Steroid-induced inhibition of nucleoside uptake in isolated mouse thymocytes

In view of the evidence suggesting a possible effect of high concentrations of steroids on membrane properties, we have investigated the effect of several steroid molecules on the uptake and incorporation of [3H]uridine is isolated mouse thymocytes. Our results demonstrate that the sex steroids, the estrogenic compound, diethylstilbestrol, and several non-hormonal steroid molecules induce a marked inhibition of nucleoside uptake. This effect, which occurs only at concentrations above 10(-6) M, is almost instantaneous but transient and does not therefore appear to be mediated through specific receptor occupancy. Since sex steroids have been shown to inhibit mitogen-induced blast transformation at concentrations close to 10(-5) M, we suggest that this membrane effect of sex steroids may partly explain their immunosuppressive effects.