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Biomedical subjects

N Thomas

Publications and source records attributed to N Thomas.

At least 127 records · Page 7Linked to original sources
PubMed1994

[Triplet and quadruplet pregnancy: management and perinatal outcome].

The frequency of multiple pregnancies with more than two fetuses has increased considerably since the introduction of methods of ovulation induction, in vitro fertilization, and embryo transfer. We have analyzed the evolution, complications, delivery and perinatal outcome of 23 triplet and 3 quadruplet pregnancies occurred during a four-year period in one medical center. The most frequent complication was preterm labor (62%). The mean gestational age at delivery was 32.5 weeks for the quadruplets and 31.5 weeks for the triplets and the mean birth weight was 1461 and 1526 for quadruplets and triplets, respectively. Perinatal mortality for the whole group was 148/1000.

Embryo Transfer↗
PubMed1993

Chemical modification of rat liver cytosolic NADP(+)-linked isocitrate dehydrogenase by N-ethylmaleimide. Evidence for essential sulphydryl groups.

Incubation of rat liver cytosolic isocitrate dehydrogenase with N-ethylmaleimide (NEM) resulted in the inactivation of the enzyme following pseudo-first order kinetics. Isocitrate affords considerable protection against inactivation whereas NADP+ enhances modification of the enzyme, suggesting localization of the modified group at the active site. Correlation of loss of activity with incorporation of [14C]NEM indicated that two sulphydryl residues/sub-unit are modified of which only one is shown to be involved in catalysis. pH dependence of the inactivation process implicates a reactive group of pKa 8.1 in catalysis. We conclude that a unique cysteine residue is essential for maximal catalytic activity of isocitrate dehydrogenase.

Animals↗
PubMed1993

Cell surface binding of colloidal iron and Limax flavus agglutinin compared by X-ray microanalysis.

The surface characteristics of tumour cells and T-cell hybridoma variants were examined by quantitative X-ray microanalysis using metal-based probes. Comparisons of populations of cells differing in invasive potential revealed differences in the binding of positive colloidal iron hydroxide, a general probe for anionic sites. Substantial differences between populations were also detected by the binding of Limax flavus agglutinin, which was used in conjunction with fetuin-gold as a specific marker for sialic acid.

Animals↗
PubMed1993

Cocaine facilitation of cryptosporidiosis by murine AIDS in male and female C57/BL/6 mice.

As cocaine may affect progression of the Human Immunodeficiency Virus (HIV) infection to Acquired Immune Deficiency Syndrome (AIDS), we used a murine model of AIDS (MAIDS) induced by LP-BM5 murine leukemia virus to examine cocaine's possible role as a cofactor for secondary parasitic infections. Dissimilarities between the sexes were observed both in the absence and presence of the cocaine. The retrovirus-infected female mice had a much higher rate of Cryptosporidiosis than the retrovirus-infected male mice. Female, but not male, retrovirus-infected mice showed approximately 20-fold more Cryptosporidium per villus section than controls. Compared to respective gender controls, male and female animals infected with the retrovirus infection manifested a heightened Cryptosporidium oocysts count regardless of cocaine treatment. Overall, female groups incurred a higher incidence of infection compared to respective male groups. To determine the role of cocaine, groups of male and female C57BL-6 mice of similar age were treated with cocaine for 4 weeks followed by termination. Cocaine synergized with retrovirus infection in female mice to cause a 30-fold increase in the number of oocyst present. The spleen size and weight of female mice was significantly greater than uninfected controls or male mice. However, due to the very slow progression to murine AIDS in the males, parasite resistance was retained, including in cocaine treated C57BL-6 mice. Thymus cell number in the retrovirus-infected female mice decreased significantly in comparison to uninfected female controls. Continued resistance to the parasite in male mice and its loss in female mice was due to the rate of immunosuppression and thus development of retrovirus-induced murine AIDS.

Animals↗
PubMed1993

Estimation of gold-labelled macromolecules attached to cell surfaces.

A method for obtaining a semi-quantitative estimation of the amount of colloidal gold label attached to a cell surface is described. The X-ray emission, in a scanning electron microscope, from an even metal coating applied by diode sputter coating is used as an internal standard. The emission from the standard is used to correct for errors which would have arisen due to factors such as variable specimen surface topography. Examples of the semi-quantitative estimation of 10-nm gold-labelled wheat-germ agglutinin to L929 murine fibroblast cells are given.

Animals↗
PubMed1993

Correlation of ultrasound assessment of endometrial growth and plasma steroid concentrations during superovulation for in vitro fertilization.

Endometrial and follicular development were investigated by ultrasound in 25 normally cycling women who received clomiphene citrate and human menopausal gonadotrophin to induce multiple follicular development for in vitro fertilization. Ultrasonic determination of endometrial thickness and reflectivity grading and follicular number were correlated with daily concentrations of estradiol (E2) and progesterone (p) in peripheral serum. Serum E2 showed a better positive correlation with endometrial thickness than with total number of developing follicles. There was a significant inverse correlation between endometrial thickness and plasma p concentration. The E2 value per follicle and E2/p ratio were both weakly correlated respectively with endometrial thickness. These data indicate that ultrasound determination of endometrial thickness is a useful ultrasonic parameter for monitoring ovarian function for in vitro fertilization. However, endometrial thickness should always be combined with total number of developing follicles, in order to reach decisions concerning timing of oocyte recovery.

Adult↗
PubMed1993

Renal handling of calcium in hypercalciuric calcium oxalate nephrolithiasis.

In order to gain further insight into the mechanisms of calcium (Ca) homeostasis in hypercalciuria, we studied 32 lithiasic patients who were divided into three groups: normocalciuric patients (NC; n = 11), patients with absorptive hypercalciuria (AH; n = 12) and patients with renal hypercalciuria (RH; n = 9). The patients were investigated on 3 occasions: during a random diet, after a Ca-restricted diet and during a Ca tolerance test. The following determinations were made: Ca intake, Ca tubular reabsorption (Ca TR), plasma 1,25-dihydroxyvitamin D [1,25(OH)2D] and parathyroid hormone (PTH) levels, natriuresis and urinary protein-bound Gla. The latter was measured as a marker of urinary nephrocalcin excretion. Ca TR was decreased in hypercalciuric patients (HC). AH but not RH patients normalized their Ca TR during fasting. Plasma PTH and 1,25(OH)2D levels were similar in all the groups on the 3 occasions. Natriuresis was elevated in RH during the fasting period (p < 0.02 vs. AH). Compared with NC, protein-bound Gla urinary excretion rates (UER) were enhanced in AH after the Ca-restricted period (p < 0.02) and in RH during fasting (p < 0.02). In AH, a strong positive correlation was found between Ca TR and protein-bound Gla UER (r = 0.79, p = 0.002) following a Ca-restricted diet. In the HC group as a whole, fasting protein-bound Gla UER were correlated to plasma 1,25(OH)2D levels (r = 0.68, p < 0.001). In conclusion, the results suggest that PTH directly or indirectly through 1,25(OH)2D increases nephrocalcin synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1993

Satisfaction and dissatisfaction in institutional practice: results from a survey of U.S. military physicians.

Because of recent concerns about the professional satisfaction of physicians in general and of military physicians in particular, the authors surveyed a national sample of 1,392 military physicians; 88% responded. Two-thirds of physicians were at least somewhat satisfied with the professional abilities of their peers and with the quality of care they were able to provide, but only 19% were satisfied with salary and 27% with practice efficiency. Characteristics of physicians that were independently related to overall satisfaction included age, recruitment pathway, workload, specialty, and perceived availability of key resources. Indicator variables for the individual medical facilities were also significantly related to global satisfaction, suggesting a separate "hospital effect" that bears additional investigation. Efforts to improve satisfaction may enhance recruitment and retention of military physicians.

Adult↗
PubMed1992

Physical fine mapping of genes underlying X-linked deafness and non fra (X)-X-linked mental retardation at Xq21.

Linkage studies and cytogenetically visible deletions associated with nonspecific X-linked mental retardation (XLMR) and a specific form of deafness (DFN3) have indicated that the genes responsible for these disorders are located at Xq21. Using DNA probes from this region, we have studied several overlapping deletions spanning different parts of Xq21. This has enabled us to assign the DFN3 gene and a gene for nonspecific XLMR to an interval that encompasses the locus DXS232 and that is flanked by DXS26 and DXS121.

Adolescent↗
PubMed1991

Optical diffraction by well-ordered muscle fibres.

We have studied the diffraction of a focussed laser beam by single fibres of glycerinated rabbit psoas muscle as a function of the angle of incidence. Diffraction efficiencies as high as 34% were observed at the first-order Bragg angle, indicative of well-ordered striated fibres with a strong periodic modulation of the refractive index. A theory is presented to account for our observations based upon the coupled-wave model developed by Kogelnik (1967) and Magnusson and Gaylord (1977) for the description of thick phase gratings in holography. We have solved the coupled-wave equations on a computer using a realistic index modulation taken from the measurements of Huxley and Hanson (1957). Comparison of theory with experiment shows that coupled-wave effects are indeed present in well-ordered muscle fibres, and the observed diffraction efficiency is in quite good agreement with what would be expected theoretically. Most importantly, the computer model allows us to calculate the diffraction efficiency for curved striations, which are observed for real muscle fibres under a microscope. The sensitivity of the diffraction efficiency to curvature of the striations may have implications for the interpretation of other optical experiments on muscle. We also consider the effects on our measurements of the focussing lens and refraction by the cylindrical fibre.

