Optical trapping of interfaces at ultra-low interfacial tension.

We achieve active control of interfacial phenomena by optically trapping the interface using the gradient forces of a strongly focussed laser beam parallel to the interface. We illustrate our technique in a phase separated colloid-polymer mixture by distorting the interface in a very controlled way. The static structure of the manipulated interface as well as its dynamic relaxation behaviour are analysed. Both the statics and dynamics can be related to the capillary wave height-height correlation functions using the fluctuation dissipation theorem up to surprisingly large deformations of the interface. To underline the novelty and potential of our approach we also show multiple interface distortions and the controlled snap-off of liquid droplets.

Comparison of early versus late initiation of GnRH antagonist co-treatment for controlled ovarian stimulation in IVF: a randomized controlled trial.

STUDY QUESTION: What is the impact of initiating GnRH antagonist co-treatment for in vitro fertilization (IVF) on cycle day (CD) 2 compared with CD 6 on live birth rate (LBR) per started cycle and on the cumulative live birth rate (CLBR)? SUMMARY ANSWER: Early initiation of GnRH antagonist does not appear to improve clinical outcomes of IVF compared with midfollicular initiation. WHAT IS KNOWN ALREADY: During ovarian stimulation for IVF, GnRH antagonist co-treatment is usually administered from the midfollicular phase onwards. Earlier initiation may improve the follicular phase hormonal milieu and therefore overall clinical outcomes. STUDY DESIGN, SIZE, DURATION: This open-label, multicentre randomized controlled trial was conducted between September 2009 and July 2011. A web-based program was used for randomization and 617 IVF-intracytoplasmic sperm injection (ICSI) patients were included. PARTICIPANTS/MATERIALS, SETTING, METHODS: Recombinant FSH (150-225 IU) was administered daily from CD 2 onwards in both groups. The study group (CD2; n = 308) started GnRH antagonist co-treatment on CD 2, whereas the control group (CD6; n = 309) started on CD 6. MAIN RESULTS AND THE ROLE OF CHANCE: There were no significant differences in clinical outcomes between the two groups. A non-significant trend towards a higher LBR per started cycle and CLBR was observed in the CD6 group compared with the CD2 group (LBR: 24.0 versus 21.5%, P = 0.5; CLBR: 29.9 versus 26.7%, P = 0.6). LIMITATIONS, REASONS FOR CAUTION: The study was terminated prematurely because no significant difference was observed in clinical outcomes after 617 inclusions. A much larger study population would be needed to detect a small significant difference in favour of either study arm, which raises the question of whether this would be relevant for clinical practice. WIDER IMPLICATIONS OF THE FINDINGS: The present study shows that the additional treatment burden and costs of starting GnRH antagonist on CD 2 instead of on CD 6 are not justified, as early initiation of GnRH antagonist does not improve LBRs. STUDY FUNDING/COMPETING INTEREST(S): This study was partially supported by a grant from Merck Serono. O.H., M.J.C.E, A.V., P.A.D., R.E.B., G.J.E.O., C.A.G.H., G.C.D.M., H.J.V., P.F.M.H. and A.B. have nothing to declare. F.J.B. has received fees and grant support from the following companies (in alphabetic order): Ferring, Gedeon Richter, Merck Serono, MSD and Roche. B.J.C. has received fees and grant support from the following companies (in alphabetic order): Ferring, Merck Serono and MSD. C.B.L has received fees and grant support from the following companies (in alphabetic order): Auxogen, Ferring, Merck Serono and MSD. B.C.J.M.F. has received fees and grant support from the following companies (in alphabetic order): Andromed, Ardana, Ferring, Genovum, Merck Serono, MSD, Organon, Pantharei Bioscience, PregLem, Schering, Schering Plough, Serono and Wyeth. J.S.E.L. has received fees and grant support from the following companies (in alphabetic order): Ferring, Gennovum, MSD, Merck Serono, Organon, Schering Plough and Serono. N.S.M. has received fees and grant support from the following companies (in alphabetic order): Anecova, Ferring, Merck Serono, MSD, Organon and Serono. TRIAL REGISTRATION NUMBER: www.clinicaltrials.gov, no. NCT00866034.

Tactoids of plate-like particles: size, shape, and director field.

