Biomedical subjects
Publications and source records attributed to S Shibata.
Verapamil, a calcium entry blocker, had a greater inhibitory effect on the positive inotropic effect of excess Ca2+ in SHR than in NWR, suggesting that the cardiac responsiveness to verapamil was enhanced in SHR.
The role of calcium ions in maintaining the circadian rhythm of suprachiasmatic nucleus (SCN) neuron activity was investigated using rat hypothalamic slice preparations. In normal Krebs solution, the firing rate of SCN neurons was higher in the light period than in the dark period. In Ca2+-free Krebs solution, SCN neuron activity was low during all periods and did not show diurnal rhythm. These results suggest that the disappearance of circadian rhythmic change of SCN neuron activity in Ca2+-free Krebs solution may be due to the disappearance of synaptic transmission in the SCN.
The present experiment was undertaken to determine the existence of alpha 1- and alpha 2-adrenoceptors in the smooth muscle of the rabbit bladder dome, trigone and proximal urethra. In the dome pretreated with propranolol (10(-6) M), phenylephrine (10(-5) M-10(-3) M) and norepinephrine (10(-7) M-10(-5) M) caused only a small contraction but norepinephrine, only at high concentrations (10(-4) M-10(-3) M), produced a small relaxation. Clonidine, however, had no effect on the dome. In both trigone and urethra, phenylephrine, clonidine and norepinephrine caused dose-dependent contractions. The contractile response to phenylephrine or norepinephrine was significantly greater than that to clonidine in the trigone but no such difference was observed in the urethra. Prazosin (10(-8) M-10(-6) M, alpha 1-adrenoceptor antagonist) produced a rightward shift of the phenylephrine and clonidine dose-response curve in both the trigone and urethra. Yohimbine (10(-8) M-10(-6) M, alpha 2-adrenoceptor antagonist) inhibited the response to clonidine without significantly affecting the responses to phenylephrine. These studies indicated that alpha 1- and alpha 2-adrenoceptors are present in both the trigone and proximal urethra. In the dome, only alpha 1-adrenoceptors are sparsely distributed.
The amplitude of the early plateau phase of the action potential and the slow action potential of cardiac muscle were much lower in hibernating chipmunks than in nonhibernating chipmunks. The frequency-dependent contraction was decreased in hibernating animals but increased in nonhibernating animals. Caffeine caused a negative inotropic effect in hibernating animals but a positive inotropic effect in nonhibernating animals. Ryanodine caused greater inhibition in hibernating animals than in nonhibernating animals. These results suggest that the respective roles of the sources of calcium for cardiac excitation-contraction coupling are changed during hibernation.
A new abnormal hemoglobin, Hb Okazaki [beta 93(F9) Cys----Arg], with an amino acid substitution at the tyrosine pocket of the beta chain as well as at the alpha 2 beta 1 contact of the quaternary structure of molecule, was discovered in a Japanese man. This hemoglobin showed increased oxygen affinity and molecular instability.
The influence of environmental light-dark cycle (LD) and bilateral enucleation on single neuronal activity in the suprachiasmatic nucleus (SCN) was examined using a hypothalamic slice preparation. Firstly, we reconfirmed previous results that the discharge rate in slices taken from animals kept on normal LD was higher during the light than during the dark period. Secondly, the day time discharge rate in the ventrolateral part of the SCN was decreased by bilateral enucleation and DD housing, while in the dorsomedial part it was unaffected. Thirdly, LL housing suppressed the discharge rates in both parts during the day and night periods. The present results suggest that the dorsomedial part of the SCN is more important in regulation of the circadian rhythm of SCN neuronal activity than the ventrolateral.
Stimulation of the optic nerve evoked two positive waves (P1 and P2) with short latencies and a following large negative wave (N) in the suprachiasmatic nucleus (SCN) of hypothalamic slice preparations. The conduction velocities of the P1, P2 and N waves were assumed to be 2.9 m/s, 0.5 m/s and 0.4 m/s, respectively. The N wave disappeared in low Ca2+ medium and all responses disappeared when TTX was added to the medium at a concentration of 10(-6) M. The results indicate that the P1 and P2 waves were responses of the optic nerve in the SCN and the N wave was that of SCN neurons. Following optic nerve stimulation 15 out of 212 single SCN neurons were excited; 10 were excited then inhibited, 14 were excited followed by rhythmic oscillation, and 4 were inhibited. The results demonstrate neuronal projections from the optic nerve to the SCN, and suggest that the major role of the excitatory influence on SCN neurons is responsible for the elevation of neuronal activity in the SCN during the daytime.
A new abnormal hemoglobin, Hb Aichi [alpha 50(CE8) His----Arg], was discovered in a young Japanese man. This variant was isoelectrofocussed between Hb A and Hb A2 and amounted to about 21% of the total hemoglobin in the hemolysate. This hemoglobin showed normal oxygen affinity but slight instability.
To define the mode of the vasorelaxing action of nicorandil as compared to nitroglycerin, the effects of the agent on the contractile response to various stimulations in rabbit aorta, cat coronary arteries and rabbit basilar arteries were evaluated. Nicorandil had a greater relaxing effect on the maximum response to norepinephrine (NE) than on the potassium (K+) response on all vascular smooth muscles used. In coronary and basilar arteries, however, the inhibitory action of nitroglycerin was not different on the response to both agonists. In coronary and basilar arteries the maximum inhibition of the NE response by nicorandil was greater than that by nitroglycerin. Nicorandil (10(-5) M) but not phentolamine (10(-5) M) inhibited the PGF2 alpha-induced contraction of the aorta. Either nicorandil or nitroglycerin suppressed the response of the aorta to the transmural stimulation. In a Ca2+-free medium containing K+ (40 mM), nicorandil decreased the response to excess Ca2+ in all preparations whereas, nifedipine (10(-6)-10(-5) M) abolished it. Nitroglycerin, however, had no effect on the Ca2+-induced contraction on basilar arteries. In a Ca2+-free medium, the residual NE-induced contraction was inhibited by nicorandil or nitroglycerin but not by nifedipine . The combined treatment with nicorandil and nitroglycerin caused a stronger suppression of residual NE response that that of a single treatment with either agent suggesting the different site of action for the two agents. These results suggest that the mode of vasorelaxing action of nicorandil may be due to the alteration (inhibition) of Ca2+ kinetics in the cell.
2,4-Dinitrotoluene (2,4-DNT) is an important industrial nitroaromatic compound. 2,4-Diaminotoluene (2,4-DAT), one of the urinary metabolites of 2,4-DNT, is carcinogenic when fed to rats. The objectives of these studies were to determine whether 2,4-DAT was formed from 2,4-DNT in rat liver and to clarify the nature of enzymes responsible for reduction of 2,4-DNT to 2,4-DAT. Data obtained from thin-layer and high-pressure liquid chromatography indicated that metabolites produced by microsomal preparations were 2-amino-4-nitrotoluene (2A4NT) and its isomer (4A2NT). This microsomal activity is probably mediated by cytochrome P-450 because the reduction is blocked by carbon monoxide and primary amines [aniline, n-octylamine, and 2,4-dichloro-6-phenylphenoxyethylamine (DPEA)]. In contrast, 2,4-DNT was metabolized via 2A4NT and 4A2NT to 2,4-DAT by cytosolic preparations. The greatest part of the reduction activity was due to cytosolic xanthine oxidase because the reduction was blocked by allopurinol. The results of this investigation suggest that reduction of 2,4-DNT to 2,4-DAT by cytosolic xanthine oxidase may play a role in 2,4-DNT hepatocarcinogenicity.
Two forms of drug administration, i.e., systemic subcutaneous administration and microinjection into the medial amygdala were employed to examine the effect of chronic administration of psychotropic drugs on muricide in olfactory bulbectomized rats. Muricide inhibition induced by the systemic doses of chlorpromazine (CPZ) 10 mg/kg and diazepam 10 mg/kg was reduced with chronic administration, while that by desipramine (DMI) 10 mg/kg and amitriptyline 30 mg/kg was augmented with chronic administration. Muricide inhibition induced by microinjection of CPZ was also reduced, while that by DMI was augmented. These results indicate that muricide by olfactory bulbectomized rats is a useful animal model for evaluating antidepressants and that a potential site of action of antidepressants is located in the medial amygdala.
The rate and pattern of neuronal discharge in the suprachiasmatic nucleus (SCN) during developmental stages were studied and compared with those of the ventromedial (VMH) and the lateral hypothalamus (LHA) using rat hypothalamic slices. The firing rate of the SCN neurons was low on the 7th and 11th days; however, it dramatically increased by the 14th day to reach the adult rate, while firing rates of VMH and LHA neurons increased gradually with age. The discharge rate of neurons in the ventrolateral part of the SCN (VL-SCN) was higher than that of the dorsomedial SCN (DM-SCN) neurons in 14-, 21- and 70-100-day-old rats. Activity of the DM-SCN neurons on day 21 were unaffected by bilateral enucleation on the third day, while activity in the VL-SCN decreased; that of both parts was significantly decreased by a constant light schedule.
All electrode reactions are either electrochemical oxidation or electrochemical reduction reactions and therefore membrane potentials are produced by redox reactions. Postsynaptic potentials are the result of spontaneous galvanic electrochemical changes produced by neurotransmitters. Action potentials denote microelectrolysis along the axon length. Threshold is proportional to charge and the higher the threshold the greater the potential energy. Resting membrane potential is thermodynamically controlled whereas action potential is kinetically controlled phenomenon.
Spatial profile of a projection from retina to the suprachiasmatic nucleus (SCN) was studied by electrophysiological method. Stimulation of contralateral optic nerve evoked the fast positive and late large negative waves in only the ventrolateral but not the dorsolateral parts of the posterior SCN. This result, in agreement with anatomical evidence suggests that the late negative wave is due to excitatory synaptic potential in the SCN and has a role for elevating the neuronal activity in the ventrolateral part of the posterior SCN daytime.
The conformational study of two basic proline-rich polypeptides from human parotid saliva, P--D and P--E of known primary structures, was performed by CD and 1H--n.m.r. spectra measurements. These polypeptides contain consecutive sequences of five prolyl residues in their amino acid sequences. The troughs in CD spectra of P--D and P--E were found at 202 and 201 nm, respectively. These wavelengths were different from the value of 206 nm of poly-L-proline form II conformation. In spite of this, the existence of poly-L-proline form II conformation was suggested in the structure of P--D, because the trough for a fragmental peptide of P--D containing five consecutive prolyl residues was found at 204 nm. No remarkable change was detected in CD and 1H--n.m.r. spectra of P--D and P--E in the range of pH 3.0-11.0. The result suggests that no folding of polypeptide which might be affected by ionic interaction exists in its structure.
The frog spinal cord was used to determine the characteristics of the actions of caroverine and diltiazem, two organic Ca2+-antagonists, on synaptic responses and L-glutamate-induced depolarization. Caroverine and diltiazem (10(-4)M) depressed the dorsal root potential (DR-DRP) induced by electrical stimulation of an adjacent dorsal root. Diltiazem also depressed the ventral root potential (DR-VRP), whereas caroverine augmented both the polysynaptic component in the ventral root reflex and the size of the DR-VRP. The root potentials induced by high frequency stimulation (20 Hz, for 1 s) were markedly depressed by these Ca2+-antagonists at a concentration of 10(-4)M. When the preparation was perfused with normal medium, the compounds depressed L-glutamate-induced depolarizations in ventral and dorsal roots. In preparations treated with tetrodotoxin (TTX) (2 X 10(-7)M), the antagonizing actions of the drugs against L-glutamate-induced depolarizations in the ventral root were markedly reduced or abolished, while significant antagonizing actions on the depolarization in the dorsal root were still observed. The increase in extracellular K+ activity induced by L-glutamate in the TTX-treated preparation was significantly reduced by the compounds. Caroverine and diltiazem had no effect on the presynaptic nerve spike and on the focal synaptic potential induced by a single stimulation of a dorsal root; however, the focal synaptic potential induced by high frequency stimulation (20 Hz, 1 s) was attenuated. Motoneuronal action potentials were abolished by the drugs, while the excitatory postsynaptic potential remained unaffected. 9 The present results suggest that caroverine and diltiazem are not specific L-glutamate antagonists in the frog spinal cord, but that they block the initiation of an action potential without affecting presynaptic nerve conduction, transmitter release or transmitter-receptor interactions. The inhibitory effects of these compounds on L-glutamate-induced K+-efflux are discussed with reference to their Ca2+-antagonizing actions.
Phentolamine caused a rhythmic contraction concentration-dependently without affecting resting tone in the detrusor muscle. Prazosin, yohimbine, propranolol, noradrenaline, clonidine or isoprenaline failed to cause the rhythmic contraction. These agents did not modify the response to phentolamine suggesting no involvement of alpha- or beta-adrenoceptors in the response to phentolamine. Chlorpheniramine, cimetidine, methysergide, SK&F 83566, atropine, bretylium, hemicholinium or tetrodotoxin failed to inhibit the response to phentolamine. These results suggest that the effect of phentolamine is not mediated through histaminergic, 5-hydroxytryptaminergic, dopaminergic or cholinergic systems, or through transmitter release from nerve endings. Prostaglandin F2 alpha (PGF2 alpha), arachidonic acid but not ATP caused rhythmic contractions which resembled the response to phentolamine. Potassium also caused a contraction with increasing resting tone. Following treatment with nifedipine, or incubation in a Ca2+-free medium, the responses to phentolamine, PGF2 alpha, arachidonic acid and potassium were markedly inhibited or abolished. Cyclo-oxygenase inhibitors such as indomethacin, aspirin and corticosterone inhibited or abolished the responses to phentolamine and arachidonic acid but did not inhibit the response to PGF2 alpha. The results suggest that the phentolamine-induced rhythmic contraction may, at least in part, result from the cyclo-oxygenase metabolite of arachidonic acid in guinea-pig detrusor muscles and a consequent increase in the transmembrane Ca2+-influx.
SGB (10(-7)-10(-5) M), a new piperazinyl antihypertensive agent, like prazosin (10(-8)-10(-6) M), a potent preferential alpha 1-adrenoceptor antagonist, inhibited the contractile response of rabbit aorta to norepinephrine and methoxamine in a competitive manner whereas in the cat coronary and rabbit basilar artery, the inhibition by SGB was not a competitive one. The potency of the inhibitory action of SGB was less than that of prazosin in all preparations used. Neither SGB nor prazosin had any inhibitory effect on the response to potassium, 5-hydroxytryptamine, prostaglandin F2 alpha, and excess Ca2+ in all preparations. In the rabbit aortic membrane preparation, the specific binding of [3H]-prazosin was inhibited, concentration-dependently, by SGB with IC50 value of 1.4 +/- 0.09 microM. These studies indicated that SGB has an alpha 1-adrenoceptor-blocking action though its potency is weaker than prazosin.