The trypanocidal activity of N-isopropyl oxamate (NIPOx) and the ethyl ester of N-isopropyl oxamate (Et-NIPOx) were tested on cultured epimastigotes (in vitro) and on murine trypanosomiasis (in vivo) using five different T. cruzi strains. When benznidazole and nifurtimox, used for comparison, were tested we found that only three of these T. cruzi strains were affected, whereas the other two strains, Miguz and Compostela, were resistant to the in vitro and the in vivo trypanocidal activity of these substances. In addition, when NIPOx was tested on cultured epimastigotes and on mice parasitaemia, trypanocidal activity was not obtained on either of these T. cruzi strains. Our experiments strongly suggest that NIPOx does not penetrate intact epimastigotes due to the polarity of its carboxylate whereas Et-NIPOx, acting as a prodrug, exhibited in vitro and in vivo trypanocidal activity in the five tested T. cruzi strains.

The effect of N-isopropyl oxamate on the activity of alpha-hydroxyacid dehydrogenase-isozyme II (HADH-isozyme II) from Trypanosoma cruzi was investigated. The kinetic studies showed that this substance was a competitive inhibitor of this isozyme. The attachment of the nonpolar isopropylic branched chain to the nitrogen of oxamate increased 12-fold the affinity of N-isopropyl oxamate for the active site of T. cruzi HADH-isozyme II. N-isopropyl oxamate was a selective inhibitor of HADH-isozyme II, since other T. cruzi dehydrogenases were not inhibited by this substance. Since HADH-isozyme II participates in the energy metabolism of T. cruzi, a trypanocidal effect can be expected with inhibitors of this isozyme. However, although it was not possible to detect any trypanocidal activity with N-isopropyl oxamate when the ethyl ester was tested as a possible trypanocidal prodrug, the expected trypanocidal effect was obtained, comparable to that obtained with nifurtimox and benznidazole.

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Se analiza el número de especies arbóreas y su importancia relativa en términos de área basal por hectárea en 235 sitios de 500 m2 en tres microcuencas de la Sierra Madre Occidental de Durango, México. El 68% de los sitios presentó de 3 a 5 especies, aunque la variación fue de 1 a 9 especies. El porcentaje de área basal registrada por Pinus teocote y P. durangensis (las dos especies de mayor importancia) es de 83%, lo cual indica que estas pueden ser usadas como criterio para clasificar fisonómicamente los bosques de esta región. En el 88.4% de los sitios, la primera especie ocupó la mitad del área basal total, la segunda ocupó la mitad del área basal restante, y así sucesivamente hasta la última especie. Este patrón se describió mediante un modelo matemático de tipo geométrico que puede ser de utilidad para el manejo silvícola del área. Se describen también las principales asociaciones arbóreas encontradas.