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Biomedical subjects

A Thomas

Publications and source records attributed to A Thomas.

At least 253 records · Page 14Linked to original sources
PubMed1997

Age of the uterus does not affect pregnancy or implantation rates; a study of egg donation in women of different ages sharing oocytes from the same donor.

The importance of age of the recipient (uterine age) with regards to pregnancy rate, delivery rate and miscarriage rate following oocyte donation was evaluated using retrospective data analysis of cases where two recipients from different age groups shared oocytes from a single donor and had equal numbers of embryos transferred. A total of 104 women (21-52 years of age) underwent a total of 104 cycles of oocyte donation. They were divided into groups according to age (group A: age 39 years or less and group B: age between 40 and 52 years). The minimum age difference between a pair of recipients was five years. Hormone replacement therapy (HRT) was given using oestradiol valerate (6 mg daily) for at least 10 days, followed by a combination of oestradiol with either intramuscular progesterone (100 mg daily), or vaginally administered micronized progesterone (300 microg daily). Women with ovarian function received down-regulation using a luteinizing hormone-releasing hormone (LHRH) analogue before hormone replacement was commenced. A total of 52 transfer cycles was performed in each age group and pregnancy, delivery and miscarriage rates were analysed as outcome measures; 20 pregnancies were achieved in each group (an identical pregnancy rate of 38.5%). In group A seven pregnancies miscarried out of 20 (35%), which was not significantly different from the rate in the older population, group B, where eight out of 20 pregnancies miscarried (40%). The delivery rate in group A was 25% (13 out of 52), again not significantly different from the delivery rate in group B of 23.1% (12 out of 52). In conclusion, using egg donation as a model, the decline in fecundity with age cannot be explained by uterine factors alone.

Adult↗
PubMed1997

Effects of oestrogen and progesterone on age-related changes in arteries of postmenopausal women.

1. Hormone replacement therapy (HRT) with oestrogen or oestrogen plus progestin may have different effects on arterial structure and function. To examine this question, carotid artery intima-medial thickness (IMT) and indices of systemic and carotid arterial compliance were measured in groups of older men, postmenopausal women not on HRT (non-HRT) and those women on long-term HRT with oestrogen alone (HRT-E) or oestrogen plus progestin (HRT-EP). 2. Sixty men, 90 postmenopausal women taking HRT and 91 not taking HRT participated in the study. The groups were similar for age, body mass index, numbers of smokers, physical activity, alcohol intake and blood pressure. 3. Plasma total cholesterol was reduced and high-density lipoprotein-cholesterol was increased in the HRT group compared with the non-HRT group; low-density lipoprotein-cholesterol, triglyceride and lipoprotein (a) values were similar in these two groups. Results for HRT-E and HRT-EP subgroups were similar. 4. Carotid IMT was significantly reduced in the HRT group compared with men and non-HRT groups. Results for HRT-E and HRT-EP subgroups were similar. 5. Mean systemic arterial compliance (SAC) was significantly greater in men than in women and was related to age; SAC was higher in both HRT-E and HRT-EP groups compared with the non-HRT group. Indices of carotid stiffness were similar in men and in non-HRT groups. The HRT-EP group showed increased carotid stiffness compared with the HRT-E group. 6. There is an apparent protective effect of long-term oestrogen therapy on carotid IMT and age-related changes in arterial stiffness. Progestin does not alter the IMT effects but may adversely influence arterial stiffness.

Aged↗
PubMed1997

Buspirone vs amitriptyline in the treatment of chronic tension-type headache.

OBJECTIVES: The aim of this study was to explore the efficacy of buspirone (BSR), in comparison with amitriptyline (AML) in the prophylactic treatment of chronic tension-type headache (CTH), in an open and randomized clinical trial. MATERIAL AND METHODS: Twenty-six CTH patients (10 men and 16 women) were treated with BSR (30 mg daily) for 12 weeks. A parallel group of 32 CTH patients (12 men and 20 women) was treated with AML (50 mg daily). The major clinical parameters evaluated were the headache index (days with headache per month), the frequency of drug use for the acute management of headaches, the patients' opinion for the treatment and the Hamilton anxiety and depression rating scales. RESULTS: During the study 9 patients dropped out (4 from the BSR group and 5 from the AML group). Twelve (54.4%) patients from the BSR group responded to treatment (> 50% reduction in the headache index), compared to 17 (60.7%) from the AML group. In the BSR group, 14 (53.8%) patients reported various mild side effects (nausea most frequently), vs 21 (65.5%) of the AML group (mouth dryness more frequently). Patients treated with AML had better opinion and used less drugs for the acute treatment of headaches than the BSR treated patients. CONCLUSION: These results suggest that BSR may be effective in the prophylactic treatment of CTH, and that further investigation in a placebo controlled study is needed.

Adult↗
PubMed1997

Recovering optic neuritis during systemic cisplatin and carboplatin chemotherapy.

INTRODUCTION: We describe bilateral optic neuropathy in a patient affected by ovarian carcinoma treated with cis-platin 160 mg/m2 and carboplatin, 640 mg/m2. The patient was followed for 1 year, when recovery appeared. The few previous descriptions of CDDP optic nerve toxicity did not report recovery. METHODS: Computerized visual field, visual evoked potentials, pattern electroretinograms, full field flash electroretinograms were recorded during follow-up. RESULTS: Optic neuritis appeared 13 weeks after cis-platin discontinuation, with right eye central scotoma; 2 days later the patient became bilaterally blind. Visual evoked potentials were initially absent, reappeared, with delayed latencies to left eye stimuli at 6 months, in both eyes at 9 months. At 1 year delayed VEPs were recorded with right eye stimuli, normal VEPs were recorded for left eye. CONCLUSION: Cis-platin can induce delayed optic neuritis, that can recover in 1 year.

Antineoplastic Agents↗
PubMed1997

Antimalarial activity of the bisquinoline trans-N1,N2-bis (7-chloroquinolin-4-yl)cyclohexane-1,2-diamine: comparison of two stereoisomers and detailed evaluation of the S,S enantiomer, Ro 47-7737.

The S,S enantiomer of the bisquinoline trans-N1,N2-bis(7-chloroquinolin-4-yl)cyclohexane-1,2-diamine, Ro 47-7737, is significantly more potent against chloroquine-resistant Plasmodium falciparum than the R,R enantiomer and the previously described racemate. Both the enantiomers and the racemate are more potent inhibitors of heme polymerization than chloroquine, and their activities are probably mediated by inhibition of this parasite-specific process. The S,S enantiomer, Ro 47-7737, was studied in more detail and proved to be a potent antimalarial in the treatment of P. vivax ex vivo and P. berghei in vivo. Its suppression of P. berghei growth in a mouse model (50% effective dose, 2.3 mg/kg of body weight) was equal to that of chloroquine and mefloquine, and Ro 47-7737 was found to be more potent than these two drugs in the Rane test, in which the curative effect of a single dose is monitored. The dose at which 50% of animals were permanently cured (34 mg/kg) was markedly superior to those of chloroquine (285 mg/kg) and mefloquine (> 250 mg/kg). When administered orally at 50 mg/kg, Ro 47-7737 also showed a faster clearance of parasites than either chloroquine or mefloquine, and unlike the other two compounds, Ro 47-7737 showed no recrudescence. In a study to compare prophylactic efficacies of oral doses of 50 mg/kg, Ro 47-7737 provided protection for 14 days compared to 3 days for mefloquine and 1 day for chloroquine. The good curative and prophylactic properties of the compound can be explained in part by its long terminal half-life. The ability to generate parasite resistance to Ro 47-7737 was also assessed. With a rodent model, resistance could be generated over eight passages. This rate of resistance generation is comparable to that of mefloquine, which has proved to be an effective antimalarial for many years. Toxicity liabilities, however, ruled out this compound as a candidate for drug development.

Animals↗
PubMed1997

Event related potentials recorded in patients with locked-in syndrome.

OBJECTIVE: To determine the possibility of recording "cognitive" event related potentials (ERPs) in locked-in patients and therefore to determine whether ERPs can have a role in differential diagnosis of coma. METHODS: ERPs to classic auditory or visual "odd ball paradigms" were recorded three to four days, seven to eight days, and 30 to 60 days after admission to the intensive care unit, in four patients affected by basilar artery thromboembolism resulting in locked-in syndrome. Two patients (one 32 year old man, one 31 year old woman) could move the eyes laterally and vertically spontaneously and on command. One patient (a 39 year old man) had a "one and half syndrome", one patient (a 40 year old woman) could only elevate the left eyelid and eye. Results were compared with data from 30 age matched controls. In the last recording session a letter recognition paradigm was applied, in which ERPs were produced by the identification of letters forming a word. Results were compared with five age matched controls. Brainstem lesions extending to the pontomesencephalic junction were found on MRI and CT. RESULTS: ERPs to the oddball paradigms were recorded in three patients in the first recording session, in all patients in the second recording session. Latency, amplitude, and topographic distribution of ERP components were inside normal limits. With the letter recognition paradigm the patients could emit a P3 component to correspond with target letters, with the same margin of error as controls. CONCLUSION: It is possible to record ERPs in patients with locked-in syndrome shortly after the acute ischaemic lesion, and therefore to assess objectively cognitive activities. Furthermore the letter recognition paradigm could be implemented to facilitate linguistic communication with patients with locked-in syndrome.

