Protective effect of TA-993, a novel therapeutic agent for peripheral circulatory insufficiency, on skeletal muscle fatigue in a rat model of hindlimb ischemia.

TA-993 (cis-(-)-2-(4-methylphenyl)-3-acetoxy-2,3-dihydro-5-(2-dimethylaminoethy l)-8-methyl1,5-benzothiazepine-4(5H)-one maleate), a new 1,5-benzothiazepine derivative, has a selective increasing action on limb blood flow in addition to an antiplatelet action. In this report we studied the effect of TA-993 on a time dependent decrease in developed tension of electrically-induced contraction of tibialis anterior muscle in a rat model of peripheral circulatory insufficiency induced by occlusion of abdominal aorta. In our preparation, the developed tension decreased by 20-30% in a sham-operated group and 30-40% in an abdominal aorta-occluded group at the end of the experimental period of 60 min. Intraduodenal administration (i.d.) of TA-993 (10 mg/kg) to the abdominal aorta-occluded rats ameliorated the decrease in developed tension to the level of the sham-operated group. Moreover, TA-993 at 10 mg/kg, i.d. significantly increased femoral arterial blood flow supplied through collateral circulation and decreased the whole blood viscosity in this model. These results suggest that TA-993 improves dysfunction of skeletal muscle contraction due to peripheral circulating insufficiency through an increase in collateral blood flow and an improvement of red blood cell deformability.

The mechanism of the increasing action of TA-993, a new 1,5- benzothiazepine derivative, on limb blood flow in anesthetized dogs: selective suppression of sympathetic nerve activity.

TA-993, (-)-cis-3-acetoxy-5-(2-(dimethylamino)ethyl)-2, 3-di-hydro-8-methyl-2-(4-methylphenyl)-1,5-benzothiazepin-4(5H)one maleate, a new 1,5-benzothiazepine derivative with l-cis configuration, has a unique and selective increasing action on limb blood flow with little influence on arterial pressure besides an antiplatelet action. We studied the mechanism of increasing action of TA-993 on limb blood flow in anesthetized dogs. In a canine blood-perfused hindlimb preparation with a donor dog, TA-993 (100 microg/kg i.v.) did not increase femoral blood flow when administered to the donor dog, but did when administered to a recipient dog. TA-993 did not show the increasing action on femoral blood flow in the presence of hexamethonium or phentolamine, whereas it did in the presence of propranolol or atropine. TA-993 also showed a weak increasing effect on heart rate, which was inhibited by any one of these blockers. TA-993 (300 microg/kg i.v.) did not alter the phenylephrine (1-100 ng/kg i.a.)- or the talipexole (3-100 ng/kg i.a.)-induced increase in perfusion pressure in an autoperfused hindlimb. These results suggest that the increasing action of TA-993 on limb blood flow is mediated by the sympathetic nervous system but that the adrenergic receptors are not likely to be the central point of action of this new agent. There is a possibility that the mechanism of the increasing action on heart rate is different from that of its increasing action on limb blood flow.

Antithrombotic action of TA-993, a new 1,5-benzothiazepine derivative, in a canine model of femoral arterial thrombosis.

TA-993 is a novel 1,5-benzothiazepine derivative of l-cis configuration, having a potent antiplatelet action and an increasing action on femoral blood flow. We evaluated the antithrombotic effect of TA-993 in a canine model of femoral arterial thrombosis. Thrombus was induced by both application of direct anodal current to the femoral artery and partial occlusion of the artery. The partial occlusion by placing an adjustable occluder on the artery and the current application were carried out 40 and 60 min after the intraduodenal administration of drugs, respectively. In control dogs, complete sustained occlusion of the femoral artery due to thrombus occurred 55.4 +/- 9.2 min after the onset of current application. TA-993 (3 and 10 mg/kg) dose-dependently prolonged the time for occlusion. Aspirin (30 mg/kg) also prolonged it. TA-993, 10 mg/kg, significantly inhibited whole-blood aggregation 60 min after the administration with a weaker potency than that of aspirin (30 mg/kg), whereas 3 mg/kg of TA-993 did not. The inhibitory effect of TA-993 (10 mg/kg) on platelet aggregation was maintained for >7 h. Moreover, TA-993 (10 mg/kg) increased femoral blood flow in spite of the partially occluded condition. These results indicate that TA-993 has an antithrombotic effect on femoral arterial thrombosis and suggest that an increasing action on femoral blood flow of TA-993 is more relevant than its antiplatelet action to the antithrombotic effect in this model.

Cardiovascular effect of a new 1,5-benzothiazepine derivative TA-993 in anesthetized dogs.

