Adrenal growth factors in the rat mammotropic pituitary tumor (MtT-F 4)

Rat mammotropic pituitary tumor (MtT-F 4) crude extracts, prepared either in phosphate buffer or in preheated acetic acid 1M, stimulated DNA synthesis of both mouse adrenal cell line (Y-1) and primary bovine adrenocortical cell cultures. Chromatography of both extracts on a carboxymethyl-Sephadex C-50 column gave one fraction with growth-promoting activity on bovine adrenal cells. The mitogenic activity of this fraction could not be related to the known hormones secreted by the tumor (prolactin, growth hormone or ACTH). A second mitogenic fraction was eluted from the column only when the extract was prepared in phosphate buffer. This fraction had some of the properties of fibroblast growth factor (FGF). These results suggest that the pituitary rat tumor MtT-F 4 secretes adrenal growth factors (other than ACTH) which could be responsible for the adrenal hyperplasia observed in rats bearing the tumor.