Dataset Information

High level of alpha2-adrenoceptor in rat foetal liver and placenta is due to alpha2B-subtype expression in haematopoietic cells of the erythrocyte lineage.

ABSTRACT: 1. Rat foetal liver contains large amounts of alpha2-adrenoceptors. The present work aimed to identify the receptor subtype and the cell type accounting for high expression and to clarify the mechanisms responsible for the sharp decrease in hepatic receptivity occurring during the late stage of foetal development. 2. Binding experiments indicated that the density of alpha2-adrenoceptors in the foetal liver (embryonic day 18; 615+/-155 fmol mg(-1) of protein) is 18 fold higher than in newborn or adult (35.2+/-4.3 fmol mg(-1)). A high amount of receptor is also found in the placenta (443+/-53 fmol mg(-1)). In both tissues, the rank order of antagonists to inhibit radioligand binding matched the pharmacological profile of the alpha2B-adrenoceptor and exclusively RNG transcripts were detected by RNase protection assays. 3. Isolation of cell fractions from foetal liver showed that alpha2B-adrenoceptor is primarily expressed by haematopoietic cells. Consistent with this view, the receptor is found to be abundant in foetal blood, carried by reticulocytes. The expression in blood gradually declines to zero at 3 weeks of age and it is not recovered following induction of reticulocytosis in adults. 4. In foetal reticulocytes, a low proportion of the receptor population is coupled to G-protein. The alpha2-agonist UK14304 has a marginal effect on cyclic AMP level but significantly increases arachidonic acid release. The function of the receptor remains to be elucidated. However, together with observations on alpha2B-knockout mice, the current finding strongly suggests a role for alpha2B-adrenoceptor during foetal haematopoiesis in rodents.

SUBMITTER: Cussac D

PROVIDER: S-EPMC1621155 | biostudies-literature | 2001 Aug

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

High level of alpha2-adrenoceptor in rat foetal liver and placenta is due to alpha2B-subtype expression in haematopoietic cells of the erythrocyte lineage.

Cussac D D Schaak S S Denis C C Flordellis C C Calise D D Paris H H

British journal of pharmacology 20010801 8

1. Rat foetal liver contains large amounts of alpha2-adrenoceptors. The present work aimed to identify the receptor subtype and the cell type accounting for high expression and to clarify the mechanisms responsible for the sharp decrease in hepatic receptivity occurring during the late stage of foetal development. 2. Binding experiments indicated that the density of alpha2-adrenoceptors in the foetal liver (embryonic day 18; 615+/-155 fmol mg(-1) of protein) is 18 fold higher than in newborn or ...[more]

PMID: 11498526

Similar Datasets

Project description:BACKGROUND:The putative myopia-controlling receptor is thought to be muscarinic acetylcholine receptor subtype M4 , because mamba toxin-3 can inhibit form-deprivation myopia in chicks at a far lower concentration than atropine. However, mamba toxin-3 is equally potent at the human α1A -, α1D -, and α2A -adrenoceptors. To test the hypothesis that α-adrenoceptors might be involved in regulation of eye growth, the treatment effects of α2 -adrenoceptor agonists brimonidine, clonidine, and guanfacine, and antagonist yohimbine, on form-deprivation myopia in the chick were measured. METHODS:Right eyes of White Leghorn chicks were goggled with diffusers to induce form-deprivation myopia; left eyes were left open as controls. Goggled eyes were injected intravitreally with 20 μL of vehicle, or 2, 20, or 200 nmol of brimonidine, clonidine, guanfacine, or yohimbine, 24, 72, and 120 hours after goggle application. Alternatively, myopia was inhibited physiologically by goggle removal for two hours, and the α2 -adrenoceptor antagonist, yohimbine, was injected to test whether it could block this type of myopia inhibition. One day after the last injection, refractive error and axial length were measured. RESULTS:Brimonidine (20 and 200 nmol) and clonidine (200 nmol) effectively inhibited experimentally induced increases in negative refractive error and axial elongation. All doses of guanfacine significantly inhibited induced negative refractive error, but only 20 and 200 nmol significantly inhibited axial elongation. Yohimbine had no effect on form-deprivation myopia, but 200 nmol reduced the myopia-inhibiting effect of goggle removal. CONCLUSION:High concentrations of α2 -adrenoceptor agonists, similar to those required by atropine, inhibited chick form-deprivation myopia; antagonism by yohimbine had no effect. High-concentration yohimbine partially interfered with emmetropisation in form-deprived chicks experiencing normal vision for two hours per day. These data support the hypothesis that treatment with high concentrations of adrenergic drugs can affect experimentally induced myopia and normal visual processes.

