Effects of antiplatelet agents on platelet aggregation induced by platelet--activating factor (PAF) in human whole blood.

Impedance aggregometry was used to evaluate the potency of anti-platelet agents on Platelet Activating Factor (PAF)--induced platelet aggregation in citrated human whole blood. Drugs were tested for ability to inhibit maximum aggregation to PAF. Dose response curves were obtained and the concentration of drug producing 50% inhibition of maximum aggregation (ED50) determined. ED50's (microM) for specific PAF antagonists WEB 2086, Ro 19-3704, FR-900452, BN 52021, L-652,731, CV 3988, WEB 2118 and 48740 RP are: 0.39, 2.4, 4.7, 19.5, 21.0, 5.32, 161.0, 924.0, respectively. ED50's for non-specific PAF antagonists, diltiazem, propranolol, ketotifen, procaine HCL, and lidocaine HCL are: 38.0, 56.0, 250.0, 513.0 and 768.0, respectively. Ibuprofen was inactive at 2300 microM. Results are consistent with concept that there are specific receptors on platelets mediating PAF-induced aggregation in whole blood. Aggregation is inhibited potently by specific and competitive PAF receptor antagonists. Whole blood aggregometry may be a valid method for predicting in vivo activity of PAF antagonists.     

Cancer: improving early detection and prevention. A community practice randomised trial.

OBJECTIVE--To test the impact of physician education and facilitator assisted office system interventions on cancer early detection and preventive services. DESIGN--A randomised trial of two interventions alone and in combination. SETTING AND SUBJECTS--Physicians in 98 ambulatory care practices in the United States. INTERVENTIONS--The education intervention consisted of a day long physician meeting directed at improving knowledge, attitudes, and skills relevant to cancer prevention and early detection. The office system intervention consisted of assistance from a project facilitator in establishing routines for providing needed services. These routines included division of responsibilities for providing services among physicians and their staff and the use of medical record flow sheets. MAIN OUTCOME MEASURES--The proportions of patients provided the cancer prevention and early detection services indicated annually according to the US National Cancer Institute. RESULTS--Based on cross sectional patient surveys, the office system intervention was associated with an increase in mammography, the recommendation to do breast self examination, clinical breast examination, faecal occult blood testing, advice to quit smoking, and the recommendation to decrease dietary fat. Education was associated only with an increase in mammography. Record review for a patient cohort confirmed cross sectional survey findings regarding the office system for mammography and faecal occult blood testing. CONCLUSION--Community practices assisted by a facilitator in the development and implementation of an office system can substantially improve provision of cancer early detection and preventive services.     

小兴凯湖的水生植被及其生态作用

本文论述了小兴凯湖水生植物的种类组成、植被类型、生物量及其在湖泊淤积和渔业中的作用。该湖属老年期湖泊,水生维管束植物共有25科56种,优势种为竹叶眼子菜、荇菜、芦、菰等。植被类型可划分为沉水植被、浮叶植被和挺水植被等三个亚型,包括12个主要植物群丛。全湖水生植物总生物量(湿重)为196380吨;以植物现存量计算,草食性鱼类的年生产力应为78.75吨。由于水生植物大量繁殖,为减缓湖泊的垫平作用,可适量放养草食性鱼类,控制住水生植物的过量繁殖;同时引种一些经济水生植物,压住水中杂草的生长。     

Decisionmaking competence and risk

Mark Wicclair criticizes Allen Buchanan's and my claim that determining an appropriate level of competence (Wicclair substitutes "decisional capacity" for "competence", the import of which I note briefly below) for health care treatment decisionmaking involves balancing respecting a patient's self-determination and protecting his or her well-being. The most important implication of this balancing is that a standard of competence should vary in significant part with the effects for the patient's well-being of accepting his or her choice. Wicclair's criticisms take two main forms. First, he considers and rejects four of the positive reasons we offer in support of a risk-related standard. Second, in rejecting our fourth reason he argues that a risk-related standard leads to faulty competence determinations -- too high a standard in some cases and too low a standard in others. If he is correct, there are no positive reasons for adopting a risk-related standard and there are as well specific reasons not to adopt such a standard in order to avoid mistaken competence determinations. My response will address both sorts of criticisms in turn.     

Assay of inorganic sulfate in biologic fluids by nonsuppressed (single-column) ion chromatography

An assay using nonsuppressed (single-column) anion chromatography was developed to determine the concentration of inorganic sulfate in biologic fluids. A conventional HPLC system with an anion-exchange column and conductimetric detector interfaced with an automatic injector and integrator was used. The mobile phase for the chromatography of urine and serum samples is 4 mM potassium hydrogen phthalate, pH 4.5, and potassium iodide is used as the internal standard. For cerebrospinal fluid samples, the mobile phase is modified by addition of 10% of a 4 mM phthalic acid solution. Results of the HPLC assay were found to correlate well (r = 0.991 and 0.999) with those of two commonly used spectrophotometric methods for urine and serum inorganic sulfate determinations. However, the concentrations determined by ion chromatography were 2.5 to 10% lower, possibly due to less assay interference by other substances following chromatographic separation of sulfate. Anion chromatography using a single-column system is a convenient and relatively inexpensive method with sufficient sensitivity for the determination of inorganic sulfate concentrations in urine, serum, and cerebrospinal fluid.     

