Effect of melamine on potassium currents in rat hippocampal CA1 neurons

As an industrially synthesized chemical, melamine has been applied in a wide range of areas. However, many questions on the adverse effect and toxicity of melamine have been emerged, recently. In this investigation, the cytotoxicity of melamine on PC12 cells was evaluated. Furthermore, the effect of melamine on the transient outward potassium current (I_A) and the delayed rectifier potassium current (I_K) in hippocampal CA1 pyramidal neurons of rat was studied using whole-cell patch-clamp technique. The results showed that melamine-induced cell death in a concentration and time-dependent manner, and produced a concentration-dependent inhibition in amplitudes of I_A and I_K at any concentrations (5 × 10⁻⁴, 5 × 10⁻⁵, and 5 × 10⁻⁶ g/ml). Moreover, at higher concentration (5 × 10⁻⁴ g/ml), melamine had observable effects of the steady-state inactivation of I_A, that is melamine shifted inactivation curve of I_A towards hyperpolarization. The spontaneous firing frequency was increased as well. These results suggest that the regulation of I_A and I_K induced by melamine would make neurons display aberrant firing properties and abnormal neuronal discharge, which could be a possible underlying mechanism for the melamine-induced neurotoxicity.     

Renal responses to acute lead waterborne exposure in the freshwater rainbow trout (Oncorhynchus mykiss)

The possible nephrotoxic effects of waterborne lead exposure (as Pb(NO₃)₂) were investigated in the freshwater rainbow trout (Oncorhynchus mykiss). Kidney lead accumulation was time-dependent, increasing upon exposure to 0.57 ± 0.01 mg dissolved Pb L⁻¹ for up to 96 h with a significantly higher burden occurring in the posterior kidney compared to the anterior segment. Urine analyses in trout exposed to 1.20 ± 0.09 mg dissolved Pb L⁻¹ revealed a significant increase in urinary lead excretion rate throughout 96 h of exposure. Urine flow rate and glomerular filtration rate (GFR) were not impacted with the exception of a significant decrease in GFR from 84 to 96 h in lead-exposed trout. Urine pH decreased significantly over time in lead-exposed fish. Correspondingly, urine ammonia excretion rate showed a marked increase from 48 h onwards. In experimental fish, urine glucose excretion was significantly greater by 96 h while urine lactate, urea and protein excretion were not significantly altered by lead exposure. The urine excretion rate of Ca²⁺ increased significantly by approximately 43% after only 24 h of lead exposure, and was maintained at a higher rate than controls for up to 96 h. Magnesium excretion increased in a time-dependent fashion, reaching a two- to three-fold rise by 96 h. In contrast, rates of Na⁺ and Cl⁻ excretion were decreased in experimental fish by approximately 30% by 48 h, this trend continuing for the duration of lead-exposure. There were no changes in any of these parameters in similarly treated control fish. Clearance ratio analyses indicated progressive decreases in the net reabsorption efficiencies of the renal system for Ca²⁺, Mg²⁺, Pb, and glucose, suggesting that the active tubular transport mechanisms for these substances were inhibited by lead exposure, while Na⁺, K⁺, Cl⁻, lactate, and protein reabsorptions were unaffected. Net ammonia secretion increased. We conclude that changes in renal function both reflect and help to minimize some of the associated disturbances in systemic physiology. Lead-induced ionoregulatory toxicity in rainbow trout, particularly the disturbance of Ca²⁺ homeostasis, is not exclusively a branchial phenomenon, but is in part a result of disruption of ionoregulatory mechanisms at the kidney. This action of lead outside the gills is critical to consider when developing guidelines for water quality.     

