Buoyant crystals halt the cooling of white dwarf stars

White dwarfs are stellar remnants devoid of a nuclear energy source, gradually cooling over billions of years1,2 and eventually freezing into a solid state from the inside out3,4. Recently, it was discovered that a population of freezing white dwarfs maintains a constant luminosity for a duration comparable with the age of the universe5, signalling the presence of a powerful, yet unknown, energy source that inhibits the cooling. For certain core compositions, the freezing process is predicted to trigger a solid-liquid distillation mechanism, owing to the solid phase being depleted in heavy impurities6-8. The crystals thus formed are buoyant and float up, thereby displacing heavier liquid downward and releasing gravitational energy. Here we show that distillation interrupts the cooling for billions of years and explains all the observational properties of the unusual delayed population. With a steady luminosity surpassing that of some main-sequence stars, these white dwarfs defy their conventional portrayal as dead stars. Our results highlight the existence of peculiar merger remnants9,10 and have profound implications for the use of white dwarfs in dating stellar populations11,12.

Perinatal morbidity among women with a previous caesarean delivery (PRISMA trial): a cluster-randomised trial

BACKGROUND

Women with a previous caesarean delivery face a difficult choice in their next pregnancy: planning another caesarean or attempting vaginal delivery, both of which are associated with potential maternal and perinatal complications. This trial aimed to assess whether a multifaceted intervention, which promoted person-centred decision making and best practices, would reduce the risk of major perinatal morbidity among women with one previous caesarean delivery.

METHODS

We conducted an open, multicentre, cluster-randomised, controlled trial of a multifaceted 2-year intervention in 40 hospitals in Quebec among women with one previous caesarean delivery, in which hospitals were the units of randomisation and women the units of analysis. Randomisation was stratified according to level of care, using blocked randomisation. Hospitals were randomly assigned (1:1) to the intervention group (implementation of best practices and provision of tools that aimed to support decision making about mode of delivery, including an estimation of the probability of vaginal delivery and an ultrasound estimation of the risk of uterine rupture), or the control group (no intervention). The primary outcome was a composite risk of major perinatal morbidity. This trial was registered with ISRCTN, ISRCTN15346559.

FINDINGS

21 281 eligible women delivered during the study period, from April 1, 2016 to Dec 13, 2019 (10 514 in the intervention group and 10 767 in the control group). None were lost to follow-up. There was a significant reduction in the rate of major perinatal morbidity from the baseline period to the intervention period in the intervention group as compared with the control group (adjusted odds ratio [OR] for incremental change over time, 0·72 [95% CI 0·52-0·99]; p=0·042; adjusted risk difference -1·2% [95% CI -2·0 to -0·1]). Major maternal morbidity was significantly reduced in the intervention group as compared with the control group (adjusted OR 0·54 [95% CI 0·33-0·89]; p=0·016). Minor perinatal and maternal morbidity, caesarean delivery, and uterine rupture rates did not differ significantly between groups.

INTERPRETATION

A multifaceted intervention supporting women in their choice of mode of delivery and promoting best practices resulted in a significant reduction in rates of major perinatal and maternal morbidity, without an increase in the rate of caesarean or uterine rupture.

FUNDING

Canadian Institutes of Health Research (CIHR, MOP-142448).

Understanding the role of flux, pressure and temperature on polymorphism in ThB2O5

A novel polymorph of ThB₂O₅, denoted as β-ThB₂O₅, was synthesised under high-temperature high-pressure (HT/HP) conditions. Via single crystal X-ray diffraction measurements, β-ThB₂O₅ was found to form a three-dimensional (3D) framework structure where thorium atoms are ten-fold oxygen coordinated forming tetra-capped trigonal prisms. The only other known polymorph of ThB₂O₅, denoted α, synthesised herein using a known borax, B₂O₃-Na₂B₄O₇, high temperature solid method, was found to transform to the β polymorph when exposed to conditions of 4 GPa and ∼900 °C. Compared to the α polymorph, β-ThB₂O₅ has smaller molar volume by approximately 12%. Exposing a mixture of the α and β polymorphs to HT/HP conditions ex situ further demonstrated the preferred higher-pressure phase being β, with no α phase material being observed via Rietveld refinements against laboratory X-ray powder diffraction (PXRD) measurements. In situ heating PXRD measurements on α-ThB₂O₅ from RT to 1030 °C indicated that α-ThB₂O₅ transforms to the β variant at approximately 900 °C via a 1st order mechanism. β-ThB₂O₅ was found to exist only over a narrow temperature range, decomposing above 1050 °C. Ab initio calculations using density functional theory (DFT) with the Hubbard U parameter indicated, consistent with experimental observations, that β is both the preferred phase at higher temperatures and high pressures. Interestingly, it was found by switching from B₂O₃-Na₂B₄O₇ to H₃BO₃-Li₂CO₃ flux using consistent high temperature solid state conditions for the synthesis of the α variant, β-ThB₂O₅ could be generated. Comparison of their single crystal measurements showed this was identical to that obtained from HT/HP conditions.

Direct evaluation of the phase diagrams of dense multicomponent plasmas by integration of the Clapeyron equations

Accurate phase diagrams of multicomponent plasmas are required for the modeling of dense stellar plasmas, such as those found in the cores of white dwarf stars and the crusts of neutron stars. Those phase diagrams have been computed using a variety of standard techniques, which suffer from physical and computational limitations. Here we present an efficient and accurate method that overcomes the drawbacks of previously used approaches. In particular, finite-size effects are avoided as each phase is calculated separately; the plasma electrons and volume changes are explicitly taken into account; and arbitrary analytic fits to simulation data as well as particle insertions are avoided. Furthermore, no simulations at "uninteresting" state conditions, i.e., away from the phase coexistence curves, are required, which improves the efficiency of the technique. The method consists of an adaptation of the so-called Gibbs-Duhem integration approach to electron-ion plasmas, where the coexistence curve is determined by direct numerical integration of its underlying Clapeyron equation. The thermodynamics properties of the coexisting phases are evaluated separately using Monte Carlo simulations in the isobaric semigrand canonical ensemble (NPTΔμ). We describe this Monte Carlo-based Clapeyron integration method, including its basic physical and numerical principles, our extension to electron-ion plasmas, and our numerical implementation. We illustrate its applicability and benefits with the calculation of the melting curve of dense carbon-oxygen plasmas under conditions relevant for the cores of white dwarf stars and provide analytic fits to implement this new melting curve in white dwarf models. While this work focuses on the liquid-solid phase boundary of dense two-component plasmas, a wider range of physical systems and phase boundaries are within the scope of the Clapeyron integration method, which had until now only been applied to simple model systems of neutral particles.

Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal

Tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances of rocky bodies in exoplanetary systems. Those abundances provide information on the composition of the nebula from which the systems formed, which is analogous to how meteorite abundances inform our understanding of the early Solar System. We report the detection of lithium, sodium, potassium, and calcium in the atmosphere of the white dwarf Gaia DR2 4353607450860305024, which we ascribe to the accretion of a planetesimal. Using model atmospheres, we determine abundance ratios of these elements, and, with the exception of lithium, they are consistent with meteoritic values in the Solar System. We compare the measured lithium abundance with measurements in old stars and with expectations from Big Bang nucleosynthesis.

A giant planet candidate transiting a white dwarf

Astronomers have discovered thousands of planets outside the Solar System¹, most of which orbit stars that will eventually evolve into red giants and then into white dwarfs. During the red giant phase, any close-orbiting planets will be engulfed by the star², but more distant planets can survive this phase and remain in orbit around the white dwarf^3,4. Some white dwarfs show evidence for rocky material floating in their atmospheres⁵, in warm debris disks^6-9 or orbiting very closely^10-12, which has been interpreted as the debris of rocky planets that were scattered inwards and tidally disrupted¹³. Recently, the discovery of a gaseous debris disk with a composition similar to that of ice giant planets¹⁴ demonstrated that massive planets might also find their way into tight orbits around white dwarfs, but it is unclear whether these planets can survive the journey. So far, no intact planets have been detected in close orbits around white dwarfs. Here we report the observation of a giant planet candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4 days. We observed and modelled the periodic dimming of the white dwarf caused by the planet candidate passing in front of the star in its orbit. The planet candidate is roughly the same size as Jupiter and is no more than 14 times as massive (with 95 per cent confidence). Other cases of white dwarfs with close brown dwarf or stellar companions are explained as the consequence of common-envelope evolution, wherein the original orbit is enveloped during the red giant phase and shrinks owing to friction. In this case, however, the long orbital period (compared with other white dwarfs with close brown dwarf or stellar companions) and low mass of the planet candidate make common-envelope evolution less likely. Instead, our findings for the WD 1856+534 system indicate that giant planets can be scattered into tight orbits without being tidally disrupted, motivating the search for smaller transiting planets around white dwarfs.

The contribution of the pericanalicular matrix to mineral content in human osteonal bone

The osteocyte lacunar-canalicular network (LCN) penetrates bone and houses the osteocytes and their processes. Despite its rather low volume fraction, the LCN represents an outstanding large surface that is possibly used by the osteocytes to interact with the surrounding mineralized bone matrix thereby contributing to mineral homeostasis. The aim of this study was to quantitatively describe such contributions by spatially correlating the local density of the LCN with the mineral content at the same location in micrometer-sized volume elements in human osteons. For this purpose, 65 osteons from the femur midshaft from healthy adults (n = 4) and children (n = 2) were structurally characterized with two different techniques. The 3D structure of the LCN in the osteons was imaged with confocal laser scanning microscopy after staining the bone samples with rhodamine. Subsequent image analysis provided the canalicular length density, i.e. the total length of the canaliculi per unit volume (μm/μm³). Quantitative information on the mineral content (wt%Ca) from the identical regions was obtained using quantitative backscattered electron imaging. As the LCN-porosity lowers the mineral content, a negative correlation between Ca content and network density was expected. Calculations predict a reduction of around -0.97 fmol Ca per μm of network. However, the experiment revealed for 62 out of 65 osteons a positive correlation resulting in an average additional Ca loading of +1.15 fmol per μm of canalicular network, i.e. an accumulation of mineral has occurred at dense network regions. We hypothesize that this accumulation happens in the close vicinity of canaliculi forming mineral reservoirs that can be utilized by osteocytes. Significant differences found between individuals indicate that the extent of mineral loading of the reservoir zone reflects an important parameter for mineral homeostasis.

Impact of Audits and Multifaceted Intervention on Vaginal Birth After Caesarean: Secondary Analysis of the QUARISMA Trial

OBJECTIVES

This study estimated the effect that a multifaceted intervention aiming to improve the quality of obstetrical care and reduce Caesarean section (CS) had on the rate of vaginal birth after Caesarean (VBAC).

METHODS

This is a secondary analysis of the cluster randomized controlled trial Quality of Care, Obstetrics Risk Management, and Mode of Delivery involving (1) audits regarding the indications for CS, (2) provision of feedback to health professionals, and (3) implementation of best practices to reduce CS rates in Quebec. The impact of intervention on VBAC, trial of labour (TOL), and maternal and neonatal morbidity was reported using adjusted odds ratios (ORs) with 95% confidence intervals (CIs).

RESULTS

Out of 105 351 women who delivered during the pre- and postintervention period, 12 493 (11.9%) had a previous CS. We observed no significant impact of the multifaceted intervention on the rates of TOL (adjusted OR 1.22; 95% CI 0.96-1.56, P = 0.11) and VBAC (adjusted OR 1.20; 95% CI 0.97-1.48, P = 0.10) in women with one previous CS. However, the rate of TOL was reduced (adjusted OR 0.38; 95% CI 0.14-0.99) in women with more than one previous CS. The intervention has no influence on maternal and neonatal morbidity.

CONCLUSIONS

A multifaceted intervention including audits, feedback to health professionals, and implementation of best practices did not affect VBAC rates or maternal and neonatal morbidity. Our results pointed out the need for decision-making processand risk management tools specific to women with previous CS.

Cortical bone properties in the Brtl/+ mouse model of Osteogenesis imperfecta as evidenced by acoustic transmission microscopy

Higher skeletal fragility has been established for the Brtl/+ mouse model of osteogenesis imperfecta at the whole bone level, but previous investigations of mechanical properties at the bone material level were inconclusive. Bone material was analyzed separately at endosteal (ER) and periosteal regions (PR) on transverse femoral midshaft sections for 2-month old mice (wild-type n = 6; Brtl/+ n = 6). Quantitative backscattered electron imaging revealed that the mass density computed from mineral density maps was higher in PR than in ER for both wild-type (+2.1%, p < 0.05) and Brtl/+ mice (+1.8%, p < 0.05). Electron induced X-ray fluorescence analysis indicated significantly lower atomic Ca/P ratios and higher Na/Ca, Mg/Ca and K/Ca ratios in PR bone compared to ER independently of genotype. Second harmonic generation microscopy indicated that the occurrence of periodically alternating collagen orientation in ER of Brtl/+ mice was strongly reduced compared to wild-type mice. Scanning acoustic microscopy in time of flight mode revealed that the sound velocity and Young's modulus (estimated based on sound velocity and mass density maps) were significantly greater in PR (respectively +6% and +15%) compared to ER in wild-type mice but not in Brtl/+ mice. ER sound velocity and Young's modulus were significantly increased in Brtl/+ mice (+9.4% and +22%, respectively) compared to wild-type mice. These data demonstrate that the Col1a1 G349C mutation in Brtl/+ mice affects the mechanical behavior of bone material predominantly in the endosteal region by altering the collagen orientation.

