Recent advances in the molecular pharmacology of the alpha 1-adrenergic receptors

Antihypertensive effect of formononetin through regulating the expressions of eNOS, 5-HT2A/1B receptors and α1-adrenoceptors in spontaneously rat arteries

One of the main pathological changes of hypertension is the dysfunction of blood vessels. We have found in our previous study that formononetin, one kind of phytoestrogens, has an acute antihypertensive effect. Therefore, we hypothesized that formononetin might produce a chronic antihypertensive effect through regulating the expressions of contractile receptors and endothelial nitric oxide synthase (eNOS) in artery. The present study was conducted to verify this effect. Male spontaneously hypertensive rats (SHRs) were divided into two groups, orally administrated formononetin (50mg/kg per day) and Tween 80 vehicle, respectively, for 8 weeks. The blood pressure was measured by tail-cuff method. Isometric tension of arterial rings was recorded by a myograph system. The mRNA and protein expression in arteries was determined with quantitative real-time polymerase chain reaction and immunohistochemistry, respectively. Results showed that the systolic blood pressure of SHRs decreased significantly in formononetin group compared to Tween 80 group. The vasoconstriction induced by phenylephrine or 5-hydroxytryptamine (5-HT) in the mesenteric artery segments in formononetin group was decreased, and the relaxation induced by acetylcholine was increased compared with that in Tween 80 group. In the mesenteric arteries of the formononetin-treated SHRs, the expressions of α(1)-adrenoceptors and 5-HT(2A/1B) receptors at both mRNA and protein levels decreased, while the mRNA and protein expressions of eNOS increased. In conclusion, formononetin has a chronic antihypertensive effect in SHRs. The antihypertensive mechanism may be associated with the down-regulation of α(1)-adrenoceptors and 5-HT(2A/1B) receptors, and the up-regulation of eNOS expression in arteries.

Endothelial alpha1-adrenoceptors regulate neo-angiogenesis

BACKGROUND AND PURPOSE

Intact endothelium plays a pivotal role in post-ischaemic angiogenesis. It is a phenomenon finely tuned by activation and inhibition of several endothelial receptors. The presence of alpha(1)-adrenoceptors on the endothelium suggests that these receptors may participate in regenerative phenomena by regulating the responses of endothelial cells involved in neo-angiogenesis.

EXPERIMENTAL APPROACH

We evaluated the expression of the subtypes of the alpha(1)-adrenoceptor in isolated endothelial cells harvested from Wistar-Kyoto (WKY) rats. We explored the possibility these alpha(1)-adrenoceptors may influence the pro-angiogenic phenotype of endothelial cells in vitro. In vivo, we used a model of hindlimb ischaemia in WKY rats, to assess the effects of alpha(1) adrenoceptor agonist or antagonist on angiogenesis in the ischaemic hindlimb by laser Doppler blood flow measurements, digital angiographies, hindlimb perfusion with dyed beads and histological evaluation.

KEY RESULTS

In vitro, pharmacological antagonism of alpha(1)-adrenoceptors in endothelial cells from WKY rats by doxazosin enhanced, while stimulation of these adrenoceptors with phenylephrine, inhibited endothelial cell proliferation and DNA synthesis, ERK and retinoblastoma protein (Rb) phosphorylation, cell migration and tubule formation. In vivo, we found increased alpha(1)-adrenoceptor density in the ischaemic hindlimb, compared to non-ischaemic hindlimb, suggesting an enhanced alpha(1)-adrenoceptor tone in the ischaemic tissue. Treatment with doxazosin (0.06 mg kg(-1) day(-1) for 14 days) did not alter systemic blood pressure but enhanced neo-angiogenesis in the ischaemic hindlimb, as measured by all our assays.

CONCLUSIONS

Our findings support the hypothesis that the alpha(1)-adrenoceptors in endothelial cells provide a negative regulation of angiogenesis.

Alpha1-adrenoceptors are required for normal male sexual function

BACKGROUND AND PURPOSE

Alpha(1)-adrenoceptor antagonists are extensively used in the treatment of hypertension and lower urinary tract symptoms associated with benign prostatic hyperplasia. Among the side effects, ejaculatory dysfunction occurs more frequently with drugs that are relatively selective for alpha(1A)-adrenoceptors compared with other drugs of this class. This suggests that alpha(1A)-adrenoceptors may contribute to ejaculation. However, this has not been studied at the molecular level.

EXPERIMENTAL APPROACH

The physiological contribution of each alpha(1)-adrenoceptor subtype was characterized using alpha(1)-adrenoceptor subtype-selective knockout (KO) mice (alpha(1A)-, alpha(1B)- and alpha(1D)-AR KO mice) since the subtype-specific drugs available are only moderately selective. We analysed the role of alpha(1)-adrenoceptors in the blood pressure and vascular response as well as ejaculation by determining these variables in alpha(1)-adrenoceptor subtype-selective KO mice and in mice with all their alpha(1)-adrenoceptor subtypes deleted (alpha(1)-AR triple-KO mice).

KEY RESULTS

The pregnancy rate was reduced by 50% in alpha(1A)-adrenoceptor KO mice, and this reduction was dramatically enhanced in alpha(1)-adrenoceptor triple-KO mice. Contractile tension of the vas deferens in response to noradrenaline was markedly decreased in alpha(1A)-adrenoceptor KO mice, and this contraction was completely abolished in alpha(1)-adrenoceptor triple-KO mice. This attenuation of contractility was also observed in the electrically stimulated vas deferens.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate that alpha(1)-adrenoceptors, particularly alpha(1A)-adrenoceptors, are required for normal contractility of the vas deferens and consequent sperm ejaculation as well as having a function in fertility.

Negative regulation of corticotropin releasing factor expression and limitation of stress response

Corticotropin releasing factor (CRF) coordinates behavioral, autonomic and hormonal responses to stress. Activation of the hypothalamic pituitary adrenal (HPA) axis with stimulation of CRF and vasopressin (VP) release from hypothalamic parvocellular neurons, and consequent secretion of ACTH from the anterior pituitary and glucocorticoid from the adrenal cortex, is the major endocrine response to stress. Current evidence indicates that the main regulator of ACTH secretion in acute and chronic conditions is CRF, in spite of the fact that the selective increases in expression of parvocellular VP and pituitary VP V1b receptors observed during prolonged activation of the HPA axis have suggested that VP becomes the predominant regulator. Following CRF release, activation of CRF transcription is required to restore mRNA and peptide levels, but termination of the response is essential to prevent pathology associated with chronic elevation of CRF and glucocorticoid production. While glucocorticoid feedback plays an important role in regulating CRF expression, the relative importance of direct transcriptional repression of the CRF gene by glucocorticoids in the overall feedback mechanism is not clear. In addition to glucocorticoids, intracellular feedback mechanisms in the CRF neuron, involving induction of repressor forms of cAMP response element modulator (CREM) limit CRF transcriptional responses by competing with the positive regulator, phospho-CREB. Rapid repression of CRF transcription following stress-induced activation is likely to contribute to limiting the stress response and to preventing disorders associated with excessive CRF production.

