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M Begeot

Publications and source records attributed to M Begeot.

At least 37 records · Page 2Linked to original sources
PubMed1988

Variations in guanine-binding proteins (Gs, Gi) in cultured bovine adrenal cells. Consequences on the effects of phorbol ester and angiotensin II on adrenocorticotropin-induced and cholera-toxin-induced cAMP production.

The corticotropin (ACTH) or cholera-toxin-induced cAMP production by cultured bovine adrenal cells increased progressively between days 0 and 7 of culture. Angiotensin II (A-II), which inhibited both basal and ACTH-stimulated adenylate cyclase of crude adrenal membranes, had no effect on ACTH-induced or cholera-toxin-induced cAMP production by fresh isolated cells (day 0) but progressively potentiated the stimulatory action of both effectors from day 0----1 to day 7 of culture. In contrast, phorbol ester had a potentiating effect on fresh isolated cells. Pretreatment of cells with pertussis toxin enhanced the potentiating effect of A-II on cells between 0 and 3 days of culture, but not after 7 days. ADP-ribosylation by cholera toxin (ribosylating alpha s proteins) or pertussis toxin (alpha i proteins), of adrenal membranes prepared from fresh isolated or cultured cells revealed an increase in alpha s and a dramatic decrease in alpha i, the ratios alpha i/alpha s on days 0, 3 and 7 of culture were 4, 0.6 and 0.1 respectively. These results indicate that (a) A-II had a double effect on ACTH-induced or cholera-toxin-induced cAMP production: one inhibitory mediated by Gi, the other stimulatory mediated by protein kinase C activation; this could explain the lack of apparent effect of A-II on fresh cells; (b) the progressive decrease of alpha i might be responsible for the appearance of the potentiating effect of A-II whereas the progressive increase of alpha s could explain the enhanced responsiveness to ACTH or cholera toxin of cultured cells.

Adenosine Diphosphate Ribose↗
PubMed1988

Vasopressin induces breakdown of phosphoinositides in adrenal tumor Y-1 cells without a steroidogenic effect.

Y-1 adrenal cells contain specific vasopressin (VP) binding sites (27,000 +/- 2,000 sites/cell) of high affinity (KD = 2.2 +/- 0.5 X 10(-9) M). VP which alone has no effect on cAMP production inhibited in a dose-dependent manner (ID50 = 3.5 +/- 0.7 X 10(-11) M) the ACTH-induced cAMP production by Y-1 cells. The inhibitory effect was completely blunted by a 24 h pretreatment of cells with 1 microgram/ml of pertussis toxin. Moreover, VP also stimulated in a dose-dependent manner (ED50 = 2.4 +/- 0.8 X 10(-9) M) the accumulation of inositol phosphates indicating that the VP receptors in Y-1 cells were of the V1 subtype. However, neither VP nor a phorbol ester (4 beta-phorbol 12-myristate 13-acetate, PMA) was able to stimulate Y-1 cell steroidogenesis. Since in a previous work we have shown that Y-1 cells contain high levels of protein kinase C, the present results indicate that the steroidogenic refractoriness of these cells to VP and PMA might involve some step beyond protein kinase C.

Adenylyl Cyclases↗
PubMed1987

The potentiating effects of phorbol ester on ACTH-, cholera toxin-, and forskolin-induced cAMP production by cultured bovine adrenal cells is not mediated by the inactivation of alpha subunit of Gi protein.

Phorbol ester (PMA) potentiates ACTH-induced cAMP production by both fresh isolated and 7-day-old cultured adrenal cells, but the effect on cultured cells was greater than in fresh cells. In cultured cells the potentiating effects of PMA were dose-dependent and were observed at each effective dose of ACTH without modification of the ED50 for this hormone. These effects of PMA do not seem to be exerted through a modification of the alpha subunit of Gi since pretreatment of the cells with Bordetella pertussis toxin did not modify the action of PMA and since the amount of alpha i in 7-day-old cultured cells was ten times lower than in fresh cells, while the potentiating effect was lower in the latter. Moreover, since PMA still exerted its potentiating action in cells stimulated by maximal concentration of cholera toxin or forskolin either alone or in combination with ACTH, it is likely that its action is not mediated exclusively by the alpha subunit of Gs. Taken together, the present results and those of the literature suggest that this potentiating effect of phorbol ester on effector-induced cAMP production might be mediated by inhibition of the beta-subunit of G proteins.

Adenosine Diphosphate Ribose↗
PubMed1987

Angiotensin II (A-II) steroidogenic refractoriness in Y-1 cells in the presence of A-II receptors negatively coupled to adenylate cyclase.

Y1 adrenal tumor cells are resistant to the steroidogenic effect of A-II though they possess specific A-II binding sites. The number of these binding sites is lower in Y1 cells than in bovine adrenal cells, but the affinity is similar in the two models. Moreover, Y1 cells are shown to contain a high level of cytosolic protein kinase C whose properties appear similar to those observed in bovine adrenal cells. However, the activation of protein kinase C by a phorbol ester (PMA) or diacylglycerol (OAG) does not induce steroidogenesis in Y1 cells. On the other hand, A-II, without any effect on adenylate cyclase in basal conditions, reduces the ACTH-induced cAMP production in Y1 cells. This inhibitory effect of A-II is not blocked by phosphodiesterase inhibitor but is completely abolished after 24 hours of pretreatment of intact cells with pertussis toxin. This inhibition is probably mediated by the inhibitory guanine nucleotide regulatory protein (Gi) since the labeled 41 KD-ADP ribosylated protein disappeared after 24 hours of pretreatment of intact cells with pertussis toxin. Moreover, the accumulation of inositol phosphates under A-II stimulation was low, which suggests that the coupling of A-II receptors with phospholipase C is reduced in Y1 cells. The Y1 cell line is probably a good model to study the post membrane events in A-II action.

Adenylate Cyclase Toxin↗
PubMed1987

[Differentiation of pituitary cells in culture].

Gonadotrophs were first detected at 18 days of gestation in normal rat fetus. Encephalectomy performed at 16 days of gestation did not modify the normal aspect of cells at term. In adenohypophysial primordia explanted from 13 days of gestation differentiated gonadotrophs were detected after culture (8 days) in medium containing insulin (minimal dose required: 0.5 microgram/ml) and transferrin (5 micrograms/ml). In contrast, in primordia explanted at 11 and 12 days of gestation, GnRH 10(-9) to 10(-12) M was required for the first 24 hours of culture to induce differentiation of cells which was obtained in synergy with insulin and transferrin. On the other hand, fetal hypothalamic GnRH and pituitary GnRH receptors were observed from 12 days of gestation which can explain the observations made on primordia explanted at 13 days. Lactotrophs first appeared at term in normal rat fetus. In vitro, differentiation of lactotrophs was not observed in primordia explanted from 13 days in the presence of insulin and transferrin alone, but it was induced by GnRH (10(-9) M) for the 24 hours of culture in the same medium. The action of GnRH was mediated through glycoproteins and specifically isolated alpha subunit. Indeed, purified LH alpha-subunit added in medium instead of GnRH induced differentiation of lactotrophs from 10(-9) M with an increase in the number of cells related to the dose of hormone. Differentiation of the two cell types is very linked in these culture conditions. Gonadotroph differentiation is regulated by an hypothalamic endocrine secretion whereas lactotroph differentiation is more dependent on a paracrine secretion.

Animals↗
PubMed1985

Ontogeny of hypothalamic luteinizing hormone-releasing hormone (GnRH) and pituitary GnRH receptors in fetal and neonatal rats.

Although it is known that LH secretion starts at 17 days of gestation in the fetal rat and that this first LH release is most likely driven by hypothalamic GnRH, an earlier role for GnRH during fetal life has been postulated with the observation that presence of GnRH is important before day 13 of gestation for the differentiation of the pituitary anlage. In order to clarify the different roles of GnRH during fetal life, we have studied the first appearance of GnRH in the fetal brain, the expression of GnRH receptors in the fetal pituitary gland, and the presence of GnRH immunoreactivity within the fetal gonadotrophs. GnRH was present in the earliest brain tissue examined (12 days of gestation). From 12-17 days, GnRH content of fetal brain remained low and then increased markedly by the end of gestation. No immunoreactive GnRH-like material could be detected in rat placental tissue throughout gestation. Binding sites for GnRH were detected as early as 12 days of gestation in fetal pituitary glands. However, binding was very low until 16 days. At 17 days, Scatchard analysis indicated the presence of high affinity, low capacity binding sites [affinity constant (Ka) = 10(10) M-1]. Intracellular presence of GnRH as seen by immunocytochemistry using ultrathin sections prepared by cryoultramicrotomy was first visible at 14 days and started to increase at 16 days. LH was first detectable in the fetal pituitary by RIA at 17 days; FSH was first detectable at 21 days, and PRL at 1 day of postnatal life. Thereafter, neonatal pituitary contents of LH, FSH, and PRL increased linearly with-time, as did the number of pituitary GnRH receptors. At 10 days of postnatal life, pituitary contents of LH and FSH were significantly higher in females than in males. In summary, hypothalamic GnRH appears early in fetal life and potentially can induce differentiation of the pituitary anlage. Conversely, the presence at 15 days of gestation of specific binding sites for GnRH and of intracellular GnRH immunoreactivity in gonadotrophs indicates that the hypophysiotropic action of GnRH clearly precedes the start of LH biosynthesis.

