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Biomedical subjects

A Weiss

Publications and source records attributed to A Weiss.

At least 397 records · Page 22Linked to original sources
PubMed1980

Polarity of Tn5 insertion mutations in Escherichia coli.

We assessed the effect of insertions of the kanamycin resistance transposon Tn5 in the lac operon of Escherichia coli on the expression of distal genes lacY and lacA (melibiose fermentation at 41 degrees C and thiogalactoside transacetylase synthesis, respectively). Every insertion mutation tested (41 in lacZ and 23 in lacY) was strongly polar. However, approximately one-third of the insertion mutants expressed distal genes at low levels due to a promoter associated with Tn5. To localize this promoter, we (i) reversed the orientation of Tn5 at several sites and (ii) replaced wild-type Tn5 with several substitution derivatives which lack Tn5's central region. Neither alteration changed the expression of distal genes. Thus, in contrast to transposons IS2 and TnA. Tn5's ability to turn on distal gene expression is not due to a promoter in its central region and therefore is not dependent on the overall orientation of Tn5 in the operon. Our results suggest that the promoter is within 186 base pairs of the ends of Tn5. It is possible that the promoter is detected in only a fraction of insertions because it overlaps Tn5-target sequence boundary.

Acetyltransferases↗
PubMed1980

Evaluation of myocardial perfusion by thallium-201 imaging at rest and during exercise. Comparison with ECG stress testing.

In order to assess the accuracy of thallium-201 cardiac imaging at rest or during exercise in detecting permanent or transient myocardial damage, we studied 49 patients with angiographically documented coronary disease (31 with previous myocardial infarction) and 29 patients with normal coronary arteries. The resting thallium scan was significantly more accurate in detecting previous myocardial infarction (31 patients) than the resting ECG (22 patients) (P < 0.01). The combination of thallium imaging and ECG stress testing revealed reversible myocardial ischemia in 41 of the 49 patients (84%), compared with 28 of 49 (57%) detected by ECG stress testing alone (P < 0.01). Thallium imaging was more accurate in ruling out coronary disease (26 of 29 patients, 90%) than ECG stress testing (19 of 29 patients, 65%) (P < 0.05). In patients with previous myocardial infarction, thallium imaging alone or in combination with ECG stress testing was not significantly more sensitive than ECG stress testing alone.

Coronary Circulation↗
PubMed1979

Radionuclide assessment of aortocoronary bypass surgery.

Rest and exercise thallium 201 myocardial scintigraphy and multiple gated radionuclide angiography were correlated with the results of clinical status, exercise electrocardiography, coronary arteriography, and contrast left ventriculography in a series of 12 prospectively studied consecutive patients before and after aortocoronary bypass operation. Patients were divided into two groups based on a comparison between preoperative and postoperative 201T1 scintigrams. Group 1 (6 patients) demonstrated improved or normal postoperative perfusion scintigrams and excellent correlation between the site of a patent graft and the improvement in myocardial perfusion on the postoperative exercise scintigrams. Regional wall motion remained normal in 3 patients and improved in 3. In Group 2 (6 patients) the postoperative 201T1 scintigrams were unchanged or worse. Each patient demonstrated graft occlusion, graft stenosis, distal disease, or a perioperative myocardial infarction. No improvement in regional wall motion occurred in 4 of these 6 patients. Neither the symptomatic response to aortocoronary bypass operation nor the response to exercise testing successfully predicted graft patency.

Adult↗
PubMed1979

Effects of ascorbic acid and sodium ascorbate on cyclic nucleotide metabolism in human lymphocytes.

L-ascorbic acid (LAA) augmented cGMP many-fold in highly purified human peripheral blood lymphocytes. The cGMP response occurred within 10 sec and persisted for at least 60 min. D-ascorbic acid (DAA) and dehydroascorbic acid (DHAA) were also equally active in enhancing cGMP concentrations but metabolic precursors of ascorbic acid and other inorganic acids did not increase cGMP levels. Determination of the amount of DHAA contaminating the LAA precluded the possibility that it was solely responsible for the enhanced cGMP levels. The sodium or calcium salts of ascorbic acid did not increase cGMP concentrations. If these neutralized preparations were acidified, increased cGMP concentrations were then noted. In broken cell preparations, LAA, DAA, and DHAA and to a lesser extent sodium ascorbate (NaA) enhanced guanylate cyclase activity while neither inhibited cAMP or cGMP phosphodiesterase (PDE) activity. The possible role of H2O2, fatty acid liberation, prostaglandin production, oxidizing-reducing agents, and free radical formation in mediating the effects of ascorbic acid on cGMP levels were evaluated, but none of these potential mechanisms were definitively proven to be a required intermediary for the cGMP enhancing activity of ascorbic acid. LAA, DHAA or NaA did not induce lymphocyte transformation or modulate lectin-induced mitogenesis.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1979

Two cases of complicated intestinal lipoma. Review of small intestinal lipomas.

Two cases of solitary small intestinal lipoma are presented. One occured in the duodenum as a submucosal pedunculated polyp with a bleeding ulcerated surface. This was diagnosed by means of the fiberoptic duodenoscope (Olympus D1G2). The second involved a large massive submucosal lipoma which formed the leading edge of an intussusception resulting in small bowel obstruction. A brief review of the pathology, complications, symptoms, radiographic diagnosis and treatment of small intestinal lipomas is given.

Aged↗
PubMed1978

Immune reactivity of cells from long-term rat renal allograft survivors.

Lewis rats receiving an LBN kidney allograft demonstrate no signs of rejection if they are pretreated with donor spleen cells and antiserum reactive with the donor alloantigen. We examined the cellular reactivity of long-term kidney allograft survivors. Normal proliferative and cytolytic responses were obtained with spleen cells from long-term survivors, in marked contrast to the diminished responses of cells from neonatally tolerant rats or the heightened cytolytic response of cells from rats that had rejected a renal allograft. Serum from long-term renal allograft survivors as well as serum obtained from rats at the time of transplantation did not suppress proliferative or cytolytic responses of normal cells. The results of this study suggest that long-term renal allograft survivors possess the precursors of those cells which are responsible for proliferative and cytolytic responses in mixed leukocyte cultures, but that they have not been sensitized to their renal allograft.

Animals↗
PubMed1978

Myocardial infarction with patent coronary arteries.

A 62-year-old patient suffered an acute anterior wall infarction as documented by clinical, electrocardiographic and enzymatic evidence. His ECG returned to a near normal pattern on the 5th day. The next day the patient died suddenly. Post mortem examination revealed a transmural anterior infarction with a mural thrombus, and a fresh thrombus in the left renal artery, but the coronary arteries were patient with only slight arteriosclerotic changes. We assume that a coronary thrombus might have been the cause of the infarction, with subsequent lysis. Such early lysis (6 days after the infarction) has not yet been demonstrated in earlier reports.

Acute Disease↗