). pp. 266-279. ISSN 0231-424X

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Abstract

For evaluating the age-related change in noradrenaline (NA)-induced contraction of isolated rat carotid artery (CA), the effect of α and β adrenoreceptor (AR) blockers and the role of nitric oxide (NO) were investigated. Methods: Concentration-response curves to NA (10⁻¹⁰–10⁻⁴ M) and α₁ agonist phenylephrine (PE; 10⁻¹⁰–10⁻⁵ M) were constructed in isolated CA rings from young and middle-aged rats. The effects of nitric oxide synthase (NOS) inhibitor (L-NAME; 100 μM), α₁-AR antagonist (prazosin; 0.1 μM), α₂-AR antagonist (yohimbine; 0.1 μM) and β-AR antagonist (propranolol; 1 μM) on NA-induced contraction of isolated CA rings were examined. In CA rings preconstricted with NA, the responses to α₂-AR agonist (clonidine; 10⁻⁷–10⁻⁵ M), β-AR agonist (isoprenaline; 10⁻⁸–10⁻⁵ M),), sodium nitroprusside (SNP; 10⁻⁹–10⁻⁵ M) were assessed. Results: The maximum contractile response of CA to NA and to PE was higher in younger than in middle-aged rats. Prazosin reduced the contractile response to NA in both groups, while propranolol, yohimbine and L-NAME did not affect NA-induced contraction in either of them. Clonidine, isoprenaline and SNP produced a dose-dependent vasorelaxation of CA rings, isoprenaline-induced vasodilatation was lower in middle-aged rats, while there was no difference in clonidine or SNP-induced relaxant effect between the two groups. Conclusions: NA-induced contraction of isolated rat CA rings is decreased in old rats, this is related to α₁-AR. β-AR mediated dilatation was compromised in middle-aged rats (endothelium-dependent). α₂-AR and SNP-mediated dilator effect seems to be unchanged.

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