Orally administered rapamycin does not modify rat aortic vascular tone

Rapamycin (RP; rapamune, sirolimus) is a potent inhibitor of vascular smooth muscle cell proliferation and migration. RP was demonstrated to reduce vascular neointimal formation in different animal models of vascular smooth muscle cell proliferation, and clinical use of RP-eluting stents promotes significant reductions in in-stent restenosis rates. However, high costs still preclude the widespread use of these devices. Oral administration of RP associated to bare metal stent delivery has been advocated as an effective and considerably less expensive alternative for restenosis prevention. It is noteworthy that the presence of RP-eluting stents has been associated with reduced endothelial-dependent vasodilation and coronary spasm. In addition, RP has been demonstrated to prevent vasculogenesis. This study evaluated the effects of RP on endothelium-dependent vascular tone and demonstrated that in vitro incubation with high concentrations of RP did not modify either contraction or relaxation of aortic rings. Similar results were obtained after in vivo administration of the drug. These findings suggest that function of adult, non-proliferative rat endothelial cells involved in vascular tone control is not affected by orally administered RP.     

N-acetylcysteine does not protect HepG2 cells against acetaminophen-induced apoptosis

Acetaminophen in large doses is well-known as hepatotoxic, and early therapy with N-acetylcysteine is frequently life-saving. However, in later stages of acetaminophen poisoning, treatment with N-acetylcysteine is not always effective. Although some of the pathways of acetaminophen toxicity and the effect of N-acetylcysteine have been elucidated, in depth information on this process is still lacking. Hepatoma-derived HepG2 cultured cells were exposed to acetaminophen (5 and 10 mM), with or without N-acetylcysteine (5 mM), for 24 and 48 hr. For the assessment of oxidative damage, apoptosis and necrosis, we followed redox status, glutathione content, nuclear fragmentation, phosphatidylserine externalization and ultrastructural changes. Variations in Ca2+ level and number of mitochondrial dense granules were also studied. Acetaminophen treatment of HepG2 cells caused oxidative damage and apoptosis. Significant decrease of cellular redox potential and glutathione content were time- and concentration-dependent. The protective effect of N-acetylcysteine was expressed by an increase of intracellular glutathione and of the level of metabolic reduction of the redox indicator Alamar Blue. The apoptogenic effect of acetaminophen was assessed by flow cytometry of annexin V binding, nuclear hypodiploidity, intracellular Ca2+, as well as by ultrastructural examination. Beyond 24 hr of acetaminophen exposure, necrosis was also noticed. We conclude that acetaminophen-induced oxidative damage in HepG2 cultured cells can be prevented by exposure to N-acetylcysteine. However, apoptosis, either early or late, here demonstrated, is not avoided by exposure to N-acetylcysteine. N-Acetylcysteine did not prevent acetaminophen-induced plasma membrane asymmetry, nuclear damage, alterations of Ca2+ homeostasis and ultrastructural changes.     

Ketamine does not impair heat tolerance in rats

Exposure to organophosphorus compounds, either pesticides or chemical warfare agents such as soman or sarin, represents a major health problem. Organophosphorus poisoning may induce seizures, status epilepticus and even brain lesions if untreated. Ketamine, an antagonist of glutamatergic receptors, was recently proved to be effective in combination with atropine sulfate as an anticonvulsant and neuroprotectant in mice and guinea pigs exposed to soman. Organophosphorus exposure may also occur in conditions of contemporary heat exposure. Since both MK-801, a more potent glutamatergic antagonist than ketamine, and atropine sulfate are detrimental for thermoregulation, we evaluated the pathophysiological consequences of ketamine/atropine combinations in a hot environment. Male wistar rats were exposed to 38°C ambient temperature and treated with atropine sulfate and/or ketamine (anesthetic and subanesthetic doses). The abdominal temperature and spontaneous locomotor activity were continuously monitored using telemetry. At the end of heat exposure, blood chemistry and the mRNA expression of some specific genes in the brain were assessed. Unlike MK-801, ketamine did not induce any deleterious effect on thermoregulation in rats. Conversely, atropine sulfate led to heatstroke and depressed the heat-induced blood corticosterone increase. Furthermore, it induced a dramatic increase in Hsp70 and c-Fos mRNA levels and a decrease in IκBα mRNA expression, both suggesting brain aggression. When combined with the anesthetic dose of ketamine, some of the atropine-induced metabolic disturbances were modified. In conclusion, ketamine can be used in hot environment and may even limit some of the biological alterations induced by atropine sulfate in these conditions.     

Increased nitroglycerin-induced relaxation by genistein in rat aortic rings.

The effect of genistein, a tyrosine kinase inhibitor, on nitroglycerin-induced relaxation was examined in rat aortic rings contracted by phenylephrine. In rat aortic rings, genistein (10(-5) M and 3x10(-5) M), a tyrosine kinase inhibitor, but not daidzein, an analogue of genistein, increased relaxation induced by nitroglycerin in a concentration-dependent manner. Iberiotoxin, an inhibitor of Ca2+ -activated K+ channels, inhibited the relaxation induced by nitroglycerin, but it did not affect the effect of genistein. Glibenclamide, an inhibitor of ATP-sensitive K+ channels, did not affect the relaxation induced by nitroglycerin. Theophylline, an inhibitor of cyclic AMP-dependent phosphodiesterase, increased the relaxation induced by nitroglycerin, and genistein (10(-5) M) failed to affect the relaxation induced by nitroglycerin in the presence of theophylline. Genistein also inhibited the activity of cyclic AMP-dependent phosphodiesterase. In addition, 6-[4-(4'-pyridyl)amino phenyl]-4,5-dihydro-3(2H)-pyridazinone hydrochloride, an inhibitor of cyclic GMP-inhibitable cyclic AMP phosphodiesterase, inhibited the relaxation induced by nitroglycerin. These results suggest that, in the rat aortic rings, genistein inhibits cyclic AMP-dependent phosphodiesterase activities, resulting in the increase of the relaxation induced by nitroglycerin.     

The angiotensin II-receptor antagonist losartan does not prevent hemodynamic or vascular tolerance to nitroglycerin.

Tolerance may involve increased production of angiotensin II. We tested the hypothesis that losartan would prevent the development of tolerance to continuous transdermal nitroglycerin (GTN). Twenty volunteers received losartan, 75 mg/day, or placebo in a randomized, double-blind, parallel fashion. After 1 week, continuous transdermal GTN, 0.6 mg/h, was given, in addition to losartan or placebo, to all volunteers for 1 week. Standing systolic blood pressure (SBP) and heart rate were measured, and forearm venous volume responses to sublingual GTN were evaluated. Measurements were made at baseline, after 1 week of losartan versus placebo, 3 h after initial therapy with transdermal GTN, and after 1 week of continuous transdermal GTN given in combination with losartan versus placebo. After sustained GTN therapy, SBP was unchanged from baseline in both groups, indicating that losartan did not prevent the development of tolerance. Tolerance also developed to the forearm venous volume responses and was not prevented by losartan. Therapy with an angiotensin II-receptor antagonist does not prevent the development of tolerance to continuous transdermal GTN.     

The potentiation of nitroglycerin-induced relaxation by PKG inhibition in rat aortic rings

• 1.1. In rat aortic rings precontracted by phenylephrine, H7 (10⁻⁵M) and staurosporine (10⁻⁷M), which inhibit PKA, PKG and PKC, and H-89 (10⁻⁶M), which inhibits PKA and PKG, potentiated relaxations induced by nitroglycerin. Forskolin-induced relaxations were not affected by H7 (10⁻⁵M).
• 2.2. Nitroglycerin-induced relaxations were not affected by calphostin-C (10⁻⁷M), which inhibits PKC, H-89 (10⁻⁷M), which inhibits PKA, and staurosporine (2 × 10⁻⁹M), which inhibits PKC.
• 3.3. Iberiotoxin (3 × 10⁻⁸M), an inhibitor of large conductance Kca channels, partly inhibited the relaxation induced by nitroglycerin and completely inhibited the potentiating effect of H7 on nitroglyc. erin-induced relaxations.
• 4.4. The potentiating effect of zaprinast (10⁻⁵M), an inhibitor of cGMP-phosphodiesterase, on nitroglycerin-induced relaxation was not affected by iberiotoxin. In the presence of methylene blue (10⁻⁵M), an inhibitor of guanylate cyclase, the residual relaxing response to nitroglycerin was not affected by H7, but it was inhibited by iberiotoxin.
• 5.5. These results suggest that the potentiation of nitroglycerin-induced relaxation by H7, staurosporine and H-89 may be due to inhibition of PKG.

     

Oral verapamil does not affect glucose tolerance in non-diabetics.

Verapamil, a calcium antagonist used to treat angina pectoris, inhibits insulin release in vitro and, when administered intravenously to humans, decreases glucose tolerance. Oral verapamil, 120 mg/day for 1 week increasing thereafter to 240 mg/day in divided doses, was given to nine non-diabetic patients with angina pectoris for 4 weeks. The glucose and insulin responses to a standard glucose load showed no significant difference before and after verapamil. Oral verapamil in the doses used in this study had no significant effect on glucose tolerance in non-diabetics.     

The potent calcitonin gene-related peptide receptor antagonist, telcagepant, does not affect nitroglycerin-induced vasodilation in healthy men

AIMS

To assess the effect of the calcitonin gene-related peptide (CGRP) receptor antagonist, telcagepant, on the haemodynamic response to sublingual nitroglycerin (NTG).

METHODS

Twenty-two healthy male volunteers participated in a randomized, placebo-controlled, double-blind, two-period, crossover study. Subjects received 500 mg telcagepant or placebo followed, 1.5 h later, by 0.4 mg NTG. To assess the haemodynamic response the following vascular parameters were measured: blood pressure, aortic augmentation index (AIx) and brachial artery diameter (BAD). Data are presented as mean (95% confidence interval, CI).

RESULTS

The aortic AIx following NTG decreased by −18.50 (−21.02, −15.98) % after telcagepant vs. −17.28 (−19.80, −14.76) % after placebo. The BAD fold increase following NTG was 1.14 (1.12, 1.17) after telcagepant vs. 1.13 (1.10, 1.15) after placebo. For both AIx and BAD, the hypothesis that telcagepant does not significantly affect the changes induced by NTG is supported (P < 0.0001). In addition, no vasoconstrictor effect of telcagepant could be demonstrated.

CONCLUSIONS

Telcagepant did not affect NTG-induced haemodynamic changes. These data suggest that NTG-induced vasodilation is not CGRP dependent.     

Comparative relaxant effects of nitroglycerin in isolated rings from various canine vascular beds

The potency of nitroglycerin to block contractions produced by norepinephrine, serotonin and KCl, was examined in isolated large artery rings obtained from the coronary, femoral, mesenteric and renal vascular bed of the dog. Nitroglycerin was a more potent antagonist (10-10,000 fold) of contractions produced by norepinephrine in the large coronary artery than in the other three vascular beds. Similarly, nitroglycerin blocked responses to serotonin and KCl (40 mM) more effectively in the coronary vs the femoral artery. These results suggest that nitroglycerin has selectivity for the large coronary artery of the dog in blocking contractions produced by three constrictor substances that have been implicated in coronary vasospasm.     

Naloxone does not modify the hemodynamic and neuroendocrine effects of clonidine in normal humans

The relationship between central opioidergic and noradrenergic central control mechanisms of blood pressure was investigated in normal men by evaluating the interference exerted by naloxone, a specific opiate antagonist, on the cardiovascular (blood pressure and heart rate) and neuroendocrine [human growth hormone (HGH) stimulation] effects of clonidine, a centrally acting alpha-adrenergic agonist, according to two different protocols. In series 1, the effects of placebo (normal saline), clonidine (0.15 mg i.v.), and naloxone (0.4 mg i.v.) were compared with that of clonidine plus naloxone (0.15 and 0.4 mg i.v., respectively), in seven normal male subjects. Clonidine decreased blood pressure and heart rate, and increased HGH levels. Naloxone administered alone (0.4 mg i.v.) did not modify blood pressure, heart rate, and HGH levels, while naloxone (0.4 mg) pretreatment left unaltered the hemodynamic and neuroendocrine effects of clonidine. In series 2, in five additional normal males, the effect of increasing doses of naloxone (0.4, 2.0, and 8.0 mg i.v.) on the pharmacodynamic activity of clonidine (0.15 mg i.v.) was further evaluated. Clonidine alone decreased blood pressure and heart rate and increased HGH levels, while naloxone pretreatment, in the whole range of doses studied, did not significantly modify the action of clonidine. These data suggest that a central opioidergic tone does not modulate the effect of central alpha-noradrenergic stimulation in normal humans.     

Subchronic administration of LY354740 does not modify ketamine-evoked behavior and neuronal activity in rats

Acute treatment with LY354740 {1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate}, a potent and selective agonist for group II metabotropic glutamate receptors (mGlu2/3), has previously been shown to block some schizophrenia-like effects of N-methyl-D-aspartate (NMDA) receptor antagonists, suggesting a novel therapeutic strategy for schizophrenia. The present study examined the effects of subchronic pretreatment with LY354740 (0.3, 3 and 10 mg/kg i.p.) on ketamine-evoked (12 mg/kg s.c.) prepulse inhibition deficits, hyperlocomotion and c-fos expression. At all doses, LY354740 failed to reverse both behavioral and neuronal effects of the ketamine. These results therefore do not support the putative antipsychotic role of LY354740.     

Recovery of vascular smooth muscle relaxation from nitroglycerin-induced tolerance following a drug-free interval. A time-course in vitro study.

Hemodynamic tolerance occurs upon continuous exposure of vascular tissues to nitroglycerin (NTG). This phenomenon is believed to be due to the depletion of the tissue sulfhydryl (SH) group, which is essential for NTG-induced increase in tissue cyclic GMP and vasorelaxation. To determine the effect of an NTG-free interval on recovery of tissue cyclic GMP accumulation and vasorelaxation following development of NTG tolerance, isolated rat aortic rings were kept in Krebs physiologic buffer at 37 degrees, precontracted with epinephrine, and exposed to NTG. The mean concentration of NTG, which relaxed the rings by 50% (EC50) upon first exposure, was 1.1 x 10(-7) M (N = 20), and vascular cyclic GMP levels after NTG increased from 21 to 46 fmol/mg (P less than 0.02). A second exposure to NTG 15 min later increased the EC50 to 1.3 x 10(-4) M and cyclic GMP levels did not change (P less than 0.001 vs first NTG exposure), indicating tolerance to NTG. However, acetylcholine-mediated relaxation of aortic rings was preserved even in NTG-tolerant rings. A second exposure of tissues to NTG separated by 30, 60, and 120 min from the first exposure progressively decreased the EC50, such that at 120 min the EC50 of NTG was 0.4 x 10(-7) M (P = NS vs first NTG exposure). Tissue cyclic GMP levels increased from 14 to 71 fmol/mg (P = NS vs first NTG exposure). These data confirm development of tolerance to the vasorelaxant effects of NTG following initial exposure. An interval of 2 hr between multiple exposures of tissues to NTG results in preservation of the smooth muscle relaxation and an increase in tissue cyclic GMP in response to NTG.     

Postsynaptic alpha 1-blockade with terazosin does not modify insulin sensitivity in nonobese normotensive subjects.

