We assessed the 5-HT3-receptor antagonist effects of 4, 5, 6, 7-1H-benzimidazole compounds which are derivatives of YM060, a potent and selective 5-HT3-receptor antagonist, in isolated guinea pig colon. YM114 (KAE-393), YM-26103-2, YM-26308-2 (3 × 10-9 to 3 × 10-8 M) produced concentration-dependent shifts to the right of the dose-response curves for both 5-HT and 2-methyl-5-HT (2-Me-5-HT). YM114 (pA2=9.08 against 5-HT, pA2=8.88 against 2-Me-5-HT), YM-26103-2 (pA2=8.27 against 5-HT, pA2 = 8.19 against 2-Me-5-HT), and YM-26308-2 (pA2 = 8.58 against 5-HT, pA2 = 8.4 against 2-Me-5-HT) showed similar pA2 values irrespective of the agonist used, suggesting that they have 5-HT3-receptor blocking activity irrespective of the N-position at the aromatic ring. Since these compounds have an asymmetric center, their enantiomers exist. The S-isomers were one to three orders of magnitude less potent than the respective R-isomer compounds, indicating that the stereochemical configuration of 4, 5, 6, 7-tetrahydro-1Hbenzimidazoles is an important determinant of their affinity for 5-HT3 receptors. These results suggest that the highly potent 5-HT3 receptor antagonism and high selectivity for 5-HT3 receptors of 4, 5, 6, 7-tetrahydro-1H-Benzimidazole derivatives are conserved irrespective of the position of the nitrogen atom in the aromatic ring and that 5-HT3, recentors favor the R-isometric conformation of these compounds.
(1s, 2s)-2-[3-(2, 2-Dimethylpropyl)-3-nonylureido] aminocyclohexane-l-yl 3-[N-(2, 2, 5, 5-tetramethyl-1, 3-dioxane-4-carbonyl)amino]propionate (F-1394), a pantotheic acid derivative, is a newly synthesized inhibitor of acyl-CoA: cholesterol acyltransferase (ACAT). In the present study, we investigated the inhibitory effects of F-1394 on the activities of ACAT. F-1394 reduced the ACAT activities in rat liver microsomes, homogenate of rabbit small intestinal mucosa and lysate of J774 macrophages with IC50 values of 6.4 nM, 10.7 nM and 32 nM, respectively. The kinetic studies showed that F-1394 exerted competitivetype inhibition, and the K; values in liver and small intestinal ACAT were 4.0 nM and 9.9 nM, respectively. The inhibitory effects of F-1394 on the activity of ACAT were more potent than that of other ACAT inhibitors or hypolipidemic agents. The study on enzyme selectivity indicated that F-1394 did not affect 3-hydroxy-3-methylglutaryl CoA reductase, acyl-CoA synthetase and cholesterol esterase. F-1394 weakly inhibited the activity of lecithine:cholesterol acyltransferase (LCAT) originating from rat plasma. The inhibitory potency of F-1394 for the activity of liver microsomal ACAT was 4, 690-fold stronger than that for the activity of LCAT. These findings indicate that F-1394 is a potent and selective inhibitor of ACAT, and its inhibition manner is the competitive type.
Biochemical effects of acute and subacute treatments with ambrein were investigated in rats by measuring the total proteins, cholesterol, triglycerides, GOT, GPT and alkaline phosphatase in the blood plasma. Also, determinations of prothrombin time (PT), partial thrombin time (PTT), thrombin time (TT) and fibrinogen level were performed. Furthermore, changes in plasma electrolyte concentration were studied. Ambrein administered i.p. did not cause any toxic symptoms in the liver as revealed by the histology of the liver tissue both in acute and subacute treatments. Ambrein itself did not significantly affect the plasma protein, cholesterol, GOT and GPT profiles, but lowered alkaline phosphatase at high doses (50 and 250 mg/kg) after subacute treatment. Thus far, no specific pattern of action of ambrein in electrolyte control has been found. However, it increased PT, PTT and TT and decreased fibrinogen levels in both the acute and subacute studies, pointing towards its potential as an anticoagulant and antifibrinogenic agent.
