Effect of prospidine administered at different times of the day on the development and growth of N-nitrosomethylurea-induced mammary tumors in Wistar rats.

The chemotherapeutic effectiveness of intraperitoneal administration of prospidine (50 mg/kg per day during the initial 14 days of study) was evaluated, on a circadian basis, on the N-nitrosomethylurea (NMU)-induced mammary tumors in female rats. Untreated rats showed a progressive increase in the mean tumor area and total tumor area/rat. At the end of treatment the average tumor area and total tumor area/rat in the animals treated at 0800, 1400 and 2000 h were significantly lower than the values in the control group by week 2. By weeks 3 and 4 the mean tumor area and total tumor area in all groups of treated rats were significantly lower than those in the untreated animals. The mean tumor area by weeks 5 and 6 in the animals treated at 0800 h were significantly lower than in the group treated at 0200 h, and the mean value by week 6 in the group treated at 1400 h was significantly lower than those from the groups treated either at 2000 h or 0200 h. The mean total tumor area/rat in rats treated at 1400 h was, by week 6, significantly lower than in animals treated either at 2000 h or 0200 h. A transient reduction in body weight was registered at the end of prospidine treatment.