A cluster-randomized trial to reduce major perinatal morbidity among women with one prior cesarean delivery in Québec (PRISMA trial): study protocol for a randomized controlled trial

Background

Rates of cesarean delivery are continuously increasing in industrialized countries, with repeated cesarean accounting for about a third of all cesareans. Women who have undergone a first cesarean are facing a difficult choice for their next pregnancy, i.e.: (1) to plan for a second cesarean delivery, associated with higher risk of maternal complications than vaginal delivery; or (b) to have a trial of labor (TOL) with the aim to achieve a vaginal birth after cesarean (VBAC) and to accept a significant, but rare, risk of uterine rupture and its related maternal and neonatal complications. The objective of this trial is to assess whether a multifaceted intervention would reduce the rate of major perinatal morbidity among women with one prior cesarean.

Methods/design

The study is a stratified, non-blinded, cluster-randomized, parallel-group trial of a multifaceted intervention. Hospitals in Quebec are the units of randomization and women are the units of analysis. As depicted in Figure 1, the study includes a 1-year pre-intervention period (baseline), a 5-month implementation period, and a 2-year intervention period. At the end of the baseline period, 20 hospitals will be allocated to the intervention group and 20 to the control group, using a randomization stratified by level of care. Medical records will be used to collect data before and during the intervention period. Primary outcome is the rate of a composite of major perinatal morbidities measured during the intervention period. Secondary outcomes include major and minor maternal morbidity; minor perinatal morbidity; and TOL and VBAC rate. The effect of the intervention will be assessed using the multivariable generalized-estimating-equations extension of logistic regression. The evaluation will include subgroup analyses for preterm and term birth, and a cost-effectiveness analysis.

Discussion

The intervention is designed to facilitate: (1) women’s decision-making process, using a decision analysis tool (DAT), (2) an estimate of uterine rupture risk during TOL using ultrasound evaluation of low-uterine segment thickness, (3) an estimate of chance of TOL success, using a validated prediction tool, and (4) the implementation of best practices for intrapartum management.

Trial registration

Current Controlled Trials, ID: ISRCTN15346559. Registered on 20 August 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2150-x) contains supplementary material, which is available to authorized users.

Baseline mineralizing surface determines the magnitude of the bisphosphonate effect on cortical bone mineralization in postmenopausal osteoporotic patients

PURPOSE

To determine the effect of short- or long-term bisphosphonate treatment on cortical bone mineralization density distribution (BMDD).

METHODS

BMDD was assessed by quantitative backscatter electron imaging in postmenopausal osteoporosis: in paired transiliac biopsy samples (n=36) at baseline and after 3 years risedronate treatment from a clinical study, in transiliac biopsy samples from patients who were treated with either risedronate (n=31) or alendronate (n=68) for 3 to 7 years from an observational study. Outcomes were related to premenopausal reference data (n=73) and to histomorphometric mineralizing surface per bone surface (MS/BS).

RESULTS

In the clinical study, patients with lower (below cohort median) MS/BS had normal cortical CaMean at baseline. After 3 years risedronate, their CaMean was not different versus baseline but increased versus reference (+2.9%, p=0.003). Among the groups of the observational study, CaMean did not exceed reference level, was similar for alendronate versus risedronate and similar between 3 to 5 years versus longer than 5 years treatment duration.

CONCLUSION

Baseline bone mineralizing surface appears to be important for the effect of bisphosphonate on cortical bone mineralization. In patients with lower baseline MS/BS, level of mineralization after treatment can exceed reference level. Whether this is beneficial in the long-term is unknown.

"That was intense!" Spirituality during childbirth: a mixed-method comparative study of mothers' and fathers' experiences in a public hospital

BACKGROUND

While spirituality is well described in end-of-life care literature, research on its place in the delivery room remains largely limited to mother-oriented qualitative studies focusing on life-threatening situations (e.g., high-risk pregnancies). Our aim was to compare mothers' and fathers' spirituality during childbirth.

METHODS

A mixed methods questionnaire was developed from our childbirth-related spirituality categorization and distributed to all parents of newborns, 12-24 h postpartum, over 45 consecutive days. Paired-sample t-tests and qualitative thematic analysis were used to compare mothers and fathers. Multiple linear regressions identified factors associated with their respective global scores (vaginal and cesarean deliveries separately).

RESULTS

The global scores for mothers (38.6/50) and fathers (37.2/50) were similarly high (N = 197; p = 0.001). Highest-ranked ("respect", "moral responsibility", "beauty of life", "gratitude") and lowest-ranked spiritual themes ("prayer", "greater than self") were in agreement. Fathers scored higher on "fragility of life" (p = 0.006) and mothers on "self-accomplishment" (p‹0.001), "letting go" (p‹0.001), and "meaningfulness" (p = 0.003). "Admission of baby in neonatal unit" was associated with higher global score for both mothers and fathers. Other factors also increased fathers' (witnessing a severe tear) and mothers' scores (birthplace outside Canada; for vaginal deliveries, religious belonging and longer pushing stage).

CONCLUSION

These first quantitative data on the prevalence of spirituality during childbirth highlight a high score for both parents, among a non-selected public hospital population. Spirituality emerges not only from unordinary situations but from any childbirth as an "intensification of the human experience". Significant differences for some spiritual themes indicate the need to consider the spirituality of both parents.

Antenatal montelukast treatment reduces uterine activity associated with inflammation in a pregnant rat model

OBJECTIVE

The potency of acute montelukast treatment, a leukotriene receptor antagonist, has been demonstrated as tocolytic on in vitro myometrial contractility. This study assessed the ability of a 48h montelukast treatment to modify in vitro contractions under inflammatory conditions in a pregnant rat model.

STUDY DESIGN

Pregnant Sprague-Dawley rats were injected intraperitoneally (gestational days 20-22) with lipopolysaccharides (LPS) 200μg/kg (4 treatments at 12h intervals) alone or combined with montelukast 10mg/kg/day or a saline solution for a 48h period. Uterine rings (n=72) were obtained by median laparotomy at day 22. Spontaneous contractile activities were compared using pharmacological compounds (oxytocin, nifedipine) along with assessment of contractile parameters. Myometrial subcellular fractions were also analyzed by Western blot to quantify oxytocin, cysteinyl leukotriene receptors and inflammation markers.

