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Biology of Reproduction 61, 388-392 (1999)
©Copyright 1999 Society for the Study of Reproduction, Inc.

Articles

Mitogenic and Antioxidant Mechanisms of Estradiol Action in Preovulatory Ovine Follicles: Relevance to Luteal Function1

Staci A. Lunda, Jenifer Murdocha, Edward A. Van Kirka, and William J. Murdoch2,a

a Department of Animal Science, University of Wyoming, Laramie, Wyoming 82071


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The objectives of this investigation were to determine the intrafollicular mechanisms and physiological consequences of estradiol actions in preovulatory ovine follicles. Acute suppression of estradiol production in proestrous ewes by an aromatase inhibitor (Arimidex) was associated with follicular lipid peroxidation, testosterone accumulation, and a granulosa cell deficiency (decreased proliferation/increased apoptosis). Estradiol-17ß stimulated granulosa proliferating cell nuclear antigen (PCNA) and protected cells from oxidative (H2O2) stress-induced apoptosis in vitro; the PCNA, but not the antiapoptotic response, was negated by the transcriptional inhibitor actinomycin D. Thus, it appears that genomic/mitotic and cytoprotective (oxygen-scavenging) modes of estradiol action operate in preovulatory follicles. Luteal (large steroidogenic cell) function was diminished following ovulation induction of estradiol-deficient follicles. It is suggested that inadequate exposure of the preovulatory follicle to estradiol caused the granulosa lutein insufficiency.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Estradiol production during proestrus is an attribute of preovulatory follicles stimulated by tonic secretion of gonadotropins. A reciprocal role for estradiol in the spontaneous feedback induction of the surge release of gonadotropins has been established [1]. How estradiol might act within the local environment to affect the folliculo-luteal transition is uncertain.

Cell numbers within a tissue are dictated by relative rates of division and death. We hypothesized that proliferative and antiapoptotic effects of estradiol in preovulatory follicles are critical determinants of luteal adequacy; differentiated small and large steroidogenic cells of the corpus luteum are derived from the theca interna and membrana granulosa, respectively [2]. Estradiol can alter cellular functions by classical receptor-mediated transcriptional and nongenomic pathways [3, 4]. A novel receptor-independent mechanism of estradiol action is based on its antioxidant properties [5]. Oxidative cellular damage due to estradiol withdrawal is a putative cause of follicular apoptosis and atresia [6, 7].

An initial study was conducted to assess follicular morphology and function in proestrous ewes in which estradiol biosynthesis was attenuated by an aromatase inhibitor. Direct effects of estradiol-17ß on indices of granulosa cell proliferation and oxidative stress-induced apoptosis were then evaluated in vitro. A final experiment was performed to determine luteal outcomes after ovulation of estradiol-deficient follicles.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Experiments were performed with the approval of the University of Wyoming Animal Care and Use Committee. Tissue excisions were made when animals were killed (i.v. Beuthanasia; Schering-Plough Animal Health, Kenilworth, NJ). Reagents were purchased from Sigma Chemical Co. (St. Louis, MO) unless indicated otherwise. The designation "n =" denotes numbers of observations per group.

Experimental Model

Mature western-range ewes were penned with vasectomized rams and observed for estrous behavior. The first day of estrus was considered Day 0. Animals were treated on Day 14 with prostaglandin (PG) F2{alpha} (10 mg i.m. dinoprost tromethamine; Pharmacia and Upjohn Co., Kalamazoo, MI) to synchronize luteal regression. Dominant antral follicles (>= 6 mm diameter) present during proestrus will consistently ovulate approximately 24 h after injection of an agonistic analogue of GnRH (5 µg i.m. des Gly10-Ala6 ethylamide) [8].

Follicular Effects after In Vivo Administration of Arimidex

Ewes were assigned at random to be given Arimidex (anastrozole; 100 mg 2,2'[-5-(IH-1,2,4-triazol-1-ylmethyl)-1,3-phenylene]-bis(2-methylpropiononitrile); Zeneca Pharmaceutical, Wilmington, DE), a specific nonsteroidal aromatase inhibitor used for the treatment of advanced breast cancer [9–11], or injection vehicle (2 ml PBS i.m.) at 12 h post-PGF2{alpha} (n = 5). Blood samples for serum analysis of estradiol-17ß [12] were collected by jugular venipuncture at 0, 12, 24, and 36 h after PGF2{alpha}.

Two preovulatory follicles were dissected from the ovaries of each ewe at 36 h post-PGF2{alpha} and their diameters determined. Fluid was gently aspirated from one follicle of each animal and assayed for concentrations of estradiol-17ß and testosterone [13]; follicular tissues were rinsed in ice-cold isotonic saline, frozen at -70°C, and analyzed for concentrations of malondialdehyde. Second follicles for morphometric analyses (number of theca/granulosa cells, nuclear pyknosis, DNA fragmentation, proliferating cell nuclear antigen) were fixed by immediate immersion in Histochoice (Amresco, Solon, OH), washed in PBS, dehydrated in a graded series of ethanol, cleared in xylene, infiltrated with paraffin, and serially sectioned at 5-µm thickness.

Malondialdehyde (MDA), a stable by-product of polyunsaturated fatty acid peroxide decomposition, was measured as an index of lipid peroxidation [14] in tissue extracts using a commercial diagnostic kit according to the manufacturer's instructions (Bioxytech LPO-586; Oxis International, Portland, OR). Briefly, supernatants of tissue homogenates (20 mM Tris buffer, pH 7.4, containing 5 mM butylated hydroxytoluene), MDA standards (2.5–20 µM 1,1,3,3-tetramethoxypropane), or sample blanks (0.2 ml) were mixed with chromogenic reagent (0.65 ml 10.3 mM N-methyl-2-phenylindole) and HCl (0.15 ml 12 N) for 1 h at 45°C. Chromophore was detected at 586 nm.

Numbers of theca interna and granulosa cells within one randomly selected area of eight different cross sections of follicular wall, stained with hematoxylin and eosin, were counted along a 200-µm length of basement membrane. Cells were classified (without knowledge of treatment) as pyknotic or not.

In situ immunofluorescence detection of internucleosomal DNA fragmentation [15] was used as an index of apoptosis [16]; images of individual theca and granulosa cells within three random fields (x1000) per sample were categorized using computer-assisted analysis (Optimas, Bothell, WA) as positively labeled (> 2 times luminance intensity of control cell background) or not reactive. Briefly, exposed 3'-OH ends of DNA were linked with digoxigenin-11-dUTP by terminal deoxynucleotidyl transferase (TdT) catalysis. Incorporated nucleotide heteropolymers were localized with antidigoxigenin Fab-fluorescein isothiocyanate. Conjugate or TdT was omitted in negative control reactions.

Immunostaining of proliferating cell nuclear antigen (PCNA) was used as a mitogenic marker within theca interna and granulosa; quantifications were made as described for DNA fragmentation analysis. Tissue sections were incubated for 30 min with a PCNA mouse monoclonal antibody (Santa Cruz Biotechnology, Santa Cruz, CA; 2 µg/ml PBS with 1.5% normal goat serum) and washed in three changes of PBS. Immune complexes were detected with a secondary goat anti-mouse IgG-fluorescein isothiocyanate conjugate (F 4143; 1:80, 10 min). Negative control reactions were performed in the absence of primary antibody.

In Vitro Effect of Estradiol on Granulosa PCNA Expression

Preovulatory follicles were isolated at 12 h after PGF2{alpha}, hemisected, and incubated in 1 ml Medium (M)-199 containing 10% fetal calf serum with or without estradiol-17ß (0.1 µg) or the transcriptional inhibitor actinomycin D (0.2 µg) [17] for 8 h at 37°C (n = 6). Granulosa PCNA immunostaining was determined as indicated for the preceding experiment.

In Vitro Effect of Estradiol on Oxidative Stress-Induced Granulosa Apoptosis

Explants of preovulatory follicular wall (12 h post-PGF2{alpha}) were incubated (1 ml M-199 + 10% fetal calf serum; 37°C) in the presence or absence of estradiol-17ß (0.1 µg) ± actinomycin D (0.2 µg) for 2 h, for 30 min ± 100 µM H2O2 [17], and then for 5.5 h (without treatments; n = 5). Granulosa cells were assessed for DNA fragmentation.

Luteal Function Following Treatment with Arimidex during the Early Follicular Phase

Arimidex (100 mg) or injection vehicle was administered to ewes (n = 3) at 12 h after PGF2{alpha}. All animals were treated with GnRH at 36 h. Jugular blood samples for serum hormonal analyses were collected at 0, 12, and 36 h post-PGF2{alpha} (estradiol-17ß); at hourly intervals for 6 h post-GnRH (LH) [18]; and daily thereafter until Day 10 of the luteal phase (progesterone) [19].

On Day 10 corpora lutea were dissected from the ovaries, weighed, and hemisected. Segments of luteal tissues were assayed for progesterone [20] or fixed in Histochoice for light microscopic quantitative analysis (Optimas; % glandular area occupied by granulosa-derived large steroidogenic cells within six randomly selected hematoxylin/eosin-stained paraffin sections/animal; x400).

Statistics

Within-animal subsample data were averaged. Treatment mean comparisons were made by Student's t-test (two-sample: control vs. Arimidex) or ANOVA and protected least-significant difference (multiple contrasts for in vitro experiments). Percentage data were transformed (arcsin) for the purpose of statistical analyses. Hormonal profiles were contrasted using a split-plot procedure [21]. Differences were considered significant at p < 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Follicular Responses to Aromatase Inhibition

The linear increase in circulatory estradiol-17ß concentrations that occurred after injection of PGF2{alpha} (luteal regression) was terminated by treatment with Arimidex at 12 h; serum levels remained very low until follicular collections at 36 h (Fig. 1). No overt side effects of Arimidex were observed.



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  		FIG. 1. Follicular phase jugular serum concentrations of estradiol-17ß in control and Arimidex-treated ewes. Means ± SE are plotted. Treatment contrasts were significantly different at 24 and 36 h.

Follicular diameters were not affected by exposure to Arimidex for the 24-h period preceding tissue collections. Follicular fluid estradiol-17ß and testosterone (aromatase substrate) concentrations were correspondingly lowered and elevated by Arimidex. Lipid peroxidation within follicular tissues was increased after Arimidex. Treatment with Arimidex reduced granulosa cell numbers and PCNA expression and increased the relative percentages of pyknosis and DNA fragmentation. Measures of theca cell functions were not altered by Arimidex (Table 1). There was no evidence of follicular leukocytic infiltration.


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  		TABLE 1. Follicular effects of aromatase inhibition.

Stimulation by Estradiol of Granulosa PCNA Expression

There was an increase in PCNA immunostaining of granulosa cells of follicular shells incubated with estradiol-17ß; the effect was negated by actinomycin D (Fig. 2).



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  		FIG. 2. In vitro effects of estradiol-17ß (E2) and/or actinomycin D (AD) on PCNA immunostaining of granulosa cells. The asterisk indicates a significant increase.

Protection by Estradiol of Oxidative Stress-Induced Granulosa Apoptosis

Fragmentation of DNA within granulosa cells of tissue explants incubated with H2O2 was suppressed by estradiol-17ß. Actinomycin D did not modify the apoptotic response to the peroxidative challenge or its reversal by estradiol-17ß (Fig. 3).



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  		FIG. 3. Protective (nontranscriptional) effect of estradiol-17ß against granulosa DNA fragmentation (apoptosis) evoked by H2O2. An asterisk indicates a significant increase.

Induction by Arimidex of Luteal Dysfunction

The marked inhibitory action of Arimidex administration during proestrus on follicular estradiol output was confirmed (data not shown). There were no differences in preovulatory patterns of GnRH-induced LH release due to treatments (Fig. 4). Jugular serum progesterone concentrations were depressed following exposure to Arimidex (Fig. 5).



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  		FIG. 4. Jugular serum concentrations of LH after injection of GnRH in ewes pretreated or not with Arimidex; patterns were not significantly different.



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  		FIG. 5. Jugular serum progesterone concentrations after ovulation of normal (control) and estradiol-deficient (Arimidex) follicles; mean comparisons were significantly different from Day 5 onward.

Two or three corpora lutea were obtained from each ewe on Day 10; an ovulation papilla at the ovarian apex indicated that follicular rupture had occurred in every instance. Corpora lutea of Arimidex-treated animals were smaller, were deficient in large steroidogenic cells, and contained less progesterone than their control counterparts (Fig. 6). There was no evidence of phagocyte influx into luteal tissues.



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  		FIG. 6. Effects of Arimidex on luteal weights, progesterone concentrations, and large-cell areas; each contrast was significantly different.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Inadequate luteal function (progesterone deficiency) is a cause of pregnancy failure. Luteal disorders that have been associated with infertility include the short-lived corpus luteum and luteal phase insufficiency [22, 23]. A premature luteolytic stimulus is the apparent cause of abbreviated luteal phases. Luteal phase insufficiency is characterized by reduced progesterone production within a cycle of relatively normal duration. A number of theories have been proposed to explain the basis of luteal phase insufficiency: defective follicular cell maturation, a suboptimal preovulatory gonadotropin surge, and/or diminished luteotropic support.

Granulosa cells are the progenitors of large lutein cells, the principal source of circulatory progesterone [2, 24]. Results of this investigation indicate that attenuation of estradiol production by preovulatory ovine follicles compromises the succession of granulosa cell proliferative and antiapoptotic events that necessitate the formation of a fully competent corpus luteum. A similar (granulosa lutein) defect was observed after induction of ovulation during the early follicular phase of ewes [25]. Follicular rupture was apparently not averted by a shortage of granulosa cells (a presumptive resource of biochemical ovulatory mediators) [26] or by an atretogenic milieu (e.g., elevated testosterone:estradiol ratio and apoptosis) [6]. The incidence of short-lived corpora lutea in postpartum cows was reduced by estradiol pretreatment [27]. Benoit et al. [28] reported that inhibition in ewes of preovulatory estradiol production with the aromatase inhibitor CGS16949A delayed the onset of luteinization but did not significantly alter subsequent circulatory profiles of progesterone.

That granulosa cell mitosis is up-regulated by estradiol is well established [29–33]. A potent antioxidant effect of estradiol-17ß (e.g., exceeding that of {alpha}-tocopherol) has only recently been realized. Reactive oxygen molecules such as H2O2, hydroxyl radicals, and superoxide anions generated during normal metabolic reactions, if not sufficiently neutralized, pose a serious threat to cellular viability [34, 35]; the transduction pathways that link toxic oxidant accumulation to apoptosis include peroxidative perturbations in membrane phospholipid dynamics, cytosolic calcium accretion, microskeletal disruption, DNA damage, and endonuclease activation [36–38]. The seminal observation that estradiol-17ß safeguarded neurons from oxidant death [39] has stimulated an interest in the potential therapeutic benefits of estrogens in the management of dementia associated with the postmenopause and Alzheimer's disease [40]. Furthermore, estradiol is a candidate inhibitor of endothelial cell apoptosis and atherosclerosis [41]. A recent study indicated that estradiol-17ß protected porcine follicular and luteal cells against an H2O2 insult primarily by a nongenomic receptor-independent mechanism [17]. Estradiol-17ß can serve directly (at high concentrations) as an oxidant scavenger [5] or as an activator of antiapoptotic (e.g., bcl-2) gene products [42].

Although estradiol enhances pituitary sensitivity to GnRH [1], preovulatory surges in secretion of LH were not affected by treatment with Arimidex; perhaps this was related to use of a potent GnRH agonist, and/or a brief exposure to estradiol upon luteal regression was sufficient to prime a full surge. Therefore, the reduction in glandular function during the consequent luteal phase was not due to diminutive preovulatory follicular gonadotropic stimulation. It also seems unlikely that a lack of postovulatory luteotropin was rate limiting to progesterone production. Indeed, small (LH responsive) theca lutein cells [2, 24] were evidently carrying the functional load of the luteal gland (i.e., complete collapse would otherwise have been expected). Apparently, theca cells of preovulatory follicles are comparatively resistant to an abrupt estradiol depletion; constitutive defenses to oxidative injury can be imparted by endogenous antioxidant enzymes (glutathione peroxidase, superoxide dismutase, catalase) [43] or efficient DNA repair processes [44, 45].

Divergent intrafollicular transcriptional/mitogenic and antioxidant roles of estradiol that influence granulosa lutein function have been defined. An understanding of the temporal cellular and hormonal interactions regulating the folliculo-luteal transformation is relevant to the design of ovulatory protocols that assure assisted reproductive success. Finally, our results lend indirect credence to the concept that antioxidants can enhance fertility [46].


   FOOTNOTES
 
1 Supported by USDA-NRI grant 9702434. Back

2 Correspondence: W.J. Murdoch, Department of Animal Science, P.O. Box 3684, 16th and Gibbon St., University of Wyoming, Laramie, WY 82071. FAX: 307 766 2355; wmurdoch{at}uwyo.edu Back

Accepted: March 11, 1999.

Received: December 23, 1998.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Karsch FJ, Moenter SM, Caraty A. The neuroendocrine signal for ovulation. Anim Reprod Sci 1992; 28:329–341.[CrossRef]
  2. Smith MF, McIntush EW, Smith GW. Mechanisms associated with corpus luteum development. J Anim Sci 1994; 72:1857–1872.[Abstract]
  3. Truss M, Beato M. Steroid hormone receptors: interaction with deoxyribonucleic acid and transcription factors. Endocr Rev 1993; 14:459–479.[Abstract/Free Full Text]
  4. Revelli A, Massobrio M, Tesarik J. Nongenomic actions of steroid hormones in reproductive tissues. Endocr Rev 1998; 19:3–17.[Abstract/Free Full Text]
  5. Mooradian AD. Antioxidant properties of steroids. J Steroid Biochem Mol Biol 1993; 45:509–511.[CrossRef][Medline]
  6. Kaipia A, Hsueh AJW. Regulation of ovarian follicle atresia. Annu Rev Physiol 1997; 59:349–363.[CrossRef][Medline]
  7. Martimbeau S, Tilly JL. Physiological cell death in endocrine-dependent tissues: an ovarian perspective. Clin Endocrinol 1997; 46:241–254.[CrossRef][Medline]
  8. Roberts AJ, Dunn TG, Murdoch WJ. Induction of ovulation in proestrous ewes: identification of the ovulatory follicle and functional status of the corpus luteum. Domest Anim Endocrinol 1985; 2:207–210.
  9. Dukes M, Edwards PN, Large M, Smith IK, Boyle T. The preclinical pharmacology of Arimidex (anastrozole; ZD 1033)—a potent, selective aromatase inhibitor. J Steroid Biochem Mol Biol 1996; 58:439–445.[CrossRef][Medline]
  10. Geisler J, King N, Dowsett M, Ottestad L, Lundgren S, Walton P, Kormeset PO, Lonning PE. Influence of anastrozole (Arimidex), a selective, non-steroidal aromatase inhibitor, on in vivo aromatization and plasma oestrogen levels in postmenopausal women with breast cancer. Br J Cancer 1996; 74:1286–1291.[Medline]
  11. Buzdar AU, Jonat W, Howell A, Plourde PV. Arimidex: a potent and selective aromatase inhibitor for the treatment of advanced breast cancer. J Steroid Biochem Mol Biol 1997; 61:145–149.[CrossRef][Medline]
  12. Field RA, Maiorano G, Hinds FC, Murdoch WJ, Riley ML. Bone ossification and carcass characteristics of wethers given silastic implants containing estradiol. J Anim Sci 1990; 68:3663–3668.[Abstract]
  13. Murdoch WJ, Dunn TG. Alterations in follicular steroid hormones during the preovulatory period in the ewe. Biol Reprod 1982; 27:300–307.[Abstract]
  14. Janero DR. Malondialdehyde and thiobarbituric acid-reactivity as diagnostic indices of lipid peroxidation and peroxidative tissue injury. Free Radical Biol Med 1990; 9:515–540.[CrossRef][Medline]
  15. Murdoch WJ. Programmed cell death in preovulatory ovine follicles. Biol Reprod 1995; 53:8–12.[Abstract]
  16. Allen RT, Hunter WJ, Agrawal DK. Morphological and biochemical characterization and analysis of apoptosis. J Pharmacol Toxicol Methods 1997; 37:215–228.[CrossRef][Medline]
  17. Murdoch WJ. Inhibition by oestradiol of oxidative stress-induced apoptosis in pig ovarian tissues. J Reprod Fertil 1998; 114:127–130.[Abstract/Free Full Text]
  18. Alexander BA, Murdoch WJ, Hallford DM, Moss GE. Seasonal effects of antihistamine on mean serum concentrations of luteinizing hormone, growth hormone and prolactin in ovariectomized ewes. Anim Reprod Sci 1994; 37:15–24.
  19. Eggleston DL, Wilken C, Van Kirk EA, Slaughter RG, Ji TH, Murdoch WJ. Progesterone induces expression of endometrial messenger RNA encoding for cyclooxygenase. Prostaglandins 1990; 39:675–683.[CrossRef][Medline]
  20. McPherson LA, Van Kirk EA, Murdoch WJ. Localization of stress protein-70 in ovine corpora lutea during prostaglandin-induced luteolysis. Prostaglandins 1993; 46:433–440.[CrossRef][Medline]
  21. Gill JL, Hafs HD. Analysis of repeated measurements of animals. J Anim Sci 1971; 33:331–336.
  22. Garverick HA, Smith MF. Mechanisms associated with subnormal luteal function. J Anim Sci Suppl 1986; 62:92–105.
  23. Fritz MA. Inadequate luteal function and recurrent abortion: diagnosis and treatment of luteal deficiency. Semin Reprod Endocrinol 1988; 6:129–144.
  24. Niswender GD, Juengel JL, McGuire WJ, Belfiore CJ, Wiltbank MC. Luteal function: the estrous cycle and early pregnancy. Biol Reprod 1994; 50:239–247.[Abstract]
  25. Murdoch WJ, Van Kirk EA. Luteal dysfunction in ewes induced to ovulate early in the follicular phase. Endocrinology 1998; 139:3480–3484.[Abstract/Free Full Text]
  26. Murdoch WJ, Cavender JL. Mechanisms of ovulation. Adv Contracept Delivery Syst 1987; 3:353–366.
  27. Day ML, Dyer RM, Wilson GW, Pope WF. Influence of estradiol on duration of anestrus and incidence of short estrous cycles in postpartum cows. Domest Anim Endocrinol 1990; 7:19–25.[CrossRef][Medline]
  28. Benoit AM, Inskeep EK, Dailey RA. Effect of a nonsteroidal aromatase inhibitor on in vitro and in vivo secretion of estradiol and on the estrous cycle in ewes. Domest Anim Endocrinol 1992; 9:313–327.[CrossRef][Medline]
  29. Erickson GF. An analysis of follicle development and ovum maturation. Semin Reprod Endocrinol 1986; 4:233–254.[CrossRef]
  30. Taymor ML. The regulation of follicle growth: some clinical implications in reproductive endocrinology. Fertil Steril 1996; 65:235–247.[Medline]
  31. Gaytan F, Bellido C, Morales C, Aguilar E, Sanchez-Criado JE. Proliferative activity of preovulatory follicles and newly formed corpora lutea in cycling rats from late proestrus to early oestrus. J Anat 1997; 191:425–430.
  32. Pointkewitz Y, Sundfeldt K, Hedin L. The expression of c-myc during follicular growth and luteal formation in the rat ovary in vivo. J Endocrinol 1997; 152:395–406.[Abstract/Free Full Text]
  33. Uilenbroek JTJ, Kramer P, Karels B, deJong FH. Significance of oestradiol for follicular development in hypogonadotrophic immature rats treated with FSH and hCG. J Reprod Fertil 1997; 110:231–236.[Abstract/Free Full Text]
  34. Buttke TM, Sandstrom PA. Oxidative stress as a mediator of apoptosis. Immunol Today 1994; 15:7–10.[CrossRef][Medline]
  35. Clutton S. The importance of oxidative stress in apoptosis. Br Med Bull 1997; 53:662–668.[Abstract/Free Full Text]
  36. Staler TF. Free radical mechanisms in tissue injury. Biochem J 1984; 222:1–15.[Medline]
  37. Horton AA, Fairhurst S. Lipid peroxidation and mechanisms of toxicity. Crit Rev Toxicol 1987; 18:27–79.[Medline]
  38. McConkey DJ, Orrenius S. Signal transduction pathways in apoptosis. Stem Cells 1996; 14:619–631.[Abstract]
  39. Behl C, Widmann M, Trapp T, Holsboer F. 17-ß Estradiol protects neurons from oxidative stress-induced cell death in vitro. Biochem Biophys Res Commun 1995; 216:473–482.[CrossRef][Medline]
  40. Henderson VW. The epidemiology of estrogen replacement therapy and Alzheimer's disease. Neurol Suppl 1997; 48:S27-S35.
  41. Spyridopoulos I, Sullivan AB, Kearney M, Isner JM, Losordo DW. Estrogen-mediated inhibition of human endothelial cell apoptosis: estradiol as a survival factor. Circulation 1997; 95:1505–1514.[Abstract/Free Full Text]
  42. Garcia-Segura LM, Cardona-Gomez P, Naftolin F, Chowen JA. Estradiol up-regulates Bcl-2 expression in adult brain neurons. Neuroreport 1998; 9:593–597.[Medline]
  43. Sagara Y, Dargusch R, Chambers D, Davis J, Schubert D, Maher P. Cellular mechanisms of resistance to chronic oxidative stress. Free Radical Biol Med 1998; 24:1375–1389.[CrossRef][Medline]
  44. Cristovao L, Rueff J. Effect of a poly(ADP-ribose) polymerase inhibitor on DNA breakage and cytotoxicity induced by hydrogen peroxide and {gamma}-radiation. Teratog Carcinog Mutagen 1996; 16:219–227.[CrossRef][Medline]
  45. Collins AR, Duthie SJ, Fillion L, Gedik CM, Vaughn N, Wood SG. Oxidative DNA damage in human cells: the influence of antioxidants and DNA repair. Biochem Soc Trans 1997; 25:326–331.[Medline]
  46. Tarin JJ, Brines J, Cano A. Antioxidants may protect against infertility. Hum Reprod 1998; 13:1415–1416.[Free Full Text]



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