Magnesium sulphate activates the L-arginine/NO/cGMP pathway to induce peripheral antinociception in mice

In the present study, we investigated whether magnesium sulphate activates the L-arginine/NO/cGMP pathway and elicits peripheral antinociception. The male Swiss mice paw pressure test was performed with hyperalgesia induced by intraplantar injection of prostaglandin E2. All drugs were administered locally into the right hind paw of animals. Magnesium sulphate (20, 40, 80 and 160 µg/paw) induced an antinociceptive effect. The dose of 80 µg/paw elicited a local antinociceptive effect that was antagonized by the non-selective NOS inhibitor, L-NOArg, and by the selective neuronal NOS inhibitor, L-NPA. The inhibitors, L-NIO and L-NIL, selectively inhibited endothelial and inducible NOS, respectively, but were ineffective regarding peripheral magnesium sulphate injection. The soluble guanylyl cyclase inhibitor, ODQ, blocked the action of magnesium sulphate, and the cGMP-phosphodiesterase inhibitor, zaprinast, enhanced the antinociceptive effects of intermediate dose of magnesium sulphate. Our results suggest that magnesium sulphate stimulates the NO/cGMP pathway via neuronal NO synthase to induce peripheral antinociceptive effects.

Anti-inflammatory and antinociceptive properties of the hydroalcoholic fractions from the leaves of Annona crassiflora Mart. in mice.

BACKGROUND: Annona crassiflora Mart., popularly known as "Araticum", is a native tree of the Brazilian Cerrado used in folk medicine for treatment of pain and inflammatory diseases. We proposed to analyze analgesic and anti-inflammatory properties of the filtrate (F1) and the precipitate (F2) of the hydroalcoholic fraction from the leaves of Annona crassiflora Mart. in mice. MATERIALS AND METHODS: Swiss mice were submitted to formalin-induced nociception test and tail-flick reflex test, to assess antinociceptive properties, and to the rota-rod test, for motor performance analyses. To evaluate anti-inflammatory properties, F1 and F2 were orally administered 1 h prior to the intrathoracic injection of carrageenan, zymosan, LPS, CXCL8, or vehicle in Balb/c mice and neutrophil infiltration was evaluated 4 h after injection. RESULTS: F1 and F2 reduced the licking time in the second phase of formalin-induced nociception test, but only F2 showed a dose-dependent response. Neither F1 nor F2 reduced the latency time in the tail-flick reflex test. In addition, motor performance alteration was not observed in F1- or F2-treated mice. F2 treatment significantly inhibited the neutrophilia induced by carrageenan, LPS, or CXCL8, but not zymosan. CONCLUSIONS: The experimental data demonstrated that hydroalcoholic fractions of Annona crassiflora Mart. leaves have remarkable anti-inflammatory and antinociceptive activities.

Tingenone, a pentacyclic triterpene, induces peripheral antinociception due to NO/cGMP and ATP-sensitive K(+) channels pathway activation in mice.

Substances derived from plants play an important role in the development of new analgesic drugs, among them, triterpenoids. The connection between the participation of L-arginine/NO/cGMP pathway and the activation of ATP-sensitive K(+) channels (KATP) has been established on the peripheral antinociception induced by various drugs. The study assessed the involvement of L-arginine/NO/cGMP/KATP pathway in the antinociceptive effect induced by tingenone, from Maytenus imbricata, against the hyperalgesia evoked by prostaglandin E2 (PGE2) in peripheral pathway. The paw pressure test was used, with hyperalgesia induced by intraplantar injection of PGE2 (2 µg). Tingenone (200 µg/paw) administered into the right hind paw induced a local antinociceptive effect, that was antagonized by l-NOArg, nonselective nitric oxide synthase (NOS) inhibitor and by L-NPA, selective neuronal NOS (nNOS) inhibitor. The L-NIO, selective inhibitor of endothelial (eNOS), and the L-NIL, selective inhibitor of inducible (iNOS), did not alter the peripheral antinociceptive effect of the tingenone. The ODQ, selective soluble guanylyl cyclase inhibitor, prevented the antinociceptive effect of tingenone, and zaprinast, inhibitor of the phosphodiesterase that is cyclic guanosine monophosphate (cGMP) specific, intensified the peripheral antinociceptive effect of the smaller dose of tingenone. Glibenclamide, ATP-sensitive K(+) channels (KATP) blocker, but not tetraethylammonium chloride, voltage-dependent K(+) channel blocker; dequalinium dichloride, blocker of the small conductance Ca(2+)-activated K(+) channel, and paxilline, a potent blocker of high-conductance Ca(2+)-activated K(+) channels, respectively, prevented the peripheral antinociceptive effect of tingenone. The results demonstrate that tingenone induced a peripheral antinociceptive effect by L-arginine/NO/cGMP/KATP pathway activation, with potential for a new analgesic drug.

Antinociceptive response in transgenic mice expressing rat tonin.

Angiotensin II (Ang II) may be produced directly from angiotensinogen by tonin. Studies have demonstrated that Ang II and its metabolite Ang-(1-7) produce antinociception in pain animal models. The aim of the present study was to determine whether the transgenic mice that express rat tonin (TGM(rTon)) show altered nociceptive behavior and investigate the possible involvement of angiotensin metabolites. Nociception was evaluated using the thermal tail-flick and chemical acetic acid writhing tests, and the drugs were administered by intracerebroventricular and subcutaneous pathways, respectively. Probabilities less than 5% (P<0.05) were considered to be statistically significant (t test; ANOVA/Bonferroni's test). The results demonstrate that the transgenic mice showed an antinociceptive effect in the tail-flick and acetic acid writhing tests. In addition, it was observed that losartan, an AT1 receptor antagonist and A-779 (D-Ala7-Ang-(1-7)), a Mas receptor antagonist attenuated the antinociceptive behavior. Our data suggest that the Ang II produced in TGM(rTon) induces antinociception via the AT1 receptor, while the Ang-(1-7) produced from Ang II induced antinociception via the Mas receptor.

