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Biomedical subjects

M L Thomas

Publications and source records attributed to M L Thomas.

At least 181 records · Page 10Linked to original sources
PubMed1985

A comparison of preoperative long saphenous phlebography with operative dissection in assessing the suitability of long saphenous vein for use as a bypass graft.

A technique for assessing the anatomy and luminal diameter of the long saphenous vein by direct injection phlebography in patients being considered for reversed femoropopliteal vein bypass surgery is described. In 25 consecutive patients, 20 single veins, four double veins and one network of veins were all correctly delineated by this technique and subsequently confirmed at operation. Five saphenous veins could not be demonstrated above the knee but at operation one vein was found to be present and double from knee to groin. The minimum mean luminal diameter of the saphenous vein estimated from the X-ray after correction for magnification was 3.5 mm +/- 1.12 which was significantly less than the mean external diameter found at operation, 4.6 mm +/- 1.33 (P less than 0.001). The vein diameter found at operation invariably proved to be larger than the luminal diameter estimated from the X-ray. This allows a confident preoperative assumption of the minimum diameter that will be obtained after dissection and distension of the vein.

Aged↗
PubMed1984

MRC OX-19: a monoclonal antibody that labels rat T lymphocytes and augments in vitro proliferative responses.

A mouse monoclonal antibody, designated MRC OX-19, has been prepared that binds to virtually all rat thymocytes, T lymphocytes and a maximum of 2% B lymphocytes. Immunoperoxidase studies on tissue sections showed no reactivity with nonlymphoid cells in intestine, thymus, spleen and lymph node. The antigen recognized by MRC OX-19 antibody was identified by metabolic and cell surface labeling of thymocytes followed by immunoprecipitation and sodium dodecyl sulfate gel electrophoresis. It is a surface glycoprotein of Mr = 69 000. When included in in vitro assays for T cell functions, MRC OX-19 increased proliferation stimulated by allogeneic spleen cells or the lectins phytohemagglutinin and concanavalin A. The antibody itself was not mitogenic and its stimulatory effect could be correlated with an increase in interleukin 2 production. Taken together the data suggest that MRC OX-19 could be the equivalent of mouse Ly-1 antigen and human T1 antigen.

Animals↗
PubMed1984

Pharmacokinetics and therapeutic efficacy of imipenem, ceftazidime, and ceftriaxone in experimental meningitis due to an ampicillin- and chloramphenicol-resistant strain of Haemophilus influenzae type b.

The pharmacokinetics and therapeutic efficacy of imipenem, ceftazidime, and ceftriaxone were compared with those of ampicillin and chloramphenicol in rabbits with experimental meningitis due to an ampicillin- and chloramphenicol-resistant strain of Haemophilus influenzae type b. The mean bacterial colony counts in cerebrospinal fluid were reduced by 49% (-1.85 log10 CFU/ml), 92% (-3.37 log10 CFU/ml), and 92% (-4.30 log10 CFU/ml) after a single dose of imipenem, ceftazidime, and ceftriaxone, respectively. The median peak cerebrospinal fluid bactericidal titers against this multiply resistant strain of H. influenzae were 1:4 for thienamycin, 1:16 for ceftazidime, and 1:256 for ceftriaxone. By contrast, no bactericidal activity was observed in cerebrospinal fluid and the mean concentrations of H. influenzae were either unchanged or slightly increased in animals treated with ampicillin or chloramphenicol.

Ampicillin↗
PubMed1984

Pharmacokinetics and bacteriological efficacy of mezlocillin in experimental Escherichia coli and Listeria monocytogenes meningitis.

The purpose of this study was to determine the pharmacokinetics and bacteriological effect of mezlocillin in experimental meningitis caused by Listeria monocytogenes and two Escherichia coli strains. The half-life of mezlocillin in cerebrospinal fluid (CSF) was approximately twice that in serum of experimentally infected animals, and the penetration of drug into CSF was 5 to 15% after a single dose and 5 to 20% after continuous-infusion experiments. The bactericidal titer in CSF for both susceptible E. coli and L. monocytogenes was 1:8, whereas for the resistant E. coli strain, titers were less than 1:2 after single doses of 50 or 100 mg of mezlocillin per kg and 1:4 with continuous infusion. After single-dose and continuous-infusion experiments, the bacteriological effect of mezlocillin in experimental L. monocytogenes infections was similar to that of ampicillin. Mezlocillin reduced the colony counts of of susceptible E. coli in CSF by 90% or more after a single dose or continuous infusion but had no appreciable effect on resistant E. coli after a single dose of 50 mg/kg. In contrast, a single dose of 100 mg of mezlocillin per kg eradicated the resistant strain from CSF, despite a bactericidal titer in CSF of less than 1:2. This unexpected finding prompted us to evaluate the effect of serum on the in vitro susceptibilities of selected coliforms to mezlocillin. The activity of mezlocillin against one susceptible and four resistant strains of gram-negative, enteric bacilli was enhanced manyfold by the addition of fresh rabbit serum; this effect was abolished by heating the serum at 56 degrees C for 30 min. This interaction of mezlocillin and serum against coliform bacteria should be examined in a larger number of experimentally infected animals and in specimens obtained from mezlocillin-treated infants.

