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Biomedical subjects

A Chatelain

Publications and source records attributed to A Chatelain.

At least 19 recordsLinked to original sources
PubMed2003

Effect of natriuretic peptides on in vitro stimulated adrenocorticotropic hormone release and pro-opiomelanocortin mRNA expression by the fetal rat pituitary gland in late gestation.

OBJECTIVE AND METHODS: We investigated the effects of individual natriuretic peptides (atrial natriuretic peptide, ANP; brain natriuretic peptide, BNP, and C-type natriuretic peptide, CNP) on rat corticotropin-releasing factor stimulated adrenocorticotropic hormone (ACTH) secretion by the pituitary gland of 21-day-old rat fetuses in vitro and on pro-opiomelanocortin gene expression using in situ hybridization. RESULTS: Graded concentrations of ANP, BNP, or CNP (10(-10), 10(-9), and 10(-8) mol/l) induced a log dose dependent inhibition of ACTH secretion induced by rat corticotropin-releasing factor (10(-10) mol/l). These natriuretic peptides showed equipotent effects on a molar basis. Moreover, ANP, BNP, or CNP at 10(-10) mol/l reduced significantly the pituitary pro-opiomelanocortin mRNA expression. In addition, the immunoreactive ANP, BNP, and CNP cells were localized in the anterior lobe, but not in the intermediate lobe of the fetal pituitary gland. CONCLUSIONS: These data suggest that the fetal pituitary gland may be both a source and a target for natriuretic peptides that might control ACTH synthesis and release via an endocrine and/or paracrine mechanism. The natriuretic peptides could participate, as well as glucocorticoids, in the control of the corticotropin-stimulating activity of the fetal rat in late gestation.

Adrenocorticotropic Hormone↗
PubMed2000

Atrial natriuretic peptide and aldosterone secretions, and atrial natriuretic peptide-binding sites in kidneys and adrenal glands of pregnant and fetal rats in late gestation in response to a high-salt diet.

OBJECTIVE: This study aimed at determining, in the term pregnant rat, whether maternal and fetal plasma atrial natriuretic peptide (ANP) concentrations were modified in response to an oral sodium load, and to investigate whether any changes in plasma concentrations were able to modify the density and affinity of the different ANP-binding site subtypes in maternal and fetal kidneys and adrenal glands. METHODS: Pregnant rats kept in metabolic cages were divided into two groups. The normal sodium diet group had free access to rat chow and tap water whereas the high sodium diet group received 1% NaCl as drinking water for 10 consecutive days from day 11 to day 21 of gestation with free access to standard rat chow. Pregnant rats from both groups were killed by decapitation on day 21 of gestation. The plasma ANP and aldosterone concentrations were determined by RIA. The density and affinity of ANP receptors were determined in the maternal and fetal adrenal glands and kidneys. RESULTS: In the pregnant rats on the high-salt diet, the sodium and water intakes, as well as the urine volume and sodium excretion, were significantly higher than in the control group. After 10 days of high-salt intake, water and sodium retentions were not significantly different in the two groups, indicating that the pregnant rats were able to excrete excess salt. The high sodium intake did not change the body weight of the pregnant rats but did increase the body weight of the fetal rats. Maternal and fetal hematocrits remained unchanged in both groups, the high sodium intake did not modify plasma sodium concentration in the maternal rats but increased that of the fetuses, indicating an accumulation of sodium in the fetal rats. The dietary sodium intake did not change the plasma ANP concentrations but significantly decreased the plasma aldosterone concentrations in both the maternal and fetal rats. In response to the high-salt diet, the density and affinity of total ANP, ANPb and ANPc receptors were not altered in the maternal isolated renal glomeruli or the adrenal zona glomerulosa membranes or the fetal adrenal gland and kidney membrane preparations. CONCLUSION: These results suggest that ANP is not involved in the regulation of water and electrolyte balance in maternal and fetal rats during salt-loaded intake.

