Kazuyasu Maruyama

Bezafibrate prevents hepatic stellate cell activation and fibrogenesis in a murine steatohepatitis model, and suppresses fibrogenic response induced by transforming growth factor‐β1 in a cultured stellate cell line

Aim:  The aim of this study was to investigate the preventive actions of bezafibrate against non‐alcoholic steatohepatitis (NASH), the activation of hepatic stellate cells (HSC), and fibrogenesis by using a model of NASH and an in vitro model.

Effects of Ritobegron (KUC-7483), a Novel Selective β3-Adrenoceptor Agonist, on Bladder Function in Cynomolgus Monkey

We evaluated the pharmacological profile of ritobegron [KUC-7483; (−)-ethyl 2-[4-(2-{[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino}ethyl)-2,5-dimethylphenyloxy]acetate monohydrochloride] and its effects on the bladder in cynomolgus monkeys by in vitro and in vivo experiments. In vitro, ritobegron decreased the resting tension of the isolated bladder in a concentration-dependent manner (EC50 8.2 ± 2.3 × 10−7 M; maximal relaxation 88.7 ± 3.7%). The β3-adrenoceptor (AR) antagonist 3-(2-allylphenoxy)-1-[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol hydrochloride (SR58894A) produced a rightward shift of this concentration-response curve without altering the maximal response (pKB value 6.56 ± 0.35). In isolated atria, ritobegron increased the atrial rate only at high concentrations (EC50 6.5 ± 1.2 × 10−5 M). Ritobegron had no effect on tracheal contraction at concentrations from 10−9 to 10−4 M, and even at the highest concentration tested, 10−3 M, the maximal relaxation it induced was only 26.7 ± 8.1%. Tests of the selectivity of ritobegron for the bladder gave values of 79.3- and 1200-fold higher versus atria and trachea, respectively. In the in vivo study ritobegron significantly decreased intravesical pressure (ED50 1.44 mg/kg) without affecting either mean blood pressure or heart rate. In conclusion, ritobegron displayed potent and selective β3-AR agonistic activity and relaxed the monkey isolated bladder, and in vivo it decreased intravesical pressure without affecting cardiovascular parameters. These results suggest that ritobegron may be a promising potential agent for the treatment of overactive bladder.

Salivation triggered by pilocarpine involves aquaporin-5 in normal rats but not in irradiated rats.

1 Using rats, we examined the muscarinic receptor subtype mediating pilocarpine‐induced parotid salivary secretion and the contributions of ion transporter systems (effluxes of K+ and Cl‐) and aquaporin‐5 (AQP5) translocation to this response in parotid glands in irradiated‐induced xerostomia. 2 Salivary secretion was significantly lower in irradiated compared with sham‐irradiated (normal) rats. In xerostomia rats, 0.4 and 0.8 mg/kg pilocarpine significantly increased parotid salivary secretion, although the salivary volume was still significantly less than in normal rats after the same dose of pilocarpine. 3 Pirenzepine (1 × 10−6 to 1 × 10−1 mol/L), AF‐DX 116 (3 × 10−6 to 3 × 10−2 mol/L) and N‐2‐chloroethyl‐4‐piperidinyl diphenylacetate (4‐DAMP; 1 × 10−8 to 1 × 10−2 mol/L) dose‐dependently displaced radioligand binding to M1, M2 and M3 receptors, respectively, in parotid membranes from both normal and irradiated rats. In each group of rats, 4‐DAMP had the highest binding affinity. Pretreatment with 4‐DAMP or pirenzepine dose‐dependently inhibited pilocarpine‐induced parotid secretion in both normal and irradiated rats, with 4‐DAMP being markedly more potent than pirenzepine. 4 Normal and irradiated‐rat parotid cells did not differ significantly in terms of pilocarpine‐induced changes in [Ca2+]i, [K+]i and [Cl‐]i. Pilocarpine markedly increased the amount of AQP5 in the apical plasma membrane of parotid cells isolated from normal but not irradiated rats. 5 Thus, pilocarpine induces parotid salivary secretion mainly via the M3 receptor subtype in both irradiated and normal rats. The reduction in this pilocarpine‐induced secretion seen in irradiated rats is due not to disturbances of intracellular Ca2+ mobilization or ion transporter systems, but rather to a disturbance of AQP5 translocation, which may be involved in the pathogenesis of X‐ray irradiation‐induced xerostomia.

