Caco-2 cell disaccharidase activities are unaffected by gestational hormones

We previously reported that lactose handling was significantly improved during late-phase pregnancy in women with a genetically determined adult-type hypolactasia. However, the adaptive mechanisms underlying the enhanced lactose digestion during pregnancy are not clear. Progesterone therapy has been associated in animals with increased intestinal lactase activity. To investigate the potential role of progesterone and estrogen as modulators of human lactase activity during pregnancy, we employed the human-derived intestinal epithelial Caco-2 cell line. Measurements of lactase and sucrase activities were performed in parallel with DNA content in progesterone- and estrogen-treated cells after 5, 10, and 30 days of confluency. Caco-2 monolayer DNA content was observed to increase with duration of culture to an equivalent extent in both hormone-treated and control cultures. Lactase and sucrase activities were similarly unaltered by incubation with either progesterone or estrogen, at any time point tested. These data demonstrate that gestational hormones do not influence intestinal cell number nor disaccharidase activity in Caco-2 cells, at the doses tested. Although these studies were carried out in a malignant cell line, our data suggest that the improved lactose handling observed during pregnancy is probably related to prolonged intestinal transit.

Endocrine modulators of necrotic neuron death

In recent years, there has been extraordinary progress in understanding the cellular and molecular cascades that mediate neuron death following necrotic insults. With this knowledge has come the recognition of ways in which these cascades can be modulated by extrinsic factors, altering the likelihood of subsequent neuron death. In this review, we consider the ability of a variety of hormones to modulate necrotic death cascades. Specifically, we will examine the ability of the stress hormones glucocorticoids and corticotropin-releasing factor, of thyroid hormone, and of pre-ischemic exposure to catecholamines to augment necrotic neuron death. In contrast, estrogen, insulin and postischemic exposure to catecholamines appear to decrease necrotic neuron death. We review the heterogeneous mechanisms that are likely to mediate these hormone effects, some possible clinical implications and the therapeutic potentials of these findings.

Androgen receptor gene expression in rat granulosa cells: the role of follicle-stimulating hormone and steroid hormones

In rat ovary, androgen receptor (AR) is predominantly expressed in granulosa cells and is developmentally regulated. However, the exact mechanism that is responsible for the regulation of AR in granulosa cells has not been elucidated. The aim of this study was to examine 1) the levels of AR messenger RNA (mRNA) expression in granulosa cells from follicles of different size and 2) the effects of FSH, 8-bromo-cAMP, androgen, and estrogen on AR mRNA levels in granulosa cells in vitro. The abundance of AR mRNA was examined by ribonuclease protection assay using 32P-labeled AR complementary RNA probe and related to that of P450aromatase (P450arom) mRNA, a well established maker of granulosa cell differentiation. In large follicles (> 400 microns in diameter), the abundance of AR mRNA was decreased to 51% of that in small follicles (< 200 microns; P < 0.01), whereas the abundance of P450arom mRNA increased to 277% (P < 0.01). In medium follicles (200-400 microns), the abundance of AR mRNA was maintained (101%), whereas the abundance of P450arom mRNA increased to 202% of that in small follicles (P < 0.05). Treatment with FSH (0-300 ng/ml) or 8-bromo-cAMP (0-4 mM) induced P450arom mRNA in the cultured granulosa cells in a dose-dependent manner; however, it did not affect the levels of AR mRNA expression. Treatment with 5 alpha-dihydrotestosterone (1 microM) resulted in a significant reduction in the abundance of AR mRNA to 67% of the control value (P < 0.05). This effect was reversed by the addition of FSH (100 ng/ml; P < 0.01). Treatment with diethylstilbestrol (1 microM), alone or in combination with FSH (100 ng/ml), did not have any significant effect, although these treatments tended to decrease the abundance of AR mRNA to 81% and 85%, respectively. Both 5 alpha-dihydrotestosterone and diethylstilbestrol dramatically enhanced the abundance of FSH-induced P450arom mRNA compared to the effect of FSH alone. These results indicate that 1) the down-regulation of AR mRNA expression takes place in granulosa cells of preovulatory follicles; 2) FSH is not directly responsible for this event; and 3) androgen down-regulates AR mRNA expression in immature granulosa cells, and this effect is reversed by FSH. We conclude that androgen and FSH jointly regulate AR mRNA expression in rat granulosa cells.

Different regions in activation function-1 of the human estrogen receptor required for antiestrogen- and estradiol-dependent transcription activation

The human estrogen receptor (ER) is a ligand-inducible transcription factor that contains two transcriptional activation functions, one located in the NH2-terminal region of the protein (AF-1) and the second in the COOH-terminal region (AF-2). Antiestrogens, such as trans-hydroxytamoxifen (TOT), have partial agonistic activity in certain cell types, and studies have implied that this agonism is AF-1-dependent. We have made progressive NH2-terminal and other segment deletions and ligations in the A/B domain, and studied the transcriptional activity of these mutant ERs in ER-negative MDA-MB-231 human breast cancer and HEC-1 human endometrial cancer cells. Using several estrogens and several partial agonist/antagonist antiestrogens, we find that estrogens and antiestrogens require different regions of AF-1 for transcriptional activation. Deletion of the first 40 amino acids has no effect on receptor activity. Antiestrogen agonism is lost upon deletion to amino acid 87, while estrogen agonism is not lost until deletions progress to amino acid 109. Antiestrogen agonism has been further defined to require amino acids 41-64, as deletion of only these amino acids results in an ER that exhibits 100% activity with E2, but no longer shows an agonist response to TOT. With A/B-modified receptors in which antiestrogens lose their agonistic activity, the antiestrogens then function as pure estrogen antagonists. Our studies show that in these cellular contexts, hormone-dependent transcription utilizes a range of the amino acid sequence within the A/B domain. Furthermore, the agonist/antagonist balance and activity of antiestrogens such as TOT are determined by specific sequences within the A/B domain and thus may be influenced by differences in levels of specific factors that interact with these regions of the ER.

Deregulated expression of c-myc in megakaryocytes of transgenic mice increases megakaryopoiesis and decreases polyploidization

Platelets, essential for vascular integrity and hemostasis, fragment from polyploid megakaryocytes, characterized by their endomitotic cell cycle. We studied the influence of overexpression of c-myc oncogene on megakaryopoiesis and endomitosis in vivo, using transgenic mice carrying c-myc fused to the estrogen receptor under the control of the platelet factor 4 (PF4) megakaryocyte-specific promoter. The rationale behind this strategy was to obtain controlled overexpression of an active c-Myc, depending on the estrogen level in the mouse circulation. Analysis of these transgenic mice revealed that the bone marrow of female transgenic mice or of estrogen-injected male transgenic mice, but not of age-matched transgenic males nor nontransgenic females, contained frequent immature myeloid cells and an increased number of megakaryocytes. Deregulated expression of c-Myc shifted the normal ploidy profile of megakaryocytes due to a significant increase in proliferating megakaryocytes and a decrease in the fraction of ploidizing cells. These transgenic mice represent a novel in vivo model for a Myc-induced myeloproliferative disorder which can be controlled.

Hormonal regulation of PKC-delta protein and mRNA levels in the rabbit corpus luteum

We have previously reported that rabbit corpora lutea exhibit a prominent phosphorylated substrate protein at 76 kDa which corresponds to the autophosphorylated form of protein kinase C (PKC) delta and that the expression of PKC-delta protein is increased in rabbit corpora lutea of pseudopregnancy at least 2-fold when serum estrogen levels are raised by the presence of an estrogen implant inserted at the time of human chorionic gonadotropin (hCG)-induced ovulation. The purpose of the experiments described herein was to evaluate further the hormonal regulation of PKC-delta in the rabbit corpus luteum. Results demonstrate that luteal PKC-delta protein and mRNA are concomitantly induced some 5-fold within 48 h in response to an ovulatory surge of hCG; that, as in corpora lutea of pseudopregnancy, luteal PKC-delta expression is relatively constant during the life span of the corpus luteum following a fertile mating; that exogenous estrogen does not modulate the induction of luteal PKC-delta during luteinization but promotes an additional two-fold increase in steady state PKC-delta mRNA (and protein) levels in corpora lutea by day 10 of pseudopregnancy; and that luteal PKC-delta expression can be abruptly and reversibly modulated upon withdrawal and subsequent replacement of an estrogen implant to pseudopregnant rabbits. These results demonstrate that an ovulatory surge of luteinizing hormone induces the expression of PKC-delta mRNA and protein in rabbit corpora lutea, and that once the corpus luteum becomes estrogen responsive, estrogen then regulates expression of PKC-delta mRNA and protein.

c-myc activation renders proliferation of Epstein-Barr virus (EBV)-transformed cells independent of EBV nuclear antigen 2 and latent membrane protein 1