Neurohypophysial hormones of the 1-month-old bovine fetus: absence of vasotocin during mammal development

The neurohypophysial hormones of the 1-month-old bovine fetus have been identified by their positions in ion-exchange chromatography and their retention times in high-pressure reverse-phase partition chromatography. Arginine vasopressin and oxytocin have been recognized. The molar ratio vasopressin/oxytocin in neurohypophysis is about 6 in the 1-month-old fetus compared with 4 in the 3-month-old fetus, 2.7 in the 7-month-old fetus and 1 in the adult. Vasotocin is virtually absent even in the early fetus (less than 0.1% of arginine vasopressin). The occurrence of a vasotocin gene expressed in the fetus but silent in the adult appears unlikely.     

Evidence that TET protein functions as a multimer in the inner membrane of Escherichia coli.

The inner membrane TET (TetA) protein, which is involved in Tn10-mediated microbial tetracycline resistance, consists of two domains, alpha and beta, both of which are needed for tetracycline resistance and efflux (M.S. Curiale, L.M. McMurry, and S.B. Levy, J. Bacteriol. 157:211-217, 1984). Since tetracycline-sensitive mutants in one domain can partially complement sensitive mutants in the other domain and since some sensitive mutants show dominance over the wild type, a multimeric structure for TET in the membrane had been suggested. We have studied this possibility by using tetA-phoA gene fusions. We fused all but the last 40 base pairs of the tetA gene with the carboxy terminus of the phoA gene for alkaline phosphatase (PhoA), whose activity requires its dimerization in the periplasm. The tetA-phoA fusion protein was under control of the tetracycline-inducible regulatory system for the tetA gene. Induction led to the synthesis of a 78,000-dalton inner membrane protein. Tetracycline resistance was expressed at reduced levels, consistent with the terminal beta domain deletion. Alkaline phosphatase activity was also present, but at low levels, suggesting that some, but not all, of the fusion proteins had their carboxy-terminal ends in the periplasm. When wild-type or mutant TET proteins were present in the same cell with the fusion protein, the tetracycline resistance level was affected (raised or lowered); however, phosphatase activity was reduced only when TET proteins with intact or near-intact beta domains were present. These findings suggest that TET functions as a multimer and that intact beta domains, on TET molecules in the heterologous multimer, either allow fewer PhoA moieties to project into the periplasm or sterically hinder PhoA moieties from dimerizing.     

Survival of Escherichia coli with and without ColE1::Tn5 after aerosol dispersal in a laboratory and a farm environment.

The survival of a laboratory strain and a naturally occurring fecal strain of Escherichia coli, with and without a Tn5-containing derivative of ColE1, was examined after aerosol dispersal in a laboratory office and a barn under ambient temperature and humidity conditions. Following the release of paired strains, air and diverse types of surfaces were assayed for the test organisms. In both environments, the number of airborne bacteria declined rapidly within the first 2 h. Longer survival was found on surfaces and varied with surface type: recovery was greatest from wood products. Organisms persisted for 1 day in the office and for up to 20 days in the barn. Survival of the fecal strain was better than that of the laboratory strain in both test environments. In general, plasmid-bearing strains fared similarly to their plasmidless parents, but in several comparisons the ColE1::Tn5-containing strain showed enhanced survival. These studies have implications for the present and proposed release of genetically engineered organisms with and without plasmid vectors.     

Measurement of cytosolic free magnesium ion concentration by 19F NMR

Fluorinated derivatives of the chelator o-aminophenol-N,N,O-triacetic acid (APTRA) have been developed, synthesized, and analyzed for use as 19F NMR indicators of free cytosolic magnesium concentration. Magnesium dissociation constants for the 4-fluoro, 5-fluoro, and 4-methyl-5-fluoro species were determined to be 3.1, 0.9, and 0.6 mM, respectively, on the basis of UV absorption measurements at 37 degrees C in 115 mM KCl and 20 mM NaCl, pH 7.1, buffered with 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid-tris-(hydroxymethyl)aminomethane. The corresponding pK values, which reflect protonation of the nitrogen atom, were determined by 19F NMR to be 4.15, 5.45, and 5.55, respectively, so that the chelators are insensitive to pH variations near the normal physiological range. The dissociation constants of these chelators for calcium ions are lower than those for magnesium but roughly 2-3 orders of magnitude above typical basal cytosolic free calcium levels, so that calcium ions will not interfere with the determinations of magnesium levels. 19F NMR studies carried out at 339.7 MHz indicate that magnesium ions are in slow exchange with the 5-fluoro and 4-methyl-5-fluoro APTRA derivatives and in fast exchange with the 4-fluoro APTRA derivative. In contrast, calcium ions were found to be in intermediate to fast exchange with all chelators. The apparent anomaly of higher thermodynamic stability of the APTRA complexes for calcium relative to magnesium but lower kinetic stability (higher k-1 values) for the calcium complexes reflects the very different association rates for the two ions. Thus, the magnesium association rates are 3 orders of magnitude slower than those for calcium ions.(ABSTRACT TRUNCATED AT 250 WORDS)