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The regeneration of adult planarians is completed inhibited by antinomycin D (AMD), although that of young animals is slightly affected. The proposed hypothesis such as the required mRNA were available prior to section must be revised. In fact, RNA synthesis does occur in spite of AMD in the young. The dose effect, degree of inhibition and rapidity of effect of the inhibitor on RNA synthesis are compared at both ages.

The effects of serotonin, dopamine and noradrenaline on RNA synthesis, estimated by the incorporation of [3H]orotic acid, were studied on regenerating fragments of planarians. Serotonin was observed to inhibit, whereas dopamine and noradrenaline had no apparent action. These three neurohormones and their antagonists were also tested on planarian cell cultures, using [3H]-uridine as tracer. RNA synthesis, inhibited by serotonin, methiothepine (serotonin antagonist) and fluphenazine (dopamine antagonist), was shown to be restored by dopamine. The effects of serotonin, dopamine and their antagonists, are discussed in relation to the adenylate cyclase system.

RNA and protein synthesis in Planarian cells cultivated in vitro was studied by histoautoradiography. In the non-differentiated cells, uptake of precursor is intense from the beginning of the culture, and sensitive to addition of trophic factor known for their activating effect on mitosis and regeneration. On the contrary the rate of incorporation in differentiated cells is low and uniform, independently of the differents factors added to the medium.

An analytical-technique for the extraction of total RNA has been employed to investigate RNA synthesis during regeneration in Planaria. Two phases in RNA synthesis were identified during the first 72 hrs. after the section.