Two genetic events contribute to the development of endemic Burkitt lymphoma (BL) infection of B lymphocytes with Epstein-Barr virus (EBV) and the activation of the protooncogene c-myc through chromosomal translocation. The viral genes EBV nuclear antigen 2 (EBNA2) and latent membrane protein 1 (LMP1) are essential for transformation of primary human B cells by EBV in vitro; however, these genes are not expressed in BL cells in vivo. To address the question whether c-myc activation might abrogate the requirement of the EBNA2 and LMP1 function, we have introduced an activated c-myc gene into an EBV-transformed cell line in which EBNA2 was rendered estrogen-dependent through fusion with the hormone binding domain of the estrogen receptor. The c-myc gene was placed under the control of regulatory elements of the immunoglobulin kappa locus composed a matrix attachment region, the intron enhancer, and the 3' enhancer. We show here that transfection of a c-myc expression plasmid followed by selection for high MYC expression is capable of inducing continuous proliferation of these cells in the absence of functional EBNA2 and LMP1. c-myc-induced hormone-independent proliferation was associated with a dramatic change in the growth behavior as well as cell surface marker expression of these cells. The typical lymphoblastoid morphology and phenotype of EBV-transformed cells completely changed into that of BL cells in vivo. We conclude that the phenotype of BL cells reflects the expression pattern of viral and cellular genes rather than its germinal center origin.

Anatomical distribution of NADPH-cytochrome P450 reductase and cytochrome P4502D forms in rat brain: effects of xenobiotics and sex steroids

Since the brain is not a homogeneous organ, but one dependent upon the well orchestrated interaction of numerous parts, pathology in one nucleus may have a large impact upon its overall function. Hence, the anatomical distribution of the P450 monoxygenase system in brain, as well as the regulation of its expression, is important in elucidating its function in that organ. In order to study these issues, female rats-both ovariectomized and not-were treated with a number of xenobiotic compounds and sex steroids. The brains from these animals were dissected into 8 discrete regions and the presence and relative level of message for P4502D and P450 reductase determined using polymerase chain reaction. Results of this investigation indicate the presence of mRNA for reductase and P4502D isoforms throughout the rat brain. In addition, quantitative PCR was utilized to demonstrate the effects of xenobiotics (phenobarbital, beta-naphthoflavone, imipramine) and sex hormones (testosterone, estrogen) on the levels of these messages in the female rat brain. Significant induction of message for P4502D forms was noted with testosterone in the absence of estrogen. The level of mRNA for reductase was not significantly influenced by any of the treatments, however. These results raise the issue of a sexual dimorphism in the rat regarding P4502D expression in brain.

Influence of thrombin on proliferation and prostaglandin production in cultured bovine endometrial cells

The control of cell proliferation by thrombin was studied in vitro in cultured epithelial and stromal cells of the endometrium. The effect of thrombin was studied after chronic treatment (72 hr) in medium containing 10% fetal bovine serum (FBS) combined or not with sex steroids. Thrombin inhibited slightly the proliferation (based on DNA measurements) only in epithelial cells (P < 0.05). 17 beta-estradiol (E) and progesterone (P4) had no mitogenic effects. The presence of functional thrombin receptors was estimated by stimulation of second messenger generation in response to increasing doses of thrombin (0-1,500 ng/ml). In confluent cultures of epithelial cells, the addition of thrombin for 10 min stimulated cAMP production by 50% with a maximal response at 500 ng/ml (P < 0.05). Similarly, in stromal cells, thrombin stimulated cAMP production in a dose-dependent manner (P < 0.01). Generation of inositol-phosphates was also stimulated by 50% in epithelial cells (P < 0.03), with a maximal response at 500 ng/ml, and by 45% in stromal cells (P < 0.01), with a maximal response at 50 ng/ml. The effect of thrombin on cell proliferation was investigated by 3H-thymidine incorporation in serum-free medium for 24 hr. Thrombin inhibited incorporation in epithelial cells (P < 0.0001) in a dose-dependent manner. Conversely, thrombin stimulated significantly incorporation of stromal cells (P < 0.05) at 50 ng/ml. The effect of sex steroids was also evaluated and it was found that E had no effect on cell proliferation, while P4 inhibited the incorporation in both epithelial (P < 0.001) and stromal cells (P < 0.001). The effect of a combined treatment with thrombin and E inhibited both epithelial (P < 0.001) and stromal cell (P < 0.001) growth, but a combination of thrombin and P4 had no additional effect on growth compared to P4 alone. Further investigation of the role of thrombin has been carried out by measuring prostaglandin (PG) responses. Addition of thrombin for 24 hr inhibited PGF2 alpha production by epithelial cells (P < 0.0001) but had no effect on PGE2 production by stromal cells. Therefore, functional receptors for thrombin appear to be present in epithelial and stromal cells of the bovine endometrium. The minimal effect of thrombin alone or in combination with sex steroids on endometrial cell proliferation in vitro combined with the evidence of functional thrombin receptor in these cells, suggest that: (1) the effect of sex steroids in cultured endometrial cells is not modulated by the presence of thrombin, and (2) other factors are necessary for the full expression of mitogenic responses to sex steroids in vitro.

