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G Pelletier

Publications and source records attributed to G Pelletier.

At least 235 records · Page 13Linked to original sources
PubMed1994

Immunocytochemical localization and biological activity of 3 beta-hydroxysteroid dehydrogenase in the central nervous system of the frog.

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyzes biosynthesis of progesterone (P) and all precursors of glucocorticoids, mineralocorticoids, androgens, and estrogens. Despite the broad interest raised by neurosteroids, the cellular localization of 3 beta-HSD has never been investigated in the brain. We took advantage of the availability of an antiserum raised against human placental 3 beta-HSD to determine the distribution of 3 beta-HSD-immunoreactive structures in the brain of the frog Rana ridibunda by the indirect immunofluorescence technique. Three populations of 3 beta-HSD-immunoreactive cell bodies were observed in the hypothalamus, namely, in the rostral region of the preoptic nucleus, the dorsal infundibular nucleus, and the dorsal part of the ventral infundibular nucleus. A dense network of 3 beta-HSD-immunoreactive nerve fibers was visualized in the dorsal area of the diencephalon, that is, in the lateral neuropil, the corpus geniculatus lateralis, and the nucleus posterolateralis thalami. Reversed-phase HPLC analysis of frog hypothalamic extracts combined with RIA detection showed the presence of substantial amounts of immunoreactive steroids coeluting with P and 17-hydroxyprogesterone (17OH-P). The synthesis of delta 4-3-keto-steroids in the frog hypothalamus was investigated using the pulse-chase technique with 3H-pregnenolone (3H-delta 5P) as a precursor. The formation of five tritiated metabolites of 3H-delta 5P was observed, one of which coeluted with 17OH-P. Conversion of 3H-delta 5P into this radioactive metabolite was significantly reduced by trilostane, a specific inhibitor of 3 beta-HSD. Immunodetection of newly synthesized steroids in HPLC fractions of hypothalamic extracts, using 17OH-P antibodies, revealed the existence of an immunoreactive steroid that exhibited the same retention time as synthetic 17OH-P. The present study provides the first immunocytochemical mapping of 3 beta-HSD, a key enzyme of the steroid biosynthetic pathway, in the CNS of a vertebrate. The data also demonstrate for the first time biosynthesis of neurosteroids in the brain of a nonmammalian vertebrate.

17-alpha-Hydroxyprogesterone↗
PubMed1993

Analysis of p53 antibodies in patients with various cancers define B-cell epitopes of human p53: distribution on primary structure and exposure on protein surface.

p53 antibodies have been found in sera of patients with breast and lung carcinomas and in children with B-lymphomas. We report here the presence of p53 antibodies in sera of patients with 11 different types of cancer. The frequency of seropositives for p53 varied among the different types of cancer, but a correlation with the frequency of p53 gene alteration was established. Using a powerful peptide enzyme-linked immunosorbent assay, we demonstrated that the immune response of patients with p53 antibodies was restricted to a small subset of peptides localized in the amino and carboxy termini of p53, whatever the type of cancer. Given the similarities of the patterns of immune responses in patients with p53 antibodies and animals hyperimmunized with human p53, we propose that the p53 humoral response is the result of a self-immunization process which is itself the consequence of p53 protein accumulation in tumor cells.

Amino Acid Sequence↗
PubMed1993

Biosynthesis of gamma-linolenic acid in developing seeds of borage (Borago officinalis L.).

delta 6-desaturation of [14C]linoleoyl-CoA or [14C]oleoyl-CoA leading to the synthesis of gamma-linolenic acid was studied in vitro with microsomal fractions from developing seeds of Borago officinalis. Time course of the reaction, effects of protein and precursor concentrations and nucleotide requirements were examined. These parameters allowed us to improve the in vitro delta 6-desaturation assay. We observed that the precursors were acylated mainly in phosphatidylcholine, diacylglycerol and triacylglycerol, and then desaturated. NADH was absolutely required when [14C]oleoyl-CoA was the precursor, but not when [14C]linoleoyl-CoA was the precursor although it stimulated the reaction. The in vitro delta 6-desaturase activity was found mainly in phosphatidylcholine, associated with enriched endoplasmic reticulum membranes (ER) from embryos. No activity was observed in ER from seed coat or seedling. During maturation of the seeds, delta 6-desaturase reached its highest activity 14 to 16 days after pollination.

Fatty Acid Desaturases↗
PubMed1993

Regulation of proopiomelanocortin gene expression in rat brain and pituitary as studied by in situ hybridization.

The major sites of POMC gene expression are the intermediate and anterior lobes of the pituitary and the arcuate nucleus of the hypothalamus. We have investigated the regulation of POMC mRNA levels in the pituitary and hypothalamus by quantitative in situ hybridization using a 35S-labeled cDNA probe encoding or POMC. In the arcuate nucleus, where the POMC-producing neurons are concentrated, adrenalectomy induced a marked decrease in POMC mRNA levels, an effect that was completely reversed by dexamethasone administration. The stimulating effect of dexamethasone was much more striking in the most caudal regions of the nucleus. Since in the anterior pituitary, glucocorticoids exert an inhibitory action on POMC gene expression, it might be suggested that POMC is differentially regulated by glucocorticoids in the anterior pituitary and the hypothalamus. Ovariectomy induced an increase in mRNA levels in the most rostral region of the arcuate nucleus, an effect that was prevented by the concurrent administration of estradiol or dihydrotestosterone. The role of dopamine was investigated following the administration of the dopaminergic antagonist haloperidol and the D2 dopaminergic receptor agonist bromocriptine. In the arcuate nucleus, bromocriptine increased and haloperidol decreased the hybridization signal. Conversely, in the intermediate lobe of the pituitary, bromocriptine markedly depressed and haloperidol increased the levels of mRNA. These results indicate that the population of POMC neurons in the arcuate nucleus is heterogeneous. They also demonstrate that POMC gene expression is regulated by central and peripheral factors and that this regulation is different in the brain and the pituitary.

Adrenalectomy↗
PubMed1993

Gangliosides and organ-specific metastatic colonization.

To investigate whether metastatic specificity is associated with a variation in the ganglioside profile of the parent cell lines, we have analyzed and compared the ganglioside content of subcutaneous (s.c.) tumors to that of the corresponding metastases. C57BL/6 mice were injected with either the Lewis lung carcinoma (3LLc) or its cloned variants, M27, exclusively metastatic to the lung, and H59, metastasizing preferentially to the liver. Gangliosides were extracted, purified and separated on HPTLC. H59 liver metastases contained significantly more GM2 (27.8%) than the H59 s.c. tumor (7.6%). The ganglioside profiles of 3LLc or M27 s.c. tumors were no different from those of their corresponding metastases. GM2 predominated in the liver (90.8%) while GM3 (48.8%) and GM2 (33.8%) were prevalent in the lung. Unidentified gangliosides designated G1, G2, G4 and G5 were present in tumor cells but absent from normal lung and liver. This study indicates that the ganglioside compositions of the 3LLc cell line and of its M27 variant were not modified under the influence of different sites of growth. Furthermore, the ganglioside profiles of the metastases were distinct from those of their respective target organs. The results of these studies suggest a possible relationship between GM2 and the establishment of H59 metastases in the liver.

Animals↗
PubMed1993

Efficacy of chemoembolization for hepatocellular carcinomas: experience from the Gustave Roussy Institute and the Bicêtre Hospital.

Chemoembolization (CE) has been used for more than 10 years to treat hepatocellular carcinoma (HCC) in our departments, and three studies have been done. The first was a retrospective study on 232 patients in which CE was performed with doxorubicin and Gelfoam with or without Lipiodol; the response rate was 41% (34.7-47.3%) and survival was better for Okuda stage I disease than for stages II and III (2-year survival 82, 29, and 0% respectively); for patients with Lipiodol retention the response rate was over 50%. The second study compared CE with doxorubicin and Gelfoam to symptomatic treatment in a randomized manner; it included 42 patients and failed to demonstrate a survival advantage (1-year survival: CE 24% vs. control 31%; NS). The third study is ongoing and tests CE with cis-platinum, Lipiodol, and Gelfoam. According to our experience prospective randomized studies are warranted to define clearly the best indications for CE in HCC.

Carcinoma, Hepatocellular↗
PubMed1993

Transfer RNA-mediated suppression of stop codons in protoplasts and transgenic plants.

We have developed a simple, rapid and sensitive assay for tRNA gene expression in plant cells. A plant tRNA(Leu) gene was site-specifically mutated to encode each of the three anticodon sequences (CUA, UUA and UCA) that recognize, respectively, the amber, ochre and opal stop codons. The suppression activity of these genes was detected by their ability to restore transient beta-glucuronidase (GUS) expression in tobacco protoplasts electroporated with GUS genes containing premature stop codons. Protoplasts co-electroporated with the amber suppressor tRNA gene and a GUS gene containing a premature amber stop codon showed up to 20-25% of the activity found in protoplasts transfected with the functional control GUS gene. Ochre and opal suppressors presented maximum efficiencies of less than 1%. This system could be adapted to examine transcription, processing or aminoacylation of tRNAs in plant cells. In addition, phenotypically normal, fertile tobacco plants expressing a stably incorporated amber suppressor tRNA gene have been obtained. This suppressor tRNA can be used to transactivate a target gene containing a premature amber stop codon by a factor of at least several hundred-fold.

Amino Acid Sequence↗
PubMed1993

Ontogeny of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) in rat testis as studied by immunocytochemistry.

The enzymatic complex 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) is a step essential in the biosynthesis of all biologically active steroids, including androgens. In order to obtain information about the expression of 3 beta-HSD during testis development, we have localized this enzyme by light microscope immunocytochemistry during fetal and postnatal periods of development in the rat. In fetal testis, the enzyme was first detected in a few Leydig cells on the 17th day of gestation. The number of labeled cells and intensity of labeling increased with fetal development. From days 19 to 21 of gestation, strongly immunoreactive Leydig cells were arranged in clusters between seminiferous tubules. During the first days following birth, the number and size of positive cells rapidly decreased so that on postnatal days 5 and 10 only small, poorly stained cells could be seen. Fifteen days after birth, positive Leydig cells appeared more numerous and localized in peri- and intertubular spaces. At the onset of puberty, the intensity of labeling markedly increased. After puberty, and during adulthood, both strongly and weakly stained Leydig cells were mainly localized in intertubular spaces. Since the fluctuations in 3 beta-HSD content revealed in the present study by immunocytochemistry appear similar to those already observed for androgen secretion, such data suggest that regulation of 3 beta-HSD by trophic hormones might play an important role in regulating testicular androgen production during fetal as well as postnatal development.

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

Opioid regulation of proopiomelanocortin (POMC) gene expression in the rat brain as studied by in situ hybridization.

Proopiomelanocortin (POMC) is the precursor of the potent opioid peptide beta-endorphin as well as a number of other active peptides. On the basis of neuroanatomical data indicating the presence of contacts between POMC neurons in the rat arcuate nucleus, it has been proposed that POMC neurons could be autoregulated. In order to investigate the role of opiates in the regulation of POMC gene expression in the rat arcuate nucleus, we studied the effects of chronic administration of the opioid drug morphine and an opiate receptor antagonist naloxone on POMC mRNA levels as measured by in situ hybridization, 4-day treatment with naloxone (4 mg/kg/day) produced a 60% increase in the number of silver grains overlying POMC neurons. Conversely, morphine (40 mg/kg/day) also administered during 4 days decreased the hybridization signal by 30%. The concomitant administration of morphine and naloxone completely prevented the effect of morphine on POMC gene expression indicating that the inhibitory influence of morphine is likely to be mediated by opioid receptors. The data obtained clearly indicate that activation of opioid receptors decreased the biosynthetic activity of POMC neurons and that conversely opiate receptor blockade caused an increase in the activity of these neurons. They are consistent with the hypothesis of an autoregulation of the POMC neuronal system by endogenous opiate peptide(s).

Animals↗
PubMed1993

Ontogeny of diazepam-binding inhibitor-related peptides (endozepines) in the rat brain.

Benzodiazepine receptors are expressed very early in the brain during embryonic life, suggesting that endogenous ligands for these receptors may play an important role during ontogenesis in the central nervous system. In the present study, the distribution and characterization of diazepam-binding inhibitor-related peptides (endozepines) in the rat brain was investigated during embryonic and postnatal development using an antibody raised against the biologically active region of the precursor molecule. Immunohistochemical labelling showed that, in newborn rats, endozepine-like immunoreactivity was present in ependymal cells of the hypothalamus. Although the number of positive cells increased by day 5, the intensity of the immunoreaction in each cell diminished. In 15-day-old rats, both the number of endozepine positive cells and the intensity of the immunoreaction increased in the ependymal layer. At day 40, a dense accumulation of immunoreactive tanycytes and glial cells was observed in the median eminence and the arcuate nucleus. Endozepines were detected by radioimmunoassay in all regions of the brain as early as embryonic day 18. The concentration of endozepine-related peptides increased in the hypothalamus and olfactory bulb during late gestation. Between birth and postnatal day 5, the levels of endozepines decreased two- to four-fold in all brain regions studied. Thereafter, endozepine concentration increased gradually until day 25. Reversed-phase high-performance liquid chromatography analysis of tissue extracts revealed that the olfactory bulb, pituitary, hypothalamus and cerebellum contained only one immunoreactive peak eluting at 39 min (peak C). In the telencephalon two peaks were observed: peak C and a second one eluting at 34 min (peak B). Peak B was present as early as embryonic day 20 and the ratio peak B/peak C gradually increased until day 25. At day 25 peak B was also detected in hippocampus, medulla oblongata, cortex and striatum extracts. In any brain region, no immunoreactivity co-eluting with the octadecaneuropeptide was observed. Sephadex G-50 gel filtration of hypothalamus extracts of 25-day-old animals, confirmed the existence of only one immunoreactive compound with an apparent molecular weight of 10,000. In the telencephalon two major species were resolved, with apparent molecular weights of 10,000 and 8800, and a minor one of 6500 mol. wt. In conclusion, the present study shows that endozepines are expressed in the rat brain as early as embryonic day 18 and the amount of endozepine-like material increases rapidly during the two days preceding birth. The results also indicate that diazepam-binding inhibitor is processed to different molecular forms depending on the brain region.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Fatty acids in some common food items in Canada.

Fat content and fatty acid (FA) composition of 100 common items in 17 food categories from the Canadian retail market were determined. Of these, 52 samples were made from partially hydrogenated fat. Their fat (in parentheses) and trans FA levels were as follows: breads (3.7% fat) 15.7%, hamburger buns (5.5% fat) 26.3%, cakes (8.7-36.7% fat) 10.1-25.7%, candies/chocolates (27.1% fat) 11.1%, cereals (1.3-12.9% fat) 9.2-33.7%, cookies (5.0-40.5% fat) 7.6-38.7%, crackers (9.2-33.0% fat) 13.8-35.4%, donuts (16.6-29.6% fat) 27.7-32.7%, french fries (pre-cooked) (4.3-4.5% fat) 32.8-42.8%, muffins (12.5-23.7% fat) 16.5-24.2%, pizza crusts (6.0-7.2% fat) 22.1-28.8%, shortenings (100% fat) 17.4-20.2%, potato chips (33.2-40.0% fat) 29.7-39.7%, and corn chips (25.0-34.2%) 29.9-33.9%. Generally the sum of saturated and trans FA in the food items made with partially hydrogenated fat was higher than that of the corresponding food items made with unhydrogenated oils. The higher levels of saturates plus trans were at the expense of the essential fatty acids (EFA). The high-fat foods, such as cakes, cookies, crackers, donuts and potato chips, made with partially hydrogenated fat, were substantially lower in EFA and contained relatively higher levels of trans polyunsaturated fatty acids (PUFA). In some samples of potato chips and french fries, the level of trans PUFA was almost the same or more than the sum of linoleic and linolenic acids.

Bread↗
PubMed1993

Ontogenesis of 3 beta-hydroxysteroid dehydrogenase delta 5-delta 4 isomerase in the rat ovary as studied by immunocytochemistry and in situ hybridization.

The enzyme complex 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5-4-ene isomerase (3 beta-HSD) is involved in the biosynthesis of all classes of active steroids, namely glucocorticoids, mineralocorticoids, and sex steroids. To obtain more information about the age-specific expression and localization of 3 beta-HSD during development in the rat ovary, two complementary cytochemical techniques were used, immunocytochemical localization with antibodies against purified human placental 3 beta-HSD, and 3 beta-HSD mRNA localization achieved by in situ hybridization with a [35S]-labeled cDNA encoding 3 beta-HSD. In the fetal ovary, no significant immunolabeling or hybridization signal could be observed. The first expression of the enzyme was observed 6 days after birth, immunolabeling as well as autoradiographic reaction being found in a few interstitial gland cells. At the 10th day of postnatal life, the theca interna cells of growing follicles appeared to be labeled with both techniques. The granulosa cells of growing follicles also exhibited hybridization signal, whereas no immunostaining could be detected in these cells at any of the time intervals studied. At puberty, 3 beta-HSD was localized in theca interna and granulosa cells of the growing and mature follicles as well as in the interstitial gland and corpus luteum cells. Similar results were obtained in 40-day-old and adult animals. The present data indicate a progressive expression of 3 beta-HSD in different morphological structures during ovarian development in the rat.

Aging↗
PubMed1993

Opioid regulation of gonadotropin-releasing hormone gene expression in the male rat brain as studied by in situ hybridization.

It is well documented that gonadotropin-releasing hormone (GnRH) release is negatively regulated by opiates. In order to investigate the role of opiates in the regulation of GnRH gene expression in the rat brain, we studied the effects of chronic administration of the opioid drug morphine and an opiate receptor antagonist naloxone on GnRH mRNA levels as measured by in situ hybridization. Four-day treatment with morphine (40 mg kg day-2) produced a 44% decrease in the number of silver grains overlying GnRH neurones. Conversely, naloxone (4 mg kg day-2) also administered during 4 days increased by hybridization signal by 22%. The concomitant administration of morphine and naloxone completely prevented the effect of morphine on GnRH gene expression indicating the inhibitory influence of morphine is likely to be mediated by opioid receptors. The present data clearly indicate that opiates can inhibit not only the release of GnRH and consequently LH secretion but also the biosynthesis of the neuropeptide as evaluated by mRNA level measurements.

Animals↗
PubMed1993

Effects of morphine and naloxone on prolactin and growth hormone gene expression in the male rat pituitary gland.

It is generally admitted that opioids can stimulate the release of both prolactin (PRL) and growth hormone (GH). In order to investigate the role of opioids in the regulation of PRL and GH gene expression in the rat pituitary, we studied the effects of chronic administration of the opioid drug morphine and an opiate receptor antagonist naloxone on both PRL and GH gene expression as measured by in situ hybridization. Four-day treatment with morphine (40 mg/kg/day) produced a 12% increase in PRL mRNA levels. Conversely, naloxone (4 mg/kg/day) decreased the autoradiographic reaction by 10%. The concomitant administration of morphine and naloxone induced no significant changes in PRL gene expression. On the other hand, treatment with morphine produced a 22% decrease in GH mRNA levels, an effect which was prevented by the concomitant administration naloxone. When injected alone, naloxone did not modify the hybridization signal. These results clearly indicate that opioids are involved not only in the regulation of GH and PRL release but also in the gene expression of the two hormones. The discordance observed between the acute effects of morphine on GH release and the effect of the opioid drug on mRNA levels remains to be clarified.

Animals↗
PubMed1993

Chronic administration of muscimol and pentobarbital decreases gonadotropin-releasing hormone mRNA levels in the male rat hypothalamus determined by quantitative in situ hybridization.

The role of GABA in the control of gonadotropin-releasing hormone (GnRH) secretion is still controversial. In order to investigate the role of the GABAergic system in the regulation of GnRH gene expression in the rat brain, we studied the effects of chronic administration (2 days) of the GABAA receptor agonist muscimol and the central-type barbiturate receptor agonist pentobarbital on GnRH mRNA levels measured by in situ hybridization. Treatment with pentobarbital produced a 24% decrease in the hybridization signal. Similarly, muscimol treatment decreased the signal by 28%. The concomitant administration of the two GABAA receptor agonists resulted in a decrease (37%) of mRNA levels which was significantly more marked than that induced by pentobarbital or muscimol alone. The present results, together with previous data, indicate that the administration of pentobarbital or muscimol can inhibit not only the release of GnRH but also the gene expression of the neuropeptide as evaluated by mRNA level measurements.

Animals↗