Biomedical subjects

S Sawyer

Publications and source records attributed to S Sawyer.

10 recordsLinked to original sources

PubMed1992

Post-transfusion recovery of function of 5-day stored platelet concentrates.

Platelets show a rapid reduction in their responsiveness to aggregating agents during storage for transfusion, but little is known about reversal of this defect in vivo after transfusion. In this study, fresh and stored platelets from the same donor (n = 12) were labelled with 111In or 51Cr, respectively, mixed, and simultaneously infused. Blood samples were taken for up to 5 d post-infusion, and the functional behaviour of the labelled platelets ex vivo was measured by retention on glass bead columns, and by whole blood aggregability to ADP, epinephrine and ristocetin. Aggregation was determined by filtering aggregated samples through a column of cotton wool to remove the aggregates, and quantitated as per cent decrease in radioactive counts. The study showed that, although infused radiolabelled 5 d stored platelets had a significantly lower aggregability towards ADP and epinephrine immediately (1 h) after infusion (32% and 29%, respectively, of fresh platelet values), a complete restoration to fresh platelet levels was found 24-72 h post-infusion, with no further change observed over the ensuing 5 d with either fresh or stored labelled platelets. A slightly (6-9%) lower adhesion to both uncoated and collagen-coated beads was found for the stored platelets throughout the 5 d period of study post-infusion. In conclusion, these studies show that, with ex vivo testing, platelets stored for 5 d quickly recovered adhesion and aggregability capabilities similar to that of fresh platelets, suggesting that the functional lesion developed during storage is quickly and completely reversed after infusion.

Adenosine Diphosphate↗

PubMed1992

Induction of erythropoietin responsiveness in murine hematopoietic cells by the gag-myb-ets-containing ME26 virus.

ME26 virus, which was generated by inserting the coding region of the acute avian leukemia-inducing virus E26 into a murine retrovirus vector, encodes a 135-kDa gag-myb-ets fusion protein. Amphotropic murine leukemia virus pseudotypes of ME26 virus induce a high incidence of erythroleukemia 2 to 4 months after injection into newborn NFS/N mice. Spleen cells from the majority of these mice proliferate to high levels in the presence of the erythroid hormone erythropoietin (Epo) and can easily be established as permanent Epo-dependent cell lines. The cell lines contain multiple copies of ME26 viral DNA and express viral message and protein. An Epo receptor mRNA of normal size can be detected in these cells, and binding studies reveal a single class of lower-affinity Epo receptor with an affinity for Epo that is in the range of that previously reported for erythroid cells. The ME26 virus-induced Epo-dependent cell lines, however, appear more immature than previously described erythroid cell lines and more closely resemble early hematopoietic precursor cells, suggesting that the virus may be activating the Epo receptor in hematopoietic cells that do not normally express it. Consistent with this idea, we are able to infect an interleukin-3-dependent myeloid cell line, FDC-P2, with ME26 virus and convert it to Epo dependence. The ME26 virus-infected FDC-P2 cells, even before growth on Epo, showed a large increase in the amount of Epo receptor mRNA. However, no ME26 viral integrations can be detected adjacent to the Epo receptor gene, indicating that the virus is not activating the Epo receptor gene by promoter/enhancer insertion. Our results are more consistent with the hypothesis that the gag-myb-ets-encoded viral fusion protein, which is known to bind DNA, is directly or indirectly activating the expression of the Epo receptor gene in these cells.

Animals↗

PubMed1992

Improved maintenance of platelet in vivo viability during storage when using a synthetic medium with inhibitors.

