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Biomedical subjects

S Shibata

Publications and source records attributed to S Shibata.

At least 595 records · Page 33Linked to original sources
PubMed1988

The mode of vasoinhibitory action of a pyridazione derivative (MCI-154), a new cardiotonic agent, on contractile responses induced by alpha-adrenoceptor agonists and 45Ca influx in isolated vascular smooth muscles.

The vasoinhibitory effects of MCI-154 (MCI), a new pyridazione derivative, on contractile responses to alpha 1- and alpha 2-adrenoceptor agonists were examined in isolated rabbit aorta. MCI (10(-8)-10(-5) M) inhibited the maximum contractile responses to clonidine and BHT-920 (BHT) in a concentration-dependent manner, but only inhibited responses to lower concentrations of methoxamine. In aortas pretreated with phenoxybenzamine however, MCI (10(-5) M) readily inhibited responses to methoxamine. MCI (10(-5) M) had no significant effect on responses to potassium or added Ca2+ in a Ca2+ free, K+-depolarizing medium. In aortas incubated in a Ca2+-free medium with EGTA, the addition of methoxamine (10(-5) M), clonidine (10(-5) M) or BHT (3 X 10(-4) M) induced a phasic contraction. The inhibitory effect of MCI (10(-9)-10(-5) M) on these phasic responses was much greater for clonidine or BHT than for methoxamine. In rabbit iliac artery caffeine (10 mM) induced a rapid phasic contraction in a Ca2+-free medium, which was inhibited by MCI (10(-7)-10(-5) M) in a concentration-dependent manner. In aortas incubated in a Ca2+-free medium with low EGTA and nifedipine (10(-6) M) in the presence of alpha-adrenoceptor agonists (methoxamine, clonidine or BHT), the addition of Ca2+ (2 mM) induced a tonic contraction. MCI (10(-8)-10(-5) M) inhibited these Ca2+-dependent, agonists-mediated responses in a concentration-dependent manner. MCI had no effect on unstimulated La3+ resistant Ca2+ binding or methoxamine-induced Ca2+ influx.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1988

Analysis of the mechanism of influenza B virus inactivation by guinea pig serum.

Normal guinea pig serum lacking detectable antiviral antibody inactivated influenza B virus via the classical complement pathway. This virus inactivation appeared to result from the steric hindrance of HA activity by the association with the virus of serum proteins presumed to be complement components. Trypsin digestion of the associated proteins fully restored the HA activity but not infectivity. It was found that the virus underwent minor disruption of the envelope and degradation of M1 protein and genomic RNA.

Animals↗
PubMed1988

The pathophysiological role of water-sodium balance and renal dopaminergic activity in overweight patients with essential hypertension.

Studies were conducted to evaluate the role of water-sodium balance and renal dopaminergic activity in the hypertensive mechanisms of overweight patients with essential hypertension (EHT). The body mass index (BMI) was correlated positively with mean arterial pressure, plasma volume, extracellular fluid volume, or total exchangeable sodium and negatively with plasma noradrenaline concentration or plasma renin activity in patients with EHT. Fractional excretion of sodium (FENa) was significantly lower in overweight patients than in normal weight patients with EHT. Hypotensive effect of sodium restriction or the natriuretic response to infused dopamine was more remarkable in overweight patients with EHT than in normal weight patients with EHT. Urinary excretion of free dopamine (UDA) was correlated positively with simultaneously measured urinary excretion of sodium or FENa and negatively with the natriuretic response to dopamine infusion. In addition, UDA was positively correlated with the BMI in normal weight patients with EHT, whereas the relation between the UDA and the BMI was significantly negative in overweight patients with EHT. These findings suggest that the expansion of body fluid volume and sodium might result from the blunted natriuretic ability due to an attenuation of the renal dopaminergic activity in overweight patients with EHT. The expansion of body fluid volume and sodium may play an important role in the hypertensive mechanisms of overweight patients with EHT.

Adult↗
PubMed1988

The vasoinhibitory action of FR 46171, a new pyridine alcohol antianginal agent, on isolated rabbit vascular smooth muscles.

