Alpha-adrenergic mRNA subtype expression in the human nasal turbinate

PURPOSE

Alpha-adrenergic receptor (AR) agonist drugs (e.g., epinephrine) are commonly used for upper airway procedures, to shrink the mucosa, retard absorption of local anesthetic agents, and improve visualization by limiting hemorrhage. Decongestant therapy often also includes alphaAR agonist agents, however overuse of these drugs (e.g., oxymetazoline) can result in chronic rhinitis and rebound increases in nasal secretion. Since current decongestants stimulate alphaARs non-selectively, characterization of alphaAR subtype distribution in human airway (nasal turbinate) offers an opportunity to refine therapeutic targets while minimizing side-effects. We, therefore, investigated alphaAR subtype expression in human nasal turbinate within epithelial, duct, gland, and vessel cells using in situ hybridization.

METHODS

Since sensitive and specific anti-receptor antibodies and highly selective alphaAR subtype ligands are currently unavailable, in situ hybridization was performed on sections of three human nasal turbinate samples to identify distribution of alphaAR subtype mRNA. Subtype specific (35)S-labelled mRNA probes were incubated with nasal turbinate sections, and protected fragments remaining after RNase treatment analyzed by light and darkfield microscopy.

RESULTS

In non-vascular tissue alpha(1d) AR mRNA predominates, whereas notably the alpha(2c) is the only alphaAR subtype present in the sinusoids and arteriovenous anastamoses.

CONCLUSION

Combined with the current understanding that AR-mediated constriction of nasal sinusoids underpins decongestant therapies that minimize secretions and shrink tissues for airway procedures, these findings suggest that alpha(2c) AR subtypes provide a novel selective target for decongestant therapy in humans.

17-Beta-estradiol directly regulates the expression of adrenergic receptors and kisspeptin/GPR54 system in GT1-7 GnRH neurons

Estradiol plays a critical role in the feedback regulation of reproduction, in part by modulating the neurosecretory activity of gonadotropin-releasing hormone (GnRH) neurons. While indirect effects of estradiol on GnRH neurons have been clearly demonstrated, direct actions are still controversial. In the current study, we examined direct effects of 17beta-estradiol upon the expression of receptors for afferent signals at the level of the GnRH neuron, using immortalized GT1-7 cells. Using RT-PCR, we confirmed the expression of mRNA for the adrenergic receptors (AR) alpha(1)A-, alpha(1)B-, alpha(1)D-, alpha(2)A-, alpha(2)C-, and beta(1)-AR, and showed for the first time that mRNAs for alpha(2)B-, beta(2)- and beta(3)-AR, for kisspeptin and its receptor GPR54 and for the novel estrogenic receptor GPR30 are expressed in GT1-7 cells. After treatment with 10 nM 17beta-estradiol, alpha(1)B-AR mRNA was significantly increased (14-fold) after 6 h as determined by real-time PCR, while alpha(1)B- and alpha(1)D-AR mRNA were significantly increased (19- and 23-fold, respectively) after 24 h. The expression of KiSS-1 and GPR54 mRNAs were also significantly increased (8- and 6-fold, respectively) after 24 h treatment of GT1-7 cells with estradiol. GPR30 mRNA expression was not affected by estradiol. Our data also showed that kisspeptin-10 (1-10 nM) can significantly stimulate GnRH release and GnRH mRNA expression in GT1-7 cells. These results suggest that the complex physiologic effects of estradiol on the function of the reproductive axis could be mediated partly through direct modulation of the expression of receptors for afferent signals in GnRH neurons.

Balloon injury alters alpha-adrenoceptor expression across rat carotid artery wall

