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Biomedical subjects

M Tuscan

Publications and source records attributed to M Tuscan.

10 recordsLinked to original sources
PubMed1992

Replication origin mutations affecting binding of pSC101 plasmid-encoded Rep initiator protein.

To investigate the role of binding sites for Rep initiation protein in the replication of pSC101, a series of plasmids was constructed which carried different combinations of mutations in three binding sites within the minimal origin of replication. Mutation of all three sites reduced the affinity of purified Rep protein for the origin by 100-fold, as measured by a competition binding assay. Mutations in individual binding sites prevented binding of Rep protein to the mutant site but not to adjacent wild-type sites. Transformation efficiency, copy number, and stability over 150 generations were measured for each of the mutant plasmids. Unlike other similar plasmids related to pSC101, the Rep binding sites were found not to be equivalent. A mutation in the site RS1, proximal to repeated sequences which serve as DnaB helicase entry sites in oriC, had a severe effect on replication activity. A similar mutation in the distal site RS3 caused a reduction in copy number, but the mutant plasmid was stably maintained despite a broadened distribution of copy number within the population. A mutation in the middle RS2 site had no significant effect on pSC101 replication.

Bacterial Proteins↗
PubMed1989

Demonstration by iodine-131-hippurate renography of a marked sensitivity of some transplanted kidneys to volume contraction.

Incidental observations made in a canine renal transplant model in which both native and transplanted kidneys were present revealed that abnormal I-131-iodohippurate renograms were derived from some of the transplanted kidneys in the presence of mild dehydration. In these cases, the renogram normalized with fluid administration. In contrast, the renograms derived from the native kidneys were unaffected by the mild dehydration of the animals. These findings demonstrate a greater sensitivity to dehydration of some transplanted kidneys when compared to normal kidneys.

Animals↗
PubMed1988

The appended curve technique for deconvolutional analysis--method and validation.

Deconvolutional analysis (DCA) is useful in correction of organ time activity curves (response function) for variations in blood activity (input function). Despite enthusiastic reports of applications of DCA in renal and cardiac scintigraphy, routine use has awaited an easily implemented algorithm which is insensitive to statistical noise. The matrix method suffers from the propagation of errors in early data points through the entire curve. Curve fitting or constraint methods require prior knowledge of the expected form of the results. DCA by Fourier transforms (FT) is less influenced by single data points but often suffers from high frequency artifacts which result from the abrupt termination of data acquisition at a nonzero value. To reduce this artifact, we extend the input (i) and response curves to three to five times the initial period of data acquisition (P) by appending a smooth low frequency curve with a gradual taper to zero. Satisfactory results have been obtained using a half cosine curve of length 2-3P. The FTs of the input and response I and R, are computed and R/I determined. The inverse FT is performed and the curve segment corresponding to the initial period of acquisition (P) is retained. We have validated this technique in a dog model by comparing the mean renal transit times of 131I-iodohippuran by direct renal artery injection to that calculated by deconvolution of an intravenous injection. The correlation was excellent (r = 0.97, P less than 0.005). The extension of the data curves by appending a low frequency "tail" before DCA reduces the data termination artifact. This method is rapid, simple, and easily implemented on a microcomputer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Amount of antibody is critical for immune complex displacement by charge competition from both rabbit glomeruli and anionic beads.

The purpose of this study was to determine the feasibility of displacing cationized bovine serum albumin (CBSA) immune complexes from glomeruli by charge competition. An in vitro model identified protamine as an effective agent for displacing 125I-CBSA from anionic beads (dextran sulfate-coated Sepharose 4B). Anti-CBSA serum prevented displacement of 125I-CBSA from anionic beads in a dose-dependent fashion. When 125I-CBSA was injected intravenously into rabbits 98% of 125I-CBSA disappeared from blood within 5 min, at which time CBSA was visualized by immunofluorescence in glomerular capillary walls but not in liver, muscle, skin, spleen or lung. By 24 h 90% of 125I-CBSA had disappeared from glomeruli. In contrast, injection of anti-CBSA antibody caused persistence of 125I-CBSA in kidney (particularly along glomerular capillary walls) for more than 7 days (detected by counting 125I in kidney, by radionuclide imaging and by immunofluorescence). Protamine administration (50 mg intravenously daily for 6 days) caused significant reduction of 125I-CBSA trapped in kidney only if the amount of anti-CBSA injected was small. Protamine did not significantly displace 125I-CBSA from glomeruli if the anti-CBSA dose was larger. Therefore both in vivo and in vitro displacement of 125I-CBSA by protamine depended upon the amount of antibody. We conclude that although charge dependent displacement of immune complexes from glomeruli is probably feasible using protamine this approach would only work in the presence of small amounts of antibody.