Toxicological effects of clofibric acid and diclofenac on plasma thyroid hormones of an Indian major carp,Cirrhinus mrigala during short and long-term exposures

In the present investigation, the toxicity of most commonly detected pharmaceuticals in the aquatic environment namely clofibric acid (CA) and diclofenac (DCF) was investigated in an Indian major carp Cirrhinus mrigala. Fingerlings of C. mrigala were exposed to different concentrations (1, 10 and 100 μg L⁻¹) of CA and DCF for a period of 96 h (short term) and 35 days (long term). The toxic effects of CA and DCF on thyroid hormones (THs) such as thyroid stimulating hormone (TSH), thyroxine (T₄) and triiodothyronine (T₃) levels were evaluated. During the short and long-term exposure period TSH level was found to be decreased at all concentrations of CA (except at the end of 14^th day in 1 and 10 μg L^−l and 21^st day in 1 μg L^−l) whereas in DCF exposed fish TSH level was found to be increased when compared to control groups. T₄ level was found to be decreased at 1 and 100 μg L^−l of CA exposure at the end of 96 h. However, T₄ level was decreased at all concentrations of CA and DCF during long-term (35 days) exposure period. Fish exposed to all concentrations of CA and DCF had lower level of T₃ in both the treatments. These results suggest that both CA and DCF drugs induced significant changes (P < 0.01 and P < 0.05) on thyroid hormonal levels of C. mrigala. The alterations of these hormonal levels can be used as potential biomarkers in monitoring of pharmaceutical drugs in aquatic organisms.     

The effects of elevated carbon dioxide and temperature levels on tilapia (Oreochromis mossambicus): Respiratory enzymes,blood pH and hematological parameters

Oreochromis mossambicus were exposed to two different temperature and carbon dioxide partial pressure levels for about two weeks, as the ambient (Control; 25 °C, 3.3 mg/L CO₂), high CO₂ (25 °C, 14 mg/L CO₂), high temperature (30 °C, 3 mg/L CO₂) and combined (30 °C, 14.1 mg/L CO₂) groups. No mortality was observed during the experiments. As a result of the study, elevated CO₂ concentrations cause negative effects on the hematological parameters. At the end of the study, while the blood Carbonic Anhydrase (CA) activity, in the high CO₂ group (25 °C, 14 mg/L CO₂), statistically increased at the 7th day compared to the control group, it decreased at the 14th day (p < 0.05). In addition, the blood CA activity, in the combined (30 °C, 14.1 mg/L CO₂) group, showed a decrease at the 14th day compared to the control group (p < 0.05). At the end of study, unlike the blood CA activity, gill, liver and kidney CA activity showed an increase in the tissues compared to the control groups (p < 0.05). Furthermore, the Na⁺, K⁺-ATPase activities were stimulated significantly in the gills in both high CO₂ and temperature groups at day 7, but it showed a significant amount of inhibition at the 14th day compared to the control groups. Overall, increasing carbon dioxide concentration in different temperatures has negative effects on the hematological parameters and respiratory enzyme of the tilapia fish. In addition, it is observed that the fish survive at negative conditions with adaptation mechanisms.     

Human Skin is Permselective for the Small,Monovalent Cations Sodium and Potassium but not for Nickel and Chromium

The molar conductance of excised human skin (Λ_skin) immersed in electrolyte solutions comprising four cationic (Na⁺, K⁺, Ni^2 +, and Cr^3 +) and five anionic (Cl^?, NO₃^?, SO₄^2 ?, CrO₄^2 ?, and Cr₂O₇^2 ?) species was determined as a function of concentration in Franz diffusion cells. Cation transport numbers for four of these electrolytes were measured in Franz cells by the electromotive force method. Parallel experiments were conducted in solutions alone to establish the validity of the technique. Molar conductance decreased with increasing concentration, following the Kohlrausch law, over a 4–12-fold concentration range. Molar conductance and cation transport values at infinite dilution were extrapolated from these data and used to estimate ionic conductances at infinite dilution. These values were subsequently used to calculate limiting ion mobilities and diffusivities in solution and skin. Results for skin showed the expected increase in cation permselectivity for monovalent cations and a 40–110-fold reduction in effective diffusivities with respect to those in solution. However, Ni^2 + and Cr^3 + were relatively less mobile in skin than in solution. Salt diffusivities calculated from ionic mobilities in skin provided a partial explanation for the difference in allergenic potency of NiCl₂compared with NiSO₄ and Cr^3 + versus Cr^6 + salts.     

