| HOME | HELP | CONTACT US | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Department of Clinical and Experimental Endocrinology, University of Göttingen, Robert-Koch-Strasse 40, D-37099 Göttingen, Germany1 Department of Anatomy, University of Kiel, Otto-Hahn-Platz 8, D-24118 Kiel, Germany
(Correspondence should be addressed to M Böttner; Email: m.boettner{at}anat.uni-kiel.de)
* (M Böttner and J Christoffel contributed equally to this work) 
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionDeclaration of InterestReferences |
|---|
activity. As the pituitary and the liver are targets for estrogen action, we assessed the effect of ovariectomy (OVX) and long-term treatment (3 months) with 17-β estradiol benzoate (E2B) and 8-PN on pituitary and liver functions in adult OVX rats. Tested doses were 6.8 and 68.4 mg/kg body weight (BW) of 8-PN and 0.17 and 0.7 mg/kg BW of E2B. Our results demonstrate that 8-PN and E2B decreased BW and increased uterus weight. The high doses of E2B and 8-PN increased serum GH and decreased serum IGF-1 levels. E2B dose dependently decreased cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) concentrations in OVX rats. The high dose of 8-PN showed an estrogenic activity regarding cholesterol and LDL regulation but had no effect on HDL concentrations. By contrast, the low dose of 8-PN augmented HDL levels compared with intact rats. Triglyceride levels were raised in response to the high E2B dose but unaffected by 8-PN treatment. Taken together, 8-PN displays an anti-atherosclerotic profile that appears to be even more beneficial than the one displayed by E2B, and thus might demonstrate a remarkable potential for the prevention of CVD associated with estrogen deficiency. |
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of InterestReferences |
|---|
Phytoestrogens are compounds found in plants and fungi that exhibit estrogenic activity both in vivo and in vitro. Some display selective estrogen receptor (ER) modulating activity and could therefore play a beneficial role in the prevention of osteoporosis, menopausal complaints, and CVD. The flavanone 8-prenylnaringenin (8-PN) was identified as the major estrogenic compound in hop (Milligan et al. 1999) and hop-containing dietary supplements are marketed for breast enhancement and advertised to reduce menopausal complaints (Coldham & Sauer 2001). In receptor-binding studies and in transfected yeast cells, 8-PN had the strongest ER activity detected for a phytoestrogen so far (Bovee et al. 2004).
Data derived from animal models suggest that 8-PN might exhibit several biological activities. It prevented bone loss in ovariectomized (OVX) rats (Miyamoto et al. 1998) and a recent study from our laboratory indicated that treatment of OVX rats with 8-PN for 3 months showed a reduction of serum luteinizing hormone (LH) and follicle-stimulating hormone indicating that 8-PN might alleviate menopausal discomforts (Christoffel et al. 2006). These data were confirmed by human studies. It could be demonstrated that daily intake over 12 weeks of a hop extract, standardized on 250 µg 8-PN, exerted favorable effects on vasomotor symptoms and other menopausal discomforts (Heyerick et al. 2006). Consistent with these findings, Rad et al. (2006) reported that a single dose of 750 mg 8-PN reduced LH serum levels in postmenopausal women. Interestingly, it appeared from these experiments that 8-PN was well tolerated by these women. A major drawback, however, was its estrogenicity in the uterus and the mammary gland (Diel et al. 2004, Christoffel et al. 2006, Rimoldi et al. 2006).
Growth hormone (GH) exerts its metabolic actions through a complicated process that is partly dependent and partly independent of insulin-like growth factor-1 (IGF-1). The liver plays a crucial role in the metabolic process. It is a target organ of GH action, the main source of IGF-1, and an estrogen-responsive organ (Leung et al. 2004). Cholesterol is synthesized in the liver and necessary for the synthesis of cell membranes, bile acids, and hormones. Low-density lipoproteins (LDLs) are the principal means by which cholesterol is transported from the liver to peripheral tissues. Oxidized LDL, however, can damage the arterial endothelium and is more likely to accumulate in the arterial intima. High-density lipoprotein (HDL) is mainly responsible for the transport of cholesterol from the periphery to the liver. HDL diminishes endothelial damage and arterial disease risk by promoting removal of excess cholesterol from the body (Godsland 2004). However, the effects of 8-PN on metabolic and lipid parameters have not been determined yet.
