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Biomedical subjects

T Iga

Publications and source records attributed to T Iga.

At least 181 records · Page 10Linked to original sources
PubMed1989

Uptake of colchicine, a microtubular system disrupting agent, by isolated rat hepatocytes.

The possible mechanism of hepatic uptake of colchicine (CLC), a microtubule system disrupting agent, was examined using isolated rat hepatocytes. The existence of a carrier-mediated active transport system for CLC was demonstrated. This transport system is saturable, is affected by metabolic inhibitors (dinitrophenol, KCN) and a SH-group blocker (p-hydroxymercuribenzoic acid but not N-ethylmaleimide), and is sensitive to temperature. Ouabain, an inhibitor of Na+, K+-ATPase, does not affect the transport system of CLC.

Animals↗
PubMed1989

Province of origin of hepatitis B surface antigen carriers among blood donors in Port Moresby.

A paper published in the Medical Journal of Australia in 1972 gave a breakdown of Port Moresby blood donors by HBS Ag carrier status and area of origin. It has lately become possible to test whether such geographical subsamples provide reliable evidence of the carrier status in the home areas, and it appears that, except for the Islands provinces, they do not. Traditional lifestyles conduce to the maintenance and spread of the virus, which is much more prevalent in the provinces than in the capital.

Blood Donors↗
PubMed1989

Light response of cultured melanophores of a freshwater teleost, Zacco temmincki.

Melanophores in the skin of the freshwater teleost Zacco temmincki are light sensitive: Melanin granules, melanosomes, in the melanophores aggregate in darkness and disperse in light. Cultured melanophores of Zacco temmincki exhibited light sensitivity in the same manner as the melanophores in isolated scales. The dark-induced aggregation response became conspicuous after 2 days in culture. The appearance of the light response was later than that of the response to norepinephrine or melatonin, which induced rapid melanosome aggregation at one day in culture. The light sensitivity of the melanophores in isolated scales differed between individuals. A high correlation was observed between the degree of dark-induced aggregation in scale melanophores and that in cultured ones.

Animals↗
PubMed1989

Facilitated transport of benzylpenicillin through the blood-brain barrier in rats.

The unidirectional influx of benzylpenicillin through the blood-brain barrier was examined with an in situ rat brain perfusion technique using purified [3H]benzylpenicillin. The major transport system of benzylpenicillin through the blood-brain barrier was via a saturable process with a one-half saturation concentration of approximately 8-30 microM. This transport system was significantly inhibited by probenecid (100 microM) and ceftriaxone (2 mM), indicating that the transport system may be shared by some organic anions including third generation cephalosporin antibiotics. These findings suggest that concomitant administration of beta-lactam antibiotics could produce a drug interaction to alter the drug penetration into the central nervous system.

Animals↗
PubMed1989

Effect of quinidine on the hepatic uptake of digoxin in guinea pigs.

Effect of quinidine on the hepatic uptake of digoxin was studied using isolated guinea pig hepatocytes and with the multiple indicator dilution method using perfused livers. The initial uptake rate of digoxin by isolated hepatocytes was significantly (p less than 0.05) decreased in the presence of quinidine or ouabain and at low temperature (27 degrees C). The influx rate constant to the liver (K1) of unbound digoxin was also decreased by quinidine or the metabolic inhibitor 2,4 dinitrophenol (DNP) in isolated perfused livers, while K1 of diazepam, which is thought to be taken up by a passive transport system, was not significantly changed in the presence of DNP. These findings suggest that an active transport system for digoxin may exist in the liver and may be inhibited by quinidine. We concluded that the quinidine-induce decreases in the hepatic distribution of digoxin may be attributed both to the decreased tissue binding and to the inhibition of uptake, which might be related to the decreased hepatic clearance.

Animals↗
PubMed1989

Relationship between the first-order intestinal absorption rate constant in vivo and the membrane permeability clearance in a perfusion system: an intragastric administration method in vivo.

