Platelet response.

Young (6-12 weeks; ○) and old (33-46 weeks; ●) c-mpl^−/− mouse platelet responses to administration of 5-FU (150 mg/kg) were compared. Elevation of platelet counts in older c-mpl^−/− mice was much greater than in young mice, and counts were higher than normal. The platelet response in control C57/Bl6 mice (▵) is also shown. Data were derived from 3 independent experiments and based on a total of 68 young and 68 old c-mpl^−/− mice and 12 C57/Bl6 mice. One day before 5-FU administration and 7 days afterward, blood samples were obtained from all mice, thereby allowing determination of baseline platelet counts and confirmation of the response to 5-FU. Thereafter, blood samples were obtained from groups of 5 to 7 young and 4 to 15 old c-mpl^−/− mice and 1 to 4 C57/Bl6 mice.