Aspirin does not inhibit adenosine diphosphate-induced platelet alpha- granule release

The involvement of metabolites of arachidonic acid in platelet-dense granule secretion and secondary platelet-platelet interactions is well characterized. However, their role in heterotypic interactions dependent on alpha-granule secretion is less well understood. Using platelet-surface expression of P-selectin as a marker of alpha-granule secretion, we have shown that: (1) aspirin treatment of platelets at doses that block dense granule secretion does not inhibit alpha-granule secretion to adenosine diphosphate (ADP); (2) synergism between epinephrine and ADP in the induction of P-selectin expression is similarly unaffected by aspirin; and (3) the ability of P-selectin to mediate adhesion of activated platelets to monocytes and polymorphonuclear lymphocytes in whole blood is also unchanged by aspirin treatment. To further explore the mechanisms responsible for platelet alpha-granule secretion, we have shown that inhibition of Na+/H+ exchange by either acidification of the extracellular medium or amiloride treatment blocked ADP-induced P-selectin expression. In contrast, incubation with the platelet lipoxygenase inhibitor 5,8,11- eicosatrynoic acid, by itself and with aspirin, did not decrease ADP- induced P-selectin expression. We conclude that platelet alpha-granule secretion in response to ADP is dependent on intact Na+/H+ exchange but is independent of the lipoxygenase- and cyclooxygenase-dependent metabolites of arachidonic acid.     

Limits of reproducibility of blood flow measurements by Doppler echocardiography

This study evaluates the variability of a quantitative Doppler echocardiographic method for blood flow calculation at the mitral and tricuspid orifice. Four subjects underwent 2-dimensional Doppler echocardiography during normal respiration and nonrespiration. Doppler recordings were integrated to determine mean temporal velocity (MTV) for each cardiac cycle separately. MTV during inspiration and expiration were compared, as were MTVs of 20 consecutive cycles during nonrespiration. Diameters of mitral and tricuspid orifice and interception angles were measured in 10 consecutive cycles at 4 predetermined moments. All results were averaged to a mean subject situation. MTVs were significantly (p less than 0.001) higher during expiration than during inspiration (12.4 and 11.0 cm-2) for the mitral orifice and lower (9.2 and 11.0 cm-2) for the tricuspid orifice. MTV at both orifices showed a significantly smaller variability (7.7% and 9.0%) during nonrespiration than during respiration (14.5% and 13.2%). Diameters of mitral orifice and tricuspid orifice were significantly (p less than 0.001) larger during diastole than during systole whereas standard error of the mean for both was 5.0%. Interception angles measured at mitral orifice are all close to 0 degrees and show minimal variability, while at the tricuspid orifice the angle varied from 15 degrees in diastole to 25.5 degrees in systole, constituting a significant difference in cosine (0.96 to 0.90).     

Differentiation of memory T cells to virus plaque-forming cells and cytotoxic T lymphocytes

The aims of this study were to define the T-cell subpopulation(s) detected by the virus plaque assay, and particularly to determine whether the virus plaque assay could be used to enumerate cytotoxic T lymphocytes. In addition, studies were undertaken to ascertain whether cell proliferation was required for development of cytotoxic effector function and virus plaque formation by these subpopulations. The results of experiments with a secondary mouse mixed lymphocyte culture (MLC) model indicated that 70 percent of virus plaque-forming cells bore the Ly 1 phenotype and 30 percent the Ly 2,3 phenotype. Three lines of evidence suggested that cytotoxic T lymphocytes (CTL) can be detected by this assay: the fact that some virus plaque-forming cells (V-PFC) bear the same Ly phenotype as CTL; the use of an inhibitor of DNA synthesis indicated that proliferating cells could be eliminated with no effect on V-PFC production and cytotoxic activity of the Ly 2,3 cell population; and that infection of primed lymphocyteswith vesicular stomatitis virus before (MLC) stimulation eliminated cytotoxic activity. In primary MLC, development of V-PFC and CTL was completely abolished by cytosine arabinoside. In contrast, in secondary MLC, some CTL and V- PFC were generated by antigenic stimulation in the absence of proliferation. However, the development of both functions became progressively more susceptible to cytosine arabinoside as the time between primary immunization and in vitro boosting is increased. It is suggested that there may be a considerable disparity between the number of existing effector cells at any given time and the cytotoxic potential, i.e. the number of cells capable of being generated by antigenic stimulation.