Plasma insulin levels and the sensitivity of peripheral tissue to insulin (SI) have pathophysiological, therapeutic, and possibly also prognostic relevance. To investigate the effects of short-term selective alpha 1-adrenergic receptor blockade in nonobese normotensive humans on glucose and lipoprotein homeostasis, we assessed SI (determined by the minimal model method of Bergman), before and after glucose load plasma, glucose, and insulin levels, serum total triglycerides and lipoprotein cholesterol fractions, and some other variables in 20 healthy young men (26 +/- 1 years old, mean +/- SEM) during placebo and after 5 weeks of terazosin administration at a dose up to 10 mg once daily. Measurements were made after 3 days of standard diet (2,500 kcal/day, 45% carbohydrates, 40% fat, and 15% proteins) and after an overnight fast. Compared to placebo, terazosin decreased the upright systolic blood pressure (placebo vs. terazosin: 125 +/- 2 vs. 117 +/- 2 mm Hg, p less than 0.05) and increased supine (63 +/- 2 vs. 70 +/- 1 beats/min, p less than 0.05) and upright (77 +/- 2 vs. 88 +/- 2 beats/min, p less than 0.01) heart rates, while the body weight was unaltered. Terazosin did not significantly modify fasting plasma glucose (5.08 +/- 0.09 vs. 5.23 +/- 0.08 mmol/L, respectively), or insulin (8.9 +/- 0.5 vs. 8.6 +/- 0.6 microU/ml), SI (14.3 +/- 1.8 vs 11.8 +/- 1.5 x 10(-4)/min/microU/ml), the areas under the insulin or glucose curves, serum total triglycerides, and cholesterol or lipoprotein cholesterol fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Desensitization of guanylate cyclase in nitrate tolerance does not impair endothelium-dependent responses

Tolerance of vascular smooth muscle to nitroglycerin could be induced by an impaired biotransformation of nitroglycerin to nitric oxide, the activator of soluble guanylate cyclase, or by desensitization of guanylate cyclase to activation with nitric oxide. The latter would imply that there would also be tolerance to nitric oxide delivered from sodium nitroprusside or endothelial cells. Therefore, endothelium-denuded segments of rabbit aorta were treated with nitroglycerin to induce tolerance, and were then assessed for mechanical response, cyclic GMP content, and activity of soluble guanylate cyclase after addition of nitrovasodilators. Nitrate tolerance decreased the vasodilation and the increase in cyclic GMP elicited by nitroglycerin, but not that elicited by sodium nitroprusside or endothelium-derived relaxing factor, in norepinephrine-contracted segments. However, soluble guanylate cyclase in the supernatants of homogenates of nitrate-tolerant aortas was desensitized to activation with nitroglycerin and sodium nitroprusside. As the guanylate cyclase was still responsive to activation by nitric oxide in the intact, tolerant smooth muscle, an impaired biotransformation of nitroglycerin rather than desensitization of soluble guanylate cyclase may be the mechanism by which nitrate tolerance develops.     

N-acetylcysteine added to saliva does not affect IgA concentration or the agglutination ofStreptococcus mutans in vitro

Summary N-acetylcysteine (NAC) or placebo were mixed with parotid or whole saliva to a final concentration of 0.004–10 mg/ml saliva. Placebo and NAC-containing parotid saliva had the same bacterial agglutinating capacity for 4 strains ofStreptococcus mutans.Immunoglobulin A (IgA) concentration in whole saliva, using ELISA and single radial immunodiffusion assays, did not reveal any differences between NAC and placebo-treated samples. NAC did not affect the immunoelectrophoretic pattern of IgA.     

N-acetylcysteine does not protect behavioral and biochemical toxicological effect after acute exposure of diphenyl ditelluride

