is2.dal.ca

In the present study, we sought to determine whether administration of caffeine, a non-selective adenosine receptor antagonist, would affect the thermal antihyperalgesic efficacy of acute amitriptyline in a rat model of neuropathic pain. Rats were rendered neuropathic by unilateral tight ligation of the fifth and sixth lumbar spinal nerves, and tested for thermal hyperalgesia using a focused beam of light. Systemic administration of caffeine (1.5-7.5 mg/kg), at the same time as amitriptyline, blocked the thermal antihyperalgesic effect of 10 mg/kg amitriptyline. The greatest degree of block exerted by caffeine was observed with 3.75 mg/kg (100% block), a dose that had no observable intrinsic effect. Spinal administration of amitriptyline (60 microg) exhibited a mild antihyperalgesic effect that was unaffected by pretreatment with intrathecal caffeine (100 microg). Peripheral administration of amitriptyline into the neuropathic paw (under brief anesthesia) produced an antihyperalgesic effect at both 30 and 100 nmol, with a greater effect being observed at 100 nmol. Coadministration of caffeine (1500 nmol) partially antagonized the effects of both doses of amitriptyline. The results of this study suggest that the thermal antihyperalgesic effect of acute amitriptyline in this model may involve enhancement of an endogenous adenosine tone. This involvement is important in light of the widespread consumption of caffeine, which may potentially act to reduce the benefits of amitriptyline in the treatment of neuropathic pain.

Online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10884512&dopt=Abstract Elavil amitriptyline

dragonar.nm.cau.ac.kr

The effects of amitriptyline, a tricyclic antidepressant, on tetrodotoxin-sensitive and tetrodotoxin-resistant Na(+) currents in rat dorsal root ganglion neurons were studied using the whole-cell patch clamp method. Amitriptyline blocked both types of Na(+)currents in a dose-and holding potential-dependent manner. At the holding potential of -80 mV, the apparent dissociation constants (K(d)) for amitriptyline to block tetrodotoxin-sensitive and tetrodotoxin-resistant Na(+) channels were 4.7 and 105 microM, respectively. These values increased to 181 and 193 microM, respectively, when the membrane was held at a potential negative enough to remove the steady-state inactivation. Amitriptyline dose-dependently shifted the steady-state inactivation curves in the hyperpolarizing direction and increased the values of the slope factors for both types of Na(+) channels. The voltage dependence of the activation of both types of Na(+) channels was shifted in the depolarizing direction. It was concluded that amitriptyline blocked the two types of Na(+) channels in rat sensory neurons by modulating the activation and the inactivation kinetics.

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Psychoneuroendocrinology. 2000 Nov;25(8):785-97.
The effect of repeated amitriptyline and desipramine administration on cytokine release in C57BL/6 mice.

Kubera M, Holan V, Mathison R, Maes M.

Department of Endocrinology, Institute of Pharmacology, Polish Academy of Sciences, Smetna 12, 31-343, Krakow, Poland.

This study examines the effects of repeated amitriptyline and desipramine administration (10 mg/kg, IP) on the immunoreactivity of saline-injected C57BL/6 mice, as evaluated by the ability of splenocytes to reduce a tetrazolium salt to formazan (MTT test), to proliferate, and to produce cytokines, such as interleukin (IL)-1, IL-2, IL-4, IL-6, IL-10 and interferon gamma (IFN-gamma). Desipramine and amitriptyline administered for one or two weeks enhance the biochemical (estimated by MTT test) and proliferative activities of splenocytes. One and two weeks administration of desipramine significantly reduces the secretion of IL-4, an anti-inflammatory cytokine. Amitriptyline administration for four weeks stimulates the proliferative activity of splenocytes and enhances IL-2 bioactivity, whereas four weeks desipramine aministration does not change these parameters in comparison to saline treated control mice. Prolonged desipramine administration (seven and 28 days) significantly increased the bioactivity of IL-1. Four weeks of prolonged administration of amitriptyline and desipramine induces a significant increase in the secretion of IL-10, a cytokine with immunosuppressive and anti-inflammatory activities. The results show that the immunoregulatory effects of tricyclic antidepressants in C57BL/6 mice depend on the drugs used and on the duration of administration.

Online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10996474&dopt=Abstract Elavil amitriptyline




Neuropharmacology. 2001;40(1):75-84.
Involvement of potassium channels in amitriptyline and clomipramine analgesia.

Galeotti N, Ghelardini C, Bartolini A.

Department of Pharmacology, University of Florence, Viale G. Pieraccini 6, I-50139, Florence, Italy.

The effect of the administration of modulators of different subtypes of K(+) channels on antinociception induced by the tricyclic antidepressants amitriptyline and clomipramine was evaluated in the mouse hot plate test. The administration of the voltage-gated K(+) channel blocker tetraethylammonium (0.01-0.5 microg per mouse i.c.v. ) prevented antinociception induced by both amitriptyline (15 mg kg(-1) s.c.) and clomipramine (25 mg kg(-1) s.c.). The K(ATP) channel blocker gliquidone (0.1-1.0 microg per mouse i.c.v.) prevented antinociception produced by amitriptyline and clomipramine whereas the K(ATP) channel openers minoxidil (10 microg per mouse i. c.v.) and pinacidil (25 microg per mouse i.c.v.) potentiated tricyclic antidepressant-induced analgesia. The administration of the Ca(2+)-gated K(+) channel blocker apamin (0.1-1.0 ng per mouse i. c.v.) completely prevented amitriptyline and clomipramine analgesia. At the highest effective doses, none of the drugs used induced behavioural side effects or impaired motor coordination, as revealed by the rota-rod test, spontaneous motility or inspection activity, as revealed by the hole board test. The present results demonstrate that central antinociception induced by amitriptyline and clomipramine involves the opening of different subtypes of K(+) channels (voltage-gated, K(ATP) and Ca(2+)-gated) which, therefore, represent a step in the transduction mechanism of tricyclic antidepressant analgesia.

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JAMA. 1978 Sep 22;240(13):1372-3.
Abuse of amitriptyline.

Cohen MJ, Hanbury R, Stimmel B.

Amitriptyline hydrocholride (Elavil) is frequently used in treating mild to moderate depressive states. A survey of 346 persons enrolled in a methadone maintenance program showed that 86 (25%) had admitted taking amitriptyline with the purpose of achieving euphoria. Thin-layer chromatography of random urine specimens over five months showed that 34% of the patients had a positive result for amitriptyline at least once during this time. These results suggest that misuse of amitriptyline is not uncommon and should be carefully considered prior to prescribing this agent to narcotic dependent persons.

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J Neurol Neurosurg Psychiatry. 2001 Jan;70(1):78-82.
Amitriptyline enhances the central component of physiological tremor.

Raethjen J, Lemke MR, Lindemann M, Wenzelburger R, Krack P, Deuschl G.

Department of Neurology, University of Kiel, Niemannsweg 147, 24105 Kiel, Germany.

OBJECTIVES: Postural tremor is a regularly encountered side effect of amitriptyline which can be strong enough to cause discontinuation of therapy. The aim was to characterise amitriptyline induced tremor and to assess if the central or reflex component of physiological tremor was modulated by this drug. METHODS: The postural hand tremor was measured in 15 patients on a clinical rating scale, by power spectral analysis of accelerometer, forearm flexor, and extensor EMG before and after the beginning of amitriptyline treatment for major depression or chronic pain syndrome. A coherence analysis between flexor and extensor muscles on the same side was performed. RESULTS: There was a clinically visible increase in postural tremor in a third of these patients. The tremor amplitude measured by accelerometer total power increased in every patient under amitriptyline. The EMG synchronisation as reflected by significant peaks in the flexor or extensor spectrum generally occurring at higher frequencies (8-18 Hz) than the accelerometric tremor frequencies (6-11 Hz) did not change. The number of patients with a significant flexor-extensor coherence in the 7-15 Hz range increased significantly under amitriptyline, the frequency bands of significant coherence corresponded with the EMG frequencies, and both were independent of changes to the hand's resonant frequency by added inertia. CONCLUSIONS: An enhancement of postural tremor under amitriptyline is a common phenomenon although not always clinically apparent. The increase in EMG-EMG coherence indicates an increased common central drive to the motor units as its frequency is not influenced by peripheral resonance or reflex mechanisms. This is the first account of a drug induced enhancement of the central component of physiological tremor.

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Life Sci. 2000 Nov 24;68(1):81-90.
Differential effects of tricyclic antidepressant drugs on membrane dynamics--a fluorescence spectroscopic study.

Sanganahalli BG, Joshi PG, Joshi NB.

Department of Biophysics, National Institute of Mental Health and Neuro Sciences, Bangalore, India.

The effect of tricyclic antidepressant drugs amitriptyline, nortriptyline, imipramine and desipramine on synaptosomal membrane and lipid bilayer was studied using steady state and time dependent fluorescence spectroscopy of lipid specific fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). The synaptosomal membrane was prepared from rat brain while liposomes were prepared from dimyristoyl phosphatidyl choline (DMPC) alone and a mixture of DMPC and cholesterol. Upon treatment with amitriptyline and nortriptyline a decrease was observed in the steady state anisotropy of DPH in DMPC liposomes as well as in rat brain synaptosomes. On the other hand, imipramine and desipramine did not cause any significant change. Amitriptyline and nortriptyline also decreased the steady state anisotropy of DPH in liposomes prepared from a mixture of DMPC and cholesterol. Fluorescence decay time and time dependent anisotropy of DPH in both the membranes were measured and the decay of anisotropy was analyzed using wobbling in cone model. Amitriptyline and nortriptyline treatment decreased the limiting anisotropy and order parameter, while the cone angle increased. Imipramine and desipramine did not cause significant change in these parameters. In addition to structural alterations, these drugs inhibited the activity of Na+-K+-ATPase in synaptosomal membrane, however, the decrease was more in case of amitriptyline and nortriptyline as compared to imipramine and desipramine. Our results suggest that the perturbation in membrane order caused by antidepressant drugs could depend on the net charge on the drug molecule.

Online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11132248&dopt=Abstract Elavil amitriptyline