Adult↗
PubMed1997

The duration of estradiol and progesterone exposure prior to progesterone withdrawal regulates oxytocin mRNA levels in the paraventricular nucleus of the rat.

The nonapeptide oxytocin (OT) is important for milk ejection during lactation, uterine contractility at parturition, and the onset of maternal behavior. Sequential exposure to estradiol (E2) and progesterone (P) followed by P withdrawal increases OT mRNA in the paraventricular nucleus (PVN), and to a lesser degree the supraoptic nucleus (SON), of the rat 48 hours after the P is removed. Although increases in PVN OT mRNA are not accompanied by changes in posterior pituitary OT peptide content, the PVN contains OT neurons that project to both the posterior pituitary (magnocellular group) and extra pituitary sites (parvocellular groups). Steroid-induced increases in OT mRNA occur in both the magnocellular and the parvocellular regions of the PVN. The latter are believed to contribute to CNS release of OT which may be important for certain behaviors including the onset of maternal behavior. The same steroid sequence that increases PVN OT mRNA also induces maternal behavior in virgin ovariectomized rats. Exposure of animals to E2 and P for 2 weeks resulted in the shortest latency to the onset of maternal behavior in ovariectomized rats, whereas exposure for 6 days was associated with a longer latency. In this study we questioned if the duration of E2 and P exposure prior to P withdrawal is an important regulator of PVN OT mRNA levels. We compared OT mRNA levels in the PVN of virgin ovariectomized rats administered no steroid or sequential E2 and P for 2 weeks versus 6 days. On day 1 animals received steroid-filled or empty capsules followed by P-filled or empty capsules on day 3. In one steroid-treated group, E2 and P were continued for 6 days and in the other group for 14 days prior to P removal. Animals were sacrificed 48 hours after P removal. Levels of OT mRNA were compared among 6 day and 2 week steroid-treated animals and sham-treated animals. The relative abundance of OT mRNA was significantly increased, P < 0.05, in animals receiving the 2-week, but not the 6-day, steroid treatment compared to sham-treated animals. Pituitary OT peptide content was not significantly different among the three groups. We conclude that the duration of steroid exposure may be an important regulator of the level of OT mRNA in the PVN of the rat.

Animals↗
PubMed1997

Subspecialist referrals in an academic, pediatric setting: rationale, rates, and compliance.

Appropriate referrals reduce healthcare costs and enhance patient satisfaction. We evaluated the subspecialty referral pattern of a managed care general pediatric office over a 4-month period. Three-hundred-forty-six referrals (267 meeting inclusion criteria) to 24 subspecialties were generated during 4,219 office visits, with five subspecialties receiving 59% of the referrals. The main objective of each referral was management (100), diagnostic assistance (75), special procedure (63), or a combination (29). Patients kept less than half of the referral appointments, with the highest (80%) and lowest (28%) compliance rates observed in cardiology and ophthalmology, respectively. Appointments made within four weeks of the referral were more likely to be kept than those with greater lag time (P = 0.001). The subspecialists prepared written, post-consultation responses to the referring physician in 73% of cases. Presumptive and post-consultation diagnoses were congruent in 78% of those cases in which both diagnoses were noted. Overall, the managed care format enabled our practice to track referral outcomes. The subspecialists' written responses also allowed for an educational exchange between physicians. Compliance with referral appointments is a substantial problem that needs to be addressed.

Academic Medical Centers↗
PubMed1997

Cholelithiasis in early infancy.

This report describes three children, age range 7 weeks to 5 months, who presented with obstructive jaundice secondary to gallstones. Previous Escherichia coli septicaemia and frusemide therapy were predisposing risk factors in two of the patients. All three were successfully treated with cholecystectomy and exploration of the common bile duct.

Ampulla of Vater↗
PubMed1996

Differential regulation of oxytocin and vasopressin messenger ribonucleic acid levels by gonadal steroids in postpartum rats.

