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PubMed1999

Differential effects of sex hormones and phytoestrogens on peak and steady state contractions in isolated rabbit detrusor.

PURPOSE: Recent evidence suggests that sex steroids may produce rapid inhibition of voltage operated Ca2+ channels (VOCCs). Detrusor smooth muscle is highly dependent upon Ca2+ influx for receptor-activated contractions. Thus, we examined the relative effectiveness of a select group of sex steroids and dietary phytoestrogens to relax detrusor contracted with the muscarinic receptor agonist, bethanechol (BE) and the purinergic P2X receptor agonist, alpha,beta-methylene ATP (alpha,beta-MeATP). MATERIALS AND METHODS: Isolated strips of rabbit detrusor were secured to isometric force transducers in a tissue bath and length-adjusted until maximum contractions were achieved. Peak (P) contractile responses were recorded for alpha,beta-MeATP (P(ATP)) and BE (P(BE)) and steady-state (SS) responses were recorded for BE (SS(BE)) in the presence and absence of selected sex steroids and phytoestrogens (10 microM, unless indicated). RESULTS: The L-type VOCC inhibitor, nifedipine (1 to 10 microM), completely inhibited P(ATP) but reduced SS(BE) by approximately 50%, whereas the VOCC and non-VOCC inhibitor, SKF 96365, inhibited SS(BE) by approximately 95%, suggesting that P(ATP) was entirely dependent on L-type VOCCs, but (BE)-induced contractions depended also on activation of non-VOCCs. 17Beta-estradiol (estradiol) and progesterone inhibited P(ATP) by approximately 60% and 20%, respectively, and 32 microM estradiol and ethinyl estradiol inhibited SS(BE) by approximately 80 and 95%, respectively. Inhibition by estradiol was potentiated, rather than blocked, by the nuclear estrogen receptor antagonist, tamoxifen. Moreover, tamoxifen alone nearly completely relaxed SS(BE). The inactive metabolite of estradiol, 17alpha-estradiol, inhibited both P(ATP) and P(BE) by approximately 40%. Testosterone had no effect on P(ATP) and P(BE). The phytoestrogen and tyrosine kinase inhibitor, genistein, inhibited SS(BE) by 44%, whereas daidzein, a phytoestrogen without tyrosine kinase inhibitory activity, produced only a 7% inhibition. None of the phytoestrogens examined inhibited P(BE), whereas all inhibited P(ATP) by approximately 20 to 35%. A comparison of inhibition of (BE) and alpha,beta-MeATP-induced contractions by selected estrogen isomers showed some distinct differences. For example, estrone did not inhibit P(BE) or SS(BE), but inhibited P(ATP) by approximately 20%, whereas DES inhibited SS(BE) by nearly 90%, but P(ATP) by a lesser degree (approximately 70%). CONCLUSIONS: Our data support the hypothesis that 17beta-estradiol, ethinyl estradiol, DES, tamoxifen and genistein may relax detrusor contractions by inhibition of both VOCCs and non-VOCCs. Moreover, our data show that genistein, a dietary phytoestrogen with tyrosine kinase inhibitory activity, selectively reduced alpha,beta-MeATP-induced peak and BE-induced steady-state contractions, sparing the maximum response to BE. Lastly, the inactive isomer, 17alpha-estradiol, inhibited both BE- and alpha,beta-MeATP-induced contractions. These data suggest that certain dietary phytoestrogens (for example, genistein) or sex steroids, especially those with weak activity at the nuclear steroid site (for example, 17alpha-estradiol), or tamoxifen may prove therapeutically useful in treating overactive bladder caused by elevated muscarinic and purinergic receptor activation.

Animals↗

PubMedDate not supplied

Cycle control, tolerability, and satisfaction among women switching from 30-35 microg ethinyl estradiol-containing oral contraceptives to the triphasic norgestimate/25 microg ethinyl estradiol-containing oral contraceptive Ortho Tri-Cyclen LO.

