Effect of KRN2391 on venous return: comparison with other vasodilators

We compared the cardiohemodynamic effects of KRN2391, a novel coronary vasodilator, with those of nicorandil, nifedipine, cromakalim, and nitroglycerin (NTG) administered intravenously (i.v.) to anesthetized open-chest dogs. KRN2391 (10 and 30 micrograms/kg) decreased mean blood pressure (MBP) and superior vena cava flow (SVCF), and increased inferior vena cava flow (IVCF), total venous return (TVR), pulmonary artery blood flow (PAF), and right atrial pressure (RAP). Administration of KRN2391 (30 micrograms/kg) decreased heart rate (HR). Nicorandil (100 and 300 micrograms/kg) decreased MBP and SVCF, and produced transient increases followed by decreases in IVCF, TVR, PAF, and RAP. HR was decreased by administration of nicorandil (300 micrograms/kg). Nifedipine (1 and 3 micrograms/kg) decreased MBP and increased SVCF, IVCF, TVR, PAF, and RAP. HR was not affected by either dose of nifedipine. Cromakalim (10 micrograms/kg) decreased MBP, SVCF, and increased HR, IVCF, TVR, PAF and RAP. Nitroglycerin (3 micrograms/kg) decreased MBP, SVCF, IVCF, TVR, PAF, and RAP. In dogs that received glibenclamide (5 mg/kg, i.v.), the changes in MBP, SVCF, IVCF, TVR, PAF, and RAP caused by KRN2391 were reduced in comparison with those in dogs that received vehicle for glibenclamide. The decreases in IVCF, TVR, and PAF induced by nicorandil were not affected by glibenclamide, but the decrease in MBP was diminished and the decrease in RAP was augmented. The hemodynamic changes caused by cromakalim were almost inhibited by glibenclamide, whereas those caused by NTG were not affected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Primary anastomosis of the trachea: management and pitfalls

The potentiating activity of SG-86[N-(2-hydroxyethyl)nicotinamide], a denitrated metabolite of nicorandil, on the adenosine-induced vasodepression was compared with that of nicorandil in anesthetized rats. Single bolus i.v. adenosine (3-100 micrograms/kg) produced dose-dependent reductions of blood pressure, accompanied by slight decreases (except for 100 micrograms/kg) in heart rate. The adenosine-induced vasodepression was significantly enhanced during i.v. infusion of either SG-86 (100 micrograms/kg per min) as well as nicorandil (10 micrograms/kg per min). The enhancement of adenosine action by them did not occur in the presence of glibenclamide (20 mg/kg i.v.). Single bolus i.v. injections of SG-86 (0.3-30 mg/kg), except for 30 mg/kg, which caused a glibenclamide-sensitive decrease by about 5-10 mmHg in mean arterial blood pressure, had no effects on blood pressure and heart rate, whereas those of nicorandil (30-300 micrograms/kg) elicited overt reduction of blood pressure, accompanied by decreases in heart rate. The present results revealed that SG-86, like nicorandil, significantly enhanced the vasodepressor response to adenosine, probably in part through KATP channel activation, and that the activity of SG-86 was about 10 times less potent than that of nicorandil.     

Systemic and coronary hemodynamic effects of repetitive cocaine administration in conscious dogs

The cardiovascular actions of cocaine are complex, and previous studies suggest that tachyphylaxis to the positive chronotropic and pressor effects of cocaine may develop after repetitive administration. We examined changes in systemic and coronary hemodynamics when single or multiple doses of intravenous (i.v.) cocaine were administered to conscious dogs. Dogs were chronically instrumented for measurement of aortic blood pressure (BP) and left ventricular pressure (LVP), LV dP/dtmax and dP/dt50, subendocardial segment length (%SS), diastolic coronary blood flow (CBF) velocity, and cardiac output (CO). Myocardial oxygen consumption was estimated by the pressure-work index (PWI). In one series of experiments, a single dose of cocaine (0.1, 0.2, 0.4, 0.8, or 1.6 mg/kg) was administered on 5 consecutive days in random fashion and peak changes in systemic and coronary hemodynamics were recorded. These doses were then randomly repeated in a second group of experiments with a 1-h interval between doses on the same day. Peak and steady-state changes in cardiovascular variables were recorded within and between each dose, respectively. In other experiments, higher doses of cocaine (0.8 or 1.6 mg/kg; separate groups) were administered four times at 1-h intervals in the same dogs and peak and steady-state changes in hemodynamics were determined. Cocaine caused dose-related increases in heart rate (HR), mean arterial pressure (MAP), LV systolic pressure (LVSP) and end-diastolic pressure (LVEDP), PWI, CO, and diastolic coronary vascular resistance and decreases in %SS when administered on different days. Cocaine also caused significant increases in baseline HR, MAP, LVSP, and PWI between doses given on the same day at 1-h intervals, but the absolute value of the peak response to cocaine of these hemodynamic parameters was independent of dosing regimen. These results were confirmed when we administered four doses of 0.8 mg/kg cocaine at 1-h intervals. The results indicate that baseline changes in systemic hemodynamic variables are a predominant feature of repetitive administration of lower doses of cocaine (< or = 0.8 mg/kg), but administration of higher doses of cocaine (> or = 8 mg/kg) at 1-h intervals caused tachyphylaxis to the hypertensive actions and myocardial oxygen consumption effects of cocaine.     

Cinematographic analysis of bovine embryo development in serum-free oviduct-conditioned medium

The effects of NG-nitro-L-arginine (NOLAG), an inhibitor of nitric oxide synthase (NOS), and of indomethacin, an inhibitor of cyclooxygenase, on the rise in cerebral blood flow (CBF) accompanying increasing levels of hypercapnia (paCO2 = 40-135 mmHg) were studied in anesthetized rats. CBF was measured by intracarotid injection of 133Xe. Progressive increases in paCO2 of 10 mmHg, at intervals of about 8-10 minutes, were associated with gradual increases in CBF until a paCO2 level of 115 mmHg was reached. No further CBF changes (from the maximum value of 446 +/- 70 ml 100 g-1 min-1) were seen with additional step increase in paCO2. Intracarotid infusion of 7.5 mg/kg NOLAG significantly attenuated the CO2-elicited CBF increase by about 45-65% at paCO2 values below 115 mmHg. Beyond this level, there was a lesser inhibition of about 27-35%. 30 mg/kg NOLAG had essentially the same effect as 7.5 mg/kg NOLAG. 50 mg/kg NOLAG, given intraperitoneally (i.p.) twice daily for 4 days, also caused an attenuated CBF response to CO2, but the inhibitory effect was significantly less than with acute NOLAG administration in the paCO2 range of 61-90 mmHg. Infusion of L-arginine, 1 g/kg/h, prevented the effect of 7.5 mg/kg NOLAG. Indomethacin, 10 mg/kg, i.v. produced a more dramatic attenuation of the response, to the extent that the steady rising curve of CBF as a function of paCO2 was almost completely abolished. With indomethacin, a moderate increase (50%) in CBF was seen at the lowest level of hypercapnia, but raising paCO2 above this level did not result in further increases in CBF. This effect could not be prevented by L-arginine. When combining 7.5 mg/kg NOLAG with 10 mg/kg indomethacin, the response to hypercapnia was totally blocked. The results suggest that NOLAG and indomethacin act through different mechanisms on the hypercapnic CBF response, and that indomethacin is the more powerful inhibitor.     

The potential risk factors associated with acute viral hepatitis in children under 5 years old]

In studies of the effects of salt intake on blood pressure (SBP, MBP, DBP), influences on heart rate (HR) are usually neglected even though the longterm load on both left ventricle (LV) and systemic arteries (SA) is better related to the product of HR x SBP (or MBP) than to pressure alone. After all, altered salt intakes often induce considerable volume-related changes in HR, and the heart operates more economically at low HR and high stroke volume (SV). Thus, about 3/4 of LV metabolism is used for the build-up of systolic tension, while the cost for SV expulsion, or for SV increases, is far lower. Moreover, low HR prolongs the diastolic period, so important for LV coronary supply. Against this background we have used results from studies in both rats and man, in which both BP and HR were followed during marked changes in salt intake, to explore how this affected the HR x SBP (or HR x MBP) product. Briefly, in ordinarily salt-resistant organisms, whether normo- or hypertensive, salt intake increases, which in man ranged from 10-20 to 250-300 mM (in rats over 100-fold), if anything reduced the computed longterm load (HR x SBP, or MBP) on LV and SA, as consequences of an efficient reflex volume control. By contrast, in salt-sensitive man, HR reflex reductions to increased salt intake were almost absent despite substantial SBP elevations, suggesting the influence of a CNS suppression of bulbar reflex centres combined with CNS neurohormonal interference with renal salt volume excretion, as in SHR.     

The rate zonal separation of organelles from dilute suspensions: the problem of a large sample volume

We previously showed that preoperative nicorandil, a hybrid potassium channel opener and nitrate compound, conferred cardioprotective effects in a hypoxia/reoxygenation model of isolated human atrial muscle by using functional recovery as an end point, and that ischaemic preconditioning surprisingly abolished the protection afforded by nicorandil. In view of this paradoxic result, this study was undertaken to assess whether ischaemic preconditioning influences any protective effect of nicorandil by using infarct size as an end point. In addition, we investigated the underlying mechanisms of the protective action of nicorandil. Rabbits underwent a midline sternotomy under anaesthesia. A left coronary branch was occluded for 30 min followed by 120 min of reperfusion. Nicorandil (100 microg/kg bolus + 10 microg/kg/min) was given intravenously 30 min before coronary occlusion and continued to the time of reperfusion (early treatment) or 5 min before reperfusion and continued throughout reperfusion (late treatment). Ischaemic preconditioning was achieved by a single episode of 5-min coronary occlusion followed by 10-min reperfusion before the 30-minute occlusion in the presence or absence of nicorandil. Risk volume and infarct volume were determined by fluorescent microspheres and tetrazolium staining, respectively. Early treatment with nicorandil conferred a significant decrease in percentage of infarct size within the risk zone (24.9 +/- 2.9%) when compared with control (39.2 +/- 4.3%; p < 0.01). Late treatment with nicorandil had no effect on infarct size (43.5 +/- 3.4%). Ischaemic preconditioning also resulted in significant reduction in infarct size (13.4 +/- 4.3%; p < 0.01 vs. control). The combination of ischaemic preconditioning with nicorandil (early treatment) showed an intermediate protective efficacy between early treatment with nicorandil alone and ischaemic preconditioning alone (18.1 +/- 4.2%; p < 0.01 vs. control). Nitroglycerin (10 microg/kg bolus + 1 microg/kg/kg/min, i.v.) given before and during ischaemia tended to reduce infarct size, but the effect was not statistically significant (28.9 +/- 2.9%; p > 0.05 vs. control). Although an adenosine triphosphate (ATP)-sensitive potassium channel blocker, 5-hydroxydecanoate (5 mg/kg, i.v.) by itself had no effect on infarct size (38.8 +/- 3.6%), the protective effect of nicorandil was abolished by 5-hydroxydecanoate (37.7 +/- 5.8%; p < 0.05 vs. early treatment of nicorandil). There were no differences in area at risk or haemodynamics between groups. Our results show that nicorandil has a protective effect against myocardial infarction in our rabbit model when infused before and during ischaemia, but not during reperfusion, and the protective effect is abolished by an ATP-sensitive potassium channel blocker. Furthermore, the addition of ischaemic preconditioning does not detrimentally influence the effect of nicorandil. This suggests that nicorandil can confer an infarct-limiting effect by opening of ATP-sensitive potassium channels with or without intermittent ischaemia, as may happen in patients with unstable angina.     

Role of K+ channel opening and stimulation of cyclic GMP in the vasorelaxant effects of nicorandil in isolated piglet pulmonary and mesenteric arteries: relative efficacy and interactions between both pathways

1. The effects of the K+ channel opener levcromakalim, the guanylate cyclase stimulant nitroprusside and the dual drug nicorandil (K+ channel opener and guanylate cyclase stimulant) were analysed in piglet isolated endothelium-denuded pulmonary (PA) and mesenteric (MA) arteries stimulated by noradrenaline (NA) or by the thromboxane A2 mimetic U46619. 2. Nicorandil, levcromakalim and verapamil were less potent in PA than in MA, the efficacy of levcromakalim was also reduced in PA. The effects of nicorandil and levcromakalim were similar in arteries pre-contracted by NA and U46619, whereas verapamil was more potent in arteries pre-contracted by NA. Nitroprusside was equipotent in MA pre-contracted by either NA or U46619 and in PA pre-contracted by NA whereas in PA pre-contracted by U46619, nitroprusside showed lower potency and efficacy. 3. The relaxant effects of levcromakalim and nitroprusside were inhibited by 10(-5) M glibenclamide and 10(-6) M ODQ, respectively. Nicorandil-induced relaxation was inhibited by ODQ in all experimental conditions, whereas glibenclamide had inhibitory effects in PA and MA pre-contracted by U46619, had no effect in PA pre-contracted by NA and in MA pre-contracted by NA it was only inhibitory in the presence of ODQ. 4. No apparent interactions were found between nitroprusside and levcromakalim as indicated by the lack of effects of pretreatment with one of them (producing 20-35% relaxation) on the potency of the relaxant response to the other. However, in PA pre-contracted by U46619, where nitroprusside or levcromakalim induced only partial relaxation, the combination of both mechanisms (either by combining nitroprusside plus levcromakalim or by nicorandil) was able to induce full vasodilatation. 5. In conclusion, K+ channel opening and guanylate cyclase stimulation are independent pathways that induce additive vasorelaxation in piglet PA and MA. The mechanism of action of nicorandil is dependent on the artery and on the nature of the agonist employed to precontract the artery. The relative efficacy of K+ channel opening vs guanylate cyclase stimulation may partially explain the preferential contribution of each mechanism to the relaxant effects of nicorandil.     