alpha(1)-Adrenoceptors (AR) mediate growth factor-like activity of catecholamines on vascular smooth muscle cells (SMC) and adventitial fibroblasts. This trophic activity is strongly augmented by balloon injury, contributes significantly to subsequent proliferation, wall hypertrophy and lumen loss and is mediated by alpha(1A)- and alpha(1B)-AR. However, it is not known how injury augments adrenergic trophic activity. The aim of the present study was to examine alpha-AR expression in rat carotid artery and to test the hypothesis that balloon injury augments a(1)-AR expression. 2. Neointima, media and adventitia were isolated at various days after balloon injury of rat carotid artery and subjected to quantitative reverse transcription-polymerase chain reaction and radioligand binding. Cultured SMC were also studied. 3. Transcripts for alpha(1A)-, alpha(1B)-, alpha(1D)- and alpha(2D)-AR were expressed in different proportions in media and adventitia from uninjured carotid artery. Injury caused a reduction by as much as 85% at day 4 in all alpha-AR mRNA (but not cyclophilin) in both the media and adventitia. In both layers, expression returned to control by day 21 for alpha(2D)-AR and by day 42 for alpha(1A)-AR, but remained reduced by 25-50% for alpha(1B)- and alpha(1D)-AR at 42 days. alpha(1)-Adrenoceptor transcripts in the neointima at 21 and 42 days after injury were expressed at levels more than 80% lower than in the media or adventitia of uninjured carotid; alpha(2D)-AR mRNA was undetectable. The density of total alpha(1)-AR binding sites was similar in the media and adventitia of uninjured carotid. Density was reduced by approximately 60% in the intima-media and adventitia 21 days after injury. To examine possible mechanisms, early passaged cultured SMC were studied that express alpha(1D)- and alpha(1B)-AR at levels similar to in vivo but that do not express other alpha-AR. Basic fibroblast growth factor caused downregulation of alpha(1D)-AR mRNA and alpha(1)-AR density, without affecting mRNA half-life, whereas transforming growth factor-beta1 had no effect. Neither growth factor altered alpha(1B)-AR message expression. 4. These data demonstrate that: (i) carotid artery expresses the same four alpha-AR genes and similar total alpha(1)-AR density in the SMC media and fibroblast-rich adventitia; and (ii) injury induced enhancement of adrenergic trophic activity is not caused by upregulation of alpha(1)-AR, but, instead, is associated with a generalized reduction in alpha-AR expression.

Ontogenesis of mRNA levels and binding sites of hepatic alpha-adrenoceptors in young cattle

Catecholamines affect hepatic glucose production through (alpha- and beta2-) adrenoceptors (AR). We studied mRNA abundance and binding of hepatic alpha-AR in pre-term (P0) calves and in full-term calves at day 0 (F0), day 5 (F5) and day 159 (F159) to test the hypothesis that gene expression and numbers of hepatic alpha-AR in calves are influenced by age and associated with beta2-AR and selected traits of glucose metabolism. mRNA levels of alpha1- and alpha2-AR were measured by real time RT-PCR. alpha1- and alpha2-AR numbers (maximal binding, Bmax) were determined by saturation binding of (3H)-prazosin and (3H)-RX821002, respectively. alpha1- and alpha2-AR subtypes were evaluated by competitive binding. alpha1A-AR mRNA levels were lower in P0 than in F0, F5 and F159 and alpha(2AD)-AR mRNA levels were lower in F159 than in P0, F0 and F5, while alpha2C-AR mRNA levels increased from P0 and F0 to F5 and F159. Bmax of alpha1-AR increased from P0 to F5, then decreased in F159. Bmax of alpha2-AR decreased from F0 to F159. Bmax of alpha1-AR was positively associated with mRNA levels of alpha1A-AR (r = 0.7), Bmax of beta2-AR (r = 0.5) and negatively with hepatic glycogen content (r = -0.6). Bmax of alpha2-AR was negatively associated with Bmax of beta2-AR (r = -0.4). In conclusion, mRNA levels and binding sites of alpha1- and alpha2-AR in calves exhibited developmental changes and were negatively associated with hepatic glycogen content.

Cytokines down-regulate alpha1-adrenergic receptor expression during endotoxemia

OBJECTIVE

The reduced pressure response to norepinephrine in septic patients has directed our interest to the regulation of alpha1-adrenergic receptors in vitro and in vivo during conditions mimicking acute sepsis.

DESIGN

Prospective animal trial followed by a controlled cell culture study.

SETTING

Laboratory of the Department of Anesthesiology.

SUBJECTS

Male Sprague-Dawley rats weighing 200 to 250 g and a mesangial cell line.

INTERVENTIONS

Experimental endotoxemia was induced in rats with lipopolysaccharide, and blood pressure dose-response studies with norepinephrine were performed. Alpha1-receptor gene expression was determined in various organs by a specific RNase protection assay, and tissue concentrations of the proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha were measured. Rat renal mesangial cells were incubated with these cytokines or with nitric oxide donors to investigate the regulation of alpha1-adrenergic receptors during severe inflammation on a cellular level.

MEASUREMENTS AND MAIN RESULTS

The pressor effect of norepinephrine was markedly diminished during endotoxemia. The animals showed down-regulated mRNA levels of alpha1A-, alpha1B- and alpha1D-receptors in all organs investigated, and the tissue concentrations of interleukin-1beta and tumor necrosis factor-alpha were highly increased during experimental endotoxemia. Incubation of cultured rat renal mesangial cells with the cytokines resulted in diminished alpha -receptor gene expression and [3H]prazosin binding capacity, whereas incubation of the cells with nitric oxide donors did not affect alpha1B-receptor expression. In line, blocking of cytokine-induced nitric oxide synthesis by coincubation of mesangial cells with N(G)-nitro-L-arginine methyl ester did not influence cytokine-induced down-regulation of alpha1B-receptors.

