We have investigate the absorption, excretion and metabolism of ³H-TJN-101 following single oral administration of the drug (4 mg/kg) in male dogs.
1. The concentration of radioactivity in the blood was determined by the dry method. The C_max of 1666ng/ml (TJN-101 base) was reached at 45 min after administration. Then, the radioactivity decreased with a half life of 3.6hr from 1 to 8hr, with a half life of 9.7hr from 12 to 48hr, and with a half life of 2.4 days from 72 to 168hr. The AUC for the first 168hr after treatment was 11.1μg·hr/ml. Plasma levels of radioactivity, as determined by the dry method, reached a maximun (2813ng/ml) at 45 min after treatment and subsequently followed a course smilar to that of its blood level. The ratio of unstable tritium in the plasma was 8 % or less until 12hr, 22% at 24hr, 58% at 48hr, 77% at 72hr, and 85 ?? 87% on and after 96hr. The distribution ratio of radioactivity in blood cell, determined simultaneously, was 4.1 ?? 13.1% until 72hr and 20.5 ?? 40.7% on and after 96hr.
2. Within 168hr after oral administration, radioactivity in the urine and feces in male dogs was 40.1% and 54.8% of the dose, respectively. Unstable tritium was not detected in any urine samples collected during the 168hr after dosing.
3. The ratio of plasma protein binding of radioac tive substances in vivo was 77.0% at 15 min after treatment and subsequently decreased with time, reaching 55.8% at 8hr.
4. When the plasma specimens collected at 15, 45, and 120 min were exam ined for unchanged TJN-101, the ratio of unchanged TJN-101 to total radioactivity was 65.2% at 15 min and decreased with time, thereafter, reaching 55.2% at 2hr. The ratio of Met. A-III was 7.1 % at 15 min and increased with time, thereafter, accounting for 13.3% at 2hr. For all samples collected on the different occasions, the percentage of radioactivity which remained at origin was 25% or more. After enzymatic hydrolysis, this percentage decreased to below 5.5%, while the percentage of the parent compound increased to 64.5 ?? 74.2%. In the case of urine and feces collected during first 48hr after dosing, radioactivity was mainly present as Met. A-III, Met. B and Met. F.

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The distribution (blood or plasma concentration) and excretion of ³H-TJN-101 were examined in male rats and dogs after intravenous administration (4 mg/kg).
1. In male rats, the blood level of radioactivity ranged from 1.00 to 1.13μg/ml (TJN-101 base) at 5 min through 1hr after dosing. Thereafter, the blood level decreased with a half-life of 1.4hr from 2 to 6hr, and with a half-life of 25hr from 8 to 72hr after drug treatment. The AUC for 168hr after treatment was 5.75μg·hr/ml.
2. Within 168hr after injection, the radioactivily excreted in urine and feces in male rats was 11.7% and 80.5% of the dose, respectively. In urine collected for 168hr, the unstable tritium equivalent to 1.2% of the administered radioactivity was detected.
3. When the concentration of radioactivity in the blood of male dogs was determined by the dry method, the level was 3.03μg/ml (TJN-101 base) at 5min, which was first measurment period after dosing. Thereafter, the blood level decreased with a half-life of 43min up to 45min, with a half-life of 2.6hr from 1 to 4hr, and with a half-life of 6.1hr from 6 to 24 hr after dosing. At 48hr, the blood level decreased below the detection limit. The AUC for 24hr after dosing was 8.56μg·hr/ml. The concentration of radioactivity in plasma, determined by the dry method, was 5.05μg/ml at 5min. Thereafter, plasma level followed a course similar to that of blood level. The ratio of unstable tritium in plasma was below 6 % until 12hr, 27% at 24hr, and 50 ?? 75% from 48 to 120hr. The distribution ratio of radioactivity in blood cell simultaneously determined was 4.7 ?? 14.0% during the first 24hr.
4. Within 168hr after injection, radioactivity excreted in urine and feces in male dogs was 38.9% and 60.0% of the dose, respectively.