We report on the storage of platelet concentrates and the effects on in vivo and in vitro platelet function tests of adding the platelet inhibitors prostaglandin E1 and theophylline to a plasma-free synthetic medium and storage in containers with reduced surface-to-volume ratio. Paired in vivo studies on platelets labeled with indium 111 after 14-day storage demonstrated higher recoveries (mean +/- SD) of 23% +/- 9% and longer survivals of 109 +/- 59 hours for the test group versus 8% +/- 10% and 19 +/- 22 hours, respectively (p less than 0.01), for the control group (synthetic medium with no inhibitors and use of standard containers). The improved viability was associated with a significantly lower glycolytic rate; better maintenance of other in vitro parameters including respiratory activity, adenosine triphosphate levels, hypotonic shock response, surface glycoprotein Ib (by flow cytometry); and improved preservation of morphologic integrity (p less than 0.05). In particular, a strong inverse correlation (r = -0.91) was observed between in vivo recoveries and the fraction of platelets negative for glycoprotein Ib. We conclude that avoidance of platelet activation by a combination of inhibitors, plasma removal, and reduced container surface improves platelet respiratory activity, adenosine triphosphate and glycoprotein Ib levels, and posttransfusion viability of platelet concentrates stored for 14 days.

Adenosine Triphosphate↗

PubMed1991

Insulin secretion, insulin sensitivity and glucose-mediated glucose disposal in Cushing's disease: a minimal model analysis.

OBJECTIVE: We wished to assess the contributions of insulin secretion, insulin sensitivity and glucose-mediated glucose disposal to glucose tolerance in subjects exposed to chronic glucocorticoid excess. DESIGN: Patients with Cushing's disease were subjected to a frequently sampled intravenous glucose tolerance test before and at least 3 months after curative surgery and compared to a control group. PATIENTS: Seven patients with clinical and biochemically proven pituitary dependent Cushing's disease and 10 healthy control subjects were studied. MEASUREMENTS: Paired glucose and insulin plasma profiles were analysed by the Minimal Model method of Bergman, which provided simultaneous estimates of the glucose decay rate, insulin secretion, insulin sensitivity and glucose-mediated and non-insulin-mediated glucose disposal. Data were evaluated by non-parametric statistical analysis and reported as median and interquartile ranges. RESULTS: Basal glucose, insulin, C-peptide and glucagon levels were significantly raised preoperatively and fell towards normal post-operatively. Glucose tolerance assessed as glucose decay rate was reduced significantly preoperatively (pre: 1.3 (0.8-2.0) vs post: 1.6 (1.5-2.6) per min x 10(2), P less than 0.05). First phase insulin release was similar in the Cushing's disease and control subjects. In contrast, second phase insulin release was significantly greater preoperatively and remained high post-operatively compared to control subjects (pre: 18.8 (16.7-23.6) vs post: 16.7 (8.5-18.8) vs control 11.1 (4.5-15.4) mU/g/min2 x 10(-2), P less than 0.002). Median insulin sensitivity was reduced by 60% preoperatively in the Cushing's disease subjects compared to the post-operative Cushing's disease and control subjects (pre: 2.1 (1.3-4.2) vs post: 5.0 (3.2-7.3) vs control 5.1 (2.2-7.2) per min/mU/l x 10(4)). Median glucose-mediated glucose disposal was reduced by 40% in the pre and post-operative Cushing's disease subjects compared to the control group (pre: 1.1 (0.6-2.1) vs post: 1.1 (0.6-2.1) vs control 1.9 (1.4-2.6) per min x 10(2)), but this was not statistically significant. However, non-insulin-mediated glucose disposal was significantly reduced in the preoperative Cushing's disease subjects (pre: 0.55 (0.08-1.59) vs control 1.43 (0.94-2.27) per min x 10(2), P less than 0.05). In the Cushing's disease subjects, glucose tolerance correlated with both insulin sensitivity (rs = 0.84, P less than 0.01) and non-insulin-mediated glucose disposal (rs = 0.56, P less than 0.05). The fractional clearance rate of insulin was unaltered by Cushing's disease. CONCLUSIONS: Cushing's disease subjects are characterized by impaired glucose tolerance due to both reduced insulin sensitivity and non-insulin-mediated glucose disposal, in the presence of enhanced insulin secretion.

