Induction of spermidine/spermine N1-acetyltransferase in needle-punctured rat lens as a model of traumatic cataract.

Isolated rat lens was punctured with a needle at a single point in the equatorial region and was incubated at 37 degrees C. Spermidine/spermine N1-acetyltransferase activity was increased about 5-fold at 8 h after the puncture. Concomitantly, putrescine content in the lens increased markedly at 8-16 h after the puncture, while spermidine levels were slightly depressed. Pretreatment of the lens with actinomycin D or cycloheximide blocked the increases of spermidine/spermine N1-acetyltransferase activity and putrescine content. Ornithine decarboxylase, on the other hand, was not induced to a detectable degree by this stimulus and 5 mM difluoromethylornithine could not block the increase of putrescine content. Polyamine oxidase showed a relatively constant activity that was sufficient for the metabolism of newly formed N1-acetylspermidine. These results suggested that, in the punctured lens, the polyamine levels were regulated predominantly by the activity of spermidine/spermine N1-acetyltransferase, but not by the induction of ornithine decarboxylase.