We studied, by means of polarized light microscopy, the shape and director field of nematic tactoids as a function of their size in dispersions of colloidal gibbsite platelets in polar and apolar solvents. Because of the homeotropic anchoring of the platelets to the interface, we found large tactoids to be spherical with a radial director field, whereas small tactoids turn out to have an oblate shape and a homogeneous director field, in accordance with theoretical predictions. The transition from a radial to a homogeneous director field seems to proceed via two different routes depending in our case on the solvent. In one route, the what presumably is a hedgehog point defect in the center of the tactoid transforms into a ring defect with a radius that presumably goes to infinity with decreasing drop size. In the other route, the hedgehog defect is displaced from the center to the edge of the tactoid, where it becomes virtual again going to infinity with decreasing drop size. Furthermore, quantitative analysis of the tactoid properties provides us with useful information on the ratio of the splay elastic constant and the anchoring strength and the ratio of the anchoring strength and the surface tension.

Magnetic field effects on tactoids of plate-like colloids.

We investigate the effect of a magnetic field on the shape and director field of nematic droplets in dispersions of sterically stabilized and charge-stabilized colloidal gibbsite platelets with a negative diamagnetic anisotropy. Depending on the magnetic field strength and tactoid size, we observe with polarized light microscopy several interesting structures, with different shapes and director fields both with and without defects. In particular, our findings provide the first experimental evidence for the existence of the split-core defect structure predicted ten years ago by Mkaddem and Gartland [Phys. Rev. E 62, 6694 (2000)]. The split-core structure is a metastable director-field configuration that can be stabilized by a sufficiently strong externally applied magnetic field but only if the diamagnetic anisotropy of the particles is negative. To account for our observations, we present a calculation of the stability regions of different shapes and director-field structures as a function of tactoid size, anchoring conditions, surface tension, elastic constants, and magnetic field strength. By fitting the experimental data to the theoretically predicted structures, we are able to extract values for the splay elastic constant, interfacial tension, and anchoring strength. Remarkably, we find significant differences between the two systems studied: for sterically stabilized gibbsite in bromotoluene the anchoring strength is one order of magnitude larger than that of aqueous gibbsite, with the latter exhibiting weak and the former strong anchoring of the director field to the interface. The splay elastic constants that we obtain are in agreement with earlier experiments, simulations, and theory, while the interfacial tension and anchoring strength are considerably larger than what was found in earlier experiments.

Orientation dependent Stokes drag in a colloidal liquid crystal.

Stokes drag on the (sub)micrometre scale plays a key role in phenomena ranging from Brownian motion to the rheology of particulate suspensions. We report the first measurement of the direction dependent Stokes drag in a nematic liquid crystal of colloidal rods, where the viscous forces are of equal importance to the elastic forces. By tracking a sedimenting sphere with combined fluorescence confocal microscopy and polarization microscopy we find that the Stokes drag for motion along the director is two times larger than for motion perpendicular to the director. This brings the unique viscoelastic properties of a colloidal liquid crystal into focus.

A Descriptive Mixed-Methods Analysis of Sexual Behavior and Knowledge in Very Young Children Assessed for Sexual Abuse: The ASAC Study.

Child sexual abuse (CSA) is a worldwide problem with serious consequences. We hypothesized that worrisome sexual behavior and knowledge would frequently be reported in children assessed after CSA. We therefore investigated (A) what types of sexual behaviors and knowledge were reported by parents of young children assessed for CSA; (B) in what cases such behaviors and knowledge were worrisome; and (C) how such children responded verbally and non-verbally during child interviews. We conducted a mixed-methods study, including qualitative inductive content analysis and quantitative analysis. It included 125 children (76 boys, 60.8%; median age 3.3 years, age range 0-11), all involved in the Amsterdam sexual abuse case (ASAC) and examined for highly suspected (n = 71) or confirmed CSA (n = 54). We identified themes from (1) the parent reports: sexual behavior (e.g., self-stimulation, touching others, imitation of sexual acts), fears and anxiety with regard to sexuality, and sexual utterances (sexual slang, references to sexual acts); and (2) the child interviews: behavioral reactions (avoidance, distractive behaviors), emotional reactions (anger, aggression), and verbal reactions (conspicuous utterances, refusal to talk about specific subjects). In 37% of the children the sexual behavior was deemed worrisome or very worrisome. Clinicians who assess children for CSA are advised to focus in particular on sexual behavior problems and inappropriate sexual knowledge.

Psychosocial symptoms in very young children assessed for sexual abuse: A qualitative analysis from the ASAC study.

