Regulation of oxytocin, oestradiol and progesterone receptor concentrations in different uterine regions by oestradiol, progesterone and oxytocin in ovariectomized ewes

The regulation of oxytocin, oestradiol and progesterone receptors in different uterine cell types was studied in ovariectomized ewes. Animals were pretreated with a progestogen sponge for 10 days followed by 2 days of high-dose oestradiol to simulate oestrus. They then received either low-dose oestradiol (Group E), low-dose oestradiol plus progesterone (Group P) or low-dose oestradiol, progesterone and oxytocin (via osmotic minipump; Group OT). Animals (three to six per time-point) were killed following ovariectomy (Group OVX), at oestrus (Group O) or following 8, 10, 12 or 14 days of E, P or OT treatment. In a final group, oxytocin was withdrawn on day 12 and ewes were killed on day 14 (Group OTW). Oxytocin receptor concentrations and localization in the endometrium and myometrium were measured by radioreceptor assay, in situ hybridization and autoradiography with the iodinated oxytocin receptor antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]-vasotocin. Oestradiol and progesterone receptors were localized by immunocytochemistry. Oxytocin receptors were present in the luminal epithelium and superficial glands of ovariectomized ewes. In Group O, endometrial oxytocin receptor concentrations were high (1346 +/- 379 fmol [3H]oxytocin bound mg protein-1) and receptors were also located in the deep glands and caruncular stroma in a pattern resembling that found at natural oestrus. Continuing low-dose oestradiol was unable to sustain high endometrial oxytocin receptor concentrations with values decreasing significantly to 140 +/- 20 fmol mg protein-1 (P < 0.01), localized to the luminal epithelium and caruncular stroma but not the glands. Progesterone treatment initially abolished all oxytocin receptors with none present on days 8 or 10. They reappeared in the luminal epithelium only between days 12 and 14 to give an overall concentration of 306 +/- 50 fmol mg protein-1. Oxytocin treatment caused a small increase in oxytocin receptor concentration in the luminal epithelium on days 8 and 10 (20 +/- 4 in Group P and 107 +/- 35 fmol mg protein-1 in Group OT, P < 0.01) but the rise on day 14 was not affected (267 +/- 82 in Group OT and 411 +/- 120 fmol mg protein-1 in Group OTW). In contrast, oestradiol treatment was able to sustain myometrial oxytocin receptors (635 +/- 277 fmol mg protein-1 in Group O and 255 +/- 36 in Group E) and there was no increase over time in Groups P, OT and OTW with values of 61 +/- 18, 88 +/- 53 and 114 +/- 76 fmol mg protein-1 respectively (combined values for days 8-14). Oestradiol receptor concentrations were high in all uterine regions in Group O. This pattern and concentration was maintained in Group E. In all progesterone-treated ewes, oestradiol receptor concentrations were lower in all regions at all time-points. The only time-related change occurred in the luminal epithelium in which oestradiol receptors were undetectable on day 8 but developed by day 10 of progesterone treatment. Progesterone receptors were present at moderate concentrations in the deep glands, caruncular stroma, deep stroma and myometrium in Group O. Oestradiol increased progesterone receptors in the luminal epithelium, superficial glands, deep stroma and myometrium. Progesterone caused the loss of its own receptor from the luminal epithelium and superficial glands and decreased its receptor concentration in the deep stroma and myometrium at all time-points. There was a time-related loss of progesterone receptors from the deep glands of progesterone-treated ewes between days 8 and 14. These results show differences in the regulation of receptors between uterine regions. In particular loss of the negative inhibition by progesterone on the oxytocin receptor by day 14 occurred only in the luminal epithelium, but is unlikely to be a direct effect of progesterone as no progesterone receptors were present on luminal epithelial cells between days 8 and 14.     

