The novel analgesic compound OT-7100 (5-n-butyl-7-(3,4,5-trimethoxybenzoylamino)pyrazolo[1,5-a]pyrimid ine) attenuates mechanical nociceptive responses in animal models of acute and peripheral neuropathic hyperalgesia.
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We investigated the effects of OT-7100, a novel analgesic compound (5-n-butyl-7-(3,4,5-trimethoxybenzoylamino)pyrazolo[1,5-a]pyrimidi ne), on prostaglandin E2 biosynthesis in vitro, acute hyperalgesia induced by yeast and substance P in rats and hyperalgesia in rats with a chronic constriction injury to the sciatic nerve (Bennett model), which is a model for peripheral neuropathic pain. OT-7100 did not inhibit prostaglandin E2 biosynthesis at 10(-8)-10(-4) M. Single oral doses of 3 and 10 mg/kg OT-7100 were effective on the hyperalgesia induced by yeast. Single oral doses of 0.1, 0.3, 1 and 3 mg/kg OT-7100 were effective on the hyperalgesia induced by substance P in which indomethacin had no effect. