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Biomedical subjects

L Levesque

Publications and source records attributed to L Levesque.

At least 37 records · Page 2Linked to original sources
PubMed1996

Widespread immunoreactivity of presenilin in neurons of normal and Alzheimer's disease brains: double-labeling immunohistochemical study.

The immunolocalization of presenilin in human brain was studied using two antibodies raised against different portions of presenilin 1 (S182) protein. A granular staining was found in the cytoplasm of neurons in cortical layers III and V. One of the antibodies, also reactive to presenilin 2 (E5-1) protein, additionally stained dendrites and axons. This was seen in normal brains as well as in brains affected by Alzheimer's disease. Less prominent immunolabeling was noted in some senile plaques. No relationship to neurofibrillary tangles was found in double-labeling experiments combined with anti-paired helical filament-tau antibody (AT8). The widespread expression of presenilin in normal brain suggests a physiological role of the protein.

Aged↗
PubMed1996

The alpha1-fetoprotein locus is activated by a nuclear receptor of the Drosophila FTZ-F1 family.

The alpha1-fetoprotein (AFP) gene is located between the albumin and alpha-albumin genes and is activated by transcription factor FTF (fetoprotein transcription factor), presumed to transduce early developmental signals to the albumin gene cluster. We have identified FTF as an orphan nuclear receptor of the Drosophila FTZ-F1 family. FTF recognizes the DNA sequence 5'-TCAAGGTCA-3', the canonical recognition motif for FTZ-F1 receptors. cDNA sequence homologies indicate that rat FTF is the ortholog of mouse LRH-1 and Xenopus xFF1rA. Rodent FTF is encoded by a single-copy gene, related to the gene encoding steroidogenic factor 1 (SF-1). The 5.2-kb FTF transcript is translated from several in-frame initiator codons into FTF isoforms (54 to 64 kDa) which appear to bind DNA as monomers, with no need for a specific ligand, similar KdS (approximately equal 3 x 10(-10) M), and similar transcriptional effects. FTF activates the AFP promoter without the use of an amino-terminal activation domain; carboxy-terminus-truncated FTF exerts strong dominant negative effects. In the AFP promoter, FTF recruits an accessory trans-activator which imparts glucocorticoid reactivity upon the AFP gene. FTF binding sites are found in the promoters of other liver-expressed genes, some encoding liver transcription factors; FTF, liver alpha1-antitrypsin promoter factor LFB2, and HNF-3beta promoter factor UF2-H3beta are probably the same factor. FTF is also abundantly expressed in the pancreas and may exert differentiation functions in endodermal sublineages, similar to SF-1 in steroidogenic tissues. HepG2 hepatoma cells seem to express a mutated form of FTF.

Amino Acid Sequence↗
PubMed1995

Development of a binding assay for the B1 receptors for kinins.

A novel binding assay to kinin B1 receptors was developed, based on the design of a high-affinity agonist ligand, [125I]Tyr-Gly-Lys-Aca-Lys-des-Arg9-BK. Binding to rabbit aortic smooth muscle cells is highly temperature-dependent (optimal at 37 degrees C); apparent binding equilibrium is reached within 30 min, and competition by kinin analogs reveals the expected correlation with the B1 receptor pharmacology. The dissociation constant (Kd) of the labeled ligand is approx. 0.2 nM and this value does not change significantly as a function of cytokine pretreatment. However, the receptor abundance (Bmax) is significantly increased (1.5-fold) by pretreating the cells with interleukin-1 (IL-1), while oncostatin M (OSM) produces a marginal increase of the Bmax. This assay may be useful in documenting the regulation of B1 receptors in pathology.

Amino Acid Sequence↗
PubMed1995

Regulation of kinin-induced contraction and DNA synthesis by inflammatory cytokines in the smooth muscle of the rabbit aorta.

1. In rabbit aortic rings, the contractile response to kinins is mediated by the B1 receptors for kinins; the response is upregulated from an initial null level in a time- and protein synthesis-dependent manner. Incubation (3 h) with human recombinant interleukin-1 beta (IL-1 beta) selectively amplified the contractile response to the B1 receptor agonist Sar-[D-Phe8]des-Arg9-BK, while it did not affect the contractile effect of other agents (angiotensin II, endothelin-1, phenylephrine). 2. Oncostatin M (OSM), but not macrophage migration inhibitory factor (MIF), increased the contractile response to the B1 receptor agonist, des-Arg9-bradykinin (des-Arg9-BK). 3. Cultured smooth muscle cells derived from the rabbit aorta exhibit a significant des-Arg9-BK-induced increase in [3H]-thymidine incorporation if pretreated with a cyclo-oxygenase inhibitor (diclofenac) and concomitantly treated with the cytokines IL-1 or OSM. Angiotensin II, endothelin-1 or phenylephrine, alone or in the presence of IL-1 beta, exerted little effect on DNA synthesis in these cells. 4. The pharmacological characterization of the mitogenic response to kinins using a set of agonist and antagonist analogues is consistent with mediation by B1 receptors. Des-Arg9-BK-induced DNA synthesis is suppressed by prostaglandin E2 by a prostacyclin mimetic (iloprost), by the Ser/Thr protein kinase inhibitor, H-7, and by a tyrosine kinase inhibitor (i.e. an erbstatin analogue). 5. B1 receptor-mediated responses and their capacity to be regulated by cytokines, are retained in rabbit aortic smooth muscle cells. Such responses could be relevant to tissue repair mechanisms and hypertrophic medial responses to injury in arteries.

Angiotensin II↗
PubMed1995

Cloning and pharmacological characterization of the rabbit bradykinin B2 receptor.

Degenerate primers, corresponding to consensus sequences of third and sixth transmembrane domains of G protein-coupled receptor superfamily, were used for the polymerase chain reaction amplification and consecutive characterization of G protein-coupled receptors present in cultured rabbit aortic smooth muscle cells. One of the isolated resulting fragments was highly homologous to the corresponding region of the bradykinin (BK) B2 receptor cloned in other species. The polymerase chain reaction fragment was used to screen a rabbit genomic library, which allowed the identification of an intronless 1101-nucleotide open reading frame which codes for a 367-amino acid receptor protein. The rabbit B2 receptor sequence is more than 80% identical to the ones determined in three other species and retain putative glycosylation, palmitoylation and phosphorylation sites. In the rabbit genomic sequence, an acceptor splice sequence was found 8 base pairs upstream of the start codon. Northern blot analysis showed a high expression of a major transcript (4.2 kilobases) in the rabbit kidney and duodenum, and a less abundant expression in other tissues. Southern blot experiments suggest that a single copy of this gene exists in the rabbit genome. The cloned rabbit B2 receptor expressed in COS-1 cells binds [3H]BK in a saturable manner (KD 2.1 nM) and this ligand competes with a series of kinin agonists and antagonist with a rank order consistent with the B2 receptor identity. The insurmountable character of the antagonism exerted by Hoe 140 against BK on the rabbit B2 receptor, previously shown in pharmacological experiments, was confirmed in binding experiments with the cloned receptor expressed in a controlled manner. By contrast, Hoe 140 competed with [3H]BK in a surmountable manner for the human B2 receptor expressed in COS-1 cells. The cloning of the rabbit B2 receptor will be useful notably for the study of the structural basis of antagonist binding and for studies on receptor regulation in a relatively large animal.

Amino Acid Sequence↗
PubMed1994

Effects of peptide and nonpeptide antagonists of bradykinin B2 receptors on the venoconstrictor action of bradykinin.

The isolated rabbit jugular and human umbilical veins respond to bradykinin (BK) by contractions that are mediated by the BK B2 type receptors. In this report, the pharmacology of recently developed BK B2 receptor antagonists is assessed by using these preparations. The nonpeptide kinin antagonist WIN 64338 (phosphonium, [[4-[[2-[[bis(cyclohexylamino)methylene]amino]- 3-(2-naphthalenyl)-1-oxopropyl]amino]phenyl]methyl]tributyl chloride monohydrochloride) demonstrates competitive and surmountable antagonism of BK in both the jugular and the umbilical veins (pA2 values of 6.14 and 5.99, respectively). WIN 64338 shows selectivity in its antagonist action as it does not inhibit the effect of various other contractile agents in either of the preparations. HOE-140 (D-Arg[hydroxyproline3,beta-thienylalanine5, D-Tic7, octahydroindol-2-yl-carbonyl residue8]-BK), a "second generation" peptide antagonist of BK, behaves as an insurmountable and irreversible antagonist in the rabbit jugular vein, but appears to be competitive in the umbilical vein (pA2 = 8.2). In the jugular vein, [L-Tic7]HOE-140 is an insurmountable antagonist about 2000-fold less potent than HOE-140; the L-Tic7 isomer demonstrates no significant antagonist activity on the umbilical vein at 30 microM. This study confirms that WIN 64338 behaves as a competitive and selective kinin antagonist of the BK B2 type receptors. The pharmacological profile of the L-Tic7 analog of HOE-140 may provide useful information in discerning the molecular interaction of noncompetitive BK antagonists with their receptors.

Animals↗
PubMed1993

Synthetic C5a receptor agonists. Pharmacology, metabolism and in vivo cardiovascular and hematologic effects.

Recent investigations have produced novel compounds that act on the receptor for anaphylatoxin C5a. These products are C-terminal analogues of C5a, some of which are modified extensively. We have measured the receptor affinities of such analogues in a binding assay on human neutrophils (PMNs). We have also characterized their pharmacological profiles in vitro on the isolated rabbit portal vein and pulmonary artery, on superoxide release by PMNs as well as in vivo in the anesthetized rabbit (acute hypotensive and neutropenic effects). The metabolic resistance of these analogues was also evaluated in the presence of different peptidases. One of these compounds, MePhe-Lys-Pro-D-Cha-Phe-D-Arg, behaved as an antagonist on the release of superoxide by neutrophils while exerting agonist activity in all other assays. Its partial agonist status was documented in a receptor down-regulation experiment on PMNs where its activity was compared with those of recombinant C5a and of protamine which behaves as a competitive antagonist on these cells. Degradation studies indicated that the discrepancy between the affinity of certain analogues in vitro and their potency in vivo was probably linked to their metabolic stability.

Amino Acid Sequence↗
PubMed1993

Vascular mode of action of kinin B1 receptors and development of a cellular model for the investigation of these receptors.

1. Kinins exert a contractile effect on rabbit aortic rings via the stimulation of B1 receptors. Des-Arg9-bradykinin (BK) is more potent than BK on this receptor type. The mode of action of des-Arg9-BK on rabbit aortic tissue has been studied by both the aortic ring contractility assay and a cellular model using cultured aortic smooth muscle cells (SMCs). 2. The des-Arg9-BK-induced contractions in rabbit aortic rings were unaffected by pretreatments with nifedipine, indomethacin, REV-5901 (a 5-lipoxygenase blocker) and LY-83583 (a guanylyl cyclase inhibitor); however, the protein kinase inhibitors H-7 and H-9 significantly reduced the maximal effect of des-Arg9-BK. 3. The contractile responses to des-Arg9-BK in calcium-free Krebs solution were slightly but not significantly attenuated in amplitude, as compared to paired control tissues bathed in Krebs solution, and sustained plateaus of contraction were observed in the absence of Ca2+. However, Ca2+ replenishment further increased the kinin-induced contraction measured in Ca(2+)-free bathing fluid. 4. Despite the lack of evidence of a mediating role for prostaglandin in the mechanical response to des-Arg9-BK, the kinin stimulated the release of prostacyclin from rabbit aorta rings measured as immunoreactive 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). 5. Smooth muscle cells (SMCs) derived from the rabbit aorta exhibit functional responses to des-Arg9-BK in acute release of 6-keto-PGF1alpha and of inositol phosphate turnover which were inhibited by pretreatment with the B1 receptor antagonist, Lys[Leu8]des-Arg9-BK, but not by the B2 receptor antagonist, Hoe-140. Preincubation of the cells with interleukin- 1 (IL-1) 20 h before stimulation with the kinin had no effect on basal inositol phosphate turnover, but potentiated the acute effect of des-Arg9-BK.6. These results suggest that second mesengers derived from the action of phospholipase C are produced by SMCs when B1 receptors are activated in rabbit aortic tissue. Intracellular calcium stores are primarily mobilized by des-Arg9-BK, although receptor-controlled calcium influx has not been ruled out, and may contribute to initiate the contractile responses. The maintenance of the contractile state involves protein kinase C activity and is consistent with a current model of SMC function. The cell model retains some of the cardinal properties of B1 receptor-mediated vascular responses: endothelium independent PGI2 release and up-regulation by the cytokine IL-1. PGI2 is not involved in the mechanical response, possible because the rabbit aorta is refractory to this prostaglandin.

