Excretion of radiolabeled estradiol in the cat (Felis catus,L): A preliminary report

The time course and end products of estradiol metabolism were studied in the domestic cat, which has been chosen as a model for steroid metabolism studies in nondomestic felidae. Radiolabeled estradiol was injected intravenously into three adult female cats; one had a spontaneous estrus, one was induced with follicle-stimulating hormone, and one had been ovariohysterectomized; feces, urine, and blood were collected daily, and the radioactivity content was determined. Feces and urine contained 47 and 1% of the injected dose (0.33 μCi), respectively. Metabolites appeared earlier in the urine than in feces (d 1 vs d 2 postinjection), and excretion was completed on d 5; no radioactivity was detected in plasma 24 h postinjection. Estradiol metabolites were excreted as unconjugated estrogens (22%) and as conjugates hydrolyzable with β-glucuronidase and acid solvolysis (7 and 50%, respectively); the remaining 14% were not recoverable with any of the above methods. The major portion of the conjugates was estradiol-17β (64–80%) while 11–16% appeared as estrone. Endogenous cycles related to the spontaneous and induced ovarian activity were monitored by observation of estrous behavior, vaginal epithelium cornification, and plasma estradiol determination. The reproductive state of each animal had no effect on the time course or type of metabolite excreted. We found low proportions of injected radioactivity excreted in the urine and high residual levels remaining after hydrolysis and extraction in the feces. These findings suggest that although feces are an abundant source of estradiol metabolite in the cat, and probably in the exotic felidae, development of noninvasive methods for monitoring ovarian cycles in these species will depend on more efficient methods for urine hydrolysis, on the resolution of problems encountered in fecal steroid analysis, or on the identification of metabolites which may be measured directly in the urine without hydrolysis or extraction.     

An estrogen receptor basis for raloxifene action in boneProceedings of Xth International Congress on Hormonal Steroids, Quebec, Canada, 17–21 June 1998.

Although controversy remains regarding direct effects of estrogen on bone, in vivo data clearly show that estrogens suppress bone turnover, resulting in decreased bone resorption and formation activity. Selective estrogen receptor modulators (SERMs), such as raloxifene, produce effects on bone which are very similar to those of estrogen. In vitro, both raloxifene and estrogen inhibit mammalian osteoclast differentiation and bone resorption activity, but only in the presence of IL-6. Data from a number of ovariectomized rat model manipulations (i.e. hypophysectomy, low calcium diet and drug combinations) demonstrate a strong parallel between the antiosteopenic effects of raloxifene and estrogen. A characteristic action of estrogens on the skeleton is inhibition of longitudinal bone growth, an effect which is not observed with other resorption inhibitors, including calcitonin and bisphosphonates. Consistent with an estrogen-like mechanism on bone, raloxifene inhibits longitudinal bone growth in growing rats. In addition to the overall similarity of the bone activity profile in animals, estrogen and raloxifene also produce similar effects on various signaling pathways relative to the antiosteopenic effect of these two agents. For example, IL-6, a cytokine involved in high turnover bone resorption following estrogen deficiency in rats, is suppressed by both raloxifene and estrogen. Raloxifene and estrogen also produce a similar activation of TGF-β3 (a cytokine associated with inhibition of osteoclast differentiation and activity) in ovariectomized rats. Like 17β-estradiol, raloxifene binds with high affinity to both estrogen receptor- (ER) and estrogen receptor-β (ERβ). Crystal structure analyses have shown that 17β-estradiol and raloxifene bind to ER with small, but important, differences in three dimensional structure. These subtle differences in the conformation of the ligand:receptor complex are likely the basis for the key pharmacological differences between estrogens and the various SERMs (i.e. raloxifene vs tamoxifen). Raloxifene also produces estrogen-like effects on serum cholesterol metabolism and the vasculature. Thus, while raloxifene exhibits a complete estrogen antagonist in mammary tissue and the uterus, it produces beneficial effects on the cardiovascular system and prevents bone loss via an estrogen receptor mediated mechanism.     

