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Viguié C, Mhaouty-Kodja S, Habert R, Chevrier C, Michel C, Pasquier E. Evidence-based adverse outcome pathway approach for the identification of BPA as en endocrine disruptor in relation to its effect on the estrous cycle. Mol Cell Endocrinol 2018; 475:10-28. [PMID: 29577943 DOI: 10.1016/j.mce.2018.02.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Revised: 02/13/2018] [Accepted: 02/14/2018] [Indexed: 02/04/2023]
Abstract
Proper cyclicity is essential to reach successful optimal fertility. In rats and mice, BPA exposure is repeatedly and reliably reported to show an adverse effect on the estrous cycle after exposures at different life stages. In humans, a possible association between modifications of menstrual cycle characteristics (e.g. length of the cycle, duration of menstrual bleeding) and sub-fecundity or spontaneous abortion has been observed. Alterations of ovarian cyclicity can therefore be definitely considered as an adverse health outcome. As a prerequisite for the EU REACH regulation to identify a substance as an endocrine disruptor and a SVHC,1 the proof has to be established that the substance can have deleterious health effects resulting from an endocrine mode of action. This review provides an overview of the currently available data allowing to conclude that the adverse effects of BPA exposure on ovarian cyclicity is mediated by an endocrine mode of action.
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Affiliation(s)
- Catherine Viguié
- Toxalim (Research Centre in Food Toxicology), INRA, ENVT, INP-Purpan, UPS, Toulouse, France
| | - Sakina Mhaouty-Kodja
- Sorbonne Universités, UPMC Univ Paris 06, INSERM, CNRS, Neuroscience Paris Seine, Institut de Biologie Paris Seine, 75005 Paris, France
| | - René Habert
- Genetic Stability, Stem Cells and Radiations, CEA, INSERM U 967, University Paris-Diderot, CEA Research Center, Fontenay aux Roses, France
| | - Cécile Chevrier
- INSERM, UMR1085, Researche Institute for Environmental and Occupational Health, Rennes, France
| | - Cécile Michel
- ANSES, Risk Assessment Department, Maisons-Alfort, France
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Expression of genes involved in BMP and estrogen signaling and AMPK production can be important factors affecting total number of antral follicles in ewes. Theriogenology 2016; 91:36-43. [PMID: 28215684 DOI: 10.1016/j.theriogenology.2016.12.023] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 12/16/2016] [Accepted: 12/21/2016] [Indexed: 11/24/2022]
Abstract
Follicular growth and ovulation of healthy oocytes is a complicated process which is regulated by several endocrine and paracrine factors as well as cross-talk between the oocyte and its surrounding somatic cells. This study compared the expression profile of some candidate genes involved in BMP signaling as well as estrogen and AMPK production in cumulus-oocyte complex (COC) of small and large antral follicles and their associated somatic cell layers in ovaries from ewes with high- and low-antral follicle count (AFC). Expression of GDF9 was increased by increasing the size of antral follicles, while BMP15 expression was decreased by follicular size. It should be noteworthy that transcription of both GDF9 and BMP15 was also detected in the adjacent cellular layers under the follicles. There was a very strong positive correlation between BMP15 and BMPR2 in ovary tissues. Expression of GDF9 was highly correlated with BMP15, BMPR1B, and BMPR2 in large antral follicles. Expression of BMP7 in small antral follicles and BMPR2 in ovary tissues was significantly increased in the high-AFC group. Expression of ESR1 and ESR2 involved in estrogen production as well as PRKAA1 which involved in AMPK production were significantly greater in large antral follicles of high-AFC. There was a very high correlation between Cyp19 and ESR1 in large antral follicles and ovary tissues. Expression of Cyp19 and PRKAA1 were positively correlated with GDF9, BMP15, and BMP7 in large follicles. In conclusion, this study suggests that apart from the BMP signaling, genes involved in AMPK and estrogen production can be pivotal players in ewe's follicular development process. In addition, a strong cross-talk can exist among AMPK, BMP signaling, and estrogen synthesis systems in ewe ovary.
