Minoru Ohtsuka

Comparison of the cardiovascular effect of FR34235, a new dihydropyridine, with other calcium antagonists.

We compared the cardiovascular effect of FR34235, a new dihydropyridine derivative, with the effects of nifedipine, nicardipine, and diltiazem on the dog using in vitro and in vivo preparations. FR34235 reduced the amplitude of coronary arterial contraction induced by K+ more so than that induced by norepinephrine in in vitro preparations. The ID50 values of FR34235 for various arterial strips contracted by K+ were smaller (1/5–1/426) than those of nifedipine and diltiazem, and almost the same as those of nicardipine. There was a greater increase in both the coronary and vertebral blood flow than in the other peripheral arterial flow in anesthetized dogs administered FR34235 (0.32–100 μg/kg i.v.), and the duration of effect was about two to three times longer than that of the other drugs. To obtain a vasodilating effect by the intraduodenal route, 10–30 times the intravenous dose of FR34235 was required, far lower than that required of nicardipine. In atrioventricular (AV) and sinoatrial node preparations, FR34235 was weaker in impairing AV conduction than nifedipine, in spite of their similar potencies in increasing coronary flow and decreasing sinus rate. FR34235 was more potent than diltiazem in increasing coronary flow, in spite of their similar potencies on AV conduction. It is concluded that FR34235 has: (a) potent vasodilating activity, probably due to inhibition of Ca2+ influx into the cells; (b) selective and long-lasting effects on the coronary and cerebral arteries in vivo; (c) a wide difference between doses that cause vasodilation and an impairing effect on AV conducting tissues; and (d) therapeutic effects after absorption from the intestinal tract.

Antianginal effects of FK409, a new spontaneous NO releaser

1 The aim of this study was to compare antianginal effects of (±)‐(E)‐ethyl‐2‐[(E)‐hydroxyimino]‐5‐nitro‐3‐hexeneamide (FK409), a new spontaneous nitric oxide releaser, with those of isosorbide dinitrate (ISDN). We used two types of rat angina model; methacholine‐ and arginine vasopressin (AVP)‐induced coronary vasospasm models. 2 In the in vitro study, FK409 showed 80 times more potent vasorelaxant effect in dog isolated coronary artery than ISDN (EC50= 16.7 ± 4.8 and 1340 ± 320 nm, respectively). 3 In the rat methacholine‐induced coronary vasospasm model, FK409 suppressed the elevation of ST segment dose‐dependently and significantly at 0.1 mg kg−1, i.d. On the other hand, ISDN suppressed it significantly at 3.2 mg kg−1, i.d. In addition, the efficacy of 3.2 mg kg−1 ISDN in the model was almost the same as that of 0.1 mg kg−1 FK409. 4 In the above experiments, FK409 and ISDN decreased mean blood pressure significantly at the maximum dose tested (1.0 mg kg−1, i.d. and 3.2 mg kg−1, i.d., respectively) but did not change heart rate at these doses. Therefore, the hypotensive effect of FK409 was 10 times weaker than the antianginal effect of the compound, while those of ISDN were almost the same. 5 In the rat AVP‐induced coronary vasospasm model, 32mg kg−1 FK409 significantly inhibited the depression of ST segment 60 min after oral administration. On the other hand, 32 mg kg−1 ISDN did not inhibit it at 60 and 120 min after oral administration. 6 In conclusion, FK409 inhibits coronary vasospasm more potently in two types of rat angina models than ISDN. In addition, FK409 shows an antianginal effect more selectively that a hypotensive effect, compared with ISDN.

