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Biomedical subjects

S L Weiss

Publications and source records attributed to S L Weiss.

At least 19 recordsLinked to original sources
PubMed2005

Prestorage leukoreduction and low-temperature filtration reduce hemolysis of stored red cell concentrates.

BACKGROUND: Universal prestorage leukoreduction in Canada created the perception that stored red cells (RBCs) are more hemolyzed than their unfiltered predecessors. A pool-split design tested the effects of leukoreduction on hemolysis of stored RBCs. STUDY DESIGN AND METHODS: Two ABO-matched units were pooled, divided, and then processed into leukoreduced (LR) and nonleukoreduced (NLR) units with the Pall LT-WB or RC-PL systems and sampled during standard processing and storage for testing of sterility, counts, hemolysis, and osmotic fragility. RESULTS: Room temperature (RT) filtration of 10 pairs of LT-WB-LR and -NLR units showed significantly different percentage of hemolysis (0.39%) and osmotic fragility (0.643%) at 42 days. Cold-stored and -filtered units (2 days at 4 degrees C before processing) were less hemolyzed, but showed a similar proportional decrease of hemolysis in LR units (0.13% vs. 0.25% at 42 days). RBCs from RC-PL systems showed the lowest hemolysis although there was a filtration effect (0.05% vs. 0.12%, 42 days). Osmotic fragility paralleled hemolysis. Segment samples gave inaccurate results. Two-day prefiltration cold storage reduced hemolysis from 0.36 to 0.07 percent (42 days, p < 0.001). RT-LR hemolysis became significantly higher by Day 10 and 4 degrees C LR by Day 12. NLR units showed hemolysis by Day 7. LR units filtered cold were less hemolyzed (p < 0.05) than RT-LR but osmotic fragility was unchanged. CONCLUSIONS: LR-RBCs prepared by any of three methods (LT-WB, RT or cold; RC-PL), filtered at 4 degrees C, were less hemolyzed during storage than nonfiltered concentrates: 4 degrees C leukoreduction is beneficial for RBCs and does not cause hemolysis or enhance fragility.

Blood Preservation↗
PubMed2004

Activation of aggressive behavior by progesterone and testosterone in male tree lizards, Urosaurus ornatus.

Testosterone is usually thought to be the major sex steroid regulating adult male territorial aggression in vertebrates. However, recent evidence has suggested a role for progesterone, as well as testosterone, in the organization of the two male reproductive phenotypes of tree lizards (Urosaurus ornatus), which differ in adult levels of territorial behavior. In the present experiment we tested whether progesterone and testosterone could also play an activational role in the expression of adult aggressive behavior. We subjected post-reproductive male tree lizards to the following treatments: sham surgery, castration, castration with progesterone supplementation, and castration with testosterone supplementation. We measured several different dimensions of aggressive behavior. Overall in these post-reproductive animals, the level of aggression from lowest to highest was: castrates, shams, progesterone-treated, and testosterone-treated. Although testosterone appears to be the more potent regulator of aggressive behavior, progesterone enhanced several measures of aggression suggesting that it could play a role in natural regulation of aggressive behavior. This initial study used very high levels of progesterone (similar to or above those experienced by hatchlings) to maximize the probability of detecting an effect. Further studies are needed to determine if natural adult progesterone levels are sufficiently high to influence aggressive behavior.

Aggression↗
PubMed2002

Effect of captivity in semi-natural enclosures on the reproductive endocrinology of female lizards.

Long-term captivity can result in abnormal behavior and physiology in many vertebrates. Here, we examine whether semi-natural, outdoor captive environments can offer a compromise, allowing much of the experimental control afforded by captivity, while providing the environmental conditions essential for normal behavior and physiology. We first determined plasma concentration of the sex steroid hormones progesterone, testosterone, and estradiol of free-ranging female striped plateau lizards (Sceloporus virgatus) throughout the reproductive season, and second, compared the results to those from conspecific females maintained in semi-natural outdoor enclosures. Among free-ranging females, levels of progesterone and estradiol were elevated during vitellogenesis, with an apparent surge in progesterone and testosterone occurring in association with ovulation. Following ovulation, estradiol fell to non-reproductive levels while progesterone remained elevated during the month-long period of gravidity. Long-term captivity in outdoor enclosures did not significantly affect progesterone or estradiol levels at any stage of the reproductive cycle, and did not affect testosterone levels during normal ovarian development and gravidity. However, (1) females with delayed oviposition in captivity had lower testosterone levels than free-ranging females with normal oviposition, and (2) when all females sampled were post-reproductive, captive females continued to have lower testosterone levels than free-ranging females. Thus, the endocrine response to captivity may be greater among post-reproductive females than among reproductive females. Our results are in marked contrast to many studies that show captivity can dramatically impair reproduction of female vertebrates.

