Hiroshi Shinyama

Phosphoramidon prevents cerebral vasospasm following subarachnoid hemorrhage in dogs: the relationship to endothelin-1 levels in the cerebrospinal fluid.

There is increasing evidence that the conversion of big endothelin-1 (big ET-1) to endothelin-1 (ET-1) is specifically inhibited by the metalloproteinase inhibitor phosphoramidon. We investigated the effect of phosphoramidon on delayed cerebral vasospasm from subarachnoid hemorrhage (SAH) using a two-hemorrhage canine model. The magnitude of the vasospasm and the drug effect were determined angiographically. On SAH Day 7, diameter of the basilar artery decreased to about 55% of the control value obtained before SAH (on Day 0). Immunoreactive ET (IR-ET) in the cerebrospinal fluid (CSF) significantly increased after SAH (on Day 7). The intracisternal pretreatment of phosphoramidon potently suppressed the decrease in diameter of the basilar artery after SAH, i.e., observed decrease was only about 20%, compared with the value before SAH. In the phosphoramidon group, IR-ET in CSF markedly increased (on SAH Day 2), but the increased levels of IR-ET significantly declined on SAH Day 7. These results clearly indicate that phosphoramidon effectively prevents delayed cerebral vasospasm. Whether the prevention is due to the inhibition of conversion of big ET-1 to ET-1 is now under study.

Phosphoramidon inhibits the conversion of intracisternally administered big endothelin-1 to endothelin-1

It is suggested that endothelin-1 (ET-1), a potent vasoconstrictor peptide, is involved in the pathogenesis of cerebral vasospasm following subarachnoid hemorrhage (SAH). We examined the effects of intracisternal administration of big ET-1 on the cerebral arteries in the absence or presence of pretreatment with phosphoramidon, an inhibitor of ET converting enzyme, in anesthetized dogs. After intracisternal administration of big ET-1 (10 micrograms/dog), the caliber of the basilar artery on the angiogram was decreased to about 59% of the control. This was accompanied by a marked increase in immunoreactive ET in the cerebrospinal fluid. Systemic arterial pressure was markedly elevated following big ET-1 injection. All changes induced by big ET-1 were effectively prevented with phosphoramidon. These data suggest that intracisternally administered big ET-1 is converted to ET-1 and that the generated ET-1 produces cerebral vasospasm and hypertension. A phosphoramidon-sensitive metalloproteinase appears to contribute to this conversion.

Antithrombin III prevents renal dysfunction and hypertension induced by enhanced intravascular coagulation in pregnant rats : Pharmacological confirmation of the benefits of treatment with antithrombin III in preeclampsia

We tested the hypothesis that enhanced intravascular coagulation in pregnancy could produce clinical symptoms similar to those of preeclampsia, such as hypertension, proteinuria, and edema. Having confirmed this, we then examined whether the pathological changes caused by intravascular coagulation could be suppressed by administration of antithrombin III (AT III), an endogenous inhibitor active to thrombin and factor X a. Intravascular coagulation was induced in Wistar rats on day 16-20 of pregnancy by 1-h arterial infusion of tissue thromboplastin (TP) through the left ventricle of the heart. One hour after the end of the infusion period, organ blood flows were measured by the radioactive ((57)Co-labeled) microsphere method, and fibrin deposition in organs was measured by radiolabeling with [(125)I] fibrinogen injected before TP infusion. Infusion of TP produced fibrin deposition in the kidney, lung, and liver, but not in the myometrium and placenta, as well as an 80% decrease in renal blood flow (RBF), with oliguria and proteinuria. TP also caused an increase in blood pressure (BP) accompanied by an increase in plasma renin activity (PRA), both of which were suppressed by bilateral nephrectomy before TP infusion. The prophylactic administration of AT III concentrates (60 or 300 U/kg intravenously (i.v.), followed by infusion of 30 or 150 U/kg/2 h, respectively) prevented all pathological changes in a dose-dependent manner. AT III increased placental blood flow regardless of the state of coagulation. These findings suggest that intravascular coagulation plays a significant part in the pathophysiology of preeclampsia and that AT III concentrates may have therapeutic potential in the treatment of this condition.

Pharmacologic profiles of GA0113, a novel quinoline derivative angiotensin II AT1-receptor antagonist.

GA0113 is a newly developed angiotensin II (Ang II) AT1-receptor antagonist having a quinoline moiety. This study was undertaken to clarify the pharmacologic profile of GA0113. In vitro profiles of GA0113 for Ang II receptors were examined in a receptor-binding assay and an Ang II-induced vasoconstriction study. Antihypertensive effects after single or repeated oral administrations were examined in conscious renal hypertensive (RH) or spontaneous hypertensive (SH) rats. Blood pressure (BP) and heart rate were measured by the tail-cuff method. GA0113 interacted with AT1 receptors in a competitive manner, but showed an insurmountable antagonistic action in Ang II-induced vasoconstriction. In RH rats, GA0113 (0.01-1 mg/kg) reduced BP with ED25 values of 0.015 mg/kg, and required 0.1 mg/kg for 24-h BP control. Repeated administration of GA0113 in SH rats (0.03-0.1 mg/kg) showed moderate onset and gradually potentiated reduction of BP, which reached a plateau after day 4 of treatment without alteration in heart rate. There was no tolerance of the hypotensive action or rebound phenomenon after cessation of the treatment. In pharmacokinetic studies, GA0113 shows excellent oral bioavailability (94%) and a long circulating half-life (12 h) in rats. These findings indicate that GA013 may serve as a highly potent and effective antihypertensive agent in humans. GA0113, with its unique chemical structure and pharmacologic and pharmacokinetic profiles may provide new possibilities in hypertension therapy.

Effects of AE0047 on renal haemodynamics and function in anaesthetized dogs

1. The effects of AE0047, a newly developed calcium channel blocker, on renal haemodynamics and function were investigated and compared with those of nicardipine in anaesthetized dogs.

Therapeutic effects of AE0047, a novel calcium antagonist, on progression of brain damage after stroke in stroke-prone spontaneously hypertensive rats

1. The potential of AE0047, a novel calcium antagonist, to remedy brain damage of stroke-prone spontaneously hypertensive rats (SHRSPs) with signs of stroke was compared with those of nicardipine and hydralazine. 2. AE0047 (1 and 3 mg/kg/day) given daily to diseased SHRSPs prevented mortality and improved neurological symptoms. Histological examination also supported the effectiveness of AE0047 against the progression of the disease. 3. Nicardipine (10 mg/kg/day) and hydralazine (10 mg/kg/day) were less effective than AE0047 in a dose equal to or more than the hypotensive dose, respectively. 4. AE0047 may be beneficial for treating the acute stage of stroke in humans by virtue of its long-lasting hypotensive action and undefined direct actions on the cerebral vasculature.

AE0047-mediated calcium channel blocking in vascular smooth muscles

1. This experiment was designed to pharmacologically characterize a novel calcium channel blocker, AE0047. 2. After 1-hr treatment with each drug (10(-6) M), K(+)-induced contraction in rat aortic strip was clearly depressed by nifedipine and manidipine and slightly depressed by AE0047. After a wash out of the preparation in drug-free medium, the inhibition of K(+)-induced contraction by nifedipine or manidipine was abolished or unchanged, respectively. In contrast, AE0047-produced inhibition was reinforced with time after removal of the drug. 3. A cell membrane depolarization-induced 45Ca uptake into tissue was depressed completely by nifedipine, but, if it was washed out, merely 20% inhibition of control remained. AE0047-produced inhibition became prominent after drug removal. Manidipine did not have the same inhibitory effect after wash out. 4. A receptor-binding study indicated that affinity of AE0047 and manidipine for the dihydropyridine-sensitive Ca channel receptor was lower than that of nifedipine. AE0047, unlike nifedipine and manidipine, inhibited [3H]PN200-110 binding more strongly when a 4-hr preincubation was used than without extended incubation. 5. The drug molecule of AE0047 was highly partitioned into the lipid bilayer of the synaptosome in canine cerebral cortices. In the synaptic membrane and liposomes, both prepared from canine cerebral cortices, the respective partition coefficients of the drug were 6997 +/- 2309 and 422 +/- 28 against 1395 +/- 161 and 24 +/- 2 of nitrendipine. 6. AE0047 showed slower onset of inhibition against K(+)-induced contraction and enhanced Ca influx compared with manidipine and nifedipine. These results may suggest that AE0047 requires a long period of time to occupy the dihydropyridine-sensitive sites within the Ca channel, which was detected by decreased specific [3H]PN200-110 binding, and to inhibit K(+)-induced Ca influx into rat aorta.

Effects of Long-term Treatment with the Calcium Antagonist Ae0047 on Cerebrovascular Autoregulation and Hypertrophy in Spontaneously Hypertensive Rats

Chronic hypertension is associated with structural and functional changes in the cerebrovascular bed, which influence cerebral circulation and its autoregulation. We examined whether or not long-term treatment of spontaneously hypertensive rats (SHRs) with the new calcium antagonist AE0047 would reverse structural changes in the cerebral vasculature and normalize the elevated lower blood pressure (BP) limit of the cerebral blood flow (CBF) autoregulation. Treating 6-month-old SHRs with a diet containing either 0.013 or 0.04% AE0047 for 8 weeks reduced BP and, at the higher dose, maintained BP at a level similar to that of age-matched Wistar-Kyoto (WKY) rats. At the end of the treatment period, CBF was measured by using the hydrogen-clearance method, and the lower limit of the autoregulation curve was estimated by repeated CBF measurement with stepwise reduction of BP through bleeding. This limit was significantly higher in untreated SHRs than in WKY rats (111 +/- 8 vs. 60 +/- 8 mm Hg). AE0047 caused a significant and dose-dependent shift in the elevated lower BP limit, which decreased to 83 +/- 9 and 75 +/- 6 mm Hg at the low and high dose, respectively. In perfusion-fixed proximal, intermediate, and distal portions of the middle cerebral artery, media thickness/external diameter (M/ED) ratios were significantly greater in untreated SHRs than in WKY rats. In AE0047-treated animals, M/ED ratios in all portions tended to be reduced halfway between those for untreated SHRs and those for WKY rats, but with no statistical significance. These results suggest that long-term treatment of patients with hypertension with AE0047 will normalize the autoregulatory threshold while preserving CBF and thereby improve tolerance to BP reduction, but the potential to ameliorate structural alterations may be small.

PREVENTATIVE AND THERAPEUTIC EFFECTS OF AE0047 ON RENAL INJURY IN STROKE‐PRONE SPONTANEOUSLY HYPERTENSIVE RATS

1. The present study was designed to investigate the preventative and therapeutic effects of AE0047 on renal injury compared with those of nitrendipine in stroke‐prone spontaneously hypertensive rats (SHRSP).

Possible mechanism for the anti-atherosclerotic action of the calcium channel blocker AE0047 in cholesterol-fed rabbits.

1. The present study was designed to investigate the anti‐atherosclerotic effect of AE0047, a calcium channel blocker, and to compare it with that of nilvadipine in cholesterol‐fed rabbits. Furthermore, the effects of AE0047 on low‐density lipoprotein (LDL) oxidation were studied in vitro.