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 modified resistant hepatocyte model, i.e. initiation with diethylnitrosamine and selection of initiated cells with 2-acetylaminofluorene and partial hepatectomy. Two weeks after selection, rats of each sex received daily subcutaneous injections of either recombinant human growth hormone (2.5 IU/kg) or saline for 6 weeks. No effects on growth of early enzyme-altered liver lesions were recorded. The longterm part of the experiment did not show any differences due to growth hormone treatment in terms of incidence or latency time for development of either malignant liver tumors or kidney tumors. Male rats developed liver tumors more frequently than the female rats whereas a higher incidence of kidney tumors was observed in the female rats. Several different malignancies at other sites were also recorded, with no differences between the groups with or without growth hormone treatment. In conclusion, no modifying effects of human growth hormone administration during the post selection phase of the resistant hepatocyte model could be demonstrated on either tumor promotion or tumor progression.