Pharmacological analysis alone has failed to clarify the role of the three alpha(1)-adrenoceptor subtypes in modulating vascular tone, due to a lack of sufficiently selective antagonists, particularly for the alpha (1B)-adrenoceptor, and the complexity when three receptor subtypes are potentially activated by the same agonist. We adopted a combined genetics/ pharmacology strategy based on the alpha(1B)-adrenoceptor knockout (KO) mouse. The potency of three alpha(1)-adrenoceptor antagonists vs. phenylephrine was tested in aorta, carotid, mesenteric, and caudal isolated arteries from KO and wild-type (WT) mice. In the KO mouse the pharmacology became straightforward, showing alpha(1D) in two major conducting arteries (aorta and carotid) and alpha(1A) in two distributing arteries (mesenteric and caudal). By combining antagonist pharmacology and genetics, we provide a simplified analysis of alpha(1)-mediated vasoconstriction, demonstrating that alpha(1D) and alpha(1A) are the major subtypes involved in vasoconstriction, with a minor but definite contribution from alpha(1B) in every vessel.

␣ 1 -Adrenergic receptors (␣ 1A , ␣ 1B , and ␣ 1D ) are regulators of systemic arterial blood pressure and blood flow. Whereas vasoconstrictory action of the ␣ 1A and ␣ 1D subtypes is thought to be mainly responsible for this activity, the role of the ␣ 1B -adrenergic receptor (␣ 1B AR) in this process is controversial. We have generated transgenic mice that overexpress either wild type or constitutively active ␣ 1B ARs. Transgenic expression was under the control of the isogenic promoter, thus assuring appropriate developmental and tissue-specific expression. Cardiovascular phenotypes displayed by transgenic mice included myocardial hypertrophy and hypotension. Indicative of cardiac hypertrophy, transgenic mice displayed an increased heart to body weight ratio, which was confirmed by the echocardiographic finding of an increased thickness of the interventricular septum and posterior wall. Functional deficits included an increased isovolumetric relaxation time, a decreased heart rate, and cardiac output. Transgenic mice were hypotensive and exhibited a decreased pressor response. Vasoconstrictory regulation by ␣ 1B AR was absent as shown by the lack of phenylephrine-induced contractile differences between ex vivo mesenteric artery preparations. Plasma epinephrine, norepinephrine, and cortisol levels were also reduced in transgenic mice, suggesting a loss of sympathetic nerve activity. Reduced catecholamine levels together with basal hypotension, bradycardia, reproductive problems, and weight loss suggest autonomic failure, a phenotype that is consistent with the multiple system atrophy-like neurodegeneration that has been reported previously in these mice. These results also suggest that this receptor subtype is not involved in the classic vasoconstrictory action of ␣ 1 ARs that is important in systemic regulation of blood pressure.The adrenergic receptor family, which includes 3 ␣ 1 , 3 ␣ 2 , and 3 ␤-receptor subtypes, is a group of heptahelical G proteincoupled receptors that mediate the effects of the sympathetic nervous system. Extensive effort has been spent in classifying the three known ␣ 1 -adrenergic receptor (␣ 1 AR) 1 subtypes (␣ 1A , ␣ 1B , and ␣ 1D ) via molecular cloning techniques (1-4) and pharmacological analyses (5). The most well characterized cardiovascular regulatory actions associated with ␣ 1 AR activation include the contraction, growth and proliferation of vascular smooth muscle cells (6 -9), increased cardiac contractility (10), and regulation of the hypertrophic program in the myocardium (11,12). In other ␣ 1 AR-expressing tissues such as liver and kidney, the function of these receptors is to regulate metabolic processes (13) and sodium and water reabsorption (14), respectively. These responses are transduced primarily via receptor coupling to the G q /phospholipase C pathway (5), which leads to the subsequent activation of downstream signaling molecules including protein kinase C and inositol 1,4,5-trisphosphate.The progress toward elucidating the distinct regulatory role of each ␣ 1...

Conventionally, the architecture of arteries is based around the close-packed smooth muscle cells and extracellular matrix. However, the adventitia and endothelium are now viewed as key players in vascular growth and repair. A new dynamic picture has emerged of blood vessels in a constant state of self-maintenance. Recent work raises fundamental questions about the cellular heterogeneity of arteries and the time course and triggering of normal and pathological remodelling. A common denominator emerging in hypertensive remodelling is an early increase in adventitial cell density suggesting that adventitial cells drive remodelling and may initiate subsequent changes such as re-arrangement of smooth muscle cells and extracellular matrix. The organization of vascular smooth muscle cells follows regular arrangements that can be modelled mathematically. In hypertension, new patterns can be quantified in these terms and give insights to how structure affects function. As with smooth muscle, little is known about the organization of the vascular endothelium, or its role in vascular remodelling. Current observations suggest that there may be a close relationship between the helical organization of smooth muscle cells and the underlying pattern of endothelial cells. The function of myoendothelial connections is a topic of great current interest and may relate to the structure of the internal elastic lamina through which the connections must pass. In hypertensive remodelling this must present an organizational challenge. The objective of this paper is to show how the functions of blood vessels depend on their architecture and a continuous interaction of different cell types and extracellular proteins.

