Morphine hyposensitivity in streptozotocin‐diabetic rats: Reversal by dietary l‐arginine treatment

Painful diabetic neuropathy (PDN) is a long‐term complication of diabetes. Defining symptoms include mechanical allodynia (pain due to light pressure or touch) and morphine hyposensitivity. In our previous work using the streptozotocin (STZ)‐diabetic rat model of PDN, morphine hyposensitivity developed in a temporal manner with efficacy abolished at 3 months post‐STZ and maintained for 6 months post‐STZ. As this time course mimicked that for the temporal development of hyposensitivity to the pain‐relieving effects of the furoxan nitric oxide (NO) donor, PRG150 (3‐methylfuroxan‐4‐carbaldehyde) in STZ‐diabetic rats, we hypothesized that progressive depletion of endogenous NO bioactivity may underpin the temporal loss of morphine sensitivity in STZ‐diabetic rats. Furthermore, we hypothesized that replenishment of NO bioactivity may restore morphine sensitivity in these animals. Diabetes was induced in male Dark Agouti rats by intravenous injection of STZ (85 mg/kg). Diabetes was confirmed on day 7 if blood glucose concentrations were ≥15 mmol/L. Mechanical allodynia was fully developed in the bilateral hindpaws by 3 weeks of STZ‐diabetes in rats and this was maintained for the study duration. Morphine hyposensitivity developed in a temporal manner with efficacy abolished by 3 months post‐STZ. Administration of dietary l ‐arginine (NO precursor) at 1 g/d to STZ‐diabetic rats according to a 15‐week prevention protocol initiated at 9 weeks post‐STZ prevented abolition of morphine efficacy. When given as an 8‐week intervention protocol in rats where morphine efficacy was abolished, dietary l ‐arginine at 1 g/d progressively rescued morphine efficacy and potency. Our findings implicate NO depletion in the development of morphine hyposensitivity in STZ‐diabetic rats.     

Unravelling the cardiovascular effects induced by α‐terpineol: A role for the nitric oxide–cGMP pathway

1. α‐Terpineol is a monoterpene found in the essential oils of several aromatic plant species. In the present study, we investigated the mechanisms underlying the cardiovascular changes induced by α‐terpineol in rats. 2. In normotensive rats, administration of α‐terpineol (1, 5, 10, 20 and 30 mg/kg, i.v.) produced a dose‐dependent hypotension (?10 ± 3, ?20 ± 8, ?39 ± 16, ?52 ± 21 and ?57 ± 23 mmHg, respectively; n = 5) followed by tachycardia. The hypotensive responses to 1, 5, 10, 20 and 30 mg/kg, i.v., α‐terpineol were significantly attenuated following the administration of N^G‐nitro‐l‐ arginine methyl ester (l ‐NAME; 20 mg/kg, i.v.; ?2 ± 1, ?5 ± 2, ?7 ± 3, ?22 ± 9 and ?22 ± 10 mmHg, respectively; P < 0.05; n = 5). 3. In 10 μmol/L phenylephrine (PE)‐precontracted mesenteric artery rings, α‐terpineol (10^?12 to 10^?5 mol/L) caused a concentration‐dependent relaxation (maximum relaxation 61 ± 6%; n = 7). After removal of the endothelium, the vasorelaxation elicited by α‐terpineol was attenuated (maximum relaxation 20 ± 1%; P < 0.05; n = 7). In addition, vasorelaxation induced by α‐terpineol in rings pretreated with 100 or 300 μmol/L l ‐NAME, 30 μmol/L hydroxocobalamin or 10 μmol/L 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one was attenuated (maximum relaxation 18 ± 3, 23 ± 3, 24 ± 7 and 21 ± 1%, respectively; n = 6; P < 0.05). 4. Furthermore, in a rabbit aortic endothelial cell line, 10^?6, 10^?5 and 10^?4 mol/L α‐terpineol induced concentration‐dependent increases in nitric oxide (NO) levels (12 ± 6, 18 ± 9 and 34 ± 12%Δ fluorescence, respectively; n = 3). 5. In conclusion, using combined functional and biochemical approaches in the present study, we were able to demonstrate that α‐terpineol‐induced hypotension and vasorelaxation are mediated, at least in part, by the endothelium, most likely via NO release and activation of the NO–cGMP pathway.     

Hepatoprotective effects of salidroside on fulminant hepatic failure induced by d‐galactosamine and lipopolysaccharide in mice

Objectives The aim was to investigate the protective effect of salidroside isolated from Rhodiola sachalinensis A. Bor. (Crassulaceae) on d ‐galactosamine/lipopolysaccharide‐induced fulminant hepatic failure. Methods Hepatotoxicity was induced by an intraperitoneal injection of d ‐galactosamine (700 mg/kg) and lipopolysaccharide (10 μg/kg); salidroside (20, 50 and 100 mg/kg) was administered intraperitoneally 1 h before induction of hepatoxicity. Liver injury was assessed biochemically and histologically. Key findings Salidroside attenuated the induced acute increase in serum aspartate aminotransferase and alanine aminotransferase activities, and levels of tumour necrosis factor‐alpha levels and serum nitric oxide. It restored depleted hepatic glutathione, superoxide dismutase, catalase and glutathione peroxidase activities, decreased malondialdehyde levels and considerably reduced histopathological changes. Histopathological, immunohistochemical and Western blot analyses also demonstrated that salidroside could reduce the appearance of necrotic regions and expression of caspase‐3 and hypoxia‐inducible factor‐1α in liver tissue. Conclusions Salidroside protected liver tissue from the oxidative stress elicited by d ‐galactosamine and lipopolysaccharide. The hepatoprotective mechanism of salidroside appear to be related to antioxidant activity and inhibition of hypoxia‐inducible factor‐1α.     

Ethyl pyruvate protects rats from phosgene‐induced pulmonary edema by inhibiting cyclooxygenase2 and inducible nitric oxide synthase expression

Phosgene is a poorly water‐soluble gas penetrating the lower respiratory tract which can induce acute lung injury characterized by a latent phase of fatal pulmonary edema. Pulmonary edema caused by phosgene is believed to be a consequence of oxidative stress and inflammatory responses. Ethyl pyruvate (EP) has been demonstrated to have anti‐inflammatory and anti‐oxidative properties in vivo and in vitro. The potential therapeutic role of EP in phosgene‐induced pulmonary edema has not been addressed so far. In the present study, we aim to investigate the protective effects of EP on phosgene‐induced pulmonary edema and the underlying mechanisms. Rats were administered with EP (40 mg kg^?1) and RAW264.7 cells were also incubated with it (0, 2, 5 or 10 µm ) immediately after phosgene (400 ppm, 1 min) or air exposure. Wet‐to‐dry lung weight ratio (W:D ratio), nitric oxide (NO) and prostaglandin E₂ (PGE₂) production, cyclooxygenase2 (COX‐2) and inducible nitric oxide synthase (iNOS) expression, and mitogen‐activated protein kinases activities (MAPKs) were measured. Our results showed that EP treatment attenuated phosgene‐induced pulmonary edema and decreased the level of NO and PGE₂ dose‐dependently. Furthermore, EP significantly reduced COX‐2 expression, iNOS expression and MAPK activation induced by phosgene. Moreover, specific inhibitors of MAPKs reduced COX‐2 and iNOS expression induced by phosgene. These findings suggested that EP has a protective role against phosgene‐induced pulmonary edema, which is mediated in part by inhibiting MAPK activation and subsequently down‐regulating COX‐2 and iNOS expression as well as decreasing the production of NO and PGE₂. Copyright © 2011 John Wiley & Sons, Ltd.