Adult↗

PubMed1990

Insulin secretion, insulin sensitivity and glucose-mediated glucose disposal in thyrotoxicosis: a minimal model analysis.

In order to evaluate simultaneously in thyrotoxic subjects the relative contributions of insulin secretion, insulin-sensitivity (SI) and glucose-mediated (SG) glucose disposal to overall glucose tolerance, seven non-obese patients with thyrotoxicosis were studied by the minimal model analysis of the frequently sampled intravenous glucose tolerance test, before and greater than 1 month after being rendered euthyroid, and compared with eight healthy control subjects. Basal glucose, C-peptide and glucagon levels were similar in all groups but, in the toxic and euthyroid states, basal insulin levels were significantly elevated compared to the control group (11.2 +/- 2.0 and 7.9 +/- 1.1 vs 5.1 +/- 0.6 microU/ml, mean +/- SE, P less than 0.02). FFA levels were raised in the thyrotoxic subjects prior to treatment (0.95 +/- 0.11 vs 0.68 +/- 0.08 and 0.54 +/- 0.08 mmol/l, P less than 0.02). Glucose tolerance (Kg) was reduced in the thyrotoxic subjects compared to the euthyroid state (1.16 +/- 0.12 vs 1.44 +/- 0.13 per min, P less than 0.025) and control group (1.44 +/- 1.0 per min, 0.05 less than P less than 0.1). First phase (phi 1) and second phase (phi 2) insulin release were both significantly elevated in the thyrotoxic and euthyroid states compared to the control group (phi 1 7.10 +/- 1.88 and 5.29 +/- 1.03 vs 1.72 +/- 0.17 microU/mg/min X 10(-2), P less than 0.01; phi 2 18.64 +/- 3.14 and 16.74 +/- 4.48 vs 9.23 +/- 0.74 microU/mg/min X 10(-2) respectively, P less than 0.02). SG was similar in all groups but SI was significantly reduced in the thyrotoxic subjects compared to the control group (2.24 +/- 0.62 vs 5.92 +/- 1.50/min/microU/ml X 10(4), P less than 0.02) and rose post-treatment in the euthyroid subjects (4.23 +/- 1.75/min/microU/ml X 10(4)). In the thyrotoxic subjects before and after treatment, log SI correlated negatively with basal FFA levels (r = -0.57, P less than 0.05) and with phi 2 (r = -0.58, P less than 0.05). The fractional clearance rate of insulin was unaltered by the thyrotoxic state. It is concluded that in thyrotoxicosis the impairment of Kg is due to reduced insulin sensitivity in the presence of enhanced insulin secretion, but glucose-mediated glucose disposal is unaltered by the toxic state.

Adult↗

PubMed1989

Statistical tests for detecting gene conversion.

Statistical tests for detecting gene conversion are described for a sample of homologous DNA sequences. The tests are based on imbalances in the distribution of segments on which some pair of sequences agrees. The methods automatically control for variable mutation rates along the genome and do not depend on a priori choices of potentially monophyletic subsets of the sample. The tests show strong evidence for multiple intragenic conversion events at two loci in Escherichia coli. The gnd locus in E. coli shows a highly significant excess of maximal segments of length 70-200 bp, which suggests conversion events of that size. The data also indicate that the rate of these short conversion events might be of the order of neutral mutation rate. There is also evidence for correlated mutation in adjacent codon positions. The same tests applied to a locus in an RNA virus were negative.

Amino Acid Sequence↗

PubMed1987

Purification of human erythroid colony-forming units and demonstration of specific binding of erythropoietin.