We previously reported that sequential estradiol and progesterone exposure followed by progesterone withdrawal increases oxytocin (OT), but not arginine vasopressin (AVP), messenger ribonucleic acid (mRNA) in the hypothalamic paraventricular nucleus (PVN) of the rat. Substitution of testosterone for progesterone and subsequent testosterone withdrawal in the estrogen-primed rat increases PVN AVP mRNA levels. At the end of pregnancy (day 21), rats are exposed to high estrogen and declining progesterone and testosterone concentrations. Coincident with these changes in circulating gonadal steroid hormones in OT and AVP mRNAs. If progesterone levels are sustained at term, OT levels are attenuated and if testosterone is sustained, AVP mRNA levels are attenuated. Immediately postpartum, however, OT and AVP mRNA levels decline compared to term levels. To further determine the role of estrogen in the regulation of OT and AVP mRNAs, we performed two experiments. In the first experiment, we administered estrogen during the peripartum period to determine if estrogen supplementation prevents the relative attenuation of OT and AVP mRNAs that is seen after parturition. Day 18 pregnant rats were given estradiol-filled or empty capsules and sacrificed on day 2 lactation. By Northern analysis, significant differences in PVN AVP, but not OT, mRNA were found between the estrogen- and sham-treated lactational animals, P < 0.02. In the second experiment, we determined if sustaining estrogen after progesterone is removed in steroid-treated ovariectomized rats is essential for the increase in OT mRNA. Ovariectomized rats were given either empty capsules or sequential estradiol- and progesterone-filled capsules and both were sustained for 12 days. When progesterone-filled capsules were removed, estradiol-filled capsules were either removed or left in place, and the animals were sacrificed 48 h later. PVN OT mRNA was analyzed by Northern blot hybridization. OT mRNA was increased in both of the steroid-treated groups to the same degree, compared to sham-treated animals, P = 0.04. In summary, estrogen supplementation during early lactation prevents the attenuation of PVN AVP, but not OT, mRNA after parturition. In the estrogen-primed ovariectomized rat, it is not necessary to sustain estrogen to see the effects of progesterone withdrawal upon PVN OT mRNA.

Animals↗
PubMed1996

Analysis of the low-frequency normal modes of the R state of aspartate transcarbamylase and a comparison with the T state modes.

Aspartate transcarbamylase (ATCase) is a classic example of an allosteric enzyme. It catalyzes the conversion of aspartate to carbamyl aspartate, which is the first substrate in the biosynthesis of pyrimidines. Although ATCase is well characterized, both structurally and biochemically, little is known at the atomic level about the large amplitude motions that govern its T-->R quaternary transition. We present the results of calculations of the very-low-frequency normal modes of the CTP-ligated R state ATCase, and we compare them with the equivalent modes in the CTP-ligated T state ATCase. The large-amplitude, delocalized modes of frequencies below 4 cm-1 contribute a large fraction of the atomic fluctuations observed experimentally. They show some ability to drive the R-state structure towards the T-state structure, by promoting some of the quaternary structure rearrangements that take place during the allosteric process. Their potential role in the T-->R transition is quantified and compared with the role of the low-frequency modes of the T state in the quaternary rearrangement.

Allosteric Regulation↗
PubMed1996

Analysis of the low frequency normal modes of the T-state of aspartate transcarbamylase.

Aspartate transcarbamylase (ATCase) is an important control enzyme in the pyrimidine biosynthetic pathway in Escherichia coli. It is a classic example of an allosteric protein and has been extensively studied biochemically, kinetically and structurally. As yet, however, a detailed model for the cooperative transition between the tensed (T) and relaxed (R) forms of the protein does not exist. In this work we have calculated the low frequency normal modes of the CTP-ligated T-state of ATCase with the aim of identifying some of the motions that could be important in initiating the transition. The calculated modes, of frequencies lower than 5 per cm, produce root-mean-square coordinate deviations for the atoms which are a substantial fraction of those derived from the crystallographic B-factors. Some of the modes result in displacements which change the quaternary structure of the protein (in particular the elongation of the protein and the relative rotation of the subunits) in such a way that the R-state structure is approached. The implication of these mode motions for the overall T-->R transition process is discussed.

Allosteric Site↗
PubMed1996

A novel Plasmodium falciparum sporozoite and liver stage antigen (SALSA) defines major B, T helper, and CTL epitopes.

In the search for subunit vaccines that are able to induce the type of sterile, protective immunity achieved by irradiated sporozoites, there is increasing evidence that defense mechanisms directed at the intrahepatic stage and Ags expressed at this stage are critical. We have initiated a systematic search for such molecules and report here the identification and partial characterization of a novel Plasmodium falciparum gene encoding a 70-kDa protein, expressed in both sporozoite and liver stages (SALSA), with a vaccine potential that stems from its antigenic features. Antigenicity and immunogenicity studies were conducted in individuals exposed to malaria, in immunized mice, and in chimpanzees, using a recombinant protein and two synthetic peptides. Results show that the SALSA nonrepetitive sequence defines 1) major B cell epitopes, as shown by a high prevalence of Abs to each peptide in three African areas differing in their level of endemicity; 2) Th epitopes, as demonstrated by lymphoproliferation and IFN-gamma secretion in cells from the individuals from one of the low transmission areas, as well as helper effect upon Ab secretion in mice; and 3) epitopes for cytolytic lymphocytes, demonstrated in immunized and sporozoite-challenged chimpanzees, and associated with MHC class I leukocyte Ags. The latter are of particular importance, because this is the only part of the malaria life cycle in which the parasite is located in a cell expressing class I Ags and because CD8+ lymphocytes were found to be responsible for protection in experimental models.