Animals↗
PubMed1998

UGA codon position affects the efficiency of selenocysteine incorporation into glutathione peroxidase-1.

A UGA codon and a selenocysteine insertion sequence in the 3'-untranslated region are the only established mRNA elements necessary for selenocysteine (Sec or U) incorporation during translation. These two elements, however, do not universally confer efficient Sec incorporation. The objective of this study was to systematically examine the effect of UGA codon position on efficiency of Sec insertion. In a glutathione peroxidase-1 (F-GPX1) expression vector, the UGA at the native position (U47) was mutated to a cysteine codon, and codons for Ser-7, Ser-12, Ser-18, Ser-29, Ser-45, Ser-93, Cys-154, Val-172, Ser-178, and Ser-195 were individually mutated to UGA and transiently expressed in COS-7 cells. 75Se incorporation at the 11 positions was 31, 72, 54, 105, 90, 100, 146, 135, 13, 11, and 43%, respectively, of 75Se incorporation at U47, suggesting that Sec is more efficiently incorporated at UGA codons positioned in the middle of the coding region rather than close to the 5' or 3' ends. Ribonuclease protection showed that these differences were not due to differences in mRNA level. When the green fluorescence protein (GFP) coding region was placed in-frame at the 5' or 3' ends of the coding region in F-GPX1 to produce chimeric 50-51-kDa GFP/GPX1 proteins, Sec incorporation at UGA codons, formerly close to the 5' or 3' ends, was increased to levels comparable to the UGA at U47. Insertion of GFP after the UAA-stop was just as effective in increasing Sec insertion efficiency as GFP inserted before the stop. These studies used a recombinant expression model that incorporated Sec at non-native UGA codons at rates equal to those of endogenous glutathione peroxidase-1 and showed that the efficiency of Sec incorporation can be modulated by UGA position; Sec incorporation at high efficiency appears to require that the UGA be >21 nucleotides from the AUG-start and >204 nucleotides from the selenocysteine insertion sequence element.

3' Untranslated Regions↗
PubMed1998

A method for assaying intestinal brush-border sucrase in an intact intestinal preparation.

Small intestinal brush-border hydrolases usually are assayed in intestinal mucosal homogenates resuspended in solutions of unphysiological ionic composition. Thus, extrapolation of measured Vmax values (maximal reaction rates at high substrate concentrations) to in vivo conditions, hence comparison with physiological substrate loads, is uncertain. We therefore have developed a sucrase assay in an intact preparation of mouse small intestine, an everted intestinal sleeve incubated in a physiological Ringer's solution. As in homogenate studies, sucrase is assayed by glucose production measured colorimetrically, but uptake of liberated glucose into the intestinal sleeve is prevented by the transport inhibitor phlorizin. The coefficient of variation of Vmax is 16% for sleeves from the same mouse and 8% for mean values from different mice. Sleeve sucrase activity is abolished by the inhibitor castanospermine. Activity in sleeves and homogenates proves to be the same when measured under identical solution conditions, but variations in assay conditions cause large activity changes from values measured in physiological solutions.

Animals↗
PubMed1998

Evolutionary matches of enzyme and transporter capacities to dietary substrate loads in the intestinal brush border.

Safety factors of enzymes and transporters are defined as the ratio of Vmax (maximal reaction rates at high substrate concentrations) to the reaction rate under actual physiological conditions. Although corresponding safety factors have been measured for macroscopic biological structures and for human-engineered structures, safety factors have been little studied at the molecular level. Some evolutionary considerations suggest that safety factors should be modestly in excess of 1.0 ("enough but not too much") and should tend to be similar for the various steps of a pathway consisting of two or more elements arranged in series. Hence we used a preparation of intact mouse small intestine to measure Vmax values (capacities) of brush-border sucrase (yielding glucose plus fructose) and of the brush-border glucose transporter, for comparison with each other and with dietary sucrose loads. Load was manipulated by varying dietary sucrose level or by studying lactating mice with increased energy requirements. Capacities both of sucrase and the glucose transporter increased with sucrose load (i.e., both proteins are inducible) and remained approximately matched to each other except on a carbohydrate-free diet. Their safety factors decreased from ca. 2.7 at low load to 1.0 at high load. Thus, neither sucrase nor the glucose transporter is the rate-limiting step for sucrose digestion; both steps are equally limiting. The modest safety factors and matched capacities must be genetically programmed through natural selection, with benefits of excess capacities being balanced against costs of biosynthetic energy and limited membrane space.