To investigate the effect of 8-PN on metabolic parameters, we implemented a long-term paradigm of OVX in adult female rats to mimic estrogen deficiency during menopause. Since ingestion is the physiological route of phytoestrogen consumption in humans, we chose oral application of the test substances. As a bioavailability of 10% was reported after oral application of isoflavones to rats (Mallis et al. 2003), we administered a low and a high dose of 8-PN. A low and a high dose of 17-β estradiol benzoate (E2B) were orally fed as positive controls. After 3 months of treatment, we assessed body and uterus weights, serum levels of GH and IGF-1, triglycerides (TGs), cholesterol, LDL, and HDL.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of InterestReferences |
|---|
17β-Estradiol benzoate (E2B purity 98.5%) was purchased from Sigma and 8-PN (purity 99.9%) was kindly supplied by Schering AG, Berlin (Germany).
Animals
All experiments were conducted according to the German animal welfare regulations under permission no. 509.42502/01-36.03 district authorities Braunschweig. All experiments conform with the guidelines given in the UFAW Handbook on the Care and Management of Laboratory Animals.
Parental female Sprague–Dawley rats were obtained from Winkelmann (Borchen, Germany) and kept under soy-free food. Offspring were raised under soy-free conditions to eliminate exposure to exogenous estrogenic compounds. Animals were kept under standard conditions: water and food made available ad libitum, lights on from 0600 to 1800 h, room temperature 23 °C, and relative humidity 55%. At the age of 4 months, rats were bilaterally OVX under isoflurane anesthesia. After 3 months of treatment, animals were decapitated under CO2 anesthesia. Uteri were removed and weighed. In order to minimize interindividual variations, blood samples were obtained between 0800 and 1200 h.
Animal diet and batches of test compound
Substances were given orally to imitate the regular route of human ingestion, including resorption restrictions and first-pass metabolism in the liver.
17-β E2 was administered as its ester E2B to improve the low oral bioavailability of E2. The doses were chosen according to experiences and standard protocol established in the laboratory (Seidlova-Wuttke et al. 2003, Rimoldi et al. 2007). 8-PN doses were chosen according to doses established for other phytoestrogens by our laboratory (Rachon et al. 2007, Rimoldi et al. 2007). The chow was provided by Ssniff special diets GmbH (Soest, Germany). Regular diet was the soy-free formulation Ssniff SM R/M, 10 mm. The supplemented chow was prepared by mixing the test substances with this formulation to homogeneity before the process of pelleting. Concentrations in 1 kg of food were: E2B low 0.0043 g and E2B high 0.0173 g, 8-PN low 0.126 g and 8-PN high 1.26 g/kg food. All batches were prepared 1 week prior to the start of the experiment. Content of 8-PN in the animal chow was determined by HPLC-UV and measured at start, mid-term, and end of the 3-month treatment period to determine stability. Animals were housed as four to six animals per cage. Food consumption was measured twice a week. The amount of food eaten was divided by the number of animals and calculated as food/animal per day. On the basis of ingested food, it was calculated after termination of the experiments that the animals received daily low and high doses of 8-PN of 6.8 and 68.4 mg/kg body weight (BW), and of E2B of 0.17 and 0.7 mg/kg BW (values calculated as free E2).
