COMPARISON OF DNA RENEWAL IN GERM-FREE AND CONVENTIONAL MICE USING [125I]IODODEOXYURIDINE AND [3H]THYMIDINE

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Abstract
Germ-free (GF) and conventional (CV) C3H mice received a single injection of 1 .mu.Ci [3H]thymidine and 3 .mu.Ci [125I]iododeoxyuridine to provide simultaneous labeling of DNA with the 2 precursors. Thymus, spleen, mesenteric lymph nodes, bone marrow (femora), small intestine, colon and skin were examined for total organ activity and rate of DNA renewal 1-8 days after injection. Precursor incorporation assayed on day 1 and lower in the thymus, mesenteric lymph nodes and femora (and to lesser extent in the spleen and colon) of GF mice as compared to CV animals. The opposite was observed in the small intestine and skin, i.e., total organ activity was higher in GF animals. Differences in precursor incorporation were partly due to differences in organ weights between the 2 groups of mice. In comparison to CV animals, DNA renewal rates were diminished in the mesenteric lymph nodes, bone marrow, colon (following a 3-day plateau) and spleen of GF mice. Little if any difference was observed between the 2 groups with respect to rate of DNA turnover in the thymus and skin. Radioactivity of the small intestine remained constant for 2 days. Thereafter intestinal activity in GF mice declined at an initial slow rate between days 2 and 5 followed by a rapid decrease between days 5 and 8. In CV mice the 1st phase of activity loss was short with the rapid decline in intestinal activity beginning on day 3. From the slopes of the regression lines, the percentage thymidine reutilization was estimated. Reutilization varied from 0 to 63% in the various organs examined, with the greatest difference between GF and CV mice occurring in the mesenteric lymph nodes.