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D Collin

Publications and source records attributed to D Collin.

At least 19 recordsLinked to original sources
PubMed2000

Critical behavior of the de gennes elastic constants near the nematic-smectic- A transition of TBBA

We have studied the behavior of elastic constants A, B, and C deduced from ultrasound velocity anisotropies in the vicinity of the nematic-smectic- A transition of terephthal-bis- p- p(')-butylaniline. A is associated with compressibility, B with layer compression, and C with the coupling between compressibility and layer compression. We show that the exponent of A is of the preasymptotic 3D- XY type, whereas those of B and C are in between the 3D- XY values and those associated with the anisotropic fixed point. This behavior is consistent with the extended crossover regime predicted by Patton and Andereck [Phys. Rev. Lett. 69, 1556 (1992)].

Journal Article↗
PubMed2000

NMR characterization of a kissing complex formed between the TAR RNA element of HIV-1 and a DNA aptamer.

This work presents the first structural analysis of an RNA-DNA complex consisting of an 18 nt RNA hairpin and a 20 nt DNA aptamer. The DNA molecule was previously selected, from a randomly synthesized library, against the transactivation response element (TAR) involved in transcriptional regulation of the HIV genome. The DNA aptamer used in the present study is an imperfect stem-loop with the sequence 5'-ACTCCCAT-3', characteristic of the selected candidates, in the apical loop. This octameric motif contains five bases complementary to the TAR loop sequence 5'-CUGGGA-3'. The use of homo- and heteronuclear NMR spectroscopy allowed assignment of the complex resonances and resolution of its secondary structure. Evidence is given for a kissing complex fold, which consists of a quasi-continuous helix formed by one stem of DNA, one stem of RNA and a central hybrid helix comprising 5 bp. Two out of helices residues of DNA and one of RNA connect the DNA-RNA loop-loop helix to the stem of either partner in the complex. In addition, two thymines of the DNA stem are engaged in a non-canonical T.T base pair.

Base Pairing↗
PubMed2000

Dynamic scaling of ultrasonic damping near the nematic-smectic- A transition of TBBA

We report a detailed study of the ultrasonic damping near the nematic-smectic- A phase transition of terephtal-bis- p-p(')-butylaniline (TBBA). Two mechanisms contribute to the damping. One is isotropic; it is associated with the critical fluctuations, and leads to a scaling behavior of the 3D- XY type which is observed up to 15 degrees C from the transition, even though the transition is first order. The other is anisotropic; it appears only in the smectic- A phase, and is associated with the relaxation of the order-parameter modulus.

Journal Article↗
PubMed1999

[Predictive factors of the delivery method in women with cesarean section scars].

OBJECTIVE: To determine the independent effect of clinical and non clinical factors on the mode of delivery after previous cesarean section. METHODS: We performed a retrospective multicenter study of 579 women who had previously undergone a cesarean section and who delivered between January 1995 and June 1997. Maternal and perinatal morbidity associated with trial of labor and elective repeat cesarean was assessed. Multiple logistic regression was used to identify prognostic factors for the outcome of a trial of labor. The odds ratios provided indicate the risk of cesarean section when the factor is present. RESULTS: The rate of successful trial of labor was 74.5%. Overall morbidity was not increased in the trial of labor group. The variables of significant predictive value were the Bishop's score (OR = 15.2 for a score < 3; 95% CI: 5.54 to 41.9), an anomaly of the pelvis (OR = 5.89; 95% CI: 2.37 to 14.7), a previous vaginal delivery (OR = 0.27; 95% CI: 0.12 to 0.60), a fetal distress (OR = 4.11; 95% CI: 2.01 to 8.43), the weight gain during pregnancy (OR = 2.01; 95% CI: 1.10 to 3.68), a delivery between 11 p.m. and 7 a.m. (OR = 0.29; 95% CI: 0.13 to 0.66), a hypertension (OR = 3.10; 95% CI: 1.09 to 8.80) and the use of an intra-uterine pressure catheter (OR = 0.26; 95% CI: 0.11 to 0.57). CONCLUSION: A trial of labor should be allowed in most of the women with previous cesarean section. The Bishop's score is the best predictor of the mode of delivery. Induction of labor and a first cesarean for dystocia do not affect the chances of vaginal birth.