Vasorelaxant mechanism of the new vasodilator, FK409

To define the vasorelaxation mechanism of FK409, we examined the effect of the compound on vascular tension and cyclic nucleotide levels in isolated rat thoracic aorta contracted with norepinephrine, and on activities of guanylate cyclase and cyclic GMP phosphodiesterase prepared from rat or rabbit thoracic aorta. FK409 (1 x 10(-9) to 1 x 10(-6) M), like nitroglycerin (1 x 10(-9) to 1 x 10(-6) M), produced a potent vasorelaxant effect associated with an increase in cyclic GMP content of the tissue. There was no change in cyclic AMP levels. The vasorelaxant effect of FK409 was independent of the integrity of the endothelium, and was unaffected by L-NG-monomethylarginine (0.1 mM) or oxyhemoglobin (1 microM). On the other hand, FK409 (3.2 x 10(-7) M) activated soluble guanylate cyclase, and the activating effect was completely inhibited by oxyhemoglobin (10 nM). Cyclic GMP phosphodiesterase was unaffected by FK409 (1 x 10(-7) to 1 x 10(-5) M). Furthermore, in rat aortic soluble fraction FK409 (3 mM) was found to liberate nitric oxide (NO) which was evaluated spectrophotometrically after diazotization of sulfanilic acid and coupling with N-(1-naphthyl)-ethylenediamine. The liberation occurred even in the absence of L-cysteine (5 mM), in contrast to the case with nitroglycerin (3 mM). These results suggest that the vasorelaxant effect of FK409 is associated with an increase in intracellular cyclic GMP, and that the cyclic GMP accumulation is due to activation of soluble guanylate cyclase. The enzyme activation is probably due to NO released from the compound molecule in the vascular smooth muscle cells.

Effects of Vamicamide on Urinary Bladder Functions in Conscious Dog and Rat Models of Urinary Frequency

PURPOSE To investigate the usefulness of vamicamide, (+/-)-(2R*, 4R*)-4-dimethylamino-2-phenyl-2-(2-pyridyl)valeramide, as a novel drug for the treatment of urinary frequency and incontinence. MATERIALS AND METHODS Urinary frequency was evaluated in specially devised conscious dog and rat models by investigating the effects of the drug on urinary bladder function of these animals by cystometrography. RESULTS In the dog model with transected hypogastric nerves, the bladder volume at micturition (bladder capacity) was less than 50% that of the sham-operated dog, and in the rat model with bilateral lesioning of nuclei basalis, a part of the brain, by ibotenic acid injection, bladder capacity was about 50% that of the sham-operated rat. Other bladder functions in both models were unchanged. In the dog model, orally administered vamicamide at 0.32 and 1.0 mg./kg. significantly increased bladder capacity and did not change residual urine volume or micturition pressure. Oxybutynin 0.10 mg./kg., one of the most popular drugs for the treatment of urinary frequency and incontinence, or atropine 0.10 mg./kg. induced significant increases in bladder capacity similarly to vamicamide at 0.32 mg./kg. In the rat model, oral vamicamide 0.32 mg./kg. also significantly increased bladder capacity and did not change micturition pressure or threshold pressure. Again, oxybutynin 0.10 mg./kg. or atropine 0.32 mg./kg. had almost the same effects as vamicamide 0.32 mg./kg. CONCLUSIONS These findings suggest that vamicamide should be useful for the treatment of urinary frequency.

Suppression of atherogenesis in cholesterol-fed rabbits treated with nilvadipine, a new vasoselective calcium entry blocker

We examined the effects of nilvadipine, a new dihydropyridine calcium entry blocker, on atherogenesis in rabbits fed a 1% cholesterol diet. The drug was given subcutaneously to the animals in hypotensive doses of 1.0 or 3.2 mg/kg/day for 10 weeks, and was well tolerated. Plasma total cholesterol increased markedly in all the cholesterol-fed rabbits, and nilvadipine had no effect on this, or on HDL-cholesterol and triglyceride levels. However, the area of Sudan IV positive intimal lesions (one of the parameters of atherosclerosis) in the aorta decreased significantly in the nilvadipine treated animals, and in addition, cholesterol and calcium content in the thoracic aorta were reduced. The reference drugs, nifedipine and nicardipine given subcutaneously in doses of 10.0 mg/kg/day either had no effect or were weaker in antiatherogenic effect than nilvadipine. The findings suggest that nilvadipine has more potent antiatherogenic activity than nicardipine or nifedipine.

A comparison of the binding characteristics of class I antiarrhythmic agents for human muscarinic m1-m3 receptors.

The binding characteristics of the class 1 antiarrhythmic agents, cibenzoline, disopyramide, disopyramide metabolite (the main active metabolite of disopyramide in humans), and pirmenol, for human muscarinic receptors (m1-m3) stably expressed in Chinese hamster ovary cells (CHO) were investigated by binding assay with [3H]N-methylscopolamine ([3H]NMS) as a ligand. All of these agents inhibited the specific [3H]NMS binding to membrane preparations in a concentration-dependent manner. The potencies of affinity of these agents for m1, m2, and m3 receptors (compared by IC50) were disopyramide > pirmenol > disopyramide metabolite > cibenzoline, pirmenol > cibenzoline > disopyramide > disopyramide metabolite, and disopyramide > disopyramide metabolite > pirmenol > cibenzoline, respectively. Some competition curves of cibenzoline, disopyramide, and pirmenol were shallow, and Hill coefficients of these curves differed from unity, suggesting that these agents have allosteric binding characteristics for human muscarinic receptors. The m2-selective ratios to m1 (IC50 m1/IC50 m2) and m3 (IC50 m3/IC50 m2) of cibenzoline were 4.0 and 16, and those of pirmenol were 6.5 and 43, respectively, whereas those of disopyramide and its metabolite ranged from 0.46 to 1.6, suggesting that cibenzoline and pirmenol exerted high selectivity to the m2 receptor. We conclude that (a) all class 1 antiarrhythmic agents in this study have inhibitory effects on human m1, m2, and m3 receptors, and some of those binding may show allosteric characterization; (b) disopyramide and its metabolite have similar affinity to m1 to m3 receptors; and (c) cibenzoline and pirmenol have high m2-selective ratios to m1 and m3.

Tolerance to the vascular effect of a novel nitric oxide-donating vasodilator, FK409

We investigated whether tolerance develops to the vasorelaxant effects of a new vasodilator, (+-)-(E)-4-ethyl-2-[(E)-hydroxy-imino]-5-nitro-3-hexenamide (FK409), in isolated canine coronary artery strips and to its hypotensive effect in rats, and whether FK409 activates soluble guanylate cyclase isolated from vascular tissues in the absence of L-cysteine. No tolerance to FK409 (0.46 nM to 0.46 microM or 1-1000 micrograms/kg, i.v.) or cross-tolerance between FK409 and glyceryl trinitrate was demonstrated in in vitro and in vivo experiments, whereas the tolerance to glyceryl trinitrate (0.44 nM to 4.4 microM or 1-1000 micrograms/kg, i.v.) was marked in both conditions. In addition, FK409 (0.1-10 microM) activated soluble guanylate cyclase without L-cysteine, but glyceryl trinitrate (1-100 microM) required the addition of L-cysteine (5 mM) for the activation of the enzyme. The results suggest that FK409 may be advantageous compared to tolerance-producing nitrates currently in clinical use, and that this property of FK409 is probably due to its independence of a sulfhydryl group donor.

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)

Subcutaneous Loperamide Prevents Gastric Lesions Induced by Necrotizing Agents in Rats

The effects of subcutaneous loperamide ongastric lesions induced by necrotizing agents wereinvestigated in the rat. Loperamide produced adose-dependent increase of gastric fluid volume andinhibition of gastric lesions caused by 0.6 N HCl orabsolute ethanol. Pretreatment with naloxone almostcompletely blocked both fluid pooling effect and mucosalprotective effect of loperamide. Omeprazole reduced the acidity of the gastric fluid in ratstreated with loperamide without significantly decreasingthe fluid volume. Various volumes of acid, given orallyimmediately before 0.6 N HCl, volume-dependently prevented gastric lesions. We conclude thatsubcutaneous loperamide protects the gastric mucosaagainst necrotizing agents through luminal dilution ofirritants, which is mediated by naloxonesensitive opiate receptors.