Project description:Subtype diversity of heterotrimeric G proteins and G protein-coupled receptors enables a wide spectrum of signal transduction. However, the significance of isoforms within receptor or G protein subfamilies has not been fully elucidated. In the present study, we have tested whether alpha(2)-adrenoceptors require specific Galpha isoforms for their function in vivo. In particular, we analyzed the role of the highly homologous Galpha(i) isoforms, Galpha(i1), Galpha(i2), and Galpha(i3), in typical alpha(2)-adrenoceptor-controlled functions. Mice with targeted deletions in the genes encoding Galpha(i1), Galpha(i2), or Galpha(i3) were used to test the effects of alpha(2)-adrenoceptor stimulation by the agonist medetomidine. The alpha(2)-adrenoceptor agonist medetomidine inhibited [(3)H]norepinephrine release from isolated prefrontal brain cortex or cardiac atria tissue specimens with similar potency and efficacy in tissues from wild-type or Galpha(i)-deficient mice. In vivo, bradycardia, hypotension, induction of sleep, antinociception, and hypothermia induced by alpha(2)-adrenoceptor activation did not differ between wild-type and Galpha(i)-knockout mice. However, the effects of the alpha(2)-agonists medetomidine or 5-bromo-6-(2-imidazolin-2-ylamino)quin-oxaline tartrate (UK14,304) on spontaneous locomotor activity or anesthetic sparing were reduced or absent, respectively, in mice lacking Galpha(i2). In microdissected locus coeruleus neurons or postganglionic sympathetic neurons from stellate ganglia, all three Galpha(i) subunits were expressed as determined by quantitative reverse transcription-polymerase chain reaction, with Galpha(i1) and Galpha(i2) dominating over Galpha(i3). Functional redundancy of the highly homologous Galpha(i) isoforms may predominate over specificity to regulate distinct intracellular pathways downstream of alpha(2)-adrenoceptors in vivo. In contrast, inhibition of locomotor activity and anesthetic sparing may be elicited by a specific coupling of alpha(2A)-adrenoceptors via the Galpha(i2) isoform to intracellular pathways.

Project description:Slow-onset adaptive changes that arise from sustained antidepressant treatment, such as enhanced adult hippocampal neurogenesis and increased trophic factor expression, play a key role in the behavioral effects of antidepressants. alpha(2)-Adrenoceptors contribute to the modulation of mood and are potential targets for the development of faster acting antidepressants. We investigated the influence of alpha(2)-adrenoceptors on adult hippocampal neurogenesis. Our results indicate that alpha(2)-adrenoceptor agonists, clonidine and guanabenz, decrease adult hippocampal neurogenesis through a selective effect on the proliferation, but not the survival or differentiation, of progenitors. These effects persist in dopamine beta-hydroxylase knock-out (Dbh(-/-)) mice lacking norepinephrine, supporting a role for alpha(2)-heteroceptors on progenitor cells, rather than alpha(2)-autoreceptors on noradrenergic neurons that inhibit norepinephrine release. Adult hippocampal progenitors in vitro express all the alpha(2)-adrenoceptor subtypes, and decreased neurosphere frequency and BrdU incorporation indicate direct effects of alpha(2)-adrenoceptor stimulation on progenitors. Furthermore, coadministration of the alpha(2)-adrenoceptor antagonist yohimbine with the antidepressant imipramine significantly accelerates effects on hippocampal progenitor proliferation, the morphological maturation of newborn neurons, and the increase in expression of brain derived neurotrophic factor and vascular endothelial growth factor implicated in the neurogenic and behavioral effects of antidepressants. Finally, short-duration (7 d) yohimbine and imipramine treatment results in robust behavioral responses in the novelty suppressed feeding test, which normally requires 3 weeks of treatment with classical antidepressants. Our results demonstrate that alpha(2)-adrenoceptors, expressed by progenitor cells, decrease adult hippocampal neurogenesis, while their blockade speeds up antidepressant action, highlighting their importance as targets for faster acting antidepressants.

