Receptors In Myometrium Research Articles

Altered gene expression of endothelin-A and endothelin-B receptors, but not endothelin-1, in myometrium and placenta from pregnancies complicated by preeclampsia.

The aim of the present study was to compare the mRNA expression of endothelin-1 (ET-1), ET-1 receptors ET(A) and ET(B) in myometrium and placenta obtained from biopsies collected from women with preeclampsia (n=10) or normal pregnant (n=12). The mRNA levels of ET-1 ET(A) and ET(B) were determined using RT-PCR and expressed as arbitrary units after correction for control GAPDH gene mRNA levels. The mRNA levels of ET-1 in myometrium and placenta were not altered in women with preeclampsia compared to normal pregnant. The mRNA expression of ET(A) was significantly reduced (p<0.05) in both placenta and myometrium from women with preeclampsia. The mRNA levels of ET(B) were similar in placentas from both preeclamptic and normal pregnant women, but higher in myometrium (p<0.05) from women with preeclampsia. These results indicate that the higher levels of ET-1 seen in preeclamptic women do not depend on an altered mRNA transcription of ET-1. The significantly reduced mRNA expression of ET(A) receptor in myometrium and placenta in women with preeclampsia might represent downregulation of the receptors due to the increased levels of ET-1 in uteroplacental circulation in this disorder. Much more research is needed before the role of ET(B) receptors in preeclampsia can be clarified.

Oxytocin Receptors in Guinea Pig Myometrium Near Term and During Labor1

Oxytocin receptors in myometrium of women, rats, and rabbits rise markedly before the onset of labor, suggesting a role in the initiation of labor. In guinea pigs, a previous study reported no such rise by one-point determination of oxytocin binding. The purpose of this study was to use a more rigorous method to determine whether the binding characteristics of myometrial oxytocin receptors change in relation to labor in guinea pigs. Competitive binding studies were carried out in microsomes from inner and outer myometrium between 42 days of gestation and labor. Binding to analogs was also tested. Data were analyzed with affinity spectra and LIGAND. Oxytocin bound to one site with a dissociation constant of 6.3 +/- 0.65 x 10(-9) M. Binding capacity was 1.0 +/- 0.1 x 10(-12) mol/mg protein. The Hill coefficient was near unity. No significant changes occurred with gestation or labor in dissociation constant, binding capacity, or Hill coefficient (all P >/= 0.2, nested ANOVA). Binding capacity was higher in the outer than in the inner layer (1.2 +/- 0.2 vs. 0.8 +/- 0.1 x 10(-12) mol/mg protein, P = 0.02), but the dissociation constants were similar. Differences existed in the dissociation constants of the analogs tested. The main conclusion is that oxytocin receptors are unlikely to have a regulatory role in the initiation of labor in guinea pigs.

Role of estradiol and progesterone receptors in myometrium during labour

International Journal of Gynecology & ObstetricsVolume 70, Issue S4 p. D30-D30 Invited communication Obstetrics: Labor Role of estradiol and progesterone receptors in myometrium during labour N.D. Gasparian, N.D. GasparianSearch for more papers by this authorE.K. Kareva, E.K. KarevaSearch for more papers by this authorL.S. Logutova, L.S. LogutovaSearch for more papers by this authorI.P. Laricheva, I.P. LarichevaSearch for more papers by this authorI.I. Levasbova, I.I. LevasbovaSearch for more papers by this author N.D. Gasparian, N.D. GasparianSearch for more papers by this authorE.K. Kareva, E.K. KarevaSearch for more papers by this authorL.S. Logutova, L.S. LogutovaSearch for more papers by this authorI.P. Laricheva, I.P. LarichevaSearch for more papers by this authorI.I. Levasbova, I.I. LevasbovaSearch for more papers by this author First published: 11 December 2003 https://doi.org/10.1016/S0020-7292(00)82597-7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume70, IssueS42000Pages D30-D30 RelatedInformation

Differential Expression of Transforming Growth Factor-β1 and Transforming Growth Factor-β Receptors in Myometrium of Women With Failed Induction of Labor, No Labor, and Preterm Labor

Differential Expression of Transforming Growth Factor-β1 and Transforming Growth Factor-β Receptors in Myometrium of Women With Failed Induction of Labor, No Labor, and Preterm Labor

Regional variations in contractile responses to prostaglandins and prostanoid receptor messenger ribonucleic acid in pregnant baboon uterus

Objectives: The aims of this study were to compare (1) the contractile responses of the lower uterine segment and fundus to prostaglandins, (2) expression of genes encoding prostanoid receptors in myo-metrium from different regions of the uterus, and (3) the distribution of expression of genes encoding prostanoid receptors (P receptors) in key intrauterine tissues. Study Design: Cesarean hysterectomy was performed in 8 pregnant baboons, not in labor, in the last third of pregnancy. Contractile responses of fresh tissue were quantified in a superfusion system. Polyadenylated ribonucleic acid was extracted from frozen tissue and gene expression was quantified by Northern blot analysis with complementary deoxyribonucleic acid probes. Results: Prostaglandin E 2 contracted strips of myometrium from the fundus but had no significant effect on strips from lower uterine segment. Prostaglandin F 2 α contracted myometrium from both regions equally. Compared with fundus tissue, lower uterine segment tissue had greater expression of EP 2 receptor messenger ribonucleic acid, less expression of EP 3 receptor messenger ribonucleic acid, but similar levels of EP 4 receptor and FP receptor messenger ribonucleic acid. EP 2 receptor, EP 3 receptor, and EP 4 receptor messenger ribonucleic acids were also detected in cervix, decidua, and chorion. EP 2 receptor messenger ribonucleic acid was most abundant in the cervix, EP 3 receptor messenger ribonucleic acid was most abundant in the myometrium, and EP 4 receptor messenger ribonucleic acid was most abundant in the decidua. Conclusions: The reduced contractile response of lower uterine segment tissue to prostaglandin E 2 is paralleled by greater inhibitory EP 2 receptor expression and less contractile EP 3 receptor expression, a pattern similar to that seen in the cervix. Drugs with selective activity at prostanoid receptor types and subtypes are likely to allow safer and more effective control of the uterus and cervix than native prostaglandins. (Am J Obstet Gynecol 1998;179:1545-52.)

Treatment of preterm labor with the oxytocin and vasopressin antagonist Atosiban.

Oxytocin is involved in the regulation of preterm and term labor but the exact effect mechanisms are not fully understood. A regulatory action by vasopressin may also exist. The concentrations of oxytocin and vasopressin V1a receptors in myometrium from pregnant women are high before and in the beginning of labor both preterm and at term. Atosiban has high affinity for both these receptors and is a competitive oxytocin and vasopressin antagonist. The inhibitory effect of Atosiban on oxytocin induced activity on isolated myometrium correlates significantly with the concentration of the oxytocin receptors. Inhibition of preterm contractions with Atosiban was first reported by Akerlund et al 1987. Goodwin et al compared the effect of Atosiban to placebo in threatening preterm labor and the antagonist was in this trial significantly more effective than placebo in reducing the frequency of contractions (55% vs. 23%, p < 0.001). The same authors also reported successful tocolysis with the drug in actual preterm labor. Atosiban is currently in phase III of clinical development and seems to have the same effectiveness but fewer side-effects compared to beta-mimetics. These properties suggests that Atosiban may offer advantages over existing therapies in acute treatment of preterm labor.

Epidermal growth factor receptors in uteroplacental tissues in term pregnancy before and after the onset of labor.

Using saturation binding assays and Scatchard analyses, we determined the concentrations and binding affinities of epidermal growth factor (EGF) receptors in human myometrium (n = 13) and decidua (n = 10) before and during labor and in placenta (n = 15), chorion (n = 17), and amnion (n = 17) before labor, during labor, and after vaginal delivery. Each tissue was individually assayed. In myometrium and chorion, EGF receptors increased significantly from 5.6 +/- 0.8 and 13.5 +/- 1.7 fmol/mg protein (mean +/- SEM) before labor to 11.1 +/- 2.8 and 26.7 +/- 3.0 fmol/mg protein, respectively, after the onset of labor (P < 0.05). In amnion, EGF receptors increased from 12.8 +/- 2.7 fmol/mg protein before labor to 33.0 +/- 2.3 fmol/mg protein during labor, but decreased significantly (5.9 +/- 1.2 fmol/mg protein) with vaginal delivery (P < 0.05). Decidual and placental concentrations of EGF receptors did not change significantly with labor. The binding affinity of EGF receptors in all tissues studied did not change significantly with labor, as reflected by their respective association and dissociation constants. Up-regulation of EGF receptors in myometrium, chorion, and amnion with spontaneous labor may enhance stimulation of prostanoid production and stimulate uterine activity.

