1. Weanling male and female rats were undernourished for 4 weeks and then rehabilitated by allowing ad libitum feeding. 2. During rehabilitation
polyamine-biosynthetic
enzymes were examined in the liver, spleen and quadriceps and gastrocnemius muscles. 3. During the first few hours of rehabilitiation there was a marked increase in liver weight, accompanied by a very marked increase in
ornithine decarboxylase activity. Increases in the activity of this
enzyme in other tissues did not occur until between 2 and 7 days of rehabilitation, at which time there were further increases in
enzyme activity in the liver. 4.
S-Adenosylmethionine decarboxylase activity also showed marked fluctuations in activity in all the tissues examined. 5. Hepatic
putrescine and
spermidine concentrations also varied during rehabilitation, but permine concentration remained relatively constant. Both
spermine and
spermidine were at normal concentrations in the liver from the 10th days of rehabilitation onwards. 6. In all of the tissues examined there were marked sex differences in the parameters studied, particularly in splenic and muscular
ornithine decarboxylase activity. 7. In the tissues of the male rats, changes in
polyamine synthesis paralled changes in
nucleic acid and
protein synthesis.