HPLC analysis
To recover 8-PN from serum in detectable amounts for HPLC-UV, enzymatic hydrolysis of potential metabolites was performed before serum extraction. 500 µl serum were mixed with 500 µl NH Acetate buffer (pH 5.0) containing 1 mg β-glucuronidase (Helix Pomatia β-Glucuronidase Type H1, Sigma) and incubated overnight at 37 °C. Samples were prepared via the Strata X solid phase extraction and eluted with ethanol. The eluted volume was evaporated till dryness in the speedVac with 4-methyl-umbelliferone (4MU) serving as an internal standard for the following reconstitution. Samples were reconstituted with 100 µl ethanol. Subsequently, samples were filtered through a polyvinylidene difluoride (PVDF) membrane (0.45 µm/4 mm) filter to remove remaining protein pollutants. An injection volume of 20 µl was chromatographed over an NC 250x4.6 mm Hypersil-ODS 5.0 µm column (Bischoff, Leonberg, Germany). Serum spikes of 4MU, 4MU-glucuronide (4MUG), and 4MU-sulfate (4MUS) were included in each preparation as duplicate controls and detected by the fluorescence of free 4MU (RF-10A XL Fluorescence Detector, Shimadzu, Hanover, Germany):4MUG and 4MUS served as controls of hydrolysis, 4MU being their reference as well as control of extraction in comparison with the internal standard. The standard curve was obtained from spikes of pooled serum, treated exactly as regular unknowns as described above.
Ethanol, acetonitrile, and water were obtained from J T Baker (Deventer, The Netherlands) and o-phosphoric acid 85% p.a. was supplied by Merck. The analysis of food and serum was performed with the same gradient. The respective extracts were eluted at a flow rate of 1 ml/min with a linear binary gradient of water containing 0.085% o-phosphoric acid (A) and acetonitrile (B): t=0 min: A 70%, t=15 min: A 25%, t=16–21 min: A 0%, t=22–29 min A 70%. The signal was detected with a u.v./visible spectrophotometer (LC-95, Perkin–Elmer, Waltham, MA, USA) at 220 nm.
Serum analysis
The blood samples were centrifuged (3000 g, 20 min) and the serum was stored at –20 °C until further analysis. GH was measured by a specific RIA supplied by the National Hormone and Pituitary Program of the NIH. Briefly, 50 µl serum were added to 200 µl rabbit -GH antibody (1:5000) and incubated at 4 °C O/N. Subsequently, 100 µl 125J-labeled tracer (20.000 c.p.m.) was added and samples were incubated for 24 h at 4 °C. After an addition of the secondary antibody (sheep -rabbit, 1:30), samples were incubated for 48 h at 4 °C and subsequently centrifuged for 1 h at 2400 g Radioactivity in the pellets was counted with a Wallac-LKB 1270 and analyzed with the RIA-CALC program. Estradiol levels were assessed using the kit Estradiol 3rd generation (DSL, Sinsheim, Germany) according to the manufacturer's guidelines. IGF-1 levels were assessed via RIA according to the manufacturer's guidelines (DSL). Cholesterol, LDL, HDL, TG, and glucose were measured with a Hitachi 902 (Boehringer Mannheim).
Statistical evaluation
Significant differences between the control and treatment groups were analyzed by one-way ANOVA followed by Newman–Keuls post hoc test (PrismTM, GraphPad, San Diego, CA, USA). P<0.05 were considered significant.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of InterestReferences |
|---|
|
|
|
|
|
|
Following OVX, LDL levels were elevated by 66% compared with intact controls (Fig. 5). E2B dose dependently decreased LDL levels to 48 and 8% respectively of OVX animals. The high dose of 8-PN attenuated the OVX-induced increase in LDL. The low dose of 8-PN did not alter the OVX-induced rise in LDL levels.
|
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of InterestReferences |
|---|
Estrogen agonistic actions of 8-PN are long known. It has been reported that 8-PN displaced E2 from rat uterine cytosol and that 8-PN competed strongly with E2 for binding to ER and ERβ (Milligan et al. 1999, 2000). Zierau et al. (2005) demonstrated that at a dose of 10–6 M 8-PN showed stimulation in a yeast-based ER assay and in an endogenously ER expressing luciferase assay. At a single dose of 10 mg/day per kg body mass 8-PN stimulated uterine wet weight, increased uterine and vaginal epithelial height, and downregulated ER and clusterin gene expression in the uterus (Diel et al. 2004). OVX rats treated with 1–30 mg/kg per day 8-PN subcutaneously for 2 weeks showed suppression of bone resorption markers and an increase in bone mineral density (Miyamoto et al. 1998).
