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Background. Liver viability depends on blood flow rate, which varies among isolated perfused livers used in different studies. We aimed to identify the minimal blood flow capable of keeping the energy charge compatible with liver viability. Materials and methods. Isolated canine livers were assigned to different groups (n = 4) with blood flow rates of 0.5 (Group I), 1.0 (Group II), and 1.5 ml/g/min (Group III). Blood gases, hematocrit, and glucose were measured over 180 min. Nucleotides, serum osmolarity, and electrolytes were also measured. Morphological changes were recorded at the end of each experiment. Results. Acid-base balance was better in livers from Group III. Electrolytes, osmolarity, hematocrit, and glucose showed no differences. Higher energy charges correlated with higher blood flow rates. On histopathology, there was evidence of more hydrostatic pressure-related changes in Group III, with no difference in necrosis or inflammatory-related alterations. Conclusions. (1) Energy charge correlates strongly with blood flow rate. (2) A rate of 1.5 ml/g/min allows for a better electrolyte, osmolarity, and acid-base balance. (3) Morphological analysis is not a sensitive predictor of organ viability as assessed by energetic potential. (4) The minimal blood flow rate required to attain an energy charge above 0.75 is 1.33 ml/g/min.

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The characteristics of a model of urolithiasis in the bladder of male Wistar rats were evaluated. Two techniques were compared: one knot of suture material through the bladder wall, or 15-throw knots inside the bladder. Rats were randomly assigned to one of six groups, according to the technique and suture material used (polyester, silk, or chromic catgut). An excretory urogram was performed at days 30, 60, and 90. At the moment of positive radiographic diagnosis, animals were sacrificed and stones were obtained. All rats were sacrificed at day 90 regardless of the x-ray results. Variables evaluated were average days to a positive urogram, average weight of all uroliths, and percentage of animals developing urolithiasis throughout the study. There were no statistical differences between groups for the average weight of stones, which ranged from 0.008 to 1.502 g for individual cases. All three materials were more lithogenic with the 15-throw knot inside technique. No significant differences were detected for lithogenesis criteria between suture materials. X-ray dispersion spectroscopy evidenced calcium phosphate composition of two stones from chromic catgut, and magnesium phosphate composition of two stones from chromic catgut, two from silk, and two from polyester. Neo-epithelization over the suture was confirmed microscopically in bladders with the one-throw technique. We conclude that (1) this is an effective model of urolithiasis, with predictability in time, composition, and amount of stone formation; (2) the presence of more suture material inside the bladder is more lithogenic; and (3) excretory urograms are highly sensitive and specific for the noninvasive diagnosis of bladder urolithiasis.

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Taking the view that morphological characteristics represent behavioral strategies of plants to cope with environmental pressures, we defined 18 life-forms, using multivariate classification techniques in a tropical semiarid ecosystem in Central Mexico. A multiple discriminant analysis confirmed the existence of these groups. A null model of random membership of species to life-forms was significantly different from our classification. Vegetation-environment relationships were examined with Detrended Canonical Correspondence Analysis (DCCA). Ordination axes were interpreted mainly be altitude and soil moisture. Response curves of life-forms along these gradients were explored fitting generalized linear models (GLIM's). We believe that the life-forms approach for the study of vegatation-environment relationships is a valid alternative to the traditional species approach usually used in physiological research because: i) life-forms number was found to be an excellent species diversity predictor, ii) this approach enables considerable reduction in the bulk of data without losing ecological information, and iii) life-forms represent ecological strategies per se and, they constitute an index of the number of different ways the desert's resources are utilized.

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Taking the view that morphological characteristics represent behavioral strategies of plants to cope with environmental pressures, we defined 18 life-forms, using multivariate classification techniques in a tropical semiarid ecosystem in Central Mexico. A multiple discriminant analysis confirmed the existence of these groups. A null model of random membership of species to life-forms was significantly different from our classification. Vegetation-environment relationships were examined with Detrended Canonical orrespondence Analysis (DCCA). Ordination axes were interpreted mainly be altitude and soil moisture. Response curves of life-forms along these gradients were explored fitting generalized linear models (GLIM's). We believe that the life-forms approach for the study of vegatation-environment relationships is a valid alternative to the traditional species approach usually used in physiological research because: i) life-forms number was found to be an excellent species diversity predictor, ii) this approach enables considerable reduction in the bulk of data without losing ecological information, and iii) life-forms represent ecological strategies per se and, they constitute an index of the number of different ways the desert's resources are utilized

