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Biomedical subjects

D Philibert

Publications and source records attributed to D Philibert.

At least 55 records · Page 3Linked to original sources
PubMed1986

Autoradiographic localization of glucocorticosteroid and progesterone binding sites in the human post-mortem brain.

The presence of glucocorticosteroid and progesterone binding sites in the human brain has been investigated with an in vitro autoradiographic approach using [3H]RU 38486. The present data revealed that the hippocampus, the entorhinal cortex, the subiculum, the fimbria and the amygdala showed a different pattern of [3H]RU 38486 labeling using various unlabeled steroids (RU 38486, RU 28362, cortisol, RU 27987 and dexamethasone). RU 38486 is the best competitor in all these structures. The hippocampus seems to possess mainly glucocorticosteroid binding sites whereas the entorhinal cortex and the subiculum reveal the presence of both glucocorticosteroid and progesterone binding sites. Furthermore, the amygdaloid complex and the fimbria show a high density of glucocorticosteroid binding sites.

Autopsy↗
PubMed1986

Corticosteroid receptors in rat hippocampal sections: effect of adrenalectomy and corticosterone replacement.

Rat brain sections, located at the hippocampal level, were used to study the effect of bilateral adrenalectomy, with or without corticosterone treatment, on the number and affinity of corticosteroid binding sites. Adrenalectomy induces an increase of corticosterone receptor binding sites whereas adrenalectomy followed by in vivo corticosterone treatment produces a 50% decrease of binding site number. Increases and decreases of binding site number were not associated with a significant modification of the affinity for corticosterone. The present data show that in vivo corticosterone modulates its own number of binding sites demonstrated by in vitro binding on brain sections, in a manner which is reminiscent of changes in cytosol receptors demonstrated by conventional biochemical methods. Thus, this in vitro method provides an alternative way to study the plasticity of hippocampal glucocorticoid receptors.

Adrenalectomy↗
PubMed1985

Mechanism of action of an antiprogesterone, RU486, in the rabbit endometrium. Effects of RU486 on the progesterone receptor and on the expression of the uteroglobin gene.

RU486 is a recently described antiprogesterone. In order to be able to understand its mechanism of action it is necessary to analyze its effect on a discrete gene product. We show here that the induction of uteroglobin mRNA by progesterone in the rabbit endometrium may be a suitable model for such studies since RU486 totally inhibits this effect without itself exerting any agonistic activity. Moreover, RU486, which does not bind to the estrogen receptor and is devoid of general antiestrogenic activity, partially inhibits the induction by estradiol of uteroglobin mRNA. Studies of the interaction between [3H]RU486 and the progesterone receptor have been undertaken with the aim of understanding the antagonistic effect of this compound. The binding to DNA-cellulose of heat-activated [3H]RU486-receptor complexes was slightly decreased (37%) when compared with that of the agonist [3H]R5020-receptor complexes (47%). Detailed analysis of this difference showed that it was due to both a decreased activation of complexes and to a diminished affinity of activated complexes towards DNA. The change in activation was shown by the fact that at high concentrations of DNA, where all activated complexes are bound, agonist-receptor complexes were bound to DNA in higher proportion than antagonist-receptor complexes. Moreover a difference was also observed when studying the binding of agonist-receptor and antagonist-receptor complexes to charged resins (phosphocellulose, DEAE-cellulose) which are known to discriminate between activated and non-activated complexes. Decreased affinity to DNA of antagonist-receptor complexes was shown by studying their binding at various concentrations of DNA, either in crude cytosol or after isolating a homogenous population of activated-receptor complexes by DNA-cellulose chromatography and by comparing the salt extraction from DNA-cellulose of agonist-receptor and antagonist-receptor complexes. Both effects (decreased activation and diminished affinity towards DNA) were relatively moderate and could account only for a small decrease in the agonistic activity of RU486. Thus, the fact that this compound is a complete antagonist without any agonistic activity can only be explained by a defect in some further step of hormone action as, for instance in the specific interaction with the regulatory regions of the uteroglobin gene. No immunological difference could be detected between [3H]R5020-receptor and [3H]RU486-receptor complexes, both interacted with the five monoclonal antibodies raised against purified R5020-receptor complexes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

RU 38486: a potent antiglucocorticoid in vitro and in vivo.