Adaptation, Physiological↗
PubMed1998

Cis-acting elements are required for selenium regulation of glutathione peroxidase-1 mRNA levels.

Classical glutathione peroxidase (GPX1) mRNA levels can decrease to less than 10% in selenium (Se)-deficient rat liver. The cis-acting nucleic acid sequence requirements for Se regulation of GPX1 mRNA levels were studied by transfecting Chinese hamster ovary (CHO) cells with GPX1 DNA constructs in which specific regions of the GPX1 gene were mutated, deleted, or replaced by comparable regions from unregulated genes such as phospholipid hydroperoxide glutathione peroxidase (GPX4). For each construct, stable transfectants were pooled two weeks after transfection, divided into Se-deficient (2 nM Se) or Se-adequate (200 nM Se) medium, and grown for an additional four days. On day of harvest, Se-deficient GPX1 and GPX4 activities averaged 13 +/- 2% and 15 +/- 2% of Se adequate levels, confirming that cellular Se status was dramatically altered by Se supplementation. RNA was isolated from replicate plates of cells and transfected mRNA levels were specifically determined by RNase protection assay. Analysis of chimeric GPX1/GPX4 constructs showed that the GPX4 3'-UTR can completely replace the GPX1 3'-UTR in Se regulation of GPX1 mRNA. We did not find any GPX1 coding regions that could be replaced by the corresponding GPX4 coding regions without diminishing or eliminating Se regulation of the transfected GPX1 mRNA. Further analysis of the GPX1 coding region demonstrated that the GPX1 Sec codon (UGA) and the GPX1 intron sequences are required for full Se regulation of transfected GPX1 mRNA levels. Mutations that moved the GPX1 Sec codon to three different positions within the GPX1 coding region suggest that the mechanism for Se regulation of GPX1 mRNA requires a Sec codon within exon 1. Lastly, we found that addition of the GPX1 3'-UTR to beta-globin mRNA can convey significant Se regulation to beta-globin mRNA levels when a UGA codon is placed within exon 1. We conclude that Se regulation of GPX1 mRNA requires a functional selenocysteine insertion sequence (SECIS) in the 3'-UTR and a Sec codon followed by an intron.

Animals↗
PubMed1997

Selenium regulation of classical glutathione peroxidase expression requires the 3' untranslated region in Chinese hamster ovary cells.

Classical glutathione peroxidase (GPX) mRNA levels fall dramatically in selenium (Se)-deficient animals, but it is not known whether this mechanism is related to the mRNA 3' untranslated region (3'UTR) sequences that have been shown to direct Se incorporation. In this study, we used recombinant GPX constructs to investigate the role of the GPX 3'UTR in Se regulation of GPX mRNA levels in Chinese hamster ovary (CHO) cells. The CHO cells were transfected with GPX (pRc/GPX), GPX lacking the 3'UTR (pRc/Delta3'UTR) or the pRc/CMV vector alone, and GPX activity and GPX mRNA levels were determined in stable transfectants grown in low Se basal medium with a range of added Se concentrations. We identified two pRc/GPX transfectants with significantly elevated GPX activity levels compared with pRc/CMV transfectants. The elevated GPX expression did not dramatically shift the amount of Se that was sufficient for GPX activity to reach the Se-adequate plateau level (100 nmol/L added Se). As expected, GPX activity was not significantly different when pRc/Delta3'UTR transfectants were compared with pRc/CMV control transfectants. Among the wild type and transfected CHO cells, Se-deficient GPX activity levels averaged 35 +/- 5% of Se-adequate levels. Selenium-deficient levels of endogenous GPX mRNA as well as recombinant pRc/GPX mRNA averaged 54-58% of Se-adequate levels; 3-4 nmol/L added Se was sufficient for maximal GPX mRNA levels. In contrast, pRc/Delta3'UTR mRNA levels in the unsupplemented cells remained at Se-adequate levels and showed no distinct Se regulation. These studies demonstrate that the GPX 3'UTR is necessary for Se regulation of GPX mRNA levels in addition to its role in Se incorporation.

Analysis of Variance↗
PubMed1997

Selenium regulation of selenium-dependent glutathione peroxidases in animals and transfected CHO cells.

