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.

1 The role of a constitutively active population of a 1D -adrenoceptors was analysed in arteries obtained from spontaneously hypertensive rats (SHR) and controls (WKY) divided into three groups: young prehypertensive, adult hypertensive, and adult animals chronically treated with captopril (50 mg kg 71 per day orally) in order to prevent the hypertensive state. 2 In adult SHR, a signi®cant increase in BMY 7378 potency (not in prazosin potency) was observed in aorta, mesenteric artery, and the ®rst and second branches of the small mesenteric arteries with respect to WKY rats. This di erence was not observed in iliac and tail arteries, which suggests an increased functional role of a 1D -adrenoceptors only in some vessels of SHR. 3 The increase in the resting tone (IRT) observed in absence of agonist, inhibited by BMY 7378, that represents the constitutively active population of a 1D -adrenoceptors, was also signi®cantly greater in aorta and mesenteric artery from adult SHR. 4 In young and captopril treated adult animals, no di erences between strains with respect to BMY 7378 potency, or IRT were observed. 5 The increase in the functional role of a 1D -adrenoceptors and their constitutive activity observed in hypertension is prevented by captopril treatment. The pathological consequence of this change is the slower rate of recovery of the basal tone after removal of an adrenergic stimulus, observed in vessels from hypertensive animals that had shown an increase in the functionality of constitutively active a 1D -adrenoceptors. This change was not observed in prehypertensive or captopril treated animals. IRT, increase in the resting tone; NA, noradrenaline; SHR, spontaneously hypertensive rats; SMA-1 and SMA-2, ®rst and second small mesenteric arterial branches; WKY, Wistar Kyoto rats

A series of O- and/or N-substituted derivatives of (+/-)-coclaurine (1a) were synthesized as simplified structural mimics of the antihypertensive alkaloid tetrandrine (2) and assayed for binding to brain cortical sites labeled with the alpha(1)-adrenergic radioligand [(3)H]prazosin or the calcium channel radioligand [(3)H]diltiazem. The introduction of O-benzyl groups on the coclaurine molecule, which exhibits only adrenergic antagonist activity, led to the appearance of calcium channel blocking activity comparable to that of tetrandrine while retaining adrenolytic activity in the same concentration range. Contraction of aortal rings with noradrenaline or KCl was relaxed more potently by some of these coclaurine derivatives than by tetrandrine, suggesting leads for the development of novel antihypertensive drugs with a dual mechanism of action.

The effect of hypertension and acute (36-h) or chronic (from age 6 to 16 weeks) antihypertensive treatment with prazosin (2 mg kg Ϫ1 per day), nifedipine (50 mg kg Ϫ1 per day), or captopril (50 mg kg Ϫ1 per day) on Ca 2ϩ mobilization due to ␣ 1 -adrenoceptor activation was analyzed in functional studies using arterial rings [four conductance/distributing vessels: aorta, main mesenteric, iliac, and tail arteries and two resistance vessels; first and second small mesenteric artery branches obtained from spontaneously hypertensive rats (SHR, 6 and 16 weeks old) and age-matched Wistar Kyoto rats (WKY)]. Maximal response to noradrenaline in the presence of extracellular Ca 2ϩ is not affected by hypertension or by the antihypertensive treatment. The extracellular Ca 2ϩ -independent contractile responses increased with age in iliac, tail, and small mesenteric arteries (SMA) and were further increased in SHR in SMA from both young and adult animals and in the main mesenteric artery of adult SHR. In main mesenteric artery, this increased contraction in SHR was associated with a higher increase in cytosolic [Ca 2ϩ ] mobilized by noradrenaline without changes in the total stored Ca 2ϩ . Acute or chronic treatment with captopril abolished the differences observed between WKY and SHR in the noradrenaline-induced contraction in mesenteric arteries loaded in Ca 2ϩ -free medium. In contrast, animals acutely treated with prazosin or chronically treated with either prazosin or nifedipine exhibit the same differences in Ca 2ϩ handling than untreated rats. In conclusion, these differences are not a consequence of increased blood pressure but precede it and can only be normalized by inhibition of the rennin-angiotensin system.High blood pressure in hypertensive humans or animals is caused by an elevation of systemic resistance, due to structural and functional changes in the wall of resistance vessels. However, at present, the mechanisms by which the most important vasoactive systems, such as sympathetic nervous system or renin-angiotensin system, contribute to the rise of vascular resistance in hypertension remain unclear (Schlaich et al., 2004).The crucial role of the increased sympathetic nervous system tone in the pathogenesis of hypertension is mediated not only by induction of cardiac hypertrophy and vascular remodeling, which, at least in spontaneously hypertensive rats (SHR), may even precede the rise of blood pressure but also by enhanced vasoconstriction (Zicha and Kunes, 1999). In hypertension, the postsynaptic ␤-adrenergic functions are attenuated, whereas ␣ 1 -adrenergic functions become dominant, although the total number of ␣ 1 -adrenoceptors remains unchanged in most vessels. The augmented vasoconstriction mediated by ␣ 1 -adrenoceptors in SHR could be due not only to a higher norepinephrine release from sympathetic nerve fibers but also to the hyper-reactivity of vessels or their supersensitivity to ␣ 1 -adrenoceptor agonists (Zicha and Kunes, 1999).Differences in Ca 2ϩ handling have been also invoked to A...