Our data reveal that the high dose of 8-PN led to a weight reduction of 20% compared with OVX animals, an effect similar to that observed to the E2B-treated animals. The effect of 8-PN is likely to be mediated via ER since ER knockout (KO) mice are obese (Ohlsson et al. 2000). Furthermore, the high dose of 8-PN mimicked the effect of E2B in increasing uterine wet weight. Since these data are part of a multi-organic risk assessment study, these data have been shown in another publication too (Rimoldi et al. 2006) and therefore are discussed there in detail.
Since it has been demonstrated that ER is expressed in GH-positive cells in the pituitary (Stefaneanu et al. 1994) and as radiolabeled estrogen was found in GH immunoreactive cells (Keefer et al. 1976), we first determined the effect of E2B and 8-PN on pituitary GH secretion. Both the high dose of 8-PN and the high dose of E2B significantly upregulated GH levels. This might be due to a direct effect on the pituitary or regulation might occur on the level of the hypothalamus. Using double-label in situ hybridization, Kamegai et al. (2001) showed that 70% of GHRH neurons contain ER mRNA indicating that both substances may directly act on GH-releasing hormone (GHRH) neurons through ER to modify GH secretory patterns. In contrast to the observed upregulation of GH, we noticed a downregulation of circulating IGF-1 by the high doses of E2B and 8-PN. This finding is in agreement with the human studies that also report reductions of IGF-1 serum concentrations following estrogen treatment (Wiedemann et al. 1976, Duursma et al. 1984). Thus, the rise in GH can partly be interpreted as a negative feedback to the fall in IGF-1, which agrees with the negative feedback between IGF-1 and GH, as has been demonstrated by Berelowitz et al. (1981) in cultured rat hypophyseal cells.
As an atherosclerotic lipid profile is a major risk factor for CVD, we next assessed serum levels of lipids and lipoproteins in our animals. E2B dose dependently decreased cholesterol and LDL concentrations. Similarly, the high dose of 8-PN attenuated the OVX-induced rise in cholesterol and LDL levels. A recent study showed that E2 inhibits the first enzyme in cholesterol biosynthesis, thus reducing the synthesis of cholesterol (Moorthy et al. 2004). Furthermore, the effect on cholesterol metabolism might at least partly be mediated by ER since ErKO but not ERβKO mice display elevated levels of total cholesterol (Ohlsson et al. 2000). The same study reports that disruption of the ER gene results in an atherogenic lipoprotein profile characterized by an increase in smaller and presumably denser LDL particles. Hence, it is likely that the effects of 8-PN on lipid metabolism are mediated via ER, particularly since 8-PN has been shown to be the most potent phytoestrogen with ER (Bovee et al. 2004). Moreover, estrogen has been demonstrated to upregulate the LDL receptor, leading to the increased clearance of LDL from the serum (Knopp 2002).
Remarkably, we observed a dose-dependent decrease of HDL levels in our E2B-treated animals whereas the low dose of 8-PN increased HDL concentrations. This finding is in accordance with the previous reports from our group that demonstrate reduced HDL levels following a 3-month treatment with subcutaneously applied E2 (Bottner & Wuttke 2006) or following a 5-day treatment with E2 valerate that was applied per gavage (Klammer et al. 2005). By contrast, the 8-PN-induced increase of HDL serum concentrations is in accordance with the results from human studies that consistently demonstrate an increase in HDL levels following estrogen treatment (Friday et al. 2001, Fait et al. 2002, Saglam et al. 2002).
Treatment with 8-PN showed no effect on TG levels whereas the supraphysiologic dose of E2B increased TG concentrations significantly. This effect might be due to the actions of E2 on hepatic TG lipase since it has been demonstrated that ethinylestradiol administration downregulates the activity of this enzyme by decreasing its mRNA levels (Staels et al. 1990). In agreement with this finding, further studies report the inhibition of hepatic lipase by E2 (Applebaum-Bowden et al. 1989, Kushwaha et al. 1990).
Our data reveal that 8-PN acts as an estrogen agonist on GH and IGF-1 secretions as well as on cholesterol and LDL serum levels. These actions are likely to be mediated mainly by ER, which is in accordance with the findings that characterized 8-PN as an ER agonist. Using a mammalian cell-based transactivation assay, Schaefer et al. (2003) demonstrated that 8-PN is the strongest plant-derived ER agonist identified so far. These results were confirmed by Bovee et al. (2004) who showed in a yeast transcription activation assay stably expressing human ER and ERβ that 8-PN is more potent with ER than with ERβ.