Animals↗
PubMed1984

Pharmacokinetic properties of mezlocillin in newborn infants.

The pharmacokinetic properties of mezlocillin were evaluated in newborn infants. Mean peak and trough concentrations of drug in plasma, after 75 mg of mezlocillin per kg given intravenously, were 252 and 72 micrograms/ml, respectively, in infants who were less than 38 weeks gestation and less than or equal to 7 days old, compared with 139 and 9 micrograms/ml, respectively, in infants greater than or equal to 38 weeks gestation and greater than 7 days old. The mean elimination half-life values were from 4.5 h in preterm infants who were less than or equal to 7 days old to 1.8 h in term infants greater than or equal to 7 days old. Median peak and trough bactericidal titers of drug in plasma from neonates treated with mezlocillin were 1:8 and 1:4, respectively, against a resistant (minimal bactericidal concentration, 512 micrograms/ml) Escherichia coli strain and 1:64 and 1:32, respectively, against a susceptible (minimal bactericidal concentration, 2 micrograms/ml) E. coli strain. We propose a dosage schedule of 75 mg of mezlocillin per kg administered every 12 h to preterm (gestational age less than 38 weeks) infants less than or equal to 7 days old, every 8 h to preterm infants greater than 7 days old or term infants less than or equal to 7 days old, and every 6 h to term infants greater than 7 days old.

Female↗
PubMed1984

Pharmacokinetics of ceftazidime in newborn infants.

Doses of 50 mg of ceftazidime per kg were administered intravenously to 29 newborn infants every 8 or 12 h for 3 to 5 days. Mean peak concentrations in plasma ranged from 102 to 124 micrograms/ml. Mean elimination half-life values ranged from 2.9 to 6.7 h and varied inversely with gestational age and plasma clearances. Peak and trough plasma bactericidal titers against an Escherichia coli and a group B streptococcus strain were at least 1:16 and 1:32, respectively.

Ceftazidime↗
PubMed1984

Maternal-fetal relationships in the parathyroidectomized rat. Intestinal calcium transport, serum calcium, immunoreactive parathyroid hormone and calcitonin.

We studied the role of the parathyroids in the adaptation of intestinal Ca transport that occurs during pregnancy, and whether maternal hypoparathyroidism causes fetal hyperparathyroidism. Serum Ca of pregnant parathyroidectomized (PTX) rats was significantly greater than nonpregnant, PTX animals. Intestinal active Ca transport was increased 2.1- and 2.2-fold by pregnancy in intact and PTX rats, respectively. Serum levels of immunoreactive parathyroid hormone (PTH) were nondetectable in PTX-pregnant rats. Fetuses from PTX rats appeared grossly normal. The serum PTH was not different in fetuses from PTX compared to fetuses from intact mothers and serum Ca, Mg, and P were normal. Thus, alleviation of maternal hypocalcemia during pregnancy in PTX rats may be due to an adaptive increase in intestinal Ca transport, which does not require the parathyroids. Fetuses from PTX mothers were euparathyroid and were protected from Ca deficiency during pregnancy.

Animals↗
PubMed1984

The use of varicography to identify the sources of incompetence in recurrent varicose veins.

We have studied patients with recurrent varicose veins which were incompletely controlled by a thigh tourniquet. We used varicography, (a phlebogram via the varices), to detect sites of incompetence. Thirty patients (mean age 46 years) were investigated, 38 limbs being subjected to varicography and surgery. A primary operation had been performed between 3 months and 30 years earlier. A non-thrombogenic contrast medium, sodium meglumine ioxaglate 320 (Hexabix 320) was used. Metal markers were placed alongside the limb to identify the site of perforating veins on the phlebograms. The principal value of the technique was in the identification of mid-thigh perforator incompetence (MTPI) as we cannot diagnose this accurately by clinical or Doppler-ultrasound examination. Varicography demonstrated MTPI in 15/38 limbs (39%) and in only one thigh was this not confirmed at exploration. Varicography can demonstrate short saphenous incompetence and this was mainly of value in 3 patients who had previously undergone attempted short saphenous ligation; in all 3 the short saphenous vein was present and had not been ligated. The technique was less useful in demonstrating recurrence in the groin. Overall varicography influenced the operation performed in 17/38 limbs (45%), its main value being in the diagnosis of MTPI.

Adult↗
PubMed1983

Reduction of the beta-Cys-gamma-Glu thiol ester bond of human C3 with sodium borohydride.