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Tyndall V, Broyde M, Sharpe R, Welsh M, Drake AJ, McNeilly AS. Effect of androgen treatment during foetal and/or neonatal life on ovarian function in prepubertal and adult rats. Reproduction 2012; 143:21-33. [PMID: 22016380 PMCID: PMC3245827 DOI: 10.1530/rep-11-0239] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 10/19/2011] [Indexed: 11/08/2022]
Abstract
We investigated the effects of different windows of testosterone propionate (TP) treatment during foetal and neonatal life in female rats to determine whether and when excess androgen exposure would cause disruption of adult reproductive function. Animals were killed prepubertally at d25 and as adults at d90. Plasma samples were taken for hormone analysis and ovaries serial sectioned for morphometric analyses. In prepubertal animals, only foetal+postnatal and late postnatal TP resulted in increased body weights, and an increase in transitory, but reduced antral follicle numbers without affecting total follicle populations. Treatment with TP during both foetal+postnatal life resulted in the development of streak ovaries with activated follicles containing oocytes that only progressed to a small antral (smA) stage and inactive uteri. TP exposure during foetal or late postnatal life had no effect upon adult reproductive function or the total follicle population, although there was a reduction in the primordial follicle pool. In contrast, TP treatment during full postnatal life (d1-25) resulted in anovulation in adults (d90). These animals were heavier, had a greater ovarian stromal compartment, no differences in follicle thecal cell area, but reduced numbers of anti-Mullerian hormone-positive smA follicles when compared with controls. Significantly reduced uterine weights lead reduced follicle oestradiol production. These results support the concept that androgen programming of adult female reproductive function occurs only during specific time windows in foetal and neonatal life with implications for the development of polycystic ovary syndrome in women.
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Affiliation(s)
- Victoria Tyndall
- MRC Human Reproductive Sciences UnitUniversity/BHF Centre for Cardiovascular Science, The Queen's Medical Research Institute47 Little France Crescent, Edinburgh, EH16 4TJUK
| | - Marie Broyde
- MRC Human Reproductive Sciences UnitUniversity/BHF Centre for Cardiovascular Science, The Queen's Medical Research Institute47 Little France Crescent, Edinburgh, EH16 4TJUK
| | - Richard Sharpe
- MRC Human Reproductive Sciences UnitUniversity/BHF Centre for Cardiovascular Science, The Queen's Medical Research Institute47 Little France Crescent, Edinburgh, EH16 4TJUK
| | - Michelle Welsh
- MRC Human Reproductive Sciences UnitUniversity/BHF Centre for Cardiovascular Science, The Queen's Medical Research Institute47 Little France Crescent, Edinburgh, EH16 4TJUK
| | - Amanda J Drake
- Endocrinology Unit University/BHF Centre for Cardiovascular ScienceThe Queens Medical Research Institute47 Little France Crescent, Edinburgh, EH16 4TJUK
| | - Alan S McNeilly
- MRC Human Reproductive Sciences UnitUniversity/BHF Centre for Cardiovascular Science, The Queen's Medical Research Institute47 Little France Crescent, Edinburgh, EH16 4TJUK
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Aromatase expression in the ovary: hormonal and molecular regulation. Steroids 2008; 73:473-87. [PMID: 18321551 DOI: 10.1016/j.steroids.2008.01.017] [Citation(s) in RCA: 219] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/24/2007] [Revised: 01/12/2008] [Accepted: 01/14/2008] [Indexed: 01/25/2023]
Abstract
Estrogens are synthesized by the aromatase enzyme encoded by the Cyp19a1 gene, which contains an unusually large regulatory region. In most mammals, aromatase expression is under the control of two distinct promoters a gonad- and a brain-specific promoter. In humans, this gene contains 10 tissue-specific promoters that are alternatively used in various cell types and tumors. Each promoter is regulated by a distinct set of regulatory sequences and transcription factors that bind to these specific sequences. The cAMP/PKA/CREB pathway is considered to be the primary signaling cascade through which the gonad Cyp19 promoter is regulated. Very interestingly, in rat luteal cells, the proximal promoter is not controlled in a cAMP dependent manner. Strikingly, these cells express aromatase at high levels similar to those found in preovulatory follicles, suggesting that alternative and powerful mechanisms control aromatase expression in luteal cells and that the rat corpus luteum represents an important paradigm for understanding alternative controls of the aromatase gene. Here, the molecular and cellular mechanisms controlling the expression of the aromatase gene in granulosa and luteal cells are discussed.