The dose of 8-PN to elicit maximal estrogenic effects (68.4 mg/kg BW) was 97 times higher than the high dose of E2B (0.7 mg/kg BW). This is due to the fact that the doses of phytoestrogens applied to elicit estrogenic effects are generally higher than those required for steroids as demonstrated by numerous studies including those for 8-PN. Diel et al. (2004) showed that an injection of a dose of 10 mg/kg per day of 8-PN stimulated uterine wet weight and increased uterine epithelial height to a similar degree as observed with a dose of 0.03 mg/kg per day of E2. Similarly, Humpel et al. (2005) demonstrated that the 8-PN-mediated prevention of bone loss required an injection of 20 mg/kg per day while E2 was effective at a dose of 0.004 mg/kg per day. The main reason for the observed differences is the fact that the estrogenic potency of 8-PN is at least 100 times lower than that of E2. In a rapid yeast estrogen bioassay, Bovee et al. (2004) reported that the relative estrogenic potency of 8-PN was 0.01 with ER and 0.0039 with ERβ.
Taken together, 8-PN displays an anti-atherosclerotic profile that appears to be even more beneficial than the one displayed by E2B 8-PN treatment did not decrease HDL levels nor increase TG serum concentrations. Thus, 8-PN displays a remarkable potential for the prevention of CVD associated with estrogen deficiency.
|
Declaration of Interest |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of InterestReferences |
|---|
|
Funding |
|---|
|
Acknowledgements |
|---|
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionDeclaration of InterestReferences |
|---|
Berelowitz M, Szabo M, Frohman LA, Firestone S, Chu L & Hintz RL 1981 Somatomedin-C mediates growth hormone negative feedback by effects on both the hypothalamus and the pituitary. Science 212 1279–1281.
Bottner M & Wuttke W 2006 Chronic treatment with physiological doses of estradiol affects the GH–IGF-1 axis and fat metabolism in young and middle-aged ovariectomized rats. Biogerontology 7 91–100.[CrossRef][Web of Science][Medline]
Bottner M, Christoffel J, Rimoldi G & Wuttke W2006aEffects of long-term treatment with resveratrol and subcutaneous and oral estradiol administration on the pituitary–thyroid–axis. Experimental and Clinical Endocrinology and Diabetes 114 82–90.[CrossRef]
Bottner M, Christoffel J, Jarry H & Wuttke W2006bEffects of long-term treatment with resveratrol and subcutaneous and oral estradiol administration on pituitary function in rats. Journal of Endocrinology 189 77–88.
Bovee TF, Helsdingen RJ, Rietjens IM, Keijer J & Hoogenboom RL 2004 Rapid yeast estrogen bioassays stably expressing human estrogen receptors and β, and green fluorescent protein: a comparison of different compounds with both receptor types. Journal of Steroid Biochemistry and Molecular Biology 91 99–109.[CrossRef][Web of Science][Medline]
Christoffel J, Rimoldi G & Wuttke W 2006 Effects of 8-prenylnaringenin on the hypothalamo-pituitary–uterine axis in rats after 3-month treatment. Journal of Endocrinology 188 397–405.
Coldham NG & Sauer MJ 2001 Identification, quantitation and biological activity of phytoestrogens in a dietary supplement for breast enhancement. Food and Chemical Toxicology 39 1211–1224.[CrossRef][Web of Science][Medline]
Diel P, Thomae RB, Caldarelli A, Zierau O, Kolba S, Schmidt S, Schwab P, Metz P & Vollmer G 2004 Regulation of gene expression by 8-prenylnaringenin in uterus and liver of Wistar rats. Planta Medica 70 39–44.[CrossRef][Web of Science][Medline]
Duursma SA, Bijlsma JW, Van Paassen HC, van Buul-Offers SC & Skottner-Lundin A 1984 Changes in serum somatomedin and growth hormone concentrations after 3 weeks oestrogen substitution in post-menopausal women; a pilot study. Acta Endocrinologica 106 527–531.