OBJECTIVE: To determine cycle control, tolerability, and satisfaction among women (aged 18-45) switching from oral contraceptives (OCs) containing 30-35 microg ethinyl estradiol (EE) to Ortho Tri-Cyclen LO (norgestimate 180/215/250 microg/EE 25 microg) and Loestrin Fe 1/20 (norethindrone acetate 1 mg/EE 20 microg). DESIGN: A subset of patients from a study comparing Ortho Tri-Cyclen LO (N = 864) with Loestrin Fe 1/20 (N = 565) was analyzed. The subset was defined as those who had taken a 30-35 microg EE-containing OC within 60 days of study start. The total number of cycles of exposure for the subset was 6,054 for Ortho Tri-Cyclen LO and 3,814 for Loestrin Fe 1/20. Additional analyses evaluated switchovers from Ortho Tri-Cyclen to Ortho Tri-Cyclen LO (N = 111). MAIN OUTCOME MEASURES: Cycle control was assessed by daily diary cards reporting the frequency, severity, and duration of bleeding/spotting. Discontinuation rates due to adverse events (AEs) were considered to reflect tolerability. Satisfaction was evaluated by questionnaire. RESULTS: The proportion of cycles in which subjects experienced breakthrough bleeding and/or spotting was significantly lower with Ortho Tri-Cyclen LO than Loestrin Fe 1/20. Discontinuations due to AEs and serious AEs were comparable for Ortho Tri-Cyclen LO (3.4% and 0.6%, respectively) and Loestrin Fe 1/20 (3.2% and 0.7%, respectively). More women on Ortho Tri-Cyclen LO versus Loestrin Fe 1/20 were very or somewhat satisfied at Cycle 6 (86% vs. 81.1%; P < 0.05) and last visit (81.6% vs. 78.1%; P < 0.05). At Cycle 6, 89.3% of Ortho Tri-Cyclen to Ortho Tri-Cyclen LO switchovers were very or somewhat satisfied, and 72.6% desired to continue taking Ortho Tri-Cyclen LO after study conclusion. Conclusions-Switchovers from OCs containing 30-35 microg EE to Ortho Tri-Cyclen LO had excellent cycle control and tolerability, and were satisfied.

Adolescent↗

PubMed2005

Alteration of the expression of adenosine triphosphate-binding cassette transporters associated with bile acid and cholesterol transport in the rat liver and intestine during cholestasis.

BACKGROUND AND AIM: Multidrug resistance protein 2 (Mrp2), Mrp3, adenosine triphosphate-binding cassette transporter g5 (Abcg5) and adenosine triphosphate-binding cassette transporter g8 (Abcg8) have been identified as bile acid or cholesterol transporter in the enterocytes as well as hepatocytes. The purpose of the present study was to evaluate intestinal and hepatic adenosine triphosphate-binding cassette transporter expressions during cholestasis. METHODS: Experiment 1: Rats were subjected to bile duct ligation or sham operation. Blood, liver and small intestines were obtained 24 and 72 h after operation. Experiment 2: Rats were divided into four groups as follows: (i) control group; (ii) diosgenin group (fed with diosgenin in diet [1%(wt/wt)] for 7 days); (iii) ethinyl estradiol group (received ethinyl estradiol [5 mg/kg daily] for 5 days); and (iv) diosgenin-ethinyl estradiol group (received ethinyl estradiol and diosgenin). After treatment, blood, bile, liver and intestines were obtained. The mRNA related to lipid and bile acid metabolism was analyzed by reverse transcription polymerase chain reaction. RESULTS: Intestinal Mrp2 and Abcg5/Abcg8 mRNA expression remarkably decreased 24 h after bile duct ligation (43% and 61%/54% of sham operation) and recovered 72 h after bile duct ligation (103% and 95%/83% of sham operation). Intestinal Mrp3 mRNA expression did not change after bile duct ligation. Intestinal Mrp2 mRNA expression was remarkably increased in diosgenin and diosgenin-ethinyl estradiol groups in comparison with the control group. There were no significant differences in intestinal Mrp3 mRNA expression among the four groups. Hepatic Mrp3 mRNA expression was remarkably increased in the D, EE and DE groups in comparison with the control group (531%, 321% and 1160% of control, respectively, P < 0.01). Hepatic Abcg5 and Abcg8 mRNA expression decreased in ethinyl estradiol and diosgenin-ethinyl estradiol groups compared with the control group and there were no differences in intestinal Abcg5 and Abcg8 mRNA expressions among the four groups. CONCLUSION: Bile duct ligation affects not only hepatic but also the intestinal Mrp2 and Abcg5 and Abcg8 expressions. Intestinal Mrp2 mRNA level was regulated by factor in the lumen (e.g. diosgenin feeding). Cholestasis by ethinyl estradiol treatment was enhanced by diosgenin and the increase in hepatic Mrp3 mRNA level might affect the enhancement.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed1976

Influence of estrogens on bone resorption in organ culture.

Estradiol benzoate, ethinyl estradiol, and human calcitonin were compared for their ability to inhibit the spontaneous or parathyroid extract-induced bone resorption in organ cultures of 19-day fetal rat fibulae. The criteria used for the assessment of bone resorption were: the release of 45Ca from paired prelabeled bone rudiments into the culture medium, the dry weight, and the number of osteoclasts per bone. Estradiol benzoate at concentrations of 1.3 X 10(-5) to 2.6 X 10(-4)M had no effect on the release of 45Ca from fetal fibulae or on the dry weight. Histologically, treated bones were well preserved and resembled the controls. Parathyroid extract (PTE) alone caused extensive bone resorption with numerous osteoclasts and enhanced 45Ca release without weight gain. The addition of estradiol benzoate to the culture medium did not prevent the resorptive action of PTE. Ethinyl estradiol alone provoked a dose-related inhibition of 45Ca release at concentrations of 3.4 X 10(-5) to 1.7 X 10(-4)M. However, this inhibition was accompanied by a decrease in bone dry weight and by various degrees of cellular damage. The same phenomenon was observed in PTE-treated fibulae. Human calcitonin, on the contrary, inhibited the release of 45Ca by decreasing the number of osteoclasts while the weight of the fibulae increased. The inhibitory action of ethinyl estradiol appears to be caused by a toxic effect on bone cells. It is concluded that estrogens have no direct physiological effect on bone resorption in vitro.

Animals↗

PubMed1998

An open-label, multicenter, noncomparative safety and efficacy study of Mircette, a low-dose estrogen-progestin oral contraceptive. The Mircette Study Group.

OBJECTIVE: The primary efficacy and safety of Mircette (brand of desogestrel/ethinyl estradiol and ethinyl estradiol), an oral contraceptive containing 150 microg desogestrel and 20 microg ethinyl estradiol given for 21 days, followed by 2 days of placebo and then 5 days 10 microg ethinyl estradiol, was evaluated. STUDY DESIGN: In a large, open-label, 18-month, multicenter trial, a total of 1143 of 1250 healthy female subjects contributed to the determination of extent of exposure, for an equivalent of 1080.8 woman-years of use. RESULTS: Absence of withdrawal bleeding occurred in 5.5% of total cycles and intermenstrual bleeding occurred in 12.0% of total cycles. Breakthrough spotting was more common than breakthrough bleeding. The Pearl Index for total pregnancies during treatment was 1.02/100 woman-years. Fewer than 3% of subjects discontinued study participation, primarily because of menstrual problems, indicating that Mircette was an oral contraceptive acceptable to the women studied. Overall 73.6% of all subjects reported one or more adverse events, and a total of 43.9% of subjects reported drug-related adverse events. The most common drug-related adverse events reported included headache (8.5%), breast pain (7.3%), dysmenorrhea (4.2%), and menstrual disorder (4.2%). There were no reports of venous thromboembolic events or of significant changes in blood pressure, lipid metabolism, or serum glucose level. CONCLUSION: The study confirmed that Mircette is a safe and efficacious oral contraceptive that is well tolerated and acceptable to women who have previously used oral contraceptives, as well as first-time users.