Glutathione peroxidase (GPX1) was the first identified selenium-dependent enzyme, and this enzyme has been most useful as a biochemical indicator of selenium (Se) status and the parameter of choice for determining Se requirements. We have continued to study Se regulation of GPX1 to better understand the underlying mechanism and to gain insight into how cells themselves regulate nutrient status. In progressive Se deficiency in rats, GPX1 activity, protein and mRNA all decrease in a dramatic, coordinated and exponential fashion such that Se-deficient GPX1 mRNA levels are 6-15% of Se-adequate levels. mRNA levels for other Se-dependent proteins are far less decreased in the same animals. The mRNA levels for a second Se-dependent peroxidase, phospholipid hydroperoxide glutathione peroxidase (GPX4), are little affected by Se deficiency, demonstrating that Se regulation of GPX1 is unique. Se regulation of GPX1 activity in growing male and female rats shows that the Se requirement is 100 ng/g diet, based on liver GPX1 activity; use of GPX1 mRNA as the parameter indicates that the Se requirement is nearer to 50 ng Se/g diet in both male and female rats. This approach will readily detect an altered dietary Se requirement, as shown by the incremental increases in dietary Se requirement by 150, 100 or 50 ng Se/g diet in Se-deficient rat pups repleted with Se for 3, 7 or 14 d, respectively. Studies with CHO cells stably transfected with recombinant GPX1 also show that overexpression of GPX1 does not alter the minimum level of media Se necessary for Se-adequate levels of GPX1 activity or mRNA. We hypothesize that classical GPX1 has an integral biological role in the mechanism used by cells to regulate Se status, making GPX1 an especially useful and effective parameter for determining Se requirements in animals.

Animals↗
PubMed1996

The selenium requirement for glutathione peroxidase mRNA level is half of the selenium requirement for glutathione peroxidase activity in female rats.

To determine critically the selenium (Se) requirement for weanling female rats, we used glutathione peroxidase (GSH: H2O2 oxidoreductase, EC 1.11.1.9) (GPX) mRNA and a number of other parameters to assess Se status. Rats were fed a basal torulayeast diet (0.007 micrograms Se/g) supplemented with Se as Na2SeO3 in graded levels from 0 to 0.3 micrograms Se/g diet for 32 d (3 rats/group). Selenium supplementation had no effect on growth, showing that the Se requirement for growth is less than 0.007 micrograms Se/g diet, whereas other parameters showed significant increases with Se supplementation. In rats fed the Se-deficient basal diet, liver Se concentration was 4 +/- 0%, plasma GPX activity was 8 +/- 1%, erythrocyte GPX activity was 40 +/- 3%, liver GPX activity was 2 +/- 1%, and liver GPX mRNA levels were 11-17% of the levels in rats fed 0.1 micrograms Se/g diet. Liver Se concentration and GPX activity in plasma, erythrocytes and liver all reached a plateau breakpoint at or near 0.1 micrograms Se/g diet, indicating that the dietary Se requirement for maximal GPX activity in growing female rats is 0.1 micrograms Se/g diet. Liver GPX mRNA levels reached the plateau breakpoint at 0.05 micrograms Se/g diet, showing that the minimum dietary Se requirement for maximal GPX mRNA levels in female rats is half of the Se requirement for maximal GPX activity. This experiment demonstrates that GPX mRNA can be used to determine the dietary Se requirement; the gap between the dietary Se necessary for maximal GPX mRNA and that for maximal GPX activity may represent an evolutionarily derived biological margin of safety.

Analysis of Variance↗
PubMed1994

Patient and physician analytic goals for self-monitoring blood glucose instruments.

The study's objective was to determine the maximum analytical error that is allowable in portable whole blood glucose meters. Interviews were conducted to derive personal reference values and significant deviations from these values for the limit of hypoglycemia, the limit of hyperglycemia, and the upper and lower limits of acceptable blood glucose for physicians and patients with diabetes at the Park Nicollet Medical Center, Minneapolis, Minnesota. Fifty patients with diabetes (30 type I and 20 type II), and 43 physicians (14 endocrinologists, 14 family practitioners, and 15 general internists) were enrolled in the study. The results showed no significant differences between type I and type II diabetic patient responses. Nor were there significant differences among family practitioner, internist, and endocrinologist responses for any of the parameters (the limit of hypoglycemia, the limit of hyperglycemia, the upper and lower limits of acceptable blood glucose for the patient, and the corresponding allowable coefficients of variation at each of these glucose levels). There were significant differences when patients were compared to physicians. Physicians require the highest degree of precision at the limit of hyperglycemia (8.4 +/- 0.28 mmol/L [150.8 +/- 5.1 mg/dL]) with a maximum allowable coefficient of variation (CV) of 7%, a CV significantly lower than that of the patients (CV = 10%). Patients require the highest precision for glucose concentration around the lower acceptable limit (4.7 +/- .013 mmol/L [84.1 +/- 2.5 mg/dL]), with an allowable CV of 8%, a CV significantly lower than that of the physicians (CV = 14%). The authors conclude that the accuracy required by patients and physicians at normal and higher glucose concentrations is achievable by currently available meters. Manufacturers should ascertain that glucose measurements are optimally accurate at glucose levels of 4.7 mmol/L (84.1 mg/dL) and have CVs no higher than 7%.

