Alkaline Ribonuclease Activity Increase in Rat

Acid azo dyes, most of them naphtholdisulfonic acid derivatives, were given intraperitoneally to rats and their effect on "alkaline" ribonuclease activity was studied in total homogenates of kidney cortex and liver. Acid treatment was used to release bound enzyme activity. Several of the dyes, including trypan blue, increased RNase activity in both organs 3 days after administration of single doses, while others, like Evans blue, were inactive. Activity was apparently bound to the sulfonic substitution in the 3, 6 positions in the naphthalene rings, substitutions in the benzidine rings being not critical. All of the active and most of the inactive compounds were taken up by tubule cells of kidney cortex and by reticular and parenchymal cells of liver. While the effect on both liver and kidney was obtained 1 day after trypan blue administration, RNase remained increased for only about 3 days in the first organ, and for at least a month in the second. However, repeated trypan blue doses increased liver enzyme activity for at least 9 days. Serum RNase activity was decreased after trypan blue administration. Ethionine administration together with trypan blue markedly blocked the effect of the dye on liver RNase activity; simultaneously given methionine partially reversed the action of the antimetabolite. This suggests that de novo synthesis of RNase is induced in liver by trypan blue. The action of ethionine on the kidney RNase response to trypan blue was less marked although significant; in view of the possible kidney uptake of the plasma enzyme, interpretation of this finding must be postponed. Results are discussed with reference to the mechanism of the structural specificity of the compounds used, cytological localization of the dyes and their mechanism of action on liver and kidney RNase. Disclosure of the participation of ribonucleic acids in the mechanism of protein synthesis led to a renewal of interest in enzymes involved in RNA synthesis and degradation (1). Moreover, the findings of Brachet (2) and others of in vivo effects of pancreatic ribonuclease (RNase) on a variety of single-celled and multicellular organisms, pointed to the need of further knowledge on the biochemistry and physiology of interand intracellular hydrolytic enzymes of this group (cf. 3). Previous work from this laboratory has shown that in mammals plasma alkaline RNase is inactivated by the kidneys (4) and suggested that the kidney enzyme could be taken up from the plasma (5). During the course of a study on the effect of administering several proteins on RNase activity of the renal cortex (6), azo dyes known to be bound to proteins were also assayed. It was found that trypan blue and some related dyes increase 105 on A ril 5, 2017 D ow nladed fom Published May 1, 1961