RESULTS

In in vitro experiments, the area under the curve, the amplitude and the duration of phasic contractions were significantly reduced following 48h of LPS+montelukast treatment comparatively to the LPS group. Moreover, in this same group, oxytocin (10^-9-10^-7M) largely decreased uterine sensitivity (p=0.04). Following LPS and montelukast treatment, the tocolytic effectiveness of nifedipine (10^-9-10^-7M) was increased (p<0.01). Western blot analysis confirmed the presence of type 1 CysLT receptors in all treated groups. Hence, montelukast treatment restored TNF-α and COX-2 basal levels.

CONCLUSION

Our results strongly suggest that montelukast treatment could facilitate a relative uterine quiescence by decreasing its sensitivity to uterotonic agent or by increasing tocolytic efficiency under proinflammatory conditions.

Neuroprotective effects of antenatal magnesium sulfate under inflammatory conditions in a Sprague-Dawley pregnant rat model

OBJECTIVE

Antenatal magnesium sulfate (MgSO₄) is recommended for fetal neuroprotection. The aim of this animal study was to assess the neuroprotective effect of in utero exposure to MgSO₄, under inflammatory conditions.

METHODS

Timed pregnant Sprague-Dawley (SD) rats (n = 29) received four intra-peritoneal (IP) injections of lipopolysaccharides (LPS; 200 μg/kg), combined with increasing concentrations of MgSO₄ (25, 50 or 100 mg/kg, n = 19) or saline solution (SS; n = 10). In the second set of experiments, animals (n = 8) received a single IP injection of i) LPS (500 μg/kg), MgSO₄ (50 mg/kg) and SS (n = 4) or ii) LPS (500 μg/kg), MgSO₄ (50 mg/kg) and IL-6 (12 μg/kg) (n = 4). Neurodevelopmental outcomes of surviving pups (n = 212) were assessed by the open field and the rotarod tests.

RESULTS

Pups' average weight at postnatal day (P) 25 was 75.77 g and 89.08 g in MgSO₄ and control groups, respectively (p = 0.02). Pups in MgSO₄ group have traveled a shorter distance and have shown reduced motor balance and coordination (p < 0.01). Average weight of pups receiving (LPS + MgSO₄+ IL-6) was 92.26 g at P25, compared to 75.86 g in (LPS + MgSO₄+SS) group (p < 0.05).

CONCLUSIONS

In our model, MgSO₄ induces pup's growth retardation and motor deficits, which may partly be related to a lower IL-6 circulating concentration.

Functional Studies of DNA-Protein Interactions Using FRET Techniques

Protein-DNA interactions underpin life and play key roles in all cellular processes and functions including DNA transcription, packaging, replication, and repair. Identifying and examining the nature of these interactions is therefore a crucial prerequisite to understand the molecular basis of how these fundamental processes take place. The application of fluorescence techniques and in particular fluorescence resonance energy transfer (FRET) to provide structural and kinetic information has experienced a stunning growth during the past decade. This has been mostly promoted by new advances in the preparation of dye-labeled nucleic acids and proteins and in optical sensitivity, where its implementation at the level of individual molecules has opened a new biophysical frontier. Nowadays, the application of FRET-based techniques to the analysis of protein-DNA interactions spans from the classical steady-state and time-resolved methods averaging over large ensembles to the analysis of distances, conformational changes, and enzymatic reactions in individual protein-DNA complexes. This chapter introduces the practical aspects of applying these methods for the study of protein-DNA interactions.

Bone matrix mineralization is preserved during early perimenopausal stage in healthy women: a paired biopsy study

Bone matrix mineralization based on quantitative backscatter electron imaging remained unchanged during the first year of menopause in paired transiliac biopsy samples from healthy women. This suggests that the reported early perimenopausal reductions in bone mineral density are caused by factors other than decreases in the degree of mineralization.

INTRODUCTION

It is unknown whether perimenopausal loss of bone mass is associated with a drop in bone matrix mineralization.

METHODS

For this purpose, we measured the bone mineralization density distribution (BMDD) by quantitative backscatter electron imaging (qBEI) in n = 17 paired transiliac bone biopsy samples at premenopausal baseline and 12 months after last menses (obtained at average ages of 49 ± 2 and 55 ± 2 years, respectively) in healthy women. For interpretation of BMDD outcomes, previously measured bone mineral density (BMD) and biochemical and histomorphometric markers of bone turnover were revisited for the present biopsy cohort.

RESULTS

Menopause significantly decreased BMD at the lumbar spine (-4.5 %) and femoral neck (-3.8 %), increased the fasting urinary hydroxyproline/creatinine ratio (+60 %, all p < 0.01) and histomorphometric bone formation rate (+25 %, p < 0.05), but affected neither cancellous nor cortical BMDD variables (paired comparison p > 0.05). Mean calcium concentrations of cancellous (Cn.CaMean) and cortical bone (Ct.CaMean) were within normal range (p > 0.05 compared to established reference data). Ct.CaMean was significantly correlated with Cn.CaMean before (R = 0.81, p < 0.001) and after menopause (R = 0.80, p < 0.001) and to cortical porosity of mineralized tissue (Ct.Po.) after menopause (R = -0.57, p = 0.02).

CONCLUSIONS

Surprisingly, the BMDD was found not affected by the changes in bone turnover rates in this cohort. This suggests that the substantial increase in bone formation rates took place shortly before the second biopsy, and the bone mineralization changes lag behind. We conclude that during the first year after the last menses, the degree of bone matrix mineralization is preserved and does not contribute to the observed reductions in BMD.

Levothyroxine treatment generates an abnormal uterine contractility patterns in an in vitro animal model

Objective

Abnormal uterine contraction patterns were recently demonstrated in uterine strips from pregnant women treated with Levothyroxine (T4). These abnormalities were correlated with an increased risk of C-section delivery and associated surgical complications. To date, no study has investigated whether uterine contractility is modified by hypothyroidism or T4 treatment. Herein, we analyze the physiological role of T4 on uterine contractions.

Study design

Female non-pregnant Sprague-Dawley rats (N = 22) were used and divided into four groups: 1) control, 2) hypothyroidism, 3) hypothyroidism treated with low T4 doses (20 μg/kg/day) and 4) with high T4 doses (100 μg/kg/day). Hypothyroidism was induced by an iodine-deficient diet. Isometric tension measurements were performed in vitro on myometrium tissues in isolated organ baths. Contractile activity parameters were quantified (amplitude, duration, frequency and area under the curve) using pharmacological tools to assess their effect.

Results

Screening of thyroid function confirmed a hypothyroid state for all rats under iodine-free diet to which T4 was subsequently administered to counterbalance hypothyroidism. Results demonstrate that hypothyroidism significantly decreased contractile duration (-17%) and increased contractile frequency (+26%), while high doses of T4 increased duration (+200%) and decreased frequency (-51%). These results thus mimic the pattern of abnormal contractions previously observed in uterine tissue from T4-treated hypothyroid pregnant women.