Animals↗
PubMed1984

Gonadotropin receptor complexes and free receptors in porcine Leydig cell cultures during recovery from hCG stimulation.

Free and occupied gonadotropin receptors were studied in vitro in porcine Leydig cells culture maintained in chemically defined medium. Free receptors were evaluated by the binding capacity for 125I-hCG. hCG bound molecules (or hCG receptor complexes) were evaluated using immunocytochemical visualization on fixed cells. Exposure to hCG for 16 hours (.5 to 50 ng/ml) induced the disappearance of free receptors. After removal of the hormone, the return to control levels was observed at 48 and 72 hours. Visualization of hCG bound at the cell surface indicates that, following continuous exposure to gonadotropins for 48 hours, hCG molecules are still present on the cell. Following short-time exposure (1 h) to hCG and 48 hrs washing the number of stained cells is very close to the initial value suggesting that the occupied sites (at 48 hours) represent the initial hormone receptor complexes. These results indicate that, during prolonged incubation, hCG binding is not reversible, that the half-life of some of the complexes at the cell surface is very long and that the receptors recovery is slow and is probably the result of a de novo synthesis.

Animals↗
PubMed1984

Influence of gonadoliberin on the differentiation of rat gonadotrophs: an in vivo and in vitro study.

The influence of gonadoliberin (GnRH) on the differentiation of rat gonadotrophs in early fetal life was studied both in vivo and in vitro by immunocytology with anti-porcine luteinizing hormone beta (pLH beta) serum. Adenohypophysial primordia explanted from 11 to 13 days of gestation were maintained in organ culture in synthetic Parker's 199 medium enriched with insulin (0.5 microgram/ml) and transferrin (5 micrograms/ml). Cultures lasted to approximate the usual gestation period (21 days). Synthetic GnRH (10(-9) or 10(-12) M) was added to the culture medium during the first day of culture only. In contrast to a previous report, immunoreactive cells were detected in the primordia explanted either at 11 or 12 days of gestation only when cultured in the presence of GnRH. The appearance of positive localization was seen by 17 days. No differences due to GnRH dosage were observed in the mean cytoplasmic area of the cells in the different experimental groups as seen at the equivalent of 21 days. GnRH was not effective in a medium deprived of insulin. GnRH, added 6 h before the end of the culture, could also release the secretory product of gonadotrophs which recently developed the presence of immunoreactive pLH beta material. In these conditions, GnRH was shown to enter the cells as observed by immunocytochemistry on sections obtained after cryoultramicrotomy. Endogenous GnRH was also detected by the same technique in fetal pituitary glands removed from 14 to 21 days of gestation. It was always localized in agranular cells and from 18 days in some granular cells considered as gonadotrophs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Evolution of lactotropes in normal and anencephalic human fetuses.

The presence of lactotropes in pituitaries removed from 15 normal fetuses, 1 normal premature infant, 3 normal infants, and 7 anencephalic fetuses or infants was studied by immunocytochemistry. These cells were first detected in normal fetuses at 18 weeks of gestation in both sexes. After 22 weeks of gestation, the number of cells increased sharply and regularly until term. Moreover, the cytoplasmic area of these cells increased significantly until term, but was decreased 4 and 5 months after birth. In all anencephalic fetuses, lactotropes were found; these cells were more numerous and often showed significantly greater cytoplasmic area than those in normal fetuses. A stimulatory effect of the fetal hypothalamus, therefore, is not essential for the development of this cell type.

Anencephaly↗
PubMed1983

Ultrastructural identification of corticotropes of the fetal rat. In-vivo and in-vitro immunocytochemistry.

Corticotropes of rat fetuses aged 16, 18 and 21 days were localized by the indirect antibody-enzyme method on semithin sections of the pituitary. The development of the ultrastructure of these cells was observed on consecutive ultrathin sections. In comparison with previous data our present results show that identification of a fetal cell type cannot be based entirely on morphological criteria. The structural peculiarities of corticotropes obtained from studies in vivo are compared with those observed in cells maintained in vitro.