Inducible gene expression by retrovirus-mediated transfer of a modified tetracycline-regulated system

The ability to regulate gene expression via exogenous stimuli will facilitate the study of gene functions in mammalian cells. In the present study, we modified the tetracycline-controlled inducible system by the addition of the ligand-binding domain of the estrogen receptor to the carboxy terminus of the tTA transactivator. A single retroviral vector can transduce both the transactivator gene and the gene of interest controlled by the tTA-inducible promoter into mammalian cells. We show that cell lines expressing the transactivator can readily be established and that expression of the gene of interest depends on the removal of tetracycline and the addition of estrogen. By using this system, cell lines with inducible expression of the G protein of vesicular stomatitis virus, a potentially toxic gene product, were established. The combination of a powerful inducible system and retrovirus-mediated gene transfer can not only be used to study gene function but may also be applied in the future to clinical trials in human gene therapy.

Influence of thrombin on proliferation and prostaglandin production in cultured bovine endometrial cells

The control of cell proliferation by thrombin was studied in vitro in cultured epithelial and stromal cells of the endometrium. The effect of thrombin was studied after chronic treatment (72 hr) in medium containing 10% fetal bovine serum (FBS) combined or not with sex steroids. Thrombin inhibited slightly the proliferation (based on DNA measurements) only in epithelial cells (P < 0.05). 17 beta-estradiol (E) and progesterone (P4) had no mitogenic effects. The presence of functional thrombin receptors was estimated by stimulation of second messenger generation in response to increasing doses of thrombin (0-1,500 ng/ml). In confluent cultures of epithelial cells, the addition of thrombin for 10 min stimulated cAMP production by 50% with a maximal response at 500 ng/ml (P < 0.05). Similarly, in stromal cells, thrombin stimulated cAMP production in a dose-dependent manner (P < 0.01). Generation of inositol-phosphates was also stimulated by 50% in epithelial cells (P < 0.03), with a maximal response at 500 ng/ml, and by 45% in stromal cells (P < 0.01), with a maximal response at 50 ng/ml. The effect of thrombin on cell proliferation was investigated by 3H-thymidine incorporation in serum-free medium for 24 hr. Thrombin inhibited incorporation in epithelial cells (P < 0.0001) in a dose-dependent manner. Conversely, thrombin stimulated significantly incorporation of stromal cells (P < 0.05) at 50 ng/ml. The effect of sex steroids was also evaluated and it was found that E had no effect on cell proliferation, while P4 inhibited the incorporation in both epithelial (P < 0.001) and stromal cells (P < 0.001). The effect of a combined treatment with thrombin and E inhibited both epithelial (P < 0.001) and stromal cell (P < 0.001) growth, but a combination of thrombin and P4 had no additional effect on growth compared to P4 alone. Further investigation of the role of thrombin has been carried out by measuring prostaglandin (PG) responses. Addition of thrombin for 24 hr inhibited PGF2 alpha production by epithelial cells (P < 0.0001) but had no effect on PGE2 production by stromal cells. Therefore, functional receptors for thrombin appear to be present in epithelial and stromal cells of the bovine endometrium. The minimal effect of thrombin alone or in combination with sex steroids on endometrial cell proliferation in vitro combined with the evidence of functional thrombin receptor in these cells, suggest that: (1) the effect of sex steroids in cultured endometrial cells is not modulated by the presence of thrombin, and (2) other factors are necessary for the full expression of mitogenic responses to sex steroids in vitro.

Hypothalamic obese, functionally castrated hens are hypersensitive to estrogenic modulation of lipid metabolism

Estradiol benzoate (E2) increases plasma lipids in hypothalamic obese, functionally castrated (OFC), obese laying (OL), and control laying hens (CONT). However, E2 reduces fattiness in OFC but not in OL or CONT hens. Antiestrogen, such as tamoxifen (TAM), reduces plasma lipids in OL and CONT, but not in OFC, hens and has no effect on fattiness in any of them. Apolipoprotein VLDL-II (apo-VLDL-II), lipoprotein lipase (LPL), and rate of lipolysis may mediate these estrogenic effects. In the present study, effects of E2 and TAM on fattiness, plasma apo-VLDL-II, in vitro lipolysis, and LPL activity in postheparin plasma and abdominal adipose tissue (AAT) were determined in OFC, OL, and CONT hens. Basomedial hypothalamic lesions were performed in 3-month-old White Leghorn hens. At the static phase, 10 months later, OFC OL, and CONT hens were divided into three subgroups and injected IM on alternate days, with either 2 mg E2/kg b.wt., 10 mg TAM/kg, or vehicle corn oil, for 5 weeks. In OL and OFC hens, body and AAT weights were higher than in CONT poullets. Food intake and ovarian weight were similar in OL and CONT, higher than in OFC hens. Plasma LPL activity was higher, whereas plasma apo-VLDL-II and stimulated lipolysis were lower in OFC than in OL and CONT hens. In OFC hens LPL activity per unit of AAT was half than in OL and CONT. Total LPL activity in AAT was similar in OFC and CONT and higher in OL hens. Levels of basal lipolysis were similar in all experimental hens. TAM did not affect any of the measured parameters in OFC hens. In OL and CONT hens, TAM depressed apo-VLDL-II, increased plasma LPL activity, but had no effects on AAT LPL activity, on stimulated lipolysis, or fattiness. E2 increased apo-VLDL-II to similar levels in all groups and reduced LPL activity in plasma and AAT of obese hens. Only in OFC hens did E2 enhance basal and stimulate lipolysis and reduce FI and fattiness. We conclude that in adult laying hens, unlike in cockerels and juvenile hens, estrogen reduces lipid incorporation in fat depots by enhancing apo-VLDL-II production that reduces plasma and AAT LPL activity. This may increase lipoprotein available for incorporation into developing yolks. The lack of estrogen in OFC hens reduces circulating apo-VLDL-II and thus increases LPL activity and amount of fat depots.

Hormone replacement therapy modifies the capacity of plasma and serum to regulate prostacyclin and endothelin-1 production in human vascular endothelial cells

OBJECTIVE

To determine if hormone replacement therapy (HRT) modifies the ability of plasma or serum to regulate the synthesis of vasodilatory prostacyclin and that of vasoconstrictive endothelin-1 by cultured human umbilical vein endothelial cells.

DESIGN

Plasma and serum collected before and during the sixth treatment cycle of HRT from 13 healthy postmenopausal women were added to cultured endothelial cells.

SETTING

Helsinki University Central Hospital, Department of Obstetrics and Gynecology, Helsinki, Finland.

PATIENTS

Thirteen postmenopausal women (> or = 1 year since their last menstruation, FSH level > 40 mIU/mL [conversion factor to SI unit, 1.00], clear vasomotor symptoms) that suffered from incapacitating menopausal symptoms necessitating the initiation of HRT were studied.

INTERVENTIONS

A combined regimen consisting of 2 mg oral E2 for 12 days followed by 2.0 mg oral E2 + 1.0 mg norethisterone acetate for 10 days and 1.0 mg E2 for 6 days.

MAIN OUTCOME MEASURES

The releases of prostacyclin, as assessed by its metabolite 6-keto-prostaglandin F1 alpha, and that of endothelin-1 by cultured human umbilical vein endothelial cells in the presence of 10% plasma or 10% serum collected from the study subjects.

RESULTS

Hormone replacement therapy enhanced the ability of plasma to stimulate prostacyclin production by 21% +/- 6% (mean +/- SEM) during the E2 + norethisterone acetate phase and tended to do so also during the E2-only phase (11% +/- 10%) but caused no change in endothelin-1 release. In contrast, HRT decreased the ability of serum to stimulate prostacyclin production by 12% +/- 5% during the E2-only phase and increased that of endothelin-1 by 8% +/- 4% during the E2 + norethisterone acetate phase.

CONCLUSION

Because plasma flushes endothelial cells in vivo, our data on the HRT-induced stimulation of the capacity of plasma to enhance the production of vasoprotective prostacyclin without a concomitant change in endothelin-1 release in cultured human umbilical vein endothelial cells may provide one new explanation for the cardiovascular protection of HRT.

The menopause and the cardiovascular system

Combining the wealth of epidemiological, metabolic and recent mechanistic data, it would appear biologically plausible that HRT, either oestrogen alone or in combination with progestogen, is cardioprotective. Further research is required, as information is lacking on cardiovascular effects of HRT instigated at an older age. There is a need to identify cardiovascular benefit, indirect and/or direct, of combined oestrogen/progestogen therapy using randomized trials. The various progestogen types and doses also need to be investigated. Studies are also required to investigate the effect of HRT use in higher risk patients with established CVD. There is scant information on the effect of HRT on blood pressure of patients with hypertension. Cardiovascular risk factor profiles and incidence surveys need to be conducted in developing countries to characterize their female population and to identify the prevalence of CVD; this needs to be undertaken before widespread recommendations on CVD prevention and the role of HRT can be made. If HRT is to be used effectively in the future treatment of heart disease in women these questions need to be addressed. At present HRT is indicated for the relief of menopausal symptoms and the prevention of osteoporosis. In women without these indications, ORT may be recommended in those who have had a premature menopause, and possibly in those who have established CHD or who are at high risk of developing CHD. It is too early to suggest a blanket recommendation for the use of HRT in the treatment of the symptoms of women with established CVD, but HRT after the menopause may at least be safely used in the secondary prevention of CHD.

Endometrial thickness is predictive of histologic endometrial maturation in women undergoing hormone replacement for ovum donation

OBJECTIVE

To determine if ultrasonographic endometrial pattern or thickness is predictive of histologic endometrial maturation in women undergoing hormone replacement for ovum donation.

DESIGN

Ultrasonographic endometrial thickness and pattern were determined and compared with histologic assessment of endometrial maturation.

PATIENTS

Forty-six women underwent 52 preparatory cycles for ovum donation. Transvaginal ultrasound (US) was performed after 14 days of E2 replacement and, after 12 days of P, an endometrial biopsy was performed. In 12 cycles, a continuous dose of 2 mg/d E2 was administered. In cycles with out-of-phase biopsies (dated earlier than day 24) and in the last 34 cycles, all women received an escalating dose of E2 before initiation of P. Additionally, the 46 women underwent 55 ETs with USs performed on cycle day 15.

RESULTS

Six women had abnormal biopsies in their first preparatory cycle on the continuous E2 protocol, which normalized with the escalating protocol. All other women had normal biopsies. Women with abnormal biopsies had significantly thinner endometrium (< or = 6 mm) but similar endometrial patterns compared with women with normal biopsies. In women having US in preparatory and transfer cycles, there were no differences in endometrial thickness or pattern between examinations.

CONCLUSIONS

Endometrial thickness > or = 7 mm in hormone replacement cycles predicts in phase endometrial histology and can replace the endometrial biopsy.

The menopause and the skeleton: key issues

There is a persuasive rationale for the use of HRT at the time of the menopause, but there are a number of factors which limit its widespread application for osteoporosis. These relate partly to the long-term efficacy of HRT when given for a finite duration at the time of the menopause, and long-term prospective studies are warranted to address this issue. A further difficulty relates to the logic of targetting women at risk of osteoporosis at the time of the menopause when the benefits and risks of HRT are largely extraskeletal. Finally, the importance of the menopause to the problems of osteoporosis have probably been overemphasized and other factors are important in determining the geographical variation in hip fracture risk as well as the increase in age- and sex-specific incidence that has occurred in many countries. The causes for this are unknown, but are clearly not related to gonadal status since these phenomena are observed both in men and in women. A plausible hypothesis is the decrease in physical activity, but this remains an hypothesis. It will be important to determine the aetiology of these phenomena so that logical preventive strategies can be developed.

Hypothalamic corticotropin-releasing hormone expression in the baboon fetus at mid- and late gestation

