Lack of effect of naltrexone on the spinal synergism between morphine and non steroidal anti-inflammatory drugs.

To enhance analgesia, the combinatorial use of analgesic drugs with proven efficacies is a widely-used strategy to reduce adverse side effects. The present study characterizes the antinociceptive interaction of intrathecal morphine co-administered with different NSAIDs using isobolographic analysis.Antinoceptive activity was evaluated using a model for acute visceral pain, the writhing test of mice. The possible involvement of opioid receptors in the mechanism of action of the intrathecal co-administration of morphine and NSAIDs was investigated using the non-selective receptor antagonist naltrexone. The study demonstrated a synergistic antinociception of intrathecal administered combinations of morphine with the following NSAIDs: diclofenac, ketoprofen, meloxicam, metamizol, naproxen, nimesulide, parecoxib and piroxicam. The supra additive effect was obtained with very low doses of each drug and it appeared to be independent of the COX-1 or COX-2 inhibition selectivity of each NSAID and was not significantly modified by intrathecal naltrexone. The findings of the present work suggest that the combination of opioids and NSAIDs has a direct action on spinal nociceptive processing, which may be achieved via mechanisms that are independent of the activation of opioid receptors. The ineffectiveness of naltrexone to reverse the analgesic activity of opioids + NSAIDs combinations indicates that other complex pain regulatory systems are involved in this effect.

Lack of effect of diet-induced hypomethylation on endothelium-dependent relaxation in rats.

BACKGROUND: Endothelial dysfunction is a key process in atherosclerosis. Hypomethylation is one of the postulated mechanisms involved in atherogenesis and is mainly secondary to a decrease in essential factors such as, folate and vitamin B12 for the biosynthesis of S-adenosylmethionine (SAM), the main methyl-group donor for methylation reactions. AIM: To investigate in an animal model, whether hypomethylation, secondary to folate or vitamin B12 deficiency, affects endothelium-dependent relaxation (EDR) induced by acetylcholine (ACh). METHODS: Adult male Wistar rats were divided into 4 groups of 12 rats each: folate and B12 deficiency (FB12D 0mg folate/kg, 0 microg/kg B12), folate deficiency (FD 0mg folate/kg and 50 microg/kg B12), B12 deficiency (B12D: 8 mg/kg folate and 0 microg/kg B12 and control diet (CD)). After eight weeks the animals were killed and thoracic aorta and liver removed. Serum concentration of homocysteine, folate and vitamin B12 were determined. Hepatic levels of SAM and S-adenosylhomocysteine (SAH) were measured, as indicator of hypomethylation. ACh-induced EDR and sodium nitroprusside (SNP)-induced endothelium-independent relaxation (EIR), in isolated aorta rings were evaluated. RESULTS: Hcy concentrations were significantly increased in the folate and B12 deficient groups. SAM and the SAM/SAH ratio were lower in the FD and FB12D than in the control and B12D group. Folate, B12 deficiency, serum Hcy levels and hepatic SAM/SAH ratio did not affect EDR neither EIR. CONCLUSIONS: In adult Wistar rats, chronic folate or folate plus vitamin B12 deficiency generates hypomethylation which is not related to an alteration of endothelial function.

Isobolographic analysis of multimodal analgesia in an animal model of visceral acute pain.

Multiple analgesic-drug combinations are commonly used in the management of acute and chronic pain in humans during multimodal or balanced analgesia. At present, these combinations are used empirically in clinical practice and are considered to be beneficial for the patient. Interactions between two antinociceptive drugs have been thoroughly examined, but the nature of interactions between three analgesics has not been studied. The antinociceptive interaction of ketoprofen (K) with a mixture of morphine (M) and paracetamol (P) was evaluated using a model of visceral acute tonic pain, the acetic-acid writhing test in mice. The i.p. administration of the combination M/P+K resulted in a significant potentiation of the antinociception induced either by K or by the synergic two-drug mixtures M/K, P/K and M/P. The effect of opioid, cholinergic, adrenergic and serotonergic antagonists on the analgesic interaction was assessed. The pretreatment of mice with atropine (1 mg/kg) did not produce any change in the synergistic interaction of the triple combination. The pretreatment with naltrexone (1 mg/kg) or tropisetron (1 mg/kg) reduced the intensity of M/P+K synergic interaction, while prazosin (0.1 mg/kg) significantly potentiated the synergy. The findings of this work suggest that the two major pathways of descending inhibitory systems, noradrenergic and serotonergic are significantly involved in the mechanism of the antinociceptive synergy induced by the triple combination. On the other hand, opioid pathways also seem to participate, since pretreatment with naltrexone reduced the synergy. In conclusion, the triple combination M/P+K induced a strong synergistic antinociceptive effect, which could be of interest for optimal multimodal clinical analgesia.

Influencia del sistema nitridérgico en la respuesta contráctil a fenilefrina de anillos de vasos usados en revascularización coronaria / Modification of phenylephrine induced contraction of human vessel rings by L-arginine and L-arginine methyl ester

Background: Endothelial dysfunction is associated to a lower production of nitric oxide and a reduction of endothelium mediated vasodilation. Aim: To study the effects of pharmacological agents that modify nitric oxide synthetase (NOS) activity on tension changes induced by phenylephrine in rings of internal mammary and radial arteries and saphenous vein. Material and methods: Vessel rings of 7 to 10 mm length were obtained from 32 patients subjected to coronary vascular surgery Fourteen samples of radial artery, 12 samples of internal mammary artery and 15 samples of saphenous vein were obtained. A maximal contraction was induced with KC1 and dose response curves for phenylephrine (FE) in the absence or presence of L-arginine and L-arginine methyl ester (L-NAME), were constructed. Results: The tension induced by FE in internal mammary artery and saphenous vein reached a maximum, near 90 percent of 80 mM KCl-induced contraction, but in the radial artery, it reached a maximum of 63 percent (p <0.05). In all vessels, the dose response curves were significantly shifted to the right by L-arginine and to the íeft by L-NAME. Conclusions: Pre-incubation of human rings with L-ARG or L-NAME, changed the response to FE induced contraction, which may be related to different degrees of endothelial nitric oxide production or NO sensitivity. The basal NO production in radial artery seems to be larger than the other vessels.

Dexketoprofen-induced antinociception in animal models of acute pain: synergy with morphine and paracetamol.

The antinociceptive activity of dexketoprofen was studied in mice using the acetic acid writhing test (acute tonic pain), the tail flick test (acute phasic pain) and the formalin assay (inflammatory pain). Isobolographic analysis was used to study the antinociceptive interactions between morphine and paracetamol co-administered with dexketoprofen. In the writhing test, the intraperitoneal administration of dexketoprofen or ketoprofen resulted in parallel dose-response curves with equal efficacy, but higher relative potency for dexketoprofen. In the tail flick test, the curves were parallel with similar efficacy and potency. The administration of morphine or paracetamol in both tests resulted in dose-response curves not parallel with that of dexketoprofen, which showed a potency between morphine and paracetamol. In the formalin assay, the antinociceptive activity of morphine during phase I was 122, 295 and 1695 times higher than dexketoprofen, ketoprofen and paracetamol, respectively. Isobolographic analysis demonstrated that the combination of sub-analgesic doses of dexketoprofen with morphine or with paracetamol was strongly synergic in all three tests. Synergistic drug combinations should improve effective pharmacological treatment of pain, minimizing drug specific adverse effects. These findings are undoubtedly worthy of additional controlled clinical trials in severe pain syndromes.

[Modification of phenylephrine induced contraction of human vessel rings by L-arginine and L-arginine methyl ester]. / Influencia del sistema nitridérgico en la respuesta contráctil a fenilefrina de anillos de vasos usados en revascularización coronaria.