Adolescent↗

PubMed1987

Oral contraceptives and breast cancer. In vitro effect of contraceptive steroids on human mammary cell growth.

The proliferative response of human mammary epithelial cells cultured in medium containing oral contraceptive steroids, singly and in combination, was measured. Cells came from 59 normal, nonmalignant atypical, and malignant breast tissue specimens. Growth of most cultures was stimulated by the estrogens 17 beta-estradiol and ethinyl estradiol, and any combination containing ethinyl estradiol. Most (75%) malignant specimens were stimulated by one or more of the progestins, whereas none of the nonmalignant cells were. For two of the estrogen/progestin combinations found in many birth control pills, malignant cells were stimulated to grow faster than nonmalignant cells. It was concluded that oral contraceptive steroids can stimulate the growth of mammary epithelia in cell culture and might do the same in vivo. These data corroborate epidemiologic data which suggest oral contraceptives might act as tumor promoters, especially in the older user, who is more likely to have malignant cells already present in the breast.

Breast↗

PubMed1986

Effects of iron overload on bile secretion and hepatic porphyrin metabolism in ethinyl estradiol-treated rats.

We investigated the effects of ethinyl estradiol (5 mg/kg body wt daily for 5 days, orally) and/or iron sorbitol (50 mg/kg body wt daily for 5 days, i.m.) on bile flow, bile salt independent fraction (BSIF), hepatic delta-aminolevulinate synthase (ALA-S) and uroporphyrinogen decarboxylase (URO-D) in female rats. Ethinyl estradiol administration was associated with a significant decrease of bile flow and BSIF and an increase in URO-D activity in comparison to control values. Iron alone did not modify biliary parameters, but significantly increased the activity of ALA-S. Combined treatment with ethinyl estradiol plus iron partially corrected the reduction of BSIF and restored the activity of ALA-S and URO-D to control levels. Thus iron appears to exert a partially protective effect against ethinyl estradiol-induced cholestasis. No porphyrinogenic effect was observed.

Animals↗

PubMed1991

Effects of sex steroids on skin 5 alpha-reductase activity in vitro.

Skin 5 alpha-reductase activity is the major factor influencing the manifestation of androgen excess. Although oral contraceptives have been useful for the treatment of androgen excess, little is known of the independent effects of the various progestins and estrogens on inhibition of skin 5 alpha-reductase activity. We incubated minces of normal genital and pubic skin with physiologic concentrations of 3H-testosterone to assess 5 alpha-reductase activity by its conversion to 3H-dihydrotestosterone. In separate experiments, 5 alpha-reductase activity was assessed before and after the addition of progesterone, medroxyprogesterone acetate, levonorgestrel, norethindrone, 17 beta-estradiol, and ethinyl estradiol. Progesterone, levonorgestrel, and norethindrone demonstrated 97 +/- 5.3%, 47.9 +/- 6.3%, and 59 +/- 4.6% inhibition, respectively, of genital skin 5 alpha-reductase activity at 10(-4) mol/L (P less than .01). Medroxyprogesterone acetate, however, failed to affect 5 alpha-reductase activity at similar doses. Estradiol exhibited 40.8 +/- 14.2% inhibition at 10(-4) mol/L (P less than .01), whereas ethinyl estradiol at concentrations from 10(-8) to 10(-4) mol/L failed to inhibit 5 alpha-reductase activity. We conclude that progesterone and the 19-nor-derivatives inhibit 5 alpha-reductase activity at high doses, whereas medroxyprogesterone acetate does not. Therefore, the 19-nor-progestin component may expand the usefulness of oral contraceptives in the treatment of hirsutism by an inhibitory action on skin 5 alpha-reductase activity.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMed1980

Reversal of ethinyl estradiol-induced bile secretory failure with Triton WR-1339.

The effects of Triton WR-1339 and phenobarbital on ethinyl estradiol bile secretory failure were examined to determine the mechanism responsible for decreased bile salt excretion. When administered to ethinyl estradiol-treated rats, Triton WR-1339 restored bile salt independent bile flow and maximum taurocholate transport, whereas phenobarbital corrected bile flow only. Ethinyl estradiol decreased the activities of Na(+)-K(+)-ATPase, 5'-nucleotidase, while increasing the activities of Mg(++)-ATPase and alkaline phosphatase. In contrast to these heterogeneous changes in surface membrane enzyme activities, the number and affinity of [(14)C]cholic acid carriers were not altered. When administered in vivo or added directly to surface membrane fractions Triton WR-1339 restored the activities of Na(+)-K(+)-ATPase and Mg(++)-ATPase of rats treated with ethinyl estradiol through a process that did not require protein synthesis (unaffected by cycloheximide). Phenobarbital also restored the activity of Na(+)-K(+)-ATPase to control levels, but, unlike Triton WR-1339 it did not correct the defect responsible for reduced bile salt secretion. Ethinyl estradiol increased the concentration of cholesterol esters in surface membrane fractions. When administered to ethinyl estradiol-treated rats, Triton WR-1339 restored cholesterol ester concentrations to normal, whereas phenobarbital did not. These combined data suggest that decreased or altered bile salt carriers or reduced sodium driving forces resulting from impaired activity of Na(+)-K(+)-ATPase are not responsible for decreased bile salt excretion in ethinyl estradiol-treated rats. It is proposed that the diverse changes in surface membrane function, which are associated with ethinyl estradiol bile secretory failure, may be the result of a generalized alteration in membrane lipid structure.

Animals↗

PubMed1998

Enhanced levels of several mitochondrial mRNA transcripts and mitochondrial superoxide production during ethinyl estradiol-induced hepatocarcinogenesis and after estrogen treatment of HepG2 cells.

Ethinyl estradiol (EE) is a strong hepatic promoter and weak complete hepatocarcinogen. Among the effects on rat liver caused by chronic exposure to non-hepatotoxic doses of EE is an initial, transient increase in hepatocyte growth followed by a subsequent inhibition (mitosuppression) of basal and/or induced liver growth. To investigate the mechanism of EE-induced mitosuppression, we performed a differential display and identified 10 genes whose expression was increased 2- to 4-fold in EE-induced, mitosuppressed livers (Chen et al., Carcinogenesis, 17, 2783-2786, 1996). We found that one of these clones was homologous to nuclear genome-encoded mitochondrial ATP synthase subunit E. Here, we describe the identification of two additional cDNAs representing transcripts whose levels were elevated during EE-induced mitosuppression as mitochondrial DNA-encoded cytochrome c oxidase subunit III and ATP synthase 6. In addition, we found that EE, estradiol and the estradiol catechol metabolites, 4-OH-estradiol and 2-OH-estradiol, increased the levels of these and other mitochondrial genome-encoded transcripts in human hepatoma HepG2 cells. We also observed that this increase can be blocked by inhibition of cytochrome P450-mediated estrogen metabolism, and that this increase is accompanied by increased mitochondrial superoxide production, which reflects increased respiratory chain activity.

Animals↗

PubMed2003

Enhanced mitochondrial gene transcript, ATP, bcl-2 protein levels, and altered glutathione distribution in ethinyl estradiol-treated cultured female rat hepatocytes.