CONCLUSIONS

Our data show that endotoxemia causes a systemic down-regulation of alpha1-receptors on the level of gene expression and suggest that this effect is likely mediated by proinflammatory cytokines in a synergistic but nitric oxide-independent fashion. We propose that this down-regulation of alpha1-adrenergic receptors contributes to the attenuated blood pressure response to norepinephrine and, therefore, to septic circulatory failure in patients.

Expression of alpha-adrenoceptor subtypes by smooth muscle cells and adventitial fibroblasts in rat aorta and in cell culture

Previous radioligand binding reports of vascular alpha-adrenoceptor (AR) density have been limited to total alpha1- or alpha2-ARs. Studies using whole blood vessel homogenates have not differentiated among receptor or mRNA expression by medial smooth muscle cells (SMCs) versus adventitial fibroblasts (AFBs). Therefore, we used quantitative reverse transcription-polymerase chain reaction and radioligand binding to measure alpha-AR subtypes in media, adventitia, and cultured SMCs and AFBs from rat aorta. Both media and adventitia expressed alpha1A-, alpha1B-, alpha1D-, and alpha2D-AR mRNAs, but in markedly different abundances. Total alpha1-AR density was the same for media and adventitia (Bmax = 101 +/- 10 versus 96 +/- 16 fmol/mg of protein). However, densities for alpha1A-, alpha1B-, and alpha1D-AR subtypes in media were 19 +/- 2, 26 +/- 4, and 55 +/- 2%, and in adventitia were 44 +/- 3, 37 +/- 5, and 19 +/- 2%. No alpha2B- or alpha2C-AR transcripts were detected in either layer or in cultured SMCs or AFBs. Total alpha1-AR densities in cultured SMCs and AFBs (Bmax = 111 +/- 4 and 48 +/- 6 fmol/mg of protein, respectively) were similar to media and adventitia, with alpha1B- and alpha1D-AR transcript levels and receptors largely sustained. However, alpha1A- and alpha2D-AR expression in cultured SMCs and AFBs was strongly reduced, compared with media and adventitia, an effect not prevented by 30 different culture conditions. Like SMCs, exposure of AFBs to norepinephrine induced protein synthesis and proliferation of AFBs. This is the first study to quantitate alpha-AR subtype expression in media and adventitia and in cultured SMCs and AFBs. In addition, we report the intriguing finding that AFBs express alpha1-ARs in similar abundance as medial SMCs and that norepinephrine induced them to proliferate.

Norepinephrine-induced migration of SW 480 colon carcinoma cells is inhibited by beta-blockers

Beta-adrenoceptors are highly expressed on SW 480 colon carcinoma cells as was assessed by flow cytometry. We investigated the influence of norepinephrine on the migration of these cells using time-lapse videomicroscopy. Norepinephrine-treatment increased the locomotor activity within the population from 25% spontaneously locomoting cells to 65% locomoting cells. The beta1/2-blocker propranolol but not the beta1-blocker atenolol inhibited this increase. The intracellular signaling solely of norepinephrine-induced locomotion involved protein tyrosine kinase activity, whereas both spontaneous and norepinephrine-induced migration were reduced by inhibiting phospholipase Cgamma and protein kinase Calpha activity. In summary, norepinephrine-induced locomotion of SW 480 cells is beta2-adrenoceptor mediated and distinct from spontaneous locomotion concerning the PTK involvement.

Expression of multiple alpha-adrenoceptor isoforms in rat CCD

In the rat cortical collecting duct (CCD), epinephrine inhibits vasopressin (AVP)-dependent water permeability and Na+ reabsorption. Although inhibition is reversed by the alpha2-adrenoceptor (AR) antagonist yohimbine, suggesting the epinephrine effect is primarily mediated by an alpha2-AR [C. T. Hawk, L. H. Kudo, A. J. Rouch, and J. A. Schafer. Am. J. Physiol. 265 (Renal Fluid Electrolyte Physiol. 34): F449-F460, 1993], there are also suggestions of an effect at an additional receptor, perhaps an alpha1-AR. For the present experiments, we used RT-PCR of total RNA extracted from 1 to 5 mm of microdissected CCDs from rat kidney to identify the alpha-AR isoforms expressed. Specific primers for the alpha2-ARs amplifying from the 6th transmembrane (TM) to the 3'-untranslated regions, revealed the presence of alpha2A and alpha2B. Western blot analysis also indicated the presence of alpha2B-AR at the protein level. Degenerate alpha1-AR primers that amplify from conserved regions of TM-1 to TM-5, as well as specific primers that amplify either the same region (alpha1B), the carboxy terminus (alpha1A), or within the third cytoplasmic loop (alpha1D), indicated the presence of all three alpha1-ARs. Measurement of transepithelial voltage in isolated perfused renal tubules indicated a small inhibitory effect mediated by alpha1-ARs. Although the functional effects of epinephrine on AVP-dependent transport processes appear to be mediated predominantly by an alpha2-AR, a small contribution to the overall alpha-AR effect may be due to simultaneous activation of an alpha1-AR.