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The pharmacological potency, absorption, distribution and excretion of N³-benzylthymidine (N³-ByTd), a new type of hypnotics, were studied in mice.
N³-Substituted thymidine derivative, N³-o, m or p-xylylthymidine, N³-m-chlorobenzylthymidine, were synthesized. Furthermore, the sugar moiety of certain derivatives was methylated. N³-ByTd and its derivatives were evaluated for hypnotic activity by intracerebroventricular (i.c.v.) administration as central depressants. N³-ByTd (2.0μmol/mouse) induced 72min lasting sleeping time by i.c.v. injection. The hypnotic activity of N³-ByTd was highest among the compounds tested. N³-ByTd also produced the decrease of mice spontaneous activity by i.v., p.o. and i.p. injection.
[³H] N³-ByTd was administered i.v. (300mg, 5.5MBq/kg) or p.o. (300mg, 7.1MBq/kg) to mice. Brain, plasma, liver, muscle, adrenal, thymus, spleen, kidney, testis, epididymis, fat and lung of the mouse were collected and then the radioactivity in each tissue was measured. The concentration of [³H] N³-ByTd decreased in two phases in the most of tissue. Trace amount of [³H]N³-ByTd was distributed to the brain, suggesting an ability to penetrate through the blood brain barrier from peripheral. The concentration of [³H] N³-ByTd in the liver and kidney were higher than that in the plasma after i.v. administration, and maximum concentration in these organs corresponded to 5.8 and 1.9% of total injection, respectively. In urine, 46.1%(i.v.) and 54.5% (p.o.) of total radioactivity were excreted within 48 hours after the administrations.
N³-Benzylthymine (N³-ByT), thymidine (Td) and thymine (T) were identified as the metabolites in the brain, liver and urine. The possible metabolic pathway of N³-ByTd is suggested to be N³-debenzylation and N³-deribosylation. It appears that N³-ByTd itself is a real hypnotic substance in mice, since these metabolites did not have any hypnotic activity.
Although incorporation of [³H] N³-ByTd into nucleic acid was also examined, there was no incorporation of ³H into RNA and DNA. N³-ByTd may effect on central nervous system as a hypnotic, but not by an endogenous compound.

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Intrarectal application of drugs has been used as an effective administration route, howsver, the absorption and distribution of drugs may be changed in pathological state of the rectum, especially in the case of hemorrhoid disease. Rectal absorption and distribution of ³H-diflucortolone valerate (³H-DFV), which is an anti-inflammatory steroid, and ¹⁴C-lidocaine (¹⁴C-LDC) in hemmorrhoid model rats were compared with that in normal rats.
The hemmorrhoid model rats, were prepared by means of application of croton oil into rectum of rats, showed high vascular permeability and edema.
³H-DFV and ¹⁴C-LDC were applied into the rectum as a suppository of combination of both drugs at the dose of 0.01mg/kg of ³H-DFV and 2mg/kg of ¹⁴C-LDC, and the anus was sealed by glue for 3h. Rectal absorption of ³H -DFV was slow and low, while that of ¹⁴C-LDC was faster than ³H-DFV. The profile and pharmacokinetic parameters (C_max, T_max and AUC) of blood kinetics of both radioactivities in the hemmorrhoid model rats were not different statistically from that observed in intact rats. These results indicate that the kinetics of rectal absorption of both drugs can't be changed by hemorrhoid disease. The radioactivity in the rectum, target tissue of anti-hemorrhoid drug, showed 100 folds higher value of that in the blood, and no difference in the radioactivities in the rectum was observed between intact and hemorroid rats. The autoradiogram revealed the uniform distribution of the radioactivities in the hemorrhoid rectum.
These results indicate that the rectal application is more effective therapy than the systemic one, and the kinetics after rectal application shows no diffe rence between intact and hemorrhoid model rats.

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The characterization of the hydrolase responsible for the ring-opening hydrolysis of simvastatin (SV) to its open acid form (SVA) was carried out using rat plasma, liver and intestinal microsomes.
The optimum pHs for the ring-opening hydrolase in plasma, liver and intestine were found to be between pH 7-8.
The values of Vmax for plasma, liver and intestine were 0.33, 0.97 and 0.24 nmol/min/mg protein, respectively, and the corresponding values of Km were 21.9, 203.3 and 567.6μM, respectively. The value of Vmax/Km for plasma hydrolase showed the largest value of 0.0154ml/min/mg protein, which is 3.2- and 38-fold larger than those for the liver and intestine, respectively.
The enzymatic hydrolysis of SV in the presence of plasma was inhibited by addition of diisopropyl fluorophosphate (DFP), bis (p-nitrophenyl) phosphate (BNPP), high concentration of physostigmine (Phys) and α-naphthyl acetate (α-NA). In liver, the enzymatic hydrolysis of SV was inhibited by DFP, BNPP, α-NA and EDTA. These results suggested that carboxylesterase might be, in part, responsible for the hydrolysis of SV in the plasma and liver. However, the difference in the inhibition patterns between plasma and liver indicated that different esterase isozymes might be responsible for the hydrolysis. On the other hand, the hydrolysis of SV by the intestine was not affected at all by the inhibitors and substrates mentioned above except EDTA, suggesting that the hydrolase in the intestine is different from those present in the plasma and liver.