In an attempt to explore the quantitative relation in the intestinal absorption between in vivo and a perfusion system, time courses of the remaining fraction in the stomach and that in the small intestine following the intragastric administration of drug solution to rats were simultaneously analyzed by a linear compartment model, using L-glucose and 3-O-methyl-D-glucose (3-O-MG) as model compounds. Derived first-order gastric emptying rate constant (kg) and first-order intestinal absorption rate constant (ka) were 0.025 and 0.018 min-1, respectively, for L-glucose and 0.033 and 0.275 min-1, respectively, for 3-O-MG. Values of the membrane permeability clearance (CLa,m) estimated in the perfusion system were 0.71 and 3.00 microliters/min/cm, respectively, for L-glucose and 3-O-MG. The operational luminal volume (Vo), given as CLa,m/Ka, of 39 microliters/cm for L-glucose was in agreement with the actual luminal volume in vivo estimated by a inulin dilution method and ranging from 20 to 60 microliters/cm, supporting the idea that CLa,m quantitatively reflects the intestinal membrane permeability in vivo and that the luminal volume in vivo is the primary factor which correlates CLa,m and Ka. The Vo of 11 microliters/cm for 3-O-MG was smaller, though still in the same order. It was also shown that the gastrointestinal absorption of 3-O-MG was gastric emptying limited.

3-O-Methylglucose↗
PubMed1989

The conjugative metabolism of 4-methylumbelliferone and deconjugation to the parent drug examined by isolated perfused liver and in vitro liver homogenate of rats.

We examined the disposition of 4-methylumbelliferone (4-MU) and its conjugative metabolites, glucuronide (4-MUG) and sulfate (4-MUS), using a single-pass rat liver perfusion system. When 4-MU was delivered, the steady-state hepatic extraction ratio for 4-MU was very high (approximately 1.0) and its conjugative metabolites, 4-MUG and 4-MUS, appeared to a large extent in the effluent perfusate. The biliary excretion rate of the 4-MUG conjugated from 4-MU was 44% of the infusion rate at the steady-state, whereas those of 4-MU and 4-MUS were less than 1% of the infusion rate. When 4-MUG was delivered, the steady-state hepatic extraction ratio for 4-MUG was very low (less than 0.05) and the removal rate of 4-MUG from the perfusate was almost identical to the excretion rate of 4-MUG into the bile, while 4-MU and 4-MUS were slightly excreted into the bile (1% of the total biliary excretion rate), suggesting that a little deconjugation of 4-MUG to 4-MU occurred in the liver. Similarly, 4-MU and 4-MUS were not detectable in the effluent perfusate. The apparent extraction ratio (Eapp) for the intracellularly conjugated 4-MUG was approximately twenty times higher than that for the pre-conjugated 4-MUG. This discrepancy between the values of Eapp for the intracellularly conjugated and pre-conjugated 4-MUG might be attributed mainly to the diffusional barrier for the metabolite between the blood and hepatocytes, as suggested in the previous simulation (J. Pharmacokin, Biopharm., 15, 399 (1987].(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Transport of imipenem, a novel carbapenem antibiotic, in the rat central nervous system.

The transport of imipenem, a novel carbapenem antibiotic, in the rat central nervous system (CNS) was studied using in vivo, in situ and in vitro experimental techniques. After i.v. bolus administration, the imipenem concentration in the cerebrospinal fluid (CSF) rose to a peak within 30 min and declined with time. The CSF/serum unbound concentration ratio of imipenem was 0.22 at 2 hr after i.v. administration, substantially higher than that reported for benzylpenicillin. By using an in situ brain perfusion technique, we found that imipenem was transported through the blood-brain barrier principally via passive diffusion with a permeability-surface area product comparable to that of mannitol. In vitro, imipenem was accumulated by the isolated choroid plexus via an active organic anion transport system, although much less rapidly than benzylpenicillin. In vivo, after i.c.v. administration, imipenem was cleared from the CNS in a manner comparable to that of mannitol with only a small probenecid-sensitive process. Imipenem thus has minimal affinity for the organic anion transport system in the choroid plexus, resulting in the slow elimination of this drug from the CNS. These results suggest that the difference between imipenem and benzylpenicillin in the ratio of CSF to unbound serum drug concentration is determined principally by the efflux process in the choroid plexus rather than the influx process through the blood-brain barrier.