Animals↗
PubMed1991

Subcellular localization of celiptium-induced peroxidative damage in rat renal cortex.

Celiptium (N2-methyl-9-hydroxyellipticinium) is an antitumor agent of the ellipticine series. We have shown a dose-dependent nephrotoxicity in rats and demonstrated a lipid overload in proximal tubular cells (unsaturated free fatty acid accumulation). We have also shown an increase in thiobarbituric acid reactive substances (TBARS), namely the 4-hydroxyalkenals, that is paralleled by a decrease in phosphatidylethanolamine in rat kidney cortex. In the present study, peroxidative damage was localized in mitochondria, microsomal and brush-border membranes of kidney cortex. Female Wistar rats were injected with a single i.v. dose of 20 mg/kg celiptium and sacrificed on day 8. Subcellular fractionation studies showed that celiptium induced alterations: 1) in mitochondria (slight increase in aldehydes), 2) in microsomal membranes (increase in free fatty acids (FFA) with in particular rises in oleic (18:1) and linoleic (18:2) acids), 3) in brush-border membranes or BBM (decrease in protein and phospholipid contents); residual membranes showed an increase in oleic and linoleic acids and a decrease in the polyunsaturated fatty acids, arachidonic (20:4) and docosahexaenoic (22:6) acids, 4) in cytosol (increase in FFA and TBARS content). Thus, celiptium induces peroxidative damage in kidneys through lipid abnormalities which predominantly occur in brush-border membranes and consist of an increase in free fatty acids and aldehydes in cytosol.

Animals↗
PubMed1991

Accuracy of colour Doppler ultrasound velocity measurements in small vessels.

Colour Doppler ultrasound offers the possibility of imaging small vessels not visible by B-mode alone. The colour Doppler image of velocities allows the course of small vessels to be imaged in the X-Y plane of the scan provided the Doppler frequency shift is of sufficient magnitude. This permits alignments of the Doppler cursor, allowing angle correction to provide true velocity measurements from the Doppler shift obtained. Before attempting to make velocity measurements, however, it is essential to be aware of the possible error in the Z plane caused by the thickness of the Doppler sample volume. To quantify this source of error, hydrophone and flow-rig measurements were performed on an Acuson 128 colour Doppler scanner with both 5 MHz linear-array and 3.5 MHz phased-array transducers. Measurements of the transmitted pulses using a point hydrophone showed that both probes employ approximately 3.5 MHz Doppler pulses (in both colour and pulsed Doppler modes). The two transducers have the same axial resolution. In colour Doppler mode the axial length of the sample volume increases automatically with depth by up to 0.5 mm. Measurements of colour and pulsed Doppler signal strength were obtained in a controlled flow rig. Both transducers produced accurate colour flow images of the phantom at their optimum depths; flow velocity errors due to Z-plane thickness are less than 5%. There was, however, substantial error outside these optimum conditions (up to 20%).

Arteries↗
PubMed1991

Efficacy of an oximate-based skin decontaminant against organophosphate nerve agents determined in vivo and in vitro.

Recent Canadian research efforts have been directed towards the development of a reactive skin decontaminant (RSD) lotion active against classical nerve agents and mustard. The formulation presently under study consists of a 1.25 molal solution of potassium 2,3-butanedione monoximate (KBDO) in polyethylene glycol methylether 550. Although this formulation has shown good efficacy, concern has been expressed as to the potential toxicity of the reaction products of KBDO and organophosphate (OP) nerve agents. This report details the high efficacy of this lotion in inactivating OPs as measured by the systemic toxicity of the OP/RSD mixtures in rats. In addition, primary cultures of chick embryo neurons were also used to test the efficacy of the RSD. By relating the anticholinesterase activity in these cultures of the OP/RSD mixture to that of pure OP standards, a sensitive measure of the value of the RSD in inactivating tabun, sarin, soman and VX was obtained. Experiments with all four nerve agents in this in vitro system provided a good correlation with the in vivo data, and also indicated that the inactivation process was time- and agent-dependent and also related to the ratio of OP to RSD.

Acetylcholinesterase↗
PubMed1991

In vitro testing of a potentially biocompatible continuous ambulatory peritoneal dialysis fluid.