Pregnancy and birth after high serum progesterone concentrations during the follicular phase in an in-vitro fertilization cycle with gonadotrophin-releasing hormone agonist suppression

This case illustrates the possibility of achieving a pregnancy and birth when elevated progesterone concentrations (> 4 ng/ml) are present during the follicular phase (from 6 days before human chorionic gonadotrophin injection) of a gonadotrophin-releasing hormone agonist/menotrophin cycle for in-vitro fertilization (IVF). The present patient underwent three IVF/embryo transfer cycles in which progesterone concentrations were repeatedly increased from the midfollicular phase onwards. A pregnancy was achieved after the first IVF attempt but ended in a miscarriage in the 19th week of gestation. During the second IVF attempt an endometrial biopsy taken on the day of oocyte retrieval revealed an endometrial advancement of 2 days. A successful pregnancy and birth was again achieved after the third IVF attempt although progesterone concentrations were considerably increased from 6 days before the ovulatory stimulus.     

Non-constrained elbow arthroplasty for mutilans deformity in rheumatoid arthritis: a report of six cases

OBJECTIVE: To analyze the effect on uterine receptivity of a decrease in E2 levels during the preimplantation period with the use of a step-down regimen in high responders undergoing IVF. DESIGN: Prospective controlled clinical study. SETTING: The Instituto Valenciano de Infertilidad. PATIENT(S): High responders in whom at least one previous IVF attempt failed in which 3-4 good-quality embryos were transferred and E2 levels were >3,000 pg/mL on the day of hCG administration. INTERVENTION(S): Gonadotropins were administered according to two different protocols. Blood samples were collected and IVF was performed. MAIN OUTCOME MEASURE(S): Serum E2 levels and reproductive outcome of IVF. RESULT(S): Estradiol levels on the day of hCG administration and throughout the preimplantation period and the number of oocytes collected were significantly lower with the use of the step-down regimen than during the previous failed cycle in which the standard protocol was used. The fertilization rate was similar and the number of good-quality embryos transferred was comparable. However, the implantation and pregnancy rates were significantly improved in patients who underwent the step-down regimen compared with those who received the standard protocol. CONCLUSION(S): With the use of a step-down regimen with FSH in high responders, our clinical results demonstrate that uterine receptivity can be improved when E2 levels are decreased during the preimplantation period.     

Mutations in hepatitis B DNA polymerase associated with resistance to lamivudine do not confer resistance to adefovir in vitro

A total of 96 women undergoing in-vitro fertilization (IVF) treatment were examined by transvaginal ultrasonography with colour and pulsed Doppler ultrasound on the 22nd day of the menstrual cycle preceding IVF. We assessed endometrial thickness, endometrial morphology, myometrial echogenicity, subendometrial vascularization, the uterine artery pulsatility index, protodiastolic notch and end diastolic blood flow in order to define a uterine score which could be correlated with the pregnancy rate. The overall pregnancy rate was 30.2%, and there was no difference between the pregnant and non-pregnant groups with regard to any of the ultrasonographic and Doppler parameters when examined separately. However, the uterine score was significantly higher in the pregnant group (15.9 +/- 2.81 versus 12.7 +/- 5.3, P = 0.002; t-test). No pregnancy occurred if the score was between 0 and 10. With a score of 11-15 there was a 34.7% chance of pregnancy, and scores >16 had a 42% chance of pregnancy. In conclusion, individual ultrasonographic and Doppler parameters are not of sufficient accuracy to predict uterine receptivity. The uterine score calculated prior to IVF cycles appears to be a useful predictor of implantation.     