Animals↗
PubMed1989

Nonlinear relationship between benzodiazepine receptor occupancy and glucose metabolic response in the conscious mouse brain in vivo.

To evaluate the relationship between the pharmacological effect of benzodiazepine (BZP) and BZP receptor (BZP-R) binding in the conscious mouse brain, a response of the local cerebral metabolic rate of glucose utilization (GU) to clonazepam (CNZ) was measured as an index for the pharmacological effect. Two glucose analogs (3-O-[3H]methylglucose and 2-[14C]deoxyglucose) method, originally presented by A. Gjedde was used for determination of GU. In the cerebral cortex, GU decreased to 70 to 80% at 60 min after i.v. administration of CNZ (0.005-1.0 mg/kg), but CNZ did not change the lumped constant, and this effect was diminished completely by the administration of a BZP antagonist, Ro-15-1788 (5 mg/kg). The maximum effect of CNZ on GU (about 30% decrease) was found at 0.1 mg/kg of CNZ, but increasing the dose to 1 mg/kg had very little additional effect. In vivo BZP-R occupancy was measured using [3H]-Ro-15-1788. Receptor occupancy increased from less than 10% at a dose of 0.005 mg/kg up to essentially 100% at doses of 1 mg/kg or greater. ID50 in dose-response curve of the receptor occupancy for CNZ and ED50 in that of decrease in GU were 0.3 and 0.007 mg/kg, respectively . A nonlinear and hyperbolic relationship was observed between the receptor occupancy and the response for the glucose metabolic rate, indicating that BZP exert the maximum glucose metabolic change at a low fractional receptor occupancy (30-40%).

Animals↗
PubMed1989

[Studies on diameter distribution of axons in the optic pathway in human glaucoma].

The distribution of diameters of axons and somas at the level of the optic nerve, lamina cribrosa and retina were compared between human glaucomatous eye and normal control eyes. At the level of lamina scleralis of the glaucomatous eye, there was a tendency for large nerve fibers to be lost in the arcuate nerve fiber area particularly in the inferior arcuate nerve fiber area, where the corresponding visual field defect was detected. The percentages of large axons and somas in the arcuate nerve fiber area decreased in the glaucomatous eye both at the level of the optic nerve, retina but most of all at the level of lamina cribrosa. These results suggest that the mode of optic nerve damage in early glaucoma is characterized by the selective damage of large nerve fibers, which is most severe at the lamina cribrosa.

Axons↗
PubMed1989

Transport of cefodizime, a novel third generation cephalosporin antibiotic, in isolated rat choroid plexus.

To characterize the transport system by which cephalosporin antibiotics are accumulated by the choroid plexus, kinetic analysis of cefodizime transport was performed. Accumulation of cefodizime was against an electrochemical potential gradient via a saturable process (Km = 470 microM, Vmax = 174 nmol/ml of tissue per min) that was inhibited by metabolic inhibitors (KCN and 2,4-dinitrophenol), hypothermia, a sulfhydryl reagent (p-hydroxymer-curibenzoic acid) and anion transport inhibitors (probenecid and 4,4'-diisothiocyanostilbene -2,2'-disulfonic acid). Accumulation of cefodizime was inhibited competitively by benzylpenicillin with an inhibition constant of aproximately 100 microM. Cefodizime inhibited competitively the accumulation of benzylpenicillin with an inhibition constant of approximately 500 microM. Kinetic analysis using 16 kinds of beta-lactam antibiotics also supported the view 1) that the transport system of cefodizime is shared by benzylpenicillin and 2) that these beta-lactam antibiotics are transported via a common transport system. These findings indicate that the major transport system of cephalosporin antibiotics in the rat choroid plexus is via a carrier-mediated active anion transport process. The affinity of beta-lactam antibiotics for this transport system in the choroid plexus may be a major factor in determining their pharmacokinetics in the cerebrospinal fluid.

Animals↗
PubMed1989

[Contributory factors for glaucomatous disc cupping. 4. Generalized expansion type and localized type].

