Polyamines and their biosynthetic decarboxylases in various tissues of the young rat during undernutrition.

1. Male weanling rats were maintained at a constant body-weight by feeding them reduced amounts of the normal diet for various periods up to 4 weeks. Control male rats were allowed free access to the normal diet and some were killed at the beginning of the experiment and others at the same ages as the experimental rats. 2. After killing by cervical dislocation the rats had their liver, quadriceps muscles and spleen removed. The tissues were weighed and the activities of the enzymes ornithine decarboxylase (ODC; EC 4.1.1.17) and S-adenosylmethionine decarboxylase (SAMD; EC 4.1.1.50) assayed in each tissue. In the liver the content of the polyamines (spermidine and spermine) and putrescine was also measured. 3. The liver and quadriceps muscles showed an over-all maintenance of weight during undernutrition, but the spleen lost weight during the first 7 d of undernutrition and then remained constant. The weight of the liver increased by approximately 50% following the daily maintenance feed, but returned to its prefeeding value by 24 h after feeding. 4. During the first 7 d of undernutrition ODC activity decreased in all three tissues, and remained fairly constant thereafter. In the liver there were marked increases in the activity of ODC during the first 4 h after the daily feed, but the activity then decreased to prefeeding values. SAMD activity tended to remain normal in the liver, decreased initially and then returned to normal in the quadriceps muscles, and remained normal initially and then decreased in the spleen. Hepatic SAMD activity showed no consistent response to the daily feed, but quadriceps SAMD activity increased significantly between 1 and 8 h after feeding. 5. Hepatic putrescine content remained constant during undernutrition whilst spermine increased slightly and was then maintained above normal for liver size. Hepatic spermidine content decreased initially and then remained constant. Putrescine increased slightly in response to the daily feed and spermidine increased considerably. Spermine content was unaffected by the daily feed. 6. It is suggested that the response of polyamine synthesis in the various tissues is primarily dependent upon the way in which nutrients are made available to the tissues. The maintenance of spermine content in the liver at the expense of spermidine may be related to differential changes in the nucleic acids.