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Biomedical subjects

T Shimamura

Publications and source records attributed to T Shimamura.

At least 235 records · Page 13Linked to original sources
PubMed1975

Cyclic AMP and immune responses: changes in the splenic level of cyclic AMP during the response of mice to antigen.

Intravenous injection of sheep erythrocytes into normal immunologically competent C57BL/6J mice results in significant and characteristic changes in the splenic level of 3':5'-cAMP with initiation of the immune response and proliferation of antibody-forming cells. The level increases 2- to 3-fold initially, peaks at 2 min, and returns to base level in an hour. Between 2 and 5 days there is a decrease, followed by a peak when the rate of proliferation of antibody-forming cells is maximal. Changes in splenic level of cAMP are thus transitory and biphasic, and they occur only in response to foreign substances that are immunogenic, such as heterologous erythrocytes, and not to antigenically inert carbon particles. They are also dependent upon the dose of immunogen. Moreover, the double-stranded hybrid of polyadenylate and polyuridylate, which acts synergistically with antigen in stimulating endogenous cAMP, is immuno-enhancing if given with sheep erythrocytes when the cAMP level is increasing, and immunosuppresive if given when cAMP is decreasing. These data provide direct evidence for a role of cAMP as a mediator in the activation and proliferation of immunocytes stimulated by antigen. With knowledge of the transitory and biphasic nature of the cAMP response induced by antigen, one can avoid indiscriminate use of drugs that modify the level of endogenous cAMP and instead employ them rationally in controlling the immune response, enhancing or suppressing it as desired.

Animals↗
PubMed1975

Reinvestigation of the taxonomy of Clostridium bifermentans and Clostridium sordellii.

The taxonomic relationships between Clostridium bifermentans and C. sordellii were reinvestigated by numerical taxonomy, studies of DNA-DNA homology and DNA duplex thermal stability, and by analysis of cell-wall sugar components. Although the results indicate that both species may be grouped into one geno-species, C. sordellii strains could be differentiated from C. bifermentans strains on the basis of a few phenetic criteria that include the inability to ferment mannose and sorbitol, the absence of mannose in the cell wall, the production of urease, the absence of arginine deaminase activity, and susceptibility to inhibition of growth by mannose.

Arginase↗
PubMed1975

An ultrastructural study of the renal medulla in experimental acute pyelonephritis.

Experimental acute pyelonephritis was produced in rats by a combination of intravenous administration of Escherichia coli, strain IMRU-54, and temporary unilateral mechanical ureteral obstruction. Structural alterations of the renal medulla were studied by light and electron microscopy. Major cellular alterations occurred in the vasa recta. Tubular and interstitial cells demonstrated minimal alterations after the brief period of acute inflammation. Polymorphonuclear leukocytes within tubular lumina contained structures resembling E. coli in nonprotoplasts-like form. Numerous protoplast-like organisms, to the exclusion of any other structural forms, were detected within the interstitium of the inner medulla. Nonprotoplast-like structures resembling E. coli were rarely observed in interstitium of the inner medulla. Following relief of ureteral obstruction, clearance of acute inflammation was rapid. In conclusion, hemoatogenous acute pyelonephritis induced by E. coli, IMRU-54, is able to inflict cytological and ultrastructural damage to structural elements of the inner and outer medulla of rats. Vasa recta incurred prominent alterations in endothelia and basement membranes, whereas tubular epithelia and interstitial cells had relatively good structural preservation. The data suggest that intravenously administered E. coli is capable to revert to a protoplast-like structure in the inner medulla.

Acute Disease↗
PubMed1975

A progressive glomerulosclerosis occurring in partial five-sixths nephrectomized rats.

A chronic renal disease was induced by 5/6 nephrectomy in young adult Wistar albino male rats. Groups of 3 rats were killed at varying time intervals from 10 to 50 weeks after nephrectomy, and the glomerular structure was studied by light and electron microscopy. By light microscopy, increase in glomerular size and hypertrophy of the visceral glomerular epithelial cells were evident as early as the tenth week. Significant degree of glomerular hyalinization started on the 25th week and gradually became more extensive in involvement towards the 50th week. By electron miscroscopy, the hypertrophied glomerular epithelia showed many osmiophilic bodies and vacuoles in their cytoplasm and fusion of foot processes. Beginning on the 30th week, increase of the mesangial matrix was quite evident, and endothelial and epithelial cells disappeared from the areas where the increase was prominent. The increased matrix gradually encroached and occluded capillary lumina and Bowman's space, leading to a formation of obsolescent glomeruli. Whether or not these glomerular changes are due to the glomerular hyperfiltration which has been known to occur after 5/6 nephrectomy remains to be elucidated.

Animals↗
PubMed1973

Vascular permeability of the renal medullary vessels in the mouse and rat.

The vascular permeability of the vessels of the renal medulla of normal rats and mice and potassium-deficient rats was studied by using ferritin, horseradish peroxidase and carbon particles as markers. Fenestrated endothelia are more permeable to ferritin and horseradish peroxidase than nonfenestrated endothelia. The ease with which the tracers are able to pass from the vascular lumina through the endothelia into the interstitium is directly related to the size of the tracers (horseradish peroxidase permeates most readily, followed by ferritin and carbon particles, in this order), suggesting the presence of a molecular sieving mechanism for the passage of substances through the capillary walls of the renal medulla. At the initial stage after injection of horseradish peroxidase and ferritin, these tracers pass from the medullary vascular lumina into the interstitium, not from the tubular lumina into the interstitium. It appears that the passage of ferritin and horseradish peroxidase through the vascular wall is enhanced in potassium-deficient rats.

Animals↗