Biomedical subjects

T Nagatomo

Publications and source records attributed to T Nagatomo.

At least 19 recordsLinked to original sources

PubMed1997

Osmotic modulation in glutamatergic excitatory synaptic inputs to neurons in the supraoptic nucleus of rat hypothalamus in vitro.

To clarify influence of osmotic stimulation on the excitatory synaptic inputs to the neurosecretory cells of the supraoptic nucleus (SON), the blind patch technique was used in rat hypothalamic slice preparations. Stable whole-cell recordings were made from 22 neurons in the SON. To observe spontaneous excitatory postsynaptic currents (sEPSCs) in the SON neurons, membrane potentials were clamped between -50 and -90mV. The effects of hypertonic stimulation on the frequency of the sEPSCs were tested in 18 SON neurons. Bath application of mannitol 30 or 60 mM increased the frequency of the sEPSCs. During the application of mannitol (60 mM), the frequency of the sEPSCs increased in 12 of 15 neurons without a change in amplitude. Hypertonic stimulation with NaCl (30 mM) had similar effects to that of mannitol. The increased frequency of miniature EPSCs (mEPSCs) during mannitol application persisted in the presence of TTX in all 8 SON neurons tested with no change in amplitude. Both the non-NMDA antagonist CNQX at 10-30 microM (n = 6) and the non-selective glutamate antagonist kynurenic acid at 1 mM (n = 3) almost completely blocked the EPSCs while the NMDA antagonist AP-5 at 10 microM had no effect on the frequency of the EPSCs in the 4 neurons tested. During application of CNQX, mannitol (60 mM) was added to the perfusion medium in 3 SON neurons. Under these conditions, mannitol had no effect on the frequency of EPSCs. We conclude that hypertonic stimulation directly influences glutamatergic inputs to the neurosecretory cells of the SON by an action on the presynaptic terminals and enhances the excitatory synaptic events.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1996

Slow association of positively charged Ca2+ channel antagonist amlodipine to dihydropyridine receptor sites in rat brain membranes.

1. No significant differences were observed in Kd and Bmax values between pH 7.2 (0.16 +/- 0.01 nM and 155.36 +/- 16.07 fmol/mg protein) and pH 10.0 (0.15 +/- 0.01 nM and 158.63 +/- 13.80 fmol/mg protein) in rat brain membranes. 2. The IC50 ratios at 0- and 270-min preincubations of amlodipine and manidipine at pH 7.2 were 23.09 and 10.25, respectively, whereas these ratios for these two drugs at pH 10.0 were 2.63 and 1.34, respectively. 3. In contrast, on treatment with nisoldipine, benidipine, SM-6586 and nifedipine, no significant differences were observed in the IC50 ratios between 0- and 270-min preincubations at pH 7.2 and 10.0.

Amlodipine↗

PubMed1996

Clinical evaluation of serum amlodipine level in patients with angina pectoris.

Serum amlodipine levels were determined in 18 patients with vasospastic angina. Patients were divided into two groups: Group A (n = 9) received amlodipine 5 mg by single daily administration, and Group B (n = 9) received 10 mg given by single daily administration for the first 3 days, then 5 mg from the 4th day on. The serum amlodipine concentration in Group A took 7 days to reach a steady state of around 8 ng/ml. The level in Group B was 8.9 ng/ml at 3 days. From these results, the optimal dosage of amlodipine in the treatment of angina pectoris is 10 mg for the initial 3 days followed by 5 mg thereafter.

Aged↗

PubMed1996

Establishment of Bcgr congenic mice and their susceptibility/resistance to mycobacterial infection.

Bcg congenic mice were developed by using C57BL/6 and DBA/2 strains of mice as progenitors. They were obtained by introgressively backcrossing the Bcgr marker of DBA/2 onto C57BL/6. After twenty successive backcrossings, the heterozygous resistant mice were mated with each other to obtain homozygous mice as the Bcgr congenic mice. The results of immunogenic and genetic markers coupled with those of an mixed lymphocyte reaction, all confirmed that the newly developed mice were highly congenic. These congenic mice were found to be resistant to in vivo infections by Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium bovis BCG.

Animals↗

PubMed1996

Proadrenomedullin N-terminal 20 peptide (PAMP) reduces inward currents and Ca2+ rises induced by nicotine in bovine adrenal medullary cells.

It has been recently reported that proadrenomedullin N-terminal 20 peptide (PAMP), which is secreted with adrenomedullin and catecholamines from the adrenal medulla, inhibits catecholamine release stimulated with nicotine. In the present study, to elucidate anticholinergic mechanisms of PAMP we employed the whole-cell patch-clamp and the intracellular Ca2+ imaging techniques in cultured bovine adrenal medullary cells. PAMP inhibited nicotinic currents and [Ca2+]i rises induced by nicotine in a dose-dependent manner (10(-9)-10(6) M). These inhibitions were selective, since PAMP alone did not induce any ionic currents, moreover it did not affect voltage-dependent Ba2+ currents or high K+ (50 mM)-induced [Ca2+]i rises. The onset of the inhibitory effect of PAMP (10(-6) M) was very rapid and reached a steady-state level within 10 sec. The effect of PAMP (10(-6) M) lasted for about 10-15 min. Desensitization process of the nicotinic current fitted to a single exponential function with a time constant of 6.4 +/- 0.3 sec. When PAMP (10(-6) M) simultaneously added with nicotine (10(-5) M), the desensitization process was facilitated and fitted to two exponentials with time constants of 0.46 +/- 0.08 and 2.5 +/- 0.8 sec. From the present results, the inhibition by PAMP of nicotinic currents which was well associated with that of nicotine induced [Ca2+]i rises leads to the attenuation of catecholamine release probably, at least in part, due to the facilitation of the desensitization process of the nicotinic currents.

Adrenal Medulla↗

PubMed1996

Slow dissociation of long-acting Ca2+ antagonist amlodipine from 3H-PN200-110 binding sites in membranes of rat hearts and brains.

The dissociation rate of amlodipine ((+/-)-3-ethyl 5-methyl 2-[(2-aminoethoxy)methyl]-4-(o-chlorophenyl)-1,4-dihydro-6-methyl- 3,5- pyridinedicarboxylate benzenesulfonate) from rat heart and brain membranes preincubated with drugs and washed out with buffer was assessed by radioligand binding assay using 3H-PN200-110 as a radioligand. The remaining KCl-induced contraction in rat aortic strips washed out after treatment with this drug and the pKi (inhibition constant) values of the drug were compared with those of nisoldipine, nifedipine, manidipine and benidipine. The inhibition of 3H-PN200-110 binding induced by nifedipine was reversed by washing, whereas that induced by amlodipine, manidipine, and benidipine was not readily reversed under these conditions. When rat aortic strips were pretreated with Ca2+ antagonists, the rank order of the inhibition of contractions induced by 50 mM KCl was manidipine = benidipine > amlodipine > nisoldipine > nifedipine, even though Ca2+ antagonists were not present in the extracellular medium. The pKi values of amlodipine in the heart and brain were 6.86 and 7.41, respectively, and these values were lower than those of the other Ca2+ antagonists. There was a good correlation between the potency of the inhibition of 3H-PN200-110 binding by drugs after the washout of membranes and the inhibition exerted by the drugs in contractions induced by 50 mM KCl after the washout of tissues, although this residual inhibition was not correlated with pKi values. Thus, these results suggest that amlodipine has a very slow rate of dissociation from 3H-PN200-110 binding sites, as do manidipine and benidipine, and this property may explain its long-lasting antihypertensive effect.

Amlodipine↗

PubMed1996

Effects of chronic administration of bopindolol on the binding characteristics of cardiac alpha 1H-, alpha 1L-, beta 1- and beta 2-adrenoceptor subtypes in cardiac muscles of spontaneously hypertensive rats (SHR).

The effects of the chronic administration of bopindolol on the binding characteristics of [3H]CGP12177 and [3H]prazosin to cardiac alpha 1H-, alpha 1L-, beta 1- and beta 2-adrenoceptor subtypes of spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were compared with those of two other beta-blockers, atenolol and propranolol. Bopindolol (1 and 3 mg/kg/d), atenolol (50 mg/kg/d) and propranolol (60 mg/kg/d) were given to 10-week-old SHR for 12 weeks. The changes in Kd and Bmax values of the myocardium of SHR treated without and those drugs were assessed by Scatchard analysis, and the ratio and Bmax values of the beta 1- and beta 2-adrenoceptor subtypes were also calculated from displacemental curves using ICI 118,551. The systolic blood pressure in SHR was dose-dependently lowered by the administration of bopindolol, and was also lowered by the administration of atenolol and propranolol. The Bmax values of beta 1- and beta 2-adrenoceptors were lowered by the administration of bopindolol (1 and 3 mg/kg/d) without any changes in the Kd values or the ratio of beta 1- and beta 2-adrenoceptors. Propranolol lowered 3-fold the affinity to the beta-adrenoceptor. On the other hand, the Kd and Bmax values of alpha 1H- and alpha 1L-adrenoceptor subtypes (high and low affinity binding sites for [3H]prazosin) were not changed by these drugs. These findings suggest that bopindolol had a beneficial effect on beta-adrenoceptors in the membranes of cardiac muscles of SHR, implying that these effects may contribute to lowering hypertension.

Adrenergic beta-Antagonists↗

PubMed1995

GABAergic inhibitory inputs to subfornical organ neurons in rat slice preparations.

To investigate GABAergic inhibitory inputs to neurons of the subfornical organ (SFO), intracellular recordings were made in rat brain slice preparations. Inhibitory postsynaptic potentials, which occurred spontaneously or were evoked by focal electric stimulation, had reversal potentials of approximately -60 mV, and were almost totally abolished by the GABAA antagonists bicuculline at 3-100 microM or picrotoxin at 50 microM. Following the application of bicuculline or picrotoxin, the resting membrane potentials were decreased by 4-8 mV. GABA at 10-100 microM and the GABAA agonist muscimol at 1-100 microM decreased the membrane resistance and the firing rate in all neurons tested. The reversal potential of the response to muscimol was similar to that for inhibitory postsynaptic potentials. The actions of muscimol persisted in the presence of 1 microM tetrodotoxin, implying that muscimol must act directly on the recorded neurons. These results suggest that there is a tonic inhibitory GABAergic input to SFO neurons which are mainly mediated through GABAA receptors.

Animals↗

PubMed1995

Transient outward current in adult rat supraoptic neurones with slice patch-clamp technique: inhibition by angiotensin II.

1. Outward potassium currents were recorded from microscopically identified supraoptic neurones of adult Wistar male rats using the whole-cell patch-clamp technique in thin-slice preparations. The basic characteristics of transient outward current (IA or A-current) and the effects of angiotensin II (AII) on the currents were studied. 2. IA was isolated by subtracting outward currents elicited by stepping from two different holding potentials to a test potential or by applying 4-aminopyridine (4-AP) at 5 mM. The isolated IA had a threshold for activation between -55 and -65 mV and was characterized by fast activation and inactivation. Values of the time to peak and the inactivation time constants for current decay at different test potentials were voltage dependent. 3. Normalized currents for activation and steady-state inactivation of IA were fitted to the Boltzmann function. The mid-points and the slope factors were, respectively, -35.0 and -14.3 +/- 0.40 mV (n = 5) for the activation curve, and -72.0 and 7.0 +/- 0.68 mV (n = 5) for the inactivation curve. 4. The time course of recovery from inactivation was best fitted to a single exponential function with the time constant of 37.8 +/- 6.6 ms (n = 6). 5. The effects of AII on IA and delayed rectifier current (IK) were investigated. According to their responses to AII, cells were classified into two groups, sensitive and low-sensitive. Bolus injection of AII (10 microM, 100 microliters) decreased the IA amplitude by 25.1 +/- 2.4% in seven (53.8%) of the thirteen neurones tested (sensitive group), whereas the other six neurones (low-sensitive group) changed by only 2.2 +/- 0.8%. Perfusion of AII (0.1 microM) decreased the IA amplitude by 21.3 +/- 3.1% in six (54.5%) of eleven neurones tested (sensitive group), whereas the other five neurones (low-sensitive group) changed only by 1.7 +/- 0.8%. Bolus injection of AII (10 microM, 100 microliters) decreased the IK amplitude 9.6 +/-1.6% mV in five (45.5%) of the eleven neurones tested (sensitive group), whereas the other six neurones (low-sensitive group) changed only by 0.46 +/- 0.27%. In the sensitive groups, the reduction of IA by AII was significantly larger than that of IK (P < 0.05). 6. Application of saralasin at 1 microM, an AII antagonist, blocked the effects of AII on IA. 7. These results suggest that the excitatory action of AII on supraoptic neurosecretory cells is mediated at least in part through suppression of IA.

Angiotensin II↗

PubMed1995

Alpha-1 and beta-adrenergic receptor blocking potencies of bopindolol and its two metabolites (18-502 and 20-785) as assessed by radioligand binding assay methods.

1. The pKi value of bopindolol for alpha 1High-subtypes in canine aorta, rat hearts and rat brain was 5.71, 5.52 and 6.56, respectively. In addition, the pKi values of these drugs in canine aorta, rat hearts and rat brain for the alpha 1Low-subtype was very low. 2. The phenylephrine induced-contractions of aortae of guinea pigs and rats were not inhibited by these agents. 3. Both bovine hearts and tracheal smooth muscles indicated that 18-502 had the highest pKi value to beta 1- and beta 2-adrenoceptor subtypes and the rank order of these beta-blocking potencies were 18-502 > bopindolol > 20-785.

Adrenergic alpha-1 Receptor Antagonists↗

PubMed1995

Thermoluminescence dosimetry of the Hiroshima atomic-bomb gamma rays between 1.59 km and 1.63 km from the hypocenter.

Gamma-ray kermas from the Hiroshima atomic bomb were measured by a thermoluminescence (TL) method using tile specimens collected from five locations on the rooftop of a building (Postal Saving Bureau), 1,591-1,635 m from the hypocenter. Four tile specimens each from five locations were sampled and quartz grains were extracted from them. TL of these grains were analyzed by the high temperature TL method and gamma-ray kermas were obtained. The results in tissue kerma, on average, are 21% higher (standard errors are 4.3-7.3%) than the DS86 estimation. The present data and the reported TL results indicate that the measured gamma-ray kermas begin to exceed the DS86 values at about 1.3 km and the discrepancy between them increases with ground distance. This discrepancy is attributed to errors in the DS86 neutron source spectrum and is supported by previous neutron activation measurements.

Gamma Rays↗

PubMed1995

Immune responsiveness in Mycobacterium avium-infected mice: changes in the proportion of T cell subsets and antibody production during the course of infection.

The C57Bl/6 susceptible (Bcgs) and its resistant (Bcgr) congenic mouse, previously developed by retrogressive backcrossing, were infected with 1 x 10(6) colony-forming units (CFU) of Mycobacterium avium and bacterial growth and their immune responses during the early and prolonged periods of infection were examined. There was a high proliferation in the liver and spleen of Bcgs mice, whereas no proliferation was observed in the Bcgr mice. Similarly, the sizes and weights of these organs were much higher than those of their Bcgr counterparts. The size and number of granulomas in Bcgs were also found to be higher than those of Bcgr. The CD3+ and CD4+ subsets increased dramatically in both mice during the early stage of infection. However, in the later phase of the infection, these populations decreased dramatically in Bcgs mice, but not in Bcgr mice, resulting in a depression in cell-mediated immune responses. No significant decrease in cell-mediated immune responses was observed in Bcgr mice even after prolonged infection. ELISA was performed to determine the antibody levels in both mice, and it was found that serum IgG and IgM levels in Bcgs were comparatively higher than those in Bcgr mice throughout the period of infection. The Bcg gene therefore may have an important role in the maintenance of resistance not only in the early phase but also in the later phase of Myco. avium infection.

Animals↗

PubMed1995

Granulomatous epididymitis related to Rhodotorula glutinis infection in a dog.

A 4-year-old, male Great Dane dog developed severe swelling of the scrotum on 9 December 1991, and the testes and epididymides were removed surgically on 12 December 1992. The cut surface of the epididymides consisted of hard connective tissue and several small abcesses with slight hemorrhage. Histopathologically, the seminiferous tubules in the testes had only a few spermatogenic cells, but Sertoli cells were well preserved. Both epididymides consisted entirely of a proliferation of fibrous connective tissue, and only a few ducts deferens containing cell debris, neutrophils, and macrophages in the lumina were present. In all lesions of the epididymides, the macrophages contained periodic acid-Schiff- and Grocott's silver-positive round granules, 5-8 microns in diameter. Microbiologically, smooth salmon-pink colonies consisting of ovoidal yeast, about 10 microns in diameter, were isolated from the samples of epididymides but not from those of the testes. The isolated yeast had microbiological characteristics of Rhodotorula glutinis. From these observations, we diagnosed the present case as granulomatous epididymitis due to Rhodotorula infection.

Animals↗

PubMed1995

Bopindolol is a slowly dissociating beta 1-adrenoceptor antagonist when compared to other beta-blockers.

This study used radioligand binding assay methods and pharmacological experiments to examine whether bopindolol, possessing a long-lasting action in addition to potent beta-adrenoceptor antagonistic effects, is a slowly dissociating antagonist. In addition, the slow dissociation of two of its metabolites, 18-502 (4-(3-tert-butylamino-2-hydroxypropoxy)-2-methyl indole) and 20-785 (4-(3-tert-butylaminopropoxy)-2-carboxyl indole), which have potent beta-blocking activities, was also assessed. The blockade of 3H-CGP12177 binding sites in rat heart and brain induced by pindolol was readily reversed by washing, whereas this inhibition by bopindolol and 18-502 was not easily reversed by washing. In addition, specific bindings of the hearts of the treatment animals with 20-785, atenolol, (+/-)propranolol, nadolol and celiprolol and of washout were 86.7, 78.8, 77.5, 82.3 and 79.9% of the control, respectively. These blockades by the treatment of each drug and washout in the brain were, however, lower than those in the hearts. On the other hand, when the left and right atria were pretreated with propranolol, bopindolol and 18-502, the inotropic and chronotropic actions of isoprenaline were inhibited by these drugs even though they were not present in the extracellular medium. Pretreatment with 20-785, atenolol and nadolol was readily reversed for both inotropic action and chronotropic rate, and inhibition by celiprolol and pindolol remained at 25% of the control at 240 min after treatment with these drugs. A good correlation between inhibitory binding percentage in the hearts and inhibitory inotropic or chronotropic actions were observed, although it was not observed in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-1 Receptor Antagonists↗

PubMed1995

Residual inhibition in density of [3H]isradipine binding sites in rat brain membrane pretreated with amlodipine.

AIM: To test changes in the density of [3H] isradipine binding sites in rat brain membrane pretreated with amlodipine and to compare with those of nifedipine and (+) SM-6586 (methyl 1, 4-dihydro-2, 6-dimethyl-3-(3-(N-benzyl-N-methylaminomethyl)-1,2,4- oxadiazolyl-5-yl)-4-(3-nitrophenyl) pyridine-5-carboxylate). METHODS: The membrane-enriched fractions were prepared from rat brain. The brain membranes were preincubated with nifedipine (10 nmol L-1), amlodipine (1 mumol L-1) and SM-6586 (1 nmol L-1) or with no antagonists added for 45 min, and washing and centrifugation were performed 3 times. They were assayed with [3H]isradipine in incubation media. The Kd and Bmax values of the membrane fractions pretreated with the drugs were determined by Scatchard analysis. RESULTS: The blockage of the [3H]isradipine binding sites induced by nifedipine was reversed by washing, enabling the low values of the specific binding sites to be observed. The blockages by amlodipine and SM-6586, on the other hand, were not readily reversed. No significant difference was found, however, between in the Kd walues of these drugs. CONCLUSION: Amlodipine and SM-6586 are Ca2+ antagonists which dissociate slowly from the Ca2+ channel in membranes.

Amlodipine↗

PubMed1995

Cardiovascular system related peptides and hypothalamic neurons.

The hypothalamus is known to be an integrative site of cardiovascular, endocrine and autonomic functions. Our previous studies, using extracellular, intracellular and/or whole cell patch-clamp recordings in rat hypothalamic slice preparations, revealed that cardiovascular related peptides such as atrial natriuretic polypeptides (ANP), B-type polypeptides (BNP), endothelin (ET), angiotensin II (AII) and interleukin-1 beta (IL-1 beta) influence the hypothalamic neurons. ANP modulated the firing rates in the supraoptic nucleus (SON). BNP inhibited the SON neurons and these effects were mediated through cGMP and cGMP-dependent protein kinase. ET also inhibited approximately 60% of SON neurons. By using slice patch-clamp techniques, AII inhibited the transient outward potassium current in the SON neurons. IL-1 beta increased the firing rate and depolarized the membrane of the most SON neurons. A new type of transmitter, nitric oxide (NO), identified as an endothelial-derived relaxing factor (EDRF), modulated the glutaminergic inputs of the SON neurons. The results suggest that cardiovascular related peptides and NO modulate the neuronal activity of neurosecretory cells in the SON.

Angiotensin II↗

PubMed1994

Kappa-selective agonists decrease postsynaptic potentials and calcium components of action potentials in the supraoptic nucleus of rat hypothalamus in vitro.

To investigate the effects of the endogenous kappa-receptor agonists dynorphin and leumorphin on neurons of the supraoptic nucleus in the rat hypothalamus, intracellular recordings were made from 62 supraoptic neurons in slice preparations. Bath application of dynorphin and leumorphin at 10(-7) M to 3 x 10(-6) M decreased the spontaneous firing rate with slight hyperpolarization of the membrane potential (-3.8 +/- 0.5 mV, mean +/- S.E.M.) but did not detectably change input resistance. The inhibitory effects were blocked by the relatively selective kappa-antagonist MR-2266. The synthetic kappa-receptor agonist U-50,488H had similar inhibitory effects on supraoptic neurons. Postsynaptic potentials evoked by electrical stimulation dorsal or dorsolateral to the supraoptic nucleus were suppressed by dynorphin and leumorphin. Morphine and [D-Ala, D-Leu]enkephalin, which are relatively selective to mu- and delta-receptors, respectively, influenced the postsynaptic potentials less. Dynorphin and leumorphin also decreased the duration of action potentials that were prolonged by either bath application of tetraethylammonium chloride at 5-10 mM or intracellular injection of Cs ions from the recording electrodes which were filled with 3 M cesium citrate. The prolongation was blocked by 1 mM MnCl2 and 2 mM CoCl2, which suggested that the components were due to voltage-dependent Ca2+ influx. The results suggest that endogenous kappa-receptor agonists inhibit neurosecretory cells of the supraoptic nucleus to suppress synaptic events and Ca2+ components of action potentials.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1994

Sodium nitroprusside modulates NMDA response in the rat supraoptic neurons in vitro.

The modulatory effects of NO on N-methyl-D-aspartate (NMDA)-induced response in neurons of the supraoptic nucleus (SON) were studied by intracellular recording and radioimmunoassay of cyclic nucleotides using the rat brain slice preparation. Depolarization induced by 100 microM NMDA was reduced by application of 1 to 3 mM of the NO-donors, sodium nitroprusside, and isosorbide dinitrate in all 8 neurons and in 6 of 10 neurons, respectively. The scavenger for NO, hemoglobin, and the inhibitor of NO synthase, NG-nitro-L-arginine (LNNA) enhanced the NMDA-induced depolarization in four neurons and two of three neurons, respectively. Intracellular cGMP accumulation induced by NMDA was significantly diminished by LNNA. However, NMDA-induced depolarization was not affected by either the protein kinase inhibitor, N-[2-(methylamino)ethyl]-5- isoquinolinesulfonamide dihydrochloride (H-8), or the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). These results indicate that NO reduces NMDA-induced depolarization in a manner that is independent of cGMP and may control the activity of the SON neurons through NMDA receptors.

Animals↗