Child sexual abuse (CSA) is a worldwide problem with serious consequences. No recognizable symptom pattern for suspected CSA has yet been identified in very young children. We aim to investigate psychosocial symptoms in a sample of children with confirmed or strongly suspected CSA and the interpretations given to such symptoms by independent clinical experts. Secondly we examined whether experts were able to identify confirmed victims of severe CSA. A qualitative study including inductive content analysis of medical files and focus group discussions with independent experts on the interpretation of psychosocial symptoms was conducted. We included 125 children (76 boys, 60.8%, and 49 girls, 39.2%; median age 3.3 years; age range 0-11) who were involved in the Amsterdam sexual abuse case (ASAC) and had been examined for strongly suspected CSA. We identified four themes among the psychosocial symptoms: problems concerning emotions, behavior, toilet training, and development, whether or not associated with the daycare center or the perpetrator. Clinical experts identified signs of posttraumatic stress disorder (PTSD), regression in continence skills (not otherwise explained), and problems triggered by exposure to the perpetrator or the abuse location as concerning symptoms for CSA. Less concerning symptoms were designated as worrisome if they were numerous and there was no clear explanation for these symptoms. A clear symptom pattern was lacking and about half of the confirmed severe victims of CSA did not display any psychosocial problems. Therefore, it is difficult for experts to identify confirmed CSA victims. Thus, the assessment of suspected CSA should be over time and multidisciplinary.

Decrease of free thyroxine levels after controlled ovarian hyperstimulation.

Controlled ovarian hyperstimulation could lead to opposing effects on thyroid function. Therefore, in a prospective study of 65 women undergoing controlled ovarian hyperstimulation, thyroid hormones, T4-binding globulin, TPO antibodies, gonadotropins, estradiol, and PRL were measured before and after controlled ovarian hyperstimulation. After ovarian stimulation (mean +/- SE of mean): free T4 decreased, 14.4 +/- 0.2 vs. 12.9 +/- 0.2 pmol/L (P < 0.0001); thyroid-stimulating hormone increased, 2.3 +/- 0.3 vs. 3.0 +/- 0.4 mU/L (P < 0.0001); T4-binding globulin increased, 25.2 +/- 0.7 vs. 33.9 +/- 0.9 mg/L (P < 0.0001); total T4 increased, 98.1 +/- 2.3 vs. 114.6 +/- 2.5 nmol/L (P < 0.0001); total T3 increased, 2.0 +/- 0.04 vs. 2.3 +/- 0.07 nmol/L (P < 0.0001); TPO antibodies decreased, 370 +/- 233 U/mL vs. 355 +/- 224 U/mL (P < 0.0001); LH decreased, 8.1 +/- 1.1 vs. 0.4 +/-0.1 U/L (P < 0.0001); FSH did not change, 6.5 +/- 0.6 vs. 7.9 +/- 0.9 U/L (P = 0.08); human CG increased, <2 +/- 0.0 vs. 195 +/- 16 U/L (P < 0.0001); estradiol increased, 359.3 +/- 25.9 pmol/L vs. 3491.8 +/-298.3 pmol/L (P < 0.0001); and PRL increased, 0.23 +/- 0.02 vs. 0.95 +/- 0.06 U/L (P < 0.0001). Because low maternal free T4 and elevated maternal thyroid-stimulating hormone levels during early gestation have been reported to be associated with impaired psychomotor development in the offspring, our findings indicate the need for additional studies in the children of women who where exposed to high levels of estrogens around the time of conception.

Effects of experimental head compression on transcutaneous scalp PO2 in fetal lambs.

Equatorial compression of the fetal head is known to occur during labor; its effect on trancutaneous scalp PO2 (PtCO2) was investigated in acute experiments in four fetal lambs. Fetal PtCO2, and oxygen tension (PaO2) and flow in a carotid artery were continuously measured. Equatorial head compression was obtained by inflating a cuff around the fetal head. A strong relationship was shown to exist between PtCO2 and PaO2 values in the normoxemic and hypoxemic fetus. Stepwise compression of the fetal head resulted in a PtCO2 of zero at cuff pressures of 40 to 50 mmHg. Laborlike fetal head compression with an intensity of 50 to 70 mmHg and a duration of one minute resulted in a 30 to 60% fall in PtCO2. Fetal PaO2 remained stable in all experiments. The present findings indicate that values of PtCO2 during fetal head compression do not reflect fetal arterial oxygen tension. This questions the reliability of transcutaneous PO2 monitoring as a method of intrapartum surveillance.