A novel aortic smooth muscle cell line obtained from p53 knock out mice expresses several differentiation characteristics

Here we report that we could obtain a highly differentiated smooth muscle cell line by screening the expression of a-smooth muscle actin from p53 knook out mice aorta. This cell revealed extended bipolar shape and expressed h-caldesmon and calponin as well as a-smooth muscle actin as protein markers of differentiated smooth muscle. Further intracellular calcium increase was induced by application of noradrenaline in a dose dependent manner and calcium oscillation was also observed in a higher dose (100 microM). Appropriate application of 5-azacytidine enhanced these tendencies and induced slow contraction by endothelin-1 and phenylephrine.

Transient expression of alpha-1B adrenoceptor messenger ribonucleic acids in the rat superior cervical ganglion during postnatal development

We have examined the developmental profile of the alpha-1 and alpha-2 adrenergic receptor messenger ribonucleic acids expression in the rat superior cervical ganglion. The expression of the six messenger ribonucleic acids was studied using reverse transcription-polymerase chain reaction. At four weeks, the dominant messenger ribonucleic acids transcripts in this sympathetic ganglion were alpha-1C, alpha-2A, alpha-2B and alpha-2C. The expression of alpha-1 genes in the superior cervical ganglion appears to be regulated during postnatal development in that two alpha-1 (alpha-1B, alpha-1C) genes were expressed at birth, three, seven and 14 days postnatal but no amplified product for alpha-1B was detected at 28 days and in the aged animals, while the alpha-1C transcript continued to be expressed. No amplified product for alpha-1D was detected in superior cervical ganglion at any of the ages studied. While all three alpha-2 genes were expressed in the superior cervical ganglion at four weeks the dominant alpha-2 messenger ribonucleic acids transcript expressed in the superior cervical ganglion was alpha-2A. This pattern of alpha-2 adrenoceptor gene expression was maintained from birth, throughout development and into old age. These results suggest that the expression of alpha-1 adrenergic receptors in the superior cervical ganglion is regulated developmentally while the expression of alpha-2 genes remains unchanged.

Cardiac alpha-adrenergic receptor expression is regulated by thyroid hormone during a critical developmental period

Although thyroid hormone is obligatory for the development of cardiac beta-adrenergic receptors, it is difficult to assign a specific role for the hormone in receptor ontogeny because beta-receptor expression is affected similarly in the adult. We have determined whether thyroid hormone plays a role in receptor development by evaluating alpha 1-adrenergic receptors, which in the adult are downregulated by thyroid hormone. Propylthiouracil given from gestational day 17 through postnatal day 5 caused significant deficits in the number of alpha 1-receptors and values resolved to normal in parallel with hormone level recovery. When propylthiouracil was administered later (postnatal days 11 through 15) only a transient deficit in alpha 1-receptor binding was seen; hyperthyroidism (triiodothyronine) could still evoke stimulation of receptor expression at this stage. The effects on receptor expression were distinguished from general effects on cell differentiation by examining alpha 2-receptors, which disappear over the first three postnatal weeks; delayed differentiation caused by propylthiouracil would slow the decline in alpha 2-receptors, whereas accelerated differentiation caused by triiodothyronine would hasten the decline. Instead, the effects were similar to those on alpha 1-receptors: perinatal propylthiouracil administration reduced, and neonatal triiodothyronine administration enhanced, alpha 2-receptor binding sites. Thus, thyroid hormone plays a role in the control of cardiac adrenergic receptor expression during a critical development period, with conjoint regulation of the multiple receptor subtypes present within the tissue. As adrenergic stimulation is important in maintaining cardiac function in the perinatal period, alterations of thyroid status during this period can be expected to result in abnormal reactivity and increased perinatal risk.

Alpha-adrenoceptors and angiotensinogen gene expression in opossum kidney cells

To investigate whether alpha (alpha)-adrenoceptor agonists have a stimulatory effect on the expression of the angiotensinogen (Ang) gene in opossum kidney (OK) cells, we used OK 27 cells with a fusion gene containing the 5'-flanking regulatory sequence of the rat angiotensinogen gene fused with a human growth hormone (hGH) gene as a reporter, pOGH (Ang N-1498/+18), permanently integrated into their genomes. The level of expression of the pOGH (Ang N-1498/+18) was quantitated by the amount of immunoreactive-human growth hormone (IR-hGH) secreted into the medium. The addition of iodoclonidine (alpha 2-adrenoceptor agonist, 10(-13) to 10(-9) M) and phorbol 12-myristate 13-acetate (PMA, 10(-13) to 10(-5) M) stimulated the expression of pOGH (Ang N-1498/+18) in a dose-dependent manner, whereas the addition of phenylephrine (alpha 1-adrenoceptor agonist, 10(-13) to 10(-5) M) had no effect. The stimulatory effect of iodoclonidine was blocked by the presence of yohimbine (alpha 2-adrenoceptor antagonist) and staurosporine (an inhibitor of protein kinase C) but not blocked by the presence of prazosin (alpha 1-adrenoceptor antagonist) or Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A). The addition of iodoclonidine, phenylephrine or PMA had no effect on the expression of pTKGH in OK 13 cells, an OK cell line, into which had been stably integrated a fusion gene, pTKGH containing the promoter/enhancer DNA sequence of the viral thymidine-kinase (TK) gene fused with a human growth hormone gene as a reporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and expression of the alpha 2C-adrenergic receptor from the OK cell line

