To assess the functional interaction between Zn²⁺ and glutamate in hippocampus, diphenylthiocarbazone (dithizone), a Zn²⁺ chelator, was used to alter the glutamate level in hippocampus in vitro and in vivo. Dithizone at the concentration of 1μM stimulated high K⁺-and veratrine-induced release of [³H] glutamate both in the presence and absence of Ca²⁺ from rat hippocampal slices preloaded with [³H] glutamate without affecting the release of [³H] γ-aminobutyric acid and [³H] acetylcholine. Metal chelators other than dithizone did not evoke the [³H] glutamate release at the concentration of 10μM. Two weeks after the intrahippocampal injection of 20μg of idthizone, both Zn²⁺ and glutamate levels of the hippocampus significantly decreased with no change in the levels of other metals, amino acids, monoamines and acetylcholine.

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The effects of L-tryptophan and the major constituents of cough medicines on the antitussive effect of dihydrocodeine were examined in a comparative study with anesthetized rats. The antitussive effect of dihydrocodeine was enhanced by simultaneous administration of noscapine or methylephedrine. In rats treated with noscapine and methylephedrine together, the effect of dihydrocodeine was more markedly enhanced. Furthermore, L-tryptophan reduced by half the antitussive ED₅₀ (AtD₅₀) of dihydrocodeine. There was no difference between the AtD₅₀ of dihydrocodeine when administered in combination with noscapine and methylephedrine and that of dihydrocodeine when combined with noscapine and L-tryptophan. The AtD₅₀ of noscapine and dextromethorphan was also reduced by about half when what was administered with L-tryptophan. By contrast, the liability with respect to physical dependence on dihydrocodeine was not enhanced by the simultaneous administration of L-tryptophan. These results suggest that L-tryptophan can be considered to be a useful constituent of antitussive preparations.

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In order to clarify the inhibitory effect of valproic acid (VPA) on the metabolic clearance of carbamazepine-10, 11-epoxide (EPO), an active metabolite of carbamazepine, in rat, the disposition of EPO from plasma and the in vitro hydration of EPO were measured in the presence of VPA, in addition to estimating the effect of the antiepileptic on uridine 5'-diphosphoglucuronyltransferase (UDPGT) activity. It was found that the elimination of EPO from plasma was hardly affected by the pretreatment of VPA (100 mg/kg/d for 7 d). However, the elimination was significantly delayed by VPA at steady-state concentration, maintained by the repeated oral administration of the drug, with a 38% decrease in total clearance and a 52% increase in the fraction of EPO eliminated unchanged in urine. The in vitro hydration of EPO was inhibited competitively by VPA at the concentrations comparable to the in vivo levels. The UDPGT activity of hepatic microsomes was also partly inhibited by VPA. These results suggest that VPA at steady state interferes with the metabolic clearance of EPO, by inhibiting the hydration of EPO and glucuronidation of carbamazepine-trans-diol, a hydrated metabolite.

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The metabolism of an orally active dopamine prodrug, N-(N-acetyl-L-methionyl)-O, O-bis(ethoxycarbonyl)dopamine (TA-870) and of dopamine (DA), were studied by use of thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) for identification and analysis of urinary and biliary metabolites after p.o. and/or i.v. administration to rats and dogs. The conjugated/free ratios of the metabolites were also determined. The urinary metabolites and order of the excretion in rats after p. o. dosing of TA-870 (30 mg/kg) were DA > homovanillic acid (HVA) > 3, 4-dihydroxyphenylacetic acid (DOPAC) > 3-hydroxyphenylacetic acid (3-HPAC). Those in dogs (33.5 mg/kg p.o.) were DA > HVA > de-ethoxycarbonylated TA-870 (DEC-TA-870) ≒ DOPAC. The urinary metabolites and order of the excretion in rats after p. o. dosing of DA (12 mg/kg, equimolar dose to TA-870) were DA > DOPAC > HVA > 3-HPAC, while those in dogs (13.5 mg/kg) were DOPAC > DA > HVA. The composition of the main urinary metabolites of TA-870 are similar in rats and dogs but after p. o. dosing of DA, excretion of DOPAC in dogs is much (ca. 3 times) higher than that in rats. After administration of DA and TA-870, 3-HPAC was found as a novel metabolite of DA, which was thought to be formed by dehydroxylation of DOPAC or DA with intestinal flora. After i.v. administration of TA-870 (30 mg/kg) to rats, the order of urinary excretion was HVA > DA > DOPAC > 3-HPAC ; the excretion of HVA being higher than that after p.o. dosing. Most of DA and DEC-TA-870 were excreted as the conjugated form in the urine. In rats, the biliary excretion of radioactivity after p. o. dosing of ¹⁴C-TA-870 was 30.7% of the dose, being lower than that in urine.