The avoidance behavior of rats in a typical step-through passive avoidance task was evaluated by using two types of time measurements that differed from traditional step-through latency (STL). The total stay-time in the light box (TL) was calculated as an index of the dark box avoidance throughout the retention trial, counting the time before and after the first step-through. The total stay-time in the far area of the light box (TF) was calculated as an index of the tendency to keep away from the dark box. TL, TF and the STL increased with electrical shock intensity at acquisition trials and gradually decreased through an extinction procedure. The discrepancy between our new measures and the STL was observed when the effects of a new drug, RS-8359, which was reported to ameliorate ischemic brain damage, were examined in ischemic animals. TL, TF and STL decreased in rats receiving brain ischemia, and we found that after treatment with RS-8359, TL and TF increased, but no effect was observed on STL. The discrepancy observed suggests that a short STL does not necessarily imply a loss of avoidance behavior. Passive avoidance tests can be more revealing about a drug''s effects when stay-time measures are used.
Effects of cholecystokinin (CCK)-JMV-180, a CCK analog, on the CCK receptor functions of isolated rabbit pancreatic acini and gallbladder smooth muscle were studied. When the pancreatic acini were incubated with increasing concentrations of CCK-8, stimulation of amylase release reached a maximum at 3 nM and then declined with the increasing concentration of CCK-8. CCK-JMV-180 also caused a dosedependent amylase release stimulation, which plateaued and remained unchanged above 300 nM at about 50% of the maximal stimulation by CCK-8. CCK-JMV-180 above 100 nM caused a rightward shift of the downstroke of the dose-response curve for CCK-8 (pA2=7.5). In the gallbladder smooth muscle, CCK-8 caused a dose-dependent contraction, but CCK-JMV-180 totally lacked this property. Instead, CCK-JMV-180 caused a rightward shift of the dose-response curve for CCK-8 (pA2=7.9). These results suggest that CCK-JMV-180 distinguishes between the CCKA receptors associated with pancreatic exocrine secretion in the acini and those involved in contraction of the isolated gallbladder smooth muscle in rabbits.
In the isolated, perfused working rat heart, ischemia (15 min) decreased the mechanical function and the tissue levels of adenosine triphosphate and creatine phosphate and increased the levels of lactate and free fatty acids. Reperfusion (20 min) did not restore the mechanical function, but restored incompletely the levels of metabolites, with the exception of free fatty acids, which increased further during reperfusion. Dilazep was given 5 min before starting ischemia until the end of ischemia. Dilazep at 5 or 10 μM decreased the cardiac mechanical function, but did not affect coronary flow in the pre-ischemic heart. Dilazep at 5 or 10 μM accelerated the recovery of mechanical function and coronary flow during reperfusion, and it attenuated metabolic changes induced by ischemia and reperfusion. Dilazep at 1 μM neither decreased the pre-ischemic mechanical function nor restored the mechanical function during reperfusion, although it attenuated the accumulation of free fatty acids during reperfusion. These results suggest that dilazep attenuates both ischemia- and reperfusion-induced myocardial damage and that the anti-ischemic action of dilazep is not due to coronary vasodilation but probably due to an energy-sparing effect and other effects that remain to be studied.
The effects of dilazep, d-propranolol and lidocaine on the mechanical and metabolic changes induced by lysophosphatidylcholine (LPC) were studied in isolated, perfused working rat heart. After a stabilization period, the heart was perfused for 5 min with LPC (10 μM) alone, LPC plus dilazep (5, 10 or 20 μM), LPC plus d-propranolol (30 or 50 μM) or LPC plus lidocaine (30 or 100 μM) and then perfused with normal Krebs-Henseleit bicarbonate (KHB) buffer for a further 20 min. Perfusion with LPC for 5 min followed by KHB for 20 min irreversibly decreased cardiac mechanical function, decreased the tissue levels of adenosine triphosphate and creatine phosphate significantly, and increased the tissue levels of lactate and free fatty acids including arachidonic acid. Dilazep or d-propranolol significantly attenuated the mechanical and metabolic changes induced by LPC, but lidocaine did not. These results indicate that the exogenous LPC causes ischemia-like changes, suggesting that LPC is one of the important factors in producing ischemia-reperfusion derangements in terms of mechanical and metabolic functions, and that both dilazep and d-propranolol can prevent the LPC-induced myocardial damage.
Intravenous infusion of oxytocin (OT) (10- 100 nmol/kg/30 min) to 8-week-old anesthetized male rats resulted in a dose-dependent increase in urine volume, which showed a peak value 30-45 min after the start of OT-infusion. Urinary excretions of sodium, chloride and potassium were also increased by OT, showing peak values at 30 - 45 min, without any increase in the creatinine level. The natriuresis by OT was accompanied by increased excretion of urinary active kallikrein, which showed a peak value 15 min after the start of OT-infusion. The urinary kinin level was also increased. Intravenous infusion of a kallikrein inhibitor, aprotinin (15 mg/kg/90 min), when started 30 min before the OT-infusion, significantly inhibited the OT-induced increase in urine volume and urinary excretion of sodium, chloride and potassium. Intravenous infusion of a bradykinin B2 antagonist, Hoe 140 (D-Arg[Hyp3, Thi5, D-Tic7, Oic8]BK, 4.5 mg/kg/90 min), when started 30 min before the OT-infusion, significantly inhibited the OT-induced increases in urine volume and urinary excretion of sodium and chloride, but not that of potassium. These results indicate that the OT-infusion induces natriuresis in male rats, and more than half of the natriuresis is mediated by a concomitant increase in excretion of urinary active kallikrein and the kinin generated.
This study investigated the roles of thromboxane A2 (TXA2), ADP and thrombin in middle cerebral artery (MCA) thrombosis in the rat. The rat MCA was occluded by a thrombus induced by the photochemical reaction of rose bengal by green light that causes endothelial damage followed by platelet adhesion, aggregation and formation of a platelet and fibrin-rich thrombus at the site of the photochemical reaction. Vapiprost, a specific TXA2-receptor antagonist; clopidogrel, which has the thienopyridine structure of ticlopidine and is a more potent inhibitor of ADP-induced platelet aggregation than ticlopidine; argatroban, a specific thrombin inhibitor; or heparin was administered intravenously before rose bengal injection. The MCA local blood flow was monitored by a laser Doppler flowmeter. The MCA was occluded by thrombus about 5 min after the initiation of the photochemical reaction. Vapiprost, clopidogrel and argatroban all significantly prolonged the time taken for the thrombotic occlusion of the MCA, but in this respect, heparin was ineffective. Our observations suggest that vapiprost and clopidogrel are useful antithrombotic agents against platelet and fibrin-rich thrombi. The effect of argatroban is attributable to inhibition of thrombin-induced platelet activation and fibrin generation. The thrombosis model described in this study is useful for understanding the mechanism(s) of thrombogenesis in the rat MCA and may be applied to other mammalian species.
Adrenomedullin is known to induce profound hypotension in vivo, but the direct effect of this peptide on isolated arteries has not been demonstrated. This study estimated the vasodilative effects of adrenomedullin in comparison with those of calcitonin gene-related peptide (CGRP) in basilar, mesenteric, coronary, renal and femoral arteries isolated from the dog. Adrenomedullin (3 to 100 nM) and CGRP (1 to 30 nM) induced concentration-dependent relaxation of these arteries with and without endothelium, and the relaxing effects were slightly greater in endothelium-intact arteries than in denuded ones. The vasodilative potency of adrenomedullin relative to CGRP was smaller in the femoral artery than in basilar, mesenteric, coronary and renal arteries.
To clarify the antiallergic effect and antiallergic mechanism of AL-3264 (N-[4-[4-(diphenylmethyl)-1-piperazinyl]butyl]-3-(6-methyl-3-pyridyl)acrylamide) in monkeys, its effects on the Prausnitz-Küstner (PK) reaction, the histamine skin reaction and leukotriene production were examined. In contrast to ketotifen and mepyramine, AL-3264 inhibited the P-K reaction, which is mainly mediated by leukotriene and histamine, more clearly than the skin reaction evoked by histamine alone. AL-3264 also inhibited the leukotriene (LT) production in the broncho-alveolar cells, suggesting that the inhibition of LT production actually contributes to the antiallergic effect of AL-3264.
The effects of lead ions (Pb2+) on neuronal calcium channels were examined in cultured hippocampal neurons. Pb2+ blocked calcium channels in a concentration-dependent manner. The current-voltage relationship of the inhibition suggested a selective blockade of high-threshold calcium channels by Pb2+ up to a concentration of 3 μM. Pb2+ (3 μM) preferentially suppressed the ω-agatoxin IVA-sensitive components of the calcium channels. These findings suggest that Pb2+ mainly affects the P-type calcium channels at low concentrations.