Effects of exogenous putrescine on the retinoic acid-induced reduction of 12-O-tetradecanoyl-phorbol-13-acetate-stimulated putrescine accumulation and rate of DNA synthesis in the hairless mouse epidermis.

Pretreatment (at 1 h) with retinoic acid (RA) inhibited both the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced wave of epidermal putrescine accumulation (which peaked at 8 h) and the first wave of epidermal DNA synthesis (which peaked at 16 h), but failed to depress the second wave of DNA synthesis (which peaked at 32 h) even with a second application of RA at 16 h. The inhibitory action of RA pretreatment on the DNA synthesis peak at 16 h was dosedependent. Thus, there may be an association between the putrescine accumulation at 8 h and the wave of DNA synthesis at 16 h. When TPA-stimulated epidermis was pretreated with RA, exogenous putrescine (given i.p.) affected neither the reduced putrescine accumulation nor the reduced first wave of DNA synthesis. However, exogenous putrescine potentiated stimulated DNA synthesis, both at 16 h after TPA and at 32 h after RA plus TPA.