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Biomedical subjects

M Bouvier

Publications and source records attributed to M Bouvier.

At least 19 recordsLinked to original sources
PubMed1995

Agonist-induced desensitization of dopamine D1 receptor-stimulated adenylyl cyclase activity is temporally and biochemically separated from D1 receptor internalization.

The regulation of the dopamine D1 receptor was investigated by using c-myc epitope-tagged D1 receptors expressed in Sf9 (fall armyworm ovary) cells. Treatment of D1 receptors with 10 microM dopamine for 15 min led to a loss of the dopamine-detected high-affinity state of the receptor accompanying a 40% reduction in the ability of the receptor to mediate maximal dopamine stimulation of adenylyl cyclase activity. After 60 min of agonist exposure, 45 min after the occurrence of desensitization, 28% of the cell surface receptors were internalized into an intracellular light vesicular membrane fraction as determined by radioligand binding and supported by photoaffinity labeling, immunocytochemical staining, and immunoblot analysis. Pretreatment of cells with concanavalin A or sucrose completely blocked agonist-induced D1 receptor internalization without preventing agonist-induced desensitization, indicating a biochemical separation of these processes. Collectively, these findings indicate that the desensitization of D1 receptor-coupled adenylyl cyclase activity and D1 receptor internalization are temporarily and biochemically distinct mechanisms regulating D1 receptor function following agonist activation.

Adenylyl Cyclases↗
PubMed1995

High prevalence of hepatitis B, C, and E markers in young sexually active adults from the Central African Republic.

The Central African Republic is located in tropical Africa, where both the human immunodeficiency virus (HIV) and hepatitis B virus (HBV) are highly endemic. The exact prevalence of hepatitis C virus (HCV) and hepatitis E virus (HEV) markers in this country is unknown. The aim of the study was to determine, according to HIV and HBV serostatus, the prevalence of these markers in young sexually active adults in the Central African Republic. One hundred and fifty-seven consecutive patients attending the National Centre for Sexually Transmitted Diseases in Bangui were included. The following serological markers were examined: (i) anti-HIV1 and anti-HIV2 antibodies; (ii) markers of HBV infection; (iii) anti-HCV antibodies; (iv) anti-HEV antibodies. Anti-HIV1 antibodies were found in 31 of the 157 patients (20%). The prevalence of anti-HBc antibodies, reflecting exposure to HBV, was 140/157 (89%) and 45 had detectable anti-HBs antibodies. Twenty-two patients (14%) were chronic carriers of hepatitis B surface antigen (HBsAg), but only one was HBe antigen-positive. Anti-HCV antibodies were found in 8 persons (5%) and anti-HEV antibodies in 38 (24%). No difference was found in the prevalence of these markers according to the presence or absence of anti-HIV antibodies. This study confirms the high rate of HIV infection, HBV exposure and chronic carriage of HBsAg in sexually active young adults in the Central African Republic. A high prevalence of HCV markers was found in this population, similar to that reported in neighbouring countries, together with a high rate of HEV markers, suggesting that HEV is endemic in this region.

Adolescent↗
PubMed1995

Pitfall of stiff shoulder: inveterated posterior dislocation.

The authors relate the observation of an inveterated bilateral posterior dislocation, occurring during a generalized epileptic attack and mimicking a painful stiff shoulder. The clinical signs (i.e. aetiologic circumstances causing a forced internal rotation, limitation or absence of external rotation) and radiological data, especially the necessity of a profile X-ray, which lead to the diagnostic are reiterated. The interest of computerized tomography in the pre-operative assessment is underscored.

Epilepsy, Tonic-Clonic↗
PubMed1995

CT and MRI evaluation of tenosynovitis of the rheumatoid hindfoot.

Thirty-nine patients with rheumatoid arthritis who had presented with tarsitis before, were investigated at the level of the rearfoot. The first 17 patients had CT with previous tenography when it was possible; the following 22 patients had MRI with gadolinium injection. Tendon involvement appeared in 52.9% of the cases on CT, and in 90% of the feet on MRI; therefore, in case of clinical or radiological signs of tarsitis, it appears that tendon involvement must be suspected. With the two procedures the tibialis posterior tendon lesions were very predominant. In the majority of the patients (31/39), there was associated involvement of two or more tendons. If there is a ruptured tendon, the authors think that one must be cautious with surgical tendinous transfer; indeed, the long-term results of this surgical procedure present a strong probability of being compromised in rheumatoid arthritis which is a progressive disease.

Adult↗
PubMed1995

Functional effects of long-term activation on human beta 2- and beta 3-adrenoceptor signalling.