Conclusion

Our data suggest that changes in myometrial reactivity are induced by T4 treatment. Thus, in conjunction with our previous observations on human myometrial strips, management of hypothyroidism should be improved to reduce the rate of C-sections in this group of patients.

Effect of endometrial ablation on premenstrual symptoms

STUDY OBJECTIVE

To evaluate the effect of endometrial ablation on 6 premenstrual symptoms for up to 1 year after treatment.

DESIGN

Prospective cohort of 59 women awaiting endometrial ablation (Canadian Task Force classification II-2).

SETTING

University tertiary care hospital.

PATIENTS

Adult women of childbearing age awaiting endometrial ablation for heavy menstrual bleeding were recruited through the gynecology clinic of the Centre Hospitalier Universitaire de Sherbrooke. Fifty-nine patients were recruited, of whom 9 were excluded. Women were eligible to participate after an initial self-evaluation of ≥ 3 out of 10 for at least 1 premenstrual symptom.

INTERVENTIONS

Women underwent endometrial ablation using the microwave, impedance-controlled, or rollerball technique.

MEASUREMENTS AND MAIN RESULTS

Women had to fill out 2 surveys at 3 time points: before surgery, 4 months after surgery, and 12 months after surgery. The first survey consisted of visual analog scales for self-evaluation of 6 premenstrual symptoms (i.e., irritability, agitation/anxiety, depression/sadness, headache, swelling/bloating, and breast tenderness), and the second evaluated the heaviness of menstrual bleeding. The severity of all 6 symptoms decreased significantly (p < .025) up to 1 year after endometrial ablation. The greatest improvement was seen in swelling/bloating, with mean decreases of 4.1 on a scale of 10 at the 4-month follow-up and 3.1 at the 12-month follow-up. Women who reported the most severe symptoms before surgery appeared to have greater improvement compared with women with milder symptoms. Significant improvements were nevertheless observed in the mild severity subgroup for 4 of the 6 symptoms studied (i.e., irritability, depression, swelling/bloating, and breast tenderness).

CONCLUSION

Women reported significant improvement for the 6 premenstrual symptoms for up to 1 year following an endometrial ablation for heavy menstrual bleeding. The improvement of these symptoms appears to be linked to the efficacy of the procedure.

[Factors associated with breastfeeding continuation in young Canadian mothers]

OBJECTIVES

Breastfeeding continuation rates are lower among young mothers, while few studies have specifically focused on this population. This study describes the factors related to continued breastfeeding beyond two months among young Canadian mothers.

METHODS

A descriptive and correlational design was used to identify and quantify the impact offactors affecting continued breast-feeding beyond two months. Data were derived from a selection of mothers 15-19 years who responded to The Maternity Experiences Survey.

RESULTS

The difference between subgroups (15-18 vs 19 years old) in terms of breastfeeding continuation was not significant, but non-smoking (OR 2.78, 95% C, 1.351 - 5.682), living with a partner (OR 1.96, 95% CI, 1.087 to 3.597), vaginal delivery (OR 2.22, 95% CI, 1.012 to 4.878) and experiencing a large number of stressful situations (RC 0.42, 95% CI, 0.221 to 0.788) promotes continued breastfeeding beyond two months. No significant relationship wasfound with pregnancy planning, prenatal preparation, the violence suffered, depressive symptoms and the availability of social support.

CONCLUSION

Some factors related to pre-and postnatal periods, in addition to sociodemographic factors influence the choice of young Canadian mothers to continue or not continue breastfeeding beyond two months. Our results will be used to guide specific interventions for young mothers in breastfeeding protection, promotion and support programmes.

Leukotriene receptor antagonist as a novel tocolytic in an in vitro model of human uterine contractility

OBJECTIVE

This study analyzed the ability of montelukast, a cysteinyl-leukotrienes receptor antagonist and anti-inflammatory agent, to produce a consistent tocolytic effect alone or in combination with nifedipine, a calcium (Ca(2+)) channel blocker currently used in clinical practice.

STUDY DESIGN

Uterine biopsies were obtained from consenting women undergoing elective cesarean sections at term (n=20). Myometrial microsomal fractions were analyzed by immunoblotting to quantify relative cysteinyl leukotrienes receptor 1 (CysLTR1) levels. Isometric tension measurements were performed in vitro on human myometrial strips (n=120) in isolated organ baths in order to establish concentration-response curves to montelukast and to quantify changes in Ca(2+) sensitivity on β-escin permeabilized tissues.

RESULTS

Immunodetection analysis revealed the presence of CysLTR1 receptor in uterine tissues, fetal membranes and placenta. A significant increase in area under the curve (AUC) was quantified following the addition of leukotriene D4 (LTD4) (0.01-0.3 μM), an end-product of the lipoxygenase pathway. Conversely, addition of montelukast produced a significant tocolytic effect by decreasing the frequency and AUC (IC₅₀=1 μM). Moreover, addition of montelukast also resulted in a reduced Ca(2+) sensitivity as compared to control tissues (EC₅₀ values of 654 and 403 nM; p=0.02 at pCa 6), while an additive effect was observed in combination with 0.1 nM nifedipine (p=0.004).

CONCLUSION

This original study demonstrates the potency of montelukast as a tocolytic agent in an in vitro human uterine model. Montelukast, in combination with nifedipine, could represent a therapeutic approach to reduce inflammation associated with prematurity while facilitating the inhibition of preterm labor.

Maternal and paternal satisfaction in the delivery room: a cross-sectional comparative study

OBJECTIVES

Maternal satisfaction during the birthing process has been well documented, whereas little is known about the fathers' birth experiences. Our objective was to evaluate and compare the birth satisfaction of mothers and fathers.

DESIGN

Comparative cross-sectional study.

SETTING

Number of participating centres: one level III maternity centre (2813 births in 2011) in Sherbrooke, Quebec, Canada.

PARTICIPANTS

200 mothers and 200 accompanying fathers/mother's partner recruited 12-24 h after the birth over a 6-week period.

PRIMARY AND SECONDARY OUTCOME MEASURES

The Birth Satisfaction Scale (BSS) was used for the mother, and it was adapted to the father's perspective. Paired-samples t tests were used for comparing mothers and fathers for the BSS global and thematic scores. Multiple linear regressions (forward stepwise method) were made to identify predicting factors of mothers' and fathers' satisfaction.

RESULTS

Global satisfaction scores for mothers (115.5/150) and fathers (114.4/150) were relatively high and similar (p=0.116). The analysis of subthemes showed that more distress during childbirth was reported by mothers (p<0.001), while less support (p<0.001) and care satisfaction (p<0.001) were reported by fathers. The use of epidural anaesthesia during vaginal birth was the sole concordant lower satisfaction predictor. For mothers, other satisfaction predictors were labour length, tearing and type of anaesthesia used in caesarean section. For fathers, lower satisfaction predictors were instrumental delivery, primary caesarean delivery and infant's distress factors after caesarean section.