The alpha 2-adrenergic receptors have been divided into four pharmacological subtypes, alpha 2A, alpha 2B, alpha 2C, and alpha 2D. The OK cell line, a cell line derived from an opossum kidney, expresses the alpha 2C-adrenergic receptor and is the prototypical cell line for the alpha 2C receptor subtype. The cloned human alpha 2C-C4 and rat RG10 receptors have been shown to express alpha 2C pharmacology. Here we report the cloning and expression of the OK alpha 2C-adrenergic receptor, OKc2. The receptor has 64% deduced amino acid identity and 21% similarity to the alpha 2-C4 receptor, giving an overall similarity of 85%. The clone, expressed in Chinese hamster ovary cells, has a pharmacology that correlates very well (r = 0.97) with that of the native OK cell alpha 2C-adrenergic receptor, and it is negatively coupled to adenylyl cyclase.

Receptor-evoked Cl- current in Xenopus oocytes is mediated through a beta-type phospholipase C. Cloning of a new form of the enzyme

Xenopus oocytes exhibit a receptor-evoked Cl- current that is mediated through the activation of phospholipase C (PLC) and release of intracellular Ca2+. The identity of PLC(s) mediating this effect is unknown. We have cloned cDNAs encoding a new form of PLC-beta from a Xenopus oocyte cDNA library. The Xenopus PLC-beta has substantial (33-64%) homology with mammalian beta 1, beta 2, beta 3, and beta 4 phospholipase C and is closest to PLC-beta 3, with 64% identity and 80% similarity. Injection of antisense oligonucleotides to a specific region of Xenopus PLC-beta results in degradation of its mRNA and significantly reduces Cl- currents evoked by both endogenous angiotensin receptors and expressed mammalian alpha 1b-adrenergic receptors and M1-muscarinic receptors as compared to responses in sense oligonucleotide-injected oocytes. Inhibition of the M1-muscarinic response by antisense oligonucleotides was nonadditive with pertussis toxin inhibition. PLC antisense oligonucleotide-injected oocytes show Cl- current responses to IP3 that are indistinguishable from sense oligonucleotide-injected oocytes. Since the receptor responses are pertussis toxin-sensitive, we conclude that we have isolated a new form of PLC-beta involved in the pertussis toxin-sensitive receptor stimulation of the Ca2+ activated Cl- current in Xenopus oocytes.

Cloning, functional expression and tissue distribution of human cDNA for the alpha 1C-adrenergic receptor

We have cloned human alpha 1C-adrenergic receptor from human prostate cDNA library. The deduced amino acid sequence of the clone (P2C4) encodes a protein of 466 amino acids that showed strong sequence homology to the previously cloned bovine alpha 1C-adrenergic receptor. The radioligand binding properties of P2C4 expressed in COS-7 cells were very similar to those of bovine alpha 1C-adrenergic receptor. With reverse-transcription polymerase chain reaction assay, we observed alpha 1C-adrenergic receptor transcripts in heart, brain, liver and prostate, but not in kidney, lung, adrenal, aorta and pituitary. The data show that the clone P2C4 encodes a human alpha 1C-adrenergic receptor cDNA, and the receptor subtype is expressed not widely but localized in several human tissues.

Functional expression of rat alpha 2B-adrenoceptor in Escherichia coli

Rat alpha 2B-adrenoceptor was expressed in Escherichia coli using 'ATG vector' containing cDNA encoding the 'non-glycosylated rat alpha 2-adrenoceptor' (RNG alpha 2). The highest receptor binding activity (using the alpha 2-adrenoceptor ligand [3H]MK 912) was found when transfected bacteria cultures were grown at 30 degrees C for about 4 h after induction with isopropyl beta-D-thiogalactopyranoside (IPTG). Saturation experiments showed that the radioligand bound to a single saturable site with a Kd of 1.42 +/- 0.09 nM and capacity of 281 +/- 6 fmol/mg protein. Binding constants of 14 compounds for the rat alpha 2B-adrenoceptor expressed in E. coli were determined and compared to the values previously obtained for the rat alpha 2B-adrenoceptor when expressed in COS cells as well as for native neonatal rat lung alpha 2B-adrenoceptors. The results indicate that when the rat alpha 2B-adrenoceptor is expressed in E. coli it retains identical ligand binding properties to those found when the receptor is present in the eukaryotic system. Expressing alpha 2B-adrenoceptors in E. coli would, therefore, seem to constitute a valid alternative in, e.g., drug screening and structure analysis of the alpha 2B-adrenoceptors.