Correlation between vasoconstrictor roles and mRNA expression of alpha1-adrenoceptor subtypes in blood vessels of genetically engineered mice

We examined the contribution of each alpha(1)-adrenoceptor (AR) subtype in noradrenaline (NAd)-evoked contraction in the thoracic aortas and mesenteric arteries of mice. Compared with the concentration-response curves (CRCs) for NAd in the thoracic aortas of wild-type (WT) mice, the CRCs of mutant mice showed a significantly lower sensitivity. The pD(2) value in rank order is as follows: WT mice (8.21) > alpha(1B)-adrenoceptor knockout (alpha(1B)-KO) (7.77) > alpha(1D)-AR knockout (alpha(1D)-KO) (6.44) > alpha(1B)- and alpha(1D)-AR double knockout (alpha(1BD)-KO) (5.15). In the mesenteric artery, CRCs for NAd did not differ significantly between either WT (6.52) and alpha(1B)-KO mice (7.12) or alpha(1D)-KO (6.19) and alpha(1BD)-KO (6.29) mice. However, the CRC maximum responses to NAd in alpha(1D)- and alpha(1BD)-KO mice were significantly lower than those in WT and alpha(1B)-KO mice. Except in the thoracic aortas of alpha(1BD)-KO mice, the competitive antagonist prazosin inhibited the contraction response to NAd with high affinity. However, prazosin produced shallow Schild slopes in the vessels of mice lacking the alpha(1D)-AR gene. In the thoracic aorta, pA(2) values in WT mice for KMD-3213 and BMY7378 were 8.25 and 8.46, respectively, and in alpha(1B)-KO mice they were 8.49 and 9.13, respectively. In the mesenteric artery, pA(2) values in WT mice for KMD-3213 and BMY7378 were 8.34 and 7.47, respectively, and in alpha(1B)-KO mice they were 8.11 and 7.82, respectively. These pharmacological findings were in fairly good agreement with findings from comparison of CRCs, with the exception of the mesenteric arteries of WT and alpha(1B)-KO mice, which showed low affinities to BMY7378. We performed a quantitative analysis of the mRNA expression of each alpha(1)-AR subtype in these vessels in order to examine the correlation between mRNA expression level and the predominance of each alpha(1)-AR subtype in mediating vascular contraction. The rank order of each alpha(1)-AR subtype in terms of its vasoconstrictor role was in fairly good agreement with the level of expression of mRNA of each subtype, that is, alpha(1D)-AR > alpha(1B)-AR > alpha(1A)-AR in the thoracic aorta and alpha(1D)-AR > alpha(1A)-AR > alpha(1B)-AR in the mesenteric artery. No dramatic compensatory change of alpha(1)-AR subtype in mutant mice was observed in pharmacological or quantitative mRNA expression analysis.

Releasing signals, secretory pathways, and immune function of endogenous extracellular heat shock protein 72

Heat shock proteins (Hsp) were first characterized as intracellular proteins, which function to limit protein aggregation, facilitate protein refolding, and chaperone proteins. During times of cellular stress, intracellular Hsp levels increase to provide cellular protection. Recently, it has been recognized that Hsp, particularly Hsp72, are also found extracellularly (eHsp72), where they exhibit potent immunomodulatory effects on innate and acquired immunity. Circulating eHsp72 levels also greatly increase during times of stress (i.e., when an organism is exposed to a physical/psychological stressor or suffers from various pathological conditions). It has been proposed that elevated eHsp72 serves a protective role by facilitating immunological responses during times of increased risk of pathogenic challenge and/or tissue damage. This review focuses on the in vivo releasing signals and immunomodulatory function(s) of endogenous eHsp72. In addition, we present data that emphasize the importance of caution when conducting in vitro immunological tests of Hsp72 function.

Reduced capacitative calcium entry in the mesenteric vascular bed of bile duct-ligated rats

In this work, we analyzed the interaction of nitric oxide (NO) with some of the mechanisms known to regulate intracellular calcium levels in order to gain insight into the mechanisms responsible for the reduced vascular pressor response to vasoconstrictors observed in an experimental model of liver cirrhosis. Specifically, we hypothesized that the entry of calcium through capacitative channels is defective in this model. The experiments were performed with isolated, Krebs-perfused and de-endothelialized mesenteric arterial bed of rats with bile duct ligation (4 weeks) and their controls. Pretreatment with thapsigargin to inhibit calcium uptake into sarcoplasmic reticulum potentiated the pressor responses to methoxamine, but the response of the cirrhotic vessels was significantly lower than that of the controls. Under the same conditions, perfusion of the mesenteries with zero calcium-Krebs resulted in lower pressor responses to methoxamine, especially in the mesenteries of the bile duct-ligated rats. To specifically analyze the entry of calcium through store-operated calcium channels, the pressor response to the addition of calcium was studied in mesenteries perfused with zero calcium-Krebs and in the presence of thapsigargin. Again, the response of the cirrhotic mesenteric beds was significantly lower than that of the control vessels. Under all these experimental conditions, the differences between control and cirrhotic responses were abolished by pretreatment with the NO synthesis inhibitor N(w)-nitro-L-arginine (NNA). These results indicate that, in the mesenteric bed of bile duct-ligated rats, an excess of nitric oxide interferes with the release of calcium from thapsigargin-sensitive internal stores and also reduces the capacitative entry of calcium into vascular muscular cells induced by the depletion of calcium from internal stores. This mechanism may have an important role in the reduced pressor response observed in the mesenteric vascular bed in cirrhosis.