Ethinyl estradiol (EE) is a strong promoter and weak hepatocarcinogen in rats. Previously, we demonstrated that EE enhanced the transcript levels of nuclear genome- and mitochondrial genome-encoded genes and respiratory chain activity in female rat liver, and also inhibited transforming growth factor beta (TGFbeta)-induced apoptosis in cultured liver slices and hepatocytes from female rats. In this study, using cultured female rat hepatocytes, we observed that EE, within 24 h, increased the transcript levels of the mitochondrial genome-encoded genes cytochrome oxidase subunits I, II, and III. This effect was accompanied by increased mitochondrial respiratory chain activity, as reflected by increased mitochondrial superoxide generation, and detected by lucigenin-derived chemiluminescence and cellular ATP levels. EE also enhanced the levels of Bcl-2 protein. Biochemical analyses indicated that EE significantly increased both the levels of glutathione (reduced [GSH] and oxidized [GSSG] forms) per mg protein in mitochondria and nuclei, while the percentage of total glutathione in the oxidized form was not affected. This finding was supported by confocal microscopy. These effects caused by EE may contribute, at least in part, to the EE-mediated inhibition of hepatic apoptosis.

Adenosine Triphosphate↗

PubMed1978

Alterations of hepatic Na+,K+-atpase and bile flow by estrogen: effects on liver surface membrane lipid structure and function.

Administration of the synthetic estrogen ethinyl estradiol (17alpha-ethinyl-1,3,5-estratriene-3,17beta-diol) decreases hepatic Na(+),K(+)-ATPase (ATP phosphohydrolase; EC 3.6.1.3) activity and bile flow to 50% and alters the composition and structure of surface membrane lipid in rats. Although the content of phospholipids was not changed by treatment, free cholesterol (130%) and cholesterol esters (400%) were increased in liver surface membrane fractions. These observations correlate with changes in membrane viscosity, as shown by electron spin resonance probes. Both rotational correlation time, using the isotropic probe methyl (12-nitroxyl)stearate, and the order parameter, determined by the anisotropic probe 5-nitroxylstearic acid, were significantly increased in liver surface membrane fractions from rats treated with ethinyl estradiol. Administration of Triton WR-1339, a nonionic detergent that corrects hepatic and serum lipid changes caused by ethinyl estradiol treatment, restored toward normal elevated membrane lipids and viscosity as well as Na(+),K(+)-ATPase activity and bile flow. Although restoration of normal liver surface membrane structure and function may be due to reversal of abnormal lipid composition, detergents also may directly alter membrane enzyme activity. Addition of Triton WR-1339 in vitro increased Na(+),K(+)-ATPase activity and reduced membrane viscosity of surface membranes from rats treated with ethinyl estradiol. Triton had no effect on either parameter in normal membrane preparations. Studies of membrane structure and function both in vivo and in vitro suggest that alterations in lipid composition may alter Na(+),K(+)-ATPase function and bile flow.

Animals↗

PubMed1975

Determination of estrogens in dosage forms by fluorescence using dansyl chloride.

A sensitive, reproducible, fluorometric procedure for the determination of estrogens in pharmaceutical preparations is presented. The estrogens are determined fluorometrically following their reaction with dansyl chloride. The optimum conditions for the reaction such as pH, reaction solvent composition variations, and speed of reaction are discussed. In addition, a linearity study of the relationship between concentration and fluorescence intensity for estrone, estradiol, and ethinyl estradiol is reported. Solvent extraction procedures based on acid-base behavior or column chromatography are used when necessary to isolate the estrogen prior to reaction with dansyl chloride and fluorometric measurement. The recovery of estrogens from spiked samples indicated that the proposed method is efficient and reproducible. Comparison of the dansyl procedure with the official NF method in the analysis of estrone aqueous suspension showed the proposed method to be accurate and more precise than the NF assay. Estrone aqueous suspension, estradiol in sesame oil, estradiol valerate in castor oil and in sesame oil (in the latter case, in the presence of testosterone), estradiol benzoate in sesame oil, and ethinyl estradiol tablets (0.5 mg/tablet) from commercial sources were satisfactorily analyzed, with average results within compendial limits and no coefficient of variation greater than 2%.