Blockade of cerebral blood flow response to insulin-induced hypoglycemia by caffeine and glibenclamide in conscious rats

The possibility that adenosine and ATP-sensitive potassium channels (KATP) might be involved in the mechanisms of the increases in cerebral blood flow (CBF) that occur in insulin-induced hypoglycemia was examined. Cerebral blood flow was measured by the [14C]iodoantipyrine method in conscious rats during insulin-induced, moderate hypoglycemia (2 to 3 mmol/L glucose in arterial plasma) after intravenous injections of 10 to 20 mg/kg of caffeine, an adenosine receptor antagonist, or intracisternal infusion of 1 to 2 mumol/L glibenclamide, a KATP channel inhibitor. Cerebral blood flow was also measured in corresponding normoglycemic and drug-free control groups. Cerebral blood flow was 51% higher in untreated hypoglycemic than in untreated normoglycemic rats (P < 0.01). Caffeine had a small, statistically insignificant effect on CBF in normoglycemic rats, but reduced the CBF response to hypoglycemia in a dose-dependent manner, i.e., 27% increase with 10 mg/kg and complete elimination with 20 mg/kg. Chemical determinations by HPLC in extracts of freeze-blown brains showed significant increases in the levels of adenosine and its degradation products, inosine and hypoxanthine, during hypoglycemia (P < 0.05). Intracisternal glibenclamide had little effect on CBF in normoglycemia, but, like caffeine, produced dose-dependent reductions in the magnitude of the increases in CBF during hypoglycemia, i.e., +66% with glibenclamide-free artificial CSF administration, +25% with 1 mumol/L glibenclamide, and almost complete blockade (+5%) with 2 mumol/L glibenclamide. These results suggest that adenosine and KATP channels may play a role in the increases in CBF during hypoglycemia.     

Effects of a K+ATP channel opener, lemakalim, on systemic, coronary and regional vascular dynamics in conscious dogs: comparison with nifedipine, adenosine, nitroglycerin and acetylcholine

The systemic, coronary and regional vascular responses to the K+ATP channel opener lemakalim were compared to other potent vasodilators (i.e., nifedipine, adenosine, nitroglycerin and acetylcholine). Experiments were performed in 12 conscious dogs 2 to 4 weeks after implantation of aortic catheters and flow probes on the ascending aorta, left circumflex coronary, celiac, mesenteric, renal and iliac arteries, and solid-state miniature pressure gauges in the left ventricular cavity. Dose-response curves induced by bolus injection (i.v.) were examined. For doses that reduced total peripheral resistance by 22%, lemakalim reduced celiac (-28 +/- 2%), mesenteric (-24 +/- 3%), renal (-17 +/- 3%) and iliac (-18 +/- 3%) vascular resistances (i.e., by amounts similar to those observed with the other vasodilators, except for adenosine, which increased renal resistance). At these doses, lemakalim induced a greater decrease (-52 +/- 3%) (P < .05) in coronary resistance, as compared with nifedipine (-35 +/- 3%), adenosine (-38 +/- 3%), nitroglycerin (-25 +/- 2%) and acetylcholine (-32 +/- 3%). However, when near maximal vasodilation was elicited, adenosine elicited the greatest (P < .05) decrease in coronary resistance (-81 +/- 1%), as compared with lemakalim (-74 +/- 2%), nifedipine (-67 +/- 2%), nitroglycerin (-63 +/- 2%) and acetylcholine (-72 +/- 1%). Both the time to maximal increases in regional blood flow and the time for recovery in all vascular beds were significantly prolonged for lemakalim compared with the other vasodilators. Thus, the K+ATP channel opener lemakalim dilates the coronary bed out of proportion to other vascular beds, is relatively more potent at lower doses than other vasodilators and exhibits a delayed and more prolonged action in all regional vascular beds.     

Action-potential duration and contractility in canine cardiac tissues: action of inotropic drugs

The goal of this study was to determine whether neuronally derived nitric oxide mediates responses of cerebral blood flow (CBF) to N-methyl-D-aspartate (NMDA). In anesthetized Sprague-Dawley rats, regional CBF of the parietal cortex was monitored by laser-Doppler flowmetry. Topical application of either NMDA or acetylcholine produced concentration-related increases in CBF. Responses of CBF to NMDA (10(-5) M) but not to acetylcholine were inhibited (0+/-3% vs 21+/-5%, p < 0.05) by 7-nitroindazole (50 mg/kg, i.p.). MK-801 (0.5 mg/kg, i.v.) and tetrodotoxin (10(-6) M, topical application) also inhibited NMDA-induced responses. These results suggest that nitric oxide of neuronal origin mediates NMDA-induced increases in CBF.     

Effects of chronic oral administration of levcromakalim on in vitro contractile responses of arterial smooth muscle

It has been shown that oral administration of 0.038-0.15 mg/kg levcromakalim elicits a dose-related antihypertensive response in spontaneously hypertensive rats (Clapham et al., Arzneim. Forsch. 41 (1991) 385). In the present study, we examined the effects of long term administration of a high dose of levcromakalim on in vitro vascular contractility. Levcromakalim (2.25 mg/kg/day) was administered to the rats for 2 weeks and the thoracic aorta was then isolated. The levcromakalim treatment markedly reduced the relaxant effect of levcromakalim itself on norepinephrine-induced contraction. Relaxant effects of sodium nitroprusside and 8-bromo-cGMP were also attenuated by the levcromakalim treatment, although the relaxant effects of verapamil and forskolin were unchanged. The levcromakalim treatment decreased the threshold concentration for KCl and norepinephrine to induce contraction. The chronic levcromakalim treatment did not affect the cGMP production due to 3-isobutyl-1-methylxanthine and/or sodium nitroprusside. The aorta isolated from spontaneous hypertensive rats did not exhibit spontaneous activity in normal solution. After treatment with levcromakalim, however, the aorta showed spontaneous rhythmic contractions. Verapamil (10 microM) completely suppressed the spontaneous activity and decreased the basal tension below the original level. Similar to the effects of chronic treatment with levcromakalim, high-K+ solution (15.4 mM) augmented the contractile response to norepinephrine in the aorta of normotensive rats and induced rhythmic contractions in the aorta of spontaneously hypertensive rats. These results suggest that chronic treatment with a high dose of levcromakalim attenuates not only the effects of levcromakalim itself but also the cGMP-mediated relaxation, possibly by desensitizing the K+ channel.     

K+ channel-opening action contributes to the preventive effects of nicorandil on U46619-induced vasoconstriction of canine large coronary arteries in vivo

The antispasmogenic effects of nicorandil on epicardial coronary artery vasoconstriction were compared with those of a K+ channel opener, cromakalim, and a nitrovasodilator, nitroglycerin, in open-chest dogs. Intracoronary administration of U46619 (0.5-1.0 micrograms), a stable thromboxane A2 analogue, reduced the external diameter of the left circumflex coronary artery with no marked alternations in systemic hemodynamics. This U46619-induced vasoconstriction of large epicardial coronary arteries was dose-dependently prevented by the intracoronary infusion of nicorandil (1-10 micrograms/kg/min), cromakalim (0.03 micrograms/kg/min) and nitroglycerin (1 micrograms/kg/min). After pretreatment with glibenclamide (3 mg/kg, i.v.), and ATP-sensitive K+ channel blocker, these effects of nicorandil and cromakalim were inhibited significantly, whereas the response to nitroglycerin remained unchanged. Nicorandil (3 micrograms/kg/min), cromakalim (0.03 micrograms/kg/min) and nitroglycerin (1 micrograms/kg/min) increased coronary blood flow. However, the inhibitory effects of each drug on the U46619-induced vasoconstriction were not influenced by the partial occlusion of the left circumflex coronary artery, which kept coronary blood flow constant. This indicates a direct antispasmogenic effect of K+ channel openers, which is independent of that mediated by the response to flow. Furthermore, our results suggest that, by this effect, nicorandil protects large coronary arteries from U46619-induced vasoconstriction.     

Effects of nitro-L-arginine on blood pressure and cardiac index in anesthetized rats: a pharmacokinetic-pharmacodynamic analysis

PURPOSE: Nitric oxide synthase (NOS) inhibitors such as Nitro-L-arginine (L-NA) are being considered for the management of hypotension observed in septic shock. However, little information is available regarding the pharmacokinetic and pharmacodynamic properties of these agents. Our objective was to examine the relationships between L-NA plasma concentration and various hemodynamic effects such as cardiac index (CI), mean arterial pressure (MAP), and heart rate (HR) elicited by L-NA administration in rats. METHODS: L-NA was infused at doses between 2.5-20 mg/kg/hr in anesthetized rats over one hour. Hemodynamic effects and plasma L-NA levels were determined. RESULTS: Infusion of L-NA resulted in dose-dependent increases in MAP and systemic vascular resistance (SVR), decreases in CI, and minimal change in HR. The relationships between the hemodynamic effects and plasma L-NA levels were not monotonic, and hysteresis was observed. Using nonparametric analysis, the equilibration half-time (t1/2,keo) between plasma L-NA and the hypothetical effect site was determined to be 51.5 +/- 6.6 min, 42.4 +/- 10.1 min, 43.4 +/- 9.0 min for MAP, CI, and SVR, respectively (n = 14). The Emax and EC50 values obtained were + 32.5 +/- 8.4 and 2.6 +/- 1.3 microg/ml for MAP and -52.9 +/- 15.6 and 3.7 +/- 1.8 microg/ml for CI, respectively. CONCLUSIONS: Although L-NA can bring about beneficial elevation of MAP, such effect is always accompanied by a stronger effect on CI depression. Dose escalation of L-NA may bring about detrimental negative inotropic effect and loss of therapeutic efficacy.     

Hemodynamic effects of amlodipine and benazeprilat in spontaneously hypertensive rats

We wished to assess the hemodynamic effects of administration of the combination of the calcium channel blocking agent amlodipine and the angiotensin-converting enzyme (ACE) inhibitor benazeprilat in conscious spontaneously hypertensive rats (SHR). In SHR previously instrumented for measurement of mean arterial blood pressure (MAP) and heart rate (HR), intravenous (i.v.) injection of amlodipine (0.25-4 mg/kg) produced dose-dependent decreases in blood pressure (BP). Administration of benazeprilat (0.1-10 mg/kg i.v.) decreased arterial MAP, and benazeprilat (10 mg/kg) effectively blocked the effects of exogenously administered angiotensin I (AI). In animals surgically prepared for measurement of BP, HR, and hindquarter, renal, and mesenteric blood flows, administration (i.v.) of the combination of amlodipine (0.5 mg/kg) with benazeprilat (10 mg/kg) evoked a decrease in BP that was greater than that elicited by monotherapy. The tachycardic response observed after administration of the combination was no different from that observed after monotherapy with amlodipine. Simultaneous administration of amlodipine and benazeprilat produced reductions in vascular resistance in the hindquarter, renal and mesenteric beds that were greater than the responses evoked by injection of either agent. The major finding of these studies was that dual therapy with amlodipine and benazeprilat produced an additive hypotensive effect in conscious SHR. Regional vasodilation accompanied the large degree of hypotension evoked by the combination.     

Effects of NMDA receptor glycine recognition site antagonism on cerebral metabolic rate for glucose and cerebral blood flow in the conscious rat

Glycine is a requisite cofactor for glutamatergic activation of the N-methyl-D-aspartate (NMDA) receptor. Antagonism of glutamate at the NMDA receptor has been shown to cause substantial changes in regional cerebral metabolic rate for glucose utilization (CMRglu) and blood flow (CBF). This study examined CMRglu and CBF changes caused by antagonism of glycine at the NMDA receptor recognition site. Rats were anesthetized with halothane and vascular access was obtained. The animals were then awakened. One hour later, either vehicle (control) or ACEA 1021 (5 mg/kg followed by 3.5 mg x kg(-1) x h(-1) or 10 mg/kg followed by 7 mg x kg(-1) x h(-1)) was infused intravenously. CMRglu and CBF were then determined. Autoradiographic analysis of 25 regions revealed effects of ACEA 1021 on CMRglu in the frontal, sensory, parietal and auditory cortices and the anteroventral and subthalamic nuclei. These changes deviated less than 15% from control. Effects on CBF were also small. The CMRglu and CBF effects of ACEA 1021 are substantially less than those previously observed for either competitive or non-competitive glutamate NMDA antagonists. We conclude that inhibition of the NMDA glycine recognition site has little or no effect on CMRglu or CBF at the doses examined. This is consistent with the absence of psychotomimetic effects observed for this class of drugs.     

Nicorandil augments regional ischemia-induced monophasic action potential shortening and potassium accumulation without serious proarrhythmia

Nicorandil is a clinically used nitrovasodilator that has a property as an opener of ATP-sensitive potassium (KATP) channels in vitro. We examined whether nicorandil at a clinically used dose augmented regional ischemia-induced monophasic action potential (MAP) shortening and increase in extracellular potassium concentration ([K+]o), and how it affected arrhythmia occurrence. Five-minute occlusion of a distal site of the left anterior descending coronary artery (LAD) was repeated at 30-min intervals in anesthetized open-chest dogs while recording MAP or measuring [K+]o with a potassium-sensitive valinomycin electrode from the epicardial center of the ischemic myocardium. Nicorandil (0.2-0.5 mg/kg) was administered intravenously (i.v.) 5 min before the third occlusion, and the data were compared with those during the second occlusion (control). During the second occlusion, MAP duration at 90% repolarization (APD90) shortened (mean rate for 5 min, 13 +/- 3%, n = 11) and [K+]o increased from 3.7 +/- 0.1 to 6.2 +/- 0.8 mM at 5 min (n = 12). These changes were reversed < or = 3 min after reperfusion. Before the third occlusion, baseline APD90 and [K+]o were not altered by nicorandil; however, the extent of occlusion-induced shortening of APD90 (25 +/- 4%) and [K+]o increase (7.8 +/- 1.6 mM) was augmented by the pretreatment. The drug effect was attenuated by a concomitant pretreatment with 5-hydroxydecanoate, a specific blocker of KATP channels (n = 2). The prevalence of ventricular fibrillation (VF) during occlusion/reperfusion sequence was reduced after nicorandil (1 of 25 vs. 5 of 25) without de novo VF. These results suggest that nicorandil at a clinical dose facilitates regional ischemia-induced activation of myocardial KATP channels without causing serious proarrhythmia. Such a property might help protect the myocardium against ischemia/reperfusion damage.     

Hepatic ischemia-reperfusion injury modification during liver surgery in rats: pretreatment with nifedipine or misoprostol

The aim of the study was to determine if pretreatment with misoprostol (a prostaglandin analogue) or nifedipine (a calcium antagonist), know protectants of the whole liver, would ameliorate the ischemia-reperfusion injury (IRI) of resected liver associated with vascular occlusion. Male Wistar rats were allocated to 5 groups (n = 20 each group): sham-operated, liver resection only, liver resection plus pretreatment with 0.1 mg/kg misoprostol, 10 mg/kg, or 2 mg/kg nifedipine during the 3 days before IRI with liver resection. Fifteen percent of the liver was made ischemic by 30-minute continuous vascular occlusion, and the remaining 85% nonischemic liver was resected. The model was designed to have survival of the rats so that liver function could be studied over 3 weeks. Seventeen of 20 control resection rats survived indicating a suitable model for study. The bilirubin level was reduced by 25% on postoperative days 3 through 23 with misoprostol. The serum alanine aminotransferase (ALT) peak was significantly lower on day 1 with misoprostol and high-dose nifedipine (both reduced to half the control resection value). There was a modest but significant reduction of serum alkaline phosphatase (SAP) for low-dose nifedipine on days 1, 2, and 23. Prothrombin had a lower peak and lower values on days 1 through 4 with misoprostol. Liver histological changes were minor, being cytoplasmic vacuolization only, and was slightly more marked in the nifedipine groups. Preoperative misoprostol 0.1 mg/kg and nifedipine 10 mg/kg each ameliorate the IRI associated with liver resection, as measured by liver function tests. Different aspects of liver function were altered by the different agents. These results justify initiating a trial for human liver resections.     

Retrospective estimation of exposure to benzene in a leukaemia case-control study of petroleum marketing and distribution workers in the United Kingdom

FK506 (tacrolimus), a potent immunosuppressant, is used for inhibiting allograft rejection in the organ transplantation field. In a preclinical toxicity study in rats, FK506 induced various toxicities, including renal and pancreatic injuries. One of these toxic findings was cataract, and we have found that cataract appeared in rats dosed orally with FK506 for 13 weeks and more. Therefore, to better elucidate the onset mechanism of FK506-induced cataract, we measured biochemical parameters, such as sorbitol, Na,K-ATPase and glutathione in the lens of rats. Rats were dosed with FK506 in oral daily doses of 0.2, 1 or 5 mg/kg for 13 weeks, the lowest dose of which approximated the expected clinical dosage. Cataract developed in the 5-mg/kg/day group, with an incidence of 25%, whereas no cataract formation was observed in the 0.2- or 1-mg/kg/day groups. Five mg/kg/day led an increase of sorbitol and a decrease of reduced type glutathione, but did not affect Na,K-ATPase activity of the lens. FK506 is known to have diabetogenicity mediated through pancreatic injury, which appears as vacuolation of islet cell in rats. Five mg/kg/day of FK506 induced an elevation of blood glucose associated with glucose intolerance, and decrease of both basal insulin level and insulin content in the pancreas, and the changes were in parallel with the cataract development in the present study. On the other hand, diabetic parameters did not change in the 0.2- or 1-mg/kg/day groups. These observation suggest that diabetes developed in the rats dosed with 5 mg/kg/day of FK506. Coadministration of a novel aldose reductase inhibitor, Zenarestat, at an oral dose of 50 mg/kg/day resulted in a reduction of incidence of the FK506-induced cataract and a decrease of sorbitol levels in the lens when compared to that in the lens of rats dosed with 5 mg/kg/day of FK506. These results suggest that FK506-induced cataract in rats is due to an accumulation of sorbitol in the lens, secondary to the diabetogenic effect of FK506. FK506 treatment at the doses of 0.2 and 1 mg/kg/day neither affected parameters indicative of diabetes nor induced cataract in rats, suggesting that the cataract would not develop with FK506 if diabetic parameters were kept under control.     

Interaction between neuronal nitric oxide synthase and inhibitory G protein activity in heart rate regulation in conscious mice

Nitric oxide (NO) synthesized within mammalian sinoatrial cells has been shown to participate in cholinergic control of heart rate (HR). However, it is not known whether NO synthesized within neurons plays a role in HR regulation. HR dynamics were measured in 24 wild-type (WT) mice and 24 mice in which the gene for neuronal NO synthase (nNOS) was absent (nNOS-/- mice). Mean HR and HR variability were compared in subsets of these animals at baseline, after parasympathetic blockade with atropine (0.5 mg/kg i.p.), after beta-adrenergic blockade with propranolol (1 mg/kg i.p.), and after combined autonomic blockade. Other animals underwent pressor challenge with phenylephrine (3 mg/kg i.p.) after beta-adrenergic blockade to test for a baroreflex-mediated cardioinhibitory response. The latter experiments were then repeated after inactivation of inhibitory G proteins with pertussis toxin (PTX) (30 microgram/kg i.p.). At baseline, nNOS-/- mice had higher mean HR (711+/-8 vs. 650+/-8 bpm, P = 0.0004) and lower HR variance (424+/-70 vs. 1,112+/-174 bpm2, P = 0.001) compared with WT mice. In nNOS-/- mice, atropine administration led to a much smaller change in mean HR (-2+/-9 vs. 49+/-5 bpm, P = 0.0008) and in HR variance (64+/-24 vs. -903+/-295 bpm2, P = 0.02) than in WT mice. In contrast, propranolol administration and combined autonomic blockade led to similar changes in mean HR between the two groups. After beta-adrenergic blockade, phenylephrine injection elicited a fall in mean HR and rise in HR variance in WT mice that was partially attenuated after treatment with PTX. The response to pressor challenge in nNOS-/- mice before PTX administration was similar to that in WT mice. However, PTX-treated nNOS-/- mice had a dramatically attenuated response to phenylephrine. These findings suggest that the absence of nNOS activity leads to reduced baseline parasympathetic tone, but does not prevent baroreflex-mediated cardioinhibition unless inhibitory G proteins are also inactivated. Thus, neuronally derived NO and cardiac inhibitory G protein activity serve as parallel pathways to mediate autonomic slowing of heart rate in the mouse.     

Should unipolar leads be implanted in the atrium? A Holter electrocardiographic comparison of threshold adapted unipolar and high sensitive bipolar sensing

1. The effects of nifedipine on both levcromakalim-induced membrane currents and unitary currents in pig proximal urethra were investigated by use of patch-clamp techniques (conventional whole-cell configuration and cell-attached patches). 2. Nifedipine had a voltage-dependent inhibitory effect on voltage-dependent Ba2+ currents at - 50 mV (Ki=30.6 nM). 3. In current-clamp mode, subsequent application of higher concentrations of nifedipine (> or =30 microM) caused a significant depolarization even after the membrane potential had been hyperpolarized to approximately -82 mV by application of 100 microM levcromakalim. 4. The 100 microM levcromakalim-induced inward current (symmetrical 140 mM K+ conditions, -50 mV) was inhibited by additional application of three different types of Ca antagonists (nifedipine, verapamil and diltiazem, all at 100 microM). In contrast, Bay K 8644 (1 microM) possessed no activating effect on the amplitude of this glibenclamide-sensitive current. 5. When 100 microM nifedipine was included in the pipette solution during conventional whole-cell recording at -50 mV, application of levcromakalim (100 microM) caused a significant inward membrane current which was suppressed by 5 microM glibenclamide. On the other hand, inclusion of 5 microM glibenclamide in the pipette solution prevented levcromakalim from inducing an inward membrane current. 6. The levcromakalim-induced K+ channel openings in cell-attached configuration were suppressed by subsequent application of 5 microM glibenclamide but not of 100 microM nifedipine. 7. These results suggest that in pig proximal urethra, nifedipine inhibits the glibenclamide-sensitive 43 pS K+ channel activity mainly through extracellular blocking actions on the K+ channel itself.