Modulation of Plasminogen Activator in Rodent Mammary Tumors by Hormones and Other Effectors¹

The production of plasminogen activator (PA) and its regulation by hormones and other effectors were studied in organ cultures of primary rat and mouse mammary tumors. PA was quantitated using the radioiodinated fibrin plate method. The level of PA in tumor tissue was 10- to 100-fold higher than that in normal rat or mouse mammary glands; the rates of PA secretion were 10- to 1000-fold higher in the tumor cultures. PA production was stimulated by prolactin and pituitary extracts in N-nitrosomethylurea- and 7,12-dimethylbenz(a)anthracene-induced rat tumors but not in mammary tumor virus-induced mouse tumors; hydrocortisone inhibited PA production in all three tumor categories. Sex hormones and agents such as cholera toxin and retinoic acid effectively modulated enzyme production by some tumors.

Three major points of interest emerge from our findings: (a) the pattern of tumor PA response to hormones differs qualitatively and quantitatively from that previously determined for the normal mammary; (b) the profile of responses of tumor PA and tumor growth to hormones shows numerous correlations suggesting that these two parameters may be coordinately regulated; (c) pituitary extracts contain an apparently novel factor that stimulates rat mammary tumor PA synthesis.