Toichi Takenaka

Comparative study on α1-adrenoceptor antagonist binding in human prostate and aorta

1. Specific binding of [3H]‐prazosin in prostatic and aortic membranes of humans was saturable and of high affinity (prostate: apparent dissociation constant, Kd= 0.35 ± 0.03 nmol/L; aorta: Kd= 0.26 ± 0.03 nmol/L). The density of [3H]‐prazosin binding sites (Bmax) for prostate and aorta was 546 ± 31 and 61.6 ± 1.6 fmol/mg protein, respectively.

Mitogenic activity of endothelin on human cultured prostatic smooth muscle cells.

The effects of endothelins on human prostatic smooth-muscle cell growth were examined. Endothelin-1 and endothelin-3 induced a concentration-dependent increase in DNA synthesis and also promoted cell growth. Use of subtype selective antagonists BQ-123 ((cyclo(D-Trp-D-Asp(ONa)-Pro-D-Val-Leu); endothelin ET(A) receptor selective) and BQ-788 ((N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methyl Leu-D-Trp-(COOMe)-D-Nle-ONa); endothelin ET(B) receptor selective), indicated that mitogenic effects of endothelin were mediated through activation of both endothelin ET(A) and ET(B) receptors. The mitogenic effects of endothelin-1 and endothelin-3 were significantly inhibited by pretreatment of the cells with pertussis toxin. However, mitogenesis due to basic fibroblast growth factor was not affected. In conclusion, endothelin has mitogenic effects on human prostatic smooth muscle cells through activation of both endothelin ET(A) and ET(B) receptors via different signalling pathways from basic fibroblast growth factor. This may contribute to smooth muscle hyperplasia associated with benign prostatic hyperplasia.

Ex vivo occupancy by tamsulosin of α1-adrenoceptors in rat tissues in relation to the plasma concentration

At 0.5-12 h after oral administration of tamsulosin (2.3 micromol/kg) in rats, there was a significant decrease in specific [3H]prazosin binding in the prostate as compared to the control value. The greater decrease occurred in the submaxillary gland. The effect of tamsulosin was mainly due to a marked reduction of [3H]prazosin binding sites (Bmax) rather than to an increase in the dissociation constant (Kd). In contrast, there was only a slight decrease or no change in the [3H]prazosin binding in the spleen, heart, and cerebral cortex of tamsulosin-administered rats at 0.5-12 h. Oral administration of terazosin (21.7 micromol/kg) significantly increased Kd values for [3H]prazosin binding with little effect on Bmax values in the rat prostate at 3 and 6 h. The greater increases in Kd values were observed in the submaxillary gland, spleen and heart at 0.5-12 h. Terazosin had a slight effect on Kd values for the cerebral cortical [3H]prazosin binding. Tamsulosin was absorbed rapidly after oral administration at a dose of 2.3 micromol/kg in rats, and at 6 h, plasma concentration decreased markedly to approximately one-twentieth of the 0.5 h peak level. alpha1-Adrenoceptor occupancy was estimated as a percentage of decrease in Bmax values for [3H]prazosin binding in tissues of tamsulosin-treated rats compared with control rats. The alpha1-adrenoceptor occupancy by tamsulosin in the prostate and submaxillary gland occurred rapidly in parallel with the rise in plasma concentration of tamsulosin, and lasted for over 12 h despite the marked decrease in plasma concentration. Consequently, it is suggested that tamsulosin produces more selective and sustained occupancy in vivo of alpha1-adrenoceptors in the submaxillary gland and prostate of rats than in other tissues.

The role of extracellular Ca2+ in carbachol-induced tonic contraction of the pig detrusor smooth muscle