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Levacher C, Gautier C, Saez JM, Habert R. Immunohistochemical localization of transforming growth factor beta 1 and beta 2 in the fetal and neonatal rat ovary. Differentiation 1996; 61:45-51. [PMID: 8921584 DOI: 10.1046/j.1432-0436.1996.6110045.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The localization of transforming growth factor beta (TGF beta) in the differentiating ovary (from fetal day 13.5 to postnatal day 14) was investigated immunohistochemically using polyclonal antibodies for TGF beta 1 and TGF beta 2. Immunostaining was undetectable in the gonadal primordium on fetal day 13.5. From fetal day 14.5 and throughout fetal life, there was intense immunostaining for TGF beta 1 and faint staining for TGF beta 2 in some ovarian somatic cells which were identified as epithelial cells at the end of fetal life. This pattern of staining was also found in the presumptive granulosa cells present between the oocytes on postnatal day 1. The staining for TGF beta 2 persisted while the staining for TGF beta 1 decreased in the granulosa cells of primordial and primary follicles of older rats. In the subsequent stages of follicular development, the staining for TGF beta 1 disappeared while faint staining for TGF beta 2 persisted in the granulosa cells of secondary and small antral (postnatal day 14) follicles. On day 14, the newly functional thecal/interstitial cells were moderately stained for TGF beta 2 and intensely stained for TGF beta 1. These results plus our previous immunolocalization of TGF beta 1 in the fetal testis [13] show that, in both sexes: (1) TGF beta 1 is detectable in the gonads on the same fetal age (day 14.5); (2) TGF beta 1 is present in the somatic cells which are the precursors of Sertoli and granulosa cells, at the time of their organization in seminiferous tubules or in primordial follicles; and (3) TGF beta 1 is largely present in cells synthesizing androgens, from the onset of their steroidogenic capacity (fetal day 16.5 for Leydig cells and postnatal day 14 for thecal/interstitial cells.
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Affiliation(s)
- C Levacher
- INSERM-INRA U 418-Université Paris 7, France
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Villalpando I, Nishioka Y, Taketo T. Endocrine differentiation of the XY sex-reversed mouse ovary during postnatal development. J Steroid Biochem Mol Biol 1993; 45:265-73. [PMID: 8499334 DOI: 10.1016/0960-0760(93)90341-s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
When the mouse Y chromosome of Mus musculus domesticus is placed onto the C57BL/6J genetic background, half of the XY progeny develop bilateral ovaries and the female phenotype, but lack regular estrous cyclicity and lose embryos after fertilization. In the present study, we compared the endocrinological activity of XY ovaries with XX ovaries during postnatal development by measuring steroids in the incubation medium by radioimmunoassay. At 1 day postpartum (d.p.p.), production of progesterone and estradiol was significant while testosterone was undetectable in both ovaries. At 14 and 35 d.p.p., amounts of testosterone and estradiol produced by XY ovaries were half of those by XX ovaries. Production of progesterone by XY ovaries was slightly higher than XX ovaries at 14 d.p.p., but only half of that at 35 d.p.p. Addition of gonadotropins increased testosterone production by XX ovaries but not by XY ovaries at either 14 or 35 d.p.p. Progesterone production in XY ovaries at 35 d.p.p. was increased by gonadotropins to a much lesser extent than in XX ovaries. Gonadotropins increased estradiol production similarly in both ovaries at 35 d.p.p. Striking differences were found in the histochemical distribution of 3 beta-hydroxysteroid dehydrogenase between XY and XX ovaries at 14, but not at 35 d.p.p. In conclusion, the XY ovary develops abnormal endocrine features during the postnatal period, which likely lead to the fertility problems at puberty.
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Affiliation(s)
- I Villalpando
- Urology Research Laboratory, McGill University, Royal Victoria Hospital, Montreal, Canada
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Josso N, Cate RL, Picard JY, Vigier B, di Clemente N, Wilson C, Imbeaud S, Pepinsky RB, Guerrier D, Boussin L. Anti-müllerian hormone: the Jost factor. RECENT PROGRESS IN HORMONE RESEARCH 1993; 48:1-59. [PMID: 8441845 DOI: 10.1016/b978-0-12-571148-7.50005-1] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- N Josso
- Unité de Recherches sur l'Endocrinologie du Dévelopement (INSERM), Ecole Normale Supérieure, Montronge, France
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Malamed S, Gibney JA, Ojeda SR. Ovarian innervation develops before initiation of folliculogenesis in the rat. Cell Tissue Res 1992; 270:87-93. [PMID: 1358455 DOI: 10.1007/bf00381883] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Sympathetic neurotransmitters have been shown to be present in the ovary of the rat during early postnatal development and to affect steroidogenesis before the ovary becomes responsive to gonadotropins, and before the first primordial follicles are formed. This study was undertaken to determine if development of the ovarian innervation is an event that antedates the initiation of folliculogenesis in the rat, Rattus norvegicus. Serial sections of postnatal ovaries revealed a negligible frequency of follicles 24 h after birth (about 1 primordial follicle per ovary). Twelve hours later there were about 500 follicles per ovary, a number that more than doubled to about 1300 during the subsequent 12 h, indicating that an explosive period of follicular differentiation occurs between the end of postnatal days 1 and 2. Electron microscopy demonstrated that before birth the ovaries are already innervated by fibers containing clear and dense-core vesicles. Immunohistochemistry performed on either fetal (day 19) or newborn (less than 15h after birth) ovaries showed the presence of catecholaminergic nerves, identified by their content of immunoreactive tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. While some of these fibers innervate blood vessels, others are associated with primordial ovarian cells, thereby suggesting their participation in non-vascular functions. Since prefollicular ovaries are insensitive to gonadotropins, the results suggest that the developing ovary becomes subjected to direct neurogenic influences before it acquires responsiveness to gonadotropins.