We have proposed that estrogen, via regulation of the placental 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) enzyme(s) catalyzing the oxidation of cortisol to its inactive metabolite cortisone, regulates the baboon fetal pituitary-adrenocortical axis and the onset of de novo production of cortisol by the fetus near term. In support of this hypothesis we have demonstrated that the increase in expression of the mRNA for the ACTH precursor proopiomelanocortin (POMC) in the fetal pituitary and in the specific activity of steroidogenic enzymes in the fetal adrenal normally observed at term were enhanced at midgestation by maternal estrogen administration. However, it is not known whether activation of the fetal pituitary reflects a concomitant increase in corticotropin-releasing hormone (CRH) mRNA expression and/or peptide production by the fetal hypothalamus. Therefore, an aim of the present study was to determine whether the increase in POMC mRNA in fetal baboons delivered at term, and at midgestation to mothers treated with estradiol, reflected an increase in hypothalamic CRH. Fetal hypothalami were obtained on Day 100 (n = 6) and Day 165 of gestation (term = Day 184) from untreated baboons (n = 5) and on Day 100 from baboons (n = 4) whose mother had been treated daily with 1.0 mg estradiol on Days 70 to 100. Hypothalamic CRH peptide concentrations were determined by RIA, and CRH mRNA expression was quantified by in situ hybridization in sections of the fetal hypothalamus through the paraventricular nucleus (PVN) using a 48-base synthetic oligodeoxynucleotide probe 3' end-labeled with [35S]dATP. The mean (+/- SE) maternal serum estradiol concentration in baboons treated with estradiol at midgestation (2.4 +/- 0.4 ng/ml) was greater (p < 0.05) than that in untreated baboons on Day 100 (1.0 +/- 0.2), but similar to that in late gestation (2.0 +/- 0.2). The mean steady-state concentration of CRH in the baboon fetal hypothalamus at midgestation (15.8 +/- 6.0 ng/g tissue) was not altered in fetuses whose mothers had been treated with estradiol (17.6 +/- 0.9 ng/g). Hypothalamic CRH concentrations in fetal baboons of late gestation (20.7 ng/g; n = 2) were also similar to mean CRH values measured at midgestation but, owing to the marked increase in weight of the fetal hypothalamus with advancing pregnancy, the content of hypothalamic CRH in late gestation (28.8 ng/structure) exceeded (p < 0.01) that at midgestation. Mean levels of CRH mRNA at midgestation when expressed per cell (17.4 +/- 1.3 grains per cell) or per unit area of PVN (375 +/- 20 grains per area) were similar to respective values in late gestation (18.3 +/- 1.1 grains per cell; 350 +/- 55 grains per area; n = 3 per group). These findings support the suggestion that the increase in fetal pituitary POMC mRNA expression and ACTH peptide previously reported to occur normally between midgestation and term are not associated with a concomitant increase in hypothalamic CRH peptide or CRH mRNA concentrations. Moreover, it would appear that by midgestation, hypothalamic CRH is available in adequate concentrations to "drive" the fetal pituitary and that it is the levels of maternal cortisol arriving within the fetal circulation, as dictated by estrogen-regulated placental 11 beta-HSD-oxidase activity, that establish the extent to which the fetal pituitary responds to CRH.

Estrogen inhibits endothelin-1 production and c-fos gene expression in rat aorta

In order to clarify the mechanism underlying the preventive effect of estrogen on atherogenesis, we investigated the role of estrogen in the regulation of endothelin-1 (ET-1) production and c-fos mRNA expression, which may contribute to atherogenesis. Plasma ET-1 concentration in ovariectomized rats (OVX) was twice as high as that in sham-operated female rats (Sham). Estradiol replacement in OVX rats (OVX + E) decreased plasma ET-1 to the level in Sham (Sham, 0.68 +/- 0.14; OVX, 1.32 +/- 0.14; OVX + E, 0.85 +/- 0.12 pg/ml). Metabolic clearance rate of ET-1 was similar in these three groups of rats, suggesting that the difference in plasma ET-1 was due to production rather than degradation. Measurement of immunoreactive ET-1 in tissue extract and immunohistochemical examination showed that expression of ET-1 in the aortic smooth muscle cells of OVX was increased. The expression of c-fos mRNA in the aorta was also increased in OVX compared with Sham and OVX + E. Intravenous infusion of ET-1 to Sham induced c-fos expression in the aorta, suggesting the contribution of ET-1 to c-fos expression. Tissue culture study revealed that DNA synthesis was increased in the aorta and femoral artery of OVX. These results suggest that inhibition of ET-1 and c-fos expression is involved in the anti-atherogenic action of estrogen.

Identification of authentic estrogen receptor in cultured endothelial cells. A potential mechanism for steroid hormone regulation of endothelial function

BACKGROUND

Estrogen plays a major role in the delayed expression of coronary heart disease (CHD) in women, and recent data indicate that postmenopausal estrogen therapy reduces the incidence of CHD by > 40%. The mechanism or mechanisms through which estrogen exerts this benefit are unknown, although effects on blood pressure, carbohydrate and lipid metabolism, and coagulation have been suggested. We hypothesized that at least part of the effect of estrogen in reducing the incidence of CHD is due to an effect on endothelial cell function.

METHODS AND RESULTS

In the present study, we examined human aortic and umbilical vein endothelial cells and bovine aortic endothelial cells for the presence of estrogen receptors (ERs) through immunoblot and mRNA analyses. Electrophoretic mobility shift assays were also performed to determine the DNA-binding properties of the putative ERs. Nuclear extracts from all three endothelial cell types were found to contain a 67-kD protein that reacted with anti-ER monoclonal antibodies specific to different domains of the ERs. Each of these types of cells expresses proteins that bind specifically to consensus estrogen-responsive elements. Finally, Northern blots verified that endothelial cells express abundant amount of mRNA for the ER.