UK-14,304 [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine]-mediated vasodilator responses were studied on wire myograph-mounted mouse aorta to determine the cells involved, mechanisms of action, and subtypes of ␣ 2 -adrenoceptors. In the presence of induced tone, UK-14,304 produced concentration-related vasodilatation that was abolished by rauwolscine, N -nitro-L-arginine methyl ester (L-NAME), or endothelium removal, indicating that endothelial ␣ 2 -adrenoceptors can release nitric oxide. In the ␣ 2A -adrenoceptor knockout mouse and the D79N mouse, a functional knockout of the ␣ 2A -adrenoceptor, these relaxant effects of UK-14,304 were lost, indicating the involvement of the ␣ 2A -adrenoceptor. UK-14,304 could also contract aorta: a small contraction occurred at high concentrations, was enhanced by L-NAME, and was absent in the ␣ 1D -adrenoceptor knockout mouse, indicating activation of the ␣ 1D -adrenoceptor. There was no evidence for a contractile ␣ 2 -adrenoceptor-mediated response. A fluorescent ligand, quinazoline piperazine bodipy, antagonized the relaxant action of UK-14,304. This compound could be visualized on aortic endothelial cells, and its binding could be prevented by rauwolscine, providing direct evidence for the presence of ␣ 2 -adrenoceptors on the endothelium. Norepinephrine reduced tone in the ␣ 1D -adrenoceptor knockout and controls, an effect blocked by rauwolscine and L-NAME but not by prazosin. This suggests that norepinephrine activates endothelial ␣ 2 -adrenoceptors. In conclusion, the endothelium of mouse aorta has an ␣ 2A -adrenoceptor that responds to norepinephrine; promotes the release of nitric oxide, causing smooth muscle relaxation; and that can be directly visualized. Knockout or genetic malfunction of this receptor should increase arterial stiffness, exacerbated by raised catecholamines, and contribute to heart failure.All three ␣ 2 -adrenoceptors have distinct, yet poorly defined, roles in the control of the vascular system. The limited selectivity of agonists and antagonists has therefore prompted the use of transgenic mouse models. The subtypes are ␣ 2A , ␣ 2B , and ␣ 2C : the mouse ortholog of the human ␣ 2A -adrenoceptor is sometimes called the ␣ 2D -or ␣ 2A/D -adrenoceptor; we use the generic term ␣ 2A -adrenoceptor (Alexander et al., 2004). They have two direct pharmacological effects on blood vessels that can modify vascular tone: a direct vasopressor action (for review, see Wilson et al., 1991;Guimaraes and Moura, 2001) and vasodilatation via endothelium-derived relaxant factors (Cocks and Angus, 1983;Vanhoutte, 2001). They also reduce sympathetic traffic centrally and inhibit transmitter release from sympathetic postganglionic nerves (Starke, 2001), although this is not well established as a physiological phenomenon in blood vessels. Available pharmacological data and knockout studies, although not definitive, present evidence for, at least, ␣ 2A -, ␣ 2B -, and ␣ 2C -adrenoceptors for vasoconstriction, ␣ 2A -and ␣ 2C -adrenoceptors for sympatho-...

1 a 1 -Adrenoceptors (ARs) play an important functional role in the liver; yet little is known about their cellular location. We identified the subtypes present in wild-type (WT) and a 1B -AR knockout (KO) mice livers at 3 and 4 months of age, and investigated their distribution in hepatocytes. 2 The fluorescent a 1 -AR antagonist quinazolinyl piperazine borate-dipyrromethene (QAPB) was used to visualise hepatic a 1 -ARs and radioligand binding with ; 3-month a 1B -AR KO -7.470.73 fmol mg À1 ; 4-month a 1B -AR KO -3072.0 fmol mg À1 . 4 In 3-and 4-month WT liver, all antagonists acted competitively. RS100329 (a 1A -selective) and BMY7378 (a 1D -selective) bound with low affinities, indicating the presence of a 1B -ARs. In 4-month a 1B -AR KO liver prazosin produced a biphasic curve, whereas RS100329 and BMY7378 produced monophasic curves of high and low affinity, respectively, indicating the presence of a 1A -ARs. 5 In conclusion, we have made the novel observation that a 1 -ARs can compensate for one another in the absence of the endogenously expressed receptor; yet there appears to be no subtype-specific subcellular location of a 1 -ARs; the WT livers express a 1B -ARs, while a 1B -AR KO livers express a 1A -ARs. This study provides new insights into both hepatocyte and a 1 -AR biology.