Interaction of cholera toxin B subunit with T and B lymphocytes

We have prepared ¹²⁵I-labeled cholera toxin B subunit (¹²⁵I-labeled CT-B, a specific activity of 98 Ci/mmol) and found that its binding to T and B lymphocytes from the blood of healthy donors was high-affinity (K_d 2.8 and 3.0 nM, respectively). The binding of labeled protein was completely inhibited by unlabeled thymosin-α₁ (TM-α₁), interferon-α₂ (IFN-α₂), and the synthetic peptide LKEKK that corresponds to residues 16–20 in TM-α₁ and 131–135 in IFN-α₂, but was not inhibited by the synthetic peptide KKEKL with inverted amino acid sequence (K_i > 10 μM). Thus, TM-α₁, IFN-α₂, and the peptide: LKEKK bind with high affinity and specificity to CT-B receptor on donor blood T and B lymphocytes. It was found that CT-B and the peptide: LKEKK at concentrations of 10–1000 nM increased in a dose-dependent manner the soluble guanylate cyclase activity in T and B lymphocytes.     

The effects of sulfur mustard exposure and freezing on transdermal penetration of tritiated water through ex vivo pig skin

The percutaneous absorption of tritiated water (³H₂O) through sulfur mustard (SM) exposed abdominal pig skin was measured using in vitro Franz-type static diffusion cells. The barrier function to water permeation following exposure to liquid SM for 8 min and excision 3 h later did not change significantly. A small, but statistically significant difference (P < 0.05) in steady state penetration (Jss), permeability coefficient (Kp) and lag time (t_L) of ³H₂O was observed between fresh skin and skin stored frozen (?20 °C) for up to two weeks. Steady-state penetration and Kp values were significantly higher (P < 0.05) in skin stored frozen compared with fresh skin. Fresh naïve skin had an average Kp of 1.65 × 10^?3 cm h^?1, whereas frozen naïve skin was 2.04 × 10^?3 cm h^?1. Fresh SM exposed skin had a mean Kp of 1.72 × 10^?3 cm h^?1, whereas frozen SM exposed skin was 2.31 × 10^?3 cm h^?1. Lag times were also shorter (P < 0.05) in skin that had been stored frozen. Frozen, SM-exposed porcine abdominal skin may be used for in vitro penetration studies, but effects of treatment and storage on the barrier layer should be taken into account.     

Effect of cadmium on the extracellular Na+, K+, and Ca2+ in the gill and small intestine of Goldfish Carassius auratus

In this study, the toxic effect of cadmium on extracellular Na⁺, K⁺, and Ca²⁺ in the gill and small intestine of goldfish Carassius auratus was determined with the technique of ion chromatograph. Two-way ANOVA indicated that the two factors (Cd²⁺ treatment and time) and the interaction factor had significant effect on the level of Na⁺, K⁺, and Ca²⁺ in the small intestine and gill. 1.0 mg/L Cd²⁺ significantly increased Ca²⁺ level in the small intestine, but Ca²⁺ level in the gill was significantly decreased by 1.0 and 5.0 mg/L Cd²⁺ at 24, 48, and 72 h. Na⁺ and K⁺ level in the small intestine and gill was increased by 1.0 mg/L Cd²⁺ at three time points, but increased by 5.0 mg/L Cd²⁺ at a certain different time. In addition, Na⁺ level was significantly decreased by 5.0 mg/L Cd²⁺ at 24 or 48 h in the small intestine and gill. The results indicated that Cd²⁺ played an important role in regulating the level of Na⁺, K⁺, and Ca²⁺ in the small intestine and gill of goldfish C. auratus. A method was constructed to investigate the extracellular Na⁺, K⁺ and Ca²⁺ in the tissues of gold fish with ion chromatography.     

