Expression Of Alpha 1-adrenergic Receptors Research Articles

Effect of Early Diabetes on the Expression of Alpha-1 Adrenergic Receptors in Aorta and Carotid Arteries of Wistar Kyoto and Spontaneously Hypertensive Rats

Hypertension and diabetes have been related to noradrenergic system impairment, especially to the response mediated by alpha-1 receptors. The aim of this work was to investigate possible changes in the expression of alpha-1 adrenergic receptors in aorta and carotid arteries of Wistar Kyoto and spontaneously hypertensive rats after 4 weeks of the onset of diabetes. Our results suggest that early diabetes modifies the expression of alpha-1 adrenergic receptors in aorta and carotid arteries of both WKY and SHR strains in a different way.

Increased alpha-1 Adrenoceptor Expression in Pregnant Rats with Subrenal Aortic Coarctation

The progression of pregnancy is associated with attenuation in vasopressor response to adrenergic agonists. In pregnancy-induced hypertension this attenuation is reverted. It is not known if this reversion involves alpha-1 adrenoceptor expression. Objective. In this work we propose that in pregnant rats with subrenal aortic coarctation there are changes in the expression of alpha-1 adrenergic receptors in the thoracic and abdominal aorta during pregnancy. Methods. We used non-pregnant, normal pregnant and pregnant with subrenal aortic coarctation female Wistar rats. Pregnancy-induced hypertension indicators, systolic blood pressure, 24 hours proteinuria, pup weight and maternal weight were measured. Dose response curves to phenylephrine were carried out to determine vascular reactivity along pregnancy. Alpha 1-adrenoceptors were detected from thoracic and abdominal aorta using immunoblot. Results. Results show significant increases in arterial pressure and proteinuria in pregnant rats with SRAC at the end of the third week. Pregnancy reduces alpha-1-A, -B and -D adrenoceptor expression and this event is reverted by subrenal aortic coarctation. This phenomenon is more apparent in the abdominal segment of the aorta. Conclusions. These findings suggest that subrenal aortic coarctation is a good animal model of pregnancy-induced hypertension and that α1-adrenoceptors participate in its physiopathology increasing their expression in a segment-dependent manner.

Altered expression and alpha‐1 adrenergic receptor mediated activity of protein kinase C in the prefrontal cortex of rats with neonatal ventral hippocampus lesions

The neonatal ventral hippocampus (nVH) lesion in rats captures many features of schizophrenia at the levels of behavior and neurobiological markers. We have previously reported enhanced expression of alpha-1 adrenergic receptors (AR) in the prefrontal cortex (PFC) of postpubertal nVH-lesioned rats and proposed that enhanced alpha-1 AR signaling might participate in some of the behavioral abnormalities observed in the nVH-lesioned rats. To assess the components of alpha-1 adrenergic signaling in nVH-lesion rats, we examined prefrontal cortical expression of protein kinase C (PKC) subtypes by Western blotting and alpha-1 AR-stimulated PKC activity by in vitro enzyme assay in postpubertal animals. Neonatal VH-lesioned animals showed significantly increased expression of membrane-bound PKC-alpha and the phosphorylated form of PKC. Cytosolic PKC-beta II and PKC-gamma expression were found to be decreased in the PFC of lesioned animals with no change in the expression of PKC-beta I either in the cytosol or membrane. PKC activity assays showed an increase in basal PKC activity in the PFC slices of nVH-lesioned animals. Stimulation of alpha-1 adrenergic receptor with different concentrations of the agonist phenylephrine (PE), while increasing PKC activity in the sham-lesioned animals surprisingly decreased the activity in nVH-lesioned animals. Increased basal levels as well as activity of prefrontal PKC and its anomalous regulation by alpha-1 adrenergic receptors may participate in the cognitive and stress-induced behavioral alterations in nVH-lesioned animals.

Alpha1-adrenergic Receptor mRNA and Inflammatory Mediator Expression in Circulating Leucocytes after Cardiac Surgery