Adult↗
PubMed1999

[Diagnosis and treatment of polycystic ovary syndrome].

Obesity, ultrasonic ovarian morphology, serum LH levels and LH/FSH ratio are inconstant symptoms of the polycystic ovary syndrome (PCOS) and are thus no longer essential for diagnosis. PCOS is diagnosed today by the finding of chronic anovulation and hyperandrogenism characterized by a high serum level of "free" testoterone. The other causes of hyperandrogenism, as well as anovulations due to hyperprolactinemia, high levels of FSH and abnormal thyroid function have to be ruled out. PCOS is very often associated with insulin resistance (IR) and hyperinsulinemia (hyper I). From in vitro and vivo studies and treatment of hyper I, it has been shown that the hyper I of PCOS stimulates androgen production. Hyper I of PCOS increases the activity of androgens: by first provoking an important decrease of the sex hormone binding globulin (SHBG) thus increasing the "free", bioactive testosterone level. and then by activating the cytochrome P 450 c 17 alpha enzymatic system that controls androgen production. Subsequent to metformin administration, the reduction of hyper I and androgen serum levels creates a favorable condition for the resumption of ovarian function and clomiphene citrate action. This explains the high percentage of ovulations and pregnancies.

Anovulation↗
PubMed1998

Prediction factors in the determination of final height in subjects born small for gestational age.

The aim of this study was to identify factors predictive of individual final height (FH) in subjects born small for gestational age (SGA). All full-term singleton subjects born SGA (birth weight and/or length <3rd percentile) during the period 1971-1978, matched with appropriate birth weight for gestational age (AGA) subjects (birth weight between 25th and 75th percentile) were followed from birth to FH and evaluated before puberty at a mean age +/- SD of 6.1 +/- 0.7 y and after puberty at a mean age of 20.8 +/- 2.0 y (subjects born SGA, n = 213; born AGA, n = 272). When adjusted for target height, a significant deficit in final height (p < 0.0001) was found in SGA as compared with AGA subjects for both male subjects (-3.99 cm with 95% confidence interval from -5.6 to -2.4) and female subjects (-3.64 cm with 95% confidence interval from -5.0 to -2.3), with 13.6% of subjects in the SGA population presenting short final stature. In a multiple regression analysis, target height and studied group (SGA or AGA) were found to be the strongest predictors of individual FH (p < 0.0001, r2 = 0.35 for male subjects, p < 0.0001, r = 0.40 for female subjects). For SGA subjects and according to a multiple stepwise linear regression model, 31% of the variability of individual FH [SD score (SDS)] and 58% of the variability of individual height gain SDS could be explained at birth from mother's height, father's height, and birth length SDS. No other variables were found to be predictive such as sex, gestational age (from 37 to 42 wk), birth weight SDS, ponderal index at birth, or risk factors during pregnancy associated with intrauterine growth retardation such as pregnancy-induced hypertension, smoking, or a history of SGA in offspring. Although a significant increase of body mass index SDS was documented before and after puberty in SGA subjects, puberty was not found to have any influence on growth outcome.

Adult↗
PubMed1998

Angiotensin I-converting enzyme gene polymorphism modulates the consequences of in utero growth retardation on plasma insulin in young adults.

In utero growth retardation has been linked to a reduced rate of cell division in the fetal organs that undergo rapid growth and to permanent changes and adaptations (programming) that may affect the physiology in adult life. In particular, in utero growth retardation as reflected by a low birth weight for gestational age has been shown to be associated with a relative insulin resistance in adults. How programming may influence glucose metabolism is not completely understood, and the possible role of genetic factors has not been explored. The angiotensin I-converting enzyme gene insertion/deletion (ACE I/D) polymorphism may predispose to insulin resistance and modulate the expression of several common cardiovascular and renal disorders, especially in people with diabetes. The possible impact of this polymorphism on plasma glucose and insulin levels was investigated in a group of young adults born at term whose length or weight at birth were in the lowest 3% of the sex and gestational age-adjusted distribution (SGA, n = 172) and a group of control individuals born with an appropriate birth weight for gestational age (AGA, n = 207). In this study, we have previously demonstrated an association between SGA and relative insulin resistance, especially in those with shorter gestational age. In the SGA group, fasting plasma glucose and insulin levels were significantly correlated (R = 0.196, P < 0.015), with this association being significant only in ACE II individuals (R = 0.539, P < 0.0009). In the AGA group, fasting plasma glucose and insulin levels were not significantly correlated. Consistent with this observation, the relationship between the ACE polymorphism and the insulin response to a glucose load was significantly heterogeneous between the AGA and SGA groups (P < 0.05); this was due to a tendency for ACE II individuals in the SGA group to exhibit increased 30-min plasma insulin levels (P < 0.05). In the SGA group, there was a significant interaction between gestational age and genotype on the insulin area (P < 0.0004); this index was inversely associated with gestational age in ACE II (P < 0.0005) and ACE ID (P < 0.005) subjects, but not in DD homozygotes (P > 0.05). The ACE D allele may thus attenuate the additive consequences of SGA and relatively short duration of gestation on insulin resistance in young adults.

