GROWTH-HORMONE ADMINISTRATION AFTER TREATMENT IN THE RESISTANT HEPATOCYTE MODEL DOES NOT AFFECT PROGRESSION OF RAT-LIVER CARCINOGENESIS

Male and female Wistar rats were treated according to a slightly modif ied resistant hepatocyte model, i.e. initiation with diethylnitrosamin e and selection of initiated cells with 2-acetylaminofluorene and part ial hepatectomy. Two weeks after selection, rats of each sex received daily subcutaneous injections of either recombinant human growth hormo ne (2.5 IU/kg) or saline for 6 weeks. No effects on growth of early en zyme-altered liver lesions were recorded. The long-term part of the ex periment did not show any differences due to growth hormone treatment in terms of incidence or latency time for development of either malign ant liver tumors or kidney tumors. Male rats developed liver tumors mo re frequently than the female rats whereas a higher incidence of kidne y tumors was observed in the female rats. Several different malignanci es at other sites were also recorded, with no differences between the groups with or without growth hormone treatment. In conclusion, no mod ifying effects of human growth hormone administration during the post selection phase of the resistant hepatocyte model could be demonstrate d on either tumor promotion or tumor progression.