The vasoinhibitory effect of FR 46171, a new pyridine alcohol derivative, on contractile responses to alpha-adrenoceptor agonists was examined in isolated rabbit aorta. FR 46171 (10(-8)-10(-5) M) inhibited the maximum contractile response to clonidine (CL) in a concentration-dependent manner, but it only inhibited the responses to low concentrations of norepinephrine (NE) and methoxamine (MO). In the aorta pretreated with phenoxybenzamine, however, FR 46171 at 10(-5) M inhibited the residual maximum response to NE and MO. FR 46171 at 10(-5) M only inhibited the response to KCl (20 mM). FR 46171 at 10(-6) and 10(-5) M also moderately inhibited the response to added Ca2+ in a Ca2+-free medium in K+-depolarized preparations. Nifedipine at 10(-6) M, by contrast, nearly abolished the responses to potassium or added Ca2+. In a Ca2+-free medium with EGTA, an addition of NE (10(-5) M), MO (10(-5) M), or CL (10(-5) M) induced a phasic contraction. The inhibitory effect of FR 46171 (10(-8)-10(-5) M) was much greater on the response to CL than that to NE or MO. In a Ca2+-free medium with low EGTA and nifedipine (10(-6) M) in the presence of an alpha-adrenoceptor agonist (NE, MO, or CL), an addition of Ca2+ (2 mM) induced a tonic contraction. FR 46171 (10(-9)-10(-5) M) inhibited the Ca2+ response, which is activated by the agonists, in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina Pectoris↗
PubMed1988

Electromechanical effects of bPTH-(1-34) on rabbit sinus node cells and guinea pig papillary muscles.

The effects of bPTH-(1-34), a synthetic preparation of bovine parathyroid hormone containing the first 34 amino acids, on electromechanical activity of isolated rabbit sinus node cells and guinea pig papillary muscles were examined by microelectrode techniques. In sinus node cells, bPTH-(1-34) (10(-7) M) decreased the cycle length of spontaneous firing (SPCL) accompanied by an increase in the maximum upstroke velocity at phase 0 (dV/dtmax) without affecting the amplitude of the action potential (APA) or the maximum diastolic potential (MDP). All the effects of bPTH-(1-34) on sinus node cells were abolished by verapamil (5 X 10(-7) M), but not by pindolol (2 X 10(-7) M). In constantly driven guinea pig papillary muscles, bPTH-(1-34) caused a positive inotropic effect (+31%). The parameters of the action potential were not significantly affected. This inotropic effect of bPTH-(1-34) was inhibited by pretreatment with verapamil or a low calcium medium (0.12 mM), but was not affected by pindolol. In contrast, ryanodine (2 X 10(-6) M), an inhibitor of internal Ca2+ release, which decreased the contraction with a prolongation of the action potential duration augmented the inotropic effect of bPTH-(1-34). In papillary muscles depolarized by 26 mM [K+]O, bPTH-(1-34) enhanced the slow action potential. In voltage clamp experiments using a single sucrose-gap method, bPTH-(1-34) caused an increase in the peak amplitude of the slow inward current, while it did not affect the outward current.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1988

Electrophysiological effects of KT-362, a new antiarrhythmic agent with vasodilating action, on isolated guinea pig ventricular muscle.

The effects of KT-362, a newly synthesized vasodilating and antiarrhythmic agent, on transmembrane action potentials were examined in isolated papillary muscles of guinea pig. KT-362 (3 x 10(-6) to 3 x 10(-5) M) caused a dose-dependent decrease in the maximum upstroke velocity (Vmax) of the action potential without affecting the resting potential. In the presence of KT-362, trains of stimuli at rates greater than or equal to 0.2 Hz led to an exponential decline in Vmax. This use-dependent block was enhanced at higher stimulation frequency. The time constant for the recovery of Vmax from the use-dependent block was 2.8-2.9 s. The curves relating membrane potential and Vmax were shifted by KT-362 (10(-5) M) in the direction of more negative potentials (8.6 mV). In papillary muscles treated with KT-362 (10(-5) M), the Vmax of test action potential preceded by conditioning clamp pulses to 0 mV was progressively decreased with increasing number of pulses, while it was little affected by the duration of each clamp pulse within the range from 10 to 700 ms. These findings suggest that KT-362 has quinidine-like use-dependent inhibitory action on the fast sodium channel of cardiac muscles by the binding to the channel mainly during its activated state. At high concentrations (greater than or equal to 3 x 10(-5) M), KT-362 also suppressed the slow action potential in K+ depolarized papillary muscles.