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Affiliation(s)
- S Malamed
- Department of Neuroscience and Cell Biology, UMDNJ-Robert Wood Johnson Medical School, Piscataway 08854
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Rouiller V, Gangnerau MN, Vayssiere JL, Picon R. Cholesterol side-chain cleavage activity in rat fetal gonads: a limiting step for ovarian steroidogenesis. Mol Cell Endocrinol 1990; 72:111-20. [PMID: 2178100 DOI: 10.1016/0303-7207(90)90101-d] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The aim of this study was to examine the first step in steroidogenesis in male and female gonads of fetal rats. Pregnenolone production was measured by radioimmunoassay in organ culture, conversion of [3H]cholesterol to [3H]pregnenolone was evaluated in isolated mitochondria and cytochrome P-450scc was revealed by immunoblotting and immunocytochemical techniques. Our results clearly showed that in fetal testes (1) pregnenolone was produced in media where testes were cultured in the presence of trilostane and spironolactone, indicating an important metabolism of pregnenolone, (2) [3H]cholesterol was converted into [3H]pregnenolone in mitochondria, (3) cytochrome P-450scc was revealed in immunoblots with a molecular weight of 50,000, (4) cytochrome P-450scc was localized in Leydig cells from 15.5-day-old fetal testes onwards. With respect to fetal ovaries, we were unable to detect any scc activity, except after treatment with dibutyryl cyclic AMP. A lag period of 18 h was necessary to induce pregnenolone synthesis. However, the immunoperoxidase staining did not localize ovarian positive cells. Cytochrome P-450scc could be revealed in postnatal ovaries by immunoblotting and some interstitial positive cells were observed with immunostaining; the reaction was enhanced in luteinizing hormone-pretreated ovaries. These data indicate that (a) the cholesterol scc activity is present in fetal testes, (b) the conversion of cholesterol to pregnenolone is a limiting step for steroidogenesis in fetal ovaries. The inductive effect of the nucleotide on the enzyme suggests that the absence of gonadotrophic receptors in fetal female gonads could explain the lack of steroidogenesis before birth.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- V Rouiller
- Laboratoire de Physiologie du Développement, CNRS, URA 307, Université Paris 7, France
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Weniger JP, Zeis A. Action of LH, FSH and (Bu)2 cAMP on the conversion of [3H]19-hydroxyandrostenedione into oestrogens by foetal and infantile rat ovaries in organ culture. JOURNAL OF STEROID BIOCHEMISTRY 1990; 35:507-10. [PMID: 2157921 DOI: 10.1016/0022-4731(90)90260-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Ovaries from 18-21-day-old foetal as well as from 2-10-day-old infantile rats were cultured in vitro in the presence of [3H]19-hydroxyandrostenedione and in the presence or absence of LH, FSH or (Bu)2 cAMP, and oestrone and oestradiol formed were determined by double isotopic dilution and recrystallization to constant specific activity. In foetal ovaries, the stimulation factor with FSH was 0.9-1.3, which was considered insignificant in comparison with the 8-13-fold stimulation obtained with (Bu)2 cAMP. At infantile stages, aromatase activity was stimulated 1.3-3.5-fold, which was close to the 3.9-fold stimulation obtained with (Bu)2cAMP. LH was ineffective at both foetal and infantile stages.
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Affiliation(s)
- J P Weniger
- Laboratoire de Zoologie et d'Embryologie Expérimentale, Université Louis-Pasteur, Strasbourg, France
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Picon R, Darmoul D, Rouiller V, Duranteau L. Activity of 3 beta-hydroxysteroid dehydrogenase/isomerase in the fetal rat ovary. JOURNAL OF STEROID BIOCHEMISTRY 1988; 31:839-43. [PMID: 2848985 DOI: 10.1016/0022-4731(88)90294-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) was examined in rat fetal ovaries. The enzymatic activity was determined by measuring the conversion of radiolabeled pregnenolone to progesterone. 3 beta-HSD, present in 14-day old fetal ovaries showed a regular increase in the course of development. Pretreatment with dcAMP for 48 h enhanced the apparent maximal velocity of the enzyme by about 5-fold without increase in the apparent Km. The increase in 3 beta-HSD activity was not due to the synthesis of pregnenolone observed after dcAMP pretreatment, but it was dependent on protein synthesis. The present results indicate that (1) 3 beta-HSD activity is present in fetal female gonads and the absence of steroid biosynthesis cannot be related to a defect in this enzyme (2) 3 beta-HSD activity is enhanced in the presence of dcAMP. The absence of gonadotropic receptors in the rat ovary before birth could explain the low level of the enzymatic activity measured in fetal ovaries.
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Affiliation(s)
- R Picon
- Laboratoire de Physiologie du Développement, U.A. C.N.R.S. no. 307, Université Paris 7, France
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Rouiller V, Gangnerau MN, Picon R. Production of C21 steroids in rat fetal ovaries. JOURNAL OF STEROID BIOCHEMISTRY 1988; 31:447-52. [PMID: 2845196 DOI: 10.1016/0022-4731(88)90314-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Female gonads of fetal and neonatal rats were cultured for 24 h in medium 199 supplemented with dibutyryl cyclic AMP (dcAMP), cycloheximide, spironolactone (an inhibitor of 17 alpha-hydroxylase) or hydroxylated cholesterol derivatives. Radioimmunoassays of pregnenolone (P5) and progesterone (P4) were performed in the media. In control medium, progesterone production developed during the second week of life whereas ovaries treated with dcAMP (1 mM) produced progesterone as early as day 14.5 of gestation. The effect of the nucleotide was reversible and the lag period of responsiveness was 12 h. Cycloheximide (1 microgram/ml) added with dcAMP completely inhibited the production of progesterone. Addition of spironolactone to the basal medium was without effect but significantly increased P5 and P4 productions in the presence of dcAMP. The inhibitory effects of spironolactone and trilostane on steroidogenesis were tested in fetal testis. Lastly, the dcAMP effect could not be mimicked with hydroxylated cholesterol derivatives (20 microM). However, an additive effect of 22-hydroxycholesterol was observed in the presence of the nucleotide. These results indicate that the in vitro production of P5 and P4 by fetal ovaries in the presence of dcAMP suggests that dcAMP induces enzymes involved in C21 steroid synthesis. Levels of action of the nucleotide are discussed.
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Affiliation(s)
- V Rouiller
- Laboratoire de Physiologie du Développement, U.A. C.N.R.S. no. 307, Université Paris 7, France
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George FW, Ojeda SR. Vasoactive intestinal peptide enhances aromatase activity in the neonatal rat ovary before development of primary follicles or responsiveness to follicle-stimulating hormone. Proc Natl Acad Sci U S A 1987; 84:5803-7. [PMID: 3039508 PMCID: PMC298951 DOI: 10.1073/pnas.84.16.5803] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
We have investigated the factors that regulate aromatase activity in fetal-neonatal rat ovaries. Ovarian aromatase activity (assessed by measuring the amount of 3H2O) formed from [1 beta-3H]testosterone) is low prior to birth (less than 0.5 pmol/hr per mg of protein) and increases to values greater than 30 pmol/hr per mg of protein between days 8 and 12 after birth. The appearance of ovarian aromatase (postnatal days 2-4) coincides with the development of primordial follicles. Fetal-neonatal ovaries maintained in serum-free organ culture do not develop aromatase activity at the expected time. Ovine follicle-stimulating hormone (0.1-1 microgram/ml), ovine luteinizing hormone (0.1 microgram/ml), or their combination failed to induce the enzyme activity in cultured fetal ovaries, whereas follicle-stimulating hormone is effective in preventing the decline in aromatase activity when postnatal day 8 ovaries are placed in culture. In contrast to follicle-stimulating hormone, dibutyryl-cAMP markedly enhances ovarian aromatase in cultured fetal ovaries. Likewise, enhancement of endogenous cAMP formation with forskolin or cholera toxin caused an increase in enzyme activity within 24 hr. Vasoactive intestinal peptide, a peptide known to occur in ovarian nerves, caused a dose-dependent increase in aromatase activity in fetal ovaries prior to folliculogenesis. Of related peptides tested, only the peptide having N-terminal histidine and C-terminal isoleucine amide was capable of inducing aromatase activity in fetal ovaries. The fact that VIP can induce aromatase activity in fetal rat ovaries prior to follicle formation and prior to responsiveness to follicle-stimulating hormone suggests that this neuropeptide may play a critical role in ovarian differentiation.
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