Predicting the oral uptake efficiency of chemicals in mammals: Combining the hydrophilic and lipophilic range

Environmental risk assessment requires models for estimating the bioaccumulation of untested compounds. So far, bioaccumulation models have focused on lipophilic compounds, and only a few have included hydrophilic compounds. Our aim was to extend an existing bioaccumulation model to estimate the oral uptake efficiency of pollutants in mammals for compounds over a wide K_ow range with an emphasis on hydrophilic compounds, i.e. compounds in the lower K_ow range. Usually, most models use octanol as a single surrogate for the membrane and thus neglect the bilayer structure of the membrane. However, compounds with polar groups can have different affinities for the different membrane regions. Therefore, an existing bioaccumulation model was extended by dividing the diffusion resistance through the membrane into an outer and inner membrane resistance, where the solvents octanol and heptane were used as surrogates for these membrane regions, respectively. The model was calibrated with uptake efficiencies of environmental pollutants measured in different mammals during feeding studies combined with human oral uptake efficiencies of pharmaceuticals. The new model estimated the uptake efficiency of neutral (RMSE = 14.6) and dissociating (RMSE = 19.5) compounds with logK_ow ranging from ? 10 to + 8. The inclusion of the K_hw improved uptake estimation for 33% of the hydrophilic compounds (logK_ow < 0) (r² = 0.51, RMSE = 22.8) compared with the model based on K_ow only (r² = 0.05, RMSE = 34.9), while hydrophobic compounds (logK_ow > 0) were estimated equally by both model versions with RMSE = 15.2 (K_ow&K_hw) and RMSE = 15.7 (K_ow only). The model can be used to estimate the oral uptake efficiency for both hydrophilic and hydrophobic compounds.     

In vitro screening of reversible and time-dependent inhibition on CYP3A by TM208 and TM209 in rat liver microsomes

TM208 and TM209, dithiocarbamate derivatives with potential anti-cancer effects, were evaluated in reversible and time-dependent cytochrome P450 (CYP) 3A inhibition assays in rat liver microsomes using testosterone as probe substrate. Both compounds were found to be weak reversible inhibitors and moderate mechanism-based inhibitors of rat CYP3A. For reversible inhibition on rat CYP3A, the K_i values of competitive inhibition model were 12.10±1.75 and 13.94±1.31 μM, respectively. For time-dependent inhibition, the inactivation constants (K_l) were 31.93±12.64 and 32.91±15.58 μM, respectively, and the maximum inactivation rates (k_inact) were 0.03497±0.0069 and 0.07259±0.0172 min^?1 respectively. These findings would provide useful in vitro information for future in vivo DDI studies on TM208 or TM209.     

Sub-anesthetic concentrations of (R,S)-ketamine metabolites inhibit acetylcholine-evoked currents in α7 nicotinic acetylcholine receptors

The effect of the (R,S)-ketamine metabolites (R,S)-norketamine, (R,S)-dehydronorketamine, (2S,6S)-hydroxynorketamine and (2R,6R)-hydroxynorketamine on the activity of α7 and α3β4 neuronal nicotinic acetylcholine receptors was investigated using patch-clamp techniques. The data indicated that (R,S)-dehydronorketamine inhibited acetylcholine-evoked currents in α7-nicotinic acetylcholine receptor, IC₅₀=55±6 nM, and that (2S,6S)-hydroxynorketamine, (2R,6R)-hydroxynorketamine and (R,S)-norketamine also inhibited α7-nicotinic acetylcholine receptor function at concentrations ≤1 μM, while (R,S)-ketamine was inactive at these concentrations. The inhibitory effect of (R,S)-dehydronorketamine was voltage-independent and the compound did not competitively displace selective α7-nicotinic acetylcholine receptor ligands [¹²⁵I]-α-bungarotoxin and [³H]-epibatidine indicating that (R,S)-dehydronorketamine is a negative allosteric modulator of the α7-nicotinic acetylcholine receptor. (R,S)-Ketamine and (R,S)-norketamine inhibited (S)-nicotine-induced whole-cell currents in cells expressing α3β4-nicotinic acetylcholine receptor, IC₅₀ 3.1 and 9.1 μM, respectively, while (R,S)-dehydronorketamine, (2S,6S)-hydroxynorketamine and (2R,6R)-hydroxynorketamine were weak inhibitors, IC₅₀ >100 μM. The binding affinities of (R,S)-dehydronorketamine, (2S,6S)-hydroxynorketamine and (2R,6R)-hydroxynorketamine at the NMDA receptor were also determined using rat brain membranes and the selective NMDA receptor antagonist [³H]-MK-801. The calculated K_i values were 38.95 μM for (S)-dehydronorketamine, 21.19 μM for (2S,6S)-hydroxynorketamine and>100 μM for (2R,6R)-hydroxynorketamine. The results suggest that the inhibitory activity of ketamine metabolites at the α7-nicotinic acetylcholine receptor may contribute to the clinical effect of the drug.     

In vitro inhibitory effects of palonosetron hydrochloride,bevacizumab and cyclophosphamide on purified paraoxonase-I (hPON1) from human serum

In this study, we investigated the effects of the drugs, palonosetron hydrochloride, bevacizumab and cyclophosphamide, on human serum paraoxonase-I (hPON1) enzyme activity in in vitro conditions. The enzyme was purified ∼231-fold with 34.2% yield by using ammonium sulphate precipitation, DEAE-Sephadex A-50 ion-exchange chromatography and Sephadex G-200 gel-filtration chromatography from human serum. hPON1 exhibited a single protein band on the SDS polyacrylamide gel electrophoresis. The inhibition studies were performed on paraoxonase activity of palonosetron hydrochloride, bevacizumab and cyclophosphamide. K_i constants were found as 0.033 ± 0.001, 0.054 ± 0.003 mM and 3.419 ± 0.518 mM, respectively. Compared to the inhibition rates of the drugs, palonosetron hydrochloride has the maximum inhibition rate. However, inhibition mechanisms of the drugs were determined as noncompetitive by Lineweaver-Burk curves.     

The role of Na+, K+-ATPase in the hypoxic vasoconstriction in isolated rat basilar artery

Hypoxia-induced cerebrovascular dysfunction is a key factor in the occurrence and the development of cerebral ischemia. Na⁺, K⁺-ATPase affects the regulation of intracellular Ca^2 + concentration and plays an important role in vascular smooth muscle function. However, the potential role of Na⁺, K⁺-ATPase in hypoxia-induced cerebrovascular dysfunction is unknown. In this study, we found that the KCl-induced contraction under hypoxia in rat endothelium-intact basilar arteries is similar to that of denuded arteries, suggesting that hypoxia may cause smooth muscle cell (SMC)-dependent vasoconstriction in the basilar artery. The Na⁺, K⁺–ATPase activity of the isolated basilar artery with or without endothelium significantly reduced with prolonged hypoxia. Blocking the Na⁺–Ca^2 + exchanger with Ni^2 + (10^− 3 M) or the L-type Ca^2 + channel with nimodipine (10^− 8 M) dramatically attenuated KCl-induced contraction under hypoxia. Furthermore, prolonged hypoxia significantly reduced Na⁺, K⁺-ATPase activity and increased [Ca^2 +]_i in cultured rat basilar artery SMCs. Hypoxia reduced the protein and mRNA expression of the α₂ isoform of Na⁺, K⁺-ATPase in SMCs in vitro. We used a low concentration of the Na⁺, K⁺-ATPase inhibitor ouabain, which possesses a high affinity for the α₂ isoform. The contractile response in the rat basilar artery under hypoxia was partly inhibited by ouabain pretreatment. The decreased Na⁺, K⁺-ATPase activity in isolated basilar artery and the increased [Ca^2 +]_i in SMCs induced by hypoxia were partly inhibited by pretreatment with a low concentration of ouabain. These results suggest that hypoxia may educe Na⁺, K⁺-ATPase activity in SMCs through the α₂ isoform contributing to vasoconstriction in the rat basilar artery.     

