Search PubMed⌕ Search

Biomedical subjects

M Dumont

Publications and source records attributed to M Dumont.

At least 127 records · Page 7Linked to original sources
PubMed1991

Acute infusions of bile salts increase biliary excretion of iron in iron-loaded rats.

The mechanisms of biliary excretion of iron are not well known. The aim of this study was to examine the effect of choleresis induced by several agents on biliary iron excretion in iron-loaded rats. Iron overload was obtained with a diet supplemented by 3% iron carbonyl during a 6-week period. Bile was collected with an external bile fistula. Biliary iron concentration was measured by atomic absorption spectrophotometry, and hepatic iron concentration was measured by a chemical method. Compared with controls, iron overload resulted in a 14-fold increase in hepatic iron concentration but only a 3.9-fold increase in biliary iron output. In iron-loaded rats, taurocholate infusion caused a 1.8-fold significant increase in biliary iron output. Dehydrocholate, given at the same dose, induced a significant but less pronounced (1.3-fold) increase in biliary iron output in spite of a higher bile flow. Taurochenodeoxycholate, tauroursodeoxycholate, and tauro-7-ketolithocholate induced an increase in biliary iron output similar to that observed with taurocholate. The canalicular bile salt-independent choleretic dihydroxydibutyl ether caused a significant but less pronounced increase in biliary iron output (1.4-fold). These results confirm that in iron-loaded rats biliary iron excretion is increased much less than hepatic iron concentration. They show that in iron loaded rats (a) bile salts can increase biliary iron secretion, and (b) this increase is related in part to choleresis and in part to bile salts themselves. This increase may be related to an interaction of iron with bile salt monomers and/or micelles.

Animals↗
PubMed1991

Circadian regulation of the biosynthesis of cardiac Met-enkephalin and precursors in normotensive and spontaneously hypertensive rats.

Preproenkephalin A mRNA (ppEnk mRNA) and immunoreactive Met-enkephalin (ir-Met-Enk) were measured in the heart of 4, 8 and 16 week-old normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. WKY rats displayed a small decrease in their cardiac concentration of free (1.3 to 1.0 pmol/g) and cryptic (enzyme processed: 5.3 to 3.7 pmol/g) ir-Met-Enk with aging while the abundance of ppEnk mRNA increased by 3.2 fold between 4 and 16 week-old animals. Similar decreases in free (1.5 to 1.0 pmol/g) and cryptic (5.6 to 4.2 pmol/g) ir-Met-Enk levels were observed in SHR with aging but the rise in the level of ppEnk mRNA was much more pronounced reaching at 16 week-old levels of 7.3 times higher than at 4 week-old and 4.3 times higher than in age-matched WKY. The lack of correlation between the concentration of free and cryptic ir-Met-Enk and the abundance of ppEnk mRNA led us to measure the level of peptides in the heart of 16 week-old animals sacrificed at 4 hr intervals over a 24 hr period. SHR rats displayed circadian variations in their heart content of free and cryptic ir-Met-Enk and increased levels (1.6 fold) of cryptic peptide as compared with WKY at the beginnings of light (6 hr) and dark (18 and 22 hr) periods, suggesting the occurrence of cyclic and transitory upregulation of cDNA transcription and/or derepression of mRNA translation.

Animals↗
PubMed1991

Structure of the human type II 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) gene: adrenal and gonadal specificity.

While classical 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase deficiency (3 beta-HSD) is a known cause of adrenal hyperplasia resulting in ambiguous genitalia and adrenal insufficiency at birth, nonclassical or late-onset 3 beta-HSD deficiency is found in an important proportion of women with androgen excess. We have previously isolated and sequenced the cDNA and gene for the human type I 3 beta-HSD, which represents the main species expressed in the placenta and skin. Recently, we isolated, sequenced, and expressed the functional cDNA encoding type II 3 beta-HSD, which is the predominant 3 beta-HSD expressed in human adrenals and gonads. The present study describes the isolation and complete sequence of the corresponding type II 3 beta-HSD gene, which is the form most likely responsible for human 3 beta-HSD deficiency. The structural gene contains four exons of 57, 231, 165, and 1,214 bp, respectively, separated by introns of 128, 3,383, and 2,162 bp. DNA sequence analysis of the 5'-flanking region reveals the existence of two putative TATA boxes situated 28 and 140 nucleotides upstream from the transcription start site whereas two putative CAAT boxes are located 57 and 38 nucleotides upstream from the TATA boxes, respectively. A restriction fragment length pattern specific for each gene has been characterized. The present findings should provide the tools required for detailed analysis of the molecular basis of 3 beta-HSD deficiency as well as of normal sex steroid biosynthesis.

