Endothelin-1 receptors in the human myometrium: evidence for different binding properties in post-menopausal as compared to premenopausal and pregnant women

Estradiol's effect on portal response to endothelin-1 after trauma-hemorrhage

BACKGROUND

The fine balance between vasoconstrictors and vasodilators maintains portal circulation. Studies have shown that portal response to endothelin-1 (ET-1), a potent vasoconstrictor, is enhanced following hemorrhagic-shock, which subsequently leads to the impaired hepatic circulation and hepatic damage. Although protective effects of 17beta-estradiol (E(2)) against hepatic damage following trauma-hemorrhage have been observed, it remains unknown whether E(2) directly improves hepatic circulation. We hypothesized that the salutary effects of E(2) are mediated, at least in part, by the attenuation of portal response to ET-1 following trauma-hemorrhage.

MATERIALS AND METHODS

Male adult Sprague-Dawley rats were randomly assigned to sham operation or trauma-hemorrhage with or without in vivo E(2) treatment. Trauma-hemorrhage included midline laparotomy and approximately 90 min of hemorrhagic shock (35 mmHg), then resuscitation with four times the shed blood volume with Ringer's lactate solution over 60 min. For the E(2) treatment group, 1 mg/kg of E(2) was added to the Ringer's lactate solution. At 5 h after the end of resuscitation, the liver was isolated and perfused in vitro to measure portal pressure responses to exogenous ET-1 (60 pmol in 150 ml perfusate, bolus) with or without E(2) (1,500 pg/ml).

RESULTS

Peak portal pressure after the administration of ET-1 was significantly higher in vehicle-treated trauma-hemorrhage group compared with the sham group. This effect was significantly attenuated in the E(2) treatment group. Furthermore, E(2) treatment restored bile production and prevented hepatic damage following trauma-hemorrhage.

CONCLUSIONS

The beneficial effects of estradiol observed following trauma-hemorrhage, at least partly, are caused by the attenuation of portal pressure response to increased ET-1.

Endothelin-secreting tumors and the idea of the pseudoectopic hormone secretion in tumors

Ectopic hormone secretion in tumor cells is here described as an amplification of hormone production already present in normal, nonendocrine tumor-originated tissue. This idea is tested on the available data regarding endothelin-1 (ET-1) secreting tumors. The endothelins are ubiquitous regulatory peptides produced by various tissues. The precursor cells of many tumor types secrete endothelins. ET-1 protein expression was detected in situ in all tested prostate cancers as well as in normal prostate tissue. The majority of hepatocellular carcinomas produce ET-1, while ET-1 is secreted by the normal hepatic stellate cells. Human breast cancer cells produce immunoreactive ET-1. Similar data exist for pancreatic tissue, the thyroid and large bowel. We can conclude that tumor cells might sustain endothelin secretions already present in the normal tumor-originated tissue. The model that is presented of the pseudoectopic hormone secretion consists of relations between a few parameters. The proportion of hormone-secreting tumors (Th) among all tumors (T) of that organ depends on the amount of the hormone-secreting cells (Ch) among all cells (C) susceptible to malignant transformation. The corrective factor (k) was introduced in the expression Th/T=Ch/C*k, to represent specific conditions altering the malignant transformation probability for a certain normal hormone-secreting cell. In prostate, breast and colon, the kvalue is predicted to be approximately 1, suggesting that ET-1-secreting normal cells are not more prone to the malignant transformation than their neighbours. In liver and pancreas, the incidence of ET-1-secreting tumors outnumbers the proportions of normal ET-1-secreting cells (k values >1). In these organs, normal ET-1-secreting cells seem more likely to turn malignant in comparison to their neighbours, perhaps due to their function, position and exposition to oncogenic factors, or even due to their ET-1 secretion. There are similar data for thyroid and adrenal glands. No ET-1 secretion was reported in kidney neoplasms. Normal renal ET-1 secreting cells might be less prone to turn malignant than other renal cells. Unlse the normal lung tissue, small cell lung cancers often secrete adrenocorticotrophic hormone (ACTH). The pancreatic islet cells do not secrete gastrin, but their tumors often do. Constant k would exceed 1 in both cases. We speculate that these tumors might originate from a small subset of cells with the described feature. Tumor cells sometimes lack features of the normal tissue, as in the cases of the steroid receptor-negative breast cancer. These tumors might originate from the hypothetical subset of receptor-free breast cells. Benign breast epithelial cells lacking oestrogen receptors have been described in cases of megalomastia. These cells might be constituents of normal breasts or, perhaps, present only in cases of increased breast cancer risk.