Vasodilation after coronary artery bypass surgery is a common complication. Inflammatory mediators influence the expression of alpha1-adrenergic receptors. Do patients requiring high doses of postoperative inotropic support have down-regulated alpha-adrenergic receptors? Is there a characteristic pattern of preoperative inflammatory mediator expression that could predict a complicated course after the operation? Forty-four patients undergoing cardiac bypass surgery with extracorporeal circulation were prospectively investigated. Five perioperative blood samples were taken (preoperative, two hours, 12 hours, 36 hours and 72 hours postoperative). The leucocyte mRNA-expression of the three alpha1-adrenergic receptor subtypes (A, B and D) and 11 different pro-inflammatory mediators were investigated with the real-time reverse transcriptase polymerase chain reaction. The patients were divided into three groups (No-noradrenaline [No-NA]= 0 microg/min, Low-noradrenaline [Low-NA]=0.1-7 microg/min, High-noradrenaline [High-NA] >7 microg/min), according to their postoperative noradrenaline requirements. Preoperatively, alpha1(A)-receptor expression was 4.9-fold (High-NA) and 18.7-fold (Low-NA) higher than the No-NA group (P=0.005) and plasma noradrenaline levels were higher in the High-NA group (P=0.005). Across all groups at 12 hours after the operation, alpha1(A) -receptor expression decreased to approximately one-fifth of preoperative levels (P=0.01); but with greater duration and magnitude of relative decrease in the High-NA group. Patients in the No-NA group had significant postoperative increases in leucocyte inflammatory mediator expression for IL-1beta, TLR4, TREM, MPO, MMP9 and TNF genes, whereas the changes in the Low-NA and High-NA groups were not significant. Low preoperative levels of noradrenaline and low expression of alpha1(A)-adrenoreceptors in leucocytes was associated with less probability of requiring noradrenaline support after cardiac surgery.

Increased α1-Adrenergic Activity in the Rat Bladder by Depletion of Ovarian Hormones

It is possible that postmenopausal loss of ovarian hormones leads to sensitization and/or over expression of alpha1-adrenergic receptors. The objective of this study was to determine whether ovariectomy enhances efferent transmission and, hence, increases contractility in the rat bladder by increasing alpha1-adrenergic receptors. This hypothesis was tested in 4 urethane anesthetized groups of female rats, including regularly cycling rats in metestrus and proestrus, and rats 4 months after ovariectomy with and without estradiol replacement, respectively. The bladder was catheterized through the urethra to measure intravesical pressure. The left femoral artery was also catheterized for local delivery of the nonspecific alpha1-adrenergic agonist phenylephrine, the alpha1-adrenergic antagonist prazosin, the specific alpha1A antagonist 5-methylurapidil or dimethyl sulfoxide (Sigma) in saline vehicle. In some rats bladder contractility was assessed by cystometry, followed by treatment with phenylephrine injected via the femoral artery. In other rats the bladder was denervated and a platinum electrode was wrapped around branches of the left pelvic nerve for electrical stimulation. The amplitude of micturition contractions and contractions evoked by phenylephrine or pelvic nerve stimulation was measured. Micturition and phenylephrine evoked bladder contractions were significantly increased in ovariectomized rats without estradiol replacement. Prazosin significantly decreased contractions evoked by pelvic stimulation in a dose dependent manner. This decrease was significantly larger in ovariectomized rats without estradiol replacement compared to that in the other groups. The inhibition of stimulation evoked contractions by 5-methylurapidil was also greater in ovariectomized rats without estradiol replacement than in rats with estradiol replacement. Results suggest that the depletion of ovarian hormones after ovariectomy enhances alpha1-adrenergic activity.

Alpha1-adrenergic receptor subtypes in peripheral blood lymphocytes of essential hypertensives.

The expression of alpha1-adrenergic receptor subtypes in peripheral blood lymphocytes was investigated in 28 essential hypertensive patients as well as in the peripheral blood lymphocytes and aorta of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Alpha1-adrenergic receptors were quantified by radioligand binding assays, employing [3H]-prazosin as the radioligand in association with compounds displaying different degrees of selectivity for alpha1A-, alpha1B- and alpha1D-adrenergic receptor subtypes. The affinity of [3H]-prazosin binding was similar in peripheral blood lymphocytes of different stage essential hypertensive and normotensive subjects or of SHR and age-matched normotensive WKY rats as well as in the aortas of SHR and WKY rats. The radioligand binding assay revealed no change in the expression of alpha1-adrenergic receptors in peripheral blood lymphocytes of essential hypertensives compared with normotensive subjects; a moderate decrease of alpha1B-adrenergic receptors and an increase of alpha1D-adrenergic receptors. The relative densities of the alpha1-adrenergic receptor subtypes were similar in the three groups of essential hypertensives. In peripheral blood lymphocytes and in aorta of SHR, [3H]-prazosin binding was significantly reduced compared with normotensive WKY rats. The expression of alpha1-adrenergic receptor subtypes in peripheral blood lymphocytes of SHR was similar to that found in peripheral blood lymphocytes of essential hypertensives. Changes of lymphocyte alpha1-adrenergic receptor subtypes in essential hypertensives are similar to those observed in lymphocytes and vascular tissues of animal models of hypertension. This suggests that assays of lymphocyte alpha1-adrenergic receptors may represent an indirect marker of their involvement in essential hypertension.

