Sunao Nakayama

Effect of Cilostazol, a Phosphodiesterase III Inhibitor, on Experimental Thrombosis in the Porcine Carotid Artery

Thrombus formation in the carotid artery is one of the common causes of transient ischemic attacks and stroke. Platelet aggregation seems to be an essential component in these processes. The present study was conducted to determine the ability of cilostazol, a phosphodiesterase III inhibitor, to prevent formation of totally occlusive thrombus in a porcine carotid artery, in comparison with ticlopidine. Castrated male Yorkshire pigs were allocated to control (n=8), cilostazol (30 mg/kg, twice a day [b.i.d] for 2 days, n=8), and ticlopidine (50 mg/kg, b.i.d. for 3 days, n=7) groups. The endothelium of the right common carotid artery was injured with electrical stimulation (150 microA) without constriction and blood flow in this region was monitored by Doppler flow probe. Arterial blood was sampled during electrical stimulation for the measurement of platelet aggregation. Total occlusion rates within 240 minutes were 87.5% (7:8), 37.5% (3:8), and 85.7% (6:7) in the control, cilostazol, and ticlopidine groups, respectively. Compared with the control group, the time to total occlusion was significantly prolonged in the cilostazol group, but not in the ticlopidine group. Consistently, platelet aggregation was significantly inhibited only in the cilostazol group. Because ticlopidine increases blood flow in the intact carotid artery before injury to a greater extent than cilostazol, direct antiplatelet action is thought to be responsible for cilostazols beneficial effect in preventing thrombotic occlusion. These results suggest that cilostazol may be useful for the inhibition of the thrombus formation in the carotid artery and for the prevention of cerebral ischemic events.

Antihypertensive activity of OPC-13340, a new potent and long-acting dihydropyridine calcium antagonist, in rats

The antihypertensive action of OPC-13340, a new dihydropyridine, was studied in rats and compared with the action of nicardipine and other dihydropyridines. OPC-13340 showed more potent and longer hypotensive action than nicardipine when administered either intraveneously (i.v.) or orally in normotensive and hypertensive rats. Among 6 compounds tested, (OPC-13340, nifedipine, nitrendipine, nisoldipine, nicardipine and diltiazem), OPC-13340 was the most potent and long-acting when administered orally to spontaneously hypertensive rats (SHR). Tachycardia after administration of OPC-13340 was less or diminished earlier than that of nicardipine. Oral administration of OPC-13340 (3 mg/kg) once daily for 13 days did not cause any rebound phenomena in SHR. The compound inhibited Ca- or K-induced contractions in isolated rat aorta and shortened action potential duration in guinea pig papillary muscle, suggesting Ca channel blocking action. OPC-13340 might be useful as a drug for once-daily therapy of essential hypertension.

Characterization of a novel nonpeptide vasopressin V2‐agonist, OPC‐51803, in cells transfected human vasopressin receptor subtypes

We discovered the first nonpeptide arginine‐vasopressin (AVP) V2‐receptor agonist, OPC‐51803. Pharmacological properties of OPC‐51803 were elucidated using HeLa cells expressing human AVP receptor subtypes (V2, V1a and V1b) and compared with those of 1‐desamino‐8‐D‐arginine vasopressin (dDAVP), a peptide V2‐receptor agonist. OPC‐51803 and dDAVP displaced [3H]‐AVP binding to human V2‐ and V1a‐receptors with Ki values of 91.9±10.8 nM (n=6) and 3.12±0.38 nM (n=6) for V2‐receptors, and 819±39 nM (n=6) and 41.5±9.9 nM (n=6) for V1a‐receptors, indicating that OPC‐51803 was about nine times more selective for V2‐receptors, similar to the selectivity of dDAVP. OPC‐51803 scarcely displaced [3H]‐AVP binding to human V1b‐receptors even at 10−4 M, while dDAVP showed potent affinity to human V1b‐receptors with the Ki value of 13.7±3.2 nM (n=4). OPC‐51803 concentration‐dependently increased cyclic adenosine 3′, 5′‐monophosphate (cyclic AMP) production in HeLa cells expressing human V2‐receptors with an EC50 value of 189±14 nM (n=6). The concentration‐response curve for cyclic AMP production induced by OPC‐51803 was shifted to the right in the presence of a V2‐antagonist, OPC‐31260. At 10−5 M, OPC‐51803 did not increase the intracellular Ca2+ concentration ([Ca2+]i) in HeLa cells expressing human V1a‐receptors. On the other hand, dDAVP increased [Ca2+]i in HeLa cells expressing human V1a‐ and V1b‐receptors in a concentration‐dependent fashion. From these results, OPC‐51803 has been confirmed to be the first nonpeptide agonist for human AVP V2‐receptors without agonistic activities for V1a‐ and V1b‐receptors. OPC‐51803 may be useful for the treatment of AVP‐deficient pathophysiological states and as a tool for AVP researches.

