Liver DNA and RNA metabolism in rats fed diets lacking methionine plus cysteine with or without restricted energy.

Ponderal parameters, soluble protein content and nucleic acid (DNA and RNA) metabolism were studied in liver of growing male Wistar rats fed with different diets: control diet (Control group) containing 10% protein (casein 9.8% plus DL-methionine 0.2%); diet 2 (Group 2) containing 10% protein, lacking Met plus Cys; and diet 3 (Group 3), containing 20% protein, lacking Met plus Cys and with 50% of energy restriction (restricted food intake by experimental design). Diets 2 and 3 were compared with the control diet to know the effects produced by the lack of Met plus Cys and the energy restriction, for an experimental period of 14 days, the animals being slaughtered on the 4th, 8th and 14th days. Food intake, body and liver weights, relative liver weight, cellular size and RNA content per organ and per mg protein decreased in groups 2 and 3, group 3 being affected more than group 2. Diet 2 produced a decrease in DNA content, due to lack of Met+Cys. Acid DNAse activity per organ diminished in group 2 on days 8 and 14, and in group 3 on the 8th day. RNA/DNA ratio diminished in group 2 and 3 due to a proportional RNA reduction with respect to the DNA content. Acid RNAse activity per organ diminished in group 2 on the 8th and 14th days, RNAse per mg of protein increased in group 3 at the end of the treatment, therefore the RNA content decreased. The content of DNA in liver is lower than RNA content in rats fed diet 2 and the opposite occurs with diet 3.