Effect of thioacetamide, growth hormone or partial hepatectomy on spermidine acetylase activity of rat liver cytosol.

Rat liver cytosol extracts catalyzed the formation of monoacetylspermidine when incubated with acetyl-CoA and spermidine. This activity was enhanced 15-fold by administration of thioacetamide (150 mg/kg). The peak of activity occurred 18-24 h after treatment with the drug and then declined reaching control levels by 76 h. Previous studies have shown that ornithine decarboxylase activity was also greatly increased over this time period. Putrescine content in the liver was increased 80-90-fold at 18-24 h and then declined. Spermidine levels were decreased significantly over the period 12-24 h after thioacetamide treatment and then increased substantially at later times. These results are consistent with the hypothesis that, at early times after administration of thioacetamide, the increase in putrescine content is brought about both by decarboxylation of ornithine and by degradation of monoacetylspermidine. Spermidine acetylase activity was also measured in liver extracts prepared after two other physiological stimuli known to enhance ornithine decarboxylase activity were used. Both growth hormone treatment and partial hepatectomy produced an early 2-3-fold increase in the cytosolic spermidine acetylase activity.