Search PubMed⌕ Search

Biomedical subjects

M L Thomas

Publications and source records attributed to M L Thomas.

At least 127 records · Page 7Linked to original sources
PubMed1991

The distribution of recurrent varicose veins: a phlebographic study.

One hundred consecutive legs in 74 patients presenting with recurrent varicose veins were investigated by varicography. Forty recurrences occurred at the groin, 80 in the thigh and 97 in the calf. Within each group different anatomical variations were encountered, and we describe the frequency of these and of certain commonly observed combinations. We also suggest possible causes, and discuss how the results of varicography may assist in surgical management.

Adult↗
PubMed1991

Novel plasmid combinations in Haemophilus ducreyi isolates from Thailand.

Thirty isolates of Haemophilus ducreyi collected in Thailand in 1984 were characterized by plasmid content. Three novel plasmids with estimated molecular masses of 1.8, 2.6, and 2.8 MDa were observed in 29 isolates, in addition to the 3.2-, 5.7-, and 7.0-MDa beta-lactamase and 4.4-MDa sulfonamide resistance plasmids. At least three of the seven plasmids were observed in each of the 29 isolates. The number and diversity of plasmids observed in these isolates of H. ducreyi distinguish them from strains previously described.

Chancroid↗
PubMed1991

CD8+ T-cell clones deficient in the expression of the CD45 protein tyrosine phosphatase have impaired responses to T-cell receptor stimuli.

CD45 is a high-molecular-weight transmembrane protein tyrosine phosphatase expressed only by nucleated cells of hematopoietic origin. To examine function, mouse CD8+ cytolytic T-cell clones were derived that had a specific defect in the expression of CD45. Northern (RNA) blot analysis indicates that the CD45 deficiency is due to either a transcriptional defect or mRNA instability. The CD45-deficient cells were greatly diminished in their ability to respond to antigen. All functional parameters of T-cell receptor signalling analyzed (cytolysis of targets, proliferation, and cytokine production) were markedly diminished. A CD45+ revertant was isolated, and the ability to respond to antigen was restored. These results support a central and immediate role for this transmembrane protein tyrosine phosphatase in T-cell receptor signalling.

Animals↗
PubMed1991

Calcium uptake by duodenal epithelial cells is increased during lactation.

It is known that duodenal absorption of calcium is increased during lactation, and, more specifically, it has been shown that duodenal active transport of calcium is increased. The energy-requiring step for this active transport process is thought to occur at the basolateral membrane of the duodenal epithelial cells, where calcium is pumped from the cell into the extracellular fluid. The present experiments were carried out to determine whether calcium uptake into duodenal epithelial cells is also altered during lactation. Uptake of 45Ca into isolated duodenal epithelial cells from lactating animals showed markedly enhanced calcium uptake when compared with cells from control animals. Uptake was calcium concentration dependent for both groups. Since duodenal epithelial cells are known to contain increased calbindin9k, a calcium-binding protein, during lactation, calcium uptake was also measured in cells that were preincubated in medium containing calcium. In these experiments, the total 45Ca uptake was reduced, but the difference between lactating and control remained. These experiments show that the uptake of calcium into duodenal epithelial cells is among the components of the transcellular calcium transport process which is enhanced during lactation.

Animals↗
PubMed1990

Tyrosine phosphatase CD45 is essential for coupling T-cell antigen receptor to the phosphatidyl inositol pathway.

Stimulation of T lymphocytes through their antigen receptor (T-cell receptor; TCR) results in the activation of a tyrosine kinase and the generation of phosphatidyl inositol (PtdIns)-derived second messengers. Several reports have indicated that CD45, a haematopoietic cell-specific surface glycoprotein with tyrosine phosphatase activity in its cytoplasmic domain, is important in lymphocyte activation. To examine the possibility that CD45 might influence proximal signal transduction events through the TCR, we have isolated a variant of the human T-cell leukaemic line, HPB-ALL, which fails to express this phosphatase. Unlike cells expressing CD45, stimulation of the TCR in the CD45-negative cell does not result in PtdIns-derived second messengers. Reconstitution of CD45 expression restored early signalling events through the TCR. To localize the site of CD45 action, the human muscarinic type 1 receptor, which also activates the PtdIns second messenger pathway, was transfected into the CD45-negative cell. Although stimulation of the TCR failed to generate PtdIns-derived second messengers, there was normal activity of the PtdIns pathway when human muscarinic receptor type 1 was stimulated, despite the absence of CD45. These data indicate that CD45 influences a cellular component that is essential for effective coupling of the TCR to the PtdIns second messenger pathway.

Antigens, CD↗
PubMed1990

The incidence of popliteal aneurysms in patients with arteriomegaly.