A randomized study of transcervical intrafallopian transfer of pronucleate embryos controlled by ultrasound versus intrauterine transfer of four- to eight-cell embryos.

OBJECTIVE: To establish the value of transcervical intrafallopian transfer of zygotes and the accuracy of fallopian cannulation. DESIGN: A prospective randomized study, comparing ultrasonically controlled transcervical intrafallopian transfer of zygotes with intrauterine transfer of cleaved embryos. SETTING: Department of IVF of the Rotterdam Academic Hospital. PATIENTS: One hundred forty-five patients with patent tubes entered the IVF program. MAIN OUTCOME MEASURE: Pregnancy rates in both groups and ultrasound (US) assessment during fallopian cannulation and ET. RESULTS: Transvaginal cannulation of the tube appears not to be sufficiently accurate when performed without US guidance. Catheter damage occurred in many cases. The previously reported superior implantation rate after intrafallopian transfer in comparison with intrauterine transfer could not be confirmed. CONCLUSIONS: Intrauterine transfer of cleaved embryos remains the method of choice in IVF.

Thyroid autoimmunity and abortion: a prospective study in women undergoing in vitro fertilization.

OBJECTIVE: To determine whether an association exists between the presence of thyroid peroxidase (TPO) antibodies before pregnancy and miscarriage in women without a history of habitual abortion. DESIGN: Prospective study and nested case-control study. SETTING: Inner-city teaching hospital. PATIENT(S): Four hundred eighty-nine women in an IVF program. INTERVENTION(S): In the prospective study, we measured levels of TPO antibodies and TSH. In the nested case-control study, we also measured levels of anticardiolipin antibodies. MAIN OUTCOME MEASURE: Miscarriage. RESULT(S): One hundred seventy-three women were observed, of whom 31% (54/173) became pregnant. Pregnancy occurred in 48% (12/25) of the antibody-positive women and in 28% (42/148) of the antibody-negative women. Among those who became pregnant, miscarriage occurred in 33% (4/12) of TPO antibody-positive women and in 19% (8/42) of TPO antibody-negative women. The TSH level was abnormal (<0.2 microIU/mL) in only one of the TPO antibody-positive women who miscarried. The presence of anticardiolipin antibodies was not associated with miscarriage. CONCLUSION(S): No association was found between the presence of TPO antibodies before pregnancy and miscarriage in women without a history of habitual abortion. The presence of TPO antibodies did not adversely affect a woman's chances of becoming pregnant.

Minimal monitoring of ovarian hyperstimulation: a useful simplification of the clinical phase of in vitro fertilization treatment.

OBJECTIVE: To investigate the feasibility of IVF treatment with minimal monitoring during ovarian hyperstimulation. DESIGN: Retrospective analysis and prospective study with real-time control group. SETTING: Transport IVF program with transport clinic and satellite clinics. PATIENTS: One hundred consecutive IVF cycles monitored at a transport clinic and 100 concurrent consecutive cycles monitored at satellite clinics, using the same stimulation-monitoring protocol and resulting in oocyte aspiration, are compared retrospectively for the number of ultrasound (US) measurements carried out during monitoring and for results of IVF treatment. No patient selection took place. After introduction of a minimal monitoring protocol at a transport clinic, a prospective study was started comparing 100 minimal monitoring cycles at a transport clinic with 100 concurrent conventional monitoring cycles at satellite clinics, all resulting in oocyte aspiration. Patients entered the retrospective or prospective study only once. In all cases the same laboratory facility was used. Monitoring of ovarian hyperstimulation was done with US measurements only. Cycles were canceled for impending ovarian hyperstimulation syndrome (OHSS) when > 35 follicles were seen to develop during hyperstimulation. RESULTS: Retrospective analysis shows no difference for the average number of US measurements at transport and satellite clinics (2.8 +/- 0.9 and 3.0 +/- 1.0; mean +/- SD). No differences were found in the number of ongoing pregnancies obtained in the two groups: 22 and 18, respectively. One case of severe OHSS occurred in the satellite clinic group. Introduction of minimal monitoring at the transport clinic gives a significant reduction of the average number of US measurements at the transport clinic compared with satellite clinics, where conventional monitoring continued to be used (1.5 +/- 0.8 versus 2.8 +/- 0.9). Ongoing pregnancies at transport and satellite clinics numbered 33 and 26, respectively. In both groups one patient developed severe OHSS. Sixty-two percent of cycles at the transport clinic were monitored with one US measurement only. No cancellations for impending OHSS occurred during the study period. CONCLUSION: A large group of patients need only one US measurement during monitoring of ovarian hyperstimulation. Minimal monitoring gives a useful further simplification of the clinical phase of IVF treatment, without adverse effects on treatment outcome and incidence of OHSS.