The molecular mechanisms of term and preterm labor: recent progress and clinical implications

Current tocolytic protocols rely largely on the use of beta-mimetics to induce myometrial quiescence and delay delivery. Unfortunately, the rapid transplacental passage and poor receptor specificity of the commonly used beta-mimetics results in widespread activation of intrauterine and extrauterine beta 1 and beta 2 receptors. The use of beta-mimetics is associated with a range of well-recognized and potentially dangerous side effects for mother and fetus. The value of continued use of beta-agonists after obtaining uterine quiescence also has been the subject of recent debate. In this article we have attempted to explore the biochemical and molecular rationale for the use of alternative therapeutic modalities in the treatment and prevention of PTL. In the light of the current view that the term "preterm labor" covers a considerable diversity of causes, we propose that a range of treatment regimes should be chosen on the basis of the diagnosis and classification of the patient according to the their particular condition. Although the measurement of several biochemical parameters have been suggested to be of use in predicting PTL, we believe that a panel of diagnostic indicators (e.g., free or total CRH, IL-6, extracellular matrix proteases, fetal fibronectin) is more likely to provide useful diagnostic information on which appropriate treatment modalities can be selected (Table 1). Because of the complex and interactive nature of the mechanisms operating within the intrauterine environment to regulate myometrial activation and uterotonin production, we speculate that a combination of tocolytics, anti-inflammatory agents, uterotonic antagonists, and receptor blockers is likely to be more effective than a monotherapeutic approach, which focuses on only one facet of the process of uterine activation for pharmacologic intervention. For example, the use of antibiotics, PGHS inhibitors, and/or beta-mimetics might be an appropriate first line of treatment for infection-associated PTL in extreme prematurity. If it is successful, this treatment might be followed by longer term use of a progestagen and/or NO donor to maintain myometrial quiescence until closer to term. Alternatively, use of progesterone or oxytocin antagonists may be effective in augmenting the actions of beta-mimetics while reducing their side effects, whereas other combinations may be useful as long-term prophylactics in women with a high risk of developing PTL. Improvements continue in our diagnostic ability to correctly identify the different causes of preterm labor. We anticipate that careful selection of differing combinations of therapeutic options will result in significant reductions in the morbidity, mortality, and healthcare costs associated with preterm birth.

Endothelin expression and responsiveness in human ovarian carcinoma cell lines

To elucidate the potential role of endothelins (ETs) as growth regulators in ovarian carcinoma cells in culture, expression of endothelins and their receptors were measured in two ovarian cancer cell lines (PEO4 and PEO14), together with the effect of the exogenous addition of endothelins on the growth of these cell lines in vitro. RT-PCR analysis of mRNA prepared from PEO4 and PEO14 indicated the presence of ET-1 and ET-3 mRNA. Immunoreactive ET-1-like peptide was found in media from cultures of both PEO4 (1.7 +/- 0.4 fmol/10(6) cells/72 h) and PEO14 (20.2 +/- 6.8 fmol/10(6) cells/72 h) cell lines. Radioligand binding studies using 125I-ET-1 and membrane fractions were consistent with PEO4 cells having two receptor sites of either high affinity (Kd = 0.065 nM, Bmax = 0.047 pmol/mg protein) or lower affinity sites (Kd = 0.49 nM, Bmax = 0.23 pmol/mg protein). Studies using membrane fractions of PEO14 cells indicated that this cell line has only a single lower affinity binding site (Kd = 0.56 nM, Bmax = 0.31 pmol/mg protein). However, RT-PCR analysis indicated the presence of mRNA from both ETA and ETB receptors in PEO4 and PEO14 cell lines. Exogenous addition of ETs to PEO4 and PEO14 cells at concentrations of 10(-10)-10(-7)M resulted in specific dose-dependent increases in cell number for ET-1 (with maximum effects at 10(-10) and 10(-9)M for PEO4 and PEO14, respectively) and ET-2 (maximum effects at 10(-8) and 10(-9)M for PEO4 and PEO14, respectively) but not for ET-3. Experiments on the growth of PEO14 cells using BQ123 (ETA-R) antagonist and "antisense" oligonucleotide against the ETA-R, in the absence of exogenous ETs, suggested that immunoreactive ET-1-like material secreted by PEO14 cells can affect their growth in an autocrine manner. These results would be consistent with ET-1 acting as a possible autocrine growth regulator in human ovarian carcinoma cells.

Endothelin receptor type A and B gene expression in human nonpregnant, term pregnant, and preeclamptic uterus

OBJECTIVE

The aim of this study was to quantify the gene expression of ETA and ETB receptors within the different uterine segments of nonpregnant, normal pregnant, and preeclamptic women.

STUDY DESIGN

Biopsy samples from the cervix, isthmus, and corpus uteri were obtained from eight nonpregnant, nine term pregnant, and seven preeclamptic women. The concentration of ETA and ETB receptor messenger ribonucleic acid were determined by a solution hybridization technique with complementary ribonucleic acid probes. Results are presented in counts per minute per microgram of total nucleic acid as mean +/- SEM.

RESULTS

The expression of messenger ribonucleic acid encoding the ETA receptor was generally higher in the upper than in the lower uterine segment in nonpregnant, normal pregnant, and preeclamptic myometrium, whereas the opposite pattern was seen with regard to ETB. During normal pregnancy the concentrations of ETA receptor messenger ribonucleic acid in the corpus and ETB receptor messenger ribonucleic acid in the isthmus were significantly elevated compared with those in nonpregnant women. This enhanced gene expression was, however, not observed in the preeclamptic group.

CONCLUSION

Our finding of segmentally differentiated endothelin receptor gene expression is compatible with a role for endothelin-1 in stimulating uterine contractions through ETA receptors during spontaneous labor and suggests a relaxing effect of the ETB receptor on the myometrium.

Endothelin expression in the uterus

The endothelins (ETs) comprise a family of 21 amino acid peptides, ET-1, ET-2 and ET-3, first demonstrated as products of vascular endothelium. Subsequent work showed that they are also found in non-endothelial cells from a variety of tissues such as breast, parathyroid and adrenal gland. At first, the ETs were recognized for their pressor effects. However, ET administration in vivo initially caused hypotension at low concentrations by triggering the paracrine release of endothelial-derived vasodilators. The ETs exert powerful contractile actions on myometrium and other types of smooth muscle and are mitogenic, or co-mitogenic for fibroblasts, vascular smooth muscle and other cells. Demonstration of extravascular ET in endometrium has revealed a powerful vasoconstrictor which might act on the spiral arterioles to effect a powerful and sustained contraction of vascular smooth muscle. ETs might also contribute to the process of endometrial repair. In addition, the ETs appear to play a fundamental role in the control of uterine function in pregnancy. Effects on myometrial contractility have been implicated in the mechanisms governing the onset of normal and pre-term labour, and the peptides are likely to be key determinants of placental blood flow by binding to vascular smooth muscle receptors in the placenta.

Decreased expression of messenger RNAs encoding endothelin receptors and neutral endopeptidase 24.11 in endometrial cancer

In this study, we used reverse transcriptase-polymerase chain reaction (RT-PCR) to compare the expression of mRNAs encoding endothelin-1 (ET-1), endothelin receptors type A (ETA-R) and type B (ETB-R) and ET-1-degrading enzyme neutral endopeptidase 24.11 (NEP) in 15 endometrial cancer tissues and 13 normal endometrial tissues. The relative levels of ET-1 mRNA in endometrial cancer tissues did not differ from those in normal endometrium. Both ETA-R and ETB-R mRNA levels were significantly lower in endometrial cancer tissue than in normal endometrium (P < 0.001). The complete lack of NEP mRNA in endometrial cancer tissues was in marked contrast to results from normal endometrium (P < 0.001). In conclusion, differential expression of mRNAs encoding ET-R and NEP in normal endometrium and endometrial cancer suggests that ET action is altered in endometrial cancer compared with normal endometrium.

Differential expression of mRNAs for endothelin-related proteins in human endometrium, myometrium and leiomyoma

The expression of mRNAs encoding endothelin-1 (ET-1) and its receptors (ETA-R and ETB-R) as well as the ET degrading enzyme, neutral endopeptidase 24.11 (NEP), was determined in tissue samples of endometrium, myometrium and leiomyoma by using a reverse transcriptase polymerase chain reaction (RT-PCR) technique. ET-1 mRNA was detected in all samples studied. The level of ET-1 mRNA was higher in endometrium than in myometrium (p < 0.01) and leiomyoma (p < 0.001). The ETA-R mRNA was more abundant in endometrium than in myometrium (p < 0.001). For ETB-R mRNA there was no difference between these tissues. In contrast to ETA-R mRNA, which was more abundant in leiomyoma than in myometrium (p < 0.01), the ETB-R mRNA was less abundant in leiomyoma (p < 0.01). The NEP mRNA was detected in all endometrial samples but not in myometrium and leiomyoma. Our results show that the expression and relative levels of mRNAs encoding ET-1, ETA-R, ETB-R, and NEP vary in different tissue compartments of the human uterus. Since the net biological action of ET-1 in a particular cell type presumably depends on the balance between the peptide itself, its receptors and degrading enzymes, these results suggest different roles for ET-1 action in uterine endometrium, myometrium and leiomyoma. The difference in relative abundance of ETA-R and ETB-R mRNAs between myometrium and leiomyoma suggests that an altered ET-R gene expression may be a contributing factor in myomal growth.

Impaired binding properties of endothelin-1 receptors in human endometrial carcinoma tissue

BACKGROUND

Endothelins, potent stimulators of smooth muscle tissue activity, were recently shown to also function as mitogens for numerous cell types. The authors investigated the properties of endothelin-1 (ET-1) receptors in human endometrial tissue compared with human endometrial carcinoma tissue.

METHODS

Tissue samples from 13 patients with endometrial carcinoma and from 12 women undergoing hysterectomy due to uterus myomatous were obtained immediately after surgical removal. Binding properties of the endothelin receptors were studied using 125I-labeled ET-1.

RESULTS

A significant difference was demonstrated between binding properties of ET-1 receptors of these two groups. The mean maximal density (Bmax) value of the normal endometrial samples was 2029 +/- 341 fmol/mg protein, whereas that of the neoplastic samples was 356 +/- 121 fmol/mg protein. No differences were found, however, between the mean dissociation constant (Kd) values of these groups.

CONCLUSIONS

These results might be compatible with the increased blood flow that characterizes malignant endometrial tissue. However, they do not indicate an important mitogenic role for ET-1 in the development of endometrial cancer.