Differential action of growth hormone in irradiated tumoral and nontumoral intestinal tissue

Growth hormone (GH) protects the intestines from antitumoral therapy, but it is not known whether or not the tumor is also protected in vivo. The aim of the present work was to determine whether GH administration modifies the response by a colonic adenocarcinoma to radiation in vitro and in vivo. BDIX rats were implanted with a colonic adenocarcinoma and two weeks later GH treatment was started. Animals were then irradiated, and four days later samples from the intestines and tumor were taken for analysis. In vitro assays were performed in parallel to confirm the effects observed in vivo. GH reduced radiation-induced intestinal injury by improving proliferation and reducing apoptosis and p53 expression. However, tumor proliferation was reduced by GH while apoptosis and p53 expression remained unchanged. A similar response was observed in vitro. Thus, GH administration before radiotherapy protects the intestines but not the implanted adenocarcinoma in the rat.