A triplet pregnancy after in vitro fertilization is a procedure-related complication that should be prevented by replacement of two embryos only.

OBJECTIVE: To investigate whether the incidence and obstetric outcome of triplet pregnancies after IVF treatment justify strict limitation of the number of embryos to be replaced to two. DESIGN: Retrospective analysis. SETTING: A transport IVF program. PATIENT(S): All patients who had more than one embryo replaced. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Obstetric outcome, pregnancy. RESULT(S): High-order pregnancies occurred in 24 cases (23 triplets and 1 quadruplet). Three patients opted for selective embryo reduction (12.5%). Three triplet pregnancies spontaneously reduced to twins. Comparison of 18 triplets, reaching at least 20 weeks' gestation, with 54 twin pregnancies shows a higher perinatal mortality in the triplet group, causing 6 out of 18 patients to be confronted with at least one perinatal death. Triplets were born at a lower gestational age, had a lower birth weight, and a higher hospital admission rate of longer duration. Replacement of two, three, or four embryos did not lead to differences in pregnancy rates in the population studied. When a pregnancy occurred after replacement of three embryos, the risk of having a triplet pregnancy was 7.5%. CONCLUSION(S): The obstetric outcome of triplet pregnancies in our population indicates that triplet pregnancies after IVF treatment have to be prevented. Selective embryo reduction is acceptable for few patients only and can therefore not be seen as a solution. Replacement of three embryos results in triplet pregnancy in an unacceptably high percentage. Replacement of two embryos only gives acceptable IVF results and is the method chosen in the IVF program in Rotterdam to prevent triplet pregnancies.

A comparison of in vitro fertilization results after embryo transfer after 2, 3, and 4 days of embryo culture.

Embryo transfer results after a 2 to 4 day period of embryo culture were compared. Two thousand two hundred ninety-seven ETs, performed in 1991 and 1992, were analyzed. Ongoing pregnancy rates after 2, 3, or 4 days of embryo culture were 23.3%, 21.9%, and 26.4%, respectively. Multiple pregnancy rates were 36.2%, 38.8%, and 32.6% per ongoing pregnancy for the three groups, respectively. The implantation rate of 73 cavitating morulae on day 4 was surprisingly high (41%) compared with that of other developmental stages. Transfer after 4 days of culture gives the ability to recognize embryos with a very high implantation potential.

The ovarian response as a predictor for successful in vitro fertilization treatment after the age of 40 years.

OBJECTIVE: To determine whether age or response to controlled ovarian hyperstimulation (COH) is a better predictor of IVF outcome in women > or = 40 years. DESIGN: Retrospective analysis. SETTING: A transport IVF program. PATIENT(S): For patients undergoing IVF treatment the correlation between treatment outcome and age and response to COH was analyzed using the data of 2,588 consecutive cycles. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Pregnancy. RESULT(S): The incidence of poor ovarian response rises significantly with increasing age. Analysis of all cycles showed a significant decrease in clinical and ongoing pregnancy rate for women > or = 40 years. Analysis of cycles with a good ovarian response showed no statistically significant differences for these parameters between women > or = 40 years and those younger. A logistic regression analysis on pregnancy showed that ovarian response contributes more to the prediction of pregnancy than age. CONCLUSION(S): Patients aged > or = 40 years with a good response to COH have a good prognosis for IVF treatment. The age limit for acceptance of patients should not be set at 40 years. Instead, the response to COH can be used to predict candidates likely to have a successful IVF outcome.

Comparison of results obtained with human serum and a protein solution as a supplement for in vitro fertilization culture medium.

A prospective controlled study was performed to compare the PRs obtained after use of a uniform IVF culture medium containing a pasteurized serum protein solution or patient serum. The ongoing PRs per ET in the serum and the protein solution group were 32% and 28%, respectively (not significant). Culture of supernumerary embryos showed blastocyst formation and even hatching with both supplements. The PR will not drop when this protein solution is used as a protein supplement in IVF culture medium instead of patient serum.

Prevalence and risk-factors for depression in elderly Turkish and Moroccan migrants in the Netherlands.

