Effect of age on the contractile response of the rat carotid artery in the presence of sympathetic drugs and L-NAME.
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.
Mansoura University Department of Medical Physiology, Faculty of Medicine Mansoura Egypt.
N M
NM
Omar
A M
AM
Abbas
H
H
Abdel-Malek
G M
GM
Suddek
D058668:Adrenergic alpha-1 Receptor Antagonists / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000375:Aging; D000818:Animals; D002339:Carotid Arteries / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D014665:Vasodilator Agents / Q000494:pharmacology
D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D014665:Vasodilator Agents; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine