Biomedical subjects

Shizuo Yamada

Publications and source records attributed to Shizuo Yamada.

48 records · Page 3Linked to original sources

PubMed2003

Cyclopropane-based conformational restriction of histamine. (1S,2S)-2-(2-aminoethyl)-1-(1H-imidazol-4-yl)cyclopropane, a highly selective agonist for the histamine H3 receptor, having a cis-cyclopropane structure.

A series of cyclopropane-based conformationally restricted analogues of histamine, the "folded" cis-analogues, i.e., (1S,2R)-2-(aminomethyl)-1-(1H-imidazol-4-yl)cyclopropane (11), (1S,2S)-2-(2-aminoethyl)-1-(1H-imidazol-4-yl)cyclopropane (13), and their enantiomers ent-11 and ent-13, and the "extended" trans-analogues, i.e., (1R,2R)-2-(aminomethyl)-1-(1H-imidazol-4-yl)cyclopropane (12) and its enantiomer ent-12, were designed as histamine H(3) receptor agonists. These target compounds were synthesized from the versatile chiral cyclopropane units, (1S,2R)- and (1R,2R)-2-(tert-butyldiphenylsilyloxy)methyl-1-formylcyclopropane (14 and 15, respectively) or their enantiomers ent-14 and ent-15. Among the conformationally restricted analogues, the "folded" analogue 13 (AEIC) having the cis-cyclopropane structure was identified as a potent H(3) receptor agonist, which showed a significant binding affinity (K(i) = 1.31 +/- 0.16 nM) and had an agonist effect (EC(50) value of 10 +/- 3 nM) on the receptor. This compound owes its importance to being the first highly selective H(3) receptor agonist to have virtually no effect on the H(4) subtype receptor. These studies showed that the cis-cyclopropane structure is very effective in the conformational restriction of histamine to improve the specific binding to the histamine H(3) receptor.

Animals↗

PubMed2003

In vitro and ex vivo effects of a selective nociceptin/orphanin FQ (N/OFQ) peptide receptor antagonist, CompB, on specific binding of [3H]N/OFQ and [35S]GTPgammaS in rat brain and spinal cord.

1. A novel selective nociceptin/orphanin FQ (N/OFQ) peptide receptor antagonist, 1-[(3R,4R)-1-cyclooctylmethyl]-3-hydroxymethyl-4-piperidyl)-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (CompB), inhibited specific binding of [(3)H]N/OFQ to crude membranes from the rat brain and spinal cord in a concentration-dependent manner and their K(i) values were 7.11 and 4.02 nM, respectively. Rosenthal analysis indicated that there was a significant increase in the K(d) value for [(3)H]N/OFQ binding in the brain and spinal cord in the presence of CompB (10 nM). 2. There was a dose-dependent increase in K(d) values for [(3)H]N/OFQ binding in the brain and spinal cord following i.v. injection of CompB at relatively low doses (0.69-6.88 micro mol kg(-1)), compared with the control values. In the spinal cord, enhancement with each dose was constantly greater and the duration of enhancement (6.88 micro mol kg(-1)) was significantly longer. 3. The degree of increase in K(d) values for [(3)H]N/OFQ binding after i.v. injection of CompB (6.88 micro mol kg(-1)) was significantly larger in the lumbar region of the spinal cord compared to other regions. 4. CompB (0.1, 0.3 micro M) shifted the concentration-effect curves of N/OFQ-stimulated [(35)S]GTPgammaS binding in the brain and spinal cord to the right. 5. The i.v. injection of CompB (6.88 micro mol kg(-1)) significantly suppressed the N/OFQ-stimulated [(35)S]GTPgammaS binding in the rat spinal cord and shifted the concentration-effect curve to the right, while it produced little inhibitory effect in the brain. The present study has shown that CompB may exhibit pharmacological effects through a predominant blockade of N/OFQ peptide receptors in the spinal cord under in vivo conditions.

Animals↗

PubMed2003

Studies on the transport of thyrotropin-releasing hormone (TRH) analogues in Caco-2 cell monolayers.

The transport mechanisms of thyrotropin-releasing hormone (TRH) and its pharmacologically active analogues ((3-methyl-His(2))TRH (MeTRH), taltirelin, montirelin, azetirelin) across Caco-2 cell monolayers were characterized. The results of kinetic analysis showed a linear relationship between the concentration (over the range 0.5-10 mM) and apical-to-basolateral transport rate of these agents. The permeability coefficients (P(app)) of these agents were not substantially different from each other, and their P(app) ratios of the basolateral-to-apical over the apical-to-basolateral transport were close to one (0.73-1.23). The cellular transport of [(3)H]MeTRH at low concentrations (3-15 nM) showed a linear relationship between the concentration and transport rate. The transport of [(3)H]MeTRH in Caco-2 cell monolayers was neither affected by TRH nor TRH analogues, and there was little difference in P(app) values between [(3)H]MeTRH and [(14)C]mannitol. The cell-per-medium ratio of [(3)H]MeTRH in the cellular uptake experiment was similar to the value of [14C]mannitol. A large excess of TRH and MeTRH did not significantly influence cell-per-medium ratios of [(3)H]MeTRH in Caco-2 cell monolayers. The k'(IAM) value, which represents lipophilicity, was decreased in the following order: montirelin > taltirelin > TRH > azetirelin, and the values varied from 0.234 to 1.028. These results indicate that a paracellular passive diffusion may be the major route for the transport of TRH and its analogues in Caco-2 cell monolayers.

Caco-2 Cells↗

PubMed2003

Relationship between development of nephrotoxicity and blood concentration of cyclosporine A in bone-marrow transplanted recipients who received the continuous intravenous infusion.

This study was undertaken to investigate the relationship between blood concentration of cyclosporine A (CsA), administered intravenously by a 24-h continuous infusion, and drug-induced nephrotoxicity or hepatotoxicity. It was investigated retrospectively in 8 patients who had received an allogeneic bone marrow transplant (BMT). The correlation between daily doses and blood concentration of CsA was not significant. Then, the data of blood concentration of CsA and renal or liver function test result were divided into 5-d periods from the date of transplantation, and the mean value for each period was calculated. The maximum values of blood urea nitrogen (BUN) and serum creatinine (SCr) were consistently observed only after the period when the 5-d mean CsA concentration reached the peak level: the maximum BUN and SCr values were witnessed at Periods 2 to 10 and at Periods 1 to 9, respectively. On the other hand, no consistent correlation was found between the 5-d mean CsA concentrations and liver function test result. We also investigated the relationship between renal function and the cumulative dose or AUC of CsA. The parameters of renal function tests reached peak levels at the cumulative dose of 4000 to 10000 mg and at the cumulative AUC of 280000 to 660000 ng/ml.h. These results suggest that: 1) a deterioration of renal function occurs usually after the peak blood concentration of CsA is attained, and 2) the monitoring of the blood concentration of CsA is useful in predicting renal dysfunction in post-BMT patients.

Adult↗

PubMed2003

Blood-brain permeability of [3H]-(3-methyl-His2)thyrotropin-releasing hormone (MeTRH) in mice: effects of TRH and its analogues.

The present study was undertaken to characterize the transport of (3-methyl-His(2)) thyrotropin-releasing hormone ([(3)H]MeTRH) across the blood-brain barrier in mice and the effects of thyrotropin-releasing hormone (TRH) and its analogues (taltirelin and montirelin) on the transport and brain distribution. Integration plot analysis was used to calculate the influx clearance (CL(in)) of [(3)H]MeTRH after intravenous (i.v.) injection in mice. Furthermore, the capillary depletion method was performed to determine whether [(3)H]MeTRH crossed the blood-brain barrier. The effects of TRH and its analogues on the brain distribution of [(3)H]MeTRH were also examined by co-injection with the radioligand. The brain distribution of [(3)H]MeTRH and [(14)C]sucrose increased with the time after i.v. injection in mice, and the level of [(3)H]MeTRH was significantly higher than that of [(14)C]sucrose 5 min after the injection. The CL(in) value of [(3)H]MeTRH was significantly higher than that of [(14)C]sucrose, and the value of [(3)H]MeTRH was reduced by co-injection with unlabeled MeTRH. Also, capillary depletion showed that [(3)H]MeTRH was distributed largely in the brain parenchyma and this distribution was significantly inhibited by co-injection of TRH and montirelin but not taltirelin. The present study indicates that the transport of [(3)H]MeTRH into the brain may be via a saturable process.

Journal Article↗

PubMed2002

Neuroprotective effect and brain receptor binding of taltirelin, a novel thyrotropin-releasing hormone (TRH) analogue, in transient forebrain ischemia of C57BL/6J mice.

Thyrotropin-releasing hormone (TRH) and some of its stable analogues have been shown to improve neurologic dysfunctions such as brain trauma in both animals and humans. Our previous study revealed that taltirelin, a novel orally active TRH analogue, binds to rat brain TRH receptors in vivo. The present study was undertaken to investigate whether taltirelin has neuroprotective effects in transient brain ischemia of C57BL/6J mice induced by bilateral carotid artery occlusion (2VO). Neuronal cell density in the hippocampal CA1 region of C57BL/6J mice was significantly (39.9%) decreased 1 week after 2VO-reperfusion, compared to the case of the sham group, and this reduction of hippocampal neuronal density was significantly suppressed by an intravenous (i.v.) injection of taltirelin (0.3 mg/kg). The i.v. injection of taltirelin at this dosage produced a significant increase in the dissociation constant (Kd) of specific [3H]MeTRH binding in sham and 2VO-reperfusion groups (33.6 and 51.4%, respectively) compared with the vehicle-treated group. These results indicate that the intravenously injected taltirelin bound to TRH receptors in the ischemic brain. There was little difference in the brain-to-plasma concentration ratio (Kp) of [14C]sucrose between the sham and 2VO groups of C57BL/6J mice, indicating that the tight junction of the blood-brain barrier may be intact in the ischemic brain. In conclusion, the study has shown that taltirelin may have a significant neuroprotective effect on the ischemic brain.

Animals↗

PubMed2002

In vivo receptor binding of benidipine and amlodipine in mesenteric arteries and other tissues of spontaneously hypertensive rats.

The present study was undertaken to characterize the in vivo 1,4-dihydropyridine (DHP) receptor binding of long-acting 1,4-DHP calcium channel antagonists in the mesenteric artery and other tissues of SHR. In vivo specific binding of (+)-[3H]PN 200-110 in the SHR mesenteric artery was significantly (36.6-49.7 %) reduced 1-8 h after oral administration of benidipine (1.84 micromol/kg). A greater reduction in (+)-[3H]PN 200-110 binding in the mesenteric artery was observed at a higher dose (5.53 micromol/kg) of this drug. This dose of benidipine also reduced significantly the in vivo specific (+)-[3H]PN 200-110 binding in the aorta but not in the myocardium and cerebral cortex. Following oral administration of amlodipine (17.6 micromol/kg), a significant (51.7-94.2 %) reduction in (+)-[3H]PN 200-110 binding was seen at 1-18 h in the mesenteric artery and at 1-12 h in the aorta. Only a slight reduction in myocardial and cerebral cortical (+)-[3H]PN 200-110 binding was seen following amlodipine administration. In contrast, oral administration of nifedipine (28.9 micromol/kg) reduced markedly in vivo (+)-[3H]PN 200-110 binding in all the tissues of SHR at 1-6 h, and the degree and time-course of the reduction did not differ significantly among the tissues. The area under the curve (AUC) for the receptor occupancy vs time was calculated from the reduction rate (%) of in vivo specific (+)-[3H]PN 200-110 binding. The ratios of the AUCmesenteric artery to AUCaorta or AUCmesenteric artery to AUCmyocardium after oral administration of benidipine and amlodipine were greater than the corresponding value for nifedipine. The degree and time-course of arterial receptor occupancy by benidipine and amlodipine agreed well with those of their hypotensive effects in the conscious SHR. In conclusion, the present study demonstrates that benidipine and amlodipine may occupy, in a more selective and sustained manner, 1,4-DHP receptors in arterial tissues than in other tissues of SHR, and thus, such receptor binding specificity may be responsible for the long-lasting hypotensive effects of these drugs.

Amlodipine↗

PubMed2002

Internalization of basic fibroblast growth factor at the mouse blood-brain barrier involves perlecan, a heparan sulfate proteoglycan.

In this study, the internalization mechanism of basic fibroblast growth factor (bFGF) at the blood-brain barrier (BBB) was investigated using a conditionally immortalized mouse brain capillary endothelial cell line (TM-BBB4 cells) as an in vitro model of the BBB and the corresponding receptor was identified using immunohistochemical analysis. The heparin-resistant binding of [125I]bFGF to TM-BBB4 cells was found to be time-, temperature-, osmolarity- and concentration-dependent. Kinetic analysis of the cell-surface binding of [125I]bFGF to TM-BBB4 cells revealed saturable binding with a half-saturation constant of 76 +/- 24 nm and a maximal binding capacity of 183 +/- 17 pmol/mg protein. The heparin-resistant binding of [125I]bFGF to TM-BBB4 was significantly inhibited by a cationic polypeptide poly-L-lysine (300 micro m), and compounds which contain a sulfate moiety, e.g. heparin and chondroitin sulfate-B (each 10 micro g/mL). Moreover, the heparin-resistant binding of [125I]bFGF in TM-BBB4 cells was significantly reduced by 50% following treatment with sodium chlorate, suggesting the loss of perlecan (a core protein of heparan sulfate proteoglycan, HSPG) from the extracellular matrix of the cells. This type of binding is consistent with the involvement HSPG-mediated endocytosis. RT-PCR analysis revealed that HSPG mRNA and FGFR1 and FGFR2 (tyrosine-kinase receptors for bFGF) mRNA are expressed in TM-BBB4 cells. Moreover, immunohistochemical analysis demonstrated that perlecan is expressed on the abluminal membrane of the mouse brain capillary. These results suggest that bFGF is internalized via HSPG, which is expressed on the abluminal membrane of the BBB. HSPG at the BBB may play a role in maintaining the BBB function due to acceptance of the bFGF secreted from astrocytes.

Animals↗

PubMed2002

Relationship between prostatic alpha(1)-adrenoceptor binding and reduction in intraurethral pressure following continuous infusion of KMD-3213 in rats.

The relationship between alpha(1)-adrenoceptor binding in rat tissues and pharmacodynamic effects of continuous infusion of KMD-3213 was examined. In vivo specific binding of [(3)H]KMD-3213 after continuous intravenous infusion of the ligand (100 pmol/kg/min for 10 min, followed by 30 pmol/kg/min for 60 or 90 min) differed largely among the tissues examined. Specific binding of [(3)H]KMD-3213 in aorta, heart, lung, and kidney was not different in terms of infusion time in the case of continuous infusion for 10, 70 and 100 min, whereas the binding in prostate, vas deferens, and submaxillary gland by 70- and/or 100-min infusion was significantly greater than that by the 10-min infusion. A similar extent of specific binding in the prostate was observed by the infusion (100 min) of a three-fold higher dose of [(3)H]KMD- 3213. Continuous intravenous infusion of KMD-3213 (100 pmol/kg/min for 10 min, followed by 30 pmol/kg/min) for 70 or 100 min significantly reduced the phenylephrine-induced increase in the mean blood pressure and that in the intraurethral pressure of anesthetized rats. Extent and time course of the KMD-3213 effect reduction in the phenylephrine-induced increase in intraurethral pressure were closely associated with those in prostatic [(3)H]KMD-3213 binding after continuous infusion of the corresponding dosage of the radioligand. The reduction in the phenylephrine-induced increase by the infusion of a three-fold higher dose of KMD-3213 was significantly greater in the case of the intraurethral pressure than in that of the mean blood pressure, thereby suggesting a greater selectivity for the alpha(1)-adrenoceptor in the lower urinary tract than for that in the vascular tissue. In conclusion, the present study has shown that specific binding of [(3)H]KMD-3213 in the rat prostate after the continuous intravenous infusion of the radioligand may be closely associated with the pharmacological effect of this drug on the lower urinary tract.

Adrenergic alpha-Antagonists↗

PubMed2002

Assay of catechol-O-methyltransferase activity in human erythrocytes using norepinephrine as a natural substrate.

BACKGROUND: Catechol-O-methyltransferase (COMT) catalyses the inactivation of catecholamines. It is widely distnbuted in most tissues in soluble (S-COMT) and membrane-bound (MB-COMT) forms. Recently, we used a new assay for COMT activity and demonstrated that COMT plays an important role in blood pressure regulation in spontaneously hypertensive rats. In order to investigate whether this is true for human hypertension, we have evaluated the erythrocyte COMT assay in humans. METHOD: The assay procedure included the use of norepinephrine (NE) as a natural substrate and the quantification of the reaction product, normetanephrine, followed by high-performance liquid chromatography separation and fluorescence or chemiluminescence detection. RESULTS: After evaluation of the method, the optimum conditions were obtained for the assay of human erythrocyte COMT. The S- and MB-COMT activities obtained were 50.6 (24.5) and 329.8 (179.4) fmol/min/mg protein, respectively [mean (standard deviation); n = 54]. The Km values for NE were 91.3 (14.1) and 11.7 (1.1) micromol/L for S- and MB-COMT, respectively (n = 6). CONCLUSION: The established assay method used to assess S- and MB-COMT activities in human erythrocytes could be useful to elucidate catecholamine metabolism in the normal physiological state as well as in the pathology of certain diseases.

Adult↗

PubMed2002

The 5-HT2 receptor antagonist reduces immobility of mice treated with the atypical antidepressant mianserin in the forced swimming test.

Effects of co-administration with the 5-HT(2) receptor antagonist LY 53857 and the antidepressant mianserin on immobility time in the forced swimming test were investigated in mice. Mianserin did not affect the immobility time at ranges from 1-10 mg/kg, although it elicited anti-immobility effects at 20 mg/kg. Co-administration of the 5-HT(2) receptor antagonist LY 53857 and a subactive dose of mianserin induced apparent anti-immobility effects. Since mianserin facilitates noradrenaline (NA) release from nerve terminals via inhibition of alpha(2) receptors, the blockade of the 5-HT(2) receptor may increase the antidepressant effect of drugs modifying NA levels in the synaptic cleft.

Animals↗

PubMed2002

In vivo measurement of 1,4-dihydropyridine receptors in mesenteric arteries of spontaneously hypertensive rats and effect of nifedipine and cilnidipine.

The present study was undertaken to measure 1,4-dihydropyridine (DHP) receptor binding sites in vivo in the mesenteric artery and other tissues of spontaneously hypertensive rats (SHR) and to examine the effect of nifedipine and cilnidipine. Specific in vivo binding of (+)-[3H]PN 200-110 in the SHR mesenteric artery was dose dependently reduced by oral administration of nifedipine at relatively low doses. Oral administration of cilnidipine (6.09 micromol/kg) significantly reduced the specific in vivo binding of (+)-[3H]PN 200-110 in the mesenteric artery, aorta, and myocardium. A significant reduction in (+)-[3H]PN 200-110 binding was seen at 1-12 h in the mesenteric artery and at 1-7 h in the aorta and myocardium. In contrast, oral administration of nifedipine (28.9 micromol/kg) markedly reduced in vivo (+)-[3H]PN 200-110 binding in all tissues of SHR at 1-6 h, and the degree and time course of the reduction did not differ much among the tissues. The area under the curve (AUC) for receptor occupancy vs. time was calculated from the reduction rate (%) of specific in vivo (+)-[3H]PN 200-110 binding. The ratio (1.4 or 1.7) of the AUC(mesenteric artery) to AUCaorta or AUCmyocardium after oral administration of cilnidipine was greater than the corresponding value (1.1) for nifedipine. In conclusion, the present study demonstrates that cilnidipine, but not nifedipine, may occupy 1,4-DHP receptors in the small artery in a more selective and sustained manner than in other tissues of SHR, and thus such receptor binding specificity may be responsible for the long-lasting hypotensive effect of this drug.

Animals↗