BACKGROUND: Western societies host increasing number of elderly labour migrants from Turkey and Morocco. The article studied the prevalence of clinically significant depressive symptoms among elderly Turkish and Moroccan migrants compared with native Dutch elderly and if differences in prevalence rates were explained by known risk factors for depression and/or ethnic, migration-related factors. METHODS: 330 Turkish, 299 Moroccan, and 304 Dutch elderly (55-74 years) were interviewed (cross-sectionally) using the Center for Epidemiologic Depression Scale (CES-D). Potential risk factors included sex, income level, marital status, ethnic origin, chronic physical illnesses, limitations in daily functioning, migration and acculturation questions. RESULTS: The prevalence of self-reported depressive symptoms (CES-D>or=16) was very high in elderly migrants, 33.6% for Moroccan and 61.5% for Turkish elderly. The prevalence of depressive symptoms in the native Dutch sample was similar to earlier studies in the Netherlands and abroad: 14.5%. Among migrants education and income level was very low and they had a high number of physical limitations and chronic medical illnesses. This only explained part of the ethnic differences found. In all three samples, depressive symptoms were associated with sex, chronic physical illness and physical limitations. In multivariate analysis, ethnic origin was uniquely associated with the presence of clinically significant depressive symptoms. Only a small number of remigration and acculturation items were associated with depressive symptoms in bivariate analysis. CONCLUSIONS: The prevalence of clinically significant depressive symptoms among elderly migrants from Turkey and Morocco in the Netherlands is very high. Ethnicity was a strong independent risk factor.

Hypogonadism in untreated male normoprolactinaemic acromegalics.

Hypogonadism is a distinct feature of acromegaly, even in the absence of hyperprolactinaemia. In 10 untreated male acromegalics, aged 24 to 46 yr, without evidence of any other disturbance of anterior pituitary function, low testosterone values were found in the presence of a normal reaction of pituitary gonadotrophins following GnRH administration. In three patients, one injection of 5000 IU hCG resulted in a sharp rise in testosterone. Although we were unable to elicit a similar reaction pattern of the GnRH-gonadotrophins-testosterone axis following administration of biosynthetic methionyl-hGH, it is suggested that suppression of testicular function in untreated acromegaly without other endocrine disturbances may be partly caused by increased somatostatin production.

Effects of instrumentation on myometrial activity in the oophorectomized ewe.

The influence of an intrauterine pressure catheter on electrical myometrial activity (EMG) was investigated in chronically instrumented oophorectomized sheep. The EMG of non-catheterized (NC) ewes (n = 4) was characterized by long-lasting but infrequently occurring bursts of electrical activity, whereas the EMG of catheterized (C) ewes (n = 4) showed short and frequent bursts. Intra-arterial administration of 0.1 mg of 17 beta-estradiol (E2) was followed in C and NC ewes by an increase in myometrial activity after an initial silent period. E2 did not essentially change the pattern of long and short bursts in either group. Intravenous administration of the prostaglandin-synthesis inhibitor naproxen changed the EMG pattern in the C ewes, both before and after E2, to a pattern resembling the EMG of NC ewes. The results of this study indicate that electrical myometrial activity is markedly influenced by the presence of an intrauterine pressure catheter, probably due to enhanced prostaglandin synthesis.

Modulation of spontaneous myometrial activity in chronically instrumented ovariectomized sheep.

The uterine electromyogram (EMG) and intrauterine pressure curves (IUP) were investigated as indicators of myometrial activity in chronically instrumented, ovariectomized ewes. Spontaneous electrical activity was characterized by rhythmic patterns of trains of bursts accompanied by IUP waves. Administration of adrenergic (propranolol or phentolamine) or cholinergic (atropine) blocking agents had no effect on spontaneous uterine activity. Both oxytocin and PGF2 alpha appeared to stimulate spontaneous myometrial activity. 17beta-Estradiol temporarily depressed uterine activity in a dose-dependent fashion. The period of relaxation was followed by a pronounced increase in activity. Progesterone treatment resulted in long-term suppression of myometrial activity. Oxytocin and PGF2alpha increased EMG and IUP activity during estradiol suppression but not after progesterone treatment. These results indicate that the myometrium is active in chronically instrumented, ovariectomized ewes. The autonomic nervous system or its receptors do not play a role in the maintenance of spontaneous myometrial activity, estradiol and progesterone suppress myometrical activity but by different mechanisms.