Hyperplastic alveolar nodule (HAN) is a representative preneoplastic state in mammary glands of mice. We investigated the effect of Sho-saiko-to (SST; a Japanese modified traditional Chinese herbal medicine containing seven medicinal plants) on the formation and growth of HAN and mammary tumour growth in SHN virgin mice which showed a high incidence of spontaneous mammary tumours. Chronic oral administration of SST reduced the number and the area of HAN and mammary thymidylate synthetase (TS) activity with slight decrease of serum prolactin level. In the established mammary tumours of mice, 20-day administration of SST reduced the activity of TS and thymidine kinase (TK) with slight reduction of serum prolactin level, though the significant change of mammary-tumour growth was not observed. These results indicate that SST may prevent the mammary tumourigenesis by suppression of the de novo pathway for pyrimidine nucleotide synthesis and the mammary tumour growth by suppression of the salvage pathway as well as the de novo pathway in mice.

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