Sixty-five patients with arteriomegaly were investigated by arteriography or digital subtraction angiography, and ultrasound or computed tomography to exclude popliteal aneurysms. In 36 (55%) patients popliteal aneurysms were demonstrated. In view of this high incidence and the known serious complications of popliteal aneurysms, we suggest that all patients with angiographic evidence of arteriomegaly should be further investigated by ultrasound or computed tomography.

Adult↗
PubMed1990

Identification of an additional member of the protein-tyrosine-phosphatase family: evidence for alternative splicing in the tyrosine phosphatase domain.

Protein-tyrosine-phosphatases (protein-tyrosine-phosphate phosphohydrolase, EC 3.13.48) have been implicated in the regulation of cell growth; however, to date few tyrosine phosphatases have been characterized. To identify additional family members, the cDNA for the human tyrosine phosphatase leukocyte common antigen (LCA; CD45) was used to screen, under low stringency, a mouse pre-B-cell cDNA library. Two cDNA clones were isolated and sequence analysis predicts a protein sequence of 793 amino acids. We have named the molecule LRP (LCA-related phosphatase). RNA transfer analysis indicates that the cDNAs were derived from a 3.2-kilobase mRNA. The LRP mRNA is transcribed in a wide variety of tissues. The predicted protein structure can be divided into the following structural features: a short 19-amino acid leader sequence, an exterior domain of 123 amino acids that is predicted to be highly glycosylated, a 24-amino acid membrane-spanning region, and a 627-amino acid cytoplasmic region. The cytoplasmic region contains two approximately 260-amino acid domains, each with homology to the tyrosine phosphatase family. One of the cDNA clones differed in that it had a 108-base-pair insertion that, while preserving the reading frame, would disrupt the first protein-tyrosine-phosphatase domain. Analysis of genomic DNA indicates that the insertion is due to an alternatively spliced exon. LRP appears to be evolutionarily conserved as a putative homologue has been identified in the invertebrate Styela plicata.

Amino Acid Sequence↗
PubMed1989

Evidence that the leukocyte-common antigen is required for antigen-induced T lymphocyte proliferation.

The leukocyte-common antigen (L-CA) is a family of large molecular weight glycoproteins uniquely expressed on the surface of all nucleated cells of hematopoietic origin. The glycoprotein consists of a heavily glycosylated exterior domain, a single membrane spanning region, and a large cytoplasmic domain that contains tyrosine phosphatase activity. To investigate the function of this family, we generated T cell clones that lacked L-CA (L-CA-). The expression of the alpha beta T cell receptor, CD3, CD4, IL-2 receptor (p55), LFA-1, Thy-1, and Pgp-1 (CD44) was normal. The L-CA- T cell clones failed to proliferate in response to antigen or cross-linked CD3; however, they could still proliferate in response to IL-2. An L-CA+ revertant was obtained and the ability to proliferate in response to antigen and cross-linked CD3 was restored. These data indicate that L-CA is required for T cells to enter into cell cycle in response to antigen.

Amino Acid Sequence↗
PubMed1989

Sequence conservation in potential regulatory regions of the mouse and human leukocyte common antigen gene.

The leukocyte common antigen is a family of glycoproteins uniquely expressed by cells of hemopoietic origin. The family is generated by alternative splicing of 3 exons, and individual members are expressed in a cell type-specific fashion. The glycoprotein consists of a heavily glycosylated exterior domain of approximately 100 kDa, a single membrane spanning region, and a cytoplasmic domain that has homology to a protein tyrosine phosphatase of 83 kDa. To further understand the regulation and structure of this family of molecules, genomic clones were isolated from mouse lambda and cosmid libraries. The genomic organization was determined from 20 genomic clones. Eighteen of the clones clustered within a 75-kilobase region, whereas the promoter region, the exons for the 5'-untranslated region, and the leader domain are located an unknown distance further 5' within in an unlinked clone. The gene is composed of 34 exons: two 5'-untranslated exons, 1a and 1b, and 32 exons that encode protein sequence. Exon 2 contains part of the 5'-untranslated region and encodes the 23 amino acids of the leader sequence. Exons 3-15 encode amino acid residues 1-538 of the external domain, exon 16 encodes residues 539-574, encompassing the membrane-spanning domain, and exons 17-33 encode residues 575-1268 of the cytoplasmic domain. Exon 33, the largest exon, contains the 1.1-kilobase 3'-untranslated region. A comparison between mouse and human (Hall, L.R., Streuli, M., Schlossman, S.F., and Saito, H. (1988) J. Immunol. 141, 2781-2787) promoter regions reveals significant homologies 5' to the transcription start site. The relationship between exon structure and glycoprotein structure is discussed.