Project description:Background & objectivesMesencymal stem cells (MSCs) derived from foetal tissues present a multipotent progenitor cell source for application in tissue engineering and regenerative medicine. The present study was carried out to derive foetal mesenchymal stem cells from ovine source and analyze their differentiation to osteogenic linage to serve as an animal model to predict human applications.MethodsIsolation and culture of sheep foetal bone marrow cells were done and uniform clonally derived MSC population was collected. The cells were characterized using cytochemical, immunophenotyping, biochemical and molecular analyses. The cells with defined characteristics were differentiated into osteogenic lineages and analysis for differentiated cell types was done. The cells were analyzed for cell surface marker expression and the gene expression in undifferentiated and differentiated osteoblast was checked by reverse transcriptase PCR (RT PCR) analysis and confirmed by sequencing using genetic analyzer.ResultsOvine foetal samples were processed to obtain mononuclear (MNC) cells which on culture showed spindle morphology, a characteristic oval body with the flattened ends. MSC population CD45⁻/CD14⁻ was cultured by limiting dilution to arrive at uniform spindle morphology cells and colony forming units. The cells were shown to be positive for surface markers such as CD44, CD54, integrinβ1, and intracellular collagen type I/III and fibronectin. The osteogenically induced MSCs were analyzed for alkaline phosphatase (ALP) activity and mineral deposition. The undifferentiated MSCs expressed RAB3B, candidate marker for stemness in MSCs. The osteogenically induced and uninduced MSCs expressed collagen type I and MMP13 gene in osteogenic induced cells.Interpretation & conclusionsThe protocol for isolation of ovine foetal bone marrow derived MSCs was simple to perform, and the cultural method of obtaining pure spindle morphology cells was established. Criteria proposed for defining MSCs by this study includes the cell adherence to culture plates, specific surface protein profiles and differentiation to osteogenic lineage. The MSCs and osteogenic differentiated cells in this ovine animal model may serve as a large source for stem cell applications in regenerative medical therapies.

Project description:Epigenetic modifications must underlie lineage-specific differentiation as terminally differentiated cells express tissue-specific genes, but their DNA sequence is unchanged. Haematopoiesis provides a well-defined model to study epigenetic modifications during cell-fate decisions, as multipotent progenitors (MPPs) differentiate into progressively restricted myeloid or lymphoid progenitors. Although DNA methylation is critical for myeloid versus lymphoid differentiation, as demonstrated by the myeloerythroid bias in Dnmt1 hypomorphs, a comprehensive DNA methylation map of haematopoietic progenitors, or of any multipotent/oligopotent lineage, does not exist. Here we examined 4.6 million CpG sites throughout the genome for MPPs, common lymphoid progenitors (CLPs), common myeloid progenitors (CMPs), granulocyte/macrophage progenitors (GMPs), and thymocyte progenitors (DN1, DN2, DN3). Marked epigenetic plasticity accompanied both lymphoid and myeloid restriction. Myeloid commitment involved less global DNA methylation than lymphoid commitment, supported functionally by myeloid skewing of progenitors following treatment with a DNA methyltransferase inhibitor. Differential DNA methylation correlated with gene expression more strongly at CpG island shores than CpG islands. Many examples of genes and pathways not previously known to be involved in choice between lymphoid/myeloid differentiation have been identified, such as Arl4c and Jdp2. Several transcription factors, including Meis1, were methylated and silenced during differentiation, indicating a role in maintaining an undifferentiated state. Additionally, epigenetic modification of modifiers of the epigenome seems to be important in haematopoietic differentiation. Our results directly demonstrate that modulation of DNA methylation occurs during lineage-specific differentiation and defines a comprehensive map of the methylation and transcriptional changes that accompany myeloid versus lymphoid fate decisions.

Dataset Information

High level of alpha2-adrenoceptor in rat foetal liver and placenta is due to alpha2B-subtype expression in haematopoietic cells of the erythrocyte lineage.

Publications

High level of alpha2-adrenoceptor in rat foetal liver and placenta is due to alpha2B-subtype expression in haematopoietic cells of the erythrocyte lineage.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets