Platelet-derived growth factor is a chemoattractant for vascular smooth muscle cells

In previous experiments (Grotendorst et al, 1981), we showed that platelet-derived growth factor promotes the migration of smooth muscle cells in vitro. Using a "checkerboard" analysis, we now establish that platelet-derived growth factor (PDGF) acts as a true chemoattractant for cultured aortic smooth muscle cells. Other growth factors such as epidermal growth factor, fibroblast growth factor, and insulin are not chemoattractants. The chemotactic response occurs before the initiation of DNA synthesis and is not affected by inhibition of DNA synthesis. Chemotaxis occurs at levels of PDGF lower than required for mitogenesis. RNA and protein synthesis are required for the chemotactic response. As found previously in bacteria and leucocytes, we find that methylation reactions are required for the chemotactic response. The possibility is discussed that PDGF acts in vivo at sites of vascular injury to attract smooth muscle cells from the medial layer to the luminal surface, and is involved in the early stages of the formation of atherosclerotic plaques.

Phenytoin metabolism in subjects with long and short plasma half-lives

Normal adult men with long and short phenytoin plasma half-lives were given 300-mg oral doses of phenytoin once daily for 15 days. Plasma levels of phenytoin (DPH) and its major metabolite (p-HPPH) were measured during the period of drug administration and for 5 days thereafter. Average steady-state plasma levels of DPH rose to 13.4 micrograms/ml in the long half-life group, compared with 3.6 micrograms/ml in the short half-life group. HPPH levels in the long half-life group were about one half of those observed in the short half-life group. The DPH/HPPH ratios in plasma specimens showed excellent correlation with the plasma half-lives of DPH and average steady-state levels, suggesting that this ratio could provide guidance in the selection of optimum dosage regimens for problem patients.

p-Nitrophenylglycosides as substrates for measurement of amylase in serum and urine

Pantrak E.K. (endpoint and kinetic) Amylase reagent (Calbiochem-Behring) is the first commercially available alpha-amylase reagent in which p-nitrophenyl-d-glycosides are used as the substrate. We describe the effect of reagent composition on reagent performance. The reagent performance compares well with that of Amylochrome reagent (Hoffmann-La Roche), Du Pont aca, and Beckman D.S. amylase reagents in assays of sera and urines. We detected no interference from increased concentrations of glucose or pyruvate in the sample. The reagent can be used in either a manual fixed-time or an automatable kinetic assay.

p-Nitrophenylglycosides as substrates for measurement of amylase in serum and urine

Pantrak E.K. (endpoint and kinetic) Amylase reagent (Calbiochem-Behring) is the first commercially available alpha-amylase reagent in which p-nitrophenyl-d-glycosides are used as the substrate. We describe the effect of reagent composition on reagent performance. The reagent performance compares well with that of Amylochrome reagent (Hoffmann-La Roche), Du Pont aca, and Beckman D.S. amylase reagents in assays of sera and urines. We detected no interference from increased concentrations of glucose or pyruvate in the sample. The reagent can be used in either a manual fixed-time or an automatable kinetic assay.

Pulsed dye laser with grating and etalon in a symmetric arrangement

Further improvements have been made to the grazing-incidence pulsed dye laser. Criteria have been established for inserting the intracavity etalon and for selecting the optimal blazed grating and its orders at grazing incidence. A new design is presented in which the grating and the etalon are arranged symmetrically. Single-mode operation and an output linewidth of the order of a few hundred megahertz (below 0.006 A) have been obtained.

Symptomatic relapse after oral vancomycin therapy of antibiotic-associated pseudomembranous colitis

Twenty patients with antimicrobiol-associated diarrhea had a symptomatic relapse after oral vancomycin therapy. All patients had stool examinations which implicated C. difficile as the causative agent, and 16 had pseudomembranous colitis. Clinical courses were characterized by resolution of symptoms with recurrence of diarrhea at 4--21 days after vancomycin was discontinued. Studies of stools collected sequentially showed that vancomycin failed to eliminate C. difficile despite susceptibility to this agent with in vitro testing. A review of our records shows the incidence os symptomatic relapse is approximately 14%. This experience emphasizes the importance of adequate follow-up in patients treated with oral vancomycin for antibiotic-associated diarrhea or colitis due to C. difficile.

Choledochitis: a lesson in applied physiology

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Colitis induced by Clostridium difficile

Clostridium difficile has been implicated as the major cause of antibiotic-associated pseudomembranous colitis. The current laboratory diagnostic test of choice is a tissue culture assay that demonstrates the presence of a cytopathic toxin neutralized by antitoxin to Clostridium sordellii. This toxin was found in stools from 42 of 43 patients with antibiotic-associated pseudomembranous colitis and in stools from 12 of 78 patients with antibiotic-associated diarrhea. Specimens from patients with gastrointestinal conditions unrelated to administration of antibiotics and those from healthy controls were uniformly negative. Neutralization of toxin by antitoxin to C. sordellii appears to represent antigenic cross-reactivity, since broth cultures of C. difficile also contain a cytopathic toxin neutralized by this antitoxin. Strains of C. difficile are susceptible to vancomycin, and the initial clinical experience with oral administration of this agent shows promising results.