Action Potentials↗
PubMed1988

Palytoxin-induced contraction and release of endogenous noradrenaline in rat tail artery.

1. The mechanism of the contractile effect of a potent marine toxin, palytoxin (PTX) on the rat isolated tail artery was examined. 2. PTX (10(-7) M) induced a contraction in the tail artery which was dependent on external Ca2+. This contraction was inhibited (by 75% or more) by 10(-6) M prazosin, 2.4 x 10(-5) M bretylium and 10(-4) M 6-hydroxydopamine (6-OHDA), and partially (by 40%) by 10(-5) M indomethacin. However, this contraction was not affected by 10(-6) M tetrodotoxin (TTX), 10(-6) M nifedipine or reserpine treatment. The PTX-induced contraction in reserpine-treated artery was partially inhibited by nifedipine and indomethacin but not by prazosin. 3. Transmural electrical stimulation induced a transient contraction which was dependent on external Ca2+. The contraction induced by electrical stimulation was inhibited by TTX, prazosin, bretylium, reserpine treatment and 6-OHDA but not by nifedipine or indomethacin. 4. PTX increased the release of noradrenaline from this artery. However PTX did not release noradrenaline from reserpine-treated arteries. PTX-induced noradrenaline release was only partially inhibited by TTX or by Ca2+-free solution. 5. These results suggest that PTX has pre- and postsynaptic effects in the rat tail artery. PTX may stimulate adrenergic nerves and release noradrenaline mainly by a TTX-insensitive and Ca2+-independent mechanism and partially by a TTX-sensitive and Ca2+-dependent mechanism. Further, PTX may also release prostaglandins and depolarize smooth muscle cell membrane to induce a contraction.

Acrylamides↗
PubMed1988

Inhibitory effect of glycyrrhetinic acid derivatives on arachidonic acid-induced mouse ear oedema.

The inhibitory effects of glycyrrhetinic acid and its derivatives were examined on arachidonic acid (AA)-induced ear oedema in mice. Of the compounds, dihemiphthalate derivatives of 18 beta-olean-12-ene-3 beta, 30-diol (IId, IId'), 18 beta-olean-9(11)12-diene-3 beta, 30-diol (IIIa, IIIa') and olean-11, 13(18)-diene-3 beta, 30-diol (IVa, IVa') showed a strong inhibition of ear oedema on both tropical (ID50, 1.9, 2.8 and 1.7 mg/ear, respectively) and oral (ID50, 90, 130 and 88 mg kg-1, respectively) administration. Topical ID50 values were approximately the same potency as nordihydroguaiaretic acid (ID50, 2.1 mg/ear). Given topically these compounds were also capable of inhibiting PGE2 and LTC4 formation at an early stage of AA-induced ear oedema. However, glycyrrhetinic acid (Ia) and deoxoglycyrrhetol (IIa), the fundamental skeletons of the derivatives, showed no detectable inhibition of oedema at a dose of 1 mg/ear (topical) or 200 mg kg-1 (oral). The most effective time for the topical administration of the compound IId against ear oedema was 0-30 min before AA application; this is different from dexamethasone which requires a time lag for reaction. The results suggest that the inhibitory effect of the hemiphthalate compounds (IId, IId', IIIa, IIIa', IVa and IVa') is a direct action, and does not involve the anti-inflammatory action of steroids mediated by the secondary formation of a reactive protein.

Administration, Topical↗
PubMed1988

Inhibitory effects of nitroglycerin on contractile responses to methoxamine and clonidine in isolated rabbit renal and femoral arteries.

The inhibitory effect of nitroglycerin (NG) on contractile responses to methoxamine (MO) and clonidine (CL) was investigated in isolated rabbit renal and femoral arteries. NG (10(-7)-10(-5) mol/l) inhibited the responses to MO and CL in a noncompetitive manner and its inhibitory effect on CL-responses was much greater than that on the MO-responses. In the presence of phenoxybenzamine, however, NG (10(-5) mol/l) markedly inhibited the residual response to MO. Contractile responses to KCl or added Ca2+ in a Ca2+-free medium containing KCl were slightly inhibited by NG. In the presence of nifedipine, NG (10(-5) mol/l) markedly inhibited residual responses to CL but it only slightly inhibited the response to MO. In a Ca2+-free medium with EGTA, MO (10(-5) mol/l) or CL (10(-5) mol/l) induced a phasic contraction. NG had a greater inhibitory effect on the response to CL than MO. In a Ca2+-free medium with EGTA, nifedipine and MO (10(-5) mol/l) or CL (10(-5) mol/l), Ca2+ induced a tonic contraction. NG inhibited the Ca2+-response in the presence of CL, but it had little or no effect on the Ca2+-response in the presence of MO. These results suggest that in rabbit renal and femoral arteries, the potent inhibitory effect of NG on the responses to CL as compared to MO may be due to differences in the amount of receptor reserves that exist for both the agonists. In addition, the inhibition of voltage-dependent Ca2+ channels may not play a major role in the vasoinhibitory action of NG. Further, NG inhibits contractile responses due to mobilization of intracellular Ca2+ much more than the responses due to receptor-activated, nifedipine-insensitive Ca2+-movement.

Animals↗
PubMed1988

Experimental cerebral infarction in the dog: electron microscopic studies of the microvasculature.

Ultramicromorphological changes of the cerebral vessels were studied by observation of ultrathin section specimens under the transmission electron microscope, vascular cast specimens under the scanning electron microscope, and freeze-fracture replica specimens under the transmission electron microscope. Extensive infarction was found in areas supplied by the middle cerebral artery, but the disturbances in the microvasculature of the lesion are not simple. Bleeding came from arterioles in the basal ganglia, a perforating arterial terminal zone, and from venules in the corticomedullary border, a cortical arterial terminal zone. The number of pinocytotic vesicles was 3 times normal in the capillaries of ischemic cortex, and vesicle size increased 1.3 times. The tight junctions revealed discontinuity of strand-composing intramembranous particles, but no obvious disruption. It is concluded, therefore, that vesicular transport plays a major role in the increase of capillary permeability during experimental infarction.

Animals↗
PubMed1988

Involvement of the medial amygdaloid nucleus in the action of imipramine in rats subjected to the forced swimming test.

A forced swimming test proposed by Porsolt is a useful method for screening antidepressants. To evaluate drug effects more objectively, vibration of the walls of a water tank caused by the escape behavior of the rat was recorded. Imipramine (IMI) increased the number of vibration and this effect was observed in the medial amygdala lesioned rat but not in the central or basolateral amygdala lesioned rat. The present result suggests that the medial amygdala is an important site of action of IMI.

Amygdala↗
PubMed1988

[Behavioral effects of quinupramine, a new tricyclic antidepressant].

The effects of a new tricyclic antidepressant quinupramine (5-(3-quinuclidinyl)-10,11-dihydro-5H-dibenz [b, f] azepine) on various animal behaviors were examined in mice and rats and compared with those of imipramine, amitriptyline and maprotiline. Quinupramine antagonized haloperidol-induced catalepsy and tetrabenazine-induced ptosis and potentiated methamphetamine- and apomorphine-induced stereotyped behavior. These effects were almost the same as or even more potent than those of imipramine and amitriptyline. Quinupramine decreased locomotor activity in mice, but potentiated methamphetamine-induced hyperactivity to a greater degree than imipramine and amitriptyline. On the other hand, quinupramine inhibited muricide in accumbens-lesioned rats, but did not prominently inhibit muricide in olfactory-bulbectomized and raphe-lesioned rats. Quinupramine decreased the duration of immobility in low doses without affecting locomotor activity, and this effect was almost the same as that of imipramine and amitriptyline and more potent than that of maprotiline. Quinupramine antagonized physostigmine lethality and oxotremorine-induced tremor, suggesting that quinupramine has a central anticholinergic action. Quinupramine, like imipramine and amitriptyline, has no effect on conditioned avoidance behavior. In conclusion, quinupramine generally has the same behavioral profile as typical tricyclic antidepressants, but it has somewhat different effects from imipramine and amitriptyline since quinupramine has a potent central anticholinergic and a weak antimuricide effect.

Animals↗