Antithrombins Wibble and Wobble (T85M/K): archetypal conformational diseases with in vivo latent-transition, thrombosis, and heparin activation

The inherent variability of conformational diseases is demonstrated by two families with different mutations of the same conserved aminoacid in antithrombin. Threonine 85 underlies the opening of the main beta-sheet of the molecule and its replacement, by the polar lysine, in antithrombin Wobble, resulted in a plasma deficiency of antithrombin with an uncharacteristically severe onset of thrombosis at 10 years of age, whereas the replacement of the same residue by a nonpolar methionine, antithrombin Wibble, gave near-normal levels of plasma antithrombin and more typical adult thromboembolic disease. Isolated antithrombin Wibble had a decreased thermal stability (Tm 56.2, normal 57.6 degreesC) but was fully stabilized by the heparin pentasaccharide (Tm 71.8, normal 71.0 degreesC), indicating that the prime abnormality is a laxity in the transition of the main sheet of the molecule from the 5- to 6-stranded form, as was confirmed by the ready conversion of antithrombin Wibble to the 6-stranded latent form on incubation. That this transition can occur in vivo was shown by the finding of nearly 10% of the proband's plasma antithrombin in the latent form and also, surprisingly, of small but definitive amounts of latent antithrombin in normal plasma. The latent transition will be predictably accelerated not only by gross mutations, as with antithrombin Wobble, to give severe episodic thrombosis, but also by milder mutations, as with antithrombin Wibble, to trigger thrombosis in the presence of other predisposing factors, including the conformational stress imposed by the raised body temperatures of fevers. Both antithrombin variants had an exceptional (25-fold) increase in heparin affinity and this, together with an increased inhibitory activity against factor Xa, provides evidence of the direct linkage of A-sheet opening to the conformational basis of heparin binding and activation.     

Low prevalence of coronary artery spasm in patients with normal coronary angiograms and unexplained ventricular fibrillation

AIMS: The aetiology of ventricular fibrillation in patients without identifiable structural heart disease is unknown. Recently, high prevalence of silent ischaemia due to coronary artery spasm has been reported in such patients. However, in at least one report, all patients had non-critical coronary artery lesions. Identification of coronary artery spasm as the underlying aetiology of ventricular fibrillation has important therapeutic implications. METHODS AND RESULTS: We performed ergonovine provocation tests in 18 patients (14 males, and four females; mean age, 36 years) with documented ventricular fibrillation in the absence of identifiable structural heart disease who had undergone aborted sudden death. In group I (n = 7) ergonovine provocation tests were performed at a mean interval of 31 months (range 21-42 months) after the index episode. These patients had already received an implantable cardioverter defibrillator, after failed electrophysiologically guided antiarrhythmic therapy. In group II (n = 11) the ergonovine provocation test was performed prospectively as part of the diagnostic evaluation. All patients were off antiarrhythmic drugs, calcium entry or beta-adrenoceptor blockers at the time of the ergonovine provocation test. Ergonovine was administered intravenously as a bolus injection, beginning with 0.05 mg followed every 3 min by incremental doses up to a cumulative maximum dose of 0.45 mg. Predefined end-points were (1) recording of ischaemic ST segment shifts of > or = 1 mm in at least two corresponding leads of the 12-lead electrocardiogram; (2) induction of ventricular tachycardia or ventricular fibrillation; and (3) administration of a cumulative dose of 0.45 mg. A positive response to ergonovine was seen in only one patient (5%) in group I in whom there developed ST segment elevation without angina and a short burst of rapid ventricular tachycardia. CONCLUSIONS: This study found a low prevalence of coronary artery spasm in patients with aborted sudden death resulting from documented ventricular fibrillation and non-apparent underlying heart disease. All patients had normal coronary angiograms and a negative history for spontaneous episodes of chest pain. The mechanism of arrhythmogenesis in such patients remains largely unknown.     

The influence of the bolus injection rate of propofol on its cardiovascular effects and peak blood concentrations in sheep

The influence of the bolus injection rate of propofol on its cardiovascular effects has not been extensively studied. We therefore examined the influence of the injection rate of i.v. bolus doses of propofol on its acute cardiovascular effects and peak blood concentrations in seven chronically instrumented sheep. Each received i.v. propofol (200 mg) over 2 min (slow injection) and 0.5 min (rapid injection) on separate occasions in random order. The rapid injection was associated with more profound decreases in mean arterial blood pressure than slow injection (35.7% vs 23.7% maximal reductions from baseline, respectively; P = 0.02). There were no significant differences between the injection rates for peak reductions in myocardial contractility, increases in heart rate, or degree of respiratory depression. Concurrently, the rapid injections were associated with significantly higher arterial (26.9 vs 11.9 mg/L) propofol concentrations in a manner consistent with indicator dilution principles. There were no differences in the peak coronary sinus concentrations between the injection rates. We conclude that the rapid injection of propofol in the context of the induction of anesthesia produced significantly higher peak arterial propofol concentrations and suggest that it is these higher concentrations that produced relatively greater reductions in arterial blood pressure from rapid injections. Implications: Propofol is injected into a vein to initiate anesthesia. It can cause a rapid decrease in blood pressure, which may be dangerous to the patient. We examined the effect of rapid and slow injection rates of propofol in sheep and found that rapid injection caused a greater decrease in blood pressure. This was because rapid injection caused higher concentrations of propofol in the blood immediately after the injection. We believe that if the same processes occur in humans, there may be little advantage in injecting propofol rapidly.     

