Polyamine metabolism in compensatory renal growth

Compensatory renal growth, following renal mass extirpation, is accompanied by multiple biochemical alterations including increased nucleic acid, protein, and polyamine synthesis. The aliphatic polyamines-putrescine, spermidine, and spermine are found in most living organisms and appear to participate in many forms of augmented growth including embryonic, regenerative, hormone-induced, and neoplastic [1–3]. While the precise biochemical function of these compounds has not been defined, increased levels of polyamines and their biosynthetic enzymes occur in association with enhanced nucleic acid and protein synthesis in rapidly growing tissues [3–6]. Polyamines apparently contribute to nucleic acid accumulation by promoting biosynthesis and retarding degradation [6–8]. The decarboxylation of ornithine to putrescine is the rate-limiting step in polyamine synthesis. The catalyst, ornithine decarboxylase, is very inducible and has a short half-life in both normal and regenerating liver (10 to 11 min) [5]. Changes in enzyme activity precede or occur simultaneously with increases in RNA, DNA, and protein concentrations [3]. In this study, alterations in renal polyamine synthesis were investigated in conjunction with other evidences of stimulated kidney growth following unilateral nephrectomy. These data are discussed in the context of previous observations regarding polyamine biosynthesis during enhanced renal growth.