BACKGROUND: Endothelial dysfunction is associated to a lower production of nitric oxide and a reduction of endothelium mediated vasodilation. AIM: To study the effects of pharmacological agents that modify nitric oxide synthetase (NOS) activity on tension changes induced by phenylephrine in rings of internal mammary and radial arteries and saphenous vein. MATERIAL AND METHODS: Vessel rings of 7 to 10 mm length were obtained from 32 patients subjected to coronary vascular surgery Fourteen samples of radial artery, 12 samples of internal mammary artery and 15 samples of saphenous vein were obtained. A maximal contraction was induced with KC1 and dose response curves for phenylephrine (FE) in the absence or presence of L-arginine and L-arginine methyl ester (L-NAME), were constructed. RESULTS: The tension induced by FE in internal mammary artery and saphenous vein reached a maximum, near 90% of 80 mM KCl-induced contraction, but in the radial artery, it reached a maximum of 63% (p <0.05). In all vessels, the dose response curves were significantly shifted to the right by L-arginine and to the left by L-NAME. CONCLUSIONS: Pre-incubation of human rings with L-ARG or L-NAME, changed the response to FE induced contraction, which may be related to different degrees of endothelial nitric oxide production or NO sensitivity. The basal NO production in radial artery seems to be larger than the other vessels.

Efecto agudo de las estatinas sobre la relajación vascular in vitro mediada por acetilcolina y nitroprusiato en vasos usados en la revascularización coronaria / Acute effect of statins on acetylcholine and nitroprusside induced vascular relaxation of vessels used for revascularization purposes

Antecedentes: Uno de los efectos pleiotrópicos de las estatinas es su capacidad de inducir relajación vascular tanto in Vitro como in Vivo cuando son administradas crónicamente, pero el efecto agudo en los vasos no ha sido estudiado en detalle. Objetivos: Evaluar los efectos agudos de las estatinas en la relajación vascular in vitro mediada por acetilcolina (ACh) y nitroprusiato en vasos usados en revascularización coronaria. Método: Se analizaron segmentos de vasos obtenidos de pacientes programados para cirugía de revascularización coronaria. Cada segmento de arteria radial, mamaria y vena safena fue dividido en dos, uno de ellos incubado durante dos horas con estatinas y el otro con solución buffer. Luego, se contrajo cada vaso con 80 mM de KCl y posteriormente con 10-4 M de noradrenalina seguido de administración de dosis acumulativas de ACh para inducir la relajación del vaso. Después de lavados repetidos, se contrae con la misma dosis de noradrenalina y se relaja con dosis creciente de nitroprusiato (NP). Resultados: La administración de KCl produjo una mayor contracción, aunque no significativa, en arterias radiales en relacióna los otros vasos, tanto en los incubados con estatinas como el grupo control. La noradrenalina produjo una mayor contracción no significativa en venas safenas; sin embargo no hubo diferencias entre los segmentos incubados con y sin estatinas. La vasodilatación por acetilcolina no se vio afectada por estatinas. La vasodilatación inducida por nitroprusiato no se modificó en presencia de estatinas en arterias radiales o mamaria. Sin embargo el tratamiento con estatina disminuyó significativamente la relajación inducida por nitroprusiato en la vena safena (p<0,05). Conclusión: Los resultados de este trabajo demuestran una respuesta diferencial de los vasos usados en revascularización coronaria frente al efecto agudo de estatina.

Synergism between paracetamol and nonsteroidal anti-inflammatory drugs in experimental acute pain.

The antinociception induced by the intraperitoneal coadministration of combinations of paracetamol with the nonsteroidal anti-inflammatory drugs (NSAIDs) diclofenac, ibuprofen, ketoprofen, meloxicam, metamizol, naproxen, nimesulide, parecoxib and piroxicam was studied by isobolographic analysis in the acetic acid abdominal constriction test of mice (writhing test). The effective dose that produced 50% antinociception (ED50) was calculated from the log dose-response curves of fixed ratio combinations of paracetamol with each NSAID. By isobolographic analysis, this ED50 was compared to the theoretical additive ED50 calculated from the ED(50) of paracetamol and of each NSAID alone obtained from ED50 dose-response curves. As shown by isobolographic analysis, all the combinations were synergistic, the experimental ED50s being significantly smaller than the theoretically calculated ED50s. The results of this study demonstrate potent interactions between paracetamol and NSAIDs and validate the clinical use of combinations of these drugs in the treatment of pain conditions.

Analgesic synergism between intrathecal morphine and cyclooxygenase-2 inhibitors in mice.