3-Hydroxysteroid Dehydrogenases↗
PubMed1991

Expression of the preproenkephalin A gene in the heart of cardiomyopathic hamsters.

The expression of the preproenkephalin A gene (Enk gene), which codes for the precursor of enkephalins, was investigated in the heart of hamsters with a hereditary cardiomyopathy at four different stages of the disease: the prenecrotic stage (30 days), the necrotic stage (60 days), the hypertrophic stage (120 days), and the final stage (200 days). In control atria and ventricles, the relative abundance of the Enk mRNA, as assessed by Northern blot analysis, did not change upon ageing. In the ventricles of cardiomyopathic hamsters, however, it increased about two- to three-fold at the necrotic stage, but was unaltered at the other time points studied; whereas in the atria, it progressively decreased to reach about half that of control hamsters at the final stage. Enkephalin levels, as measured by radioimmunoassay, decreased at 60 days in both the atria and ventricles of control hamsters, and also in the atria of cardiomyopathic hamsters, and remained stable thereafter, corresponding to one-third to one-half of those at 30 days. However, in the ventricles of cardiomyopathic hamsters, the peptide level decreased only slightly, the consequence being that at 60, 120, and 200 days, it was about two- to three-fold that of control hamsters. The lack of correlation between peptide levels and the relative abundance of the Enk mRNA suggests that translational and (or) post-translational mechanisms are important in the control of the expression of the Enk gene in the heart of hamsters.

Aging↗
PubMed1991

Structure and expression of a new complementary DNA encoding the almost exclusive 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase in human adrenals and gonads.

The 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta HSD) enzyme catalyzes the oxidation and isomerization of delta 5-3 beta-hydroxysteroid precursors into delta 4-ketosteroids, thus leading to the formation of all classes of steroid hormones. In addition, 3 beta HSD catalyzes the interconversion of 3 beta-hydroxy- and 3-keto-5 alpha-androstane steroids. Clinical observations in patients with 3 beta HSD deficiency as well as our recent data obtained by Southern blot analysis using a human placental 3 beta HSD cDNA (type I) as probe suggested the existence of multiple related 3 beta HSD isoenzymes. We now report the isolation and characterization of a second type of cDNA clone (arbitrarily designated type II) encoding 3 beta HSD after screening of a human adrenal lambda gt22A library. The nucleotide sequence of 1676 basepairs of human 3 beta HSD type II cDNA predicts a protein of 371 amino acids with a calculated molecular mass of 41,921 daltons, which displays 93.5% and 96.2% homology with human placental type I and rhesus macaque ovary 3 beta HSD deduced proteins, respectively. To characterize and compare the kinetic properties of the two isoenzymes, plasmids derived from pCMV and containing type I or type II 3 beta HSD full-length cDNA inserts were transiently expressed in HeLa human cervical carcinoma cells. In vitro incubation with NAD+ and 3H-labeled pregnenolone or dehydroepiandrosterone shows that the type I protein possesses a 3 beta HSD/delta 5-delta 4 isomerase activity higher than type II, with respective Km values of 0.24 vs. 1.2 microM for pregnenolone and 0.18 vs. 1.6 microM for dihydroepiandrosterone, while the specific activity of both types is equivalent. Moreover, incubation in the presence of NADH of homogenates from cells transfected with type I or type II 3 beta HSD indicates that dihydrotestosterone is converted into 5 alpha-androstane-3 beta, 17 beta-diol, with Km values of 0.26 and 2.7 microM, respectively. Ribonuclease protection assay using type I- and type II-specific cRNA probes revealed that type II transcripts are the almost exclusive 3 beta HSD mRNA species in the human adrenal gland, ovary, and testis, while type I transcripts correspond to the almost exclusive 3 beta HSD mRNA species in the placenta and skin and represent the predominantly expressed species in mammary gland tissue. The present data show for the first time that adrenals and gonads express a type of 3 beta HSD isoenzyme that is distinct from the type expressed in the placenta.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Glands↗
PubMed1991

Bone mass in endometriosis patients treated with GnRH agonist implant or danazol.