Adolescent↗
PubMed1996

Effect of nerve growth factor on the expression of cell cycle regulatory proteins in PC12 cells: dissection of the neurotrophic response from the anti-mitogenic response.

PC12 cells treated with nerve growth factor (NGF) undergo a G1 block and differentiate. Expression of selected cell cycle regulatory proteins was studied under culture conditions which permit observation of a differentiation response independently from a mitogenic or anti-mitogenic response. The expression of all cell cycle regulatory proteins studied is modulated by NGF addition to exponentially-growing cultures in the presence of serum. While levels of most of these proteins decrease, accumulation of cyclin D1 and the cyclin-dependent kinase inhibitor p21 Cip1/WAF1 is observed. Cyclin D1 associated kinase activity is inhibited, correlating with an increase in p21 protein. PC12 cells, synchronized by serum starvation, undergo morphological and functional differentiation in the presence of NGF. Neither cyclin D1 nor p21 are present in such cultures, nor is their expression upregulated by NGF, indicating that they are not required for this process. Removal of serum from differentiated PC12 cells results in loss of these proteins, but has no effect on differentiation or the nonproliferative state in presence of NGF. Together, the results indicate that cyclin D1 and p21 are not necessary for differentiation per se, nor are they required for maintenance of the differentiated state in the absence of serum.

Animals↗
PubMed1996

Drug-induced apoptosis in B-cell chronic lymphocytic leukemia: relationship between p53 gene mutation and bcl-2/bax proteins in drug resistance.

We investigated the relationship among chemosensitivity to drug-induced apoptosis in vitro, the presence of p53 gene mutations, and the expression of bcl-2 and bax proteins in B-cells from B-cell chronic lymphocytic leukemia (B-CLL) patients. Apoptosis was induced with a camptothecin analogue, 9-amino-20(s)-camptothecin, or a purine analogue, fludarabine. Cell death was monitored by propidium iodide staining and FACS analysis. Drug-induced apoptosis in B-CLL cells was p53-independent. Immunoblot analysis of bcl-2 and bax expression revealed a correlation between drug-induced apoptosis and the ratio of endogenous levels of bcl-2 to bax proteins. B-CLL cells with none to low bcl-2/bax ratios were drug-sensitive as compared to cells with intermediate to high ratios that were drug-resistant (P = 0.015). Prior to drug treatment, bax protein migrated as a single species of 21 kDa. Following drug-induced apoptosis, anti-bax specific protein complexes of 36-42 kDa were up-regulated. Using two-dimensional gel electrophoresis, bax complexes were disrupted under reducing conditions to reveal homo- and heterodimers of 18 and 21 kDa suggesting that disulfide interactions were required for complex formation. The de novo appearance of the 18 kDa anti-bax specific protein together with its increased expression in drug-sensitive B-CLL B-cells undergoing cell death suggests a role for this protein in the regulation of apoptosis.

Apoptosis↗
PubMed1996

Nerve growth factor-induced accumulation of PC12 cells expressing cyclin D1: evidence for a G1 phase block.

The anti-proliferative effect of nerve growth factor (NGF) on the rat pheochromocytoma cell line PC12 has been previously shown to be accompanied by the accumulation of cells in either the G1 phase with a 2c DNA content, or with a 4c DNA content characteristic for G2/M, as evidenced by flow cytometric analysis of DNA distribution using propidium iodide. Herein, these apparently conflicting results are clarified. The present studies indicate that a simple DNA distribution profile obtained by this technique can confound interpretation of the biological effects of NGF on cell-cycle distribution due to the presence of tetraploid cells. Using cyclin D1 and incorporation of bromodeoxyuridine as markers of respectively, G1 and S phase, we show that PC12 cultures can have a considerable amount of tetraploid cells which, when in the G1 phase, have a 4c DNA content and express cyclin D1. During exposure to NGF, this population increases, reflecting the accumulation of cells in the G1 phase of the cell cycle. The data presented, support the possibility that events affecting the expression or action of G1 regulatory proteins may be involved in the molecular mechanism of the anti-mitogenic effect of NGF.

Adrenal Gland Neoplasms↗