Adrenal Glands↗
PubMed1999

Effects of water deprivation on atrial natriuretic peptide secretion and density of binding sites in adrenal glands and kidneys of maternal and fetal rats in late gestation.

The effects of water deprivation for 3 days were studied in pregnant rats and their fetuses on day 21 of gestation. Maternal water deprivation induced a significant decrease of the body weight in both maternal and fetal rats. This weight loss was accompanied by significant increases in plasma osmolality and haematocrit in both maternal and fetal rats. Similarly, dehydration significantly decreased plasma atrial natriuretic peptide (ANP) concentrations and increased plasma aldosterone concentrations in maternal and fetal rats. Water-deprived maternal rats presented a significant increase in total ANP receptor density in isolated renal glomeruli and adrenal zona glomerulosa membranes. This increase was due to a significant increase in ANPc receptor density in both renal glomeruli and adrenal zona glomerulosa. The densities of total ANP, ANPb and ANPc receptors in fetal kidneys and adrenal glands were not affected by maternal dehydration. These results suggest that the dehydrated maternal rat is able to up-regulate the number of its ANP receptors in its kidneys and adrenal glands, in response to a decrease in plasma ANP concentrations. In contrast, the fetal rat does not seem to be able to regulate its own ANP receptors in response to maternal dehydration, in spite of a decrease in plasma ANP concentrations.

Adrenal Glands↗
PubMed1996

Nanocapillarity and Chemistry in Carbon Nanotubes

Open carbon nanotubes were filled with molten silver nitrate by capillary forces. Only those tubes with inner diameters of 4 nanometers or more were filled, suggesting a capillarity size dependence as a result of the lowering of the nanotube-salt interface energy with increasing curvature of the nanotube walls. Nanotube cavities should also be less chemically reactive than graphite and may serve as nanosize test tubes. This property has been illustrated by monitoring the decomposition of silver nitrate within nanotubes in situ in an electron microscope, which produced chains of silver nanobeads separated by high-pressure gas pockets.

Journal Article↗
PubMed1995

Molecular forms of atrial natriuretic peptide in atria and plasma from fetal and adult female rats.

Molecular forms of atrial natriuretic peptide (ANP) were determined by chromatography on Sephadex G50 fine coupled with a radioimmunoassay for rANP(1-28) in left and right atrial extracts and acidified plasmas from 17-, 19- and 21-day-old fetuses and adult female rats. Chromatographic analyses revealed two immunoreactive peaks of rANP with an apparent molecular weight of about 25 and 12 kD, respectively, in all atrial extracts from fetal and adult rats. Only one immunoreactive peak of rANP with an apparent molecular weight of about 3 kD was detected in all fetal plasmas. The 25- and 12-kD ANP molecular forms isolated from fetal atrial tissue and incubated with thrombin for 30 min at 37 degrees C were converted to ANP material with a molecular weight of about 3 kD. These results suggest that the two high molecular weight forms stored in fetal atrial tissue should be precursors of circulating rANP molecules, and the rat fetus should possess the same posttranslational processing of the precursor molecule as the adult rat as early as day 17 of gestation.

Aging↗
PubMed1994

Characteristics and developmental changes of ANP-binding sites in rat adrenal glands during the perinatal period.

The binding of rANP(1-28) to receptors was studied on crude adrenal membranes from fetal rats between day 17 of gestation and term and also neonatal rats between weeks 1 and 4. The binding assays were carried out using 125I-rANP(1-28) as radioligand incubated with membrane preparations (2 mg/ml) for 90 min at 22 degrees C. The binding was specific, saturable and reversible. The Scatchard analysis of the binding data revealed a single class of binding sites of high affinity (kd approximately 10(-10) mol/l) which did not change significantly at all stages of development studied. The binding sites presented a higher affinity for ANP analogues which contained the C-terminal phenylalanine arginine residue. The number of ANP receptors expressed per adrenal increased regularly in fetal and neonatal rats and the perinatal evolution of these concentrations of ANP receptors was related to the increase in the size of the adrenals. When the concentrations of ANP receptors was expressed per microgram DNA, the concentrations of ANP receptors were higher in neonatal rats than in fetal rats and reflected the number of receptors per cell. These results suggest that these binding sites mediate the biological actions of ANF in the adrenal gland during the perinatal period.