Covalent inhibition of recombinant human carboxylesterase 1 and 2 and monoacylglycerol lipase by the carbamates JZL184 and URB597

Carboxylesterase type 1 (CES1) and CES2 are serine hydrolases located in the liver and small intestine. CES1 and CES2 actively participate in the metabolism of several pharmaceuticals. Recently, carbamate compounds were developed to inhibit members of the serine hydrolase family via covalent modification of the active site serine. URB597 and JZL184 inhibit fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively; however, carboxylesterases in liver have been identified as a major off-target. We report the kinetic rate constants for inhibition of human recombinant CES1 and CES2 by URB597 and JZL184. Bimolecular rate constants (k_inact/K_i) for inhibition of CES1 by JZL184 and URB597 were similar [3.9 (±0.2) × 10³ M^?1 s^?1 and 4.5 (±1.3) × 10³ M^?1 s^?1, respectively]. However, k_inact/K_i for inhibition of CES2 by JZL184 and URB597 were significantly different [2.3 (±1.3) × 10² M^?1 s^?1 and 3.9 (±1.0) × 10³ M^?1 s^?1, respectively]. Rates of inhibition of CES1 and CES2 by URB597 were similar; however, CES1 and MAGL were more potently inhibited by JZL184 than CES2. We also determined kinetic constants for spontaneous reactivation of CES1 carbamoylated by either JZL184 or URB597 and CES1 diethylphosphorylated by paraoxon. The reactivation rate was significantly slower (4.5×) for CES1 inhibited by JZL184 than CES1 inhibited by URB597. Half-life of reactivation for CES1 carbamoylated by JZL184 was 49 ± 15 h, which is faster than carboxylesterase turnover in HepG2 cells. Together, the results define the kinetics of inhibition for a class of drugs that target hydrolytic enzymes involved in drug and lipid metabolism.     

Endothelial and neural factors functionally involved in the modulation of noradrenergic vasoconstriction in healthy pig internal mammary artery

The role of endothelial and neural factors as modulators of neurogenic- and noradrenaline-induced vasoconstriction was examined in healthy pig internal mammary artery (IMA). Tetrodotoxin-, guanethidine-sensitive electrical field stimulation (EFS)-, and noradrenaline-elicited contractions were significantly diminished by prazosin (n = 8, P < 0.001) and less so by rauwolscine, indicating functional α₁- and α₂-adrenoceptor-mediated noradrenergic innervation of the IMA. Endothelium removal reduced neurogenic (n = 8, P < 0.01) but augmented noradrenaline responses (n = 8, P < 0.01), suggesting the release of two endothelium-dependent factors with opposite effects. In the presence of endothelium, neurogenic and exogenous noradrenaline vasoconstrictions were enhanced by l-NOArg (n = 7, P < 0.05 and P < 0.01 respectively) and ODQ (n = 7, both P < 0.05); in denuded arteries, nNOS inhibition with N^ω-propyl-l-arginine increased neurogenic contraction (n = 7, P < 0.05). Western blotting indicated the presence of neural and endothelial origin NO (n = 6, P < 0.001). Tetraethylammonium (n = 9, P < 0.001), iberiotoxin (n = 7, P < 0.001) and 4-aminopyridine (n = 8, P < 0.01) enhanced vasoconstrictions revealing a modulatory role of big conductance Ca²⁺-activated K⁺ (BK_Ca) and voltage-dependent K⁺ (K_v) channels in noradrenergic responses. Bosentan pretreatment (n = 8, P < 0.05) suggested endothelin-1 as the inferred contractile neurogenic endothelial-dependent factor. Indomethacin-induced inhibition involved a muscular prostanoid (n = 9, P < 0.05), functionally and immunologically localized, and derived from cyclooxygenase (COX)-1 and COX-2, as revealed by Western blots (n = 5, P = 0.1267). Thus, noradrenergic IMA contractions are controlled by contractile prostanoid activation and endothelin-1 release, and offset by BK_Ca and K_v channels and neural and endothelial NO. These results help clarify the mechanisms of vasospasm in IMA, as the preferred vessel for coronary bypass.     