Morphological and biochemical studies of human colony-forming units-erythroid (CFU-E) have been hindered by their extreme rarity. Since burst-forming units-erythroid (BFU-E) develop into CFU-E, we used normal human blood BFU-E to generate large numbers of highly purified CFU-E in vitro. Using density centrifugation, sheep erythrocyte rosetting, surface immunoglobulin-positive cell depletion, adherence to plastic, and negative panning with monoclonal antibodies, human blood BFU-E were purified from 0.017 to 0.368%, a 22-fold purification with a 43% yield. The panned cells were cultured in methylcellulose with recombinant erythropoietin (rEp) and conditioned medium for 9 d. These cells were then collected and CFU-E were further purified using adherence and density centrifugation. This yielded almost 10(7) erythroid colony forming cells with a purity of 70 +/- 18%. Analysis of these cells by light and electron microscopy showed 94% erythroid cells. The prominent cell was a primitive blast with high nuclear/cytoplasmic ratio, dispersed nuclear chromatin and a distinct large nucleolus. The relation between the number of erythroid colonies and the number of day 9 cells plated in plasma clots was a straight line through the origin with a maximum number of erythroid colonies at 1 U/ml of rEp and no erythroid colonies without rEp. Specific binding with 125I-rEp showed that 60% of the binding was inhibited by excess pure erythropoietin (Ep), but not by albumin, fetal calf serum, and a variety of growth factors or glycoproteins. By days 12-13 of cell culture, when the progenitor cells matured to late erythroblasts, specific binding markedly declined. In this study, human CFU-E have been isolated in sufficient purity to characterize the morphology of these rare cells and in sufficient numbers to measure specific binding of Ep.

Antibodies, Monoclonal↗

PubMed1986

Distribution of transposable elements in prokaryotes.

We consider models for the distribution of the number of elements per host genome for families of transposable elements (TEs). The hosts are assumed to be prokaryotes. These models assume a constant rate of infection of uninfected hosts by TEs, replicative transposition within each host, and a reduction of the fitness of a host dependent on the number of TEs it contains. No provision was made for the deletion of individual TEs within a host or for recombination, since both are relatively rare events in prokaryotes. These models mostly assume that the TE performs no function for the host, and that the reduction in fitness with increased copy number is due to effects such as the impairment of beneficial genes by transposition or homologous recombination. We also consider a model in which the TEs can convey a selective advantage to the host. The equilibrium distributions of copy number are determined for these models, and are of a variety of classical types. Relevant parameters of the models are estimated using data on the distribution of insertion sequences in natural isolates of Escherichia coli.

Biological Evolution↗

PubMed1979

Genetic drift in sex-linked lethal disorders.

A model is considered to calculate effects of genetic drift on the expected proportion of new mutants amongst males affected by a sex-linked recessive lethal. We show how to relate the number of cases of the disorder in males to the expected deviations from the deterministic value of the proportion of new mutants. For small values of alpha (= 3N mu), where N is the size of the female population, and mu is the mutation rate from wild-type to lethal allele, the standard deviation (SD) of the proportion of new mutants is large. However, if alpha more than 50, the potential effect of genetic drift is probably less important than the many other sources of error and bias.

Gene Frequency↗

PubMed1976

Role of activated macrophages in resistance of mice to infection with Trypanosoma cruzi.

The role of the activated macrophage in resistance of mice to infection with Trypanosoma cruzi was investigated with use of mice that had not been infected with T. cruzi but whose macrophages were activated by Toxoplasma gondii or Besnoitia jellisoni. Mice with activated macrophages were significantly more resistant to intra-peritoneal challenge with the Tulahuen strain of T. cruzi than were controls. The role of serum factors in resistance to T. cruzi was excluded by the demonstration of no difference between survival of T. cruzi in serum from mice with activated macrophages and in that from controls. As the only modality of resistance to T. cruzi in this in vivo model appeared to be the activated macrophage, this cell was investigated in vitro. Activated macrophages were shown to be able to inhibit completely multiplication of T. cruzi, whereas significant multiplication of the parasite occurred in control macrophages. Both in vivo and in vitro data suggest that the activated macrophage may play a major role in resistance to infection with T. cruzi.

Animals↗