Amino Acid Sequence↗
PubMed1989

Fetal radius length: a critical evaluation of race as a factor in gestational age assessment.

Growth of the fetal radius was examined ultrasonographically in a prospective cross-sectional study of 290 white and 63 black patients between 12 and 43 weeks' gestation. The mean of radius length and 95% predictive intervals were calculated for each week. The most efficient description of the data was given by a simple log-linear model. The slopes for the white and black study groups estimated were distinctly different. Consequently, a single equation was estimated that considers race when assessing gestational age from radius length.

Female↗
PubMed1989

Thigh circumference in the detection of intrauterine growth retardation.

Intrauterine growth retardation (IUGR) is associated with an increase in perinatal mortality as well as long-term neurobehavioral morbidity. Despite the increasing sophistication of antenatal fetal assessment, the diagnosis of growth retardation remains difficult. Since the fetal effects of growth inhibition are variable, no one ultrasonic parameter can diagnose with certainty the growth-retarded fetus. The reduction of thigh circumference with IUGR is secondary to the muscle wasting that is characteristic of this disease process. The sensitivity (77.8%) and specificity (75%) of thigh circumference may make it a useful additional sonographic parameter in the evaluation of fetal growth retardation.

Embryonic and Fetal Development↗
PubMed1989

A comparison of the value of hyoscine butylbromide and glucagon on aorto iliac intravenous digital subtraction.

The diagnostic quality of intravenous subtraction aorto-iliac arteriograms was assessed in 60 patients randomly allocated to receive either hyoscine butylbromide or glucagon as an inhibitor of bowel peristalsis. The examinations in patients receiving hyoscine butylbromide showed statistically significantly less artefact due to bowel movement than those receiving glucagon. Furthermore, glucagon is 20 times more expensive than hyoscine butylbromide. Neither drug produced significant ECG changes or side effects. We conclude that intravenous hyoscine butylbromide should be used routinely, except where specifically contra-indicated, in all patients undergoing IV-DSA of the aorto-iliac segments.

Adolescent↗
PubMed1989

The value of the lateral projection in preoperative assessment of abdominal aortic aneurysms by IV-DSA.

25 consecutive patients with known abdominal aneurysms were examined pre-operatively by IV-DSA. In all patients a lateral view was taken in addition to the standard posteroanterior view. The state of the visceral arteries was best assessed on the lateral projection. In 24% of examinations the renal arteries could not be visualised satisfactorily in the lateral view. In 37% of the 19 patients in which the distance between the renal arteries and the aneurysm neck could be measured there was a greater than 1 cm discrepancy between the two projections indicating that both views are necessary for accurate measurement. It is concluded that both a lateral and a postero-anterior projection should be routinely taken for IV-DSA in pre-operative assessment of abdominal aortic aneurysms.

Aged↗
PubMed1988

The relationship between long bone growth rate and duodenal calcium transport in female rats.

Studies were carried out to determine the relationship between long bone growth and duodenal calcium (Ca) transport in female rats and the regulation of these two parameters by ovarian hormones. Female rats were ovariectomized (ovx) at 6 weeks of age. Some animals were implanted with silastic implants containing either estradiol or progesterone at the time of ovx. Studies were carried out 3 weeks later when the rats were 9 weeks old. Ovx resulted in an increase in long bone growth rate and duodenal Ca transport without any alteration in circulating levels of parathyroid hormone or 1,25-dihydroxyvitamin D [1,25-(OH)2D]. Animals receiving estradiol exhibited decreased long bone growth rate and duodenal Ca transport relative to ovx animals. These animals were mildly hypercalcemic and had lower levels of 1,25-(OH)2D than ovx or intact animals. The results of these studies suggest that the effects of ovarian hormone status on duodenal Ca transport are more closely related to long bone growth rate than to circulating levels of 1,25-(OH)2D. Further studies are required to determine whether the two parameters are coregulated by some as-yet-unidentified factor or whether bone growth is able to emit some signal, directly or indirectly, to increase duodenal Ca transport.

Animals↗
PubMed1988

Sonographic assessment of the first trimester fetus. A cautionary note.

Ultrasound has the potential for diagnosing fetal abnormalities in utero with a high degree of accuracy. During the first trimester, peculiarities of fetal development may suggest to the novice sonographer an abnormality where one does not exist. Similarly, particular anatomic structures may appear normal in the first trimester, yet evolve into an obvious abnormality later in gestation. For these reasons, the ultrasonic diagnosis or exclusion of a congenital anomaly in the first trimester should be made only with caution.

Adult↗