The antiglucocorticoid activity of RU 38486, was studied both in vitro and in vivo. In vitro studies, RU 38486 was characterized by a high affinity (3 times higher than that of dexamethasone) for the cytosolic glucocorticoid receptor in rat hepatoma tissue culture (HTC) cells. This high affinity was due to a very low dissociation rate of the complexes formed with the receptor. In whole cells it was a potent full antagonist of dexamethasone-induced tyrosine aminotransferase (TAT) activity: the IC50 was 6-7 times lower than the concentration of the dexamethasone used. It was devoid of any glucocorticoid activity up to a concentration of 10 microM. In in vivo studies using adrenalectomized rats, RU 38486 totally inhibited dexamethasone-induced hepatic tryptophan oxygenase (TO) activity. It is also the first pure antagonist of dexamethasone-induced hepatic TAT. However, doses as high as 5 mg/kg of body weight were required for a 50% inhibition of the effect of dexamethasone at 0.01 mg/kg. RU 38486 did not display any glucocorticoid effect on these two responses up to 50 mg/kg.

Animals↗
PubMed1984

In vitro binding of tritiated glucocorticoids directly on unfixed rat brain sections.

We describe a new technique for measuring specific in vitro binding of tritiated adrenal steroids on unfixed cryostat brain sections. The specific binding of [3H]corticosterone represents about 70% of the initial binding. Kinetic studies show that specific binding for [3H]corticosterone reaches equilibrium after 15 min incubation at room temperature. Scatchard analysis of [3H]corticosterone in vitro binding gives a linear plot with an apparent dissociation constant (Kd) and a number of binding sites (Bmax) in the range of 10(-8) M and 100 fmol/mg protein, respectively. [3H]Dexamethasone binding under the same conditions gives a similar Kd and a Bmax of 55 fmol/mg protein. The order of potency for the relative binding affinity for [3H]corticosterone labeled sites is as follows: corticosterone greater than progesterone, dexamethasone, RU 38486 (a "pure" antiglucocorticoid), RU 26988 (a "pure" glucocorticoid), aldosterone greater than estradiol, testosterone. Anatomical studies reveal that sections at the level of the hippocampus bind more [3H]corticosterone and [3H]dexamethasone in vitro than more rostral sections taken at the level of the septum. Adrenalectomy increases the capacity of [3H]corticosterone to bind to these sites and perfusion of the brain to remove transcortin and other blood proteins does not modify [3H]corticosterone binding. We conclude that it is possible to measure in unfixed frozen brain sections glucocorticoid binding sites.

Adrenalectomy↗
PubMed1984

RU 38486: potent antiglucocorticoid activity correlated with strong binding to the cytosolic glucocorticoid receptor followed by an impaired activation.

In order to explain the potent antiglucocorticoid activity of RU 38486 and the absence of agonist effect in spite of its very strong interaction with the cytoplasmic glucocorticoid receptor (GR), we investigated the compound's ability to promote GR "activation" and nuclear translocation. We have compared the dissociation-rates of the "non-activated" (molybdate stabilized) and of the "activated" (25 degrees C pre-heated) GR complexes formed either with [3H]RU 38486 or with different tritiated glucocorticoid agonists. While agonists dissociated more slowly from the "activated" than from the "non-activated" complex, RU 38486 dissociated much faster from the "activated" than from the "native" receptor. This difference of activation was confirmed in a DNA-cellulose binding assay. The affinity of the "activated" RU 38486-GR complex for DNA was much lower than that of the dexamethasone-GR complex. Finally, the in vitro nuclear uptake of [3H]RU 38486 was compared with that of [3H]dexamethasone after incubation with thymus minces at 25 or 37 degrees C. A very weak or nearly undetectable level of specific uptake of [3H]RU 38486 was observed in purified nuclei, whatever the concentration or the time of incubation used. These observations suggest that while glucocorticoid agonists form with the non-activated receptor a complex able to be activated into a more stable form (lower k-1), RU 38486 interacts strongly with the non-activated receptor (impeding the binding of DM) but the complex is "transformed" by heat to a less stable form (higher k-1), unable to translocate properly into the nucleus in order to trigger a glucocorticoid response.

Animals↗
PubMed1984

Paradoxical involvement of glucocorticoid receptors in the aldosterone-induced impairment of ACTH secretion from perifused pituitary glands.

The present investigation was aimed at examining whether interaction of aldosterone with specific mineralocorticoid receptors at the level of the pituitary gland may account for the inhibitory effect of that steroid on ACTH secretion. By using pituitaries from neonatal rats, which we show to completely lack specific mineralocorticoid receptors but to contain a functional glucocorticoid receptor system, we demonstrated the persistence of aldosterone-induced inhibition of ACTH release from perifused glands. Conversely, when the glucocorticoid receptors sites were blocked in pituitaries from mature rats by means of a potent antiglucocorticoid (RU 38486), thus leaving unaltered mineralocorticoid binder, aldosterone no longer dampened hormonal output. We conclude that the latter steroid affected corticotropic activity by interacting not with its proper and specific receptor, but rather with the glucocorticoid binding sites.