Integrin expression in normal and out-of-phase endometria

Integrins have recently been proposed as having a major role in endometrial receptivity. Different patterns of integrin expression have been described during the normal endometrial cycle, and the co-expression of several integrins, mainly alpha1, alpha4 and beta3 has been considered as specific to the 'window of implantation'. In the present study 55 infertile patients underwent two endometrial biopsies during a single menstrual cycle. An early biopsy was done on postovulatory days 6-8, and a late biopsy was performed on postovulatory days 10 to 12. Histological dating as well as immunohistochemical evaluation of alpha1, alpha4, beta1, beta3, beta5, alpha(v)beta3 integrin expression and oestrogen and progesterone receptors were determined in all endometrial biopsies. Oestradiol and progesterone serum concentrations in serum were evaluated on the same days of the endometrial samplings. Nine out of the 55 midluteal biopsies (16.4%) showed out-of-phase endometria, but all biopsies were in phase in the late luteal phase. Differences in integrin expression between in- and out-of-phase biopsies were observed only for alpha(v)beta3 integrin glandular expression during the midluteal phase. Alpha(v)beta3 integrin glandular expression was found in all late luteal phase biopsies. Alpha(v)beta3 expression was closely correlated with histological maturation of the endometrium appearing suddenly at postovulatory day 6-7 and being expressed by all endometria dated as postovulatory day > or = 8, irrespective of midluteal endometrial biopsies being in phase or out of phase. No differences in integrin expression were detected between patients with or without endometriosis or between patients who became spontaneously pregnant and those who did not. In conclusion, further studies are necessary before patterns of integrin expression may offer an alternative to predict uterine receptivity and implantation potential.     

Hormone replacement for pregnancy in functionally agonadal women after transfer of thawed embryos in the in vitro fertilization program--problems of placental incompetence

Experience with hormonal substitution of sterile women treated within the IVF programme by means of donated oocytes changed completely views on endocrinological prerequisites of successful implantations and the further development of early pregnancy. While the effect of oestrogens and progesterone on endometrial proliferation and receptivity has been elaborated in great detail in the literature, data on the substitution of early pregnancy and the onset of placental competence are much scarcer. 1. The placenta is during the 15th week of pregnancy already fully competent and hormonal substitution can be probably terminated already sooner. 2. From the shape of the curves (as compared with steroid levels in spontaneous pregnancies) the authors conclude that the used doses (in particular of progesterone were higher than physiological. 3. Pregnancy of women with primary or secondary ovarian failure is an ideal in vivo model for investigation of the receptivity of the endometrium, the problem of implantation and function of the foetoplacental unit. Available data are not uniform and therefore in this very interesting field further investigations are needed.     

Estrogen and progesterone receptors, cell proliferation, and c-fos expression in the ovine uterus during early pregnancy

To evaluate uterine growth during pregnancy and the potential roles of estrogen and progesterone in regulating uterine cell proliferation and c-fos expression, ewes were assigned randomly to slaughter on day 12 after estrus (nonpregnant, NP), and on days 12, 18, 24, or 30 after mating (pregnant, P) in Exp 1 (n = 7 ewes/day) and on days 12 or 14 after estrus and on days 12, 14, 16, 18, 21, or 24 after mating in Exp 2 (n = 3-6 ewes/day). In Exp 1, endometrial expression of c-fos mRNA was evaluated, and labeling index was determined both in vitro (incorporation of 3H-thymidine) and in vivo (iv injection of bromodeoyxuridine [BrdU], a thymidine analog). Endometrial expression of the c-fos proto-oncogene was increased by approximately 10-fold on days 18, 24, and 30 P compared with day 12 NP or P. Labeling index (proportion of cells incorporating 3H-thymidine or BrdU, which provides an index of the rate of cell proliferation) of endometrial caruncular and intercaruncular tissues was low for day 12 NP or P, increased on day 18 P, and remained elevated on days 24 P and 30 P. On day 18 P, labeling index also was greater for gravid than nongravid horns for both caruncular and intercaruncular tissues. In Exp 2, estrogen receptors (ER), progesterone receptors (PR), and proliferating (BrdU-positive) cells were immunolocalized. The percentage of cells exhibiting specific staining for ER, PR, and BrdU was quantified morphometrically for epithelial, stromal, and glandular tissues within luminal and deep regions, as well as for myometrial tissues. For luminal epithelium and glands, the rate of cell proliferation increased dramatically by day 18 P, even though ER and PR levels were low in these compartments. Conversely, the rate of cell proliferation remained low throughout early pregnancy in deep glands, deep stroma, and myometrium, in association with sustained or transient increases in ER and PR levels. For luminal stroma, the rate of cell proliferation increased by day 21 P even though ER levels were low and PR levels remained high. Thus, during early pregnancy, c-fos expression increased concomitantly with increased endometrial cell proliferation. In addition, during early pregnancy, ER and PR levels were inversely related to the rate of cell proliferation in most of the uterine tissue compartments except luminal stroma, which exhibited increased cell proliferation even though ER levels were low and PR levels remained high.     

