Archivos de biologia y medicina experimentales最新文献

Experimental myotonia was induced in rats by 2,4-dichloro-phenoxyacetic acid (2,4-D). After 4 to 24 h of treatment, the anterior tibialis muscles exhibited increased fatigue at low frequency (30 Hz) nerve stimulation, but they developed normal tension at high-frequency (100 Hz) stimulation. Glycogen content and the activities of glycogen phosphorylase, lactate dehydrogenase and malate dehydrogenase remained normal. The absence of correlation between fatigability and energetic metabolism in this experimental model of myotonia suggests a dysfunction in excitation-contraction coupling.

From three-dimensional diameter measurements of eleven kinds of cells pertaining to five different organs, which were excised from eleven adult mammals (nine species) whose body weight range was 40 g to 450 kg, we calculated the corresponding cell soma areas (A), volumes (V), and finally their area-volume ratios (A/V). The dissimilarities among these eleven cell types could be established quantitatively by means of a cluster analysis. The dendrograms for cell areas (A), volumes (V), and their corresponding area-volume ratios (A/V), yielded similar groupings when cell areas and volumes were compared, yet the grouping of the area-volume ratios (A/V) for the eleven types of cells was different. These results were corroborated by means of the principal components analysis, where five distinct cell groupings could be established. The relationship between cellular morphometry, oxidative metabolism, and body mass, was established by means of the fractal geometry of the transport systems (respiration and circulation), which provides the tools for the scale-dependent analysis of the surfaces across which the transport of metabolites is performed.

The aim of the present study was to submit Huxley's allometric equation (Y = aMb) to a dimensional analysis; in this equation Y is any biological variable, a is the mass-coefficient, M represents body mass, and b the mass-exponent. The dimensions of each of its components is thoroughly analyzed by means of the MLT-system of physics, as is the dimensionality of the whole equation. The relationship between the dimensional analysis and the postulates of some theories of biological similarity is discussed. In conclusion, parameter a of the allometric equation is always dimensionless, while the physical dimensions of the dependent variable Y can be defined by means of the power function Mb.

The fertilization of a human egg, often thought of as initiating the life of a person, is in reality but the beginning of a beginning for one or more individuals. While pronuclear fusion establishes a diploid genome, this is at first a structural entity without function. No significant RNA synthesis occurs between germinal vesicle breakdown and early cleavage, and in fact embryonic genes do not begin to find expression until about the 4- to 8- cell stage. Gene expression then progressively spreads throughout the genome, during prenatal development and beyond. The progressive nature is well shown in the early mouse embryo by the widening range of energy sources utilizable, by the rising levels of glycogen storage and by the increasing uptake of nucleic acids and protein precursors. While HCG-B RNA is transcribed in human embryos about 2 days after fertilization, it is not expressed until 16-cell stage is not linked to physical or functional integration, each cell being inherently capable of giving rise to an entire person (together with a complex of placental structures); alternatively, cells from separate embryos on being brought together can jointly lead to the establishment of a chimeric individual. Multiplicity can also originate later, the primitive streak stage being the normal time for monozygotic twinning. Only when that stage has passed does true individuality exist, for (excluding anomalies) just one person can now eventuate. The gene-transfer function of fertilization can be replaced or augmented by intranuclear or intra-blastocyst gene injection, or by the use of teratocarcinoma or embryo-stem cells.

This review summarizes evidence favouring two kinds of anatomical correlates of cerebral lateralization. The first, cortical asymmetries, is widely accepted today. It is now known that there are significant asymmetries in brain regions corresponding to the so-called "language areas". These asymmetries are present at the level of gross anatomy (i.e., length of the Sylvian fissure), and at a more detailed cytoarchitectonic level. Furthermore, it is known that, in different subjects, the extent of the asymmetries correlates well with the degree of functional lateralization. The second anatomical variable is commisural connectivity. The corpus callosum has been postulated as pivotal in the workings of a lateralized brain. There have been controversial reports suggesting a correlation between callosal structure and parameters related to brain lateralization, such as sex and handedness. Together with analysing these results, this review considers some aspects of the fine structure and development of the corpus callosum. These considerations lead to the proposal of specific hypotheses about the relation between brain lateralization and commisural connectivity.