Adrenocorticotropic Hormone↗
PubMed1984

The effect of the antimineralocorticoid RU 28318 on aldosterone biosynthesis in vitro.

The effect of RU 28318, a specific and highly potent aldosterone antagonist on mineralocorticoid biosynthesis has been studied using a new in vitro model which combined three original features: (1) a very specific radioimmunoassay for aldosterone (2) a simplified perifusion system and (3) frog interrenal tissue which spontaneously produces high amounts of aldosterone. A dose-related inhibition of aldosterone production was observed for doses ranging from 10(-5) to 10(-3) M of RU 28318. The intermediate dose of 10(-4) M caused 71% inhibition of aldosterone production. Long term infusion of RU 28318 for 8 h led to a significant, stable and reversible inhibition of aldosterone production. In addition, we provide evidence that RU 28318 is capable of blocking the stimulation of aldosterone secretion induced by synthetic ACTH or by angiotensin II analogue. The present results demonstrate that RU 28318 is responsible for a significant and reversible inhibition of spontaneous, ACTH-induced and angiotensin II-induced aldosterone biosynthesis in vitro.

Adrenal Glands↗
PubMed1984

Cytosolic and nuclear sex steroid receptors in meningioma.

To determine the nature of the hormone dependency of meningioma, particularly whether progestin receptor (PR) and tumor growth are estrogen-dependent, we measured the cytosol estrogen receptor (ER) and PR separately by an exchange assay with [3H]R 2858 (for ER) and [3H]RU 27987 (for PR) in 21 meningiomas. We correlated these receptors with age, plasma estradiol and progesterone concentrations, histological subtypes, clinical data such as uterine fibromas, and finally preoperative glucocorticoid therapy. ER was detected at low levels in the cytosol and in the nucleus of a few tumors whereas PR was found in 20 of 21 cases at moderate to high levels, usually with higher concentrations in the cytosol than in the nucleus. No clear relation could be drawn between either cytosol or nuclear ER and PR levels and estradiol and progesterone plasma concentrations, or with the other parameters. On the contrary, a clear correlation could be drawn between cytosolic PR and androgen receptor (AR) concentrations (measured with [3H]R 1881 in the presence of triamcinolone acetonide), leading to several hypotheses of hormonal regulation in meningioma.

Adult↗
PubMed1983

Steroid hormone receptors in human meningiomas, gliomas and brain metastases.

Progestin, estrogen, androgen, glucocorticoid as well as mineralocorticoid receptors (PR, ER, AR, GR and MR, respectively) were all evaluated with specific synthetic radioligands (biochemical assays) in 25 meningiomas, 9 gliomas and 4 brain metastases. In meningiomas the main steroid hormone receptors appeared to be the progestin receptor, present in 24/25 cases (mean level: 7 105 fmol/gT) and the androgen receptor, present in 23/25 cases (mean level: 2 265 fmol/gT). Progestin receptor levels were found to be significantly lower in meningiomas of the fibroblastic subtype whereas none of the steroid hormone receptors were detected in the anaplastic case. On the other hand, glucocorticoid receptor levels were related to the preoperative glucocorticoid therapy. In gliomas only estrogen receptors (2/9 cases) and especially androgen receptors (8/9 cases) were noticeable: the latter seemed to be related to the histological types and to the sex of patients. No receptors were found in any of the four studied metastases, including one from breast cancer. The biochemical characterization of the receptors as well as their relevance to tumor biology and to the physiology of the normal tissues where tumors arise, were discussed, and biochemical data were compared with those previously reported.

Adult↗
PubMed1983

[Binding of tritiated corticosterone by brain sections of adrenalectomized rats].

In the present work we describe a new technique which permits us to study the specific binding of tritiated corticosterone in brain sections of adrenalectomized Rats. Under these conditions, the specific binding of the glucocorticoid represents 60 to 70% of the initial binding. The apparent dissociation constant and the number of binding sites, determined by Scatchard analysis, are in the range of 10(-8) M and 100 fmoles/mg of protein respectively.

Adrenalectomy↗
PubMed1982

[The effects of an antiprogesterone steroid in women: interruption of the menstrual cycle and of early pregnancy].

RU-486 is a steroid which possesses a great affinity for the progesterone receptor, does not have a progesterone activity, but is indeed a strong antagonist of progesterone effects in animals. Oral administration induces the interruption of the luteal phase of the menstrual cycle and that of early pregnancy in women. Its mode of administration and its properties enable us to envisage a new methodology for menstrual cycle regulation and human birth control.

Abortifacient Agents↗