Ovary-independent estrogen receptor expression in neonatal porcine endometrium

Effects of age and ovariectomy (OVX) at birth on uterine growth, endometrial development, and estrogen receptor (ER) expression were determined for intact and OVX gilts (n = 5 per day) hysterectomized on postnatal days (PND) 0, 15, 30, 60, 90, or 120. Uteri were evaluated histologically, and ER protein and mRNA expression were characterized immunohistochemically and by in situ hybridization. OVX did not affect uterine weight or endometrial thickness until after PND 60, when both increased more rapidly in intact gilts. Neither did it affect genesis of uterine glands, which were present and which proliferated after PND 0, or endometrial ER expression patterns in glandular epithelium (GE), luminal epithelium (LE), or stroma (S) between PND 0 and 120. Endometrium was ER negative at birth. On PND 15, the ER signal was strong in GE, weak in S, and effectively absent in LE. Thereafter, although the ER signal remained strong in GE and increased through PND 60 in S, it was not evident consistently until after PND 30 in LE. The data indicate that 1) porcine uterine growth and endometrial morphogenesis are ovary-independent processes before PND 60; 2) uterine gland genesis is associated temporally with development of ER-positive endometrial GE and S; and 3) regulation of endometrial ER expression is ovary independent between PND 0 and 120. The results establish the ER as a marker of GE differentiation and implicate this receptor in mechanisms regulating endometrial morphogenesis in the neonatal pig.     

Comparison of transdermal versus oral estradiol on endometrial receptivity

OBJECTIVE: To compare the effects of oral micronized E2 with transdermal E2 on endometrial receptivity in women undergoing oocyte donation. DESIGN: Prospective, randomized, crossover trial. Serum E2 and P concentrations were measured on cycle days 14 and 22 (luteal day +8). Endometrial biopsies were obtained on day 22 and read in a blinded fashion for histology and beta-3-integrin expression. SETTING: University-based donor oocyte program. PATIENTS: Twenty-seven patients presenting for donor oocytes. MAIN OUTCOME MEASURES: Endometrial histology and beta-3-integrin expression. RESULTS: The endometrial glandular histology in women given oral micronized E2 was delayed by a mean of 1.6 days in comparison to that of women given transdermal E2. Seventy percent of women given oral E2 displayed a lag > or = 4 days whereas 29.6% given transdermal E2 displayed a similar lag. Serum E2 levels were 1,194 +/- 108.8 pg/mL (mean +/- SEM; conversion factor to SI unit, 3.671) in women on oral micronized E2 and 117.4 +/- 14.0 pg/mL in those on transdermal E2. CONCLUSION: The supraphysiologic serum E2 levels associated with oral micronized E2 may have a deleterious impact on endometrial receptivity. The development of more physiologic hormone replacement protocols may enhance endometrial receptivity and lead to improved clinical pregnancy rates.     

P300 subcomponents reflect different aspects of psychopathology in schizophrenia

With the results presented in this paper we devised an alternative method to precisely date the rat endometrium in relation to the estrous cycle. This is done by the exclusive use of scanning electron microscopy. Owing to its short estrous cycle (4 to 6 days, depending on age), the rat is ideally suited for the examination of cyclic changes occurring in the uterine epithelium. The cycle stage of rats predated by vaginal smear cytology was verified through the measurement of hormones relevant to the estrous cycle, i.e. estradiol-17-beta (E2), progesterone (P), luteinizing hormone (LH), and follicle stimulating hormone (FSH). Based on scanning electron images surface changes could thus be correlated to the cyclic variations of blood levels of sex hormones. The appearance of pseudoglands, the most prominent aspect during the cycle, is correlated with decreasing estrogen and rising progesterone levels. Pseudoglands are formed by apoptosis and necrosis of epithelial cells, and are most numerous during estrus. They had in previous studies been classified as genuine uterine glands.     

