Summary: 1. S-1, a new oral anti-tumor drug, is composed of 5-fluoro-l-(tetrahydro-2-furanyl) 2,4(1H,3H)-pyrimidinedione (Tegafur, FT), 5-chloro-2,4-dihydroxypyridine (Gimestat, CDHP) and potassium 1,2,3,4-tetrahydro-2,4-dioxo-1,3,5-triazine-6-carboxylate(potassium otastat, Oxo) at a molar ratio of 1 : 0.4: 1. FT which is masked compound of 5-Fluorouracil (5-FU) plays a role as an effector com pound. Both CDHP and Oxo which do not have antitumor activity themselves play roles as modulators.After administration of S-1 or FT to tumor bearing rats, the Cmax and AUC of 5-FU were 20.8 pmol/ml and 207.6 pmol•hr/ml, in FT group and 1,192.0 pmol/ml and 5,203.0 pmol•hr/ml, in S-1 group. Thus, the S-1 group showed higher plasma 5-FU levels by 57 times in Cma., and by 25 times in AUC than those in the FT group. Similar to the plasma concentration, the concentration of 5-FU in tumor in the S-1 group was also higher than that in the FT group by 23 times in Cmax and by 16 times in AUC.2. After administration of S-1 to tumor bearing rats, the plasma concentration of CDHP, the reversible competitive inhibitor of dihydropyrimidine dehydrogenase (EC1.3.1.2), showed a Cm value of 2,054.8 pmol/ml at 30 min post-dose. The concentration of Oxo, the inhibitor of orotate phosphoribosyltransferase (EC2.4.2.10), in small intestine showed a Cmax value of 36,156.5 pmol/g at 30 min post-dose, and showed still high concentration of 2,813.6 pmol/g even at 3 hr post-dose.3. AUC of 5-FU in plasma and various tissues after administration of S-1 were found to be greater than those AUC after administration of UFT (combination of FT and uracil). AUC of fluoroureidopropionic acid (FUPA) and fluoro-/3-alanine (FBAL) in the S-1 group were smaller than those in the UFT group.

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The supply and consumption of alkalinity in Sawano-ike Pond was investigated to reveal the mechanisms of pH fluctuation in the pond. Alkalinity in the bottom layer at the deepest point of the pond increased in summer, but in-pond generation of alkalinity was estimated to be very small because of the low depth of water in the pond. According to the calculations of water budget and solute balance, subsurface water, the alkalinity of which is moderately high, accounted for 45% of the total influx during a period of relatively high water level. The predicted concentrations of major ions and alkalinity in the pond calculated from the mass balance coincided well with measured concentrations. The relatively high pH values of the pond water during a period of high water level are considered to be mainly caused by alkalinity supplied by influxes, especially subsurface water. During a period of relatively low water level, predicted alkalinity exceeded measured alkalinity by 29%, indicating the occurrence of in-pond consumption of alkalinity with a resultant decrease in pH.

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