Biomedical subjects

A S Lorenti

Publications and source records attributed to A S Lorenti.

4 recordsLinked to original sources

PubMed2001

[Hepatic stem cells].

The presence of hepatic stem cells had been postulated for a long time, until several papers on the pathogenesis of hepatic diseases have recently revealed their presence. Hepatocytes belonging to liver parenchyma show morphological, biochemical and functional differences, as well as different proliferation capacity and pattern of gene expression. Hepatocytes and ductal biliary cells have a common embryologic origin: the endodermal multipotential cells, that migrate and differentiate in response to signals received from the portal mesenchyma. Hepatic regeneration is normally produced through activation of mature cells. However, when the hepatic damage is very extensive, the activation of facultative stem cells localized in the Hering canal, produces the oval cells, with bipotential capacity. Specific antigenic markers for these cells and others shared with fetal cells have been developed, Cells with characteristics similar to those oval cells described in rodents were found in the human liver. A new insight on this subject has opened up with the obtention of hepatic cells from bone marrow stem cells. In this sense, several experiments were carried out using animal and human models. These and others performed with different cellular types obtained from bone marrow, indicate that hematopoietic stem cells could be itinerant cells subject to tissue specific differentiation. The activation of stem cells in order to generate new hepatocytes and ductal biliary cells, is relevant in terms of the study of the pathophysiology of several diseases, such as cancer or the regenerative activity of hepatic parenchyma after massive destruction.

Animals↗

PubMedDate not supplied

Sensibility assay for topical agents. A new method.

We present a new laboratory method to test the sensibility of clinically isolated strains to topical agents. It is a method of dilution of the whole cream in a solid medium. The cream is weighted, suspended in sterile water, and maintained at 45 degrees C. Then a volume of that suspension is added to the agar, maintained at 45 degrees C also. The mixture is agitated and plated. Afterwards 25 strains are inoculated by a Multinoculator (Cetin, Bs. As., Argentina). After incubation (18 hours at 37 degrees C), the results are obtained by observing the presence or absence of bacterial development. The minimal inhibitory concentration is calculated as the lowest concentration that inhibited growth. It is a simple, economical, and reproducible method.

Anti-Infective Agents, Local↗

PubMedDate not supplied

[Bacteriochlorophyll a synthesis in Rhodopseudomonas palustris].

By means of electron microscope it was demonstrated that photosynthetically-grown Rhodopseudomonas palustris exhibits an intracytoplasmic membrane system (Figure 1a), which is not observed in aerobically-dark grown bacteria (Figure 1b). The content of bacteriochlorophyll alpha and the enzyme activity of succinil-CoA-synthetase, ALA-sinthetase and ALA-dehydratase in several media grown Rhodopseudomonas palustris could be measured. Aerobically-dark grown cells do not synthetize bacteriochlorophyll alpha and the activity of ALA-synthetase is lower than in photosynthetically-grown cells (Table 1), suggesting a possible regulatory role for this enzyme in the pigment biosynthesis. Some inhibitors of electron transport and uncouplers of photophosphorylation inhibit both the bacterial growth and bacteriochlorophyll alpha biosynthesis (Table 2), while the levels of ALA-synthetase are not affected. If the incubation in the presence of these kinds of compounds is prolongated, the effects disappear. Although the regulatory role of ALA-synthetase should be very important, apparently it would not be the unique regulatory factor for bacteriochlorophyll alpha biosynthesis in Rhodopseudomonas palustris.

5-Aminolevulinate Synthetase↗

PubMedDate not supplied

[Effect of light intensity on the biosynthesis of bacteriochlorophylls in Rhodomicrobium vannielii and Rhodopseudomonas palustris].

The activity of aminolevulinate-synthetase in crude extracts of R. vannielii was determined. Its properties are very similar to those of the enzyme from R. palustris. With increasing light intensity on cultures of both microorganisms, their specific growth rates increases and the concentration of bacteriochlorophyll decreases. ALA-synthetase exhibits a dual-pattern; its activity remains at a high constant level up to 4 x 10(4) erg cm-2 seg-1, decreasing at higher light intensities (Figures 1 and 2). The activity of succinil-CoA-synthetase of both microorganisms and ALA-dehydrase of R. palustris remain constant over the entire range of light intensities used, but the ALA-dehydrase of R. vannielii shows the same dual-pattern as ALA-synthetase (Table 1), namely a constant high level at the lower light intensities, decreasing at the higher ones. With dialysis the activity of ALA-synthetase of both microorganisms decreases only in extracts from low light intensity grown bacteria, while it did not decrease in extracts from bacteria grown at high light intensities.

5-Aminolevulinate Synthetase↗