Before treatment, the trabecular bone mineral content of the lumbar spine and femoral neck was not significantly different between endometriosis patients and age-matched controls (N = 26). In 17 subjects treated with a monthly goserelin implant, serum estradiol (E2) levels were suppressed into the menopausal range. Mean decreases from pre-treatment values in the lumbar spine and femoral neck were -5.7 and -3.8% at 3 months and -8.2 and -7.7% at 6 months of treatment, respectively; lumbar spine values were significantly different (P less than .05) from those of the control group, whose values changed little during the same period. Significant increases over baseline values were also observed in urinary calcium-creatinine ratio and serum alkaline phosphatase. In nine danazol-treated subjects, serum E2 levels were generally within the early follicular-phase range. There were no significant changes in bone assessments. Normal menses returned within 2 months after cessation of either medication. Six months after goserelin treatment, the lumbar spine and femoral neck bone mineral content was still reduced but to values not significantly different from the pre-treatment and control values; urinary calcium-creatinine ratio was decreased, whereas serum alkaline phosphatase was still elevated. The rapid and deep suppression of ovarian steroidogenesis by a monthly goserelin implant induced significant bone loss compared with the control and danazol groups. This loss was not reversed completely 6 months after cessation of treatment, but bone densities at that time were not different from those of controls. Studies of larger numbers of patients followed for longer periods will be required to resolve the question of complete reversibility.

Adult↗
PubMed1990

Characterization of human 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase gene and its expression in mammalian cells.

Three beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase (3 beta-HSD) catalyze the oxidative conversion of delta 5-3 beta-hydroxysteroids to the delta 4-3-keto configuration and is therefore essential for the biosynthesis of all classes of hormonal steroids, namely progesterone, glucocorticoids, mineralocorticoids, androgens, and estrogens. Using human 3 beta-HSD cDNA as probe, a human 3 beta-HSD gene was isolated from a lambda-EMBL3 library of leucocyte genomic DNA. A fragment of 3 beta-HSD genomic DNA was also obtained by amplification of genomic DNA using the polymerase chain reaction. The 3 beta-HSD gene contains a 5'-untranslated exon of 53 base pairs (bp) and three successive translated exons of 232, 165, and 1218 bp, respectively, separated by introns of 129, 3883, and 2162 bp. The transcription start site is situated 267 nucleotides upstream from the ATG initiating codon. DNA sequence analysis of the 5'-flanking region reveals the existence of a putative TATA box (ATAAA) situated 28 nucleotides upstream from the transcription start site while a putative CAAT binding sequence is located 57 nucleotides upstream from the TATA box. Expression of a cDNA insert containing the coding region of 3 beta-HSD in nonsteroidogenic cells shows that the gene encodes a single 42-kDa protein containing both 3 beta-hydroxysteroid dehydrogenase and delta 5-delta 4-isomerase activities. Moreover, all natural steroid substrates tested are transformed with comparable efficiency by the enzyme. In addition to its importance for studies of the regulation of expression of 3 beta-HSD in gonadal as well as peripheral tissues, knowledge of the structure of the human 3 beta-HSD gene should permit investigation of the molecular defects responsible for 3 beta-HSD deficiency, the second most common cause of adrenal hyperplasia in children.

3-Hydroxysteroid Dehydrogenases↗
PubMed1990

Opposite effects of estrogen and the progestin R5020 on cell proliferation and GCDFP-15 expression in ZR-75-1 human breast cancer cells.