The functional effects of long-term activation of beta-adrenoceptors were investigated by measuring adenylyl cyclase activity, cyclic AMP accumulation and cyclic AMP-dependent protein kinase activity in CHW and L cells expressing either human beta 2- or beta 3-adrenoceptors. Pre-incubation of CHW and L cells expressing beta 2-adrenoceptors with 10 microM isoprenaline for 24 h produced a marked reduction in the total receptor number and dramatically reduced the capacity of the receptor to stimulate adenylyl cyclase maximally. In contrast, the ability of beta 3-adrenoceptors number was observed in L but not in CHW cells. Maximal levels of intracellular cyclic AMP concentrations were reached during the first hour of receptor activation with isoprenaline in all four cell lines. In the absence of phosphodiesterase inhibitors, cyclic AMP decreased to basal levels within 24 h of continuous stimulation. This phenomenon occurred more rapidly in cells expressing the beta 2- than the beta 3-adrenoceptors. These results confirm that, at the level of adenylyl cyclase stimulation and cyclic AMP accumulation, the beta 3-adrenoceptor is more resistant than the beta 2-adrenoceptor to long-term desensitization. However, when cyclic AMP-dependent protein kinase activity was considered, a 24 h stimulation of beta 2- and when cyclic AMP-dependent protein kinase activity was considered, a 24 h stimulation of beta 2- and beta 3-adrenoceptor expressing cells led to the desensitization of the kinase in L but not in CHW cells. In conclusion, long-term desensitization may have distinct functional effects on cell signalling depending on the receptor subtype and the cell type considered. These findings might have practical implications for future strategies involving long-term therapies with receptor agonists.

Adenylyl Cyclases↗
PubMed1995

Characterization of the vasorelaxant activity of tyramine and other phenylethylamines in rat aorta.

We recently reported that tyramine caused concentration-dependent relaxation of rat aorta, which was endothelium independent and was not exerted via alpha 1-adrenoceptors (AR), alpha 2AR, beta 1AR, beta 2AR, or receptors for 5-hydroxytryptamine, histamine, and adenosine. The present studies were done on endothelium-denuded strips to determine structure-vasorelaxant activity after blockade of beta AR by propranolol plus irreversible blockade of alpha 1AR with benextramine. Vasorelaxation under these conditions was limited to noncatecholamines, and their vasorelaxant potencies were methoxyphenamine > tyramine > p-hydroxyephedrine > L-amphetamine > L-ephedrine > phenylethylamine > synephrine > methoxamine > octopamine. beta 3AR agonists (BRL 37344 and CGP 12177A) did not produce vasorelaxation, although tyramine could compete for cyanopindolol binding to murine L cells expressing human beta 2AR or beta 3AR. There was no significant specific binding of [3H]tyramine to aortic membrane preparations after the inhibition of monamine oxidase. Yohimbine, which has a high affinity for Drosophila tyramine receptors, also caused dose-dependent vasorelaxation like tyramine. It is concluded that tyramine and several other phenylethylamines produce relaxation of rat aorta, which does not involve any of the known adrenoceptors but may be exerted via novel tyramine receptors.

Animals↗
PubMed1995

Serotonergic antagonists differentially inhibit spontaneous activity and decrease ligand binding capacity of the rat 5-hydroxytryptamine type 2C receptor in Sf9 cells.

The activities of serotonergic antagonists as inverse agonists at the rat 5-hydroxytryptamine (5-HT)2C serotonin receptor were compared with their potencies in promoting receptor "down-regulation," after expression of the recombinant receptor in the baculovirus/Sf9 insect cell system. Baculovirus expression yielded high levels of 5-HT2C receptors (up to 10(6) receptors/cell), which were functionally coupled to polyphosphoinositide turnover in Sf9 cells through a pertussis toxin-insensitive pathway. The expressed receptor exhibited spontaneous activation of inositol phosphate production, which was inhibited in a dose-dependent manner by serotonergic antagonists, consistent with inverse agonist activity. The potencies of antagonists as inverse agonists correlated with their respective binding affinities determined in competition binding studies with membrane preparations. The maximal inhibition of spontaneous activity ranged from 32% inhibition for mianserin to no effect for spiroxatrine, indicating that antagonists differ in their intrinsic inverse efficacies. Antagonist treatment of intact Sf9 cells or membranes containing the 5-HT2C receptor, followed by washout of residual drug, resulted in a decrease (up to 90%) in the number of binding sites for [3H]mesulergine and [3H]5-HT, with no change in the affinity for [3H]mesulergine. The decrease in binding was irreversible, was not due to the presence of residual antagonist, and was not observed after treatment with agonists. This effect of antagonists in membranes was dose dependent, but the rank order of potency was clearly different from that for inverse agonist activity, indicating that the two effects reflect distinct actions of antagonists at the 5-HT2C receptor. The relative abilities of antagonists to produce loss of binding showed a good correlation with their reported abilities to down-regulate 5-HT2 receptors in vivo after chronic treatment, suggesting that these actions reflect the same underlying process.