Evidence that α1B-adrenoceptors are involved in noradrenaline-induced contractions of rat tail artery

The present study characterizes the alpha(1)-adrenoceptor subtypes mediating contractions to noradrenaline in isolated ring preparations of rat tail artery. Concentration-response (E/[A]) curves to noradrenaline were apparently monophasic (pEC(50) 6.47) but became biphasic in the presence of the selective alpha(1A)-adrenoceptor antagonist (+/-)-1,3,5-trimethyl-6-[[3-[4-((2,3-dihydro-2-hydroxymethyl)-1,4-benzodioxin-5-yl)-1-piperazinyl]propyl]amino]-2,4(1H,3H)-pyrimidinedione (B8805-033). Whereas the first phase of contraction to noradrenaline remained nearly unaffected in the presence of B8805-033 (0.03-3 microM), the second phase was concentration-dependently shifted to the right (pK(B) 8.06). In the presence of B8805-033 (3 microM), noradrenaline-induced contractions (pEC(50) 6.55) were antagonized in a competitive manner by prazosin (pK(B) 9.24), tamsulosin (pK(B) 8.55), 2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane (WB 4101; pK(B) 7.81), spiperone (pK(B) 7.69), 4-amino-2-[4-[1-(benzyloxycarbonyl)-2(S)-[[(1,1-dimethylethyl)amino]carbonyl]-piperazinyl]-6,7-dimethoxyquinazoline (L-765,314; pK(B) 7.31), 5-methylurapidil (pK(B) 6.55), 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY 7378; pK(B) 6.43), and 8-[2-(1,4-benzodioxan-2-ylmethylamino)ethyl]-8-azaspiro[4.5]decane-7,9-dione (MDL 73005EF; pK(B) 5.71), and were also antagonized by 100 microM chloroethylclonidine. N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alpha-dimethyl-1H-indole-3-ethanamine (RS-17053) behaved as a noncompetitive antagonist (apparent pA(2) 6.55). Antagonist affinities obtained under these experimental conditions correlated highly with affinities at native and cloned alpha(1B)-adrenoceptors. Pretreatment of arterial rings with B8805-033 (3 microM) followed by receptor inactivation with chloroethylclonidine (100 microM) yielded monophasic E/[A] curves to noradrenaline (pEC(50) 6.14). Noradrenaline-induced contractions were competitively antagonized by tamsulosin (pK(B) 10.32), 5-methylurapidil (pK(B) 8.66), RS-17053 (pK(B) 8.44), B8805-033 (pK(B) 7.87), BMY 7378 (pK(B) 6.54), and L-765,314 (pK(B) 6.41). Antagonist affinities obtained under these experimental conditions correlated highly with affinities at native and cloned alpha(1A)-adrenoceptors. It is concluded that the contraction to noradrenaline in rat tail artery is mediated by both alpha(1B)- and alpha(1A)-adrenoceptors, each component of contraction being separable by use of selective alpha(1A)-adrenoceptor blockade and alpha(1B)-adrenoceptor alkylation, respectively.

MAP kinase-dependent induction of clock gene expression by alpha 1-adrenergic receptor activation

While peripheral oscillators can be reset by humoral factors such as glucocorticoid hormones, indirect neural communications involving sympathetic and parasympathetic neurons from the suprachiasmatic nucleus to various peripheral tissues suggest that autonomic nerve innervations also function in the resetting and synchronization of peripheral tissues. To study the role of sympathetic adrenergic signaling on clock gene expression, we constructed NIH3T3 cells that stably expressed each of three alpha(1)-adrenergic receptor subtypes (alpha(1A), alpha(1B) and alpha(1D)). We found that noradrenaline transiently induced the expression of mPer1, mPer2, and mE4bp4 1-2 h after alpha(1)-receptor activation. The extent and time course of clock gene mRNA induction by noradrenaline or the alpha(1)-receptor agonist phenylephrine (PE) was similar to that seen by 50% horse serum shock. Clock gene mRNA induction by PE was inhibited by U0126, a MEK inhibitor, suggesting involvement of the mitogen-activated protein kinase signaling pathway. We also found that both mPer1 and mPer2 mRNAs were induced in the mouse liver 60 min after PE injection. These results suggest that although humoral factors are important for entrainment of the peripheral clock, the autonomic nervous system may also be involved in the process.

Possible role of alpha-adrenoceptor subtypes in acute migraine therapy

Even though the underlying mechanisms for the pathophysiology of migraine attacks are not completely understood, little doubt exists that the headache phase is explained by dilatation of cranial, extracerebral blood vessels. In this context, experimental models predictive for anti-migraine activity have shown that both triptans and ergot alkaloids, which abort migraine headache, produce vasoconstriction within the carotid circulation of different species. In contrast to the well-established role of serotonin (5-hydroxytryptamine; 5-HT) 5-HT1B receptors in the common carotid vascular bed, the role of alpha-adrenoceptors and their subtypes has been examined only relatively recently. Using experimental animal models and alpha1- and alpha2-adrenoceptor agonists (phenylephrine and BHT933, respectively) and antagonists (prazosin and rauwolscine, respectively), it was shown that activation of either receptor produces a cranioselective vasoconstriction. Subsequently, investigations employing relatively selective antagonists at alpha1- (alpha1A, alpha1B, alpha1D) and alpha2- (alpha2A, alpha2B, alpha2C) adrenoceptor subtypes revealed that specific receptors mediate the carotid haemodynamic responses in these animals. From these observations, together with the potential limited role of alpha1B- and alpha2C-adrenoceptors in the regulation of systemic haemodynamic responses, it is suggested that selective agonists at these receptors may provide a promising novel avenue for the development of acute anti-migraine drugs.

2-(Anilinomethyl)imidazolines as alpha1 adrenergic receptor agonists: alpha1a subtype selective 2'-heteroaryl compounds

The structure-activity relationship of 2'-pyrrole, pyrazole and triazole substituted 2-(anilinomethyl)imidazolines as alpha(1) adrenergic agonists was investigated. The size and orientation of substituents, as well as the position of the heteroatoms, were found to have a profound effect on the potency and selectivity of the molecules. Potent alpha(1A) subtype selective agonists have been identified.

Systemic overexpression of the alpha 1B-adrenergic receptor in mice: an animal model of epilepsy

PURPOSE

A lack of selective alpha1-adrenergic receptor (alpha1-ARs) agonists and antagonists has made it difficult to clarify the precise function of these receptors in the CNS. We recently generated transgenic mice that overexpress either wild-type or a constitutively active mutant alpha 1B-AR in tissues that normally express the receptor. Both wild-type and mutant mice showed an age-progressive neurodegeneration with locomotor impairment and probable stress-induced motor events, which can be partially reversed by alpha 1-AR antagonists. We hypothesized that the wild-type and mutant mice may exhibit spontaneous epileptogenicity as compared with normal (nontransgenic) mice.

METHODS

Normal, wild-type, and mutant mice were studied. Twenty mice (1 year old) underwent prolonged video-EEG monitoring over a 4-week period. Raw EEG data were blindly analyzed by visual inspection for the presence of interictal and ictal epileptic activities.

RESULTS

During the acute postoperative period (< or = 3 days), both wild-type (26.1 +/- 8.07 spikes/day) and mutant mice (116.87 +/- 55.13) exhibited more frequent interictal spikes than did normal mice (2.17 +/- 0.75; p value, <0.05), but all three groups showed EEG and clinical seizures. During the later monitoring periods (>3 days), wild-type and mutant mice showed more frequent interictal spikes (15.44 +/- 4.07; p < 0.01; and 6.05 +/- 2.46; p < 0.05, respectively) as compared with normal mice (0.41 +/- 0.41), but only mutant mice had spontaneous clinical seizures (means +/- SEM).