Adult↗
PubMed1992

CT in upper gastrointestinal tract perforations secondary to peptic ulcer disease.

Computed tomographic (CT) scans of 11 patients with perforations of the stomach or duodenum were reviewed to determine the variety and relative conspicuity of findings. Five patients had de novo presentation due to perforation of peptic ulcers, two had perforations at ulcer repair sites, and the remaining four patients had ulcer perforations following unrelated surgery. CT allowed recognition of at least one component of bowel perforation, such as extra-gastrointestinal gas and/or contrast, in most patients. In only three patients (27%), however, could these findings be specifically related to a perforation of the stomach or duodenum from the CT scans alone.

Adult↗
PubMed1988

Comparative imaging of gallbladder cancer.

We reviewed various imaging approaches in 22 patients with gallbladder cancer. Nineteen had had ultrasonography and nine computed tomography performed. A gallbladder mass or diffuse wall thickening was seen by ultrasonography in 42% and computed tomography in 33% of patients. A significant number of patients had no gallbladder wall abnormality detected by ultrasonography (37%) or computed tomography (56%). Performing both ultrasonography and computed tomography improved the diagnostic rate; in this subgroup the detection rate was 51%. Cholelithiasis, dilated biliary ducts, the liver metastases were associated findings. Percutaneous cholangiography in jaundiced patients revealed the level of bile duct occlusion and often suggested the diagnosis. Radionuclide hepatobiliary imaging simply revealed non-visualization of the gallbladder.

Adult↗
PubMed1988

Stage IB cervical carcinoma: comparison of clinical, MR, and pathologic staging.

In patients with stage IB cervical carcinoma (carcinoma confined to the cervix), accurate staging is essential in order to determine the best treatment strategy--that is, whether to use surgery alone or surgery in combination with pre- or postsurgical radiation therapy. Currently, decisions regarding the management of patients are made on the basis of clinical staging that has an error rate of 34-39% (when surgical staging is used as the standard). To investigate the value of MR in staging patients with IB cervical cancer, we performed prospective MR examinations in 27 patients who had cervical carcinoma. Of these, 10 were clinically staged as having IB cervical carcinoma and underwent radical hysterectomy, providing specimens for pathologic correlation. In six of these 10 patients, the extent of disease had been underestimated during clinical examination under anesthesia. These six patients would have received radiation therapy before surgery had the MR information been used at the treatment-planning stage. MR imaging correlated better with surgical pathology than did clinical examination under anesthesia in determining the location and extent of tumor. MR imaging should be used in conjunction with clinical staging to determine appropriate therapy in patients with stage IB cervical carcinoma.

Adult↗
PubMed1986

Mirizzi syndrome simulating a tumor by ERC.

ERC was initially performed on a patient with right upper quadrant pain and jaundice. The filling defect in the CHD was felt to be a tumor. A correct preoperative diagnosis of Mirizzi's syndrome was made by CT.

Aged↗
PubMed1986

Sonographic examination of the abdominal aorta through the left flank: a prospective study.

Ultrasonographic evaluation of the abdominal aorta is most often done with the patient in the supine position. The right lateral decubitus position, which views the aorta through the left flank has, until now, been considered unsatisfactory for aortic evaluation. One hundred consecutive patients were prospectively examined for visualization of the aorta both through the left flank and the anterior abdomen. Twenty-one patients were then comparatively examined from the right coronal and left coronal approach. These studies showed that the aorta was clearly visualized using the left flank approach in the majority of patients (96 per cent). The combined approach yielded 99 per cent satisfactory visualization, and in a few select cases (13 per cent) the left flank was actually superior. The left flank approach was superior when directly compared with the right flank in 42 per cent of patients and comparable in 48 per cent. The right flank approach was superior in only 10 per cent.

Adult↗