In the present study a newly formulated dialysis solution (HDF) was tested for its effects on phagocyte viability and function as well as its ability to support bacterial growth. This solution differs from standard CAPD solution (NPD) by the inclusion of histidine to buffer the fluid to pH 6.7. Low-dextrose HDF (1.36% w/v dextrose) did not significantly decrease the viability or inhibit any of the PMN functional parameters measured (phagocytosis, LTB4 release or respiratory burst activation) when compared to control buffer. NPD (1.36% w/v dextrose) at low pH as well as all high-dextrose dialysis solutions (NPD and HDF) significantly inhibited most PMN functions independently of reduced viability. Peritoneal mesothelial cell viability was unaffected by either low- or high-dextrose HDF but was significantly reduced by NPD (1.36 and 3.86% dextrose) at pH 5.2. The inhibitory effects of low dextrose dialysis solutions were confirmed as being partly related to their low initial pH. High-dextrose dialysis fluids, however, inhibit PMN function by a mechanism which, in addition to initial pH, appears to be directly related to their dextrose content but not their osmolality.

Bacteria↗
PubMed1991

Time course study of lipid peroxidation induced by N2-methyl-9-hydroxyellipticinium acetate or celiptium in rat renal cortex.

Celiptium is an ellipticine derivative with renal toxic side effects. It has recently been characterized as a lipid overload in proximal tubular cells where loss of total phospholipids (in particular phosphatidylethanolamine) and of polyunsaturated fatty acids are linked to the accumulation of unsaturated free fatty acids and aldehydes. A time course study of celiptium-induced peroxidative damage showed that a single dose of 40 mg/kg of celiptium induced no change in total or individual phospholipids of rat renal cortex. On the other hand, free fatty acids and thiobarbituric acid reactive substances increased as early as 1 hr after celiptium injection. 4-Hydroxynonenal (4-HNE) also increased whereas polyunsaturated fatty acids levels decreased at 6 and 24 hr. After 24 hr no change was detected in microsomal phospholipids. In contrast, the brush-border membranes showed alterations such as decrease in total phospholipids and polyunsaturated fatty acids levels accompanied by increase in aldehydes. It appears that peroxidative damage occurs in brush-border membranes of celiptium-treated rat kidneys with preferential losses of phosphatidylethanolamine (PE, 30%) and phosphatidylcholine (PC, 14%).

Animals↗
PubMed1991

Mineralization of linear alkylbenzene sulfonate by a four-member aerobic bacterial consortium.

A bacterial consortium capable of linear alkylbenzene sulfonate (LAS) mineralization under aerobic conditions was isolated from a chemostat inoculated with activated sludge. The consortium, designated KJB, consisted of four members, all of which were gram-negative, rod-shaped bacteria that grew in pairs and short chains. Three isolates had biochemical properties characteristic of Pseudomonas spp.; the fourth showed characteristics of the Aeromonas spp. Cell suspensions were grown together in minimal medium with [C]LAS as the only carbon source. After 13 days of incubation, more than 25% of the [C]LAS was mineralized to CO(2) by the consortium. Pure bacterial cultures and combinations lacking any one member of the KJB bacterial consortium did not mineralize LAS. Three isolates carried out primary biodegradation of the surfactant, and one did not. This study shows that the four bacteria complemented each other and synergistically mineralized LAS, indicating catabolic cooperation among the four consortium members.

Journal Article↗
PubMed1991

Nephrotoxicity of an ellipticine derivative (N2-methyl-9-hydroxyellipticinium acetate) in rat: a defect of urinary concentrating ability.

The antitumor drug celiptium (N2-methyl-9-hydroxyellipticinium) is an ellipticine derivative effective in experimental tumors and in man. The major side effect is nephrotoxicity. The impairment of renal function is studied in rats following a single i.v. dose of 20 mg/kg celiptium and a long-term study (day 2 to day 60). A loss of body weight is noted in celiptium-treated animals between day 4 and day 15, and recovery occurs between day 15 and day 60. Histologic study shows cortical lesions characterized by focal necrosis of proximal tubules without any glomerular, interstitial, and vascular alterations on day 8. It is to be noted that any medullary lesions were not shown. A polyuria and a decreased creatinine clearance are reported on day 8. We were interested in a special study of this polyuria. For this study, rats were water deprived between day 6 and day 8 following celiptium administration. The decrease of urinary osmolality is not recovered after dehydration and exogenous vasopressin derivative (dD AVP) does not correct the renal concentration defect. AVP plasma levels increase after dehydration. These results suggest a pitressino-resistant urinary concentrating inability in celiptium-treated rats.

Acute Kidney Injury↗