The incorporation of radioactive phosphorus into the nucleic acids of different rabbit tissues

Abstract

Comparison was made between radioactivity of whole deoxyribonucleic acids (DNA''s) isolated from a number of different rabbit tissues after p32 administration and of their constituent deoxyribonucleotides. The conclusion is that it is justifiable to take the activity of the isolated DNA as a true measure of P uptake. The course of incorporation of p32 into the DNA, nuclear ribonucleic acid (RNA), cytoplasmic RNA and inorganic phosphate of rabbit appendix, bone marrow, intestinal mucosa, kidney, spleen and thymus was followed between 2 hours and 7 days. Tissues are divided into 3 groups with respect to DNA turnover: (a) kidney in which the renewal of DNA is very small; (b) intestinal mucosa, spleen and thymus which show moderate turnover rates for DNA; (c) appendix and bone marrow in which the rate of DNA renewal is very rapid. In all tissues the turnover of nuclear RNA was much more rapid than that of DNA or cytoplasmic RNA. Only in bone marrow and appendix did cytoplasmic RNA give lower specific activity values than DNA. X-irradiation of abdominal viscera and femora produced a marked inhibition of p32 incorporation into DNA, nuclear RNA and cytoplasmic RNA of appendix and bone marrow. Delayed depression of the uptake of p32 by the DNA, nuclear RNA and cytoplasmic RNA of thymus was also noted. Only small changes were noted in kidney nucleic acids, both nuclear RNA and cytoplasmic RNA showing slightly elevated activities 2 hours after irradiation and low values after 20 and 49 hours. Phenyl-hydrazine induced hemolytic anemia with resultant hyperplasia of bone marrow causes a twofold increase in activity of bone marrow DNA and a tenfold increase in the activity of spleen DNA. The cytoplasmic RNA''s of bone marrow and spleen also showed greatly increased activities but comparatively small changes were found in uptake of P32 by the nuclear RNA''s oi these tissues. The metabolism of appendix, kidney and thymus nucleic acids did not appear affected by this treatment.