Animals↗
PubMed1994

Importance of peptide amino and carboxyl termini to the stability of MHC class I molecules.

An influenza virus matrix peptide in which either the charged amino or carboxyl terminus was substituted by methyl groups promoted folding of the class I human histocompatibility antigen (HLA-A2). A peptide modified at both termini did not promote stable folding. The thermal stability of HLA-A2 complexed with peptides that did not have either terminus was approximately 22 degrees C lower than that of the control peptide, whereas matrix peptide in which both anchor positions were substituted by alanines had its stability decreased by only 5.5 degrees C. Thus, the conserved major histocompatibility complex class I residues at both ends of the peptide binding site form energetically important sites for binding the termini of short peptides.

Amino Acid Sequence↗
PubMed1994

Desensitization, phosphorylation and palmitoylation of the human dopamine D1 receptor.

The regulation and post-translational modifications of the human dopamine D1 receptor were studied in the baculovirus-eukaryotic cell expression system. Baculovirus constructs containing either the DNA encoding the dopamine D1 receptor or a DNA encoding a c-myc epitope tagged dopamine D1 receptor (c-myc-dopamine D1 receptor) were used to infect Spodoptera frugiperda (Sf9) insect cells. Expressed dopamine D1 and c-myc-dopamine D1 receptors bound agonists and antagonists with affinities and a rank order of potency characteristic of a classical dopamine D1 receptor pharmacological profile. In membrane preparations from cells expressing c-myc-dopamine D1 receptor, the photoaffinity label [125I](3-methyl-2-[4'-azidophenyl]-2,3,5-tetrahydro-2H-3-benzazepine) ([125I]MAB) bound specifically upon photolysis. A major broad band of approximately 48 kDa was detected. This species was identified in immunoblots by the monoclonal antibody raised against the c-myc epitope of c-myc-dopamine D1 receptor was isolated by immunoprecipitation from whole cells and was shown to be post-translationally modified by phosphorylation and palmitoylation. Exposure of cells expressing c-myc-dopamine D1 receptor to dopamine for 15 min resulted in a reduction in the maximal dopamine stimulated adenylyl cyclase activity, which was accompanied by an increased phosphorylation of the receptor and a rapid redistribution of surface c-myc-dopamine D1 receptor as detected by in situ immunofluorescence. Dopamine exposure also resulted in an increased level of incorporation of [3H]palmitic acid into the receptor. Thus, we provide the first evidence that the human dopamine D1 receptor undergoes agonist-dependent desensitization, phosphorylation and palmitoylation.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1994

Ethical issues involved in establishing a registry for familial Alzheimer's disease.

In January 1992, the IMAGE Project extended the establishment of its registry of familial Alzheimer cases to all areas of the province of Quebec, for collection of epidemiological and clinical data, as well as biological samples. The aim is to study genetic transmission patterns of Alzheimer's disease (AD) and to provide a sampling framework for further etiologic and risk factor studies. The IMAGE registry already includes data of a population-based study in the Saguenay-Lac-St-Jean area; the project to collect data on familial AD (FAD) cases across the province of Quebec is known as the ALGENE Initiative. The registry is thus a collection of "AD families" for both familial and sporadic cases. The establishment of the registry involves several steps in the field work: recruitment and selection of families; collection of information on family medical history; selection of informative families and genetic testing for AD/FAD by linkage analysis. As AD is not homogeneous in its etiology and since we do not know if, in the event that genetics is involved in AD whether or not penetrance of the gene(s) is high, we must be aware of the "genetic horizons" of AD in collecting and conserving data on families of cases, and in the genetic testing for AD/FAD by linkage analysis. Families who choose genetic testing must be aware of the implications of our undertaking, assured of the confidentiality of the test and, at the same time, they must understand its limitations. The experimental nature of our research project raises ethical dilemmas. This article examines these initial considerations of the field work involved in developing a registry pertaining to genetic testing for AD/FAD by linkage analysis and offers some preliminary observations on the experience of the first year of this project.

Aged↗
PubMed1994

Beta-adrenergic receptor desensitization in the early stage of hereditary cardiomyopathy in hamsters.