Further chemical evidence has been obtained using NaB3H4 to support our previous assignment of a thiol ester bond in human C3 (Tack, B. F., Harrison, R. A., Janatova, J., Thomas, M. L., and Prahl, J. W. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 5764-5768). Following trypsin activation of human C3 in the presence of NaB3H4, 3H was shown to have incorporated specifically into the alpha'-chain of C3b. Subsequent fragmentation of [3H]C3b with porcine elastase further localized the label to the C3d subdomain. Under identical conditions, native C3 or C3 pretreated with trypsin (C3b) showed low reactivity with NaB3H4. A tryptic peptide containing the 3H label was isolated following digestion of [3H]C3b on activated thiol-Sepharose. After hydrolysis and saponification of the peptide hydrolysate, amino acid analysis indicated that the 3H had been incorporated into alpha-amino-delta-hydroxyvaleric acid, the product expected from reduction of an ester bond involving a glutamyl residue. On sequence analysis of the labeled peptide, the 3H was shown to reside at the position of the glutamyl residue previously proposed to be involved in the thiol ester bond. The residue at this position was confirmed as alpha-amino-delta-[3H] hydroxyvaleric acid by high performance liquid chromatography analysis and, after back hydrolysis, by amino acid analysis. These data significantly strengthen earlier studies which indicated the presence of a beta-Cys-gamma-Glu thiol ester bond in human C3.

Borohydrides↗
PubMed1983

Effects of forskolin on bone. Stimulation of cyclic AMP accumulation and calcium efflux from chick embryo tibiae in organ culture.

Forskolin (FSK), an activator of adenylate cyclase in many tissues, was investigated to determine its potential for studying cyclic AMP-mediated, physiological events in bone. Tibiae from 14-day chick embryos were cultured in modified Eagle's medium for up to 8 hr, and the cyclic AMP and Ca2+ efflux responses to parathyroid hormone (PTH) and FSK were observed. FSK caused a concentration-related increase in tissue cyclic AMP, with 10(-6) M FSK producing a cyclic AMP response of similar magnitude to that elicited by 10(-6) M PTH (1-34). However, while 10(-6) M PTH was the maximally-activating PTH concentration, a further elevation was produced by 10(-5) M FSK. Chick embryo tibiae cultured for 8 hr in the presence of PTH exhibited a concentration-related stimulation of Ca2+ efflux up to 10(-6) M PTH. When this physiological effect was examined in bones cultured in the presence of FSK, a biphasic response to increasing FSK concentrations was found; Ca2+ efflux was stimulated by 10(-6) M and 3 X 10(-6) M FSK, but not by 10(-7) M or 10(-5) M FSK. In summary, concentrations of FSK, which produced tissue cyclic AMP accumulation similar to that produced by physiologically effective PTH concentrations, also resulted in net Ca2+ efflux from bone. These results indicate that FSK may be a useful agent for studying the role of cyclic AMP in the response of bone to hormones.

Animals↗
PubMed1983

Molecular nature of the W3/25 and MRC OX-8 marker antigens for rat T lymphocytes: comparisons with mouse and human antigens.

The mouse monoclonal antibodies W3/25 and MRC OX-8 have been used to distinguish rat T lymphocyte subpopulations. In the peripheral T lymphocyte population, W3/25 antibody recognizes an antigen on the Thelper (Th) subset, while MRC OX-8 antibody recognizes an antigen on the Tsuppressor/cytotoxic (Ts/c) subset. To determine the nature of these antigens, rat thymocytes were either metabolically labeled with [35S]L-methionine or surface-labeled at sialic acid residues by periodate oxidation followed by [3H]NaBH4 reduction. Thymocytes were solubilized with nonionic detergent, the antigens immunoprecipitated and the molecular weights determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Using metabolically labeled cells, W3/25 antibody immunoprecipitated an antigen that electrophoresed under reducing conditions as a broad band between 48 000-53 000 Mr. Unreduced samples migrated between 46 000-50 000 Mr. Surface-labeled W3/25 antigen, electrophoresed under reducing conditions, separated into two bands of 44 000 and 52 000 Mr. Metabolically labeled MRC OX-8 antigen was identified as a protein of at least two chains of 39 000 and 34 000 Mr. There was also a fainter band at approximately 67 000 Mr. Unreduced samples indicated a more complex structure with bands at 70 000, 110 000 and 165 000 Mr. Surface-labeled MRC OX-8 antigen was of similar nature. These data, when considered with functional and tissue distribution data, suggest that W3/25 antigen is equivalent to T4 in man and MRC OX-8 antigen is equivalent to T8 in man, and Lyt-2 in mouse.

Animals↗
PubMed1983

Contrast agent-induced thrombophlebitis following leg phlebography: meglumine loxaglate versus meglumine lothalamate.

A comparison was made of the incidence of venous thrombophlebitis resulting from the use of a high-osmolality contrast medium (Conray 60%, meglumine ioxaglate) and a low-osmolality contrast medium (Hexabrix 59%, meglumine iothalamate). In 30 patients with varicose veins, Conray was injected into one leg and Hexabrix into the other. The incidence of thrombophlebitis was then determined using the iodine-125 fibrinogen uptake test in a prospective, randomized, double-blind study. There was significantly less thrombophlebitis with Hexabrix than with Conray and the authors conclude that Hexabrix is safer for phlebography. Hexabrix is also stable in solution, only slightly more expensive than Conray, and one fifth the cost of metrizamide.

Adult↗