Ionization-specific analysis of human intestinal absorption

This study presents a mechanistic QSAR analysis of human intestinal absorption of drugs and drug-like compounds using a data set of 567 %HIA values. Experimental data represent passive diffusion across intestinal membranes, and are considered to be reasonably free of carrier-mediated transport or other unwanted effects. A nonlinear model was developed relating %HIA to physicochemical properties of drugs (lipophilicity, ionization, hydrogen bonding, and molecular size). The model describes ion-specific intestinal permeability of drugs by both transcellular and paracellular routes, and also accounts for unstirred water layer effects. The obtained model was validated on two external data sets consisting of in vivo human jejunal permeability coefficients (P_eff) and absorption rate constants (K_a). Validation results demonstrate good predictive power of the model (RMSE = 0.35–0.45 log units for log K_a and log P_eff). High prediction accuracy together with clear physicochemical interpretation (log P, pK_a) makes this model particularly suitable for use in property-based drug design. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4039–4054, 2009     

Serum antioxidant enzyme activities and oxidative stress parameters as possible biomarkers of exposure in veal calves illegally treated with dexamethasone

Low doses of the synthetic glucocorticoid dexamethasone (DEX) are often illegally used, alone or in association with steroids and β-agonists, to improve meat performances in cattle. As it is known that oestrogens and β-agonists may generate reactive oxygen species (ROS) and induce oxidative stress, the effects of illicit DEX protocols on the antioxidant status and oxidative stress parameters were measured in veal calves.Ten cross-bred male veal calves were given DEX (0.4 mg/day administered per os, for 23 days or 2 mg pro capite, injected intramuscularly on days 14 and 21 after the beginning of the oral DEX administration). Five further animals were used as controls. Blood samples were withdrawn before (T₀), and 4 (T₁), 10 (T₂), 14 (T₃), 21 (T₄) and 28 (T₅) days. Antioxidant enzyme activities (AOEs), the serum antioxidant capacity (SAC) and ROS were measured in sera.Calves orally treated showed a significant increase of both glutathione peroxidase isoforms (P < 0.05) and SAC (P < 0.05), too.Antioxidant enzymes have already been used as biomarkers (BMs) of response, measured in target or in surrogate tissues. Our results suggest glutathione peroxidase and SAC as possible BMs of illicit oral low-dose administration of DEX in cattle.     

Human urotensin II in internal mammary and radial arteries of patients undergoing coronary surgery

AimsInternal mammary (IMA) and radial artery (RA) have different incidence of vasospasm and long-term patency rates in arterial grafting. We compared the vasoreactivity of human urotensin II (hU-II) and its receptor with mechanism investigations in IMA and RA.MethodsIMA and RA taken from patients undergoing coronary bypass surgery were studied in organ baths. Urotensin receptor expression was determined by RT-PCR.ResultshU-II contracted IMA with pD₂ of 8.57 ± 0.41 and 45.4 ± 9.1% E_max of contraction to 100 mM KCl, whereas caused less contractile responses in RA (pD₂:8.30 ± 0.79, E_max:20.4 ± 4.8%, p < 0.05). Nifedipine inhibited hU-II-contraction in IMA. In U₄₆₆₁₉-precontraction, hU-II elicited comparable relaxation in IMA (pD₂:8.39 ± 0.43, E_max:56.1 ± 4.0%) and RA (pD₂:9.03 ± 0.46, E_max:65.2 ± 7.1%). The relaxation was abolished by endothelium denudation and by indomethacin, oxadiazoloquinoxalinone or N^ω-nitro-l-arginine, oxyhemoglobin, and Ca²⁺-activated K⁺ channel (K_Ca) blockers. Urotensin receptor mRNA was detected in both arteries.ConclusionshU-II is an important spasmogen in arterial grafts with receptors expressed in IMA and RA. hU-II elicits stronger contraction in IMA than in RA and a moderate endothelium-dependent relaxation attributable to nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor with involvement of K_Ca activation. The relaxant response of endothelium-intact IMA and RA to hU-II demonstrates the importance of preservation of endothelium in these grafts.     