The role of extracellular Ca2+ in the toniccontractile response to muscarinic receptor stimulation was investigated in isolated detrusor smooth muscle from the pig urinary bladder.Carbachol (10−8 −10−5 M) produced a concentration-dependent contractile response in isolated pig detrusor smooth muscle strips consisting of an initial phasic component followed by a tonic component. During the plateau of the tonic contractions induced by carbachol at the submaximal concentration of 10−6 M, the inhibiting effects of atropine, EGTA, nifedipine (a voltage-dependent calcium channel antagonist), H-7 [a protein kinase C (PKC) inhibitor] and YM 934 (a potassium channel opener) on the contractions were evaluated. Atropine (10−10 −3 × 10−8 M) concentration-dependently inhibited the tonic contractions induced by carbachol. In the same experimental conditions, EGTA (4 mM) and nifedipine (10−9 −3 × 10−7 M) depressed the tonic contractions in a concentration-dependent manner as did H-7 (10−5 −3 × 10−5 M) and YM934 (10−8 -10−6 M). However, H-7 (10−5-3 × 10−5 M) and YM934 (10−6 M) were very weak in inhibiting the contractions induced by KCl (50 mM) in isolated pig detrusor smooth muscle strips.These results suggest that the tonic-contractile response induced by carbachol in pig detrusor smooth muscle strips is dependent mainly on depolarization of the cell membranes and an influx of extracellular Ca2+, and also suggest that this depolarizing response may be due to inactivation of ATP-sensitive potassium channels through muscarinic activation of PKC.

Adrenoceptor blocking, hemodynamic and coronary effects of YM-09538, a new combined α- and β-adrenoceptor blocking drug, in anesthetized dogs

Abstract In anesthetized dogs, YM-09538, a new sulfonamide-substituted phenylethylamine, competitively antagonised the phenylephrine-induced vasopressor response with a DR 10 of 0.50 mg/kg i.v. and the isoproterenol-induced positive chronotropic response with a DR 10 of 0.66 mg/kg, i.v., indicating that YM-09538 blocks both α 1 - and β 1 -adrenoceptors almost to the same extent. YM-09538 was 4 times more potent than phentolamine in blocking α 1 -adrenoceptors and 3 times less potent than propranolol in blocking β 1 -adrenoceptors. YM-09538 non-selectively blocked cardiac β 1 - and vascular β 2 -receptors and was devoid of intrinsic β-sympathominetic and local anesthetic activities. In anesthetized closed-chest dogs, YM-09538 resembled propranolol in reducing heart rate, cardiac output, max. dLVP/dt and left ventricular cardiac work but differed from propranolol in decreasing total peripheral resistance, in increasing femoral blood flow, in causing larger falls in arterial blood pressure and in decreasing pulmonary arterial pressure. In non-ischemic myocardium, transmural flow and coronary vascular resistance were respectively strongly increased and decreased and the endo/epi flow ratio was slightly but not significantly reduced. In ischemic myocardium, YM-09538 also increased transmural flow and since endocardial and epicardial flows were augmented to the same extent, the endo/epi flow ratio remained unchanged. All these hemodynamic and coronary effects of YM-09538 can be accounted for the drugs combined α- and β-adrenoceptors blocking properties.

Pharmacologic Profiles of Ym934, a Novel Potassium Channel Opener

Pharmacologic profiles of YM934, a newly synthesized 1,4-benzoxazin derivative K channel opener were evaluated in in vitro and in vivo experiments. In isolated rat portal vein, YM934 and a benzopyran derivative K channel opener lemakalim inhibited the frequency of spontaneous rhythmic contractions concentration de-pendently, with IC50 values of 14 and 38 μM, respectively. These inhibitory effects were competitively antagonized by glibenclamide (an ATP-sensitive K channel blocker; 10-7-3 x 10-6 M). In isolated rabbit aorta, YM934 (10-8-10-6 M) and lemakalim (10-8-l0-6 M) relaxed the contractions induced by 20 mAf KC1 concentration dependency but were ineffective against the contractions induced by 50 mM KC1. YM934 (10_8-3 x KT6 M) and lemakalim (3 x 10-8-10-5 M), but not the calcium antagonist nifedipine, relaxed the contractions induced by norepinephrine (NE 10-6 M) or prostaglandin F2α (PGF2α 3 x 10_6 M) in the aorta. In pentobarbital-anesthetized dogs, YM934 (1–10 μg/kg intravenously, i.v.) dose-dependently increased coronary artery blood flow (CBF), and decreased total peripheral resistance (TPR) and mean blood pressure (MBP). YM934 selectively increased CBF, but had little effect on vertebral, carotid, mesenteric, renal and femoral artery BF. These vasodilatory effects of YM934 were antagonized by glibenclamide. YM934 is a potent K channel opener and possesses potent vasodilatory effects, with particularly pronounced effects on the coronary artery. These effects of YM934 may, like lemakalim, be mediated by opening of ATP-sensitive K channels.