Postnatal development of 3H-rauwolscine binding sites in the dorsal lateral geniculate nucleus and the striate cortex of the tree shrew (Tupaia belangeri)

Noradrenaline has been shown to play an important role within the visual system of the brain. To analyze the postnatal development of alpha2-noradrenergic receptors in the visual system of tree shrews, we localized and quantified binding sites for the antagonist [3H]-rauwolscine by in vitro-autoradiography in the dorsal lateral geniculate nucleus and the striate cortex at different postnatal ages. At birth, the dorsal lateral geniculate nucleus is only slightly labeled by [3H]-rauwolscine. During the postnatal period, the number of binding sites increases to reach a maximum around postnatal day 20. Since the young tree shrews open their eyes at approximately day 19, it appears that this high concentration of alpha2-adrenoceptors is related to eye opening. In the adult animal, [3H]-rauwolscine labeling shows a laminated pattern in the dorsal lateral geniculate nucleus. Laminae 1, 2, and 3 are more strongly labeled than laminae 4, 5, and 6. In the striate cortex, the pattern of [3H]-rauwolscine-binding sites changes dramatically during the early postnatal period. Immediately after birth, there is only one layer, located within the subplate zone, which is labeled. From postnatal day 5 onwards, all cortical layers which can be distinguished on histologically stained sections reveal [3H]-rauwolscine-binding sites, but in layer IV, which is known to receive major inputs from the dorsal lateral geniculate nucleus, there is very little labeling during the first two postnatal weeks. In this layer, a large number of [3H]-rauwolscine-binding sites occurs between postnatal day 15 and 20, that is slightly before and around the time of eye opening.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and expression of the mouse homolog of the human α2-C2 adrenergic receptor

Three subtypes of alpha 2 adrenergic receptors have been identified in the human and rat. The subtype located on human chromosome 2 (alpha 2-C2) is unique in that it is expressed mainly in the peripheral tissues and lacks sites for N-linked glycosylation. We isolated the gene encoding the mouse homolog of the human alpha 2-C2 adrenergic receptor (M alpha 2-2H). The deduced amino acid sequence of the M alpha 2-2H shows 82% and 96% identity to the human alpha 2-C2 and the rat RNG alpha 2 adrenergic receptors, respectively. Southern blot analysis demonstrated that the M alpha 2-2H was encoded by a single copy gene and was distinct from the mouse homologs of the alpha 2-C4 and alpha 2-C10 adrenergic receptors. When expressed in COS-7 cells, the M alpha 2-2H exhibited a pharmacological profile similar to the human alpha 2-C2 and rat RNG alpha 2 receptors.

Expression of renal alpha 1-adrenergic receptor subtypes in established hypertension

Radioligand binding studies were undertaken in renal membranes of normotensive and hypertensive rats in order to test the hypothesis that there are alterations in renal alpha 1-adrenergic subtypes of genetic hypertensive animals. The highly selective competitive compound, (+)-niguldipine, was used to distinguish high-affinity (alpha 1a) from low-affinity (alpha 1b) sites, after initial studies demonstrated that this compound had greater selectivity than 5-methylurapidil in distinguishing alpha 1a and alpha 1b sites in rat renal membranes. In contrast to the significant difference in the blood pressure of the spontaneously hypertensive rats (delta BP = 74 mm Hg), there was no difference in the renal alpha 1-adrenergic receptor density. Membranes from the whole kidneys of spontaneously hypertensive rats (SHRs) possessed 31% alpha 1a and 69% alpha 1b sites with -log(Ki) values of 10.0 +/- 0.3 and 7.1 +/- 0.1, respectively, for (+)-niguldipine. However, these values were not different from those obtained from renal membranes of the normotensive Wistar-Kyoto (WKY) rats. These results indicate that in spite of the elevated blood pressure during the established phase of hypertension, the number, the affinity, and the ratio of the alpha 1a and alpha 1b appear not to be responsible for the manifestation of hypertension during this phase.