Adult↗
PubMed1997

Reduced final height and indications for insulin resistance in 20 year olds born small for gestational age: regional cohort study.

OBJECTIVE: To investigate whether the association between low birth weight and increased risk of developing impaired glucose tolerance, insulin resistance, hypertriglyceridaemia, and hypertension in middle age is apparent by the age of 20 in people born small for gestational age. DESIGN: Regional cohort study. SETTING: Maternity registry, Haguenau, France. SUBJECTS: 236 full term singleton babies born small for gestational age (birth weight or length, or both, below third centile) during 1971-8 and 281 with normal birth weight (between 25th and 75th centile). All subjects were contacted and evaluated at a mean (SD) age of 20.6 (2.1) years. MAIN OUTCOME MEASURES: Adult height; concentrations of glucose, insulin, and proinsulin during an oral glucose tolerance test; lipid and fibrinogen concentrations; and blood pressure. RESULTS: After sex and target height were adjusted for, subjects who had been born small for gestational age were significantly shorter at age 20 than those with a normal birth weight (men 4.5 cm shorter (95% confidence interval 6.0 to 3.0 cm); women 3.94 cm shorter (5.2 to 2.7 cm)). After sex and body mass index were adjusted for, mean plasma glucose concentration 30 minutes after a glucose load, fasting insulin concentration (in women), and insulin and proinsulin concentrations 30 and 120 minutes after a glucose load were significantly higher in subjects who had been born small for gestational age than in those with a normal birth weight. Mean lipid and fibrinogen concentrations and blood pressure were not different between the two groups. CONCLUSIONS: Intrauterine growth retardation has long term consequences such as reduced final height Raised insulin and proinsulin concentrations are present in young adults born small for gestational age and could be markers of early changes in insulin sensitivity.

Adolescent↗
PubMed1997

The Aspergillus nidulans transcription factor AlcR forms a stable complex with its half-site DNA: a NMR study.

The Aspergillus nidulans transcription factor AlcR is shown by NMR and gel retardation assay to form a stable complex with oligonucleotide sequences comprising the consensus half-site 5'-TGCGG-3'. Apparent microM dissociation constants are evaluated by both methods. The measured lifetime of the complex is 74+/-7 ms at 20 degrees C with the following DNA sequence: 5'-C1G2T3G4C5G6G7A8T9C10-3'. The major chemical shift variations upon binding involve both the two adjacent GC pairs (G6 and G7) and, clearly, the AT pairs at both ends of the consensus sequence (T3 and A8), suggesting additional contacts of the protein with the DNA. This extensive and strong interaction with the half-site is another example of the variability in contacts of the fungal DNA-binding proteins containing Zn2Cys6 domains with their consensus sites. It is the first demonstration that a binuclear cluster protein can bind to DNA as a monomer with strong affinity.

Aspergillus nidulans↗
PubMed1997

[Pre-ovulatory peaks of gonadotropins. Recent data].

From recent data we know that: The duration of the LH peak seems to be more important than its amplitude for the induction of ovulation. Ovulation induction by hCG is not physiological; the absence of an FSH surge, and the long duration of LH activity would contribute to some of the luteal phase abnormalities. Recombinant hLH, on the other hand could give better results provided its action last about 48 hours. The results, however, are not as expected, probably because of the type of isoforms injected. The circulating FSH and LH isoforms found during the preovulatory peak of gonadotropins have a much higher in vitro biological activity than those found at other periods of the cycle. The production of FSH and LH recombinant of different biological activity is in process. The mechanism of the preovulatory peak of gonadotropins is still not fully understood. The respective role of GnRH and of the ovarian steroids has yet to be precisely determined in the human being. Ovarian peptides very probably also play a role.