Diphenyl ditelluride (PhTe)₂ is a versatile molecule used in the organic synthesis and it is a potential prototype for the development of novel biologically active molecules. The mechanism(s) involved in (PhTe)₂ toxicity is(are) elusive, but thiol oxidation of critical proteins are important targets. Consequently, the possible remedy of its toxicity by thiol-containing compounds is of experimental and clinical interest. The present study aimed to investigate putative mechanisms underlying the toxicity of (PhTe)₂ in vivo. We assessed behavioral and oxidative stress parameters in mice, including the modulation of antioxidant enzymatic defense systems. In order to mitigate such toxicity, N-acetylcysteine (NAC) was administered before (3?d) and simultaneously with (PhTe)₂ (7?d). Mice were separated into six groups receiving daily injections of (1) TFK (2.5?ml/kg, intraperitonealy (i.p.)) plus canola oil (10?ml/kg, subcutaneously (s.c.)), (2) NAC (100?mg/kg, i.p.) plus canola oil s.c., (3) TFK i.p. plus (PhTe)₂ (10?µmol/kg, s.c.), (4) TFK i.p. plus (PhTe)₂ (50?µmol/kg, s.c.), (5) NAC plus (PhTe)₂ (10?µmol/kg, s.c.), and (6) NAC plus (PhTe)₂ (50?µmol/kg, s.c.). (PhTe)₂ treatment started on the fourth day of treatment with NAC. Results demonstrated that (PhTe)₂ induced behavioral alterations and inhibited important selenoenzymes (thioredoxin reductase and glutathione peroxidase). Treatments produced no or minor effects on the activities of antioxidant enzymes catalase and glutathione reductase. Contrary to expected, NAC co-administration did not protect against the deleterious effects of (PhTe)₂. Other low-molecular-thiol containing molecules should be investigated to determine whether or not they can be effective against ditellurides.     

Sildenafil does not improve nitric oxide-mediated endothelium-dependent vascular responses in smokers

AIMS: To examine the hypothesis that sildenafil, a phosphodiesterase type 5 inhibitor that inhibits cGMP breakdown, could enhance nitric oxide-mediated vasodilation and reverse endothelial dysfunction in chronic smokers. METHODS: Flow-mediated dilation of the brachial artery and forearm postischemic reactive hyperemia (both nitric oxide-mediated responses) were measured before and after sildenafil 50 mg and placebo in a double-blind, randomized, crossover study in 9 men who were chronic smokers (21 +/- 3 pack years). RESULTS: There was no significant change in flow-mediated dilation after either sildenafil (0.18%, 95%CI -1.7-2%) or placebo (0.24%, 95%CI -2.8-3.3%) (P = 0.88 and 0.8, respectively). Sildenafil had no significant effect on resting forearm blood flow or postischemic reactive hyperemia (P = 0.39 and 0.7, respectively). Resting heart rate and blood pressure were unaffected by sildenafil. CONCLUSIONS: Acute sildenafil administration did not improve endothelial function in chronic smoking men.     

Trimetazidine does not modify blood levels and immunosuppressant effects of cyclosporine A in renal allograft recipients

Aims In renal allograft recipients, trimetazidine (Vastarel^® ) was proposed to be associated with the classic immunosuppressant treatments because it displays anti-ischaemic effects which may protect against cyclosporine A nephrotoxicity. The objective of this work was to assess the possibility of coadministering cyclosporin A, Sandimmun^® , and trimetazidine.
Methods Twelve renal transplant patients were selected on the basis of the stability of their cyclosporine A blood concentrations for the previous 3 months. They received trimetazidine, 40  mg twice daily orally for 5 days. Other coadministered drugs were kept unchanged during the study. Before and after trimetazidine administration, cyclosporine A blood concentrations, plasma interleukin-2 and soluble interleukin-2 receptor levels were measured.
Results The data showed that neither cyclosporin A blood pharmacokinetic parameters, C _max, t _max , AUC, nor the concentrations of interleukin-2 and soluble interleukin-2 receptors were significantly modified.
Conclusions Therefore, it was suggested that trimetazidine may be coadministered with cyclosporine A without cyclosporine A dosage adjustment.     

Sucralose sweetener does not modify radiolabeling of blood constituents and morphology of red blood cells

Effects of sucralose on the labeling of blood constituents with technetium-99m (^99mTc) and on the morphology of red blood cells (RBC) were evaluated. Blood samples from Wistar rats were treated with sweetener, and the labeling of blood constituents with (^99mTc) was performed. Radioactivity in blood constituents was counted, and the percentage of incorporated radioactivity (%ATI) was determined. Blood smears were prepared for morphology evaluation of RBC. No significant alterations in %ATI of blood constituents and morphology of RBC were observed.