Metal Complexation in Xylem Fluid : II. THEORETICAL EQUILIBRIUM MODEL AND COMPUTATIONAL COMPUTER PROGRAM

Theoretical considerations of metal complex formation in aqueous solutions were used to develop a computer program (CHELATE) to calculate all equilibrium species (free metal ions, metal complexes, etc.) in any user-defined system, such as xylem fluid. Mass-balance equations were established to describe each free metal ion and each free ligand concentration as a function of solution pH, total metal or total ligand, hydrogen-association constants, and the stability constants of known metal complexes. A default data base can be altered by the user to define any desired system covered by the stored equilibrium data. The program can currently handle nine metal ions, 35 ligands, and 500 complex species. The validity of the program was confirmed by using experimental test systems in which free-metal ion activity measurements were made with ion-selective electrodes.     

Rapid return of cyclo-oxygenase active platelets in dogs after a single oral dose of aspirin

A single dose of oral aspirin in human subjects inhibits the aggregation response of platelets to arachidonate and other agents for approximately one week after ingestion. In the present study we have evaluated the rate at which cyclo-oxygenase active platelets return to the circulation in humans and dogs and compared the response curves obtained to improvements in cyclo-oxygenase activity produced by the aspirin platelets. After a single dose of aspirin, dog platelet function was compromised for several days. Normal responses to arachidonate and other aggregating agents were restored six days after aspirin, and the pattern of recovery was the same for dogs and human subjects. However, cyclo-oxygenase active platelets returned to the circulation in dogs more rapidly than in humans and chemical competence was restored in both species well before correction of the defective response to aggregating agents. The delay of 1-3 days before return of significant numbers of cyclo-oxygenase active platelets most likely reflects acetylation of bone marrow megakaryocytes by the drug. More rapid return of chemically competent cells in dogs than humans probably relates to the more rapid turnover and shorter life span of canine platelets. The basis for the discrepancy in return of chemical integrity compared to functional activity after aspirin in vivo compared to simultaneous correction of chemistry and function when 10% normal platelets are added to aspirin platelets in vitro remains unresolved.     

Age-dependent changes in the response of the lamb ductus arteriosus to oxygen and ibuprofen.

Circular strips of ductus arteriosus from lambs of gestational age between 90 and 144 days (term 147 days) were studied in vitro at low (8--16 torr (1 torr = 133.322 Pa)) and high (426--622 torr) PO2. Potassium- and oxygen-induced contractions increased with the gestational age and attained a maximum at term. At low PO2, ibuprofen, a blocker of prostaglandin synthesis, produced a dose-dependent contraction of the ductus at all ages and enhanced the potassium-induced contraction of the immature ductus (90--124 days). Both effects were relatively greater in the 103- to 107-day gestational group. At that age, ibuprofen also potentiated the oxygen-induced contraction. These findings, while confirming that a prostaglandin is involved in ductus patency, indicate that the prostaglandin-relaxing mechanism becomes functional at an early stage of gestation and reaches maximal activity before term. The existence of an active, prostaglandin-mediated relaxation in the preterm ductus may account, in part, for the reduced responsiveness of the vessel to oxygen. It is confirmed that ibuprofen and other nonsteroidal antiinflammatory drugs are well suited for the management of the premature infant with patent ductus arteriosus.     

Cell wall characteristics of Pseudomonas aeruginosa and its carbenicillin-induced L-form.

L-forms of Pseudomonas aeruginosa were induced and cultured on a medium supplemented with carbenicillin. Morphological studies of the passaged variant revealed the presence of a triple-layered cell wall similar to that found in the parent species. Furthermore, the L-form was found to be more susceptible to gentamicin, kanamycin, tetracycline and colistin sulphate. Chemical analysis of the lipopolysaccharide fraction showed a difference in phosphorus content, and changes in cell wall envelope fatty acid content were also exhibited. It is suggested that these differences may influence the transport of certain antibiotics through the cell wall.     

Rapid separation of low molecular weight solutes from liposomes without dilution

Liposomes can be separated from low molecular weight solutes on minicolumns of Sephadex G-50 made from the barrels of 1- or 5-ml plastic syringes. Excess fluid is first removed from the Sephadex beads by centrifugation and a mixture of liposomal entrapped and free solute is applied to the column bed. The centrifugation is repeated forcing the liposomal material through the column into a test tube while the free solute is quantitatively retained in the Sephadex. The procedure is applicable to a variety of solutes and 92 to 100% recovery is achieved for both charged and neutral liposomes. This technique has advantages over other methods for separating extraliposomal solutes from liposomes. Numerous samples can be processed simultaneously within minutes with no dilution of the liposomal preparation. Nonentrapped solute within the Sephadex can be easily recovered in a small volume of water or buffer.     

Amylase polymorphism: studies of sera and duodenal aspirates in normal individuals and in cystic fibrosis.

Prior genetic studies of the human pancreatic amylase (Amy2) locus have been directed principally to the electrophoretic analysis of serum and urine, on the assumption that these fluids receive negligible contributions from the salivary (Amy 1) locus. In support of that assumption was the observation that the isozyme bands were lacking in patients with cystic fibrosis and in a postpancreatectomy patient. We have examined the sera of 97 patients having cystic fibrosis and find normal levels of serum amylase. On electrophoresis, three-quarters of the cystic fibrosis patients have a pattern (F-pattern) not observed in normal sera. The pattern is characterized by the absence of Pa 1. Comparative electrophoresis and mixing experiments indicate that the F-pattern is of salivary origin and is unmasked in cystic fibrosis by the absence of a pancreatic contribution. The normal serum pattern is considered to be an admixture of salivary and pancreatic amylase. On the assumption that duodenal fluids might more closely reflect the pancreatic (Amy 2) locus, electrophoretic studies were performed on 148 normal individuals and 37 individuals with cystic fibrosis. Electrophoretic phenotypes in duodenal aspirates are more complex than previously reported in studies of urine and serum; presumably because of the higher concentrations of amylase in the aspirates. Comparative electrophoresis and mixing experiments indicate that the phenotypes observed in duodenal aspirates also reflect admixture of pancreatic and salivary amylase. This recognition of pancreatic and salivary admixture in sera fortunately does not alter our prior understanding of the genetics of the Amy 2 polymorphism. The extensive studies which led to the delineation of the Amy 2 polymorphism were essentially based on the presence or absence of a variant band which proves now to be outside the zone of admixture.