The aim was to study reutilization of DNA nucleotide bases in the liver and spleen of young and adult mice. The experiments were performed on 128 mice, 16 animals in each: 8 young (body weight 20–27 g) and 8 adult (42–49 g). All animals were given 14 C-thimidine s.c. 1 mCi every 24 hours for 72 hours. Control groups were sacrified 24 hours (intact 0) and/or 72 hours after completed 14 C-thymidine administration (intact 48). Laparotomy (LAP), partial hepatectomy (PH), splenectomy (SX), PH+SX (PHSX), LAP + hydrocortisone administration (1.3 mg per 10 g body weight) (LAPH), PH + hydrocortisone application (PHH) were implemented 24 hours after 14 C-thymi- dine administration in the experimental groups. Animals were sacrificed 48 h after the operations. Specific activity of liver and spleen DNA (SADNA) were estimated. The data were treated statistically using the unpaired t-test (Jandel Scientific software). Selected results are presented as mean and SEM in disintegrations per minute (dpm) x 10 3 per mg of DNA. There was no difference in liver SADNA between controls and experimental groups in young mice (all results were between 6.06 and 6.48). Liver SADNA in adult groups were: 3.15 ± 0.6 in intact 0, 2.03 ± 0.15 in intact 48 (p < 0.05), 2.1 ± 0.18 in LAP, 4.18 ± 0.42 in PH (p < 0.001), 2.1 ± 0.24 in LAPH, 3.72 ± 0.40 in PHH (p < 0.001), 2.54 ± 0.30 in SX and 4.2 ± 0.42 in PHSX group (p < 0.01). There are evident differences in reutilization of DNA nucleotide bases in young and adult animals. The redistribution of 14 C-thymidine is more evident in adult mice, especially after PH, and is not suppressed by SX and hydrocortisone administration.

        Key words: reutilization, partial hepatectomy, specific activity of DNA, mice, liver regeneration.