The analgesic effects of the intrathecal coadministration of morphine with nimesulide, meloxicam and parecoxib, preferential cyclooxygenase-2 (COX-2) inhibitors, were studied in mice using a chemical model of visceral pain, the acetic acid writhing test. Isobolographic analysis was used to characterize the interactions between mixtures of morphine with each non-steroidal anti-inflammatory drug. Antinociception dose-response curves were analyzed to obtain the ED50's of each drug. A dose response curve for fixed ratio mixtures of morphine with COX-2 inhibitors was then performed and the observed ED50's were plotted on a two-dimensional isobologram. All the combinations tested showed synergistic interactions and the strength of the interaction was ranked as: morphine/parecoxib>morphine/meloxicam>morphine nimesulide. The results demonstrate that the intrathecal coadministration of COX-2 inhibitors significantly enhance morphine-induced antinociception and could result in an opioid sparing action which may be useful in the clinical treatment of severe pain. A sparing action means that less opioids have to be administered to obtain a given analgesic effect. Since intrathecal morphine is often used in clinical pain situations, the opioid sparing effect resulting from the synergy observed with the coadministration of COX-2 inhibitors may be clinically relevant. One of the most significant advantages should be the reduction of opioid toxicity which often acts as a major obstacle in pain treatment.

Hypotensive effect of dopamine: synergism induced by fenoldopam or levodopa.

OBJECTIVE: The effects of the co-administration of fenoldopam (FD) or levodopa (LD) with dopamine (DA) on arterial blood pressure were studied in rats to assess the possibility of synergic effects that might be of some clinical importance. METHODS AND RESULTS: Mean arterial blood pressure (MBP) in the carotid artery of anaesthetized rats was registered. All agents induced dose-dependent reductions in mean arterial blood pressure when administered in a non-cumulative schedule to rats pretreated with phentolamine. For each drug, the doses that induced a 50% of reduction in basal mean arterial blood pressure, (ED50) calculated by standard linear regression analysis of the log dose-response curve and were 5.49 mg/kg, (n=10), 2.86 mg/kg, (n=11) and 0.445 mg/kg, (n=12), for FD, LD and DA, respectively. The interactions were evaluated by simultaneous administration of different fixed ratios of DA with FD (1:12.3) or DA with LD (1:6) and obtaining dose-response curves and ED50's for each mixture. An isobolographic analysis was then performed, which demonstrated that the co-administration had synergistic effects as illustrated by statistically higher reductions of blood pressure under each combination as compared to theoretical calculated additive effects. CONCLUSIONS: The present results show that in the rat, after alpha-adrenergic blockade, the association of DA and FD could inappropriately potentiate the hypotension induced by both drugs.

Spinal synergy between nonselective cyclooxygenase inhibitors and morphine antinociception in mice.

The antinociception induced by the intrathecal coadministration of combinations of morphine with the nonsteroidal anti-inflammatory drugs (NSAIDs) naproxen, piroxicam, metamizol, diclofenac and ketoprofen was studied by isobolographic analysis in the acetic acid writhing test of mice. The effective dose that produced 50% antinociception (ED(50)) was calculated from the log dose-response curve of intrathecally administered fixed ratio combinations of morphine with each NSAID. By isobolographic analysis, this ED(50) was compared to the theoretical additive ED(50) calculated from the ED(50) of morphine and of each NSAID alone. As shown by isobolograms, all the combinations were synergistic, the experimental ED(50)'s being significantly smaller than the theoretically calculated ED(50)'s. The results of this study demonstrate potent interactions between morphine and NSAIDs and validate the clinical use of the combinations of opioids and NSAIDs in pain treatment, even by the intrathecal route.

Neostigmine interactions with non steroidal anti-inflammatory drugs.