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Cyanate ion is continuously produced by spontaneous degradation of urea both in healthy human blood and in blood of patients with uremia on intermittent hemodialysis. The cyanate ion is trapped irreversibly by amino groups as N-carbamyl groups and reversibly by sulfhydryl groups as S-carbamyl groups. Consequently, these reactions keep the cyanate ion levels in plasma extremely low. Plasma proteins may play an important role in the detoxication of cyanate ion.

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Isolated rat pancreatic β cells in monolayer culture were shown to be protected from the cytotoxic effect of streptozotocin (STZ) by allopurinol. Pretreatment with allopurinol for 2 h caused dosedependent inhibition of the decreased secretion of insulin by the cells induced by STZ (2 mM, for 1 h), 500μM allopurinol causing complete inhibition of this effect of STZ. Pretreatment with allopurinol (250μM) also prevented the rapid decrease in intracellular adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide concentrations in β cells induced by treatment with STZ. High performance liquid chromatography revealed that the intracellular concentration of uric acid in STZ-treated cells was about 3 fold that of control cells. This finding suggests that the reaction of xanthine oxidase is facilitated in the cells exposed to STZ probably due to an increased supply of substrate resulting from decrease in intracellular ATP. Based on these results, a possible mechanism of the effect of allopurinol on the cytotoxic effect of STZ via xanthine oxidase is discussed.

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We previously demonstrated that the antitumor efficacy of various antitumor agents such as 5-fluorouracil and cisplatin against experimental solid tumors was enhanced by pre- or simultaneous administration of human epidermal growth factor (hEGF). In the present study, the combined therapy by hEGF and mitomycin C (MMC) as an antitumor agent was studied in A431 solid tumor-bearing mice to determine the dosage schedule of hEGF. When MMC alone was injected intraperitoneally (2 mg/kg) every 7th day to the tumor-bearing mice, tumor weights increased to 2138±285 mg from 282±41 mg during 22 d. Tumor weight in every day treatment of hEGF alone for 21 d increased to the same extent in the treatment by MMC alone. On the other hand, the increase of the solid tumor weight in the every day treatment and in the every 7th day treatment of hEGF, in combination with the every 7th day administration of MMC, were as follows ; from 282±41 mg to 1522±357 mg (71.2±16.7% of MMC alone) and from 280±44 mg to 1245±150 mg (58.2±7.0% of MMC alone), respectively, demonstrating a greater antitumor potency of MMC in the combination with the every 7th day treatment of hEGF. Both combined therapies did not affect the toxicity of MMC as evaluated by decrease in nontumorous body weight. Single subcutaneous administration of hEGF to A431 tumor-bearing mice caused the decrease of the binding capacity of hEGF to A431 tumor cells by 80% 24 h after the administration. However, the decreased binding capacity recovered to the untreated control level 4 d after the administration of hEGF. In conclusion, the every 7th day treatment of hEGF was superior than the every day treatment in its function to increase the susceptibility of A431 solid tumor to MMC.

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