BB10010/MIP-1 alpha reduces the number of proliferating cells in the small intestine, strongly suggesting a radioprotective potential in this organ. This study was designed to optimize BB10010 administration for maximal radioprotection. In single administration protocols 1 or 4 mg/kg of BB10010 was injected into mice 2, 4 or 10 hr before death. In double administration protocols an initial dose of either 0.4 or 200 microg/kg, and a second dose (2.5 hr apart) of 200 microg/kg 4 hr before death were administered. The number of vincristine-arrested metaphases were counted on individually microdissected crypts from the midpoint of the small intestine. When compared to the smaller doses of BB 10010 used in our previous studies, the higher doses used in these experiments did not result in any further reduction in the number of proliferating cells under any of the protocols assessed. Furthermore, some values were found to be above not only those observed with the smaller doses, but also above untreated controls. It is concluded that a single dose of 200 microg/kg of BB10010 offers the most consistent reduction of mitotic cells, and is, therefore, considered optimal for assessment of radioprotection.
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