Adrenal Glands↗
PubMed1994

Effect of blood volume expansion on basal plasma atrial natriuretic factor and adrenocorticotropic hormone secretions in the fetal rat at term.

The effect of a blood volume expansion (1-1.5% of body weight) on atrial natriuretic factor (ANF) and adrenocorticotropic hormone (ACTH) secretions were investigated in 21-day-old rat fetuses injected intravenously through the umbilical vein with 50 microliters of isotonic saline. Basal ANF and ACTH concentrations were determined in the plasma with specific radioimmunoassays over a 30-min observation period. The basal plasma ANF concentration increased rapidly 1 min after blood volume expansion and then decreased to the control value 5 min later. The basal plasma ACTH concentration decreased during the first 10 min after injection and then increased to the control value 30 min after intravascular volume load. The results suggest that the fetal rat in late gestation is able to respond to blood volume expansion by increasing ANF secretion.

Adrenocorticotropic Hormone↗
PubMed1994

Effects of corticotropin-releasing factor, arginine vasopressin and oxytocin on the polymorphism of plasma adrenocorticotropic hormone in the rat fetus in late pregnancy.

The effects of rat corticotropin-releasing factor (rCRF, 1.25 pmol/50 microliters/fetus), arginine vasopressin (AVP, 5 pmol/50 microliters/fetus) and oxytocin (OT, 12.5 pmol/50 microliters/fetus) alone or in association were investigated in 21-day-old rat fetuses injected intravenously through the umbilical vein. Blood samples were collected 15 and 30 min after injection for the determination of corticosterone concentration and the different plasma molecular adrenocorticotropic hormone (ACTH) forms isolated by chromatography on Sephadex G50 fine. All the plasma samples chromatographed 15 and 30 min after injection of the different peptides showed 3 different molecular ACTH forms: big ACTH (> 20,000 molecular weight), intermediate ACTH (= 13,000) and little ACTH (= 4,500). The injection of rCRF or AVP alone and rCRF in association with AVP or OT increased the concentrations of big ACTH 15 min and little ACTH 30 min after injection. The injection of OT alone or in association with AVP did not change the concentration of the 3 molecular ACTH forms 15 and 30 min after injection. The rise of big ACTH 15 min after injection was not associated with a significant increase in plasma corticosterone concentration, whereas the increase in little ACTH 30 min later enhanced plasma corticosterone concentration. Our results suggest that rCRF or AVP alone and rCRF in association with AVP or OT injected intravenously in the fetal rat produced a selective release of the molecular ACTH forms and the increase in the plasma corticosterone concentration occurred when the proportion of little ACTH which is the predominant ACTH form in the fetal rat was enhanced.

Adrenocorticotropic Hormone↗
PubMed1994

Effects of rat corticotrophin-releasing factor, arginine vasopressin and oxytocin on the secretions of adrenocorticotrophic hormone and corticosterone in the fetal rat in late gestation: in vivo and in vitro studies.