Angiotensin Receptors in Myometrium and Myometrial Vessels from Uteri of Women during the Follicular and Luteal Phases of the Menstrual Cycle and in Late Pregnancy

1. Receptors for angiotensin II were identified and characterized in membrane fractions from myometrial samples obtained at non-pregnant hysterectomy in women of reproductive age. Specific binding was also measured in paired samples of vascular and "vessel-free' myometrium. 2. A single class of high-affinity receptor sites was identified in the total myometrial preparations (n = 10), with a median equilibrium dissociation constant (Kd) of 0.122 nmol/l (range 0.065-0.465 nmol/l) and concentration of receptor sites (Bmax) of 149 fmol/mg protein (range 105-435 fmol/mg). Receptor characterization studies using losartan (an angiotensin type 1 receptor antagonist) and PD123177 (an angiotensin type 2 receptor antagonist) showed the myometrium to contain almost entirely type 2 receptors. 3. The median Kd and Bmax for specific angiotensin II binding in isolated myometrial vessel homogenates were 0.086 nmol/l (range 0.060-0.433) and 260 fmol/mg protein (range 197-737 fmol/mg) respectively. Vascular specific binding density was always higher in dissected out myometrial vessels than in paired vessel-free myometrium (median 372 compared with 120 fmol/mg protein; n = 20; P < 0.001). The specific binding in the paired samples was strongly correlated (r = 0.8904, P < 0.0001). 4. The specific binding of 125I-labelled angiotensin II in "vessel-free' myometrium was higher in samples from the follicular phase than in samples from the luteal phase (median 144 compared with 37 fmol/mg; P < 0.02). A similar trend was found in the vessels themselves, but this failed to reach statistical significance (459 compared with 225 fmol/mg; P = 0.051). 5. It is suggested that the down-regulation of the angiotensin type 2 receptors in the luteal (secretory) phase is a preparation for pregnancy, removing an inhibitory factor to uterine growth and vascularization and allowing greater prostacyclin synthesis.

Total and unbound cytosolic estrogen and progesterone receptors in myometrium and fibroid after gonadotropin-releasing hormone agonist treatment: Fernandez-Mentoli M.E.; Diez-Gibert O.; Samaniego J.M.; Balaguero L.; Navarro M.A. ESP Fertil Steril 1995 63/3 (522–5270)

International Journal of Gynecology & ObstetricsVolume 51, Issue 2 p. 194-194 Citations from the literature endocrinology Total and unbound cytosolic estrogen and progesterone receptors in myometrium and fibroid after gonadotropin-releasing hormone agonist treatment Fernandez-Mentoli M.E.; Diez-Gibert O.; Samaniego J.M.; Balaguero L.; Navarro M.A. ESP Fertil Steril 1995 63/3 (522–5270) First published: November 1995 https://doi.org/10.1016/0020-7292(95)96769-QAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume51, Issue2November 1995Pages 194-194 RelatedInformation

Decrease in myometrial beta-adrenergic receptors with prenatal cocaine use

To determine if cocaine use during pregnancy is associated with a reduction in the number or affinity of beta-adrenergic receptors in human myometrium. Myometrium was obtained at cesarean delivery of five women who reported using cocaine during pregnancy and from ten controls. Saturation binding assays were performed on the myometrial membrane fractions using [125I]-cyanopindolol to determine beta-adrenergic receptor concentration and affinity. The percentages of beta 1- and beta 2-adrenergic receptors were determined in three cocaine users and four control patients by performing competition binding assays using the beta 2 antagonist ICI 118,551. Results were compared using unpaired Student t tests. Women who reported using cocaine during pregnancy had a significantly lower mean (+/- standard deviation) concentration of myometrial beta-adrenergic receptors than did controls (22 +/- 8 versus 52 +/- 23 fmol/mg protein, respectively). There was no difference in the receptor affinity constants between cocaine users and controls (16 +/- 2 pmol/L for both groups). The percentages of beta 1- and beta 2-adrenergic receptors in the myometrium of the cocaine-use group and control group were similar: 86 +/- 1% beta 2 in the cocaine-use group and 83 +/- 7% beta 2 in the control group. Cocaine use during pregnancy may be associated with a down-regulation of beta-adrenergic receptors in human myometrium. This could result in a decreased capacity for uterine relaxation and, consequently, a predisposition to preterm labor.

Total and unbound cytosolic estrogen and progesterone receptors in myometrium and fibroid after gonadotropin-releasing hormone agonist treatment

To study the changes in bound and unbound cytosolic estrogen receptor (ER) and progesterone receptor (PR) in fibroid and myometrium after treatment with gonadotropin-releasing hormone agonists (GnRH-a). Prospective randomized study. A tertiary institutional hospital. Thirty premenopausal women with normal regular menstrual cycles and uterine fibroids. Patients were randomized to receive buserelin acetate for 3 months (n = 20) or no treatment (n = 10) before hysterectomy. Bound and unbound ER and PR. In nontreated women, values of unbound ER and PR in fibroid were higher than in myometrium. There were no differences in total receptors. The total and unbound ER in myometrium was higher in treated than in nontreated women. There were no differences in fibroid. The higher content of unbound hormone receptors in fibroid correlates with an exacerbation of the hormone dependence of this tissue compared with myometrium. The increase of total and unbound ER in myometrium after treatment suggests a higher level of synthesis or a lower level of degradation of receptors in this tissue.

ETA and ETB endothelin receptors in human myometrium characterized by the subtype selective ligands BQ123, BQ3020, FR139317 and PD151242.

ETA selective (BQ123, FR139317, PD151242) and ETB selective (BQ3020) ligands were used to define the binding characteristics and contractile function of endothelin receptor subtypes in human myometrium. In saturation binding assays with 10 microns-thick tissue sections [125I]endothelin-1 (ET-1) bound with a single affinity to receptors in the myometrium (Kd, 1.19 +/- 0.17 nM) and adjacent endometrium (Kd, 1.39 +/- 0.51 nM). Competition binding assays in myometrium revealed a heterogeneous population of receptors with BQ123 (Kd ETA, 1.43 +/- 0.33 nM; Kd ETB, 39.91 +/- 9.06 microM), FR139317 (Kd ETA, 2.54 +/- 0.87 nM; Kd ETB, 89.79 +/- 24.34 microM) and BQ3020 (Kd ETA, 4.57 +/- 0.58 microM; Kd ETB, 90.07 +/- 19.53 nM). The presence of these receptors in myometrium was confirmed by saturation assays with the new ETA selective ligand [125I]PD151242 (Kd, 0.93 +/- 0.08 nM; Bmax 138.7 +/- 1.0 fmol/mg protein) and the ETB selective [125I]BQ3020 (Kd, 0.62 +/- 0.07; Bmax 44.5 +/- 1.1 fmol/mg protein). Reverse-transcriptase PCR assays detected mRNA encoding both receptor subtypes in myometrium. Autoradiography with radiolabelled PD151242 and BQ3020 demonstrated that ETA receptors were the predominant subtype in the myometrium and identified a population of ETB receptors in the endometrium. In tissue bath experiments, an ET-1-induced increase in contractility of myometrial strips was antagonized by 10 microM FR139317 but not by BQ123 at the same concentration. The ETB agonist BQ3020, which is a potent agonist in animal tissue, did not increase contractility when tested at concentrations up to 2 microM.

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

We investigated the binding properties of the endothelin receptors in the human myometrium in clinical situations associated with different ovarian steroid levels. Binding properties of the endothelin receptors were studied in myometrial membranes from post-menopausal women (n = 12), myomatous premenopausal women (n = 14) and pregnant women (n = 14), using 125I-labelled endothelin-1. The mean (+/- SD) maximal receptor density (Bmax) was significantly higher in samples from premenopausal and pregnant women than from post-menopausal women (983 +/- 196, 1116 +/- 201 and 490 +/- 145 pmol/g protein, respectively). Receptor affinity (Kd) did not differ significantly between these groups. Among the pregnant women, mean Bmax and Kd values were similar in those who electively underwent Caesarean section prior to the onset of labour and those operated on during the second stage of spontaneous labour. Binding properties of myometrial membranes of either pre or post-menopausal women were unaffected by the presence of high levels of beta-oestradiol or progesterone in the medium. Among samples of premenopausal women, no significant difference was found in binding properties between those operated on either during mid-follicular phase or during mid-luteal phase. In clinical situations associated with relatively high levels of ovarian steroids, the density of endothelin receptors in the myometrium is higher than in situations associated with low ovarian steroid level. Ovarian steroids may exert their influence via the production of other mediators. Changes in density of the endothelin receptor, induced by change in ovarian steroids activity, might play a role in the regulation of myometrial contractility.

Endothelin in rabbit uterus during pregnancy.

Specific immunostaining for endothelin-1 (ET-1) was observed in the uterine mucosa of pregnant and nonpregnant rabbits. During gestation, giant cells immunopositive for ET-1 were identified in either endometrium or myometrium. In the latter, they were located in close proximity to the muscular fibers. High-affinity (dissociation constant = 0.25 nM) high-capacity [maximal binding (Bmax) = 7 pmol/mg protein] receptors for ET-1 were present in myometrial membranes of estrous rabbits. During pregnancy the concentration of ET-1 receptors progressively decreased (Bmax on day 29 = 4 pmol/mg protein), rising again at the time of spontaneous delivery. Conversely, ET-1 receptors in the aorta did not change during pregnancy and parturition. The presence of giant cells immunopositive for ET-1 in close proximity to the myometrial cells, together with the evidence of an increase in ET-1 receptors in myometrium of parturient rabbits, suggests a paracrine role for endometrial ET-1 during delivery. Because we previously demonstrated that oxytocin releases ET-1 from endometrial cells in primary culture and that endometrial and myometrial oxytocin receptors abruptly rise at the time of parturition, we propose that ET-1 might participate in the complex cell-to-cell interactions that occur during labor.

Regulation of Myometrial β2-Adrenergic Receptors by Progesterone and Estradiol-17β in Late Pregnant Rats1

Rat myometrium exhibited a marked decrease in the concentration of beta 2-adrenergic receptors immediately before parturition, i.e., in the last 6 h of pregnancy. This phenomenon continued until the withdrawal of myometrial progesterone (-94% from Day 18 of pregnancy to term) and coincided with the sharp increase (+200%) of the myometrial concentration of estradiol. A linear positive correlation was found (r2 = 0.645) between the concentration of beta 2-adrenergic receptors and the log ratio of myometrial concentration of progesterone/myometrial concentration of estradiol (P/E2), suggesting a modulation of beta 2-adrenergic receptors by steroids. In rats with estrogen-dominated uteri (intact of ovariectomized late pregnant rats injected with estradiol), there was no change either in concentration or affinity of beta 2-adrenergic receptors relative to untreated control pregnant rats. In contrast, rats with progesterone-dominated uteri (intact or ovariectomized late pregnant rats treated with progesterone or ovariectomized rats) have an increased number of beta 2-adrenergic receptors, with a decreased affinity of these receptors compared to untreated control pregnant rats or to estrogen-treated rats. These results suggest that progesterone regulates the number of beta 2-adrenergic receptors in myometrium of late pregnant rats. The mechanisms by which progesterone exerts this regulation remains to be elucidated.

Oxytocin and vasopressin: distinct receptors in myometrium.

The binding characteristics of [3H]oxytocin [( 3H]OT) and [3H]lysine vasopressin [( 3H]LVP) to nonpregnant human myometrium were investigated. Binding of both radioligands was saturable, time dependent, and reversible. Whereas [3H]OT was found to bind to a single class of sites with high affinity [Kd, 1.5 +/- 0.4 (+/- SEM) nM] and low capacity [maximum binding (Bmax), 34 +/- 6 fmol/mg protein], [3H]LVP bound to two classes of sites, one with high affinity (Kd, 2.2 +/- 0.1 nM) and low capacity (Bmax, 198 +/- 7 fmol/mg protein) and another with low affinity (Kd, 655 +/- 209 nM) and high capacity (Bmax, 5794 +/- 1616 fmol/mg protein). The binding of the labeled peptides also displayed a marked difference in sensitivity to Mg2+ and guanine nucleotides. These differences in binding characteristics as well as the differences in potency of analogs in competing for [3H]OT and [3H]LVP binding indicate the presence of distinct receptors for OT and vasopressin in human myometrium. Pharmacological characterization of the high affinity binding sites for [3H]LVP indicated that these are of the V1 subtype. Although, as suggested by others, vasopressin and OT can bind to the same sites, the presence of distinct receptors for both peptides provides an explanation for the previously reported difference in myometrial responsiveness to OT and vasopressin.

Transient uterine refractoriness after oxytocin administration in ewes.

Steroid-primed, ovariectomized ewes were treated intravenously with 2 doses of 1 microgram oxytocin at intervals of 1, 2, 4 or 6 h. The initial dose resulted in increases in 13,14-dihydro-15-keto-PGF-2 alpha in the peripheral circulation from 173 to 667 pg/ml within 5 min; subsequent doses caused responses of 23 +/- 1, 23 +/- 6, 54 +/- 12 and 62 +/- 10% respectively of the initial dose. Concentrations of oxytocin receptor in myometrium, caruncular endometrium and intercaruncular endometrium were, respectively, 185 +/- 33, 128 +/- 7 and 105 +/- 14 fmol/mg protein at 2 h after saline injection and 147 +/- 27, 195 +/- 52 and 170 +/- 50 fmol/mg protein at 2 h after administration of 1 microgram oxytocin. The dose of oxytocin administered was shown to raise circulating concentrations to levels characteristic of those observed during spontaneous episodes of release of oxytocin at luteolysis. Oxytocin administration therefore results in transitory uterine refractoriness which may be due to failure of a post-receptor response and this may contribute to the episodic nature of uterine prostaglandin secretion.

Estrogen and progesterone receptor and hormone levels in human myometrium and placenta in term pregnancy

Estradiol and progesterone receptors in the myometrium, decidua, placenta, chorion, and amnion of eight women who underwent elective cesarean section at term were determined by means of an exchange assay. The hormone levels in the peripheral plasma and cytosol of these tissues were measured by radioimmunoassays. Maternal plasma and the placenta had high concentrations of estradiol and progesterone, with the placenta having 12 times more progesterone than in maternal plasma but only half the concentrations of estradiol in maternal plasma. The decidua and placenta had detectable levels of cytosol and nuclear estradiol receptors, but the myometrium had no measurable cytosol estradiol receptors, whereas the chorion and amnion had neither cytosol nor nuclear estradiol receptors. However, the chorion and amnion had significantly higher concentrations of estradiol in the cytosol than those in the decidua and myometrium. Only the decidua and myometrium had cytosol and nuclear progesterone receptors, but the placenta, amnion, and chorion had neither cytosol nor nuclear progesterone receptors. In contrast, progesterone hormone levels were significantly higher in the placenta, amnion, and chorion than in the decidua and myometrium. The findings indicate that, in the term pregnant uterus, (1) the placenta, amnion, and chorion are rich in progesterone, estradiol, and nuclear estradiol receptors but have no progesterone receptors, (2) the decidua and myometrium have nuclear estradiol and progesterone receptors, and (3) the myometrium has a higher progesterone/estradiol ratio than that of the peripheral plasma, thus suggesting a highly progesterone-dominated uterus.

Oestrogen binding proteins in the female genital trac

We have estimated the binding characteristics of an oestrogen binding protein in the human vagina and in the human myometrium. The specificities of these binding proteins were analyzed in binding studies using competitors and ligands with different structural features representing the various elements considered to be of importance for binding. The specificity of an oestrogen binding protein in human myometrium was found to be similar to those of oestrogen binding proteins in human breast tumour tissue and in human MCF-7 cells. This specificity was also similar to those of oestrogen receptors in myometrium, endometrium and vagina of the rat. However, the specificity of an oestrogen binding protein in the vagina of postmenopausal patients was different. The vaginal oestrogen-binding protein displayed similar high affinities for 17β-oestradiol, 17α-oestradiol and oestriol but low affinity for diethylstilbestrol. The equilibrium dissociation constants for [ 3H]oestriol and [ 3H]17β-oestradiol were 4.3 × 1 −10M and 4.0 × 10 −10M respectively and the concentration of this protein varied between 30 and 170 fmol/mg vaginal cytosol protein. We conclude that the human vagina contains an oestrogen binding protein with characteristics different from those of oestrogen receptors present in myometrium and breast tumour tissue.

Alpha-adrenergic receptors in myometrium of pregnant and nonpregnant pigs until day 19 postestrus.

Binding of [3H] dihydroergocryptine (DHE) to myometrium was studied in cyclic and pregnant gilts. The binding was saturable and of high affinity (Kd = 2-4 nM). DHE binding was inhibited by phentolamine, phenoxybenzamine, epinephrine and norepinephrine, but almost not at all by propranolol or isoproterenol. DHE appears to be bound to an alpha 2-adrenergic receptor because yohimbine had a much greater ability to compete for DHE binding sites than did prazosin. The concentration of DHE binding sites in the myometrium was greatest during the luteal phase of the estrous cycle as has been previously reported for sheep. The decrease at estrus did not appear to be associated with a change in the alpha 2-adrenergic receptor dominance in myometrial membranes. Embryo migration to the site of implantation may be associated with reduced concentration of DHE binding sites on Days 10 to 12 of pregnancy in pigs.