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PubMed1997

Concentrations of adenosine and its metabolites in the rat retina/choroid during reperfusion after ischemia.

PURPOSE: Little is known about the nature of biochemical disturbances during reperfusion after retinal ischemia. Previous studies have suggested that adenosine is responsible for regulation of retinal blood flow soon after ischemia has ended. Therefore, in this study we measured concentrations of adenosine and its metabolites in the rat retina/choroid after brief (10 min) or prolonged (60 min) periods of ischemia, and the functional consequences of inhibiting adenosine metabolism. METHODS: Ischemia was produced in anesthetized rats by ligation of the central retinal artery. The eyes were frozen in situ and purine nucleoside concentration was determined by high performance liquid chromatography. The functional effects of pre-ischemic inhibition of xanthine dehydrogenase/xanthine oxidase were assessed by measurement of the electroretinogram before, during, and up to 7 days following 60 min ischemia. RESULTS: Changes in the concentrations of adenosine and its metabolites were significant early in the reperfusion period, and were greater in magnitude and occurred earlier in prolonged, compared to brief, ischemic periods. Concentrations of adenosine, inosine, and hypoxanthine remained elevated for 30 min following the end of 60 min ischemia, and xanthine concentration was significantly elevated until 60 min after the end of either 10 or 60 min of ischemia. The onset of its peak value after ischemia was delayed in comparison to that of adenosine. Ischemia-evoked increases in xanthine concentration were attenuated by inhibition of adenosine deaminase or xanthine oxidase/xanthine dehydrogenase. Pre-ischemic inhibition of xanthine oxidase/xanthine dehydrogenase by oxypurinol (40 or 80 mg/kg intraperitoneally [IP]) resulted in a significant improvement in recovery of the a and b waves of the electroretinogram in comparison to a saline-treated control group. CONCLUSIONS: These results indicate that adenosine is a major component of the biochemical changes that occur after retinal ischemia. Long-lasting increases in xanthine concentration during reperfusion after ischemia could be a source of oxygen free radicals that may contribute to delayed injury of the retina, attempts to decrease xanthine concentration would ideally be initiated within one hour after the end of ischemia.

Adenosine↗

PubMed1985

A simplified radioimmunoassay for antibodies causing immune cytopenia.

A two-step, solid-phase radioimmunoassay for the measurement of antibodies directed against platelets, neutrophils, and red blood cells is described. Cells to be tested or standard solutions of human IgG (HIgG) first are incubated with excess 125I goat anti-human IgG. Unbound 125I anti-IgG is adsorbed in a second step to polystyrene balls (PB) coated with excess human IgG. Inhibition of binding in this second step is related directly to the level of cell associated IgG. The amount of cell bound IgG is determined by comparison to a inhibition curve for standard IgG solution. The method was evaluated by quantitating antibody levels in patients with clinical evidence of immune cytopenias.

Antibodies↗

PubMed1979

Managing the change process.

Change is a normal and expected phenomenon in the 20th century, but how well are health professions educators prepared to deal with necessary educational change? This article presents a conceptual model for the change process, which provides a framework for adopting an innovation. Although a systems model is used, the human factors associated with change are emphasized. The model provides a basis for action, but the limitations of a static, inflexible viewpoint are discussed. The manager of the change process must be sensitive and responsive to human factors. To be successful, the manager must capitalize on his/her intuitive and creative capabilities. The phenomenon of change may be disruptive to an educational organization. The manager of change may not be in a comfortable position, but the manager who perseveres will see innovations adopted, experience personal growth and contribute to the professional development of others.

Faculty↗