CONCLUSIONS

These data indicate that endothelial cells constitutively possess the potential for transcriptional regulation of target genes by estrogen. The evolutionary conservation of this receptor in bovine and human endothelial cells suggests a common mechanism for estrogen regulation of endothelial function.

Male reproductive health and environmental xenoestrogens

Male reproductive health has deteriorated in many countries during the last few decades. In the 1990s, declining semen quality has been reported from Belgium, Denmark, France, and Great Britain. The incidence of testicular cancer has increased during the same time incidences of hypospadias and cryptorchidism also appear to be increasing. Similar reproductive problems occur in many wildlife species. There are marked geographic differences in the prevalence of male reproductive disorders. While the reasons for these differences are currently unknown, both clinical and laboratory research suggest that the adverse changes may be inter-related and have a common origin in fetal life or childhood. Exposure of the male fetus to supranormal levels of estrogens, such as diethlylstilbestrol, can result in the above-mentioned reproductive defects. The growing number of reports demonstrating that common environmental contaminants and natural factors possess estrogenic activity presents the working hypothesis that the adverse trends in male reproductive health may be, at least in part, associated with exposure to estrogenic or other hormonally active (e.g., antiandrogenic) environmental chemicals during fetal and childhood development. An extensive research program is needed to understand the extent of the problem, its underlying etiology, and the development of a strategy for prevention and intervention.

Estrogen and apoptosis in the developing sexually dimorphic preoptic area in female rats

Effect of estrogen on apoptotic cell death was studied in the two sexually dimorphic neuronal groups in the developing rat preoptic area (POA): the anteroventral periventricular nucleus of the POA (AVPvN-POA); and the sexually dimorphic nucleus of the POA (SDN-POA). A specific labelling of nuclear fragmentation was performed by terminal deoxynucleotydyl transferase(TdT)-mediated dUTP-biotin nick end-labeling method (TUNEL method) to demonstrate apoptosis. In the AVPvN-POA whose size is larger in females than in males, the number of TUNEL-positive cells was not significantly different between day 5 control and female pups sacrificed 10 h after 25 micrograms estradiol benzoate (EB) injection. However, TUNEL-positive cells showed a significant increase in the female pups sacrificed 24 h after EB injection, compared to that shown in the control female pups. In the SDN-POA whose size is larger in males than in females, EB injection significantly decreased TUNEL-positive cells in the female pups sacrificed 24 h after EB injection, compared to that in controls. These results suggest that estrogen regulates the neuronal number by facilitating apoptotic cell death in the developing AVPvN-POA or by inhibiting it in the developing SDN-POA.

3,4,3',4'-Tetrachlorobiphenyl acts as an estrogen in vitro and in vivo

Polychlorinated biphenyls (PCBs) are one of the most widespread, persistent man-made products in the ecosystem giving rise to serious environmental contamination and potential hazard to health. The PCBs, in common with other compounds such as the dioxins, have been shown to exert some biological actions mediated through the aryl hydrocarbon receptor. Evidence for interaction of PCBs with other nuclear receptors has been sparse. Here we present evidence that 3,4,3',4'-tetrachlorobiphenyl (TCB) (PCB77), a PCB with high toxicity and significant bioaccumulation, can act as an estrogen with actions mediated through the estrogen receptor. Evidence is presented from multiple assay systems including 1) ligand binding to estrogen receptor in a competitive binding assay, 2) ligand ability to induce estrogen receptor binding to DNA, 3) ligand regulation of gene expression from a transfected exogenous (ERE-tk-CAT) or an endogenous (pS2) estrogen-regulated gene, 4) ligand regulation of cell growth in estrogen-dependent human breast cancer cell lines MCF7 and ZR-75-1, and 5) ligand activity in the immature mouse uterine weight bioassay in vivo. These results demonstrate that TCB (PCB77) can be included in the increasing list of environmental pollutants that possess the ability to mimic estrogen action and be termed an environmental estrogen. Since the concentrations of TCB used here (10(-9) M; 292 ng/liter) are not incompatible with levels of PCB/TCB found in human tissues, these results may have physiological relevance. Use of multiple approaches to study estrogenic action demonstrates that one congener can act as both an agonist and antagonist of estrogen action and that the magnitude of these effects can alter according to the molecular environment.