Isolation and Amino Acid Sequence of Flavostatin, a Novel Disintegrin From the Venom of Trimeresurus flavoviridis

Flavostatin, a novel disintegrin purified from the venom of Trimeresurus flavoviridis, consists of 68 amino acids, including an Arg-Gly-Asp sequence and 12 Cys residues at positions highly conserved among disintegrins. The N-terminal sequence of flavostatin was identical to those of triflavin and flavoridin, previously reported disintegrins from the Trimeresurus flavoviridis venom. Differences among the C-terminal sequences of these disintegrins are considered to affect their biological potencies. Isolated flavostatin inhibited ADP collage, and thrombin receptor agonist peptide-induced platelet aggregation in human platelet-rich plasma with an IC50 range of 59 to 98 nM. Contrary to expectations, these values were similar to those for triflavin.

Decreased contractile effect of endothelin-1 on hyperplastic prostate

1. The contractile activity, binding activity and localization of endothelin (ET)-1 were evaluated in human nonhyperplastic (control) and hyperplastic prostates. 2. ET-1 caused contraction of both prostates in a dose-dependent manner. However, this contraction was markedly decreased in hyperplastic prostates. 3. Bmax and Kd values of hyperplastic prostates were greater than those of the control. 4. The muscle and proliferative epithelium of hyperplastic prostates showed strong staining for the anti-ET-1 antibody. However, the glandular epithelium of control prostates was weakly stained. 5. These findings indicate that responsiveness to ET-1 is decreased, though the ET-1 and ET-1 receptors increase in the hyperplastic prostate. Namely, the increase in ET-1 receptors is not effective in regulating the contractile response of the prostate, because its expression is rather dominant in proliferated gland. 6. These suggest that ET-1 may not have an important role in the release of the obstructive symptoms of benign prostatic hypertrophy.

Dopamine DA1 receptor agonist activity of YM435 in the canine renal vasculature

1. The renal vasodilatory effect of YM435 was used as an index of its dopamine DA1 receptor agonist activity and compared with that of dopamine in pentobarbital-anesthetized dogs. 2. Intrarenal arterial administration of YM435 (0.1 to 10 micrograms) and dopamine (1 to 100 micrograms) produced a dose-dependent increase in renal blood flow. The doses of YM435 and dopamine required to cause a 30-ml/min increase in renal blood flow were 2.0 and 26.8 micrograms intra-arterially (IA), respectively. YM435 was therefore 13 times more potent than dopamine in this effect. 3. The selective dopamine DA1 receptor antagonist, SCH 23390, but not the selective dopamine DA2 receptor antagonist, nemonapride, caused dose-dependent, parallel shifts to the right in the dose-responsive curve of YM435. 4. The present results demonstrate that YM435 is a potent and selective dopamine DA1 receptor agonist.

Renal effect of YM435, a new dopamine D1 receptor agonist, in anesthetized dogs

The renal effects of YM435 ((-)-(S)-4-(3,4-dihydroxyphenyl)-7,8-dihydroxy -1,2,3,4-tetrahydroisoquinoline hydrochloride hydrate), a dopamine D1 receptor agonist, were investigated in anesthetized dogs. Intravenous infusion of YM435 (0.1-3 micrograms/kg per min) increased renal blood flow and decreased mean blood pressure in a dose-dependent manner with little effect on heart rate. Glomerular filtration rate, urine flow and urinary sodium excretion were concomitantly increased. The renal effect of YM435 by intravenous infusion at 0.3 microgram/kg per min was completely blocked by treatment with the selective dopamine D1 receptor antagonist SCH 23390 (7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazep ine hydrochloride). Furthermore, intravenous infusion of YM435 (0.3 microgram/kg per min) reversed the angiotensin II-induced decreases in renal blood flow, glomerular filtration rate, urine flow and urinary sodium excretion, and prevented the decrease in renal blood flow, glomerular filtration rate and urine flow induced by renal nerve stimulation and platelet-activating factor (PAF). These results suggest that intravenous administration of YM435 produces renal vasodilating and diuretic/natriuretic effects by stimulation of dopamine D1 receptors, and demonstrate that YM435 can inhibit angiotensin II-, renal nerve stimulation- and PAF-induced renal dysfunction.