Influence of propranolol on high energy phosphate and tissue acidosis in regional ischemic myocardium of pigs: assessment with arterial pressure and respiration gated in vivo 31-phosphorus magnetic resonance spectroscopy

In an attempt to define the metabolic abnormalities of the ischemic myocardium, the changes in high energy phosphates, inorganic phosphate and intracellular pH were serially and quantitatively evaluated in ischemic porcine hearts having no collateral circulation, using arterial pressure and respiration gated in vivo 31P magnetic resonance spectroscopy. The protocol was also modified for propranolol pretreatment (0.6 mg/kg intravenously) to define its effect on the metabolism of ischemic myocardium. In the non-treated group, creatine phosphate was rapidly depleted by 10 minutes after ischemia; by 40 minutes, ATP and intracellular pH gradually decreased to 10 +/- 11% of control and to 5.90 +/- 0.26, respectively, and inorganic phosphate rose to 303 +/- 43% of control. In the propranolol treated group, the concentrations of creatine phosphate and ATP were higher, and those of inorganic phosphate and tissue pH were similar compared with controls during 40 minutes of ischemia. This suggests that the beneficial effect of propranolol on the ischemic myocardium is due to the preservation of ATP, an essential energy resource for numerous enzymatic reactions in viable myocardium.

Protective effect of carteolol, a β-blocker, on myocardial cellular damage in ischemic and reperfused pig hearts: Assessment with gated in vivo 31-phosphorus magnetic resonance spectroscopy and electron microscopy

To assess the effect of carteolol, a beta-blocker, on ischemia and reperfusion, changes in the ultrastructure of myocytes and energy metabolism were studied by 31P-NMR in 41 pig hearts without collateral circulation. The left anterior descending coronary artery was occluded for 20 min and reperfused for 120 min in three groups: seven pigs (group 1, no treatment with carteolol; group 2, pre-ischemia treatment with carteolol (10 micrograms/kg); group 3, post-ischemia treatment with carteolol before reperfusion). Other groups of five pigs were killed after 120 min of ischemia (group 4, no treatment; group 5, pre-ischemia treatment) or 20 min of ischemia (group 6, no treatment; group 7, pre-ischemia treatment). After 20 min of ischemia, ATP was higher in groups 2 (76 +/- 9% of the baseline value) than in group 1 (59 +/- 5%) and group 3 (60 +/- 10%). However, the difference disappeared after 30 min of ischemia. After 120 min of reperfusion, ATP showed much better recovery in group 2 (92 +/- 9%) than in groups 1 (66 +/- 7%) and 3 (68 +/- 10%). Ischemic injury, as viewed by light and electron microscopy, was milder in group 7 than in group 6 after 20 min occlusion, but the myocytes were almost normal after 120 min reperfusion in groups 1 to 3. The heart rate, blood pressure and rate pressure product showed no significant difference among the groups. These results indicate that pre-ischemia treatment with carteolol provided protection against ischemic cellular injury and accelerated the repletion of ATP during reperfusion, but the post-ischemia treatment did not lead to recovery of ATP. Therefore, the favorable effect during reperfusion of pre-ischemia treatment with carteolol depends on its protective effect during ischemia.