Differential involvement of central and peripheral α2 adrenoreceptors in the antinociception induced by aerobic and resistance exercise.

BACKGROUND: Several studies have demonstrated antinociception induced by exercise; however, the specific mechanisms for this effect are not well understood. Thus, we investigated the involvement of α2-adrenergic receptors (α2-ARs) in the antinociceptive effect produced by exercise in rats and mice. METHODS: Male Wistar rats performed acute aerobic (AA) and acute resistance exercise protocols, and male α2A/α2C-ARs knockout mice and their wild-type mice were also submitted to AA. RESULTS: After the exercise protocols, the nociceptive threshold of rats and wild type was increased, (except in knockout mice). This effect was reversed by yohimbine, a nonselective α2-ARs antagonist (4 mg/kg, subcutaneously [s.c.]); rauwolscine, a selective α2C-ARs antagonist (4 mg/kg, s.c.); BRL 44408, a selective α2A-ARs antagonist (4 mg/kg, s.c.) and guanethidine, a selective inhibitor of transmission in adrenergic nerves (30 mg/kg, intraperitoneal). Furthermore, when given intrathecally or intracerebroventricularly, yohimbine did not alter antinociception induced by exercise protocols. In addition, α2-ARs expression in rat brains did not change after AA and acute resistance exercise. CONCLUSION: These results suggest a peripheral involvement of α2-ARs in the antinociception induced by aerobic and resistance exercise.

Sirtuin 1 regulates SREBP-1c expression in a LXR-dependent manner in skeletal muscle.

Sirtuin 1 (SIRT1), a NAD(+)-dependent protein deacetylase, has emerged as a main determinant of whole body homeostasis in mammals by regulating a large spectrum of transcriptional regulators in metabolically relevant tissue such as liver, adipose tissue and skeletal muscle. Sterol regulatory element binding protein (SREBP)-1c is a transcription factor that controls the expression of genes related to fatty acid and triglyceride synthesis in tissues with high lipid synthesis rates such as adipose tissue and liver. Previous studies indicate that SIRT1 can regulate the expression and function of SREBP-1c in liver. In the present study, we determined whether SIRT1 regulates SREBP-1c expression in skeletal muscle. SREBP-1c mRNA and protein levels were decreased in the gastrocnemius muscle of mice harboring deletion of the catalytic domain of SIRT1 (SIRT1(Δex4/Δex4) mice). By contrast, adenoviral expression of SIRT1 in human myotubes increased SREBP-1c mRNA and protein levels. Importantly, SREBP-1c promoter transactivation, which was significantly increased in response to SIRT1 overexpression by gene electrotransfer in skeletal muscle, was completely abolished when liver X receptor (LXR) response elements were deleted. Finally, our in vivo data from SIRT1(Δex4/Δex4) mice and in vitro data from human myotubes overexpressing SIRT1 show that SIRT1 regulates LXR acetylation in skeletal muscle cells. This suggests a possible mechanism by which the regulation of SREBP-1c gene expression by SIRT1 may require the deacetylation of LXR transcription factors.

Probable involvement of alpha(2C)-adrenoceptor subtype and endogenous opioid peptides in the peripheral antinociceptive effect induced by xylazine.

Xylazine is an alpha(2)-adrenoceptor agonist extensively used in veterinary and animal experimentation. Evidence exists that alpha(2)-adrenoceptor agonists can activate opioid receptors via endogenous opioid release. Considering this idea and the multiple alpha(2) subtypes currently known (alpha(2A), alpha(2B), alpha(2C) and alpha(2D)), the aim of this study was to investigate which alpha(2) receptor subtype mediates xylazine-induced peripheral antinociception and possible opioid receptor and endogenous opioid involvement. The rat pressure test was used; the hyperalgesia was induced by intraplantar injection of prostaglandin E(2) (2 microg). Xylazine was administered locally (25, 50 and 100 microg) into the right hind paw of Wistar rat alone and after either alpha(2)-adrenoceptor antagonist yohimbine (5, 10 and 20 microg/paw), the alpha(2) antagonists to alpha(2A), alpha(2B), alpha(2C) and alpha(2D) subtypes (BRL 44 480, imiloxan, rauwolscine and RX 821002; 20 microg/paw, respectively) the opioid receptor antagonist naloxone (12.5, 25 and 50 microg) and the enkephalinase inhibitor bestatin (400 microg/paw). Intraplantar injection of xylazine (50 and 100 microg) induced peripheral antinociception; however, a dose of 25 microg/paw did not significantly reduce the hyperalgesic effect. Yohimbine, rauwolscine and naloxone prevented action of xylazine 100 microg/paw. BRL 44 480, imiloxan and RX 821002 were ineffective in blocking xylazine antinociception. Bestatin (400 microg/paw) potentiated the antinociceptive effect of xylazine 25 microg/paw. The present results provide evidence that the peripheral antinociceptive effect of xylazine probably results from activation of alpha(2C)-adrenoceptors and also by the release of endogenous opioids that act on their receptors.