0231–424X/$ 20.00 © 2013 Akadémiai Kiadó, Budapest Acta Physiologica Hungarica, Volume 100 (3), pp. 266–279 (2013) DOI: 10.1556/APhysiol.100.2013.3.3 Effect of age on the contractile response of the rat carotid artery in the presence of sympathetic drugs and L-NAME NM Omar 1 , AM Abbas 1 , H Abdel-Malek 2 , GM Suddek 3 1 Department of Medical Physiology, Faculty of Medicine, Mansoura University, Mansoura, Egypt 2 Department of Clinical Pharmacology, Faculty of Medicine, Mansoura University, Mansoura, Egypt 3 Department of Pharmacology and Toxicology, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt 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 α 1 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), α 1 -AR antagonist (prazosin; 0.1 μM), α 2 -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 α 2 -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 α 1 -AR. β-AR mediated dilatation was compromised in middle-aged rats (endothelium- dependent). α 2 -AR and SNP-mediated dilator effect seems to be unchanged. Keywords: noradrenaline, carotid artery, aging, alpha adrenergic receptors, beta adrenergic receptors Adrenergic receptors (ARs) represent major regulators of the cardiovascular system. At the vascular level, α- and β-ARs play a pivotal role in balancing vascular tone and blood pressure homeostasis (14). Although the α 1 -adrenoceptor subtype, linked to vasoconstriction, is the predominant postsynaptic receptor in vascular smooth muscle, the postsynaptic α 2 -adrenoceptor subtype also mediates constriction of vascular smooth muscle (15). However, it has been also reported that the α 2 -adrenoceptor agonist produced a vasodilatation in isolated dog coronary arteries (22), in precontracted preparations of the rat superior mesenteric artery (1), and in canine femoral and rat tail arteries (20). On the other hand, β-ARs mediate relaxation of vascular smooth muscle cells (14), and other data indicate that β-AR-mediated- vasorelaxation, at least in part, is endothelium- and NO-dependent (16). The effect of age on vascular reactivity of different vascular beds to different agonists and antagonists has been studied either in vivo or in vitro. Thus, responses to α 1 -adrenoceptor agonists in blood vessels have been shown to increase (24), decrease (12) or remain the same (32) with aging. On the other hand, vascular reactivity studies conducted in the aorta of aging Corresponding author: Hala Abdel-Malek Department of Clinical Pharmacology, Faculty of Medicine, Mansoura University PO Box 35516, Postal code 1231, Mansoura, Egypt Phone: (+2)-050-0109172054; E-mail: halaabdel@hotmail.com