Adrenocorticotropic Hormone↗
PubMed1983

Comparative study in vivo and in vitro of the differentiation of immunoreactive gonadotropic cells in fetal rat anterior pituitary.

In order to study the mechanisms of the differentiation of gonadotropic cells in fetal rat, an immunocytochemical study was performed in vivo and in vitro with antiporcine beta-LH serum. In vivo, the size of the immunoreactive cells increased greatly between 18 and 19 days of gestation and after a slight increase was observed until 21 days. In vitro, no immunoreactive cells were detected in primordia explanted from 11 to 15 days and cultured until 21 days, in a medium Parker's 199 without any addition. In contrast immunoreactive cells were detected in primordia explanted from 14 days and cultured until 21 days in a medium Parker's 199 containing 20% dialyzed fetal calf serum as well as in the presence of normal fetal calf serum. When the medium Parker's 199 was enriched with insulin (0.5-10 micrograms/ml) and transferrin (5 micrograms/ml) immunoreactive cells were first detected in primordia explanted from 13 days independently of the dose of insulin. However, the size of the immunoreactive cells remained lower than in vivo even at a period equivalent to term. These results suggest that insulin was probably one of the factors stimulating the differentiation of this cell type but other specific factors are needed before 13 days. The comparison of the development of the size of the cells in vivo and in vitro also indicates that other factor(s) acting probably from 18 days of gestation in addition with insulin are required to assure the complete development of these cells.

Animals↗
PubMed1983

Immunocytochemical visualization of luteinizing hormone-human chorionic gonadotropin (LH-hCG) receptors in Leydig cells in primary culture.

Visualization of human chorionic gonadotropin (hCG) binding sites was obtained by immunocytochemical reaction on Leydig cells cultured in chemically defined medium. After a short in vitro incubation with hCG or luteinizing hormone (LH), the cells were fixed and the bound molecules were revealed using anti-hCG or anti-LH antisera. In both cases the immunocytochemical reaction appeared as granulations at the cell surface. After prolonged (48 hr) culture in the presence of 0.5, 5, or 50 ng/ml of hCG, the hormone receptor complex is still visible. Similarly, following short exposure to hCG (0.5 or 50 ng/ml) and one or two days of culture without hCG, the immunocytochemical reaction is still present. These observations suggest that the half-life of the bound hormone is very long. This in vitro system in which the amount and time of hormone exposure are precisely defined provides arguments in favor of a long-term maintenance of the receptor complexes at the cell surface.

Animals↗
PubMed1983

Gonadotropin releasing hormone (GnrH) stimulates immunoreactive lactotrope differentiation.

To study lactotrope differentiation in the fetal rat, immunocytochemistry was performed on pituitary primordia explanted from 13-day-old fetuses and cultured in different synthetic media until the equivalent of 21 days. Lactotropes were detected only by antirat prolactin antiserum when the synthetic medium was enriched with GnRH (10(-9)M). These results indicate that lactotrope differentiation may partly depend on stimulatory factors such as GnRH.

Animals↗
PubMed1982

Comparative study in vivo and in vitro of the differentiation of immunoreactive corticotropic cells in fetal rat anterior pituitary.

In order to study the mechanisms of the differentiation of adenohypophysial corticotropic cells, an immuno-cytological study was performed in fetal rat anterior pituitary in vivo and in vitro with antisera against beta-(1-24) and alpha-(17-39) ACTH and beta-LPH, alpha- and beta-endorphins. In vivo, these cells appeared at 16 days of gestation without any difference in the timing of appearance of the two immunoreactivities. The same immunoreactivity was also detected in adenohypophysial primordia explanted from 12 to 15 days of gestation and maintained in organ culture until 21 days by using either medium containing fetal calf serum or medium containing insulin and transferrin instead of fetal calf serum. These immunoreactive cells were first detected in the different experimental primordia after a minimal period of culture, corresponding to a final equivalent of 16 days as in vivo. However, the mean cytoplasmic area of immunoreactive cells increased in relation to the day of explantation whatever the duration of culture. These data suggest: (1) the nature of culture medium used in this study has no influence on the differentiation of the corticotropic cells; (2) this cell type seems to be committed precociously (before day 12) by one or several substances of unknown origin; (3) the normal development seems to require the presence of factors (before day 14) whose nature and origin remain to be elucidated.

Adrenocorticotropic Hormone↗
PubMed1981

Immunocytological determination of gonadotropic and thyrotropic cells in fetal rat anterior pituitary during normal development and under experimental conditions.

