Differential regulation of human platelet responses by cGMP inhibited and stimulated cAMP phosphodiesterases.

Platelets contain two cAMP phosphodiesterases (PDEs) which regulate intracellular cAMP levels, cGMP-inhibited cAMP PDE (PDE3A) and cGMP-stimulated PDE (PDE2A). Using the PDE3 inhibitor, milrinone and the PDE2 inhibitor, erythro-9-(2-hydroxyl-3-nonyl)adenine (EHNA), we have explored the contribution of each PDE to the regulation of platelet function. Inhibition of PDE2 resulted in higher levels of intracellular cAMP than inhibition of PDE3A suggesting this PDE may be the more important regulator of cAMP in human platelets. However, a concentration-dependent inhibition of agonist-induced aggregation was observed with milrinone while little effect was seen with EHNA. In addition, we observed a concentration-dependent inhibition in the increase of intracellular Ca2+ with PDE3 inhibition and significantly less with PDE2 inhibition. PDE3 inhibition also resulted in a concentration-dependent increase in cAMP-mediated phosphorylation of the vasodilator-stimulated phospho-protein (VASP) whereas there was no significant increase with PDE2 inhibition. In each of these experiments, synergism was noted with the combination of milrinone and EHNA. These results suggest that cAMP pools may be localized and the various PDEs regulate specific pools. These data also suggest that inhibitors of PDE3A may be more effective antiplatelet agents.

Residues F16-G33 and A784-N823 within platelet thrombospondin-1 play a major role in binding human neutrophils: evaluation by two novel binding assays.

The thrombospondin-1 (TSP1) structural requirements within its heparin-binding domain (HBD)(30 kd) or within the other domains of the molecule (450 kd) that interact with neutrophils (PMNs) have not been delineated. Synthetic peptides based on the HBD, a TSP1 proteolytic fragment lacking the HBD, a large C-terminal domain of TSP1 (210 kd), a TSP1 recombinant fragment (rTSP1(784-932)), and a monoclonal antibody directed against the TSP1 type 3 repeats (mAb D4.6) were utilized to map such structural requirements on TSP1. Synthetic peptides containing a heparin-binding motif and encompassing residues F16-G33 or A74-S95 of TSP1 competed quantitatively with iodine 125-labeled TSP1 for binding to heparinagarose beads. However, only F16-G33 was a competitor of TSP1 binding to PMNs, suggesting that the sequence F16-G33 within the HBD plays a role in PMN binding. The interaction site within the 450-kd fragment was further narrowed. A TSP1 -derived proteolytic fragment (210 kd), a recombinant TSP1 fragment (rTSP1(784-932)), and a type 3 repeat anti-TSP1 monoclonal antibody (mAb D4.6) competed for the binding of 125I-labeled TSP1 to PMNs. The N-terminal of rTSP1(784-932) and C-terminal sequence analysis of TSP1-210 kd delineated the structural requirements for the second binding region for PMNs-namely, residues A784-N823.

Comparaçäo das propriedades mecânicas das hastes femorais bloqueadas AO-ASIF-FMRP: parte II - hastes implantadas em fêmures humanos "in vitro" / Comparison of the mechanical properties of AO-ASIF and FMRP blockaded femoral nails: part II - nails implanted in human femora \"in vitro\"

Nesta segunda parte, foi analisado o comportamento mecânico de hastes AO e FMRP femorais bloqueadas de l2mm de diâmetro e 400mm de comprimento, implantadas em dez pares de fêmures humanos frescos. Foi ressecado segmento diafisário extenso, resultando em um fragmento proximal de l2cm, um distal de l4cm e um gap entre os dois de l6cm. As hastes foram travadas inicialmente de forma usual.Foram feitos testes de inclinaçao da baste dentro dos fragmentos distal e proximal, nos sentidos ântero-posterior e medial-lateral e testes de carga axial excêntrica. Os espécimes foram analisados em máquina universal de testes. Os testes de inclinaçao mostraram superioridade estatisticamente significante dos espécimes FMRP da fixaçao no fragmento proximal e uma forte tendência à melhor fixaçao também no fragmento distal. Para tornar semelhante a distância entre os parafusos de travamento distais das bastes FMRP e AO, os parafusos dos espécimes FMRP foram mudados da posiçao convencional, o que enfraqueceu significantemente a fixaçao nas inclinaçoes, indicando a importância da inserçao em posiçao afastada dos dois parafusos distais de travamento no sistema FMRP. O segmento distal foi adicionalmente encurtado para 12 e 10cm, o que nao modificou de forma importante a fixaçao analisada nos testes de inclinaçao. O fato foi imputado ao já avantajado canal medular do fragmento distal antes da ressecçao. A fixaçao dependia, entao, só dos parafusos distais de bloqueio e nao do apoio cortical da diáfise. Os testes de carga axial excêntrica mostraram nítida superioridade do sistema FMRP em todos os espécimes, os quais sofreram deformaçao significantemente menor e resistiram à carga máxima que o sistema AO. Relevância clínica - Ernbora exista a possibilidade do uso de hastes mais calibrosas no sistema AO, para hastes de l2mm de diâmetro o comportamento mecânico é nitidamente superior no sistema FMRP. Os dados obtidos referendam o uso clínico do sistema FMRP, a julgar pelo lado da resistência mecânica. Estes resultados encorajam o uso clínico do sistema FMRP, a julgar pelo lado da resistência mecânica.

Production of a hemolytic factor by Candida albicans.

Candida albicans exhibits hemolytic activity when grown on glucose-enriched blood agar. This activity is present on intact organisms, and it is secreted into the culture medium. Hemoglobin released from lysed erythrocytes can restore the transferrin-inhibited growth of C. albicans. We conclude that C. albicans expresses a hemolytic factor which allows it to acquire iron from host erythrocytes.