雌激素信号通路概述

过去几十年,人们一直认为雌激素信号通路是雌激素与细胞核中的雌激素受体(ER)结合,作用于雌激素受体反应元件调节基因表达,从而改变细胞功能。雌激素不但与核ER结合,也能与膜ER结合激活PI3K信号通路。G蛋白偶联受体(GPR30)也能与雌激素结合,激活PI3K信号通路。雌激素通过结合不同雌激素受体改变细胞生理功能。我们对雌激素信号通路做简要综述。     

Estrogen, alcohol and breast cancer risk

Estrogen replacement has been used for many years to reverse the hypoestrogenic symptoms of menopause and prevent osteoporosis. Studies have found that estrogen replacement also decreases cardiovascular risk. In addition, social use of alcohol has been found to decrease cardiovascular risk. Therefore, both estrogen replacement therapy and alcohol use have been proposed to have cardiovascular benefits, and are often used in combination. Epidemiologic evidence indicates that estrogen replacement therapy after menopause increases breast cancer risk. Regular alcohol consumption is also associated with increase in risk. However, interactions between the two are poorly understood. In addition, if alcohol alters circulating estrogen levels in estrogen users, this may have implications in terms of altering the risks:benefit ratio of estrogen replacement in an undesirable direction. For example, there are data suggesting that the use of both alcohol and estrogen may increase breast cancer risk more than the use of either one alone. Data support both acute and chronic effects of alcohol in raising circulating estrogen levels in premenopausal women on no hormonal medications. In postmenopausal women studies focusing on acute effects of alcohol on estrogen metabolism indicate that alcohol has a much more pronounced effect in women using estrogen replacement than in those who do not. Studies evaluating chronic effects of alcohol ingestion on circulating estrogens in postmenopausal women are needed.     

Excretion of radiolabeled estradiol metabolites in the slow loris (Nycticebus coucang)

The excretion pattern of estradiol was studied in the slow loris Nycticebus coucang) and the ring-tailed lemur (Lemur catta) in order to compare steroid excretion in two representative prosimian species. Daily urinary estrone conjugate measurements in the female loris provided little information when applied over prolonged periods. As a result of these negative data, a metabolic study was performed to determine if estrogen excretion patterns in the slow loris differed from those in the lemur, where urinary assays proved a useful tool in characterizing reproductive cycles. Radio-labeled estradiol was injected intravenously, and serial urine and fecal collections were analyzed for radiolabeled metabolites. The results of these studies demonstrate that more than 92% of the radiolabel was excreted in the feces of the loris, in contrast to only 16% excreted in the feces of the lemur.     

Naturally occurring menopause in cynomolgus monkeys: changes in hormone, lipid, and carbohydrate measures with hormonal status

Naturally occurring post-menopausal (PM) female cynomolgus monkeys (Macaca fascicularis) were identified. Their sex hormone profile was characterized and compared with younger pre-menopausal females before and after ovariectomy (OVX). PM females had lower estrogens and increased follicle-stimulating hormone (FSH) concentrations. Two PM females had diabetes mellitus and elevated androgens (androstenodione and dihydroepiandrosterone sulfate). Non-diabetic PM females were given parenteral E(2) which normalized FSH, and caused improvements in body weight, plasma lipids and lipoprotein cholesterol. Androgens remained lower with E(2) treatment. OVX induced comparable increases in FSH seen with the PM monkeys, however they had lower body weights, and had higher estrone and androstenodione concentrations. Natural menopause occurs in cynomolgus monkeys and hormone changes with OVX are similar however, differences in sex hormones that can relate to body mass and age may be important. E(2) treatment restored estrogen levels and induced improvements in the lipid profile of PM females.     

Estradiol,progesterone, and sex hormone-binding globulin in female rhesus monkeys (Macaca mulatta)

We measured the concentrations of estradiol, progesterone, and the sex hormone-binding globulin capacity (rhSHBG) in serum of female rhesus monkeys (Macaca mulatta). Although the serum rhSHBG capacity was altered by the removal of ovarian hormones, presumably estradiol, acute changes in serum estradiol and progesterone did not influence SHBG capacity. There appears to be a relatively low threshold for the effect of estradiol on rhSHBG capacity. The threshold must be present for a finite length of time to have that effect.     

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin, 12-O-tetradecanoylphorbol-13-acetate and 17β-estradiol on estrogen receptor regulation in MCF-7 human breast cancer cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exhibits remarkably potent antiestrogenic activity. To further elucidate the role of estrogen receptor (ER) regulation in this response, we examined the effects of exposure to TCDD in MCF-7 human breast cancer cells on ER mRNA levels by using an RNase protection assay, on ER accumulation by using an ER immunocytochemical essay (ER-ICA), and on ER function by competitive binding assays under conditions of saturating 17β-estradiol (E₂). Comparative studies were conducted with E₂ and 12-O-tetradecanoylphorbol-13-acetate (TPA), as both compounds are known to suppress ER expression. Our results indicate that 1 nM E₂ and 100 nM TPA both suppress ER mRNA levels as early as 4 h after exposure and to 33.6% and 16.5% of control levels, respectively, after 72 h. In contrast, no significant effect on ER mRNA levels was attributed to exposure to 10 nM TCDD. A greater than 50% reduction in positive staining was observed by ER-ICA after 72 h exposure to 1 nM E₂ and to 100 nM TPA, while only an 11% reduction in positive staining was observed with 10 nM TCDD. Specific binding of [³H]E₂ under saturating conditions (10 nM E₂) in whole cells was reduced by 50% in cultures exposed to 100 nM TPA, although no effect on binding was observed with exposure to 10 nM TCDD. In contrast, specific binding using subsaturating 1 nM [³H]E₂ was depressed by 49% in MCF-7 cells exposed to 10 nM TCDD for 72 h. This depression was inhibited by a 1-h treatment with 5 μM α-naphthoflavone, which inhibits TCDD-induced, P450-mediated, E₂ metabolism, and subsequent E₂ depletion. In conclusion, while TPA and E₂ effectively down-regulate ER expression, TCDD, under antiestrogenic conditions, has little if any effect on total ER levels in MCF-7 cells, and thus ER modulation is probably not necessary for the suppression of estrogenic activity in MCF-7 cells by TCDD. © 1996 Wiley-Liss, Inc.     

BRCA1, Hormone, and Tissue-Specific Tumor Suppression

Germline mutations of BRCA1 predispose women to breast and ovarian cancers. Elucidating molecular mechanism of tissue- and gender-specific phenomena in BRCA1-related tumors is a key to our understanding of BRCA1 function in tumor suppression. This review summarizes studies in recent years on the link between BRCA1 and estrogen/progesterone signaling pathways, as well as discusses various models underscoring a triangle relationship among BRCA1, estrogen and genome instability.     

MS-KIF18A, a kinesin, is associated with estrogen receptor

The study of MS-KIF18A kinesin protein is focused on its cellular distribution and association with a cargo protein. Indirect immunofluorescence (IF) analyzed the intracellular distribution of endogenous MS-KIF18A and the transfected enhanced green fluorescence protein (eGFP)-MS-KIF18A in osteogenic cells. In both cases, the proteins were localized at the plasma membrane, cytosol, and nucleus. Bioinformatics analysis suggested interactions between MS-KIF18A and estrogen receptor (ERalpha) which were further elucidated by immunoprecipitation (IP). We identified interaction between endogenous MS-KIF18A with 66 and 46 kDa isoforms of ERalpha in MBA-15 cells. Moreover, MS-KIF18A and 66 kDa ERalpha complex has been demonstrated between ectopically expressed proteins in COS-7 cells. We have shown that anti-MS-KIF18A antibody immunoprecipitated the ERalpha and pERK in cells challenged with 17beta-estrogen (17beta-E2). The hormone activation induced mitogen-activated protein kinases (MAPK) pathway and increased p-ERK. The activation was interfered when cells were pre-treated with either ICI-182,780 or MAPK inhibitor PD98059 prior the challenge with 17beta-E2 that resulted in a decrease in association between MS-KIF18A and p-ERK1/2. The obtained results suggest a role for the proteins in a non-genomic response of MBA-15 cells challenged with 17beta-E2. This study presents a novel interaction between MS-KIF18A and ER that may have important physiological and pharmacological implications for estrogen action in various cells.     

