Altered Metabolism of DNA in Rat Thymus, an Early Response to Cortisol

Slices of thymus glands, prepared from adrenalectomized rats treated with cortisol for 1 hr, released over twice as much DNA into the incubation medium as did slices from control rats during a 2-hr incubation period. The material released was identified as DNA by its precipitation in cold acid, its solubilization in hot acid, its ultraviolet absorption, its reaction with diphenylamine, and its susceptibility to purified DNAase. Slices of thymus prepared from rats 2 hr after cortisol treatment incorporated thymidine- methyl-3H into DNA at only about 50% ofthe rate of control slices when 0.01 mM 3H-thymidine was added to the incubation medium. In contrast, incorporation of 3H-thymidine into DNA was not depressed when the labeled thymidine was present at the 1 mM level in the incubation medium. These findings suggest that in cortisol- altered tissue higher levels of deoxyribonucleotides dilute the labeled thymidine nucleotides, thus leading to a decreased incorporation of label when the tracer is added in low concentration. (Endocrinology80: 297, 1967)