It is widely recognized that there are two types progressive disc cupping in glaucoma. One of them is the localized type (L type) in which the cupping extends to a certain direction and the other is the generalized expansion type (G type) in which the cupping expands generally. We evaluated the optic disc in 86 eyes with primary open angle glaucoma (G type 44 eyes L type 42 eyes) to evaluate correlations of age and visual field defects between the 2 groups. Our study revealed that G type patients were significantly younger than those with L type when matched according to visual field defects. We also found that G type was revealed as the nasal step alone but not in L type. These results suggest that in G type, the optic nerve head is diffusely damaged by elevated intraocular pressure and the total nerve fibers are destroyed uniformly. On the other hand, in L type, the vulnerable portion of the optic nerve head is selectively damaged and nerve fibers constituting the optic rim area are destroyed. As a result, L type is likely to form cupping notch and reveal Bjerrum scotoma. These facts correspond to the anatomical structures of nerve fiber layers.

Adult↗
PubMed1988

Effects of basic drugs on the hepatic transport of cardiac glycosides in rats.

The effects of some basic and acidic drugs on the hepatic uptake of digoxin and ouabain were studied in isolated rat hepatocytes. Digoxin accumulated against a concentration gradient, and its initial uptake was energy- and temperature-dependent. Digoxin competitively inhibited the uptake of ouabain (Ki = 1.3 microM), which was reported to be transported by a carrier-mediated active transport system. All basic drugs tested (verapamil, dipyridamole, amiodarone, nifedipine, diltiazem, ajmaline, chlorpromazine, imipramine, disopyramide, quinidine, procainamide, propranolol and lidocaine: 50 microM) except for procainamide, propranolol and lidocaine significantly (P less than 0.05) reduced the uptake of digoxin, whereas acidic drugs (salicylic acid and phenytoin) had no effect. The same inhibitory effects were observed for ouabain uptake, whereas the uptake of alanine was not changed by these drugs. Quinidine inhibited the uptake of ouabain in a noncompetitive manner (Ki = 88 microM). These basic drugs had no effect on the permeability of the cells assessed by the trypan blue exclusion test and succinate-simulated oxygen consumption. But carbonylcyanide-m-chlorophenyl hydrazone-stimulated oxygen consumption decreased in the presence of some basic drugs and correlated with their inhibitory effects on digoxin uptake. Therefore, one of the mechanisms of the inhibitory effects of these drugs on digoxin uptake was the inhibition of oxidative phosphorylation. These basic drugs had no effect on the microtubular system, which was assessed by the measurement of tubulin polymerization and colchicine binding to tubulin. The results of our study suggested that many basic drugs have a potential to inhibit the hepatocellular uptake of cardiac glycosides.

Animals↗
PubMed1988

Dialyzable serum cofactor(s) required for the protein-mediated transport of DL-propranolol into rat brain.

To elucidate the characteristics of promotion factor(s) in rat serum required for the protein-mediated transport of drugs into the brain, we examined the brain uptake of DL-propranolol as a model drug using the in vivo brain uptake index (BUI) method in rats. The protein-mediated transport was not observed in rats injected with the buffer solution containing either various concentrations of purified rat alpha 1-acid glycoprotein (alpha 1-AGP) or rat albumin. When the filtrate from rat serum was used as an injection vehicle to which a physiological concentration of purified rat serum protein(s) was added, the protein-mediated transport of DL-propranolol was observed in the rat brain. Moreover, the ability of protein-mediated transport of DL-propranolol was reduced in rats injected with the dialyzed serum compared with the undialyzed serum. These results suggest that the dialyzable promotion factor in serum is required for the protein-mediated transport of DL-propranolol into the brain.

Animals↗
PubMed1988

In vivo evidence for the specific binding of human beta-endorphin to the lung and liver of the rat.