Expression of adrenergic receptors in individual astrocytes and motor neurons isolated from the adult rat brain

Attempts to show the distribution of adrenergic receptors (ARs) in autoradiographs of a brainstem motor nucleus following elimination of motor neurons yielded the unexpected result of an increase in beta-AR density. This increase was related to the gliosis accompanying the motor neuron degeneration. To determine the cells on which the AR subtypes were located, we dissociated cells from various regions of the adult rat brain and subsequently identified astrocytes by glial fibrillary acidic protein (GFAP) immunofluorescence. Slides containing the astrocytes were prepared for autoradiography using the nonselective beta ligand 125I-iodocyanopindolol (125ICYP) or the alpha 1 ligand 125IBE 2254 (125I-HEAT). The addition of the selective beta 1 blocker betaxolol or the beta 2 blocker ICI 118.551 to the incubation medium to displace 125ICYP binding was used to determine the binding of beta-AR subtypes. The great majority (greater than 88%) of isolated astrocytes sampled from the trigeminal motor nucleus, cerebral cortex, striatum, and cerebellum showed beta-AR binding. Astrocytes from the first three regions had similar average densities of beta-ARs, whereas the density in cerebellar astrocytes was 2- to 3-fold greater. The beta 2-AR subtype was proportionally greater than the beta 1 subtype in each region. Reactive astrocytes isolated from the trigeminal motor nucleus after degeneration of motor neurons showed a beta-AR density nearly 2-fold greater than resting astrocytes from the same region, with the beta 1 subtype showing the greater proportional increase. There was no beta-AR binding on trigeminal motor neurons. Astrocytes also showed a significant level of alpha 1-AR binding. No differences in alpha 1-AR binding were found in normal astrocytes isolated from the different regions, nor was there an increase in reactive astrocytes. In contrast, trigeminal motor neurons had an alpha 1-AR density nearly 10 times greater than astrocytes. In terms of the NE modulation of synaptic responses in motor neurons, the distribution of ARs would permit NE to act indirectly through alpha 1 and beta receptors on astrocytes and directly through alpha 1 receptors on motor neurons.

A mechanism for testosterone modulation of alpha-1 adrenergic receptor expression in the DDT1 MF-2 smooth muscle myocyte

Previous reports have confirmed that steroid hormones modulate the expression of adrenergic receptors on the surface of smooth muscle myocytes. The present study was undertaken to evaluate the mechanism by which testosterone modulates alpha-1 adrenergic receptor expression in the DDT1 MF-2 transformed smooth muscle cell. Utilizing 3H-prazosin radioligand binding studies, alpha-1 adrenergic receptors were noted to increase more than 2 fold in response to incubation with 10(-8)M testosterone for 96 hours. Dihydrotestosterone similarly stimulated a significant increase in alpha-1 receptors; whereas, estradiol and hydrocortisone appeared to suppress the expression of this receptor in DDT myocytes. The testosterone effect was dose related with a maximal response observed in response to 10(-7)M testosterone at both 48 and 96 hours. Kinetic experiments utilizing 10(-8)M testosterone demonstrated a peak effect on alpha-1 receptor expression at 96 hours, and maintenance of the effect for at least 168 hours (7 days). The testosterone effect was completely prevented at both 48 and 96 hours by inhibition of transcription with actinomycin-D, or inhibition of translation with cycloheximide. Consistent with the receptor binding studies, RNA blotting studies have demonstrated maximal alpha-1 receptor mRNA levels at 48-96 hours of testosterone stimulation. In conclusion, these in vitro experiments have confirmed the physiologic concentrations of testosterone stimulate the increased expression of alpha-1 receptors in the DDT1 MF-2 myocyte after a delay of 48-96 hours; and that this effect appears to be mediated by transcription, translation, and synthesis of new proteins in these genital tract myocytes.

Alternative mRNAs encoding the alpha 1b-adrenergic receptor are expressed in a tissue-dependent manner in the Sprague-Dawley rat

Probing total cellular and poly [A+] RNA isolated from various rat tissues with a full-length cDNA encoding the hamster alpha 1-adrenergic receptor results in detection of two transcripts, 3.3 kb and 2.7 kb, which probably both encode the alpha 1b-adrenergic receptor subtype. Both the 3.3 kb and 2.7 kb mRNAs were found to be associated with hepatic polysomes which suggests that these mRNA species are translated into protein. Using non-overlapping 5' and 3' cDNA probes, large sequence differences were not evident between the 3.3 kb and 2.7 kb mRNAs, although the 3'-probe hybridized to a 4.0 kb mRNA in addition to the two smaller transcripts in poly [A+] RNA isolated from renal cortex, but not other tissues. The relative amounts of the 3.3 kb and 2.7 kb mRNAs varied considerably among the five tissues studied. However, the ratio of the two transcripts remained relatively constant in the same tissue taken from animals at different developmental ages. Currently, the physiological significance of multiple alpha 1b-adrenergic receptor gene transcripts is unclear. However, our results suggest that alpha 1b-adrenergic receptor gene expression in the rat is under complex regulatory control that in part is tissue-dependent.