The beta-adrenergic receptor (beta AR)/adenylyl cyclase signalling pathway was examined in cardiac membranes from cardiomyopathic Syrian hamsters. Three stages were examined during the progression of this hereditary cardiomyopathy (30 days old, prenecrotic phase; 60 days old, necrotic phase; and 120 days old, compensatory phase). Isoproterenol-stimulated adenylyl cyclase activity was decreased by 32 +/- 16% in 30-day-old cardiomyopathic hamsters, compared with age-matched controls. This was not accompanied by any change in the fluoride- or forskolin-stimulated activities, suggesting that the decrease reflects a perturbation of the receptor-mediated stimulation. Neither the density nor the subcellular distribution of the beta AR, as assessed by [125I]iodocyanopindolol binding assays, was affected in these animals. However, the agonist binding properties of the beta AR were significantly affected. Indeed, the effect of guanyl nucleotides on isoproterenol binding was decreased in 30-day-old cardiomyopathic hamsters. Given that guanyl nucleotide sensitivity is correlated with the ability of the beta AR to productively interact with Gs protein, these results suggest that the decreased beta-adrenergic-stimulated adenylyl cyclase activity results from a functional uncoupling of the beta AR with no change in receptor density. The desensitization of the beta-adrenergic-stimulated adenylyl cyclase was transient, since no change in isoproterenol-stimulated adenylyl cyclase was detected in 60- and 120-day-old hamsters, compared with age-matched controls. Similarly, the receptor number and distribution were not affected at those ages.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1994

Characterization, expression, and hormonal control of a thymic beta 2-adrenergic receptor.

In the present study, we have characterized the beta 2-adrenergic receptor (beta 2-AR)-adenosine 3',5'-cyclic monophosphate (cAMP) system of the rat thymus gland and examined the hormonal regulation of the thymic beta 2-AR gene expression under physiological or pharmacological conditions accompanied by marked alterations of the sex steroid hormone milieu. We report here that membrane preparations of female rat thymic tissue contain iodocyanopindolol binding sites that exhibit pharmacological properties typical of a beta-AR. Detailed analysis by computer modeling of the binding potencies of a large series of beta 1- and beta 2-adrenergic agonists and antagonists revealed predominantly the beta 2-AR subtype (78%) in rat thymus. This inference from radioligand binding studies was corroborated functionally by the rank order of potencies of a series of adrenergic agonists to stimulate the production of cAMP. Northern blot analysis, using a human beta 2-AR cDNA as a probe, revealed the presence of a mRNA of 2.3 kb, which is consistent with the size of the beta 2-AR mRNA found in other rat tissues. Physiological regulation of specific beta 2-AR in the rat thymus was indicated by significant increases in both receptor concentration and steady-state levels of beta 2-AR mRNA during the diestrous 2 and proestrous phases of the rat estrous cycle and pregnancy, whereas castration sharply reduced beta 2-AR numbers and transcript levels within the thymus. The modulation of the thymic beta 2-AR-cAMP signaling system by the preexisting sex steroid milieu, coupled with the sex-dependent adrenergic modulation of thymic cell-mediated immune response, may contribute to the various sex-related alterations in immune responsiveness and could play a role in sexually related immune disorders.

Adenylyl Cyclases↗
PubMed1994

Inverse agonist activity of beta-adrenergic antagonists.

Agonist-independent properties of the human beta 2-adrenergic receptor (beta 2AR) were studied using the baculovirus expression system in Sf9 cells. In the absence of agonist but in the presence of GTP, membranes from cells expressing the beta 2AR exhibited higher levels of cAMP production than did membranes from uninfected cells or from cells infected with wild-type baculovirus. The increase in cAMP production was proportional to the number of beta 2AR expressed, up to 40 pmol/mg of membrane protein, and it could be inhibited in a dose-dependent manner by beta AR antagonists. The increase and its reversal both were independent of the possible presence of contaminating catecholamines in the culture medium and thus appear to reflect spontaneous beta 2AR activity and direct antagonist-receptor interactions, respectively. The maximal level of inhibition varied among the beta AR ligands tested, to yield the following rank order of "inverse efficacy"; timolol > or = propranolol > alprenolol > or = pindolol > labetalol > dichloroisoproterenol. The same rank order was observed using membranes prepared from Chinese hamster fibroblasts expressing beta 2AR. The effect of timolol was partly blocked by labetalol and dichloroisoproterenol, in an apparently competitive manner. The intracellular cAMP content of Sf9 cells cultured in serum-free medium was also increased by the expression of beta 2AR, and that increase was reversed by timolol and propranolol, consistent with observations in membrane preparations. The properties revealed by the expression of the beta 2AR in Sf9 cells suggest two agonist-independent traits of G protein-linked receptors, i.e., 1) that unliganded receptors are able to activate G proteins both in membrane preparations and in whole cells and 2) that antagonists may mediate their effects not only by preventing the binding of agonists but also by decreasing the propensity of the receptor to assume an active state.

Adrenergic beta-Agonists↗