Specific binding of human beta-endorphin (beta-EP) was demonstrated in the lung and liver of the rat in vivo by the following lines of evidence, using [125I-Tyr27]beta-EP as a radiolabeled tracer. First, the tissue-to-serum concentration ratios of the intact labeled peptide 15 min after intravenous administration were decreased significantly in the lung and liver by a simultaneous injection of unlabeled beta-EP (48.5 nmol/kg), whereas in the other tissues such a decrease was not observed. Second, serum concentrations of the preadministered labeled peptide were increased rapidly after an additional intravenous injection of unlabeled beta-EP via the femoral vein, but not via the carotid artery into the heart. Third, the immunoreactive labeled beta-EP (125I-beta-EP), which was purified on a Sephadex G-50 column and did not specifically bind to the rat brain membranes, did not accumulate in the lung and liver and was not displaced by unlabeled beta-EP in vivo, in contrast to [125I-Tyr27]beta-EP, the commercially available HPLC-purified labeled peptide. Fourth, an additional injection of dynorphin (1-13) or ethylketocyclazocine (kappa agonist) also increased the serum concentrations of preadministered [125I-Tyr27]beta-EP but injection of Ala2-D-Leu5-enkephalin (delta agonist) or naloxone (mu antagonist) did not, suggesting kappa-type binding sites in the lung.

Animals↗
PubMed1988

Comparative assessment of the resistance of the unstirred water layer to solute transport between two different intestinal perfusion systems.

The resistance of the unstirred water layer to solute transport was estimated in two different intestinal single-pass perfusion systems for a comparative study, using D-glucose as a model compound. One is a well established perfusion system in anesthetized rats as a standard (system A). The other is the one in unanesthetized rats for comparison (system B). It was demonstrated that in system B as well as in system A the resistance of the unstirred water layer to D-glucose transport should be taken into account and this resistance, accordingly, the effective thickness of the unstirred water layer (delta) which is assumed to be in proportion to its resistance, could be described as a function of the perfusion rate by using a film model. The delta decreased with increasing perfusion rate and was larger in system A than in system B at each perfusion rate; 785 microns in system A versus 319 microns in system B at the perfusion rate of 0.16 ml/min and 337 microns versus 184 micron at that of 2.95 ml/min. Thus in system B the effective thickness, accordingly, the resistance, of the unstirred water layer was reduced to about 50% of that in system A, but the resistance of the unstirred water layer could still account for 85% of the total resistance at the maximum as far as D-glucose absorption was concerned, while 93% in system A. These results suggest that, compared with perfusion experiments in anesthetized rats (system A), the resistance of the unstirred water layer is reduced but cannot be left out of consideration even if perfusion experiments are performed in unanesthetized rats (system B). And the lower resistance of the unstirred water layer in system B was attributed to a turbulent flow in contrary to a laminar flow in system A.

Animals↗
PubMed1988

Kinetic analysis of in vivo receptor-dependent binding of human epidermal growth factor by rat tissues.

Kinetic analysis of the tissue distribution of human epidermal growth factor (hEGF) in rats was performed in vivo. The plasma disappearance half-life of [125I]hEGF was prolonged by coadministration of unlabeled hEGF, indicating saturation of the mechanism for hEGF removal from the systemic circulation. To analyze the contribution of each tissue to the uptake of hEGF, the amount of [125I]hEGF taken up by each tissue was determined after coadministration of various amounts of unlabeled hEGF. Kinetic analysis of the data yielded the following results. (1) Among the tissues examined, the distribution of [125I]hEGF to the liver, kidney, small intestine, stomach, and spleen was much greater than that accounted for by the distribution to the extracellular space of each tissue. (2) The binding (or uptake) of hEGF by these tissues showed remarkable saturation, which may represent the receptor-dependent binding (or uptake) mechanism. (3) The apparent binding (or uptake) clearance per gram of tissue at the low dose (in the range of first-order kinetics), defined with regard to the arterial plasma concentration, was greatest in the kidney, followed by the liver and small intestine. The larger binding (or uptake) clearance of the kidney compared with that of the liver can be attributed to the higher plasma flow rate (per gram of tissue) in the kidney. However, the intrinsic ability to take up hEGF was much greater in the liver than that in the kidney. The hepatic binding (or uptake) of hEGF at the low dose was almost limited by the hepatic plasma flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