CONCLUSIONS

The selective overexpression of the alpha 1B-AR is associated with increased in vivo spontaneous interictal epileptogenicity and EEG/behavioral seizures. These results suggest a possible role (direct or indirect) for the alpha 1B-ARs in the development and expression of epileptogenicity.

Mice expressing the alpha(1B)-adrenergic receptor induces a synucleinopathy with excessive tyrosine nitration but decreased phosphorylation

We had previously reported that systemic overexpression of the alpha(1B)-adrenergic receptor (AR) in a transgenic mouse induced a neurodegenerative disease that resembled the parkinsonian-like syndrome called multiple system atrophy (MSA). We now report that our mouse model has cytoplasmic inclusion bodies that colocalize with oligodendrocytes and neurons, are positive for alpha-synuclein and ubiquitin, and therefore may be classified as a synucleinopathy. Alpha-synuclein monomers as well as multimers were present in brain extracts from both normal and transgenic mice. However, similar to human MSA and other synucleinopathies, transgenic mice showed an increase in abnormal aggregated forms of alpha-synuclein, which also increased its nitrated content with age. However, the same extracts displayed decreased phosphorylation of alpha-synuclein. Other traits particular to MSA such as Purkinje cell loss in the cerebellum and degeneration of the intermediolateral cell columns of the spinal cord also exist in our mouse model but differences still exist between them. Interestingly, long-term therapy with the alpha(1)-AR antagonist, terazosin, resulted in protection against the symptomatic as well as the neurodegeneration and alpha-synuclein inclusion body formation, suggesting that signaling of the alpha(1B)-AR is the cause of the pathology. We conclude that overexpression of the alpha(1B)-AR can cause a synucleinopathy similar to other parkinsonian syndromes.

Transgenic studies of alpha(1)-adrenergic receptor subtype function

Mice with altered alpha(1)-adrenergic receptor (AR) genes have become important tools in elucidating the subtype-specific functions of the three alpha(1)-AR subtypes because of the lack of sufficiently subtype-selective pharmacological agents. Mice with a deletion (knockout, KO) or an overexpression (transgenic, TG) of the alpha(1A)-, alpha(1B)-, or alpha(1D)-AR subtypes have been generated. The alpha(1)-ARs are the principal mediators of the hypertensive response to alpha(1)-agonists in the cardiovascular system. Studies with these mice indicate that alpha(1A)-AR and alpha(1B)-AR subtypes play an important role in cardiac development and/or function as well as in blood pressure (BP) response to alpha(1)-agonists via vasoconstriction. The alpha(1B)- and alpha(1D)-subtypes also appear to be involved in central nervous system (CNS) processes such as nociceptive responses, modulation of memory consolidation and working memory. The ability to study subtype-specific functions in different mouse strains by altering the same alpha(1)-AR in different ways strengthens the conclusions drawn from these studies. Although these genetic approaches have limitations, they have significantly increased our understanding of the functions of alpha(1)-AR subtypes.

Direct catecholaminergic-cholinergic interactions in the basal forebrain. III. Adrenergic innervation of choline acetyltransferase-containing neurons in the rat

The central adrenergic neurons have been suggested to play a role in the regulation of arousal and in the neuronal control of the cardiovascular system. To provide morphological evidence that these functions could be mediated via the basal forebrain, we performed correlated light and electron microscopic double-immunolabeling experiments using antibodies against phenylethanolamine N-methyltransferase (PNMT) and choline acetyltransferase, the synthesizing enzymes for adrenaline and acetylcholine, respectively. Most adrenergic/cholinergic appositions were located in the horizontal limb of diagonal band of Broca, within the substantia innominata, and in a narrow band bordering the substantia innominata and the globus pallidus. Quantitative analysis indicated that cholinergic neurons of the substantia innominata receive significantly higher numbers of adrenergic appositions than cholinergic cells in the rest of the basal forebrain. In the majority of cases, the ultrastructural analysis revealed axodendritic asymmetric synapses. By comparing the number and distribution of dopamine beta-hydroxylase (DBH)/cholinergic appositions, described earlier, with those of PNMT/cholinergic interactions in the basal forebrain, it can be concluded that a significant proportion of putative DBH/cholinergic contacts may represent adrenergic input. Our results support the hypothesis that the adrenergic/cholinergic link in the basal forebrain may represent a critical component of a central network coordinating autonomic regulation with cortical activation.

The alpha(1D)-adrenergic receptor directly regulates arterial blood pressure via vasoconstriction

To investigate the physiological role of the alpha(1D)-adrenergic receptor (alpha(1D)-AR) subtype, we created mice lacking the alpha(1D)-AR (alpha(1D)(-/-)) by gene targeting and characterized their cardiovascular function. In alpha(1D)-/- mice, the RT-PCR did not detect any transcript of the alpha(1D)-AR in any tissue examined, and there was no apparent upregulation of other alpha(1)-AR subtypes. Radioligand binding studies showed that alpha(1)-AR binding capacity in the aorta was lost, while that in the heart was unaltered in alpha(1D)-/- mice. Non-anesthetized alpha(1D)-/- mice maintained significantly lower basal systolic and mean arterial blood pressure conditions, relative to wild-type mice, and they showed no significant change in heart rate or in cardiac function, as assessed by echocardiogram. Besides hypotension, the pressor responses to phenylephrine and norepinephrine were decreased by 30-40% in alpha(1D)-/- mice. Furthermore, the contractile response of the aorta and the pressor response of isolated perfused mesenteric arterial beds to alpha(1)-AR stimulation were markedly reduced in alpha(1D)-/- mice. We conclude that the alpha(1D)-AR participates directly in sympathetic regulation of systemic blood pressure by vasoconstriction.

alpha(1)-Adrenoceptor agonists: the identification of novel alpha(1A )subtype selective 2'-heteroaryl-2-(phenoxymethyl)imidazolines

Novel 2'-heteroaryl-2-(phenoxymethyl)imidazolines have been identified as potent agonists of the cloned human alpha(1)-adrenoceptors in vitro. The nature of the 2'-heteroaryl group can have significant effects on the potency, efficacy, and subtype selectivity in this series. alpha(1A) Subtype selective agonists have been identified.

