Molecular Pharmacology, Vol 3, 219-224, Copyright © 1967 by the American Society for Pharmacology and Experimental Therapeutics

The Effect of Cortisol, Administered in Vivo, on the in Vitro Incorporation of DNA and RNA Precursors by Rat Thymus Cells

¹ Department of Pharmacology, Stanford University School of Medicine, Palo Alto, California 94304

Cortisol, administered in vivo, decreases the rate at which radioactive labeled deoxycytidine and uridine are incorporated into macromolecular material by rat thymus cells incubated in vitro. The degree of inhibition of uridine conversion to acid-insoluble material, observed after 3 hr of cortisol treatment, remains constant at both high and low levels of precursor specific activity, whereas the inhibition of deoxycytidine-³H incorporation observed using precursor of high specific activity is obliterated when the labeled precursor is diluted with large amounts of the nonradioactive compound. This observation is consonant with the hypothesis that one action of cortisol on rat thymocytes is to increase the intracellular pool of DNA precursors and not, as has been supposed, to inhibit the rate of DNA synthesis. Inhibition of RNA synthesis does seem to occur within a few hours after cortisol administration.

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ACKNOWLEDGMENTS This work was supported by Grant CAO5672 from the National Cancer Institute, National Institutes of Health, and Public Health Service Training Grant GM322 from the Division of General Medical Sciences.