The effects of rat corticotrophin-releasing factor (rCRF), arginine vasopressin (AVP) and oxytocin (OT) were investigated in vivo in 21-day-old rat fetuses injected through the umbilical vein and in vitro on perifused anterior pituitary glands from 21-day-old rat fetuses. In vivo, rCRF (1.25 pmol.50 microliter-1.fetus-1), AVP (5 pmol.50 microliter-1.fetus-1) alone and rCRF in association with AVP or oxytocin (12.5 pmol.50 microliter-1.fetus-1) increased plasma adrenocorticotrophic hormone (ACTH) and corticosterone levels only 30 min after the start of injection. During the first 10 min of the sampling period, the injection of these peptides alone or in combination and the injection of saline decreased the plasma ACTH concentration, which was lower than that of uninjected fetuses, but had no effect on the plasma corticosterone concentration. In vitro, the release of ACTH by perifused anterior pituitary glands was increased strongly by rCRF (4 pmol/0.5 ml) but only slightly by AVP (92 pmol/0.5 ml) and oxytocin (198 pmol/0.5 ml). Arginine vasopressin and oxytoxin potentiated the release of ACTH stimulated by rCRF in vitro but not in vivo. Our results suggest that rCRF is the major peptide that controls ACTH secretion in the fetal rat at term. In conclusion, the rise of the ACTH level observed only 30 min after injection of rCRF or AVP suggests the existence of a factor able to inhibit the ACTH response after injection of these peptides. This factor might be elicited by the blood volume expansion.

Adrenocorticotropic Hormone↗
PubMed1993

ACTH secretion from isolated hypophysial anterior lobes of male and female newborn rats: effects of corticotrophin-releasing factor, arginine vasopressin and oxytocin alone or in combination.

ACTH release by the anterior pituitary lobes of 8-day-old newborn rats (males and females) in the presence of rat corticotrophin-releasing factor (rCRF), arginine vasopressin (AVP) and oxytocin, given alone or in association, was measured in vitro. Rat CRF and AVP induced a dose-dependent release of ACTH in both sexes, while oxytocin was unable to stimulate ACTH secretion except at the highest dose tested. No sex-related difference was noted for any of the responses. Oxytocin (1 nmol/l) potentiated the response to rCRF (0.20 nmol/l) by the anterior pituitary lobes of females but not by those of males. This oxytocin potentiation was abolished when female newborn rats were injected at birth with testosterone (1 mg). AVP (1 nmol/l) alone stimulated ACTH release from the anterior pituitary lobes of the newborn rats of both sexes and markedly potentiated the ACTH response to rCRF. Although no difference between the sexes was noted for basal levels of AVP and oxytocin in the hypothalamus, the neurointermediate lobe and the peripheral plasma, the present data on the sex-related effect of oxytocin on the newborn adenohypophysis could, in part, explain why ACTH release in response to ether stress was previously reported to be more lasting in females than in males on day 8 postpartum.

Adrenocorticotropic Hormone↗
PubMed1990

Development of adenylate cyclase activity in rat adrenal glands during the perinatal period.

Adenylate cyclase activity was studied in crude adrenal membranes from fetal and newborn rats. Basal adenylate cyclase activity was higher in fetal than in newborn rats. ACTH(1-24) (1 mumol/l), guanosine (beta,gamma-imido diphosphate) (Gpp(NH)p) (10 mumols/l) and forskolin (100 mumols/l) stimulated the activity of the enzyme at all stages studied. The sensitivity of the enzyme to ACTH was maximal on days 17 and 19 of gestation. When Gpp(NH)p was added to ACTH(1-24), the response was significantly higher than that induced by Gpp(NH)p alone. Forskolin and Gpp(NH)p alone increased the adenylate cyclase activity and the sensitivity of the enzyme to these compounds was higher in newborn rats than in fetuses. Treatment of 21-day-old rat fetuses with ACTH increased the response of adenylate cyclase to Gpp(NH)p alone or to forskolin whereas treatment with dexamethasone did not modify the response of the enzyme to either Gpp(NH)p alone or forskolin. Our results show that the change in the responsiveness of adenylate cyclase takes place immediately after birth during the first week and ACTH is able to induce a maturation of the fetal adrenal adenylate cyclase system.

Adenylyl Cyclases↗
PubMed1989

Ontogeny of ACTH(1-24) receptors in rat adrenal glands during the perinatal period.