The importance of appropriate controls, animal feed, and animal models in interpreting results from low-dose studies of bisphenol A

Interpreting results of studies that report only negative effects is problematic. A number of published studies to determine whether chemicals with estrogenic activity can cause effects at low doses have not taken into account the possibility that the commercial animal feed being used can mask effects of even potent estrogenic drugs such as diethylstilbestrol (DES). In addition, the sensitivity of the strain of animal being used for the specific category of chemical being tested has not always been described. For environmental chemicals, such as the estrogenic polycarbonate plastic monomer bisphenol A, DES is an appropriate positive control for estrogenic effects, and using an appropriate low dose of DES can eliminate the possibility of false-negative conclusions of safety when the above or other variables contribute to the negative outcome. Only when simultaneous positive effects of low doses of a positive control chemical such as DES and negative effects of environmentally relevant low doses of the test chemical are demonstrated within the same experiment are conclusions of no effect of the test chemical warranted, and this has not been reported for bisphenol A in any study. Instead, more than 90 refereed journal publications have reported effects due to exposure to low doses of bisphenol A in a wide variety of animals (for references see: http://rcp.missouri.edu/endocrinedisruptors/vomsaal/vomsaal.html). However, due to lack of attention to the importance of appropriate positive controls, a small number of studies reporting negative effects of bisphenol A have created a false sense of controversy regarding low-dose effects of bisphenol A.     

Sexual differentiation of the zebra finch song system: Positive evidence,negative evidence,null hypotheses,and a paradigm shift

Permanent sex differences in the brain are found in many vertebrates, and are thought to be induced by sex differences in secretion of gonadal steroid hormones during critical periods of early development. This theory has received support primarily from many experiments conducted on mammals, but also from studies on other vertebrate classes, including birds. The only avian neural dimorphism that has allowed extensive tests of this hypothesis is the neural circuit for song in passerine birds, which is much larger in males than in females. Experiments in zebra finches have yielded contradictory results. Although it is relatively easy to induce masculine patterns of development in genetic females with estrogen, it has not been possible to induce feminine patterns of development in males with any treatments, including antiestrogens and inhibitors of estrogen synthesis. Moreover, genetic females that develop with large amounts of functional testicular tissue but with virtually no ovarian tissue nevertheless have a feminine song circuit. The latter studies fail to support the idea of steroid induction of sexual differentiation. An alternative to the steroidal control hypothesis is that nonhormonal gene products expressed in the brain early in development trigger sexually dimorphic patterns of development. Although current evidence in several neural and nonneural systems indicates that sexual differentiation of some somatic phenotypes cannot be explained by the actions of gonadal steroids, the idea of direct genetic (nonhormonal) induction of sexual differentiation has yet to be proved. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 572–584, 1997     

Efficacy of levonorgestrel when administered as an irradiated,slow‐release injectable matrix for feline contraception

Reliable and safe methods of reversible contraception are needed for use in zoo felids. The efficacy of levonorgestrel (LNG) as a contraceptive, when delivered as a cesium‐irradiated, slow‐release, injectable matrix, was tested in domestic cats as a model for exotic cats. An increase (P = 0.0017) in body weight was observed in treated but not control queens (P = 0.2146). All control queens (n = 6), which received injections of matrix only, but none of the LNG‐treated queens (n = 6) became pregnant during the trial. Levonorgestrel was effective in preventing pregnancy for at least 36 weeks after two injections of drug‐loaded formulations (40 mg/kg body weight), administered 68 days apart. Throughout the study, all control queens displayed luteal activity and fluctuating fecal estradiol concentrations, whereas the LNG‐treated queens displayed lower estradiol concentrations and no luteal activity after treatment. We conclude that LNG, when delivered as a cesium‐irradiated, slow‐release, injectable matrix, is an effective contraceptive in domestic cats, reducing follicular activity, and thus, preventing mating and luteal activity. Zoo Biol 20:407–421, 2001. © 2001 Wiley‐Liss, Inc.     

核因子增强雌激素受体与雌激素效应元件的结合

利用体外翻译系统,翻译了能与雌激素效应元件（ＥＲＥ）结合的全长的人雌激素受体（ｈＥＲ）。制备了切除卵巢的雌性大鼠子宫核抽提物,在雌激素存在下,此核抽提物能增强ｈＥＲ与ＥＲＥ的结合。此核抽提物在５０℃保温１５ｍｉｎ后,明显减弱了增强ｈＥＲ－ＥＲＥ结合的作用。提示了核抽提物中存在着能增强ｈＥＲ－ＥＲＥ结合的雌激素依赖的热敏感性的辅助因子。在大肠杆菌中表达了谷胱甘肽转硫酶（ＧＳＴ）融合的雌激素受体的ＤＮ