Fait T, Malkova J & Zivny J 2002 Effect of hormone replacement therapy on the cardiovascular system. Ces
Gynekologie 67 285–293.
Friday KE, Dong C & Fontenot RU 2001 Conjugated equine estrogen improves glycemic control and blood lipoproteins in postmenopausal women with type 2 diabetes. Journal of Clinical Endocrinology and Metabolism 86 48–52.
Godsland IF 2004 Biology: risk factor modification by OCs and HRT lipids and lipoproteins. Maturitas 47 299–303.[CrossRef][Web of Science][Medline]
Heyerick A, Vervarcke S, Depypere H, Bracke M & De Keukeleire D 2006 A first prospective, randomized, double-blind, placebo-controlled study on the use of a standardized hop extract to alleviate menopausal discomforts. Maturitas 54 164–175.[CrossRef][Web of Science][Medline]
Hulley S, Grady D, Bush T, Furberg C, Herrington D, Riggs B & Vittinghoff E 1998 Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. Heart and Estrogen/progestin Replacement Study (HERS) Research Group. Journal of the American Medical Association 280 605–613.
Kamegai J, Tamura H, Shimizu T, Ishii S, Sugihara H & Wakabayashi I 2001 Estrogen receptor (ER), but not ERβ, gene is expressed in growth hormone-releasing hormone neurons of the male rat hypothalamus. Endocrinology 142 538–543.
Keefer DA, Stumpf WE & Petrusz P 1976 Quantitative autoradiographic assessment of 3H-estradiol uptake in immunocytochemically characterized pituitary cells. Cell Tissue Research 166 25–35.[CrossRef][Web of Science][Medline]
Klammer H, Schlecht C, Wuttke W & Jarry H 2005 Multi-organic risk assessment of estrogenic properties of octyl-methoxycinnamate in vivo A 5-day sub-acute pharmacodynamic study with ovariectomized rats. Toxicology 215 90–96.[CrossRef][Web of Science][Medline]
Knopp RH 2002 Risk factors for coronary artery disease in women. American Journal of Cardiology 89 28E–34Ediscussion 34E–35E.[CrossRef][Web of Science][Medline]
Kushwaha RS, Foster DM, Murthy VN, Carey KD & Bernard MG 1990 Metabolic regulation of apoproteins of high-density lipoproteins by estrogen and progesterone in the baboon (Papio sp). Metabolism 39 544–552.[CrossRef][Web of Science][Medline]
Leung KC, Johannsson G, Leong GM & Ho KK 2004 Estrogen regulation of growth hormone action. Endocrine Reviews 25 693–721.
Mallis LM, Sarkahian AB, Harris HA, Zhang MY & McConnell OJ 2003 Determination of rat oral bioavailability of soy-derived phytoestrogens using an automated on-column extraction procedure and electrospray tandem mass spectrometry. Journal of Chromatography. B. Analytical Technologies in the Biomedical and Life Sciences 796 71–86.[CrossRef][Web of Science]
Milligan SR, Kalita JC, Heyerick A, Rong H, De Cooman L & De Keukeleire D 1999 Identification of a potent phytoestrogen in hops (Humulus lupulus L.) and beer. Journal of Clinical Endocrinology and Metabolism 84 2249–2252.
Milligan SR, Kalita JC, Pocock V, Van De Kauter V, Stevens JF, Deinzer ML, Rong H & De Keukeleire D 2000 The endocrine activities of 8-prenylnaringenin and related hop (Humulus lupulus L.) flavonoids. Journal of Clinical Endocrinology and Metabolism 85 4912–4915.
