[Mechanism of the formation of single-stranded DNA breaks under the effect of prednisolone on rat liver thymocytes].

Rat liver thymocytes were incubated in vitro with prednisolon, and molecular weight of single-stranded DNA was estimated in alkaline lysates of nuclei by viscosity methods. The number of single-stranded breaks was estimated, which originate in DNA after 3 hours of incubation with prednisolon at a concentration of 3-10(-9) M--3-10(-4) M. Maximal hormone effect was produced within 30 min., and it remained constant for the rest 3 hours of the incubation. Cycloheximide prevented hormone-induced DNA depolymerization, and actinomycin D only slightly inhibited the formation of single-stranded DNA breaks, originated after 30 min. incubation of thymocytes with prednisolon, were repaired after their washing and reincubation in the fresh medium for 1 hour at 37 degrees C. The washing of thymocytes and their reincubation for 3 hours resulted in the decrease of the molecular weight of single-stranded DNA. Possible mechanism of the formation of single-stranded DNA breaks in prednisolon-induced thymocytes is discussed.