The appearance and relative distribution of immunoreactive gonadotropic and thyrotropic cells of the anterior pituitary of normal rat fetuses were studied by immunocytology with anti-rat luteinizing hormone serum, anti-porcine luteinizing hormone beta serum, anti-bovine thyrotropic hormone serum after saturation with bovine luteinizing hormone. The thyrotropic cells appeared at 17 days of gestation. They were preferentially localized in the dorsal part of the anterior lobe. The gonadotropic cells localized in the ventral part of the same lobe, appeared 1 day later. The number of immunoreactive cells of the two populations increased until the end of gestation. In the pituitaries of 21-day-old rat fetuses encephalectomized at 16 days of gestation, the same number of gonadotropic and thyrotropic cells was observed as in control fetuses at the same age. Gonadotropic cells were also observed in rat adenohypophysial primordia explanted at 14 days of gestation and maintained in organ culture for 7 days. Thyrotropic cells were stained when the primordia were explanted at 15 days of gestation and cultured for 6 days. No immunoreactive gonadotropic or thyrotropic cells were detected when explantation was performed before 14 days of gestation. These results clarify the problem of the role of hypothalamus on the differentiation of these two cell types.

Animals↗
PubMed1979

[Hypothalamic influence on differentiation of the immunoreactive ACTH beta-LPH, alpha- and beta-endorphin containing cells in adenohypophysial primordia of rat fetus in organ culture (author's transl)].

Adenohypophysial primordia were isolated in rat fetuses from day 12.5 to day 15.5 of gestation. The organ culture employed for maintenance of the primordia was made up according to Watanabe et al. (1973). The fixation of primordia in Bouin Hollande's solution was performed after 9, 8, 7 or 6 days of culture when the normal duration of pregnancy was achieved. The cultivated primordia were immunologically studied using different antisera: anti-alpha(17-39)ACTH, anti-beta(1-24)ACTH, anti-beta-LPH, anti-alpha and anti-beta-endorphins, with immunoperoxidase or immunofluorescence techniques, including control experiments of the specificity of the antisera. A similar study was performed on pituitaries removed from normal rat fetuses from day 16.5 of gestation and each day up to birth, and fixated immediately. In vivo the first cells reacting with all the antisera used in this study were observed on day 16.5 of gestation; their number increased during gestation (Fig. 1 A, B and C). Immunoreactive cells with the different antisera could be detected in primordia isolated on day 12.5 of gestation after 9 days of culture. Numerous groups of cells were observed in primordia of older fetuses (Fig. 2 A and B). These data indicate that the corticotropic cells in rat fetuses could start to be differentiated without stimuli from the hypothalamus since primordia were isolated before the appearance of this cell type in normal rat fetuses and before the differentiation of the hypothalamus. The presence of ACTH and other peptides such as beta-LPH or beta-endorphin would support the hypothesis of a common precursor in this cell type existing early in gestation. Similar results were obtained in human fetuses.

Adrenocorticotropic Hormone↗
PubMed1978

Immunocytological localization of LH, FSH, TSH and their subunits in the pituitary of normal and anencephalic human fetuses.

Immunostaining with antisera to oLH, hCG, hLH, pLHbeta, hFSH, hFSHbeta, hTSHalpha and bTSH was used to delineate the gonadotropic and thyrotropic cells of the human fetal anterior pituitary. Hypophyses from 29 normal fetuses, 3 newborn infants, and 5 totally ancencephalic fetuses were used. Several controls to check for the specificty of the immunocytological reaction were made. In normal fetuses, observations showed that: 1) the alpha subunit was detected from the eighth week and throughout gestation without sex differences; 2) intact LH was detected during the third month, however, age and sex differences were observed during the fourth and fifth months; 3) intact FSH was detected in female fetuses from the beginning of the fourth month, a sex difference was observed; 4) LH and FSH were detected in the same cells; 5) the thyrotropic cells were detectable from 15 weeks of gestation and their number increased during gestation without sex difference; 6) at birth the gonadotropic cells were scarce and were located in the ventromedian zone of the anterior pituitary, while the thyrotopic cells remained numerous and were located in the dorsomedian zone. In amencephalic fetuses: 1) the alpha subunit existed at each stage studies; 2) the reaction induced by anti-pLHbeta and anti-hFSHbeta sera was alwys very weak regardless of sex or age; 3) the thyrotropic cells were more numerous in comparison to the gonadotropic cells. These data are discussed in terms of the relationship of the hypophysiotropic hypothalamic factors to the appearance and evolution of the glycoprotein hormones and their subunits.

Anencephaly↗