Miyamoto M, Matsushita Y, Kiyokawa A, Fukuda C, Iijima Y, Sugano M & Akiyama T 1998 Prenylflavonoids: a new class of non-steroidal phytoestrogen (Part 2). Estrogenic effects of 8-isopentenylnaringenin on bone metabolism. Planta Medica 64 516–519.[Web of Science][Medline]
Moorthy K, Yadav UC, Mantha AK, Cowsik SM, Sharma D, Basir SF & Baquer NZ 2004 Estradiol and progesterone treatments change the lipid profile in naturally menopausal rats from different age groups. Biogerontology 5 411–419.[CrossRef][Web of Science][Medline]
Ohlsson C, Hellberg N, Parini P, Vidal O, Bohlooly YM, Rudling M, Lindberg MK, Warner M, Angelin B & Gustafsson JA 2000 Obesity and disturbed lipoprotein profile in estrogen receptor--deficient male mice. Biochemical and Biophysical Research Communications 278 640–645.[CrossRef][Web of Science][Medline]
Rachon D, Vortherms T, Seidlova-Wuttke D & Wuttke W 2007 Dietary daidzein and puerarin do not affect pituitary LH expression but exert uterotropic effects in ovariectomized rats. Maturitas 57 161–170.[CrossRef][Web of Science][Medline]
Rad M, Humpel M, Schaefer O, Schoemaker RC, Schleuning WD, Cohen AF & Burggraaf J 2006 Pharmacokinetics and systemic endocrine effects of the phyto-oestrogen 8-prenylnaringenin after single oral doses to postmenopausal women. British Journal of Clinical Pharmacology 62 288–296.[CrossRef][Web of Science][Medline]
Rimoldi G, Christoffel J & Wuttke W 2006 Morphologic changes induced by oral long-term treatment with 8-prenylnaringenin in the uterus, vagina, and mammary gland of castrated rats. Menopause 13 669–677.[CrossRef][Web of Science][Medline]
Rimoldi G, Christoffel J, Seidlova-Wuttke D, Jarry H & Wuttke WEffects of chronic genistein treatment in mammary gland, uterus, and vaginaEnvironmental Health Perspectives115Suppl_1 2007 62–68.[Medline]
Rossouw JE, Anderson GL, Prentice RL, LaCroix AZ, Kooperberg C, Stefanick ML, Jackson RD, Beresford SA, Howard BV, Johnson KC et al. 2002 Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial. Journal of the American Medical Association 288 321–333.
Saglam K, Polat Z, Yilmaz MI, Gulec M & Akinci SB 2002 Effects of postmenopausal hormone replacement therapy on insulin resistance. Endocrine 18 211–214.[CrossRef][Web of Science][Medline]
Schaefer O, Humpel M, Fritzemeier KH, Bohlmann R & Schleuning WD 2003 8-Prenyl naringenin is a potent ER selective phytoestrogen present in hops and beer. Journal of Steroid Biochemistry and Molecular Biology 84 359–360.[CrossRef][Web of Science][Medline]
Seidlova-Wuttke D, Hesse O, Jarry H, Christoffel V, Spengler B, Becker T & Wuttke W 2003 Evidence for selective estrogen receptor modulator activity in a black cohosh (Cimicifuga racemosa) extract: comparison with estradiol-17beta. European Journal of Endocrinology 149 351–362.[Abstract]
Staels B, Jansen H, van Tol A, Stahnke G, Will H, Verhoeven G & Auwerx J 1990 Development, food intake, and ethinylestradiol influence hepatic triglyceride lipase and LDL-receptor mRNA levels in rats. Journal of Lipid Research 31 1211–1218.[Abstract]
Stefaneanu L, Kovacs K, Horvath E, Lloyd RV, Buchfelder M, Fahlbusch R & Smyth H 1994 In situ hybridization study of estrogen receptor messenger ribonucleic acid in human adenohypophysial cells and pituitary adenomas. Journal of Clinical Endocrinology and Metabolism 78 83–88.[Abstract]
Wiedemann E, Schwartz E & Frantz AG 1976 Acute and chronic estrogen effects upon serum somatomedin activity, growth hormone, and prolactin in man. Journal of Clinical Endocrinology and Metabolism 42 942–952.
Zierau O, Hamann J, Tischer S, Schwab P, Metz P, Vollmer G, Gutzeit HO & Scholz S 2005 Naringenin-type flavonoids show different estrogenic effects in mammalian and teleost test systems. Biochemical and Biophysical Research Communications 326 909–916.[CrossRef][Web of Science][Medline]
Received in final form 20 May 2008
Accepted 22 May 2008
Made available online as an Accepted Preprint 22 May 2008
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | CONTACT US | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