Receptor-activated Ca2+ increases in vibrodissociated cortical astrocytes: a nonenzymatic method for acute isolation of astrocytes.

A new nonenzymatic method for the acute isolation of astrocytes from rat cerebral cortex is described. A vibratory device was used to dissociate the cells from thin brain slices, and the method yielded fresh and relatively well-preserved astrocytes without previous enzyme incubation. These cells were examined in a microspectrofluorometric system for measurement of changes in intracellular free calcium concentrations ([Ca2+]i), and their expression of various neurotransmitter receptors was determined. Acutely isolated glial fibrillary acidic protein (GFAP)-positive astrocytes (p7-p18) were seen to respond to the metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD, 10(-4) M) with increases in [Ca2+]i, and this response was blocked by (RS)-1-aminoindan-1,5 dicarboxylic acid (AIDA, 10(-3) M), an antagonist to group 1 metabotropic glutamate receptors. The delta-opioid receptor agonist D-Pen2, D-Pen5-enkephalin (DPDPE, 10(-6) M) evoked [Ca2+]i increases that were blocked by the delta-opioid antagonist ICI 174.388 (10(-5) M). The astrocytes failed to respond to 5-hydroxytryptamine (5-HT, 10(-5) M), although the same cells subsequently were found to respond to other agonists. Furthermore, [Ca2+]i responses evoked by phenylephrine (10(-5) M) were blocked by prazosin (0.2x10(-6) M), suggesting the expression of alpha1-adrenergic receptors on the acutely isolated astrocytes. The cells were also shown to react with [Ca2+]i increases in response to depolarization with high extracellular potassium concentrations (50x10(-3) M). The signals induced by depolarization were not seen in Ca2+-free buffer, indicating the presence of voltage-activated calcium channels in these cells. Thus, the present study confirms some of the results earlier obtained in cell cultures, suggesting that cortical astrocytes in vivo express glutamate, opiate, and adrenergic receptors, coupled to increases in [Ca2+]i, whereas no receptors for 5-HT could be detected.

Insulin and insulin-like growth factor I differentially induce alpha1-adrenergic receptor subtype expression in rat vascular smooth muscle cells.

Hyperinsulinemia has been implicated as an important risk factor for the development of accelerated cardiovascular disease. We wondered if insulin or IGF-I induced expression of alpha1 adrenergic receptors in vascular smooth muscle cells (VSMCs) which could enhance smooth muscle contraction and cell growth activated by catecholamines. Rat aortic VSMCs were incubated with insulin or IGF-I for various times and expression of alpha1 receptors was detected using [3H]prazosin binding. Both insulin and IGF-I increased alpha1 receptor number; also, these peptides increased expression of the alpha1D receptor gene with no change in expression of the alpha1B receptor gene as detected by RNase protection assays. Using Western blotting, we found that these peptides increased expression of the alpha1D receptor subtype in these cells. Increased expression of the alpha1D receptor mRNA was inhibited by the receptor tyrosine kinase inhibitor genistein and the PI 3-kinase inhibitor wortmannin but was not inhibited by protein kinase C inhibitor H7 or the L-type calcium channel blocker nifedipine. Preincubation of cells with insulin or IGF-I enhanced subsequent norepinephrine stimulation of mitogen activated kinase activity. These results suggest that insulin/IGF-I regulate expression of alpha1 receptors in VSMCs and potentially enhance the effects of catecholamines in settings of hyperinsulinemia.

Angiotensin II induces transcription and expression of alpha 1-adrenergic receptors in vascular smooth muscle cells.

Angiotensin II (ANG II) induces vascular smooth muscle contraction and functions as a growth factor stimulating vascular smooth muscle cell (VSMC) hypertrophy. We wondered whether ANG II might induce expression of alpha 1-adrenergic receptors (ARs) in cultured VSMCs, which would then potentially accentuate the effects of catecholamines in the cells. Rat VSMCs were preincubated with phenoxybenzamine to inactivate alpha 1-ARs; the cells were then treated with ANG II for 24 h. ANG II-treated cells expressed an increased number of alpha 1-ARs compared with controls, suggesting that ANG II increased the rate of alpha 1-AR synthesis. ANG II markedly induced accumulation of alpha 1A/D- and alpha 1B-AR mRNAs in a concentration- and time-dependent manner. This effect of ANG II was blocked by the specific ANG II-receptor agonist [Sar1-Ile8]ANG II. ANG II-induced accumulation of alpha 1A/D-AR mRNAs was completely abolished by transcriptional inhibitor actinomycin D. ANG II markedly increased the transcriptional rate of the alpha 1A/D-AR gene without changing stability of alpha 1A/D-AR mRNAs. Protein kinase C (PKC) activator 4 beta-phorbol 12-myristate 13-acetate also induced accumulation of alpha 1A/D-AR mRNAs, and PKC inhibitor H-7 completely blocked ANG II-induced accumulation of the alpha 1A/D-AR mRNAs. Neither the biologically inactive ANG II analogue des-Phe8-ANG II nor the calcium ionophores A-23187 and BAY K-8466 induced alpha 1A/D-AR mRNAs. Finally, ANG II preincubation increased alpha 1-AR agonist phenylephrine-stimulated expression of the c-fos gene.(ABSTRACT TRUNCATED AT 250 WORDS)