Electrophysiological effects of SD-3212, a new antiarrhythmic agent with vasodilator action, on guinea-pig ventricular cells.

1 The effects of SD‐3212 on transmembrane action potentials were examined in right ventricular papillary muscles and in single ventricular myocytes isolated from guinea‐pig hearts. 2 In papillary muscles, SD‐3212 ≥ 3 μm caused a significant decrease in the maximum upstroke velocity () of action potential without affecting resting membrane potential. The inhibition of was enhanced at higher stimulation frequencies. 3 In the presence of SD‐3212, trains of stimuli at rates ≥ 0.5 Hz led to a use‐dependent inhibition of . The time constant for the recovery of from the use‐dependent block was 1.3 s. 4 Voltage‐dependence of inhibition by SD‐3212 was investigated in single myocytes. The curves relating membrane potential and were shifted by SD‐3212 (10 μm) in a hyperpolarizing direction by 6.2 mV. 5 In myocytes treated with SD‐3212 (10 μm), the of test action potentials preceded by conditioning clamp to 0 mV was decreased progressively as the clamp pulse duration was prolonged. of test action potentials following a long (1 s) 0 mV clamp recovered at a time constant ranging from 1.01 to 1.22 s, being shorter at the more negative potential within a range from −70 to −90 mV. 6 These findings suggest that the primary electrophysiological effect of SD‐3212 is a use‐ and voltage‐dependent inhibition of sodium channels. From the onset and offset kinetics of the use‐dependent block, SD‐3212 is located between fast and intermediate kinetic Class‐I drugs. From the state‐dependence of sodium channel block, SD‐3212 belongs to inactivated channel blockers.

Comparison of the Effects of Four α1-Adrenoceptor Antagonists on Ejaculatory Function in Rats

OBJECTIVE To compare the effects of four α(1)-adrenoceptor (AR) subtype-selective antagonists on ejaculatory function in rats to investigate whether the differences in their modes of action-based on their selectivities for the α(1A)-AR subtype-would be related to the prevalence of ejaculation disorder (EjD). METHODS The effects of α(1)-AR antagonists on noradrenaline-induced contractions were studied in rat isolated seminal vesicles, vas deferens, bladder trigone, and prostate. Male rats were given α(1)-AR antagonists orally and, 1 hour after the drug administration they were cohoused in pairs for 1 hour with untreated female rats certified to be in estrus. The number of copulatory plugs (NP) present after mating was measured as a marker of EjD. Drug effects on ejaculatory function (ie, on NP) were compared with those on the prostatic urethra (ie, phenylephrine-induced increase in intraurethral pressure [IUP]). RESULTS All α(1)-AR antagonists concentration-dependently inhibited noradrenaline-induced contraction in all 4 tissues, and there were no differences in the rank order of potencies (tamsulosin > silodosin > alfuzosin > naftopidil) among the tissues. All α(1)-AR antagonists dose-dependently decreased NP and inhibited the phenylephrine-induced increase in IUP. There was little difference in the dose ratio ID(50) value (dose required to produce 50% inhibition) for NP/ID(50) value for IUP response among the four drugs. Drug potencies associated NP and IUP correlated closely with affinities for the human α(1A)-AR. CONCLUSION α(1)-AR antagonists cause EjD as a class effect that depends on affinity for α(1A)-AR. Differences in α(1A)-AR selectivity would be unlikely to be related to the incidence of EjD.

