Endocrine mediation of psychosocial stressor effects on mouse mammary tumor growth

We have demonstrated that differential housing alters the growth rate of the androgen-responsive Shionogi mouse mammary carcinoma (SC115). In the present study we wished to determine if changes in plasma levels of hormones or a shift in the responsiveness of the tumor cells to hormones was responsible for the differential tumor growth rates observed. Plasma testosterone and corticosterone levels were assayed 24 h, 3 days and 1 week post tumor cell/vehicle injection. Also 3 weeks post injection androgen and glucocorticoid receptor binding capacity (Bmax) and binding affinity (Kd) and the in vitro responsiveness of tumor cells to dihydrotestosterone and hydrocortisone were measured. At 24 h post injection, plasma testosterone levels were significantly increased in mice with large tumors, but remained low in mice with small tumors. Plasma corticosterone levels were significantly elevated in mice with small tumors compared to those of mice with large tumors at all time points measured. Androgen and glucocorticoid receptor binding capacity and binding affinity of tumor cells did not differ among groups. Further, all groups tested had the ability to respond to dihydrotestosterone and hydrocortisone in vitro. These data indicate that an effect of housing condition on plasma levels of steroid hormones may, in part, mediate the differential tumor growth rates observed in this model.