SUMMARY
The effects of single and continuous administrations of a synthetic gluco-corticoid (dexamethasone) on eosinophil numbers and distribution have been studied. Absolute blood eosinophil counts were made, and the turnover of the eosinophils was examined by continuous infusion of tritiated thymidine to label the deoxyribonucleic acid of all newly formed cells.
Dexamethasone equivalent to less than 200 μg. cortisone/100 g. rat/day produced disappearance of eosinophils from the blood and the normal output of glucocorticoids is therefore probably less than this.
Single administrations of dexamethasone produced a blood eosinopenia within 2 hr. due to removal and destruction of eosinophils by the reticulo-endothelial system. Continuous dexamethasone administration reduced the number of proliferating eosinophil cells in the marrow, with a consequent reduction in the number of eosinophils in the tissues.
Udaka, Shigezo (The Institute of Physical and Chemical Research, Komagome, Bunkyo-ku, Tokyo, Japan). Pathway-specific pattern of control of arginine biosynthesis in bacteria. J. Bacteriol. 91:617-621. 1966.-To compare control mechanisms of arginine biosynthesis in various bacteria, activities of several enzymes of the arginine pathway were measured in cells cultivated under repressed and partially derepressed conditions. Nineteen strains of bacteria tested appeared to have two types of pathways, closely related to each other. The partially derepressed levels of enzymes varied from bacterium to bacterium. The degree of inhibition of enzyme 2 (the second of eight enzymes concerned with arginine biosynthesis) and the repressibility of enzymes by arginine also appeared to vary from species to species. On the other hand, enzyme 2 was found to be the site of end-product inhibition only in the bacteria having a particular pathway. These results suggest that the bacteria have their own species-specific control mechanisms and that there is a pathway-specific pattern of control in arginine biosynthesis. The implications of the results are discussed from the viewpoint of evolution of control mechanisms.
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