Cloning, expression, and pharmacological characterization of a human alpha 2B-adrenergic receptor

An alpha 2-adrenergic receptor subtype has been isolated from a human genomic spleen library using the human 5-hydroxytryptamine1A receptor gene (also known as G-21) as a probe. This adrenergic receptor gene encodes a protein of 450 amino acids and does not contain any consensus sequences for N-linked glycosylation in its amino terminus or extracellular loops. This receptor is also distinguished by the presence of 12 consecutive glutamic acid residues in the region of its third intracellular loop. The deduced amino acid sequence shows greatest homology to previously cloned human alpha 2-adrenergic receptors and has structural similarities to other guanine nucleotide-binding protein-coupled receptors. The DNA encoding the human alpha 2 receptor was stably transfected into mouse fibroblast Ltk- cells and radioligand binding studies were performed using the alpha 2 antagonist [3H]rauwolscine. [3H]Rauwolscine bound with high affinity (Kd = 0.33 nM) and in a saturable manner (Bmax = 1.4 pmol/mg of protein). Pharmacological characterization of this receptor indicated a rank order of potency of yohimbine greater than prazosin greater than oxymetazoline. Additionally, 100 microM 5'-guanylylimidodiphosphate, produced a rightward shift in the epinephrine competition curve, with resultant increases in both the Ki value and Hill coefficient, suggestive of a functional interaction of the cloned receptor with native guanine nucleotide-binding protein(s) of Ltk- membranes. The data presented here are consistent with previous biochemical and pharmacological studies on alpha 2 receptors and are supportive of the designation of this receptor as an alpha 2B subtype.

Rabbit myometrial oxytocin and alpha 2-adrenergic receptors are increased by estrogen but are differentially regulated by progesterone

Both myometrial oxytocin and alpha 2-adrenergic receptors are induced by estrogen. To compare the regulation of these two receptor populations by progesterone, we measured myometrial receptor concentration in ovariectomized steroid-treated and in pregnant rabbits. To control for the effects of estrogen withdrawal, we used concomitant rather than sequential presentation of estrogen and progesterone in ovariectomized rabbits. Estradiol increased both myometrial oxytocin and alpha 2-adrenergic receptor concentrations in ovariectomized rabbits after 8 days of treatment. Simultaneous progesterone administration during the last 4 days of estradiol treatment reversed the induction of oxytocin, but not alpha 2-adrenergic, receptors. Similarly, administration of the antiprogestin RU 38486 to pregnant rabbits on day 27 of gestation resulted in premature delivery and evoked an increase in myometrial oxytocin receptor concentration mimicking that observed at term (day 31). However, RU 38486 did not significantly affect alpha 2-adrenergic receptor concentration. Our data provide further support for involvement of oxytocin receptors in parturition, but do not indicate a comparable function for myometrial alpha 2-adrenergic receptors.

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-(beta 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.

Regulation of brain adrenergic receptors during aging

Recent studies in our laboratory suggest that the synthesis of alpha- and beta-adrenergic receptors in certain tissues from brain and pineal gland may be impaired with age. This decreased ability of the aged brain to synthesize adrenergic receptors may explain the loss of these receptors in selected brain regions during the aging process, as well as the reduced capacity of aged brain tissue to increase or up-regulate the density of these receptors in response to reduced noradrenergic activation of the tissues or to reduced estrogen levels. The reduced adaptability of brain adrenergic receptors, in turn, may account for the decreased ability of aged individuals to adjust their physiological responses to a changing environment.

Turnover of adrenergic receptors under normal and desensitized conditions

Alpha 1 and beta adrenergic receptor metabolism was investigated by studying receptor reappearance after an irreversible blockade. Phenoxybenzamine was used to irreversibly block alpha 1 adrenergic receptors both in vitro in the BC3H1 cell line and in vivo in rat submaxillary glands. In these two systems, the alpha 1 adrenergic receptor reappearance followed a monoexponential kinetic allowing to determine the half-life of the receptor (23h in vitro, 33h in vivo) as well as the rate of receptor synthesis and degradation. the receptor reappearance was due to receptor synthesis since it was blocked by cycloheximide. The irreversible blockade of beta adrenergic receptors was done with an alkylating beta adrenergic antagonist that we recently developed: Br-pindolol (1). This ligand has high efficiency and blocked at 10(-7)M 80-90% of the beta adrenergic receptors present in C6 glioma cells in culture. After this irreversible blockade, receptors reappeared only during cell division. At confluency, when cells did not significantly divide, receptor synthesis could hardly be detectable. Therefore, at confluency, the metabolic stability of the beta adrenergic receptor is considerable, compared to that of the alpha 1 adrenergic receptor. This stability was confirmed by the observation that after an almost complete "down-regulation" of the beta adrenergic receptor, receptor repopulation of the C6 glioma cells was total and occurred in the presence of cycloheximide.