Castor Oil↗

PubMed1985

Effects of natural and synthetic estrogens and progestins on glycogen deposition in female mice.

Glycogen deposition and glucose tolerance were examined in female mice after 24 days of oral treatment with natural (17 beta-estradiol and progesterone) and synthetic (ethinyl estradiol and norethisterone acetate) sex steroids, administered individually and in estrogen-progestin combination. Doses were 5 micrograms/kg/day for estrogens and 1 mg/kg/day for progestins. Compared with diestrus control mice, each treatment increased glycogen deposition in liver, uterus, heart and biceps femoris muscle. 17 beta-Estradiol produced the greatest increments. Progesterone produced considerably smaller increments and antagonized the glycogenic effects of 17 beta-estradiol. Ethinyl estradiol and norethisterone acetate generally induced similar changes in glycogen deposition. Treatments containing 17 beta-estradiol improved glucose tolerance. Although glucose tolerance was not significantly altered by the other sex steroid treatments, the changes in glycogen deposition indicate important effects on tissue carbohydrate metabolism.

Animals↗

PubMed1984

Hormonal consequences of missing the pill during the first two days of three consecutive artificial cycles.

The hormonal effects of the deliberate omission of a low-dose combined oral contraceptive pill (30 micrograms ethinyl estradiol + 150 micrograms levonorgestrel) during the first two days of three consecutive artificial cycles were studied in 10 women. The plasma levels of estradiol, progesterone, levonorgestrel and--whenever justified--of LH were measured three times weekly (Mondays, Wednesdays and Fridays) throughout a 90-day period, and the ovarian reaction to the prolongation of the pill-free period from 7 to 9 days was assessed. One subject (with a premature LH surge) showed a marked follicular and an inadequate luteal activity in 2 of 3 cycles. The remaining cycles were characterized by a varying degree of follicular activity associated with the absence of any luteal function. None of the subjects exhibited peripheral steroid levels indicating a normal ovulatory cycle. The results are interpreted as suggesting that repeated prolongation of the pill-free period from 7 to 9 days might result in a gradual increase in ovarian activity.

Adult↗

PubMed1994

Estrogen action on hepatic synthesis of angiotensinogen and IGF-I: direct and indirect estrogen effects.

In the present study effects of estrogens (natural estradiol and synthetic ethinyl estradiol) on liver derived proteins (angiotensinogen, IGF-I) were investigated in vivo in ovariectomized rats and in vitro in a rat hepatoma cell line (Fe33). The aim of this study was to establish both an animal and an in vitro model for quantification of the hepatic activity of given estrogenic compounds, and to study underlying mechanisms as regards the question of direct or indirect mode of estrogen action. In ovariectomized rats subcutaneous (s.c.)-treatment for 11 days with either estradiol (E2) or ethinyl estradiol (EE) (dose range 0.1-3 micrograms/animal/day) induced a comparable dose-dependent increase in uterine weight indicating a similar estrogenic potency of the two estrogens. Equipotency was also found as regards the effects on IGF-I plasma levels which dose-dependently decreased by about 50% at the highest dose tested (3 micrograms/animal/day). The decrease in IGF-I serum levels was accompanied by a significant 40% decrease in liver IGF-I mRNA. In contrast angiotensinogen plasma levels were affected only by EE (60% increase for the 3 micrograms/animal/day dose) but not by E2. When rats, in addition to ovariectomy, were also hypophysectomized (substituted with human growth hormone and dexamethasone) angiotensinogen again increased by 80% upon administration of 3 micrograms/animal/day EE, whereas IGF-I remained unaffected by EE. In a rat hepatoma cell line (Fe33) which is stably transfected with an estrogen receptor expression plasmid, 10 nmol/l EE for 24 h caused a 2.4-fold increase in angiotensinogen mRNA level. We conclude from our studies that estrogen effects on angiotensinogen serum levels in the rat are direct effects via the hepatic estrogen receptor, whereas estrogen effects on IGF-I serum levels are indirect effects, the primary target of estrogen action being probably the pituitary. The changes in angiotensinogen serum levels in the rat model are comparable to the situation in humans indicating the rat model and the Fe33 model to be useful tools to study the hepatic activity of estrogenic compounds.