Electrophysiological effects of Ro 22–9194, a new antiarrhythmic agent, on guinea‐pig ventricular cells

1 Cardiac effects of Ro 22–9194 were examined in papillary muscles and single ventricular myocytes isolated from guinea‐pigs and compared with those of moricizine. 2 In papillary muscles, both Ro 22–9194 (≥ μm) and moricizine (≥ μm) caused a significant dose‐dependent decrease in the maximum upstroke velocity (V̇max) and a shortening of the action potential duration. 3 In the presence of either drug, trains of stimuli at rates ≥ 0.2 Hz led to an exponential decline in V̇max. This use‐dependent block was enhanced at higher stimulation frequencies. A time constant (τR) for V̇max recovery from the use‐dependent block was 9.3 s for Ro 22–9194 and 26.4 s for moricizine. 4 The curves relating membrane potential and V̇max in single myocytes were shifted by Ro 22–9194 (30 μm) or by moricizine (3 μm) in a hyperpolarizing direction by 8.4 mV and 8.0 mV respectively. 5 In myocytes treated with Ro 22–9194 (30 μm), a 10 ms conditioning clamp to 0 mV caused a significant decrease in V̇max of the subsequent test action potential; further prolongation of the clamp pulse duration resulted in a modest enhancement of the V̇max inhibition. In the presence of moricizine (3 μm), a similar conditioning clamp > 200 ms caused a significant V̇max reduction; the longer the clamp pulse duration, the greater the V̇max reduction. 6 Ro 22–9194 ≥ 30 μm caused a slight decrease of calcium inward current (ICa) of myocytes without affecting the delayed rectifier potassium current (IK). 7 These findings suggest that the primary electrophysiological effect of Ro 22–9194 as an antiarrhythmic agent is, like moricizine, a use‐ and voltage‐dependent inhibition of sodium channels. From the onset and offset kinetics of the use‐dependent block, Ro 22–9194 belongs to the intermediate kinetic Class I drugs, while moricizine is a slow kinetic drug. From the state‐dependence of sodium channel block, Ro 22–9194 may belong to activated channel blockers, while moricizine belongs to inactivated channel blockers.

Na+ channel blocking effects of cibenzoline on guinea-pig ventricular cells

The effects of cibenzoline on transmembrane action potentials were examined in right ventricular papillary muscles and in single ventricular myocytes isolated from guinea-pig hearts. In papillary muscles, cibenzoline > or = 3 microM caused a significant decrease in the maximum upstroke velocity (Vmax) of the action potential without affecting the action potential duration. The inhibition of Vmax was enhanced at higher stimulation frequencies. In the presence of cibenzoline, trains of stimuli at rates > or = 0.2 Hz led to a use-dependent inhibition of Vmax. The time constant for Vmax recovery (tauR) from the use-dependent block was 26.2 s. The use-dependent block of Vmax with cibenzoline was enhanced and tauR was shortened when the resting potential was depolarized by high (8, 10 mM) [K+]o. The curve relating membrane potential and Vmax in single myocytes was shifted by cibenzoline (10 microM) in a hyperpolarizing direction by 7.1 mV. In myocytes treated with cibenzoline (10 microM), a 10-ms conditioning clamp to 0 mV caused a significant decrease in Vmax of the subsequent test action potential; the Vmax inhibition was enhanced modestly in association with a prolongation of the 0 mV clamp pulse duration. In the presence of cibenzoline (3 microM), application of a train of depolarizing pulses (10 ms, 200 ms) to myocytes from the resting level (-80 mV) to 0 mV resulted in a progressive Vmax reduction in a pulse number-dependent manner. Unlike glibenclamide (30 microM), cibenzoline (10 microM) did not prevent the hypoxia-induced shortening of action potential duration in papillary muscles. These findings indicate that the onset and offset kinetics of use-dependent Na+ channel block by cibenzoline are slow. Given its state dependence, cibenzoline may be a blocker of activated Na+ channels. The inhibitory action of this compound on the ATP-sensitive K+ current (I(K), ATP) would be minimal or negligible at concentrations causing sufficient Na+ channel block.

