Figure 1. Experimental protocol for inflammation-associated rat colon carcinogenesis. A total of 127, 6-week-old male F344 rats were divided into eight groups. Animals in groups 1-3 were subcutaneously (s.c.) injected twice with 1,2-dimethylhydrazine (DMH) dissolved in physiological saline(40 mg/kg body wt.) during the first week. DMH treatment was followed by a 1-week-administration of 1% dextran sodium sulfate (DSS) in the drinking water during the second week. Rats in group 4-8 were s.c. injected with 1 ml of saline and group 4 and 5 rats were administered 1% DSS during the second week. All animals were maintained without any chemical treatment during the third week. At the beginning of the fourth week, group 2, 4 and 6 rats were fed 1% ethanol-extracted propolis (EEP); group 3, 5 and 7 rats were fed 1% water-extracted propolis (WEP); and group 1 and 8 rats were fed basal MF powdered diet containing 1.5% dextrin. Administration of EEP or WEP was continued until the end of the 32nd-week. At week 12, 15 rats each from groups 1-3 were sacrificed for analysis of aberrant crypt foci (ACF) and all remaining animals were sacrificed at the end of week 32.