The mRNA levels for the three alpha1-adrenoceptor subtypes, alpha1A, alpha1B, and alpha1D, were quantified by real-time RT-PCR in arteries from Wistar rats. The alpha1D-adrenoceptor was prominent in both aorta (79.0%) and mesenteric artery (68.7%), alpha1A predominated in tail (61.7%) and small mesenteric artery (73.3%), and both alpha1A- and alpha1D-subtypes were expressed at similar levels in iliac artery. The mRNA levels of the alpha1B-subtype were a minority in all vessels (1.7-11.1%). Concentration-response curves of contraction in response to phenylephrine or relaxation in response to alpha1-adrenoceptor antagonists on maximal sustained contraction induced by phenylephrine were constructed from control vessels and vessels pretreated with 100 micromol/l chloroethylclonidine (CEC) for 30 min. The significant decrease in the phenylephrine potency observed after CEC treatment together with the inhibitory potency displayed by 8-{2-[4-(2-methoxyphenyl)-1-piperazinyl]-8-azaspiro (4,5) decane-7-dionedihydrochloride} (BMY-7378, an alpha1D-adrenoceptor antagonist) confirm the relevant role of alpha1D-adrenoceptors in aorta and iliac and proximal mesenteric arteries. The potency of 5-methylurapidil (an alpha1A-adrenoceptor antagonist) and the changes in the potency of both BMY-7378 and 5-methylurapidil after CEC treatment provided evidence of a mixed population of alpha1A- and alpha1D-adrenoceptors in iliac and distal mesenteric arteries. The low potency of prazosin (pIC50 < 9) as well as the high 5-methylurapidil potency in tail and small mesenteric arteries suggest the main role of alpha1A/alpha1L-adrenoceptors with minor participation of the alpha1D-subtype. The mRNA levels and CEC treatment corroborated this pattern and confirmed that the alpha1L-adrenoceptor could be a functional isoform of the alpha1A-subtype.

In human and animal hypertension models, increased activity of G-protein-coupled receptor kinase (GRK) 2 determines a generalized decrease of ␤-adrenergic vasodilatation. We analyzed the possibility of differential changes in the expression and functionality of ␣ 1A , ␣ 1B , ␣ 1D , ␤ 1 , ␤ 2 , and ␤ 3 -ARs also being involved in the process. We combined the quantification of mRNA levels with immunoblotting and functional studies in aortas of young and adult spontaneously hypertensive rats (SHRs) and their controls (Wistar Kyoto). We found the expression and function of ␤ 1 -adrenoceptors in young prehypertensive SHRs to be higher, whereas a generalized increase in the expression of the six adrenoceptors and GRK2 was observed in aortas of adult hypertensive SHRs. ␣ 1D -and ␤ 3 -Adrenoceptors, the subtypes that are more resistant to GRK2-mediated internalization and mostly expressed in rat aorta, exhibited an increased functional role in hypertensive animals, showing two hemodynamic consequences: 1) an increased sensitivity to the vasoconstrictor stimulus accompanied by a decreased sensitivity to the vasodilator stimulus (␣ 1D -ARs are the most sensitive to agonists, and ␤ 3 -ARs are the least sensitive to agonists); and 2) a slower recovery of the basal tone after adrenergic stimulus removal because of the kinetic characteristic of the ␣ 1D subtype. These functional changes might be involved in the greater sympathetic vasoconstrictor tone observed in hypertension.Although there is growing evidence that essential hypertension is related to the overactivity of the sympathetic nervous system, the exact causes are still poorly understood. The adrenergic-dependent increase in vascular resistance could reflect an imbalance between vasoconstrictor and vasodilator mechanisms related to changes in both the expression and function of ␣ 1 -adrenoceptors (ARs), which mediate vasoconstriction, ␤-ARs, which mediate vasodilatation, and/or changes in G-protein-coupled receptor kinases (GRKs), the key regulators of the ␤-ARs (Feldman and Gros, 2006;Penela et al., 2006).