TA-993 is a new 1,5-benzothiazepine derivative having l-cis configuration and shows a potent antiplatelet aggregating action. We studied its cardiovascular effect in anesthetized dogs by using diltiazem as a reference compound. TA-993 (> or = 10 microg/kg, i.v.) significantly increased blood flows of common carotid, brachial, and femoral arteries. The peak of its effect was observed approximately 60 min after the administration, and the peak level was maintained until > or = 300 min after the administration. TA-993 (100 microg/kg, i.v.) slightly increased cardiac output in the same manner. However, TA-993 did not cause any persistent effects on arterial pressure, LVdP/dtmax, or vertebral, coronary, superior mesenteric, and renal blood flows. TA-993 caused concentration-dependent vasorelaxation in the isolated canine femoral artery contracted with 40 mM K+, but its potency was approximately 1/20 that of diltiazem. The increasing action of TA-993 on femoral blood flow was completely inhibited by pretreatment with hexamethonium in anesthetized dogs. These results indicate that TA-993 has a selective increasing action on common carotid, brachial, and femoral blood flows and suggest that the action is mediated by the autonomic nervous system.

Cardiovascular effects of 1,5-benzothiazepine derivatives having a l-cis and d-cis configuration in anesthetized dogs.

TA-993, a new 1,5-benzothiazepine derivative having a l-cis configuration, has a selective increasing action on limb blood flow, in addition to an antiplatelet aggregating action. The cardiovascular action of TA-993 is quite different from diltiazem, which is a well-known 1,5-benzothiazepine derivative having a d-cis configuration. Therefore, we compared the cardiovascular actions of d-cis and l-cis isomers of TA-993 with those of diltiazem. l-cis-Diltiazem, as well as TA-993, progressively increased femoral, brachial and common carotid blood flow with little change in arterial pressure or vertebral blood flow. However, the peak response to l-cis-diltiazem (20 min after the administration) was observed earlier than that to TA-993 (60 min after the administration). On the other hand, d-cis-TA-993, as well as diltiazem, caused transient hypotension, tachycardia and increases in vertebral, brachial, femoral and common carotid blood flow. Furthermore, their peak effects were observed immediately after the administration. Potency ratios of the vasorelaxing effects of TA-993, l-cis-diltiazem and d-cis-TA-993 to diltiazem in the isolated and K+-contracted canine femoral artery were 0.096, 0.032 and 1.209, respectively. pA2 values for TA-993 and diltiazem against Ca2+-induced contractions in the isolated and K+-depolarized canine saphenous artery were 5.50+/-0.11 and 7.12+/-0.18, respectively. These results indicate that TA-993 shares a common profile with l-cis-diltiazem, and suggest that 1,5-benzothiazepine derivatives of a l-cis configuration are a different class of drug from that of the d-cis configuration.

Prolongation of the life span of cardiomyopathic hamster by the adrenergic beta 1-selective partial agonist denopamine.

Influence of cardiotonic agents on the prognosis of heart failure depends on the individual therapeutic agents, and favorable and unfavorable effects of these agents have been reported in clinical trials. We studied the effect of the cardiotonic agent denopamine on the life span of cardiomyopathic hamsters (BIO 14.6 strain) in the heart failure period. Non-treated hamsters started to die at 40 weeks of age, and their survival rate decreased to 23.8% at the age of 65 weeks. Hamsters treated with denopamine (400 ppm in diet) from 36 weeks of age did not die until the age of 52 weeks, except in cases of accidental death. The survival rate of this group at 65 weeks of age was about 40%. Survival rates of these 2 groups were significantly different (P < 0.05) when animals with accidental death were excluded. To elucidate the mechanism of the effect of denopamine, we performed several experiments after dietary treatment with denopamine for 4 to 6 weeks from 37 weeks of age. Denopamine treatment lowered plasma levels of noradrenaline and dopamine (P < 0.05), but affected neither the cardiac contractility nor the beta-adrenoceptor density. In summary, denopamine significantly decreases the mortality of cardiomyopathic hamsters. Its effect to lower the plasma catecholamine levels may be responsible for the beneficial effect of denopamine.

Prolonging action of imidapril on the lifespan expectancy of cardiomyopathic hamsters.

We studied the effect of imidapril, a novel angiotensin-converting enzyme (ACE) inhibitor, on lifespan expectancy of cardiomyopathic (CM) hamsters of BIO 14.6 strain, one of the representative models of congestive heart failure (CHF). Imidapril was consecutively administered to hamsters by mixing it in their diet at a concentration of 480 ppm (approximately 30 mg/kg/day) or 1,600 ppm (approximately 120 mg/kg/day) from age 26 weeks. Only several control hamsters died before age 54 weeks, but their survival rate decreased to 23.7% at age 73 weeks. The survival rates of 480-ppm and 1,600-ppm imidapril groups at age 73 weeks were as high as 75.7 and 68.4%, respectively (p < 0.01 vs. control hamsters). Macroscopic and microscopic pathology in imidapril-treated groups was milder than that in control animals in general, but differences were not statistically significant when animals were divided into survivors and fatalities except for the presence of mural thrombus in the heart. We further studied the effects of imidapril on blood pressure (BP), in vivo cardiac function, cardiac beta-adrenoceptor distribution, and plasma catecholamine levels after dietary treatment with 480 ppm imidapril for 8-10 weeks from age 37 weeks. Imidapril-treated animals showed improved cardiac function under urethane anesthesia. These results indicate that imidapril prolongs lifespan expectancy of CM hamsters and suggest that a hemodynamic effect of imidapril is involved in its beneficial effect.

Antithrombotic effect of TA-993, a novel 1,5-benzothiazepine derivative, in conscious rats.

Since reported experimental models of thrombosis are not suitable for comparison of several drugs by oral administration, we developed a convenient model for this purpose by applying direct current through an intravascular electrode. In conscious rats, which were implanted with anodal electrodes in the abdominal aorta on the day before the experiment, application of 200 microA of direct current induced the formation of a platelet-rich thrombus around the intravascular electrode. Using this model, we studied the antithrombotic effect of the novel antiplatelet agent TA-993, (-)-cis-3-acetoxy-5-(2-(dimethylamino)ethyl)-2,3-dihydro-8-methyl-2-(4- methylphenyl)-1,5-benzothiazepin-4(5H)-one maleate, and compared its effect with other antiplatelet agents. TA-993 at doses of 30 mg/kg, p.o. or more by single administration or at doses of 10 mg/kg or more by repeated administration dose-dependently suppressed the thrombus formation. Aspirin (10 mg/kg, p.o. or more), cilostazol (100 mg/kg, p.o.) and ticlopidine (30 mg/kg, p.o. or more) also suppressed the thrombus formation by single administration. These results suggest that TA-993 has a comparable antithrombotic effect with other antiplatelet agents, and thus it is a possible remedy for thrombotic and embolic diseases.

[The effects of insulin and glucose on the utilization of non-esterified fatty acid in the resting rat skeletal muscle].

The present study was undertaken to clarify the effects of insulin and glucose on the utilization of non-esterified fatty acid (NEFA) in the resting rat skeletal muscle using the perfusion technique. The 24hr-starved and non-starved rat hind limbs were perfused for one hour with the perfusion mediums containing 1mM palmitate and various concentrations of glucose and insulin, and sampling was performed to calculate the clearance of NEFA (F value). In the absence of glucose, the F value of the starved rat hind limb was less than that of the non-starved rats, independently of insulin concentrations (0 and 125 microU/ml) in the perfusion medium (p < 0.02). Moreover, there was no influence of insulin on the F value in both the starved and the non-starved groups. In the presence of 13.9mM glucose, there were no statistically significant differences in the F value without insulin between the non-starved and starved groups. However, the F value was increased in the presence of 62.5 or 125 microU/ml insulin, compared with that in the absence of insulin (p < 0.001), although when the insulin concentration was elevated to 500 microU/ml, it was decreased. Both in the non-starved and the starved groups independently of insulin concentrations, the F value in the glucose-added condition was increased, compared with that in the absence of glucose. These results indicated that the utilization of NEFA in the resting rat skeletal muscle was facilitated by the moderate supply of glucose, although it was suppressed by the presence of abundant glucose.

Acute hemodynamic effects of the active metabolite of imidapril, (4S)-3-((2S)-2-[N-((1S)-1-carboxy-3-phenyl-propyl)amino]propionyl)-1- methyl-2-oxoimidazolidine-4-carboxylic acid, and enalaprilat in anesthetized dogs.

The hemodynamic effects of imidapril, a novel nonsulfhydryl angiotensin-converting enzyme inhibitor, were examined in anesthetized dogs by the intravenous injection of its active metabolite 6366A ((4S)-3-((2S)-2-[N-((1S)-1-carboxy-3- phenylpropyl)amino]propionyl)-1-methyl-2-oxoimidazolidine-4-carboxylic acid, CAS 89371-44-8) and were compared to those of enalaprilat. 6366A (1-100 micrograms/kg) reduced the blood pressure and total peripheral resistance in a dose-dependent manner, while causing no marked changes in heart rate, LV dp/dtmax, and pulmonary arterial pressure. The cardiac output and stroke volume were slightly increased. Blood flow in the common carotid artery, the vertebral artery, and the femoral artery was reduced or tended to decrease, while the superior mesenteric arterial blood flow was increased. These effects were similar to those of enalaprilat. 6366A did not inhibit the pressor response of angiotensin II, but markedly inhibited that of angiotensin I, and the effects of 6366A on regional blood flow were opposite to those of angiotensin II. Thus, 6366A appears to produce its hemodynamic effects by angiotensin converting enzyme inhibition, as does enalaprilat. 6366A also tended to decrease myocardial oxygen consumption. These results suggested that the hemodynamic effects of imidapril on the heart and on regional blood flow are similar to those of enalapril.

Electrocardiographical findings of WBN/Kob rats.

Electrocardiographical (ECG) investigations were carried out on 4 and 12 week old WBN/Kob and Wistar male rats. In comparison with Wistar rats which showed ECG findings typical of those of normal rats, WBN/Kob rats showed significantly larger QRS complex amplitude, smaller T wave amplitude, longer QRS duration, and longer QT interval at 4 weeks of age. This tendency became clearer at 12 weeks of age. There were no changes in serum inorganic ion concentrations or cardiac histopathology suggestive of these ECG changes in WBN/Kob rats. These ECG findings in WBN/Kob rats are considered to be a hereditary characteristic of the strain.