The stimulatory effect of muramyl dipeptide (MDP) on the proliferation processes in parenchymal organs of rats.

The administration of muramyl dipeptide (MDP) in a single dose of 2 mg/kg increased markedly the utilization of 3H-thymidine for the synthesis of DNA thymine in liver, kidney and thymus, while no effect has been observed in spleen. Higher doses of MDP (5 mg and 10 mg) did not further increase the effect, but, on the contrary, in some tissues such as thymus, the effect was abolished. The repeated administration of 1 mg/kg of MDP for 7 days, contrary to single administration, had no effects. The measurement of proliferation activity in the experiment where DNA in the organs has been previously labeled with 3H-thymidine, has shown that the repeated administration of MDP (1 mg/kg) led to a more rapid decay in specific activity of DNA thymine in liver, kidney and thymus, but no effect was seen in spleen. The activities of thymidine kinase in the cytosole fraction of thymus and spleen after a single administration of MDP (1 mg/kg), are influenced in different ways. While in thymus the enzyme activity increased between 16 and 24 h, not being markedly changed in the early intervals, in spleen a significant decrease in phosphorylation of 14C-thymidine can be observed as early as 2 h after administration, and the decrease persists up to 48 h.