Binding of ACTH to receptors was studied on crude adrenal membranes from fetal and newborn rats. 125I-Labelled ACTH(1-24) was used as the radioligand, the steroidogenic potency of which was 100-fold lower than that of unlabelled ACTH(1-24). Binding was specific, rapidly equilibrated and temperature dependent. Scatchard analysis of the binding data revealed a single class of binding sites with a dissociation constant of about 100 nmol/l at all stages of development studied. The concentration of ACTH receptors expressed per mg membrane proteins decreased in fetuses between days 17 and 21 of gestation and remained stable in newborn rats from weeks 1 to 4. The number of ACTH receptors expressed per adrenal increased regularly in fetal and newborn rats. The perinatal evolution of these concentrations of ACTH receptors is related to the increase in the size of the adrenals and the changes in cytoplasmic structures of the adrenocortical cells. When the number of ACTH-binding sites was expressed per microgram DNA, maximum values occurred in fetuses on day 19 of gestation, and minimum values in newborn rats, 1 week after birth. There was an excellent correlation between the plasma levels of immunoreactive ACTH and corticosterone and the number of ACTH receptors per microgram DNA during the perinatal period. Other results suggest that ACTH is able to up-regulate the number of its own receptors.

Adrenal Glands↗
PubMed1988

Corticotrophin-releasing factor immunoreactivity in the hypothalamus of the rat during the perinatal period.

Corticotrophin-releasing factor-41 (CRF-41) immunoreactivity has been measured in hypothalamic extracts of fetal (on days 17, 19 and 21 of gestation), neonatal (1, 2, 3 and 4 weeks of age) and adult rats with a specific radioimmunoassay developed for synthetic rat CRF-41. The hypothalamic content (fmol) and concentration (fmol/mg protein) of immunoreactive CRF-41 gradually increased with age. Chromatography of hypothalamic extracts on Sephadex G-50 Fine showed one single peak of immunoreactive CRF-41 which co-eluted with synthetic rat CRF-41. The retention time of hypothalamic CRF-41 during high-performance liquid chromatography was identical to that of synthetic rat CRF-41 at all stages investigated. These results are consistent with the development of neurones containing CRF-41-like molecules in both the hypothalamus and the median eminence of the fetus, as well as with the hypothalamic control of the cortico-stimulating function of the pituitary gland as early as day 19 of gestation.

Aging↗
PubMed1987

Effects of chronic maternal dexamethasone treatment on the hormones of the hypothalamo-pituitary-adrenal axis in the rat fetus.

Different hormones of the hypothalamo-pituitary-adrenal axis (corticotropin-releasing factor, adrenocorticotropic hormone, corticosterone) were measured in brain pieces (stalk, median eminence, hypothalamus), hypophyses, adrenals and plasma of 21-day-old rat fetuses from mothers which were given either plain tap water or water containing dexamethasone acetate (10 micrograms/ml) from day 15 to 21 of gestation. Dexamethasone induced drastic reduction of body weight (-66% vs. controls), severe atrophy of the adrenals (-83%) and a sharp drop in their corticosterone content (-74%). Fetal plasma corticosterone levels were below the lower limit of detection of the competitive corticosteroid-binding globulin (CBG) radioassay (less than 0.01 microgram/ml). Both atrophy and severe reduction of the adrenal activity in fetuses from dexamethasone-treated females were in good correlation with a drastic decrease in plasma adrenocorticotropic hormone (ACTH) levels which were below the lower limit of detection of the radioimmunoassay (RIA) used (less than 10 pg/ml) and a significant reduction in pituitary ACTH content (-93%). The low corticostimulating activity of the fetal hypophyses was associated with a drop in both corticotropin-releasing factor (CRF) hypothalamic content (-57%) and concentration (-67%). The effects of dexamethasone on plasma and pituitary ACTH concentrations in 21-day-old fetuses were compared to those, previously reported, of encephalectomy and decapitation performed on day 16 of gestation. The reported data were consistent with the present results, suggesting both pituitary and hypothalamic sites for the in vivo inhibiting action of dexamethasone on the rat hypothalamic-pituitary-adrenal axis in late gestation.