CONCLUSIONS

This study highlights differences in mothers' and fathers' birth satisfaction and in their predictors. It is thus important to take into account the birth experience of each parent and to support parents accordingly by adapting care provision surrounding childbirth. More research on this topic from the prenatal to the postnatal period is suggested, as it might have an impact on parents' satisfaction and on early parenthood experience.

Chronic levothyroxine and acute T3 treatments enhance the amplitude and time course of uterine contractions in human

This study compares the functional consequences of levothyroxine (T4) treatment during pregnancy as well as the acute affects of triiodothyronine (T3) on spontaneous uterine contractile activities observed in vitro. Uterine biopsies were obtained from consenting women undergoing elective caesarean at term (n = 28). Spontaneous contractile activities from T4-treated pregnant women (n = 8) were compared with control patients (n = 20) by isometric tension measurements. Effects of acute T3 and T4 on control tissues were also monitored. Area under the curve, amplitude, time to peak, duration, and frequency were quantified. In uterine strips from women treated for hypothyroidism, phasic uterine contractions of larger amplitude (+77%) were observed, with a prolonged duration at 90% relaxation (+138%) and reduced frequency (-55%) compared with values of the control group. The addition of exogenous T3 in vitro on control strips induced a significant increase in the duration of the contractions and a significant decrease in frequency (P < 0.05), which partially mimics the results obtained in strips from T4-treated women. Significant modifications of contractile properties were observed in strips from pregnant women treated with levothyroxine, consistent with those observed with the addition of exogenous T3. Clinical practices of modern obstetrics should take into account the effect of thyroid hormones on uterine contractions' time course to ensure a tighter followup at the end of pregnancy to achieve safer delivery.

Constitutive regulatory activity of an evolutionarily excluded riboswitch variant

The exquisite specificity of the adenine-responsive riboswitch toward its cognate metabolite has been shown to arise from the formation of a Watson-Crick interaction between the adenine ligand and residue U65. A recent crystal structure of a U65C adenine aptamer variant has provided a rationale for the phylogenetic conservation observed at position 39 for purine aptamers. The G39-C65 variant adopts a compact ligand-free structure in which G39 is accommodated by the ligand binding site and is base-paired to the cytosine at position 65. Here, we demonstrate using a combination of biochemical and biophysical techniques that the G39-C65 base pair not only severely impairs ligand binding but also disrupts the functioning of the riboswitch in vivo by constitutively activating gene expression. Folding studies using single-molecule FRET revealed that the G39-C65 variant displays a low level of dynamic heterogeneity, a feature reminiscent of ligand-bound wild-type complexes. A restricted conformational freedom together with an ability to significantly fold in monovalent ions are exclusive to the G39-C65 variant. This work provides a mechanistic framework to rationalize the evolutionary exclusion of certain nucleotide combinations in favor of sequences that preserve ligand binding and gene regulation functionalities.

Molecular insights into the ligand-controlled organization of the SAM-I riboswitch

S-adenosylmethionine (SAM) riboswitches are widespread in bacteria, and up to five different SAM riboswitch families have been reported, highlighting the relevance of SAM regulation. On the basis of crystallographic and biochemical data, it has been postulated, but never demonstrated, that ligand recognition by SAM riboswitches involves key conformational changes in the RNA architecture. We show here that the aptamer follows a two-step hierarchical folding selectively induced by metal ions and ligand binding, each of them leading to the formation of one of the two helical stacks observed in the crystal structure. Moreover, we find that the anti-antiterminator P1 stem is rotated along its helical axis upon ligand binding, a mechanistic feature that could be common to other riboswitches. We also show that the nonconserved P4 helical domain is used as an auxiliary element to enhance the ligand-binding affinity. This work provides the first comprehensive characterization, to our knowledge, of a ligand-controlled riboswitch folding pathway.

Comparative study between transcriptionally- and translationally-acting adenine riboswitches reveals key differences in riboswitch regulatory mechanisms

Many bacterial mRNAs are regulated at the transcriptional or translational level by ligand-binding elements called riboswitches. Although they both bind adenine, the adenine riboswitches of Bacillus subtilis and Vibrio vulnificus differ by controlling transcription and translation, respectively. Here, we demonstrate that, beyond the obvious difference in transcriptional and translational modulation, both adenine riboswitches exhibit different ligand binding properties and appear to operate under different regulation regimes (kinetic versus thermodynamic). While the B. subtilis pbuE riboswitch fully depends on co-transcriptional binding of adenine to function, the V. vulnificus add riboswitch can bind to adenine after transcription is completed and still perform translation regulation. Further investigation demonstrates that the rate of transcription is critical for the B. subtilis pbuE riboswitch to perform efficiently, which is in agreement with a co-transcriptional regulation. Our results suggest that the nature of gene regulation control, that is transcription or translation, may have a high importance in riboswitch regulatory mechanisms.

Bacterial genetic regulation is mostly performed at the levels of transcription and translation. Recently discovered riboswitches are RNA molecules located in untranslated regions of messenger RNAs that modulate the expression of genes involved in the transport and metabolism of small metabolites. Several riboswitches have recently been shown to employ various regulation mechanisms, but no general rules have yet been deduced from these studies. Here, we have analyzed two adenine-sensing riboswitches of Bacillus subtilis and Vibrio vulnificus that differ by the level at which they control gene expression, which is transcription and translation, respectively. We find that, beyond the obvious difference in transcriptional and translational modulation, riboswitch regulation mechanisms of both adenine riboswitches are fundamentally different. For instance, while the adenine riboswitch from B. subtilis performs co-transcriptional binding for gene regulation, the riboswitch from V. vulnificus relies on reversible ligand binding to achieve gene regulation during mRNA translation. In agreement with co-transcriptional binding of the B. subtilis riboswitch, we find that transcriptional pausing is crucial for gene regulation. Our results suggest that the nature of gene regulation control, that is transcription or translation, may have a high importance in riboswitch regulatory mechanisms.