Identifying patient needs in the context of the medication use situation

This study was designed to assess junctional zone contractions (JZ) during cycles of in-vitro fertilization (IVF) and embryo transfer in oocyte donors exposed to a long protocol regime for ovarian stimulation. Real-time transvaginal ultrasound and advanced audio-visual and computer technology were used to evaluate the contraction pattern, frequency and velocity. At the time of down-regulation JZ contractions were not observed. After 7 days of superovulation all patients displayed cervico-fundal, fundo-cervical and random contractions. Cervico-fundal waves dominated the picture at the time of human chorionic gonadotrophin injection. However, the activity was strongest on the day of oocyte retrieval. At that time the percentage of opposing waves increased and fundo-cervical waves disappeared. The highest wave frequency and velocity (4.29+/-0.68 waves/min and 2.73+/-0.54 mm/s respectively) were observed at the time of oocyte retrieval. All patients had some JZ activity on days 2, 3 and 4 after oocyte retrieval but regular wave-like contractility gradually decreased and only single random movements were seen on day 4 after oocyte retrieval. In conclusion, JZ activity throughout the IVF cycle is more exaggerated when compared to the results reported from observations of the natural cycle but follows a similar pattern. This fact can probably be explained by the vastly different hormone levels. Higher JZ activity and correspondingly increased mobility of the endometrium may impair its receptivity and affect implantation.     

Levonorgestrel-releasing intrauterine device-wearing women express contraceptive glycodelin A in endometrium during midcycle: another contraceptive mechanism?

Intrauterine devices (IUDs) exert contraceptive action by interfering with sperm transport, ovum development, fertilization and implantation. Glycodelin A (GdA) is a uterine glycoprotein that has local contraceptive activity by inhibiting sperm-egg binding. GdA is normally absent from endometrium during the fertile midcycle and it is not expressed until the fifth postovulatory day. The phase of menstrual cycle addressed in this study covers the phase when conception is most likely to follow an unprotected intercourse and when GdA is normally absent. We present here evidence that levonorgestrel-releasing IUD (LNg-IUD) is accompanied by 'inappropriate' expression of GdA in endometrium between days 7 and 16 of the menstrual cycle (six out of six cases). The same was also found in copper-releasing IUD (Cu-IUD)-wearing women, but less frequently (four out of 11 cases, P < 0.0345, Fisher's exact test). In-situ hybridization localized GdA mRNA into endometrial glands in the midcycle endometrium, confirming the cellular site of synthesis. Based on the potent inhibitory activity of GdA on sperm-egg binding, the presence of GdA in uterine glands of IUD wearers may lead to prior exposure of sperm to contraceptive GdA, thus contributing to the contraceptive activity of the IUD.     

The mutagenicity of benzo[a]pyrene in mouse small intestine

OBJECTIVE: To determine the effects of controlled ovarian hyperstimulation (COH) on endometrial maturation. DESIGN: Prospective, before and after evaluation of midluteal endometrial biopsies in oocyte donor's spontaneous and subsequent COH cycles. SETTING: Tertiary academic medical center assisted reproductive technologies clinic. PATIENT(S): Nineteen oocyte donors. INTERVENTION(S): Exogenous gonadotropins, endometrial biopsies. MAIN OUTCOME MEASURE(S): Endometrial histology and an immunohistochemical marker of uterine receptivity, the alphavbeta3 vitronectin. RESULT(S): Glandular and stromal dyssynchrony was more common after COH in 16 (80%) of 20 cycles than 6 (30%) of 20 spontaneous cycles (P <.05). Glandular lag was more frequent in COH cycles and unaffected by progesterone administration. The beta3 subunit of the alphavbeta3 vitronectin receptor was present in 9 (45%) of 20 spontaneous and 2 (10%) of 20 COH cycles (P <.05). CONCLUSION(S): Exogenous gonadotropin use in healthy reproductive age women did not result in endometrial evidence of a luteal phase defect. A greater incidence of glandular-stromal dyssynchrony resulted from the use of exogenous gonadotropins. The presence of alphavbeta3 was noted in most endometrial specimens demonstrating in phase glandular maturation. We conclude that endometrial dyssynchrony that results from delayed glandular development most likely represents a normal histologic variant.     

