Changes in polyamine levels during aging were measured in 3-, 10- and 26-week-old female mice. The level of polyamines in pancreas, brain, and uterus was maintained during these periods. The level of spermidine slightly decreased in intestine, and decreased significantly in thymus, spleen, ovary, liver, stomach, lung, kidney, heart and muscle during these periods. In skin, the level of spermidine was maximal in 10- week-old mice and markedly reduced in 26-week-old mice. The results suggest that maintenance of polyamine levels may play important roles in the function of the pancreas, brain and uterus in 3- to 26-week-old mice. We next looked for polyamine-rich food materials as a dietary source of polyamines. Foods found to be rich in polyamines included wheat germ, rice bran, black rice, Philippine mango, green pepper, Japanese pumpkin, nuts, fermented pickles, pond smelt, turban shell viscera, whelk viscera, salted salmon roe, salted cod roe, beef intestine (boiled) and liver of eel, beef, pork and chicken; and, as previously reported, soybean, fermented soybean (natto), mushrooms, orange and green tea leaf. These results offer useful information when it becomes necessary to ingest polyamines from food.

Polyamines (putrescine, spermidine and spermine) are present at millimolar concentrations in both prokaryotic and eukaryotic cells and play regulatory roles in cell growth (1–3). Stimulation of cell growth by polyamines is mainly due to the enhancement of specific kinds of protein syntheses which are important for cell growth (4–7). Accordingly, it is important to keep the polyamine content at an optimal level to maintain the function of various organs. However, it is known that polyamine content decreases with the progress of cell growth in Escherichia coli (8) and that polyamine content in six different rat tissues decreases with aging (9). The intracellular levels of polyamines are regulated at various steps including synthesis, degradation, uptake and excretion (10, 11). The importance of polyamine ingestion from food was suggested by the finding that the antitumor effects of the inhibitors of polyamine biosynthesis were enhanced in mice bearing P388 leukemia or Lewis lung carcinoma when a polyamine-deficient diet was used (12). It has been also shown that polyamines are readily taken up by the gut and enter the systemic circulation in rats (13, 14) and mice (12). To keep the polyamine content at an optimal level in various organs, it is presumably important to ingest polyamines from food as people become older, because it is known that the activity of one of the key polyamine biosynthetic enzymes, ornithine decarboxylase, decreases with increasing age in rats (15). In this context, the polyamine contents in 70 typical kinds of food were measured previously (13, 16).

The components of the elution buffer and the o-phthalaldehyde solution are described in the previous communication (17). The flow rate of the elution buffer and the o-phthalaldehyde solution were 0.2 ml/min, and fluorescence was measured at an excitation wavelength of 340 nm and an emission wavelength of 455 nm. The retention times for putrescine, cadaverine, spermidine, agmatine and spermine were 27, 38, 51, 89 and 102 min, respectively. Values shown in the table (nmol/g wet weight) are means of duplicate determinations of each sample. Polyamine contents in each food were measured using at least two different samples. If the difference in polyamine contents of the two samples was large, both values are shown in the Table 1. Measurement of Protein Content—Protein content in mouse tissues was measured using 5% TCA precipitate according to the method of Lowry et al. (18).

Thus, rice mixed with black and brown rice, and bread mixed with wheat germ are recommended as a source of polyamines. Among vegetables, beans, seeds and mushrooms, the following were rich in polyamines: green pepper, broccoli, broccoli sprout, Japanese radish leaf, turnip leaf, Japanese pumpkin, all kinds of beans, fermented soybeans (natto), pine seed, nuts and all kinds of mushrooms. Putrescine and cadaverine were included in fermented cheese and pickles, especially in blue cheese, shibazuke (Lactobacillus-fermented cucumber) and nukazuke (Lactobacillus-fermented cucumber with salted rice-bran paste). It has been reported that spermine in human milk prevents the occurrence of allergies in children (20). Our data confirmed the presence of spermine in human milk, but not in bovine milk. Among fish, shellfish and meat, polyamines were rich in pond smelt, turban shell viscera, whelk viscera, salted cod roe, salted salmon roe, codfish milt, beef intestine (boiled), and liver of eel, beef, pork and chicken. Among fruits, putrescine levels were high in orange and Philippine mango, and spermidine levels were high in durian and Philippine mango. Putrescine and cadaverine were also present in soy sauce, soybean paste and fish sauce. Among beverage and alcohol, polyamines were included in green tea leaf. However, polyamines contents were low in green tea extracted from green tea leaf. Agmatine was rich in Japanese sake (rice wine). Putrescine was included more in beer than in wine. Sake lees contained putrescine, cadaverine and agmatine. It has been reported that the optimal concentrations of spermine, spermidine and putrescine for stimulation of globin synthesis are 0.08, 0.4 and 8 mM, respectively (21). 