Folding of the lysine riboswitch: importance of peripheral elements for transcriptional regulation

The Bacillus subtilis lysC lysine riboswitch modulates its own gene expression upon lysine binding through a transcription attenuation mechanism. The riboswitch aptamer is organized around a single five-way junction that provides the scaffold for two long-range tertiary interactions (loop L2–loop L3 and helix P2–loop L4)—all of this for the creation of a specific lysine binding site. We have determined that the interaction P2–L4 is particularly important for the organization of the ligand-binding site and for the riboswitch transcription attenuation control. Moreover, we have observed that a folding synergy between L2–L3 and P2–L4 allows both interactions to fold at lower magnesium ion concentrations. The P2–L4 interaction is also critical for the close juxtaposition involving stems P1 and P5. This is facilitated by the presence of lysine, suggesting an active role of the ligand in the folding transition. We also show that a previously uncharacterized stem–loop located in the expression platform is highly important for the riboswitch activity. Thus, folding elements located in the aptamer and the expression platform both influence the lysine riboswitch gene regulation.

Bone matrix quality and plasma homocysteine levels

It has recently been reported in the clinical literature that blood homocysteine levels correlate well with fracture risk, although a couple of reports exist to the opposite. Bone strength depends on both bone quantity and quality. The purpose of the present study was to investigate possible correlations between plasma homocysteine levels and bone material properties (Bone Mineral Density Distribution; BMDD, and collagen cross-link ratio). In the present study, femoral heads from subjects (N=19, females, age range 70-95 years old) with known homocysteine plasma levels were investigated. The bone material was collected during hemiarthroplasty surgery. We have determined collagen cross-link ratio and bone mineralization density distribution (BMDD) in bone tissue from patients with acute femoral neck fractures, by Fourier Transform Infrared Imaging (FTIRI) and quantitative Backscattered Electron Imaging (qBEI), respectively. The collagen cross-link ratio that was spectroscopically determined was pyridinoline/divalent cross-links (pyr/divalent). The BMDD variables quantified were: CaMean: the weighted mean calcium concentration; CaPeak: the most frequent Ca concentration; CaWidth: the width of the distribution, a measure of the mineralization homogeneity; CaLow: the percentage of bone area that is mineralized below the 5th percentile in the reference range; CaHigh: the percentage of bone area that is mineralized above the 95th percentile in the reference range. There was a significant correlation between plasma homocysteine levels and collagen cross-link ratio in areas of primary mineralized bone (p<0.0001), unlike the case of trabecular bone surfaces undergoing resorption (p>0.05). On the other hand there was no correlation in any of the BMDD parameters and plasma homocysteine levels (p>0.05). The results are consistent with the known effect of homocysteine on collagen post-translational modifications. These changes were independent of bone mineral characteristics. The results of the present study offer a mechanism by which homocysteine affects bone quality, but caution should be exercised since all patients examined had sustained fracture.

Riboswitches: ancient and promising genetic regulators

BAIT AND SWITCH: Metabolite-sensing riboswitches make use of RNA structural modulation to regulate gene expression, as illustrated in the scheme, in response to subtle changes in metabolite concentrations. This review describes the current knowledge about naturally occurring riboswitches and their growing potential as antibacterial cellular targets and as molecular biosensors. Newly discovered metabolite-sensing riboswitches have revealed that cellular processes extensively make use of RNA structural modulation to regulate gene expression in response to subtle changes in metabolite concentrations. Riboswitches are involved at various regulation levels of gene expression, such as transcription attenuation, translation initiation, mRNA splicing and mRNA processing. Riboswitches are found in the three kingdoms of life, and in various cases, are involved in the regulation of essential genes, which makes their regulation an essential part of cell survival. Because riboswitches operate without the assistance of accessory proteins, they are believed to be remnants of an ancient time, when gene regulation was strictly based on RNA, from which are left numerous "living molecular fossils", as exemplified by ribozymes, and more spectacularly, by the ribosome. Due to their nature, riboswitches hold high expectations for the manipulation of gene expression and the detection of small metabolites, and also offer an unprecedented potential for the discovery of novel classes of antimicrobial agents.

Functional studies of DNA-protein interactions using FRET techniques

Protein-DNA interactions underpin life and play key roles in all cellular processes and functions including DNA transcription, packaging, replication, and repair. Identifying and examining the nature of these interactions is therefore a crucial prerequisite to understand the molecular basis of how these fundamental processes take place. The application of fluorescence techniques and in particular fluorescence resonance energy transfer (FRET) to provide structural and kinetic information has experienced a stunning growth during the past decade. This has been mostly promoted by new advances in the preparation of dye-labeled nucleic acids and proteins and in optical sensitivity, where its implementation at the level of individual molecules has opened a new biophysical frontier. Nowadays, the application of FRET-based techniques to the analysis of protein-DNA interactions spans from the classical steady-state and time-resolved methods averaging over large ensembles to the analysis of distances, conformational changes, and enzymatic reactions in individual Protein-DNA complexes. This chapter introduces the practical aspects of applying these methods for the study of Protein-DNA interactions.

A loop loop interaction and a K-turn motif located in the lysine aptamer domain are important for the riboswitch gene regulation control

The lysine riboswitch is associated to the lysC gene in Bacillus subtilis, and the binding of lysine modulates the RNA structure to allow the formation of an intrinsic terminator presumably involved in transcription attenuation. The complex secondary structure of the lysine riboswitch aptamer is organized around a five-way junction that undergoes structural changes upon ligand binding. Using single-round transcription assays, we show that a loop-loop interaction is important for lysine-induced termination of transcription. Moreover, upon close inspection of the secondary structure, we find that an unconventional kink-turn motif is present in one of the stems participating in the loop-loop interaction. We show that the K-turn adopts a pronounced kink and that it binds the K-turn-binding protein L7Ae of Archaeoglobus fulgidus in the low nanomolar range. The functional importance of this K-turn motif is revealed from single-round transcription assays, which show its importance for efficient transcription termination. This motif is essential for the loop-loop interaction, and consequently, for lysine binding. Taken together, our results depict for the first time the importance of a K-turn-dependent loop-loop interaction for the transcription regulation of a lysine riboswitch.

Disuse and orchidectomy have additional effects on bone loss in the aged male rat

INTRODUCTION

A severely osteopenic rat model was obtained by combining orchidectomy (ORX) and disuse (due to local paralysis induced by botulinum toxin [BTX] in the quadriceps muscle).

METHODS

Forty-two aged male rats (5-6 months old) were randomized into three groups: 18 were SHAM operated; 6 were ORX; and 18 were ORX and BTX injected in the right hindlimb. One, two, and three months after surgery, bone mass (BV/TV) and microarchitectural parameters (Tb.Th, Tb.N, Tb.Sp, Tb.Pf, and structure model index [SMI]) were measured by microcomputed tomography (microCT) on the primary and secondary spongiosa of the femur. Osteoid parameters (OS/BS, O.Th), the number of osteoclasts (Nb.Oc), and the mineral apposition rate (Ct.MAR, Cn.MAR) were measured by histology. The serum tartrate-resistant acid phosphatase (TRAcP) 5b activity was measured by immunoassay.