Animals↗
PubMed1994

[The biological activity of luteinizing hormone (LH)].

In vitro bioassay (BIO) is a very specific and sensitive method for determining levels of luteinizing hormone (LH). It provides a means of evaluating the values obtained with routine radioimmunoassays (RIA). Serum levels with bioassay are higher than those obtained with radioimmunoassay. The LH BIO/LH RIA ratio measures the difference between the two methods and gives a means of evaluating the quality of the LH secreted. The LH BIO/LH RIA ratio is significantly higher at the summit than at the nadir of the LH serum pulses. This ratio also increases after administration of GnRH. The differences in the quality of the LH can be explained by micro-heterogenicity. Immunofluorometric assay of LH (LH FIA) is much more sensitive than either the LH BIO or the LH RIA assays. Unlike the LH BIO/LH RIA ratio, the LH BIO/LH FIA ratio remains unchanged during LH pulses and after administration of GnRH. This difference can be explained by the lack of sensitivity but also by the lack of specificity of the LH RIA. LH RIA is not reliable when the serum levels of LH are low. However, RIA is valid when the serum levels of LH are increased as occurs in polycystic ovary syndromes.

Adolescent↗
PubMed1993

[Functional hypothalamic amenorrheas. I. Physiopathology].

Functional hypothalamic amenorrhea are very probably due to a decrease of the frequency of the secretory pulses of LH, ie of GnRH. This decrease could be the consequence of a chronic hypersecretion of the corticotropin releasing hormone (CRH). CRH seems to act on the hypotalamic pulse generator of GnRH through the effect of the endogenous opioid peptides of the central nervous system. Opioid receptor antagonists restore normal pulse frequency of LH in most cases. Research is being done to try to elucidate the cause of the failure to such treatment: dopamine in among other mechanisms, supposed to play an essential role.

Amenorrhea↗
PubMed1993

[Functional hypothalamic amenorrheas. II. Clinical aspects].

The most important causes of the functional hypothalamic amenorrhea (FHA), that are psychological stress, physical stress and weight loss, are associated with a decrease of the frequency of the LH secretory pulses and with a state of hypercortisolism. The slowing down of the LH pulse frequency is difficult to demonstrate in clinical practice. The classical symptoms of FHA which are low gonadotropin levels, and hypogonadism are not very specific. The diagnosis of FHA is therefore one of exclusion. Recent physiopathological studies have individualised new symptoms that are hypercortisolism, hypoprolactinaemia and an important increase in the night serum levels of melatonine, all of which could help to confirm the diagnosis. FHA is relatively frequent and its treatment with pulsatile GnRH administration or naltrexone is very successful.

Amenorrhea↗
PubMed1991

[The corpus luteum and progesterone secretion].

The pulsatility of LH secretion has been known only since 1970. The pulsatility of progesterone secretion has now also been shown. The frequency and amplitude of these pulses vary during the three phases of the luteal period. The first or early luteal (EL) phase lasts four days starting from the peak of LH. There is no pulsatility of progesterone during EL. The frequency of LH pulsatility is 103 +/- 8 minutes. The second or mid luteal (ML) phases, from +6 to +9 days after the peak of LH, is characterised by pulses of LH and of progesterone, most often in positive crossover correlation and with 7 to 14 pulses per 24 hours. The frequency of LH pulsatility is 166 +/- 33 minutes according to Filicori. The amplitude of LH secretion is 4 to 40 ng/ml. The third or late luteal (LL) phase, occurring at +11 days before the menstrual period, has the same characteristics in terms of quality but shows variations in frequency and amplitude towards a decrease. Thus the amplitude of progesterone secretion is 2.8 to 9 ng/ml (Veldhuis). In the opinion of clinicians, the corpus luteum is independent up to LH+ 5 days. The injection of hCG during this time is ineffective. A single progesterone level is sufficient if the result is 10 ng/ml or more. The problem remains complex concerning results below 10 ng/ml. The solution suggested for the present is that described by Olive: during ML and/or LL, three samples in the morning at hourly intervals and two endometrial biopsies during two consecutive cycles.

Biopsy↗