We have recently demonstrated that physiological concentrations of androgens caused a marked inhibition of basal and 17 beta-estradiol (E2)-induced cell growth in ZR-75-1 human breast cancer cells. Moreover, these steroids exert effects on GCDFP-15 (gross cystic disease fluid protein-15) expression that are opposite to their above-indicated actions on cell proliferation. The synthetic progestin R5020 (17.21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione), on the other hand, causes a potent inhibition of E2-induced ZR-75-1 cell growth. In order to further characterize the hormonal regulation of GCDFP-15 expression and to better understand the antagonism between progestin and estrogen action in breast cancer cells, we have studied the effect of R5020 on both GCDFP-15 expression and cell growth in ZR-75-1 cells. After a 10-day incubation, the 4-fold stimulatory effect of 1 nM E2 on cell growth was 60% decreased by maximal effective concentrations of R5020 (greater than 1 nM) while, in the absence of E2, R5020 had no effect. The mitogenic action of E2 was accompanied by a 75% inhibition of GCDFP-15 secretion while nanomolar concentrations of R5020 induced 1.4- and 5.2-fold increases in GCDFP-15 secretion in control and E2-treated ZR-75-1 cells, respectively. While E2 caused a marked inhibition of GCDFP-15 mRNA levels, R5020 induced a maximal 2- to 3-fold increase (above control) in GCDFP-15 mRNA accumulation in cells simultaneously incubated with E2.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoproteins↗
PubMed1990

Alterations of heart dynorphin-A in the development of spontaneously hypertensive rats.

In order to investigate the pathophysiological role of heart dynorphin-A (Dyn-A) in genetic hypertension, immunoreactive (ir)-Dyn-A was measured in heart extracts of spontaneously hypertensive rats (SHR) and compared with that of age matched Wistar (WR) and Wistar Kyoto (WKY) rats. Heart ir-Dyn-A contents in 8 week-old WK (84 fmol/g tissue) were not significantly different from those of age matched WKY (109 fmol/g tissue). In control WKY, the levels of ir-Dyn-A did not significantly vary with the age (from 109 to 117 fmol/g) except in 16 week-old animals which displayed a significant increase (238 fmol/g tissue) compared to younger animals. In SHR, the heart content of ir-Dyn-A displayed a 6.5 fold increase at 8 weeks compared to age matched WKY. Older SHR showed a return of their heart ir-Dyn-A content to control (12 week-old) or below control values (16 week-old; 121 compared with 238 fmol/g tissue in WKY). Heart ir-Dyn-A in WKY and SHR eluted as a single peak on mu-Bondapak HPLC, corresponding with the retention time of synthetic Dyn-A. A local function for cardiac ir-Dyn-A is suggested by the presence in heart membrane preparations of a high affinity binding site for the kappa selective opioid ligand, [3H]U-69593, with KD of 6.4 (WKY) and 8.5 (SHR) nM and Bmax of 3.7 (WKY) and 3.6 (SHR) pmol/g protein. The alterations in the levels of cardiac ir-Dyn-A during the development of hypertension in SHR were analyzed in regard with the reported effects of Dyn-related peptides on heart natriuretic and sympathetic functions.

Animals↗
PubMed1990

Influence of backward perfusion on ursodeoxycholate-induced choleresis in isolated in situ rat liver.

Ursodeoxycholate-induced bicarbonate-rich hypercholeresis was studied in isolated in situ forward- or backward-perfused rat livers. Both spontaneous bile flow and bile acid secretion were similar regardless of the direction of the perfusion. The choleretic effect of tauroursodeoxycholate infusion (400 nmol.min-1.100 g-1 body weight) was not significantly different in forward- or backward-perfused livers either. Ursodeoxycholate infusions at low rate (800 nmol.min-1.100 g-1 body weight) induced similar bile flow, bile acid output and bicarbonate output in both forward- and backward-perfused livers. Net ursodeoxycholate uptake, measured as [14C]ursodeoxycholate uptake over the bile acid infusion period (30 min), was not significantly different during forward- or backward-perfusion (4.8 and 5.1 mumol/g liver, respectively); i.e., approx. 67% of infused dose (approximately 7.5 mumol/g liver per 30 min). A 2-fold increase in the dose of ursodeoxycholate infusion (1600 nmol.min-1.100 g-1 b.wt.) induced additional enhancement in both bile flow and bicarbonate biliary secretion, but not in bile acid uptake or output, in forward-perfused livers. Moreover, infusion of the same dose of ursodeoxycholate to backward-perfused livers had a significantly lower choleretic effect (-29%, p less than 0.001) even though ursodeoxycholate uptake and biliary output were similar regardless of perfusion direction. Net ursodeoxycholate uptake, was only 2.4 mumol/g liver; i.e., approx. 16% of infused dose (approximately 15 mumol/g liver per 30 min). These findings indicate that a process related with the hepatic microanatomy may be involved in the hypercholeretic response to ursodeoxycholate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Interactions between estrogens, androgens, progestins, and glucocorticoids in ZR-75-1 human breast cancer cells.