Adrenocorticotropic Hormone↗
PubMed1987

The biological activity of different molecular forms of ACTH on corticosterone production by perifused foetal rat adrenal glands in vitro.

The responsiveness of perifused adrenal glands removed from rats at various stages of gestation to similar immunological quantities (2 ng) of 'big' approximately equal to 30,000 mol wt), 'intermediate' (congruent to 13,000 mol wt) and 'little' (approximately equal to 4500 mol wt) ACTH isolated by gel filtration chromatography from an acid extract of pituitary glands of 21 day-old rat foetuses was determined. This immunological quantity failed to induce a maximal response of the foetal adrenals. Corticosterone was determined in the effluent perifusion by a radiocompetition assay. On days 17 and 19 of gestation, intermediate and little ACTH had, on a weight basis, the same corticosteroidogenic activity, but on day 21 the little was more potent than the intermediate form. The corticosterone release by these two forms of ACTH was log-dose dependent. The biological activity of big ACTH was very low on day 17, slightly increased until day 21 but remained significantly lower than that of intermediate and little forms. Big ACTH added to little ACTH in the perifusion medium did not modify the corticosteroidogenic activity of little ACTH on days 17, 19 and 21 of gestation.

Adrenal Glands↗
PubMed1987

[Perinatal influence of sex hormones on the differential activation of corticotrope function during stress in the male and female].

The stress-induced activation of the corticostimulating function of the pituitary gland was noted to vary according to sex in both the adult and the newborn. The pituitary response in testosterone or estradiol-injected females at the time of birth was similar to that of intact males, in contrast, the castration of the males performed just before the postnatal surge of plasma testosterone was unable to modify at the 8th day, the male characteristic evolution in response to ether inhalation. Present data suggest--in the male, prenatal differentiation of the neuroendocrine pathways involved in the pattern of ACTH release in response to ether inhalation, probably in correlation with the peak of plasma testosterone on day 19 of gestation--in the female, the existence of androgen--sensitive structures in early postnatal life. An alpha stimulatory effect of norepinephrine on these neuroendocrine pathways was suggested. Present report also discuss--the catecholaminergic control of CRF X producing neurons--the sex dependent AVP and/or oxytocin (OT) release induced by a stress--the AVP and OT potentiation of CRF-induced ACTH release.

Adrenocorticotropic Hormone↗
PubMed1986

Effects of progesterone induced postmaturity on CBG and pituitary-adrenal activities in the rat foetus.

CBG and pituitary-adrenal activities were investigated in intact rat foetuses, in newborns spontaneously delivered by vaginal way and in postmature foetuses from mothers with delayed parturition caused by daily progesterone injection from day 20 of gestation. The postmature foetuses had lower body weights and higher adrenal weights on day 22, 23 and 24 of gestation than newborns of the same conceptional age. The corticosterone binding capacity of the plasma as well as the binding capacity of CBG for corticosterone decreased in intact foetuses for the last 3 days of gestation and stayed very low in pups from day 0 to day 8 postpartum. These parameters decreased more slowly in postmature foetuses; however, the differences between the latter and intact foetuses or newborns were not statistically significant. Similar evolution occurred in intact pregnant and suckling females as well as in females with prolonged gestation. The fall in CBG activity in normal rat pups and the subsequent rise in free steroids could explain a sharp decrease in plasma ACTH levels as well as the drop in adrenal and plasma corticosterone concentration. In foetuses with prolonged gestation, the same phenomenon did not occur. Stress conditions produced by maintaining growing foetuses in utero and the development of severe jaundice maintained high ACTH levels. In contrast, the fall in adrenal and plasma corticosterone concentrations in spite of the high level of circulating ACTH could be mainly due to the progesterone inhibition of the steroidogenic activity of the foetal adrenals.

Adrenocorticotropic Hormone↗