Interconversion of Aliphatic Polyamines in Isoproterenol-Stimulated Mouse Parotid Glands12

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Abstract
The metabolism of spermidine, and especially putrescine formation from spermidine during the prereplicative period of cell proliferation, was investigated in isoproterenol-stimulated mouse parotid glands. The rate of spermidine synthesis from putrescine decreased significantly about 4 h after isoproterenol treatment, whereas the putrescine level increased at this time. Spermidine synthesis began to increase from 6 h after isoproterenol treatment, and was maximal 8 to 10 h after treatment. Administration of isoproterenol resulted in a gradual decrease in the spermidine concentration to a minimum of about 80% of the control level after 6h. This decrease was accompanied by increased conversion of spermidine to putrescine. The degradation of spermidine to putrescine contributed to the increase in the putrescine level in the parotid glands in the very early stage after isoproterenol treatment, the contribution reaching more than 70% at 4 and 6 h after treatment. No increased degradation of spermidine to putrescine was observed in the liver or kidney, where cell proliferation was not accelerated by isoproterenol. Administration of isoproterenol had little effect on conversion of spermidine to spermine or the reverse reaction in parotid glands. These results show that the increase in the putrescine level observed in mouse parotid glands soon after isoproterenol treatment is due to not only an increase in ornithine decarboxy-lase activity but also enhanced conversion of spermidine to putrescine. The results also suggest that putrescine is not merely used for spermidine synthesis in the early prereplicative stage, and that the two amines may be of different importance for growth in this system.

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