Interaction of nitric oxide with calcium in the mesenteric bed of bile duct-ligated rats

We have analysed the interaction of NO with calcium in order to study the molecular mechanisms responsible for the vascular hyporesponse of liver cirrhosis. The experiments have been performed in the isolated and perfused mesenteric arterial bed of rats with bile duct ligation (BDL) and their controls. While perfusing the vessels with normal Krebs, methoxamine (MTX) or KCl produced a lower pressor response in the BDL mesenteries. The NO synthesis inhibitor N(w)-nitro-L-arginine (NNA) potentiated those responses and abolished the differences between groups. The administration of MTX under perfusion with zero calcium-Krebs, to analyse the intracellular release of calcium, also induced a lower response in the BDL mesenteries and NNA potentiated and normalized the response. To investigate calcium entry, the vessels were perfused with zero-calcium Krebs containing high potassium to open voltage-dependent calcium channels. Then, the addition of calcium (10(-1) - 3 x 10(-3) M) produced a lower pressor response in the BDL vessels, that was corrected by NNA. To study calcium entry through receptor-operated channels, the vessels were perfused with zero-calcium Krebs containing MTX. The addition of calcium elevated the perfusion pressure less in the BDL mesenteries than in the control and NNA potentiated the responses and eliminated the between groups differences. When calcium entry through both voltage- and receptor-operated channels was simultaneously analysed, similar results were obtained. In the mesenteric bed of bile duct ligated rats, an excess of nitric oxide affects vascular calcium regulation through an interaction with both calcium entry and intracellular calcium release.

alpha(1B)- and alpha(1D)-Adrenergic receptors exhibit different requirements for agonist and mitogen-activated protein kinase activation to regulate growth responses in rat 1 fibroblasts

We compared DNA replication, protein biosynthesis, and mitogen-activated protein kinase (MAPK) activity in Rat 1 fibroblasts stably expressing either the alpha(1B)-adrenergic receptor (AR) or alpha(1D)-AR subtypes. Activation of both the alpha(1B)-AR and alpha(1D)-AR inhibited DNA synthesis (as assessed by [(3)H]thymidine incorporation). In contrast, both receptors stimulated protein biosynthesis (as measured by [(35)S]methionine incorporation) and activated extracellular signal-regulated kinase (ERK)1/2. Importantly, these responses were agonist-dependent for the alpha(1B)-AR, but were agonist-independent for the alpha(1D)-AR. Agonist activation of the alpha(1B)-AR resulted in increased p38 kinase activity, but not c-Jun NH(2)-terminal kinase (JNK) activity, whereas the alpha(1D)-AR activated JNK but not p38 kinase. Unlike ERK1/2, JNK activity was increased by agonist treatment in the alpha(1D)-AR cells. An ERK1/2-pathway inhibitor PD98059 had no effect on phenylephrine-mediated inhibition of DNA synthesis in either cell line but blocked protein biosynthesis mediated by both receptors. The p38 kinase inhibitor SB203580 blocked alpha(1B)-AR effects on [(3)H]thymidine and [(35)S]methionine incorporation in alpha(1B)-AR-expressing cells, but had no effect on alpha(1D)-AR-mediated growth responses, consistent with the inability of the alpha(1D)-AR to activate p38 kinase. Therefore, alpha(1B)- and alpha(1D)-ARs mediated similar growth responses but differ with respect to the MAPK family member involved and the requirement for agonist.

2-(Anilinomethyl)imidazolines as alpha(1)-adrenoceptor agonists: the identification of alpha(1A) subtype selective 2'-carboxylic acid esters and amides

2-(Anilinomethyl)imidazolines with 2'-esters or 2'-amides are potent agonists of the cloned human alpha(1)-adrenoceptors in vitro. The size and shape of the ortho substituent can have significant effects on the potency, efficacy, and subtype selectivity of these 2-(anilinomethyl)imidazolines. alpha(1A)-subtype selective agonists have been identified.

Phe-308 and Phe-312 in transmembrane domain 7 are major sites of alpha 1-adrenergic receptor antagonist binding. Imidazoline agonists bind like antagonists

Although agonist binding in adrenergic receptors is fairly well understood and involves residues located in transmembrane domains 3 through 6, there are few residues reported that are involved in antagonist binding. In fact, a major docking site for antagonists has never been reported in any G-protein coupled receptor. It has been speculated that antagonist binding is quite diverse depending upon the chemical structure of the antagonist, which can be quite different from agonists. We now report the identification of two phenylalanine residues in transmembrane domain 7 of the alpha(1a)-adrenergic receptor (Phe-312 and Phe-308) that are a major site of antagonist affinity. Mutation of either Phe-308 or Phe-312 resulted in significant losses of affinity (4-1200-fold) for the antagonists prazosin, WB4101, BMY7378, (+) niguldipine, and 5-methylurapidil, with no changes in affinity for phenethylamine-type agonists such as epinephrine, methoxamine, or phenylephrine. Interestingly, both residues are involved in the binding of all imidazoline-type agonists such as oxymetazoline, cirazoline, and clonidine, confirming previous evidence that this class of ligand binds differently than phenethylamine-type agonists and may be more antagonist-like, which may explain their partial agonist properties. In modeling these interactions with previous mutagenesis studies and using the current backbone structure of rhodopsin, we conclude that antagonist binding is docked higher in the pocket closer to the extracellular surface than agonist binding and appears skewed toward transmembrane domain 7.

Hypotension, autonomic failure, and cardiac hypertrophy in transgenic mice overexpressing the alpha 1B-adrenergic receptor

alpha(1)-Adrenergic receptors (alpha(1A), alpha(1B), and alpha(1D)) are regulators of systemic arterial blood pressure and blood flow. Whereas vasoconstrictory action of the alpha(1A) and alpha(1D) subtypes is thought to be mainly responsible for this activity, the role of the alpha(1B)-adrenergic receptor (alpha(1B)AR) in this process is controversial. We have generated transgenic mice that overexpress either wild type or constitutively active alpha(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 alpha(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 alpha(1)ARs that is important in systemic regulation of blood pressure.

Heterogeneous control of blood flow amongst different vascular beds

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Increased vascular adrenergic vasoconstriction and decreased vasodilation in blacks. Additive mechanisms leading to enhanced vascular reactivity

Blood pressure reactivity is enhanced in young black subjects through mechanisms that are poorly understood. We compared alpha-adrenergic-mediated vasoconstrictor and ss-adrenergic vasodilator sensitivity and their relation to sympathetic activity in blacks and whites. Ten healthy black (age, 29.9+/-2.4 years) and 10 white (age, 28.3+/-1.9 years) men were studied. Forearm blood flow was measured with strain-gauge plethysmography after the intrabrachial artery administration of phenylephrine (1.25 to 20 microgram/min) and isoproterenol (60 and 400 ng/min) after application of lower-body negative pressure and after a cold pressor test. Forearm and systemic norepinephrine spillover were measured with a radioisotope dilution technique. alpha-Adrenergic vasoconstriction was markedly increased (ANOVA P=0.008) and ss-adrenergic vasodilation decreased (ANOVA P=0.02) in blacks. Phenylephrine (10 microgram/min) decreased forearm blood flow by 58.0+/-2.5% in blacks but only by 26.6+/-6.0% in whites (P<0.001). Vasoconstrictor response to endogenous norepinephrine, stimulated by a cold pressor test, resulted in a higher forearm vascular resistance in blacks than in whites (107.3+/-13 versus 64.8+/-13 mm Hg. mL(-)(1). 100 mL(-)(1), P=0.03). There were no significant ethnic differences in basal or stimulated forearm or systemic norepinephrine spillover. Increased vasoconstrictor and decreased vasodilator responses in blacks were not correlated. Increased sympathetically mediated vascular tone caused by enhanced vasoconstriction and attenuated vasodilation, effects that would be additive, and not increased sympathetic activity could enhance vascular reactivity and may play a role in the pathogenesis of hypertension in blacks.

Alpha 1-adrenergic receptor regulation: basic science and clinical implications

Adrenergic receptors (ARs) are members of the G-protein-coupled receptor family, which includes alpha 1ARs, alpha 2ARs, beta 1ARs, beta 2ARs, beta 3ARs, adenosine, muscarinic, angiotensin, endothelin receptors, and many others that are responsible for a large variety of physiologic effects through G-protein coupling. This review focuses on alpha 1ARs and their regulation at both the mRNA and protein levels. Currently, three alpha 1AR subtypes have been characterized both pharmacologically and at the gene level: alpha 1aAR, alpha 1bAR, and alpha 1dAR. These are expressed in a species- and tissue-dependent manner. Mutagenesis approaches have been extremely valuable in the identification of key residues that govern alpha 1AR ligand binding and signaling. These studies reveal that alpha 1ARs have evolved an exquisitely sensitive regulation of their activity in which any disruption of the native structure has profound effects on subsequent function and effector coupling. Significant advances have also been made in the elucidation of signaling pathway components, resulting in the identification of novel pathways that can lead to pathologic conditions. Specific topics include mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and G-protein-coupled receptor cross-talk pathways. Within this context, recent studies identifying underlying transcriptional mechanisms involved in the regulation of the alpha 1AR subtypes are also discussed. Finally, given the potentially important role of alpha 1ARs in the vasculature, as well as in the pathology of many diseases, such as myocardial hypertrophy and benign prostatic hyperplasia, the clinical relevance of alpha 1AR distribution, pharmacology, and therapeutic intervention is reviewed.

In situ hybridization and immunocytochemistry of alpha1-adrenoceptors in human peripheral blood lymphocytes

1 alpha1-Adrenoceptor subtypes were investigated in cytospin centrifuged preparations of human peripheral blood lymphocytes by in situ hybridization and immunocytochemistry. 2 In situ hybridization cytochemistry revealed alpha1A-, alpha1B-, and alpha1D-receptor mRNA in human peripheral blood lymphocytes. Lymphocytes hybridized for alpha1A receptor subtype represented approximately 30% of total lymphocytes, those hybridized for alpha1Beta- and alpha1D-receptor subtypes averaged 42 and 25% of total lymphocytes, respectively. 3 Cytospin centrifuged lymphocytes exposed to anti-alpha1A-, alpha1Beta- or alpha1D-receptor protein antibodies, developed specific immunostaining. Approximately 27% of total lymphocytes were immunoreactive for alpha1A-receptor protein, 40% displayed alpha1B-receptor protein immunoreactivity and 22% alpha1D-receptor protein immunoreactivity. Analysis of percentages as well as of lymphocyte morphology of in situ hybridized and immunolabelled lymphocytes suggests the co-expression of mRNA receptor signal and protein receptor immunostaining in the same lymphocyte. 4 The demonstration of both alpha1-adrenoceptor mRNA and receptor protein subtypes suggests that alpha1-adrenoceptors may have a role in regulating lymphocyte function. 5 The possibility of demonstrating receptor protein immunoreactivity in a small amount of blood, such as that required for preparing cytospin-centrifuged lymphocytes, may stimulate research to evaluate the role of these receptors in lymphocytes and to establish if assessment of lymphocyte alpha1-adrenoceptors may represent a marker of their status in health and disease.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Anion transport in heart

Anion transport proteins in mammalian cells participate in a wide variety of cell and intracellular organelle functions, including regulation of electrical activity, pH, volume, and the transport of osmolites and metabolites, and may even play a role in the control of immunological responses, cell migration, cell proliferation, and differentiation. Although significant progress over the past decade has been achieved in understanding electrogenic and electroneutral anion transport proteins in sarcolemmal and intracellular membranes, information on the molecular nature and physiological significance of many of these proteins, especially in the heart, is incomplete. Functional and molecular studies presently suggest that four primary types of sarcolemmal anion channels are expressed in cardiac cells: channels regulated by protein kinase A (PKA), protein kinase C, and purinergic receptors (I(Cl.PKA)); channels regulated by changes in cell volume (I(Cl.vol)); channels activated by intracellular Ca(2+) (I(Cl.Ca)); and inwardly rectifying anion channels (I(Cl.ir)). In most animal species, I(Cl.PKA) is due to expression of a cardiac isoform of the epithelial cystic fibrosis transmembrane conductance regulator Cl(-) channel. New molecular candidates responsible for I(Cl.vol), I(Cl.Ca), and I(Cl.ir) (ClC-3, CLCA1, and ClC-2, respectively) have recently been identified and are presently being evaluated. Two isoforms of the band 3 anion exchange protein, originally characterized in erythrocytes, are responsible for Cl(-)/HCO(3)(-) exchange, and at least two members of a large vertebrate family of electroneutral cotransporters (ENCC1 and ENCC3) are responsible for Na(+)-dependent Cl(-) cotransport in heart. A 223-amino acid protein in the outer mitochondrial membrane of most eukaryotic cells comprises a voltage-dependent anion channel. The molecular entities responsible for other types of electroneutral anion exchange or Cl(-) conductances in intracellular membranes of the sarcoplasmic reticulum or nucleus are unknown. Evidence of cardiac expression of up to five additional members of the ClC gene family suggest a rich new variety of molecular candidates that may underlie existing or novel Cl(-) channel subtypes in sarcolemmal and intracellular membranes. The application of modern molecular biological and genetic approaches to the study of anion transport proteins during the next decade holds exciting promise for eventually revealing the actual physiological, pathophysiological, and clinical significance of these unique transport processes in cardiac and other mammalian cells.

Characterization of alpha(1)-adrenoceptor subtypes in the eye

The presence of the alpha(1)-adrenoceptor subtypes in various parts of the pig and rabbit eyes was investigated using [(3)H]-prazosin radioligand binding. The characterization of the subtypes was achieved by performing competition experiments with various subtype selective drugs. In the pig retina, both alpha(1A)- and alpha(1B)-adrenoceptors were detected and the proportion of sites was 70% alpha(1A)- and 30% alpha(1B)-adrenoceptors, respectively. In the pig iris, ciliary body and choroid, which are melanin-rich tissues, the non-specific binding of [(3)H]-prazosin was too high to detect any of the alpha(1)-adrenoceptor subtypes. However, in the albino rabbit iris, ciliary body and retina both alpha(1A)- and alpha(1B)-adrenoceptors were detected. The proportion of sites in the iris was 60 % alpha(1A)- and 40% alpha(1B)-adrenoceptors, respectively. In the ciliary body and rabbit retina the proportion of sites were 70% alpha(1A)- and 30% alpha(1B)-adrenoceptors. Only the alpha(1A)-adrenoceptor subtype was detected in the rabbit choroid.

Selective blockade by nicergoline of vascular responses elicited by stimulation of alpha 1A-adrenoceptor subtype in the rat

The alpha 1-adrenergic blocking activity of nicergoline was re-examined in rats, with a particular emphasis on alpha 1-adrenoceptor subtypes. In pithed rats, nicergoline and prazosin infused at a single small dose (0.5 microgram/kg/min i.v.) produced a substantial and identical shift to the right of the control dose pressor response curve to the specific alpha 1-agonist cirazoline (ED50 = 4.0 +/- 0.1, 4.0 +/- 0.1 and 0.9 +/- 0.01 microgram/kg i.v. for nicergoline, prazosin and vehicle respectively). In the isolated perfused mesenteric vascular bed, nicergoline strongly inhibited the pressor responses elicited by cirazoline, with approximately 40-fold higher potency (pA2 = 11.1 +/- 0.3) than prazosin (pA2 = 9.5 +/- 0.3). Conversely, nicergoline was 20-fold less potent than prazosin to antagonize the contractile effects of cirazoline in isolated endothelium-denuded aorta (pA2 = 8.6 +/- 0.2 and 9.9 +/- 0.2 for nicergoline and prazosin respectively). Pretreatment of mesenteric vascular beds with chloroethylclonidine did not significantly modify nicergoline antagonistic potency (pA2 = 10.6 +/- 0.2). Nicergoline displaced [3H]-prazosin bound to rat forebrain membranes pretreated with chloroethylclonidine (pKi = 9.9 +/- 0.2) at concentrations 60-fold lower than in rat liver membranes (pKi = 8.1 +/- 0.2). Finally, of the nicergoline metabolites studied, lumilysergol acted as a modest alpha 1 antagonist (bromonicotinic acid was devoid of alpha 1 antagonist activity). In conclusion, nicergoline is a potent and selective alpha 1A-adrenoceptor subtype antagonist, an alpha 1-adrenoceptor subtype which is mainly represented in resistance arteries.

The role of circulating catecholamines in the regulation of fish metabolism: an overview

The physiological role of the catecholamines (CA), adrenaline and noradrenaline in fish has been frequently reviewed, but the metabolic consequences of these hormones have received less attention. The purpose of this review is to examine the recent literature dealing with CA actions on whole fish and tissue metabolism. The CA increase glucose production both in vivo and in vitro, at least in isolated hepatocytes. Although the data are less clear, lipid mobilization is also a consequence of elevated circulating CA. The difficulty with using the whole fish for such studies is that CA may alter other circulating hormone levels, CA turnover in the circulation quickly, and it is difficult to define precisely the tissue being affected. Much of our understanding is derived, therefore, from the study of isolated tissues, and especially the hepatocyte. Catecholamines stimulate both glycogenolysis and gluconeogenesis in hepatocytes isolated from a large number of fish species. This review examines the steps involved in the signal transduction system, from the binding of CA to alpha- and beta-adrenoceptors to the ultimate effects of specific enzyme phosphorylation. Recent literature demonstrates that the complexity of the adrenoceptor system noted for mammals, also is expressed in fish. Adrenoceptor subtypes are specific to species, to tissues and to function of the tissues, and these issues are discussed especially as they are related to external and to internal stressors. Future research will pursue better definitions of the adrenoceptor systems, molecular biology of the components of these receptor systems and development of alternative cell models. There still remains a poor explanation of the reason for the diversity of adrenoceptor systems, and there are a number of fish systems that may provide unique opportunities to understand this question.

Characterization of alpha1-adrenoceptor subtypes in the pig

The identities of the alpha1-adrenoceptor subtypes present in various tissues of the pig were studied using [3H]prazosin radioligand binding. The subtypes were characterized by performing competition experiments for various subtype selective drugs. In the cerebral cortex, spleen and heart, both alpha1A- and alpha1B-adrenoceptors were detected. In the liver was found only the alpha1A-subtype, while in the aorta was found only the alpha1B-subtype. An alpha1-adrenoceptor subtype was present in the adrenal gland with a high affinity for prazosin, the pKd value being 9.6, but with relatively low affinities for other alpha1-adrenoceptor binding drugs. The adrenal gland alpha1-adrenoceptor did not seem to represent the classical alpha1D-subtype, since drugs selective for the alpha1D-subtype in other species, including BMY7378 and SKF104856, showed low affinities for the pig adrenal gland alpha1-adrenoceptor.

Cloning of chicken and mouse alpha 1b adrenergic receptor

A partial cDNA encoding most of the third intracellular loop of the chicken alpha 1b adrenergic receptor subtype, obtained by reverse transcription-polymerase chain reaction (RT-PCR) techniques using degenerate primers derived from mammalian sequences, was used to isolate an alpha 1b adrenergic receptor cDNA from brain. The cDNA encodes a potential protein of 507 amino acids and Northern hybridization of poly(A)+ RNA from chicken brain of different developmental stages detected a single 3.5 kb transcript. Analysis of receptor expression indicated that the alpha 1b adrenergic receptor is widely distributed in chicken tissues, specially kidney and liver. cDNA and genomic clones encoding sequences of the mouse alpha 1b adrenergic receptor were also isolated.

Proximal nephron Na+/H+ exchange is regulated by alpha 1A- and alpha 1B-adrenergic receptor subtypes

Activation of alpha 1-adrenergic receptors (alpha 1-AR) increases Na+/H+ exchange (NHE) in proximal tubule. NHE mediates the majority of active Na+ absorption in the proximal tubule. Three alpha 1-AR subtypes have been detected in kidney by molecular and binding techniques. We detected message for all three alpha 1-AR subtypes in mouse proximal tubule cells through reverse transcription-polymerase chain reaction and Northern analysis. To determine the alpha 1-AR subtypes that regulate NHE in mouse proximal tubule cells, two strategies were used: (i) antisense oligodeoxynucleotides (ODNs) to selectively inhibit expression of alpha 1A-, alpha 1B-, and alpha 1D-AR subtypes and (ii) subtype-selective alpha 1-AR antagonists. Streptolysin-O permeabilization was used to introduce antisense and sense ODNs into cells three times over 72 hr. Western blot analysis of membranes prepared from cells treated with alpha 1B-AR antisense ODN demonstrated that alpha 1B-AR protein expression was reduced by 90% at 72 hr compared with control or sense ODN treatments. Functional regulation of NHE by alpha 1-ARs was determined by alpha 1-AR agonist changes in intracellular pH (pHi) in cells grown on coverslips and loaded with 2',7'-bis(2-carboxyethyl)-5(6)carboxyfluorescein-acetoxymethyl ester. Antisense ODNs for alpha 1B-AR significantly reduced phenylephrine (PHE)-induced maximal changes in pHi by 49%. The PHE-induced changes in pHi observed in cells treated with alpha 1A-AR antisense ODNs was reduced by 42%. The selective alpha 1A-AR antagonist WB-4101 and the alpha 1B-AR antagonist spiperone reduce PHE-induced pHi increases to a comparable extent. No significant changes in pHi were observed with cells treated with alpha 1D-AR antisense ODNs or the alpha 1D-AR antagonist BMY 7378 compared with untreated cells. Combined treatment with alpha 1A- and alpha 1B-AR antisense ODNs and antagonists additively inhibits PHE-induced delta pHi by 90%. We conclude that alpha 1A and alpha 1B-AR but not alpha 1D-ARs regulate NHE in proximal tubule cells.

Alpha-adrenoceptors and vascular regulation: molecular, pharmacologic and clinical correlates

This manuscript is intended to provide a comprehensive review of the alpha-adrenoceptors (ARs) and their role in vascular regulation. The historical development of the concept of receptors and the division of the alpha-ARs into alpha 1 and alpha 2 subtypes is traced. Emphasis will be placed on current understanding of the specific contribution of discrete alpha 1- and alpha 2-AR subtypes in the regulation of the vasculature, selective agonists and antagonists for these receptors, the second messengers utilized by these receptors, the myoplasmic calcium pathways activated to initiate smooth muscle contraction, as well as the clinical uses of agonists and antagonists that work at these receptors. New information is presented that deals with the molecular aspects of ligand interactions with specific subdomains of these receptors, as well as mRNA distribution and the regulation of alpha 1- and alpha 2-AR gene transcription and translation.

Characterization of the alpha1B-adrenergic receptor gene promoter region and hypoxia regulatory elements in vascular smooth muscle

We previously demonstrated that alpha1B-adrenergic receptor (AR) gene transcription, mRNA, and functionally coupled receptors increase during 3% O2 exposure in aorta, but not in vena cava smooth muscle cells (SMC). We report here that alpha1BAR mRNA also increases during hypoxia in liver and lung, but not heart and kidney. A single 2.7-kb alpha1BAR mRNA was detected in aorta and vena cava during normoxia and hypoxia. The alpha1BAR 5' flanking region was sequenced to -2,460 (relative to ATG +1). Transient transfection experiments identify the minimal promoter region between -270 and -143 and sequence between -270 and -248 that are required for transcription of the alpha1BAR gene in aorta and vena cava SMC during normoxia and hypoxia. An ATTAAA motif within this sequence specifically binds aorta, vena cava, and DDT1MF-2 nuclear proteins, and transcription primarily initiates downstream of this motif at approximately -160 in aorta SMC. Sequence between -837 and -273 conferred strong hypoxic induction of transcription in aorta, but not in vena cava SMC, whereas the cis-element for the transcription factor, hypoxia-inducible factor 1, conferred hypoxia-induced transcription in both aorta and vena cava SMC. These data identify sequence required for transcription of the alpha1BAR gene in vascular SMC and suggest the atypical TATA-box, ATTAAA, may mediate this transcription. Hypoxia-sensitive regions of the alpha1BAR gene also were identified that may confer the differential hypoxic increase in alpha1BAR gene transcription in aorta, but not in vena cava SMC.

Distribution of alpha 1a-, alpha 1b- and alpha 1d-adrenergic receptor mRNA in the rat brain and spinal cord

The technique of in situ hybridization with specific ribonucleotide probes was used to determine the distribution patterns of mRNA encoding the alpha 1a-, alpha 1b- and alpha 1d-adrenoceptor (AR) subtypes in rat brain and spinal cord. The expression pattern of alpha 1a-AR mRNA has not been reported previously, and was found to be widespread throughout the rat central nervous system. High levels were found in regions of the olfactory system, several hypothalamic nuclei, and regions of the brainstem and spinal cord, particularly in areas related to motor function. Regions expressing moderate levels of mRNA for this receptor were the septum, bed nucleus of the stria terminalis, cerebral cortex, amygdala, cerebellum and pineal gland. Low expression levels were detected in the hippocampal formation. Most nuclei in the basal ganglia and thalamus expressed extremely low or undetectable levels of alpha 1a-AR mRNA. The expression patterns of the alpha 1b- and alpha 1d-AR mRNAs were similar to those described using oligonucleotide probes in earlier studies. High expression of alpha 1b-AR mRNA was noted in the pineal gland, most thalamic nuclei, lateral nucleus of the amygdala and dorsal and median raphe nuclei. Moderate expression levels were noted throughout the cerebral cortex, and in some olfactory, septal, and brainstem regions. The distribution of alpha 1d-AR mRNA was the most discrete of the three receptors examined. Expression was strong in the olfactory bulb, cerebral cortex, hippocampus, reticular thalamic nucleus, regions of the amygdala, motor nuclei of the brainstem, inferior olivary complex and spinal cord. Comparison of the distributions of the alpha 1a-, alpha 1b- and alpha 1d-AR mRNA suggests unique functional roles for each of these receptors.

Alpha 1D- and alpha 1A-adrenoceptors mediate contraction in rat renal artery

To investigate the alpha 1-adrenoceptor subtype(s) mediating contraction in rat renal artery, we have compared the effect of the alpha 1-adrenoceptor antagonists, 5-methylurapidil, BMY 7378 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl) ethyl) 8-azaspiro (4.5) decane-7,9-dione 2HCl) and chloroethylclonidine on functional responses to noradrenaline. A clear blockade by chloroethylclonidine (10(-4) M) of noradrenaline-induced contraction was observed and, along with this effect. pKB values of 9.12 and 8.40 for BMY 7378 and 9.75 and 10.06 for 5-methylurapidil were obtained, indicating that the renal artery expresses the alpha 1D-adrenoceptor subtype as the one involved in contraction and not only the alpha 1A subtype as has been reported.