Effects of Cortisone on Thymidine Incorporation by Various Nonlymphoid Tissues of the Weanling Rat 1

Summary

Acute effects of both high and low doses of cortisone upon the incorporation of radioactive thymidine have been examined in a variety of non-lymphoid tissues of the weanling rat. It is shown (a) that thymidine incorporation by different tissues varies over an enormous range in its sensitivity to suppression by cortisone administration, and (b) that at low doses of hormone all the tissues studied are clearly separable into two distinct classes: those in which cortisone produces a profound suppression of thymidine incorporation, and those which are completely unresponsive to the hormone. The pattern of response observed thus far suggests the generalization that thymidine incorporation is particularly susceptible to suppression in tissues which are composed of stable cell populations and in which DNA synthesis is primarily a concomitant of new cell accretion (“growth”) rather than one of cell renewal. The phenomenon of cortisone-induced suppression of thymidine incorporation in individual tissues sensitve to low doses of hormone may provde a convenient model for studies of biochemical mechanisms underlying the well-known suppression of somatic growth which occurs at comparable doses both in experimental animals and in children.