Ornithine decarboxylase basal activity in liver, oesophagus and lung of vitamin A deficient rats, and the effect of retinoic acid.

Ornithine decarboxylase (ODC, EC 4.1.1.17) activity was measured, without exogenous stimulation, in the liver, oesophagus and lung of Wistar rats which were vitamin A deficient or supplemented with retinol or retinoic acid. The enzyme basal activity in such deficiency conditions was higher, when compared with controls, in the oesophagus and especially in the lungs. Retinoic acid normalized enzyme activity only at high doses (300 micrograms/day). In the liver, initial retinol deficiency did not sensitively modify ODC activity, and retinoic acid then stimulated the enzyme abnormally. This phenomenon could not be observed at later stages of vitamin deficiency (but there again without cytological abnormalities or thymidine incorporation disturbances): liver ODC response then became comparable to that of other tissues. These results highlight the particular basal hyperactivity of pulmonary ODC during the initial stages of vitamin A deficiency, indicative of an enhanced tendency to cell proliferation. A special stimulating effect of retinoic acid on ODC, contemporary with early deficiency, was observed in the liver; this effect was not observed at a later stage in normally fed rats.