Animals↗
PubMed1984

Constant intrarenal infusion of PGE1 into a canine renal transplant using a totally implantable pump.

A method was devised whereby PGE1 could be administered to a canine renal transplant recipient on a chronic basis. PGE1 was stored in the reservoir of an implantable pump and delivered continuously in high doses directly into the renal transplant artery. In the model studied a contralateral untreated transplant from the same donor served as a control. Sequential renal scans were used to study the effect of intraarterial PGE1 on the rejection process. Continuous delivery of PGE1 into the renal transplant artery did not prevent allograft failure under these conditions; blood flow diminished similarly in both PGE1-treated and untreated transplants. There were, however, striking differences in the histologic appearance of treated and untreated transplants. PGE1 perfusion resulted in the appearance of large numbers of polymorphonuclear leukocytes but few lymphocytes. In the untreated control allograft, however, the findings were typical of lymphocyte-mediated acute rejection. The distinctive differences noted histologically suggested that the local administration of PGE1 influenced the mechanism by which graft failure occurred. The ability to manipulate cell populations infiltrating an allograft represents a potentially important means for modifying the immune response.

Alprostadil↗
PubMed1983

Quantitative hepatic arterial perfusion scintigraphy and starch microspheres in cancer chemotherapy.

Hepatic arterial infusion chemotherapy results in a higher concentration of drug delivered to the tumor with less systemic exposure than is possible with intravenous therapy. However, extrahepatic blood flow and/or shunting to the lung can impose a limitation. This study describes a quantitative method for calculating the extrahepatic component and monitoring its changes due to a new adjunctive therapy, degradable starch microspheres (DSM). DSM temporarily occlude the hepatic arterial circulation, thereby increasing the uptake of therapeutic drugs. Twenty patients with metastatic liver cancer underwent hepatic arterial perfusion scintigraphy (HAPS) using Tc-99m MAA to determine blood-flow distribution and to quantitate extrahepatic uptake. The percent shunt index (PSI) was determined at baseline and after each incremental dose of DSM. The baseline PSI ranged from 6-26% (mean 12.3 +/- 5.8 s.d.) and changed progressively after each injection of DSM/Tc-MAA suspension. The patterns of change in shunting are described. Quantitative HAPS provides a means of measuring the extrahepatic component, warns of potential side effects, and helps guide chemotherapeutic decisions.

Adult↗
PubMed1982

Computing adrenal uptakes with compact, fixed-size regions.

In planar nuclear medicine imaging of the adrenal gland, there are three requirements for an uptake determination: finding the region of interest, subtracting 'background', and converting cps to muCi. A computer program that covers each requirement is outlined. The region of interest is determined by a nearest-neighbor region-growing technique. It starts from an operator-chosen center, searches for the hottest pixels, and terminates when a fixed-size region is found. If the resulting region is unacceptable, recourse to a second level of searching, which produces a more compact region, is possible. Background from underlying and overlying tissue is estimated from the average counts/pixel in a narrow 'ring' surrounding the adrenal. Conversion to muCi is carried out by use of a calibration equation which requires a value for the adrenal depth. This value may be obtained from a lateral view. The program is available in listing form. For use with a Medical Data Systems A2 computer, files can be transferred directly. Parameters which should be changed for the use of the program with another camera-collimator system are noted.

Adrenal Glands↗
PubMed1982

Perfusion scintigraphy (Tc-99m MAA) during surgery for placement of chemotherapy catheter in hepatic artery: concise communication.

In 17 patients receiving regional hepatic chemotherapy, Tc-99m macroaggregated albumin imaging was used to aid arterial catheter placement and to assess perfusion patterns. Intraoperative imaging with a portable gamma camera allowed immediate monitoring of hepatic and extrahepatic perfusion patterns and assisted catheter manipulation when necessary to achieve optimal flow distribution. In all 12 patients with standard hepatic arterial anatomy, complete perfusion of both lobes of the liver was achieved, although three of them required intraoperative catheter manipulation and repeat imaging after initial placement. The remaining five patients had aberrant hepatic arterial anatomy, and complete perfusion was more difficult to achieve; they exemplified the need for dual catheters, ligation of accessory hepatic branches, and repeated imaging.

Adenocarcinoma↗
PubMedDate not supplied

Distortion introduced in radionuclide camera views by multiformat imagers.

The degree of spatial distortion of radionuclide camera images introduced by the multiformat imager is compared in six different cameras. The instruments tested were the Ohio Nuclear 110 and 410S, Searle Pho Gamma LFOV, and the General Electric 400T. We found image nonlinearity variations of 4 to 25%; this illustrates the need for industrial standards applied to imager spatial distortion performance.

Photography↗