RESULTS

ORX induced a decrease of BV/TV, Tb.N and an increase of Tb.Sp, Tb.Pf, and SMI on both primary and secondary spongiosa. ORX and BTX had cumulative effects on bone loss, since differences were maximized on the right femur. The decrease in BV/TV reached -65%. Osteoid parameters and mineral apposition rate increased during the time course of the study. A peak of serum TRAcP was found at 7 days post-ORX. TRAcP levels reached the highest values in the ORX-BTX groups and the effect lasted longer than in the group with ORX alone. The association of ORX-BTX induced a greater bone resorption, due to the removal of complete trabeculae, compared to ORX alone.

CONCLUSION

This model induced a severe and rapid bone loss and can be used to explore pharmacological- and biomaterial-based countermeasures.

Evaluation of an injectable bone substitute (betaTCP/hydroxyapatite/hydroxy-propyl-methyl-cellulose) in severely osteopenic and aged rats

The use of injectable biomaterials is of interest in osteoporotic patients to locally restore bone mass in sites at risk of fracture. An injectable bone substitute (IBS1 made of betaTCP/hydroxyapatite as a calcium phosphate substitute and hydroxy-propyl-methyl-cellulose as a polymer carrier) was used in a severely osteopenic rat model obtained by combining orchidectomy (ORX) and disuse (paralysis induced by botulinum toxin - BTX). Fifty-six aged male rats were randomized into three groups: 18 were SHAM operated; 38 were ORX and BTX injected in the right hindlimb; they constituted the OP (osteoporotic) group. One month after ORX-BTX surgery, 20 of these OP rats received a IBS1 injection in the right femur (OP-IBS1 rats). Animals were studied at the time of IBS1 injection 1 month post ORX-BTX (M1), 1 month (M2) and 2 months (M3) after IBS1 injection. Bone mass (BV/TV) and microarchitectural parameters were measured by microCT. BV/TV was decreased after ORX-BTX; ORX and BTX had cumulative effects on bone loss (differences maximized on the right femur). BV/TV (combining the volume of both bone and material in OP-IBS1 rats) was elevated at M1 but decreased at M2. Marked bone formation was found onto the biomaterial granules but bone had a woven texture. A marked increase in the number of nonosteoclastic TRAcP+ cells was found in the implanted area. IBS1 induced new bone formation shortly after implantation but both IBS1 and woven bone were resorbed without inducing lamellar bone. Biomaterial trials must be conducted with long-term implantation periods, in aged osteoporotic animals.

Relations between Radiograph Texture Analysis and Microcomputed Tomography in Two Rat Models of Bone Metastases

AIMS

Osteolytic (Walker 256, W256) and osteoblastic (MatLyLu, MLL) metastases were induced to investigate their effect on bone architecture by microcomputed tomography (microCT) and texture analysis of radiographs.

METHODS

Fischer and Copenhagen rats received an intracardiac injection with W256/MLL cells, respectively. Femur and tibia radiographs were analyzed by texture analysis with run lengths and fractal algorithms. Microarchitecture was analyzed on primary and secondary spongiosa by microCT.

RESULTS

W256 and MLL induced a decrease of trabecular bone mass, a disconnection of trabeculae and an increased conversion of plates into pillars. On radiographs and 3-dimensional models of W256 rats, a disappearance of the primary spongiosa was observed. On radiographs and 3-dimensional models of MLL rats, osteolytic lesions were observed as disseminated dark areas. Run length and fractal analyses were altered in both metastases.

CONCLUSION

W256 and MLL cells induced two different patterns of osteolysis. Texture analysis of radiographs is a useful technique to explore trabecular bone changes.

High affinity Ca2+ -Mg2+ ATPase in the distal tubule of the mouse kidney

The purpose of this study was to investigate whether Ca2+ -Mg2+ ATPase in the distal tubule (where calcium transport is active, against a gradient, and hormone dependent) presents some characteristics different from those observed in the proximal tubule, and whether these characteristics are likely to shed light on the respective roles of this enzyme at the two sites of the nephron. The Ca2+ - and Mg2+-dependent ATP hydrolysis was measured in microdissected segments of the distal nephron, the kinetic parameters were determined, and the influence of magnesium upon the sensitivity to calcium was examined. Results were compared with those obtained in the proximal tubule, and in purified membranes as reported by others. In the distal tubule, low concentrations of Mg2+ (less than 10(-7) M) did not influence ATP hydrolysis. At concentrations above 10(-7) M, Mg2+ increased ATP hydrolysis according to Michaelis kinetics (apparent Km = 11.3 +/- 2.4 microM, Vmax = 219 +/- 26 pmol.mm-1.20 min-1). The addition of 1 microM Ca2+ decreased the apparent Km for Mg2+ and the Vmax for Mg2+. Similar results were obtained in the proximal tubule. At low Mg2+ concentrations, Ca2+ also stimulated ATP hydrolysis according to Michaelis kinetics with an apparent Km value for Ca2+ of 0.18 +/- 0.06 and 0.10 +/- 0.03 microM Ca2+ (ns) and a Vmax of 101 +/- 12 and 89 +/- 9 pmol.mm-1.20 min-1 (ns) in the distal and proximal tubules, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of practolol on exercise tolerance and cardiac haemodynamics and metabolism in patients with coronary artery disease

Sixteen male patients with typical angina pectoris secondary to coronary atherosclerosis performed two daily standardized exercise tests during two consecutive days. Three hours before each exercise they received placebo or 400 mg practolol administered orally in double-blind fashion in order to complete a cross-over design. Practolol significantly prolonged the exercise duration by 30.6% and delayed the appearance time of ischaemic electrocardiographic changes by 67.7%. Maximal heart rate, systolic pressure, and pressure-rate product were also reduced after medication. In order to investigate further the effects of this beta blocking agent, myocardial function and metabolism at rest and during supine exercise were assessed in 12 male patients with coronary artery disease before and after practolol 30 mg, iv. At rest, practolol produced a decrease in tension-time index (18%), cardiac index (17%), heart rate (10%), and stroke index (7%). A significant reduction was also observed in resting stroke work index (14%) and systolic and mean aortic pressure (6%). Left ventricular end-diastolic pressure remained unchanged. During supine exercise, only time-tension index (12%), heart rate (12%), and cardiac index (10%) were significantly reduced after the beta blocking agent. Practolol did not significantly change the arterial glucose, lactate, inorganic phosphate, potassium, calcium, magnesium, pH, PCO2, or PO2. The beta blocking agent did not modify the myocardial extraction of any of these substrates at rest or during exercise. In the dosage used in both studies, practolol significantly improved the exercise tolerance and reduced the ischaemic manifestations. The efficacy of practolol in angina pectoris may result mostly from its ability to decrease heart rate and systolic pressure during exercise.