Zn2+, derived from cell preparation,partly attenuates Ca2+-dependent cell death induced by A23187, calcium ionophore,in rat thymocytes

A23187, a calcium ionophore, is used to induce Ca²⁺-dependent cell death by increasing intracellular Ca²⁺ concentration ([Ca²⁺]_i) under in vitro condition. Since this ionophore also increases membrane permeability of metal divalent cations such as Zn²⁺ and Fe²⁺ rather than Ca²⁺, trace metal cations in cell suspension may affect Ca²⁺-dependent cell death induced by A23187. Therefore, the effects of chelators for divalent metal cations, EDTA and TPEN, on the A23187-induced cytotoxicity were cytometrically examined in rat thymocytes. The cytotoxicity of A23187 was attenuated by 1 mM EDTA while it was augmented by 50 μM EDTA and 10 μM TPEN. These changes were statistically significant. The A23187-induced increase in Fluo-3 fluorescence intensity, a parameter for [Ca²⁺]_i, was significantly reduced by 1 mM EDTA while it was not the case for 50 μM EDTA and 10 μM TPEN. The intensity of FluoZin-3 fluorescence, a parameter for [Zn²⁺]_i, increased by A23187 was respectively reduced by 50 μM EDTA and 10 μM TPEN. It is suggested that the attenuation of A23187-induced cytotoxicity by 1 mM EDTA is due to the chelation of extracellular Ca²⁺ and Zn²⁺ while the augmentation by 50 μM ETDA or 10 μM TPEN is due to the chelation of extracellular Zn²⁺. The Tyrode’s solution without thymocytes contained 32.4 nM of zinc while it was 216.9 nM in the cell suspension. In conclusion, trace Zn²⁺, derived from cell preparation, partly attenuates the Ca²⁺-dependent cell death induced by A23187.     

Effects of taurine on contractions of the porcine coronary artery

The actions and mechanisms of taurine on vascular contractions have been studied in the isolated porcine coronary artery. Taurine depressed histamine-, serotonin-, KCl- and CaCl₂-induced contractions in a concentration-dependent manner, with maximal contractions being depressed by 43.4%, 46.2%, 33.3% and 43.3%, respectively. Taurine relaxed arterial rings that were precontracted by either 30 mM KCl or 0.3 μMU46619, a thromboxane A₂ analog, in a concentration-dependent manner, and the maximal relaxations were 39.4% and 38.7%, respectively. The vasorelaxations were nearly abolished by pretreatment with either the inward rectifier K⁺ channel (K_IR) inhibitor, BaCl₂ or the ATP sensitive K⁺ channel (K_ATP) inhibitor, glibenclamide, and were attenuated by the Ca²⁺-activated K⁺ channel (K_Ca) inhibitor tetraethylammonium. Denudation of the endothelium, and treatment with the nitric oxide synthase inhibitor, L-NAME, the cyclooxygenase inhibitor, indomethacin, or the voltage gated K⁺ channel (K_V) inhibitor 4-aminopyridine did not affect the relaxation. The present results show that taurine antagonizes and relaxes the contractions of the porcine coronary artery, and suggest that the activation of K_IR,K_ATP and K_ca may be involved in taurine-induced relaxation of the porcine coronary artery.