The liver represents the principal pathway for sterol excretion from the organism. In addition, the major proportion of serum lipoproteins is catabolized in the liver. It is known that diosgenin and bean diet markedly induce biliary cholesterol output. In this series of studies we characterized the catabolism of several lipoprotein particles in animals fed diosgenin or a bean-rich diet (biliary cholesterol output is increased greater than 300% in these animals). Human low density lipoprotein (hLDL) and rat high density lipoprotein apo-E free (rHDL) were labeled with 125I. Rat chylomicrons were labeled with cholesterol-(3H)-oleate. hLDL clearance increased from 381 +/- 39 to 628 +/- 44 (microliters/h x 100 g body wt) (p less than 0.005) in bean-fed rats. The half life (t1/2) decreased from 12.4 +/- 1 to 9.8 +/- 0.7 h (p less than 0.005) in these rats. The clearance of rHDL apo-E free increased from 579 +/- 8 to 680 +/- 36 (microliters/h x 100 g body wt) (p less than 0.05) in diosgenin-fed animals. The t1/2 significantly decreased from 8.2 +/- 0.7 h to 7.0 +/- 0.3 h (p less than 0.05) in these rats. In contrast, chylomicron clearance and t1/2 were not modified by the diosgenin or bean diets. These results are consistent with the hypothesis that the number and/or affinity of the B/E and A-I receptors, but not E receptors are increased in rats fed biliary cholesterol hypersecretory diets. These studies suggests the presence of a functional inter-relationship between the biliary and sinusoidal pathways of hepatic cholesterol.

Five different lines of tailless mice bearing different t recessive haplotypes (tAn, tMo, tRa, tLa and tQu) have been established in our laboratory and maintained in combination with the brachury chromosome (T). These t haplotypes were derived from widely separated Chilean wild mouse populations. The immunoelectrophoretic typing for Ss and Slp isotypic variants of C4 showed that all lines had the Ss-High. Slp-negative phenotype suggesting that the t haplotypes might be associated with similar S regions of the major histocompatibility system of the mouse.

Intravenous infusion of free fatty acid (FFA) 20 mg.kg-1.min-1 produces pulmonary edema, hypoxemia, hyperventilation and increase in the alveolar surfactant content in rabbits in less than 15 min. We tried to study the role of leukotrienes (LT) and the effects of PGI2 in pulmonary response to FFA. We used Piriprost an inhibitor of LT synthesis or Epoprostenol (Prostacyclin: PGI2) in 4 series of rabbits treated with FFA or its vehicle. Piriprost given as an aerosol (0.1% W/W in THAM) scarcely modified the morphofunctional changes induced by FFA. The only pulmonary effect prevented by Piriprost was the increase in surfactant content (disaturated phosphatidylcholine: DSPC) in broncho-alveolar lavage gluid (BAL). PGI2 administered in a dose of 0.1 micrograms.kg-1.min-1 5 minutes prior to a 15 min infusion of FFA was also unable to prevent most of the effects of FFA on the lung. Only the increase in DSPC in BAL was prevented by PGI2. Some animals received a smaller dose of FFA, because they died earlier. Piriprost, as well as PGI2, shortened the survival time of rabbits treated with FFA. This decrease in the survival rate of animals treated with FFA could account for the lack of increase in DSPC post-FFA. Since other morphofunctional changes induced by FFA were scarcely modified by both Piriprost or PGI2, our results suggest that it is unlikely that either leukotrienes on PGI2 may have a significant effect on pulmonary disturbances induced by FFA.

Melatonin disturbs the reproductive process in seasonal but not in continuous breeders: however, it delays sexual development in the rat. The testicular function of rats injected daily with melatonin from 20 up to 25, 30, 35 or 40 days of age was analyzed. The spermatogenic and androgenic activity of testes was assessed by light microscopy and by the capacity for binding hCG and producing testosterone in vitro, respectively. In addition, LH, FSH and testosterone plasma levels were measured and 3B-hydroxysteroid dehydrogenase activity of Leydig cells was assessed histochemically to aid in the interpretation of results. Rats treated with melatonin for 15 or 20 days presented at the end of the juvenile period, abnormal progression of spermatogenesis and decreased ability of their Leydig cells to produce testosterone both in vivo and in vitro. This was associated with a lower number of binding sites for hCG and diminished production of testosterone in response to receptor and post-receptor mediated stimulation of steroidogenesis. Melatonin caused a marked decrease in LH serum levels. The diminished LH supply to the testis probably interfered with differentiation or impaired the functional ability of Leydig cells. As a consequence, testicular testosterone production was insufficient to support normal spermatogenic progression and growth and development of the sexual accessory organs.