Polyamine metabolism in compensatory renal growth.
The aliphatic polyamines, putrescine, spermidine, and spermine, appear to play an important role in many forms of rapid growth including embryonic, regenerative, hormone-induced, and neoplastic. While the exact biochemical function of polyamines is unclear, current evidence suggests they are probably involved in the biosynthesis and accumulation of nucleic acids and proteins. Increased levels of polyamines and their biosynthetic enzymes are associated with augmented kidney growth stimulated by renal mass extirpation, as well as by various hormones, toxins, and carcinogens. These observations are reviewed and additional data is provided pertaining to alterations in polyamine metabolism during compensatory renal growth following unilateral nephrectomy (uni). To further explore the effect of growth stimuli on renal polyamine synthesis, an in vitro system was employed which previously provided evidence for a circulating renal growth factor after unilateral nephrectomy. These in vitro observations underscore the rapid inducibility of ornithine decarboxylase, the rate limiting enzyme for polyamine biosynthesis; illustrate the association of polyamine and nucleic acid synthesis during enhanced kidney growth; and support the existence of a circulating renal growth regulator which apparently contributes to compensatory responses following loss of functional renal parenchyma.