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The dose-dependent pharmacokinetics of suplatast tosilate, (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy) phenylcarbamoyl]ethyl]dimethylsulfonium p-toluenesulfonate(IPD-1151T) after oral administration to male rats at dose of 10, 100, 1000mg/kg, and the sex-related disposition of IPD-1151T were studied after oral (100mg/kg) or intravenous administration of M-1 (6.6 mg/kg).
1. After oral administration of IPD-1151T to male rats, the C_max and AUC_0-t of unchanged IPD-1151T base (IPD-1151T base) in the plasma and the quantity of IPT-1151T base excreted in urine and feces were increased in proportion to administered dose. These suggested that disposition of IPD-1151T base was independent of dose.
2. After oral administration of IPD-1151T to female rats, the AUC_0-t of IPD-1151T base in female rats was 1.6 times higher than that in male rats, however C_max of IPD-1151T base in female rats was of same level as that in male rats. The amount of IPD-1151T base excreted to urine in female rats was similar to that in male rats. From these results, it seemed that disposition of IPD-1151T base did not essentially differ between male and female rats.
3. In order to clarify sex difference in the IPD-1151T disposition, the pharmacokinetics of M-1, which was the first metabolite gradually generated from IPD-1151T base, was studied. After intravenous administration of M-1 to male and female rats, plasma clearance, t_1/2 and AUC_0-∞ of M-1 in plasma were similar in male and female rats, respectively. It suggested that there was no essentially difference between male and female rats at the degree of M-1 metabolisms when IPD-1151T was administered.

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As physiological and anatomical factors affecting intestinal drug absorption, unidirectional water flow, solvent drag, absorptive site blood flow and electrophysiological parameters such as membrane resistance and capacitance were examined. Effects of some absorption enhancers on the two absorption pathways, the transcellular and paracellular pathways, were also examined from the alteration of the above factors. One of the effective enhancers, sodium caprate (C10), increased the following absorption parameters for the paracellular pathways : (i) the equivalent pore radius which was obtained by the water absorption ; (ii) the permeabilities of water-soluble nonelectrolytes and ionic drugs ; (iii) junctional resistance and basolateral membrane capacitance which were obtained by impedance analysis. The C10 effects on the trancellular pathway were found in the membrane perturbation which was obtained by fluorescence polarization. For the action mechanism of C10 in the paracellular pathways, the C10 effect on the physiological regulation of membrane, stimulation of C10 to contraction of perijunctional actomyosin ring, is now under investigation.

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To evaluate the relationship between the pharmacological effect of benzodiazepine (BZP) and BZP receptor binding in the conscious mouse brain, a response of the glucose utilization (GU) to clonazepam (CNZ) was measured as an index for the pharmacological effect. GU was measured by the simultaneous use of [¹⁴C] 2-deoxyglucose (2DG), the glucose analogue which can be phosphorylated in the brain, and [³H] 3-O-methylglucose (3MG), the nonmetabolizable glucose analogue. The distribution volume of unphosphorylated 2DG in the brain was not significantly different from that of 3MG (VM), indicating that the phosphorylation rate of 2DG can be estimated by subtracting VM from apparent volume of distribution of 2DG. By this double tracer technique, it is possible to determine GU within 10min after administration of both tracers. Pharmacological and pathophysiological changes of the isotope correction factor (lumped constant) can also be estimated by this technique.
In the cerebral cortex, GU decreased to 70 ?? 80% at 60 min after i.v. administration of CNZ (0.005 ?? 1.0mg/kg), and this effect was completely diminished by the administration of a benzodiazepine antagonist, Ro-15-1788 (5mg/kg). The maximum effect of CNZ on GU (about 30% decrease) was found at 0.1mg/kg of CNZ, but increasing the dose to 1mg/kg had very little additional effect. In vivo BZP receptor occupancy, measured using [³H] Ro-15-1788, increased from less than 10% at a dose of 0.005mg/kg up to essentially 100% at doses of 1mg/kg or greater. ID50 in dose response curve of the receptor occupancy for CNZ and ED50 in that of decrease in GU were 0.3mg/kg and 0.007mg/kg, respectively. A nonlinear and hyperbolic relationship was observed between the receptor occupancy and the response for the glucose metabolic rate, indicating that BZP exerts the maximum glucose metabolic change at a low fractional receptor occupancy (30 ?? 40%). By using positron emission tomography, these techniques can be applied to living human brain, which makes it possible to determine the optimal doses of BZP in the effective therapeutic drug monitoring.
Furthermore, a mathematical allosteric coupling model has been proposed to des cribe the process by which binding to the GABA/benzodiazepine receptor complex initiates a biological response. The modeling exercise shows that the benzodiazepine concentration required for half-maximal biological response is lower than that required for half-maximal receptor binding. The degree of discrepancy between the two profiles (receptor occupancy and biological response) concerning benzodiazepine concentration dependency increased with the decrease in the dissociation constants based on the GABA receptor-benzod iazepine receptor interaction. This model offers a simple explanation for discrepancies between receptor occupancy-concentration profile of benzodiazepine and biological response-concentration curve that are often observed in vivo and/or in vitro.

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To develop novel strategies for tissue selective drug delivery, studies on drug distribution mechanism in tissues have become more important. The present review focus on some of the important factors that should be considered in regulating the drug distribution in tissues, i.e., tissue binding, plasma binding and membrane permeability. Especially, a role of specific transport system has been discussed to utilize for the drug permeation pathway at the tissue plasma membrane.

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