The human breast cancer cell line ZR-75-1 possesses androgen, estrogen, progesterone, and glucocorticoid receptors, thus offering a good model to study the specific role of each class of steroids in the control of breast cancer growth. Although the stimulatory action of classical estrogens (E2 and estrone) is well known, we have found a potent mitogenic effect of the adrenal estrogen androst-5-ene-3 beta,17 beta-diol (delta 5-diol) at concentrations within the range of those found in the serum of adult women, thus suggesting that delta 5-diol might be the most important estrogen in women. Androgens, on the other hand, exert a potent inhibitory effect on basal ZR-75-1 cell growth and completely reverse the stimulatory effect of estrogens on the same parameter. The antiproliferative effect of androgens was completely prevented by the antiandrogen OH-FLU, thus suggesting an action mediated by the androgen receptor. Part of the effect of androgens can be explained by the marked inhibition of estrogen receptor binding and mRNA levels by androgens. The antiproliferative effect of androgens is additive to that exerted by antiestrogens. Progestins, on the other hand, exert a specific antiproliferative effect in the presence of estrogens, the effect of progestins being antagonized by the stimulatory action of insulin on cell growth. Medroxyprogesterone acetate (MPA), a compound frequently used in the treatment of breast cancer in women, exerts its main inhibitory action through an androgen receptor-mediated action, whereas its glucocorticoid-like activity could play an additional role at high concentrations. All four classes of steroids are present, to various extents, as lipophilic esters of long-chain fatty acids. It is of interest to mention that all steroids that inhibit ZR-75-1 breast cancer cell growth (androgens, progestins, and glucocorticoids) stimulate the secretion and mRNA levels of gross cystic disease fluid protein-15 (GCDFP-15), whereas estrogens have the opposite effects, thus suggesting that GCDFP-15 could well be a good marker for monitoring the response to androgens, progestins, and antiestrogens during the course of breast cancer therapy.

Androgens↗
PubMed1990

Effect of acid-base balance on biliary bicarbonate secretion in the isolated perfused guinea pig liver.

Secretin-induced choleresis is of ductal origin and involves bicarbonate transport. Its mechanism is unknown. To determine the relative effects of systemic pH, PCO2, and bicarbonate concentration on secretin-stimulated bicarbonate transport, states of acute metabolic and respiratory acidosis or alkalosis were created in isolated perfused guinea pig livers with or without secretin infusion. During spontaneous secretion conditions, biliary bicarbonate secretion was not correlated with perfusate pH (7.19-7.62) or perfusate PCO2 (23.9-59.7) but was significantly correlated with perfusate bicarbonate concentration (17.5-37.9 mM). Under secretion infusion (25 mU/min), bile flow and biliary bicarbonate concentration increased significantly (109 and 51%, respectively). Biliary bicarbonate secretion was not correlated with perfusate pH (7.19-7.60) but was significantly correlated both with perfusate bicarbonate concentration (14.6-36.8 mM) and PCO2 (25.8-54.3 mmHg). Spontaneous and secretin-induced bile flow were correlated with biliary bicarbonate concentration. The correlation between biliary bicarbonate secretion and PCO2 during secretin-induced choleresis supports the hypothesis that secretin-induced biliary bicarbonate secretion could, at least in part, involve a transport of H+ (or OH-) rather than HCO3- itself and that intracellular pH could play a role in the regulation of this secretion. Amiloride (5 X 10(-4) M) did not influence secretin-induced biliary bicarbonate secretion. This result suggests that the Na(+)-H+ exchange is not involved in bicarbonate secretion by ductular cells.

Acid-Base Equilibrium↗