1. The common mechanism of action of non-steroidal anti-inflammatory drugs (NSAIDs) is the inhibition of the enzyme cyclo-oxygenase (COX), however, this inhibition is not enough to completely account for the efficacy of these agents in several models of acute pain. 2. It has been demonstrated that cholinergic agents can induce antinociception, but the nature of the interaction between these agents and NSAIDs drugs has not been studied. The present work evaluates, by isobolographic analysis, the interactions between the cholinergic indirect agonist neostigmine (NEO) and NSAIDs drugs, using a chemical algesiometric test. 3. Intraperitoneal (i.p.) or intrathecal (i.t.) administration of NEO and of the different NSAIDs produced dose-dependent antinociception in the acetic acid writhing test of the mouse. 4. The i.p. or i.t. co-administration of fixed ratios of ED(50) fractions of NSAIDs and NEO, resulted to be synergistic or supra-additive for the combinations ketoprofen (KETO) and NEO, paracetamol (PARA) and NEO) and diclofenac (DICLO) and NEO administered i.p. However, the same combinations administered i.t. were only additive. In addition, the combinations meloxicam (MELO) and NEO and piroxicam (PIRO) and NEO, administered either i.p. or i.t., were additive. 5. The results suggest that the co-administration of NEO with some NSAIDs (e.g. KETO, PARA or DICLO) resulted in a synergistic interaction, which may provide evidence of supraspinal antinociception modulation by the increased acetylcholine concentration in the synaptic cleft of cholinergic interneurons. The interaction obtained between neostigmine and the NSAIDs could carry important clinical implications.

Inhibidores selectivos de la COX-2 (ISC-2): evidencias actuales sobre su real eficacia y seguridad / COX-2 selective inhibitors (C2SI): update evidence of their efficacy and safety

A principios de la década pasada, fueron descubiertas dos isoformas de la enzima ciclooxigenasa, encargada de catalizar la producción de postaglandinas a partir del ácido araquidónico. La COX-1, expresada en forma constitutiva a nivel gastrointestinal, renal y plaquetario, y la COX-2, enzima principalmente inducible en proceso como la inflamación, el dolor y la fiebre. Numerosos estudios, han demostrado tanto la eficacia, como la seguridad gástrica y plaquetaria de los inhibidores selectivos de la COX-2, en estudios fase II y en estudios clínicos fase III. Basados en estos estudios, en 1999 fueron aprobados por la FDA, dos inhibidores selectivos, celecoxib y refecoxib, para su uso en pacientes con artrosis y artritis reumatoídea. Estos fármacos se encuentran también disponibles en nuestro país. Estudios recientes demuestran, sin embargo, que ambas isoformas de COX, participarían en el proceso inflamatorio, y por lo tanto, su eficacia analgésica y antiinflamatoria, serían menor a la obtenida con los antiinflamatorios no esteroidales tradicionales. Por otro lado, tanto a nivel gástrico como renal se ha visto participación de la COX-2 en procesos fisiológicos, como la resolución de la inflamación en mucosas dañadas y en la embriogénesis renal en ratas. Por último, existen varias evidencias que demuestran funciones fisiológicas de la COX-2, en sitios tan disímiles como el sistema nervioso central y el colon. En estas localizaciones ha sido implicada en la patogenia de la enfermedad de Alzheimer y del cáncer de colon, lo que abre la posibilidad de desarrollar nuevas líneas de investigación, destinadas a encontrar nuevos tratamientos para éstas y otras patologías

Potenciación cruzada entre antihistamínicos-H1 y atropina en el tratamiento de los síndromes respiratorios inducidos por histamina y por acetilcolina en acures / Cross-potentiation between H1-antihistamninies and atropine in the treatment of the respiratory syndrome induced by histamine and acetilcholine in guinea pigs

Se estudió el efecto de los antagonistas específicos sobre una condición experimental del acure que simula el asma, producida por dos agonistas distintos, acetilcolina (Ach) e histamina (H). Se midió el tiempo de aparición de los síntomas secuenciales (disnea, asfixia y colapso) y su variación bajo el efecto del antagonista específico de la H (feniltoloxamina, FTX) y de la Ach (atropina). En el asma producida por los dos agonistas, H y Ach, el antagonista específico fue potenciado por el antagonista no específico en sus efectos sobre todos los síntomas. Por el contrario, en la intoxicación de acure por H indovenosa, los efectos fueron estrictamente aditivos, al igual que sobre el músculo liso aislado. Los resultados fueron analizados estadísticamente para indicar la magnitud del sinergismo de potenciación. La potenciación es atribuida a la intervención de distintos receptores y/o a la variación de sensibilidad de un receptor bajo la acción de un agonista. Además, la liberación de varios mediadores por autoestimulación debida al agonista puede tener influencias