The effect of cadaverine was nearly equal to that of putrescine (22), and that of agmatine was less than that of putrescine (23). Since the effective concentration of each polyamine on cell growth was nearly parallel with that of protein synthesis (21), it is thought that polyamines are effective in the order spermine > spermidine > putrescine = cadaverine > agmatine in terms of stimulating cell growth. The content of spermine in food was in the order turban shell viscera (770–32,700 nmol/g) > chicken liver > pork liver > beef liver > wheat germ > salted cod roe > beef intestine (boiled) > chicken heart > eel liver > Japanese pumpkin. Spermine content in these foods was more than 500 nmol/g. The content of spermidine was in the order turban shell viscera (166–91,500 nmol/g) > wheat germ > agaricus dried > black soybean > soybean > shimeji mushroom > eringi mushroom > fermented soybean (natto) > green pepper > maitake mushroom. Spermidine content in these foods was more than 700 nmol/g. The content of putrescine was in the order green pepper (1,180–2,690 nmol/g) > pond smelt > shibazuke (Lactobacillus-fermented cucumber) > orange > codfish milt > nukazuke (Lactobacillus-fermented cucumber with salted rice-bran paste) > matsutake mushroom > Philippine mango > oyster sauce > corn. Putrescine content in these foods was more than 800 nmol/g. The content of cadaverine was in the order fish sauce (nam pla) (3,900 nmol/g) > gorgonzola cheese > pond smelt > fermented soybeans (natto) > blue cheese > whelk viscera > sake lees > black soybean > soybean.

Although the levels of polyamines, especially spermidine, decreased in most tissues in mice, the levels in pancreas, brain and uterus were maintained between 3 and 26 weeks of age. Many digestive enzymes are synthesized in pancreas and many ion channels such as K+ channels and NMDA receptors exist in brain. In uterus, protein synthesis may be active due to menstruation. Since stimulation of protein synthesis (6) and modulation of ion channels (24, 25) are the most important functions of polyamines, mechanisms to maintain their levels may exist in these tissues. In human, polyamine content in maturating erythrocytes was reported to be lower than that in younger erythrocytes when they were age-separated by density (26). In human, it has been reported that spermine deficiency is a cause of Snyder-Robinson syndrome (27); that spermine in human milk during the first postnatal month prevents the occurrence of allergies (20); and that administration of a-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, causes hearing loss, although this may be due to a side effect of DFMO rather than the decrease in polyamine content (28, 29). In mice or rats, a decrease in polyamines caused hair loss and infertility in females (30), pancreatitis (31), and impairment of spatial learning (32). Furthermore, ingestion of polyamines inhibited gastric ulceration (33) and stimulated maturation of intestine (34) in rats. On the contrary, the antitumor effects of polyamine biosynthesis inhibitors were enhanced in mice bearing P388 leukemia or Lewis lung carcinoma when a polyamine-deficient diet was used (12). 

These results suggest that ingestion of polyamine-rich food may be helpful for maintenance of health especially in old age. However, cancer patients should avoid polyaminerich food, as mentioned above (12). Our results offer useful information about when it becomes necessary to ingest or to avoid ingestion of polyamines. Since the decrease in spermidine was most marked among the three polyamines, either food containing the three polyamines or spermidine-rich food is recommended in the diet. In this respect, some food contained norspermidine [N-(3-aminopropyl)-1,3-diaminopropane], which is eluted at 45 min on HPLC under our experimental conditions and functions similarly to spermidine in the stimulation of protein synthesis (22). These foods are eggplant, tomato, gorgonzola cheese, shibazuke, pond smelt, soy sauce (tamari) and fish sauce (nam pla). In animal cells, however, polyamines also contribute to cell growth through eIF5A formation from spermidine, which is an essential protein for cell growth (35, 36). The function of spermidine cannot be replaced by norspermidine for the formation of active eIF5A. Thus, we should keep in mind to ingest spermidine-rich food together with norspermidinerich food.We thank Dr. K. Williams for his kind help in preparing the manuscript. The work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, Culture and Technology, Japan; and Tokyo Biochemical Research Foundation, Japan.