Absence of exacerbation of myocardial stunning in anesthetized dogs treated with KAD-1229, a novel hypoglycemic agent

The effect of (+)-momocalcium bis[(2S,3a,7a-cis)-alpha-benzylhexahydro-gamma-oxo-2-isoindolinebutyrate]dihydrate (KAD-1229), a novel hypoglycemic agent with a chemical structure different from that of the sulfonylureas, on myocardial stunning was assessed in anesthetized dogs by comparison with that of glibenclamide, a sulfonylurea. Even though their hypoglycemic effects were of similar magnitude, glibenclamide (1 mg/kg, i.v.), but not KAD-1229, exacerbated the myocardial stunning induced by occlusion/reperfusion of the descending coronary artery. In a receptor-binding experiment, unlabeled glibenclamide completely inhibited [(3)H]glibenclamide binding to the myocardium, but KAD-1229 did not. These results suggest that the difference in binding properties of KAD-1229 and glibenclamide toward cardiac sulfonylurea receptors is one of the causes of their different effects on myocardial stunning. It is likely that KAD-1229 is highly specific for pancreatic sulfonylurea receptors and is speculated to be a safer hypoglycemic agent than, at least, glibenclamide.

Effects of Silodosin, an α1A-Adrenoceptor Antagonist, and Distigmine, an Acetylcholinesterase Inhibitor, and Their Combined Effects on Impaired Voiding Function in Zucker Diabetic Fatty Rats

Background/Aims: To evaluate the effects of silodosin (α1A-adrenoceptor antagonist) and distigmine (acetylcholinesterase inhibitor), alone or in combination, on voiding dysfunction in Zucker diabetic fatty (ZDF) rats, a type 2 diabetes model, by pressure flow study. Methods: Male ZDF rats were anesthetized with urethane and a catheter was implanted into the bladder through the dome. Saline was continuously infused into the bladder at 6 ml/h to induce the micturition reflex. Intravesical pressure and micturition volume were recorded continuously and various urodynamic parameters were calculated using a waveform analysis system. Results: Increased bladder capacity, residual volume, and urethral resistance and decreased maximum detrusor contraction velocity and urine flow rate, considered to be detrusor underactivity-like symptoms, were observed in ZDF rats. Although both silodosin and distigmine improved impaired voiding function, administration of both drugs in combination was more effective than either drug alone. Conclusions: ZDF rats showed symptoms suggestive of detrusor underactivity, and silodosin tended to ameliorate these symptoms in ZDF rats. These results suggested that an α1A-adrenoceptor antagonists may be effective against the voiding disorder accompanying not only bladder outlet obstruction but also deficiency of bladder function. Moreover, combined administration of an α1A-adrenoceptor antagonist with an acetylcholinesterase inhibitor may have additive efficacy in clinical use.

Efficacy of Mitiglinide Combined with Dapagliflozin in Streptozotocin-nicotinamide-induced Type 2 Diabetic Rats and in Zucker Fatty Rats.

The efficacy of the combination of the rapid-acting insulin secretagogue mitiglinide and the sodium-glucose cotransporter 2 (SGLT2) inhibitor dapagliflozin was explored in streptozotocin-nicotinamide-induced type 2 diabetic (STZ-NA) rats and in Zucker fatty (ZF) rats. The STZ-NA rats were prepared at 8 weeks of age. At 9 weeks of age, the combination study was conducted by oral glucose tolerance test (OGTT). At 13 weeks of age, ZF rats were dosed orally with dapagliflozin once daily up to the 22(nd) day. At days 15 and 22, the combination study was conducted by OGTT. In 2 different animal models, plasma glucose levels were strongly suppressed by the combination of mitiglinide and dapagliflozin as compared with either drug alone. The urinary glucose excretion was drastically elevated in the dapagliflozin group, but the combination with mitiglinide suppressed it about 50%. In STZ-NA rats, the plasma insulin secretion by the combination of both drugs was about at the same level as in the mitiglinide group. In ZF rats, the plasma insulin secretion by the combination of both drugs was less than mitiglinide group. Thus, in 2 different animal models, the combination of mitiglinide and dapagliflozin showed stronger antihyperglycemic action accompanied by less insulin secretion than mitiglinide alone, and reduced the urinary glucose excretion as compared with dapagliflozin used alone. These results indicate that the combination of mitiglinide and dapagliflozin can be a promising combination for the treatment of diabetic patients.