Thiamine tetrahydrofurfuryl disulfide improves energy metabolism and physical performance during physical-fatigue loading in rats

Impaired energy metabolism is considered a possible cause of fatigue. The thiamine derivative, thiamine tetrahydrofurfuryl disulfide (TTFD), is prescribed and is also an over-the-counter drug for the attenuation of fatigue. It is readily absorbed from the intestinal tract and converted into thiamine pyrophosphate (TPP), which plays an important role as a cofactor for enzymes of metabolic pathways involved in the production of adenosine triphosphate (ATP). We postulated that TTFD has an anti-fatigue effect by improving energy metabolism during physical-fatigue loading. Here, we initially used the forced swimming test to determine whether daily TTFD or thiamine for 5 days has anti-fatigue effects on weight-loaded rats. The swimming duration of TTFD-, but not of thiamine-treated rats, was significantly longer than that of control rats (P < .05). Based on these findings, we examined changes in the levels of thiamine and its phosphate esters in various organs and the effect of TTFD on ATP levels in skeletal muscle after forced swimming, to determine the cellular mechanisms of the anti-fatigue effect of TTFD. Daily TTFD resulted in a characteristic distribution of thiamine and its phosphate esters in rat skeletal muscle, liver, kidney, heart, brain, and plasma. Furthermore, daily TTFD attenuated the decrease in ATP content in the skeletal muscle caused by forced swimming with a weight load for a defined period (150 s). These results indicate that TTFD exerts anti-fatigue effects by improving energy metabolism during physical fatigue.

Absence of interactive effects of trans-1,2-cyclohexanediol, a major metabolite of the side-chain of candesartan cilexetil, on digoxin-induced arrhythmias in dogs

trans-1,2-Cyclohexanediol, the major metabolite of the cilexetil moiety of candesartan cilexetil (CC), has been reported to have potent pro-arrhythmic effects in dogs with congestive heart failure (CHF), especially when co-administered with digoxin. To verify this and to clarify the clinical relevance and the underlying mechanisms, a series of in vivo and in vitro experiments was conducted. When CC up to 300 mg/kg was administered orally to intact dogs, no changes in the electrocardiograms (ECG) or the required cumulative doses of ouabain to induce ventricular arrhythmias were observed. In dogs with CHF, intravenous bolus administration of trans-1,2-cyclohexanediol at 4 mg/kg followed by continuous infusion at 0.1 mg x kg(-)(1) x min(-)(1) had no effects on the ECG parameters, the type, incidence, and onset time of digoxin-induced arrhythmias or the metabolism of digoxin. In an in vitro experiment using isolated guinea pig papillary muscle, trans-1,2-cyclohexanediol (1 - 100 micromol/L) showed no effects on any parameter of the action potentials. Because no effects were observed in these experiments where the exposure levels of trans-1,2-cyclohexanediol were extremely high compared to those in humans given the maximum therapeutic dose of CC, it is unlikely that CC would induce arrhythmias in clinical use even in patients treated with cardiac glycosides.

Bile acids influence hepatic chemiluminescence in normal and oxidative-stressed rats

The aim of the present study was to clarify whether bile acids influence chemiluminescence (CL) in the liver in vivo. Hepatic CL was determined on the surface of the liver of anaesthetized rats by using a photon counter. In normal rats, hepatic CL was significantly decreased 30 min after enteral administration of chenodeoxycholic acid (CDCA) or deoxycholic acid (DCA), but returned to its initial level 3 h later, after part of the CDCA administered was metabolized. Ursodeoxycholic acid (UDCA) and cholic acid had no effect on CL. In contrast, hepatic CL was markedly increased 30 min after CDCA or DCA administration in rats given either buthionine sulphoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase, or diethyldithiocarbamate (DDC), an inhibitor of both superoxide dismutase and glutathione peroxidase. Chenodeoxycholic acid further increased the CL of BSO- or DDC-treated rats during inhalation of oxygen via a tracheal cannula. Coadministration of UDCA eliminated the effects of CDCA on the hepatic CL of normal and BSO- or DDC-treated rats with or without oxygen inhalation. We conclude that cytotoxic bile acids, such as CDCA, increase CL in the antioxidants-depleted or oxidative-stressed liver in vivo, but that UDCA prevents CDCA from developing CL.

Effects of a new endothelin receptor antagonist, TAK-044, on myocardial stunning in dogs

The effects of a new endothelin receptor antagonist, TAK-044, (cyclo[D-alpha-aspartyl-3-[(4-phenylpiperazin-1-yl)carbonyl]L-alan yl-L-alpha aspartyl-D-2-(2-thienyl)glycyl-L-leucyl-D-tryptophyl]disodium salt, on ischemic and post-ischemic myocardial dysfunction (stunned myocardium) were studied in anesthetized open-chest dogs. A short (15 min) occlusion of the left anterior descending coronary artery followed by 5-h reperfusion significantly reduced myocardial segment shortening during and after the ischemic period in the ischemic region. Regional myocardial blood flow was also decreased significantly 10 min after the occlusion, whereas it returned almost completely to its pre-ischemic value 5 h after reperfusion TAK-044 (3 mg/kg,i.v.) administered 10 min before occlusion significantly improved the reduced myocardial segment shortening in the ischemic region during and after occlusion. Cardiovascular hemodynamics and regional myocardial blood flow in a TAK-044-treated group were identical to those in the control group. These results indicate that endogenous endothelin contributes to the cause of ischemic and post-ischemic myocardial dysfunction without changing either hemodynamics or regional myocardial blood flow.

Antihypertensive and cardiovascular effects of a new potassium channel opener, TCV-295, in rats and dogs

The antihypertensive and cardiovascular properties of a new potassium channel opener, TCV-295, were studied in rats and dogs. In conscious, spontaneously hypertensive rats (SHR), TCV-295 (0.03-1 mg/kg orally, p.o.) reduced blood pressure (BP) dose dependently with slow onset of action. The antihypertensive effects induced by TCV-295 lasted much longer than those of levcromakalim and nisoldipine, and the reflex tachycardia it evoked was less marked than that evoked by these drugs as compared at doses showing similar maximal hypotensive effects. Glibenclamide (30 mg/kg intravenously, i.v.) inhibited the TCV-295-induced BP decrease in anesthetized rats. In a 4-week chronic dosing study in SHR, TCV-295 (0.3 mg/kg/day p.o.) produced neither potentiation nor tolerance to its antihypertensive action and no rebound hypertension occurred when drug treatment was discontinued. In anesthetized normotensive dogs, TCV-295 (4.5 micrograms/kg/min i.v.) induced BP reductions accompanied by reductions in systemic vascular resistance. TCV-295 also reduced resistances of the coronary, vertebral, mesenteric, and renal vascular beds, and the most marked effect was observed in the coronary vasculature. Myocardial O2 consumption was reduced by TCV-295, possibly owing to afterload decrease. These results suggest that TCV-295 has a desirable profile for an antihypertensive agent.

Effects of TCV-309, a novel PAF antagonist, on circulatory shock and hematological abnormality induced by endotoxin in dogs

We investigated the effects of TCV-309, a novel platelet activating factor (PAF) antagonist, on circulatory dysfunction and hematological abnormalities in experimental canine endotoxin (ET) shock. ET caused biphasic hypotension with a decrease in cardiac output (CO), left ventricular systolic pressure (LVP) and its dp/dt(max). The first hypotensive phase occurred within 15 min, and the second phase between 90 and 180 min following the injection of ET. Pulmonary vascular resistance (PVR) abruptly increased at 15 min with a partial recovery, and was then sustained at twice the basal value throughout the experiment. TCV-309 attenuated the hypotension, the decrease in CO, LVP and its dp/dt(max), and the increase in PVR. TCV-309 had no significant effect on the increase in TPR. The decrease in plasma fibrinogen and the increase in hematocrit and plasma lactate were significantly attenuated by TCV-309. These data suggest that PAF may be a key mediator leading to shock in sepsis.

Effects of a new endothelin antagonist, TAK-044, on post-ischemic acute renal failure in rats

Protective effects of a new endothelin (ET) receptor antagonist, TAK-044, were studied in a model of acute renal failure (ARF) in rats. ARF was induced by clamping the left renal pedicle for 45 minutes with contralateral nephrectomy and subsequent reperfusion of the left kidney. Plasma creatinine concentration (Pcr) increased to 2.28 mg/dl 24 hours after reperfusion of the ischemic kidney. Intravenous administration of TAK-044 (1-10mg/kg) prior to renal occlusion dose-dependently but partially attenuated the increase in Pcr and the morphological damages of the kidney. ET-1 and ET-3 increased perfusion pressure in isolated kidney preparations with similar potency, indicating that the renal vasoconstriction evoked by these ET isomers is mainly via ETB receptors, and TAK-044 (10nM) shifted the ET-1 dose-response curve to the right by a factor about 10. In a rat renal membrane fraction, ET-1 showed competitive inhibition of specific [125I]ET-1 binding with an IC50 value of 0.34nM and a Hill slope of 1.10. ET-3 did so with a higher IC50 value (3.3nM) and a lower Hill slope (0.56), suggesting that rat kidney contains both ETA and another receptor subtype, probably ETB. TAK-044 inhibited ET-1 binding with an IC50 value of 6.6nM and a Hill slope of 0.41. Plasma concentrations of immunoreactive TAK-044 were maintained over 7nM for 8 hours following i.v. injection of 10mg/kg TAK-044. These results suggest that endogenous ET is involved in the pathogenesis of post-ischemic ARF, at least, in part and that TAK-044 provided protective effects against ARF by blocking ET receptors, possibly both ETA and ETB receptors in renal vasculature and parenchymal cells.

Cardiovascular effects of endothelin in dogs: positive inotropic action in vivo

Endothelin, administered i.v. to anesthetized dogs, dose dependently increased the cardiac output, left ventricular systolic pressure (LVSP), and maximum upstroke velocity (max dp/dt) of the LVSP for about 10 min without changing the heart rate. Thereafter the cardiac output decreased to below the control level but max dp/dt decreased to the control level. The arterial pressure and total peripheral resistance showed an initial, transient decrease followed by a sustained increase. These results suggest that endothelin has positive inotropic and long-lasting vasoconstrictive effects preceded by transient vasodilatation in vivo.

Positive inotropic and vasoconstrictive effects of endothelin-1 in in vivo and in vitro experiments: characteristics and the role of L-type calcium channels

Cardiac and vascular effects of endothelin-1 (ET-1) were studied in hemodynamic models in vivo and in isolated artery and heart tissues. The hemodynamic changes induced by ET-1 (30-300 pmol/kg i.v.) in dogs were increases in blood pressure, cardiac output, and ventricular contractility. Ring preparations of canine coronary artery and rabbit thoracic aorta showed vasoconstrictive responses to ET-1 (10(-10) M and over) with an EC50 of 3-10 x 10(-9) M. Nifedipine 10(-5) M did not reverse these effects completely. ET-1 had positive inotropic effects from 10(-10) M in rabbit papillary muscles. It lengthened the action potential duration by 16% and increased the developed tension by 180% (10(-8) M). In contrast, Bay K 8644 (10(-7) M) produced similar lengthening (17%) in the duration with only a 37% increase in the tension. This suggests a difference in the mechanisms of the positive inotropic effects between these two agents. We conclude that ET-1 has positive inotropic and vasoconstrictive effects, and that these ET-1-induced contractions in ventricular muscles and arteries cannot be explained thoroughly by the increase in currents through voltage-dependent calcium channels.

Calcium channel blocking action of franidipine hydrochloride (CV-4093.2HCl) in vitro and in vivo

The calcium-channel blocking action of franidipine (CV-4093.2HCl) was investigated in vitro and in vivo. CV-4093.2HCl inhibited the 60 mM K+-induced contraction of rabbit aorta and those of coronary, renal, mesenteric and femoral arteries of dog less potently than nifedipine and nicardipine. In dog portal and femoral veins, CV-4093.2HCl inhibited K+-induced contraction as potently as nifedipine and nicardipine did. The inhibitory effect of this drug was fully developed by pretreatment for 60 min, and it lasted long after washout. The drug inhibited both K+-induced 45Ca-influx and K+-induced contraction at a similar concentration range in rabbit aorta and dog portal vein, but had no effect on 45Ca-efflux from either vessel. On the other hand, in the isolated, perfused kidneys and mesenteric vascular beds of SHR, CV-4093.2HCl inhibited K+-induced vasoconstriction more effectively than did nifedipine. Moreover, in pithed rats (i.v.) and ganglion-blocked conscious SHR (p.o.), CV-4093.2HCl inhibited more potently alpha 2-adrenergic pressor responses than did nicardipine. These pharmacological properties of CV-4093.2HCl, especially those seen in the isolated, perfused kidney and mesenteric vascular beds, may be responsible for its potent and long-lasting action as an antihypertensive agent.