Bibliothek

Notizen: Weed density was sampled in a number of quadrats in five crops and at eight locations in Italy. For every location and species of crop and weed, a mean/variance pair was calculated. The relationship between these two parameters was significantly influenced by crop and, to a lesser extent, by site, but not by species of weed. The goodness of fit of the negative binomial distribution to the samples was assessed. Its k exponent was estimated on the basis of the observed variance/mean regression. A good fit was found for weed populations with fewer than 10 plants m−2. The applicability of a sequential sampling procedure based on the negative binomial distribution to a weed control strategy that uses a threshold density is discussed. Denombrement de la fréquence des adventices et applicabilité a une méthode d'échantillonnage séquentiel pour un desherbage integré La densité en adventices a étééchantillonnée dans plusieurs cadres dans 5 cultures et à 8 endroits en Italic. Pour chaque lieu et espèce de culture et de mauvaise herbe un couple moyenne/variance a été calculé. La relation entre ces deux paramètres était très dépendante de la culture et à un degré moindre du lieu, mais n'était pas influencé par l'espèce d'adventice. La validité de l'application de la distribution binomiale négative aux échantillons a été estimée. Son coefficient k était estimé sur la base de la regression observée sur variance/ moyenne. Une bonne adéquation a été mise en évidence pour des populations inférieures à 10 plantes m−2 L'applicabilité d'un protocole d'échantillonnage séquentiel basé sur la distribution binomiale négative, à une stratégic de désherbage utilisant un seuil de densité est discutée. Frequenzverteilung in Unkraut-Vegetationsaufnahmen und Aufnahmemethode im Rahmen der integrierten Unkrautbekämpfung Auf der Basis der Dichte von Unkräutern in 5 Kulturen an 8 Orten in Italien wurden Mittelwert und Varianz berechnet. Das Verhältnis dieser beiden Parameter wurde durch die Kulturpflanzenart signifikant, weniger durch den Ort und gar nicht durch die Unkrautart beeinflußt. Die Güte der Anpassung an dienegative Binomialverteilung der Erhebungsdaten wurde bestimmt. Ihr k-Exponent wurde nach der beobachteten Varianz/Mittelwerts-Regression bestimmt. Für Populationsdichten von 〈 10 Pflanzen m−2 ergab sich eine gute Anpassung. Die sich aus der negativen Binomialverteilung ergebende Bekämpfungsstrategie aufgrund von Schadensschwellen wird diskutiert.

Notizen: Apoptosis provides a mechanism for clearance of unwanted cells in a variety of situations in which programmed or physiological cell death occurs; but the premature death of defensive cells could promote infection, inflammation and concomitant disease. We detected high values of apoptosis in polymorphonuclear cells (PMN) elicited from crevicular sulci of smokers affected by adult periodontitis. To learn more about the effects of nicotine on the periodontal environment, we studied its ability to modulate the apoptosis of two phagocytic lines, PMN and mononuclear cells, which are continuously recruited from gingival vessels to prevent or control plaque extension. Brief exposure of PMN to nicotine concentrations ranging from 0.01 to 0.3% shortened, in a dose-dependent relationship, the lag culture time required to observe at fluorescent microscopy the morphological traces of apoptosis. These observations were confirmed by specific tools of apoptosis: DNA fragmentation on gel electrophoresis and expression of the apoptosis-signaling receptor Fas/Apo-1. The apoptotic effect excited by nicotine on these first line defensive cells may be an important feature of the pathogenesis of periodontal disease. As for mononuclear leukocytes, nicotine was unable to induce apoptotic modifications on cells observed up to 72 h culture time, but the drug inhibited IL-1β release and procoagulant activity (PCA) expression. The conflicting role played by these lipopolysaccharide (LPS)-induced monocyte functions in the inflammatory process is a further intrigue in the mechanism by which nicotine compromises the oral health.

Notizen: Abstract Following exposure to calcium ionophore A23187, washed peripheral blood mononuclear cells (MNC) aggregated and formed thromboxane, like platelets. However, while aspirin strongly inhibited platelet aggregation and thromboxane formation, it had a little effect on the aggregation of MNC. In about 50% of the samples studied, aggregation of MNC was associated with the secretion of ATP. However studies in which exogenous ATP or ADP were used, suggested that the aggregation of MNC is independent of the secretion of nucleotides. MNC from 2 thrombasthenic patients failed to aggregate and bound 9–10 fold less radiolabelled fibrinogen than those from normals when challenged with A23187. However, fibrinogen, which plays a major role in the aggregation of platelets, did not appear to be involved in the aggregation of MNC. A differing behavior of these two types of cells was also found when the effect of plasma was studied on the aggregation response to A23187. Indeed, citrated plasma greatly enhanced the aggregation of platelets while it suppressed the response of MNC. This inhibitory effect of plasma was not detected when heparinized plasma was substituted for citrated plasma. We conclude that the aggregation of MNC in response to A23187 does not involve basic events known to play a major role in the aggregation of platelets. The response to A23187 may be an important probe for understanding basic mechanisms and pathophysiological significance of the aggregation of MNC.

Notizen: Abstract Retinoids exhibit a wide spectrum of activities, including antiinflammatory properties. We have investigated the effect of retinoic acid (RA) and retinyl acetate (RAc) on the production of reactive oxygen metabolites and the release of lysosomal enzymes by human polymorphonuclear leukocytes (PMN). Incubation of PMN with RAc or RA (1–100 μM) caused a dose-dependent inhibition (upto 90%) in O 2 − production and chemiluminescence induced by phorbol myristate acetate (PMA), N-formyl-methionylleucyl-phenylanaline (fMLP), opsonized zymosan or ionophore A23187. Both retinoids (1–100 μM) also inhibited, in a dose-dependent way, degranulation induced by fMLP (upto 85% at the highest concentration of RA). These inhibitory effects appear irreversible, since they persist after the drugs are removed and the cells washed before stimulation. Inhibitors of cyclo-oxygenase activity such as acetylsalicylic acid and indomethacin did not influence the effects of RAc. In contrast, BW755, an inhibitor of both cyclooxygenase and lipoxygenase, reversed the inhibitory action of RAc, suggesting that the effect of retinoids occurs possibly through the mediation of lipoxygenase products. The modulation of PMN oxidative metabolism and degranulation might help explain the antiinflammatory properties of retinoids.