Antithrombin reactions with alpha- and gamma-thrombins

Human alpha-thrombin with high clotting activity and its proteolyzed derivative gamma-thrombin with virtually no clotting activity reacted in an essentially identical manner with antithrombin. The two enzyme forms bound proflavin with similar constants and showed identical behavior with small substrates. No significant differences were found for the antithrombin reactions (measured by proflavin displacement or active site titration) with respect to kinetics, extent of reaction, or effect of added heparin. The enzyme--antithrombin complexes could not be dissociated with sodium dodecyl sulfate (NaDodSO4) but the NaDodSO4-denatured complexes were dissociated by hydroxylamine treatment. The gamma-thrombin-antithrombin complex has an approximate molecular weight of 75 000 by disc gel electrophoresis as compared with 100 000 for the alpha-complex, consistent with the polypeptide structures of the two proteins. The gamma-thrombin--antithrombin complex did not inhibit clotting catalyzed by alpha-thrombin. In addition, fibrinogen did not affect the reaction of gamma-thrombin with antithrombin or antithrombin--heparin. Thus, the antithrombin and antithrombin--heparin reactions do not involve the fibrinogen recognition sites which are destroyed by proteolytic conversion of alpha-thrombin to the noncoagulant gamma form.

Demonstration of diphtheria toxin receptors on surface membranes from both toxin-sensitive and toxin-resistant species

A detailed binding study of 125I-labeled diphtheria toxin to isolated cell surface membrane-enriched fractions is reported. The study was undertaken to determine if toxin-resistant species exhibit a defet in either the binding step or the transport step of the intoxication process. Surface membrane fractions were obtained from liver and mammary glands of toxin-sensitive species, rabbit and giunea pig, and toxin-resistant species, rat mouse. All membrane fractions exhibited reversible binding of 125I-toxin which was competitively inhibited by unlabeled toxin. Toxin receptors from liver co-purified with plasma membranes and the plasma membrane marker 5'-nucleotidase. One-half saturation of all receptors occurred between 5 x 10(-8) and 1.8 x 10(-7) M. Scatchard plots were nonlinear and concave upwards. Total receptor sites ranged from 3.4 to 16 pmol/mg of membrane protein, tissue differences being more pronounced than difference between sensitive and nonsensitive species. Over 95% of the toxin specific binding was inhibited by removal of divalent cation from the medium or by the inclusion of 1 mM ATP, procedures which have been shown to protect sensitive cells from intoxication by diphtheria toxin. We conclude that the rat and mouse have surface membrane receptors for diphtheria toxin and that the toxin insensitivity of these species results from a defect in or a lack of the transport process.

Microencapsulated charcoal hemoperfusion: a possible therapeutic adjunct in digoxin toxicity

Attempts to remove substantial quantities of digoxin by either peritoneal or hemodialysis, have been unsuccessful due to their low clearance rate. The present study determined the in-vivo clearance rate for digoxin of a single microcapsule of 300 gm of activated charcoal. The clearance rate was 55 +/- 5 ml/min (mean +/- SEM) in the first hour and 48.4 +/- 4 ml/min in the second; these values are approximately five-fold higher than with other dialysis techniques. No evidence of a post-dialysis rebound increase in serum digoxin levels was found, implying that peripheral tissues can rapidly release digoxin to the diminishing serum pool. Preliminary data obtained suggest a beneficial effect on arrhythmias and lowering of the myocardial to serum rate of digoxin after hemoperfusion.

Effect of an adenosine deaminase inhibitor on the uptake and metabolism of arabinosyl adenine (Vidarabine) by intact human erythrocytes

Tritium-labeled vidarabine was incubated with fresh citrated human blood in the absence and presence of an adenosine deaminase inhibitor, co-vidarabine was rapidly deaminated to form ara-Hx with minimal incorporation into the erythrocytes. Ara-HxMP was identified as the major component in the erythrocytic nucleotide pool, together with small amounts of IMP, adenosine nucleotides and traces of arabinosyl nucleotides. Addition of the inhibitor completely protected vidarabine from enzymatic deamination and resulted in much greater accumulation of vidarabine 5'-mono-, di-, and triphosphates in the erythrocytes.

Specificity of thrombin: evidence for selectivity in acylation rather than binding for p-nitrophenyl alpha-amino-p-toluate

The lysyl ester analogue p-nitrophenyl alpha-amino-p-toluate hydrobromide was synthesized, and its reactions with thrombin, trypsin, and plasmin were studied by stopped-flow and conventional methods. Kinetic parameters were compared with those determined for the arginyl ester analogue, p-nitrophenyl p-guanidinobenzoate hydrochloride, with these enzymes. By following nitrophenol release or proflavin absorption changes in the stopped-flow spectrophotometer, the constants Ks (enzyme-substrate binding), k2 (acylation), and k3 (deacylation) were determined. The major findings were: (1) Ks values were similar regardless of the substrate or the enzyme; (2) k3 was approximately the same for the reaction of the lysyl ester analogue with any enzyme; (3) k2 for the lysyl ester analogue was 1100 times greater with trypsin than with thrombin; and (4) k2 with thrombin was 60 times greater for the arginyl than for the lysyl ester analogue. The results suggest that the limited cleavage of lysyl bonds by thrombin is due in part to restricted acylation rather than substrate binding. The active site of thrombin, compared with that of trypsin, appears to have a more stringent requirement for the spatial relationship between the cationic group and the bond cleaved in substrates.