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In this paper we report the results of a study to determine the frequencies of spontaneous micronucleated erythrocytes (MNE) in peripheral blood of 35 mammalian species. The main goal was to find mammals with a high spontaneous frequency of MNE that could, therefore, be good candidates for biomonitoring genotoxic agents in their natural habitat. We obtained 187 peripheral blood samples, but in 13 of the species we could only sample one individual. A wide range in the number of MNE (1/434 to 0/40,000 erythrocytes) was observed. Since the number of individuals per species is not high enough, this results should be cautiously considered. The cat, mouse, giraffe, pig, opossum and capuchin monkey seem to be suitable species for biomonitoring for genotoxic events.

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The effects of postischemic reperfusion were investigated in 14 isolated rabbit hearts in Langendorff preparation. Seven were controls and the others were reperfused with a sodium 7.5% and dextran 60 (60,000 MW) solution diluted with Krebs-Henseleit buffer to a sodium concentration of 150 mEq/l. The incidence of arrhythmias was lower in this group (p = 0.034). Coronary flow was higher than in controls (p = 0.035), the levels of isoenzyme MB of creatine kinase were lower than in controls (p = 0.035), myocardial water content was also lower (p = 0.047), and histological damage was reduced (p = 0.018). It was concluded that early reperfusion with 7.5% sodium chloride, 6% dextran 60 solution has a protective effect in the treatment of cardiac reperfusion injury.

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The technique used by our group for the extraction of the canine autoperfused heart-lung block is described. This was used in 30 dogs, having a success rate of 24 total extractions and function times from 30 minutes to 13 hours." The complications observed were: arterial rupture upon cannulation, aortic rupture upon binding, ventricular fibrillation before completing extraction, and bleeding of the block with subsequent emptying of the reservoir. It is concluded that the technique described is adequate for the extraction of the canine block, although it is still necessary to know better its hemodynamic, biochemical and respiratory behavior.

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Cysts of Tritrichomonas muris are reported. The morphology of this evolution stage is described under light and electron microscopy. The biologic and epidemiologic importance of this finding is discussed.

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Se describen formas quísticas de Tritrichomonas muris tal y como se observan a fresco, teñidas con hematoxilina y en preparaciones estudiadas al microscopio electrónico. Se comenta la importancia del hallazgo desde los puntos vista biológico y epidemiológico

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An electron microscope model was used to study the effect of rat peritoneal macrophages on Toxoplasma gondii. 10(7) tachyzoites were injected i.p. in 30 days-old rats. After 1, 2, 4, 8 and 24 h peritoneal exudate was withdrawn and infected phagocytic cells were prepared for electronic microscope studies. Toxoplasma organisms inside of rat macrophages showed remarkable lesions such as vacuolization and organisms were totally lysed inside of macrophages of more than 8 h infection rats. The results confirm at molecular level, the importance of rat macrophages in the natural adaptation of this rodent to T. gondii.

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Se hizo un estudio al microscopio electrónico del efecto de los macrófagos de la rata blanca sobre el Toxoplasma gondii. Ratas blancas de un mes fueron inoculados i.p. con 10**7 taquizoitos y después de 1,2,4,8 y 24 horas se les extrajo el exudado periotoneal el cual fue procesado para el estudio al microscopio electrónico de las células fagocíticas infectadas. Los toxoplasmas observados dentro de los macrófagos de ratas mostraron lesiones muy evidentes tales como formación de vacuolas y destrucción de la membrana celular. Este efecto fue aumentando conforme pasaba el tiempo de infección y ya después de 8 horas todos los organismos estaban lisados. Estos resultados confirmam a nivel molecular, la importancia de los macrófagos en la adaptación natural de la rata blanca al T. gondii

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Groups of "immunized" and "non-immunized" hamsters were inoculated weekly with 2, 10 or 20 mg of cortisone acetate per 100 gr of body weight and infected with Leishmania mexicana or L. braziliensis. Doses of 10 and 20 mg of cortisone were excessive, since the animals died with bacterial infections before they developed leishmaniasis. Inflammation and necrosis were more evident in animals inoculated with cortisone and L. mexicana. Furthermore, this strain caused lesions in lymphatic ganglia of immunosuppressed animals, but was not observed in those inoculated with L. braziliensis. There was no difference between the pathological findings in nonimmune and immune hamsters. These results could indicate that passive immunization with dead antigen is not effective.

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