Epidemiology, laboratory detection, and therapy of penicillin-resistant streptococcal infections

The excitatory effect of presynaptically released glutamate is tightly regulated and terminated by high affinity sodium-dependent glutamate transporters. The regulation of the glial glutamate transporter GLT-1 is potentially important in synaptic modulation. Using astroglial cultures prepared from the rat cerebral cortex, we found that the delta-opioid receptor agonist [D-pen2,D-pen5]-enkephalin decreases and glutamate increases the expression of the GLT-1 transporter mRNA. Corresponding changes in the uptake kinetics were found after incubation for 48 h with the respective agonists when glial glutamate uptake was measured in primary astroglial cultures. The data suggest that long-term receptor activation induces alterations in glial glutamate uptake properties.     

Range of motion and complications after postburn heterotopic bone excision about the elbow

OBJECTIVE: To review the results of surgical management of heterotopic ossification about the elbow in burned patients. DESIGN: Retrospective analysis with long-term patient follow-up. MATERIALS AND METHODS: Eleven patients with 16 elbows requiring surgery were admitted between January 1, 1982 and December 31, 1993. A posterior approach to the elbow with release of the encased ulnar nerve +/- anterior transposition and transolecranon osteotomy to access extensive bone formation in the olecranon fossa was employed. Eight patients (11 elbows) were available for long-term follow-up conducted at mean 50 +/- 13 months after surgery. Long-term follow-up consisted of measurement of range of elbow motion, as well as clinical assessment of ulnar nerve function. MAIN RESULTS: For the 11 elbows examined postoperatively, the mean range of motion preoperatively in flexion-extension was 11 degrees +/- 5 degrees compared to 89 degrees +/- 12 degrees postoperatively (p < 0.001). Three patients with poor long-term results had ankylosis of the joint preoperatively. Of four patients with ulnar nerve paresis preoperatively, none had ulnar nerve dysfunction at follow-up. Of 16 elbows operated on, four (25%) had postoperative complications. Two suffered soft-tissue breakdown with hardware exposure requiring abdominal flap closure, one early failure of olecranon fixation, and one late infected hardware. CONCLUSIONS: Surgery for both limited range of motion as well as ulnar nerve compression is effective in cases of heterotopic ossification about the elbows of burned patients. Early operative intervention is indicated in progressive disease, particularly ulnar nerve palsy, if soft-tissue quality is adequate. Complications with 25% of elbows suggest that use of olecranon osteotomy for joint access may warrant review.     

Inhibition of expression of the lysine-rich 30 kDa surface antigen of Entamoeba dispar by the transcription of its antisense RNA

The gene coding for the 30 kDa lysine rich surface antigen (Ed-Ag) that is present on membrane surfaces of Entamoeba dispar trophozoites has been characterized. A specific monoclonal antibody MAb 318-28 prepared against this antigen reacts with all E. dispar strains tested, but not with any of the antigens of E. histolytica. In order to understand the function of this antigen, we constructed two plasmids, pEdA-9 and pEdA-Rev, in which the antigen-coding sequence was introduced into the pEhAct-Neo shuttle vector in the direct and opposite orientation, respectively. When E. dispar trophozoites were transfected with pEdA-9, only a slight increase was observed in the expression of the antigen. However, when E. dispar trophozoites were transfected with pEdA-Rev, the expression of the native 30 kDa antigen was significantly inhibited. This inhibition was proportional to the level of resistance of the E. dispar culture to the neomycin derivative G418. Cytopathic assays detected only a slight difference between untransfected, pEdA-9 transfected and pEdA-Rev transfected trophozoites.     

The Imbrication Model for the integration of social services in a community

An innovative model for organising social services in a community, the Imbrication Model, is contrasted with two traditional models, the Entrepreneurial and the Umbrella Agency. The structural characteristics and dynamics of the three models are illustrated with actual case histories. Imbrication Model calls for the interlocking of personnel from several agencies, with the purpose of redirecting the dysfunctional interagency rivalry prevalent in the traditional models. Imbrications at all organisational levels--Board of Directors, Administrators and Staff--facilitate adoption of the superordinate goal of providing clients with the best services available, regardless of which particular agency delivers the service. Few observers of the current social service scene would challenge the statement that needs for service are unlimited and resources limited. In the USA the imbalance between needs and resources persists despite a decade of massive governmental programmes intended to alleviate social ills. Recent substantial cutbacks in federal funds, moreover are not likely to improve the situation. The resource shortage involves more than a limitation of funds. Deliverers of service and competent programme administrators are also on critically short supply. These shortages are more often than not exacerbated by a chronic spirit of competition among agencies and programmes at the local level. Three organizational models for the delivery and administration of social services, two conventional and one of more recent date, are examined in this article. The innovative model, which has been named the Imbrication Model, explicitly calls for redirecting interagency rivalry and competition. Its ambitious goal is to integrate the efforts of those attempting to meet a community's social service needs.