The effect of estradiol-17β on polyamine synthesis and accumulation was studied in the uterus of the castrated rat. A single injection of estradiol-17β produced more than a 2-fold increase in ornithine decarboxylase (ODC) activity within 24 hr. A more dramatic elevation of the spermidine synthesis enzyme [Sadenosyl- L-methionine decarboxylase (SAME)] was detected, i.e., SAMD activity was 8-fold higher than control values by 18 hr. Increased pools of putrescine and spermidine follow directly the temporal increases in the enzymes. Putrescine concentration tripled and spermidine concentration doubled within 24 hr. Thereafter, both putrescine and spermidine concentrations gradually decreased. The spermine level also was elevated in this system; it reached a level 2-fold higher than controls within 24 hr, peaked within 72 hr, and thereafter declined markedly and was not significantly higher than controls by 96 hr. Actinomycin D and cycloheximide essentially abolished the increases in both ODC and SAMD activities when administered simultaneously with estradiol-17β. ODC turns over very rapidly in rat liver (half-life 10-20 min). In this study we estimated the half-life of SAMD in the estradiol-stimulated uterus and in rat liver by plotting the decline in enzymatic activity at various times after cycloheximide administration. In both rat liver and in the estradiol- stimulated uterus, SAMD had a calculated half-life of 60 min. Thus, it has a half-life 3-4 times greater than ODC. (Endocrinology88: 1397, 1971)
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Russell et al. (1971) studied this question.