6-Ketoprostaglandin F1 alpha↗
PubMed1993

Development and in vivo evaluation of metabolically resistant antagonists of B1 receptors for kinins.

The B1 receptors for kinins are selectively stimulated by bradykinin (BK) and Lys-BK metabolites that do not have the C-terminal arginine, des-Arg9-BK and Lys-des-Arg9-BK, respectively. B1 receptors mediate a definite subset of the cardiovascular effects of kinins in normal and septic animals. We have studied the metabolism of the best selective B1 antagonist, Lys[Leu8]des-Arg9-BK, in order to support the rational design of new antagonists that have increased metabolic stability. The affinity of the new compounds was evaluated using the pA2 scale and was based on the antagonism of the contractile effect of kinins in the rabbit isolated aortic preparation. Acetylation of the alpha-amino group of the N-terminal Lys residue provided an excellent protection from the degradation by rabbit blood plasma. This and the inhibitory effect of amastatin on the metabolism of Lys[Leu8]des-Arg9-BK indicated that aminopeptidase M (AmM) is the major route of inactivation for this class of peptides in plasma. Various other modifications afforded a more or less complete resistance to purified angiotensin I converting enzyme (ACE). One analog, Ac-Lys[MeAla6, Leu8]des-Arg9-BK, was found resistant to the above-mentioned enzymes and to neutral endopeptidase-24.11 extracted from rabbit kidney. This antagonist, although 100 times less potent than the parent peptide Lys[Leu8]des-Arg9-BK on the rabbit aortic preparation, was equipotent in vivo against the hypotensive effect of a B1 agonist in lipopolysaccharide-treated rabbits, and unlike the original compound, its effect was persistent after the end of the infusion. Ac-Lys[MeAla6, Leu8]des-Arg9-BK does not antagonize B2 receptors either in vitro or in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Comparison of two classes of non-peptide drugs as antagonists of neutrophil receptors for f-Met-Leu-Phe. Pyrazolons and iodinated radiographic contrast agents.

The radiographic contrast agent sodium diatrizoate (DTR) reportedly inhibits f-Met-Leu-Phe-induced chemotaxis in human neutrophils. DTR is also an ingredient of Ficoll-Paque, a density centrifugation medium widely used to purify human polymorphonuclear leukocytes (PMNs). Exposure of PMNs to DTR during preparation had no detrimental effect on subsequent binding characteristics of tritiated f-Met-Leu-Phe, probably owing to a rapid dissociation of DTR from the PMN receptors. DTR competed directly with f-Met-Leu-Phe for receptor binding, but was 160- and 640-fold less potent than phenylbutazone and 1,2-diphenyl-4-[3-(1-naphthyl)-propyl]-3,5-pyrazolidinedione (DPN; an analog of phenylbutazone), respectively. Iohexol and the methylamide of DTR did not compete with [3H]f-Met-Leu-Phe in receptor binding, supporting the existence of a definite interaction between iodinated aromatic molecules and the f-Met-Leu-Phe receptor. DTR did not inhibit prostaglandin synthesis, as did DPN. Both drugs inhibited chemotactic peptide-induced release of superoxide anion in a concentration-dependent manner, and were relatively selective for f-Met-Leu-Phe, as opposed to C5a. Both drugs at 10 microM interfered non-selectively with chemotactic peptide-induced beta-glucuronidase release from PMNs. Available non-peptide antagonists of f-Met-Leu-Phe exhibited other pharmacodynamic properties that could make them unsuitable for future in vivo studies designed to probe the physiological role of the receptor.

Binding, Competitive↗
PubMed1991

The interaction of 3,5-pyrazolidinedione drugs with receptors for f-Met-Leu-Phe on human neutrophil leukocytes: a study of the structure-activity relationship.

The 3,5-pyrazolidinedione (3,5-P) drugs, phenylbutazone and sulfinpyrazone, have been reported to bind to receptors for the chemotactic peptide, f-Met-Leu-Phe, and to behave as functional antagonists of f-Met-Leu-Phe in human and rabbit neutrophils. To explore the structure-activity relationship of this family of drugs for f-Met-Leu-Phe receptor binding, 36 drugs with the 3,5-P structure, a structure related to antipyrine, or an unrelated structure were tested as competitors for the binding of f-Met-Leu-Phe-Lys-fluorescein isothiocyanate on human neutrophils by flow cytometric analysis. Only drugs possessing the 3,5-P ring were significant competitors. The five most potent 3,5-Ps behaved as selective antagonists of f-Met-Leu-Phe-induced superoxide anion release by neutrophils. The potency was not correlated to the pKa or to their capacity to inhibit prostaglandin E2 released from culture fibroblasts but instead appeared to be correlated to their apparent octanol-buffer partition coefficients. The most potent f-Met-Leu-Phe antagonist identified, 1,2-diphenyl-4-(3-(1-naphthyl)-propyl)-3,5-pyrazolidinedione (DPN), may also possess an improved pharmacodynamic specificity compared with phenylbutazone and sulfinpyrazone, as it was less potent than phenylbutazone in the inhibition of prostaglandin synthesis and it was not cytotoxic. DPN may be a prototype for a valuable new class of anti-inflammatory drugs.

Binding, Competitive↗
PubMed1991

{Critical review of studies on social support and its relation to the well-being of people suffering from dementia}.

Many people suffering from dementia live at home, in spite of the demands that such a situation puts on those who care for them. The role of helper is usually assumed by a particular family member who is therefore more likely to feel the impact of the caregiving responsibility. Researchers are concerned with the relationship between the well-being of these helpers and their informal social support. This article presents a critical review of 21 studies of that relationship. The various dimensions of social support considered in the studies are analyzed, as are the methodological limits. A discussion of findings about the relationships between social support and well-being completes the analysis. It appears that researchers have a limited conception of social support and assess only a few of its many dimensions in a variety of ways. Very few authors explicitly specify underlying assumptions or a theory relevant to their conceptualization of social support. The weakness and the diversity of this conceptualization are reflected in the measurement tools which consist of a few ad hoc questions on social support in nearly 50% of the studies. Few studies consider the support availability, duration, conflict, and reciprocity. The buffering effect model of support is examined in one study. Inadequate sample size, unrepresentative samples, and lack of control in regard to confounding variables are among the methodological problems identified. When researchers use an evaluative approach to measure social support, the relationships between support and well-being are more often significant than when a descriptive approach is used. In future studies, researchers should be careful to better articulate the theoretical notions proposed in studies on caring for a family member with dementia at home with those coming from studies on social support in general. It is important for researchers to strengthen their study design and to carry out longitudinal studies; they must also try to understand how the influence of society works. From this perspective, one avenue for the future might involve studying the sequence of relationships between stress, support, coping strategies, and well-being. This is all the more important because at the present time certain studies on the caring of persons with dementia are based on a conceptual framework of stress. Such a framework considers support as a mediating factor.

Caregivers↗
PubMed1990

Reversal of diabetes in BB rats by transplantation of encapsulated pancreatic islets.

Prolonged survival of pancreatic islet allografts implanted in diabetic BB rats was achieved by encapsulation of individual islets in a protective biocompatible alginate-polylysine-alginate membrane without immunosuppression. Intraperitoneal transplantation of the encapsulated islets reversed the diabetic state of the recipients within 3 days and maintained normoglycemia for 190 days. Normal body weight and urine volume were maintained during this period, and no cataracts were detected in the transplant recipients. In contrast, control rats receiving transplants of unencapsulated islets experienced normoglycemia for less than 2 wk. These results demonstrated that microencapsulation can protect allografted islets from both graft rejection and autoimmune destruction without immunosuppression in an animal model that mimics human insulin-dependent diabetes.

Alginates↗
PubMed1989

Periovulatory follicular fluid hormone levels in spontaneous human cycles.

We measured follicular fluid hormone levels in 48 normally cycling infertile women who underwent follicle puncture and oocyte retrieval during diagnostic laparoscopy at time-bracketed intervals after an endogenous LH surge. Follicular fluid LH, FSH, PRL, estrone (E1), estradiol (E2), progesterone (P), androstenedione (A), and testosterone (T) concentrations and P/E2 and A/E2 ratios were determined. Oocytes were classified as germinal vesicle (gv), metaphase I (mI), metaphase II (mII), or degenerating (dg). Follicular fluid (ff) hormone levels then were correlated with the stage of oocyte maturation. There were no differences in ff E1 or E2 levels at any stage of oocyte maturation, except that the mean ff E2 concentration was significantly (P less than 0.05) lower in ff containing dg oocytes [2,474 +/- 1,435 (+/- SE) nmol/L] than in those containing the other oocyte stages. The mean P levels were significantly (P less than 0.0001) higher in ff containing mI (48,781 +/- 10,240 nmol/L) and mII (41,801 +/- 11,098 nmol/L) oocytes than in ff containing gv oocytes (1371 +/- 696 nmol/L). The mean A level was highest (P less than 0.01) in dg-associated ff. Similarly, T was highest (P less than 0.05) in ff containing dg (52 +/- 14 nmol/L) oocytes than in ff containing mI (10.7 +/- 10.1 nmol/L) or mII (10.1 +/- 4 nmol/L) oocytes, and it was also elevated (P less than 0.05) in gv ff (72 +/- 33 nmol/L) compared to mII ff. The above differences also were reflected in the P/E2 ratio, which was significantly higher (P less than 0.05) in mI and mII ff, as well as in the A/E2 ratio, which was higher (P less than 0.05) in ff containing mI and mII oocytes compared to ff containing gv or dg oocytes. These data define the evolving changes in the microenvironment of the follicular fluid of preovulatory follicles of normally cycling women. They also provide reference points for analysis of ff obtained from women during stimulated cycles intended for in vitro fertilization.

Adult↗
PubMed1988

Effects of photoperiod, the pineal gland and the gonads on agonistic behavior in female golden hamsters (Mesocricetus auratus).

Four studies were conducted to determine the role of photoperiod, the pineal gland and the gonads in the regulation of intrasex agonistic behavior in female hamsters. In the first experiment animals maintained under Long or Short photoperiods were tested in same or opposite photoperiod pairs. Under both testing conditions, Short-day animals tended to exhibit a higher ratio of offensive to defensive behaviors, which was due primarily to a reduced level of defensive behavior in Short-day groups. In the second experiment animals under Long and Short photoperiods were tested following sham surgery or pinealectomy. Short-day sham animals exhibited the highest level of offensive behavior, the lowest level of defensive behaviors and the highest offensive/defensive ratio; pinealectomy eliminated the Short-day advantage. In the third experiment, Long-day animals receiving exogenous melatonin showed a higher level of agonistic responding than animals injected with control vehicle, indicating that Short-day effects are probably mediated through pineal melatonin. The results of the last experiment in which ovariectomy to Long-day animals was not able to mimic the effects of photoperiod or exogenous melatonin indicated that the photoperiod effects on aggression are probably not mediated through the gonads.

Aggression↗
PubMed1988

Characteristics of in vitro steroidogenesis in a woman with hyperandrogenism, a granulosa cell tumor and polycystic ovary disease. A case report.

A 20-year-old woman presented with hyperandrogenism presumed to be due to an androgen-secreting granulosa cell tumor. In order to confirm this unusual presentation, short-term tissue culture steroidogenesis of the granulosa cell tumor and contralateral polycystic ovary was performed. Testosterone and androstenedione were produced only by the polycystic ovary, whereas the tumor was producing estradiol and progesterone. The studies of in vitro steroidogenesis prevented an incorrect interpretation of the clinical presentation.

Adult↗