Stromal progesterone receptors mediate the inhibitory effects of progesterone on estrogen-induced uterine epithelial cell deoxyribonucleic acid synthesis

The role of epithelial and stromal progesterone (P) receptors (PR) in the regulation of uterine epithelial DNA synthesis by P was investigated by analyzing the four types of tissue recombinants prepared with uterine stroma (S) and epithelium (E) from wild-type (wt) and PR knockout (PRKO) mice: wt-S + wt-E, PRKO-S + PRKO-E, wt-S + PRKO-E, and PRKO-S + wt-E. 17-Beta estradiol (E2) stimulated DNA synthesis in all four types of tissue recombinants. On the other hand, P inhibited E2-induced DNA synthesis only in tissue recombinants prepared with wild-type (PR-positive) stroma (wt-S + wt-E or wt-S + PRKO-E) but not knockout (PR-negative) stroma (PRKO-S + wt-E or PRKO-S + PRKO-E). These results clearly demonstrate that the inhibitory effect of P on uterine epithelial DNA synthesis is mediated by stromal PR. Epithelial PR is neither necessary nor sufficient for P inhibition of E2-induced epithelial DNA synthesis.     

Histological evaluation of endometrium on the day of oocyte retrieval after gonadotrophin-releasing hormone agonist-follicle stimulating hormone ovulation induction for in-vitro fertilization

The objective of this study was to evaluate the histopathological characteristics of endometrial biopsies taken on the day of oocyte recovery in in-vitro fertilization (IVF) cycles with a satisfactory response to ovulation induction. A group of 33 patients who went through ovulation induction for IVF, and in whom an endometrial polyp was suspected on transvaginal ultrasonography during the monitoring phase, were studied. Following oocyte recovery, hysteroscopy, polypectomy and endometrial curettage were performed. Dating of endometrial glands and stroma was carried out in the tissue not containing the polyps. The total dose of follicle stimulating hormone (FSH), duration of ovulation induction, peak oestradiol and luteinizing hormone (LH) concentrations, thickness of endometrium and number of oocytes were recorded and compared to the endometrial dating of the specimens. In 15 cycles (45.5%), the endometrium was classified as 'in phase' (group I), 'advanced' by 2-4 days in a further 15 (45.5%, group II), and in the remaining three cycles (9%) it was delayed in maturation (group III). Younger age was correlated with advanced staging of the endometrium (r = -0.42; P = 0.015). Women with 'in phase' and 'advanced' maturation were similar in their response to ovulation induction; however, there was a strong correlation between advanced dating of endometrium and number of oocytes retrieved (r = 0.49; P = 0.04). Endometrial staging on the day of oocyte retrieval varied widely in patients treated by the same gonadotrophin-releasing hormone agonist (GnRHa)/FSH protocol for ovulation induction. This difference was not predictable by parameters monitored through the cycles.     

Localization and sex steroid regulation of androgen receptor gene expression in rhesus monkey uterus

OBJECTIVE: To characterize the cellular sites and hormonal regulation of uterine androgen receptor gene expression in the monkey. METHODS: Ovariectomized rhesus monkeys (five in each group) were treated with placebo (the control group), estradiol (E2), E2 plus progesterone, or E2 plus testosterone by sustained-release pellets administered subcutaneously. After 3 days of treatment, uteri were removed and uterine sections were analyzed by in situ hybridization for androgen receptor messenger RNA (mRNA). RESULTS: Androgen receptor mRNA was detected in endometrial stromal cells and myometrial smooth muscle cells, with lesser expression in endometrial epithelial cells. Both E2 and E2 plus progesterone treatment doubled androgen receptor mRNA levels in stromal cells (P < .01), whereas E2 plus testosterone treatment increased stromal androgen receptor mRNA levels by about five-fold (P < .001) compared with placebo treatment. In the endometrial epithelium, E2 alone did not increase androgen receptor mRNA levels significantly. However, the E2 plus progesterone and E2 plus testosterone treatments increased epithelial androgen receptor mRNA levels by 4.3 and 5 times, respectively (P = .008 and P < .002, respectively). Androgen receptor mRNA was distributed homogeneously in smooth muscle cells across the myometrium. Estradiol treatment alone did not increase myometrial androgen receptor mRNA levels significantly, but the E2 plus progesterone and E2 plus testosterone treatments increased myometrial androgen receptor mRNA levels by 1.8 and 2 times, respectively (P = .001 and P < .001, respectively). CONCLUSION: Androgen receptor gene expression was detected in all uterine cell compartments where it was subject to significant sex steroid regulation. The fact that androgen receptor mRNA levels were consistently up-regulated by a combined E2 plus testosterone treatment while E2 treatment alone had little or no effect shows that a collaborative action of E2 and testosterone enhances androgen receptor expression in the monkey uterus.     

Iron deposition at mineralization fronts and osteoid formation following chronic cadmium exposure in ovariectomized rats

Integrins are heterodimeric glycoproteins that have been found to undergo dynamic temporal and spatial changes in distribution in the endometrium during the menstrual cycle in women. Likewise the extracellular matrix (ECM) ligands for these receptors are likely to play a role in the establishment of a receptive endometrium. To develop primate models to study the role of these molecules in the cascade of molecular events leading to implantation, integrin expression and associated changes in ECM were investigated during the menstrual cycle and in early pregnancy in the baboon. Antibodies specific for the integrins (alpha(1-6) and alpha(v); beta1, beta3, and beta4) and ECM (laminin, collagen IV, fibronectin) were utilized. In addition, cytokeratin and alpha-smooth muscle actin were used as epithelial, stromal, and smooth muscle cell markers, respectively. Endometrium was obtained in duplicate or triplicate during the menstrual cycle and early pregnancy. Changes observed during the natural menstrual cycle were confirmed using ovariectomized, steroid-treated animals. Constitutively expressed integrins on the endometrial epithelium included the collagen/laminin receptors: alpha2, alpha3, alpha6, and beta4. The pattern of expression correlated well with the distribution of ECM in this tissue. Collagen IV was confined to the basement membrane of glandular epithelium and blood vessels. Laminin immunostaining was found in the basement membrane, mostly in the stroma of the basal region, in the glandular endometrium and vasculature. Fibronectin was present throughout the stroma but not in the basement membrane. The collagen receptor alpha1 beta1 and fibronectin receptor alpha4 beta1 appeared in the glandular epithelium in the luteal phase. As in the human, alpha1 and alpha4 disappeared from the glandular epithelium with the establishment of pregnancy. In contrast, the alpha4 beta3 vitronectin receptor appeared in the glandular epithelium only in pregnancy or following long-term steroid treatment with estrogen and progesterone but not during the time of uterine receptivity associated with the initial period of embryo attachment. Osteopontin, an ECM ligand for alpha(v) beta3, was coexpressed with this integrin in invading cytotrophoblasts, glandular epithelium, and decidualizing stromal cells. Decidualization in the baboon was associated with changes in integrin expression similar to those found in humans: there was an increase in alpha1, alpha3, alpha6, beta1, and alpha(v) beta3 in the decidualized stromal cells. Laminin and collagen IV expression also increased at the implantation site and throughout the endometrium. In contrast, fibronectin expression was most evident at the implantation site and corresponded to alpha5 expression on the invading cytotrophoblasts. In summary, marked similarities were found in the expression of ECM and the integrin receptors between the baboon and the human endometrium throughout the menstrual cycle and in pregnancy. Cycle-specific integrins, alpha1, and alpha4, were present on epithelial cells during the secretory phase. Delayed expression of alpha(v) beta3 in baboon endometrial glands correlated closely with the time of enhanced glandular secretory activity in this primate. The baboon appears to be an excellent model for the investigation of the role of integrins and ECM leading to successful implantation.