Angiotensinogen↗

PubMed1991

Regulation of hepatic apolipoprotein synthesis in the 17 alpha-ethinyl estradiol-treated rat.

Regulatory mechanisms of hepatic apolipoprotein synthesis were studied in groups of male Sprague-Dawley rats made severely hypolipidemic by treatment with pharmacological doses of 17 alpha-ethinyl estradiol. Treatment resulted in a marked reduction of plasma cholesterol and apolipoproteins B, A-I, and A-IV. Hepatic apoA-I mRNA and apoA-I synthesis were increased in the ethinyl estradiol-treated animals. Hepatic apoA-IV protein synthesis rates were unaltered; however, a reduction of the apoA-IV mRNA level was observed. Diet-control studies suggested the effects of 17 alpha-ethinyl estradiol on apoA-I, unlike those on apoA-IV, appeared to be related to the steroid and not to reduced caloric intake. Livers of control and ethinyl estradiol-treated rats synthesized both apoBH and apoBL. Total hepatic apoB (apoBL plus apoBH) synthesis and apoB mRNA levels in the ethinyl estradiol-treated rats were similar to ad libitum fed or diet-controls. In ad libitum fed and diet-control rats, 21% and 32%, respectively, of newly synthesized hepatic apoB was apoBH. In contrast, 47% of the newly synthesized apoB in the ethinyl estradiol-treated animal was apoBH. Nucleotide sequence analysis of hepatic apoB mRNA confirmed a marked decrease in the proportion of the apoBL mRNA in ethinyl estradiol-treated animals. After cessation of 17 alpha-ethinyl estradiol treatment, the hepatic apolipoprotein A-I synthesis rate, apolipoprotein A-I and A-IV mRNA levels, and the apoBH and apoBL synthesis rates, as well as plasma apolipoprotein and cholesterol levels, returned to normal. A major finding of the present study is that pharmacological doses of ethinyl estradiol do not affect total hepatic apoB synthesis, but increase the relative amount of apoBH synthesized.

Animals↗

PubMed1985

Solubilization of the 17 alpha-ethinyl estradiol-stimulated low density lipoprotein receptor of male rat liver.

Pharmacological doses of 17 alpha-ethinyl estradiol induce a low density lipoprotein (LDL) receptor in the liver of male rats. Our aim was to solubilize this receptor. Isolated liver membranes (8,000-100,000 g fraction) from male rats treated with 17 alpha-ethinyl estradiol and from control rats were solubilized in 1% (w/v) Triton X-100. Using Amberlite XAD-2, more than 90% of the detergent was then removed. Liposomes were prepared by precipitating the solubilized proteins with acetone in the presence of phosphatidylcholine. The receptor activity of these liposomes was assayed using human 125I-labeled LDL. Filtration was used to separate bound from free 125I-labeled LDL. The assay was optimized; 0.25 mM CaCl2, 25 mM NaCl, pH 8.0, were chosen as the standard conditions. Binding of 125I-labeled LDL was dependent on Ca2+. Liposomes containing solubilized membrane proteins from treated rats displayed Ca2+-dependent binding which was 11 times higher than for control rats. The specific binding of 125I-labeled LDL was saturable with a Kd = 18 micrograms/ml. 125I-Labeled LDL was displaced by unlabeled lipoproteins containing apolipoproteins B and E and by dimyristoylphosphatidylcholine liposomes containing purified apolipoprotein E, but not by HDL3. The binding was abolished by pronase and was inhibited by suramin. Ligand blotting with 125I-labeled LDL revealed one band of protein with an apparent molecular weight of 133,000 daltons. These properties are characteristic of the low density lipoprotein receptor.

Animals↗