α1‐Adrenergic Receptors in Neuronal Cultures from Rat Brain: Increased Expression in the Spontaneously Hypertensive Rat

Neuronal cells in primary culture from 1-day-old brains of normotensive, Wistar-Kyoto strain (WKY) and spontaneously hypertensive (SH) rats have been utilized to study the expression of alpha 1-adrenergic receptors. Binding of a selective alpha 1 antagonist, [125I]2-[beta-(4-hydroxy-3-iodophenyl)-ethylaminomethyl]-tetralone ([125I]HEAT) to neuronal membranes prepared from primary brain cultures of WKY and SH rats was 75-80% specific, rapid, and time-dependent although the binding was 1.5-2 times higher in neuronal membranes from SH rat brain cultures. Kinetic analysis of the association and dissociation data demonstrated no significant differences between rat strains. Competition-inhibition experiments provided IC50 values for various antagonists and agonists in the following order: prazosin less than phentolamine less than yohimbine less than phenylephrine less than norepinephrine less than propranolol, suggesting that [125I]HEAT bound selectively to alpha 1-adrenergic receptors. Scatchard analysis of the binding data provided straight lines for both strains of rats, indicating the presence of a homogeneous population of binding sites. It also showed that the increase in the binding in neuronal cells from SH rat brains over those from normotensive WKY controls was a result of an increase in the number of alpha 1-adrenergic receptors. Incubation of neuronal cultures from both strains of rats with phenylephrine, an alpha 1-adrenergic agonist, caused a time- and dose-dependent decrease in the binding of [125I]HEAT. This decrease was due to a decrease in the number of alpha 1-adrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased alpha 1-adrenergic receptor-mediated inositide hydrolysis in neurons from hypertensive rat brain.

The expression of alpha 1-adrenergic receptors and norepinephrine (NE)-stimulated hydrolysis of inositol phospholipid has been studied in neuronal cultures from the brains of normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SH) rats. Binding of 125I-2-[beta-(4-hydroxyphenyl)-ethyl-aminomethyl] tetralone (HEAT) to neuronal membranes was 68-85% specific and was rapid. Competition-inhibition experiments with various agonists and antagonists suggested that 125I-HEAT bound selectively to alpha 1-adrenergic receptors. Specific binding of 125I-HEAT to neuronal membranes from SH rat brain cultures was 30-45% higher compared with binding in WKY normotensive controls. This increase was attributed to an increase in the number of alpha 1-adrenergic receptors on SH rat brain neurons. Incubation of neuronal cultures of rat brain from both strains with NE resulted in a concentration-dependent stimulation of release of inositol phosphates, although neurons from SH rat brains were 40% less responsive compared with WKY controls. The decrease in responsiveness of SH rat brain neurons to NE, even though the alpha 1-adrenergic receptors are increased, does not appear to be due to a general defect in membrane receptors and postreceptor signal transduction mechanisms. This is because neither the number of muscarinic-cholinergic receptors nor the carbachol-stimulated release of inositol phosphates is different in neuronal cultures from the brains of SH rats compared with neuronal cultures from the brains of WKY rats. These observations suggest that the increased expression of alpha 1-adrenergic receptors does not parallel the receptor-mediated inositol phosphate hydrolysis in neuronal cultures from SH rat brain.

Age-dependent changes in expression of alpha 1-adrenergic receptors in rat myocardium

The expression of alpha 1-adrenergic receptors within ventricular myocardium of rats ranging in age from 21 days of fetal life to 24 months after birth was measured from [ 125I] 2-(β hydroxy phenyl) ethylaminomethyl tetralone binding isotherms. No difference was observed in binding affinity between any of the age groups studied. The number of alpha 1-adrenergic receptors was found to be 60–120% higher in membranes from fetal or immature rats up to 25 days of age when compared with adult animals. The increased expression of alpha 1-adrenergic receptors in the developing heart relative to that observed in adult heart is consistent with the hypothesis that alpha 1-adrenergic receptor stimulation may modulate protein synthesis and growth in mammalian myocardium.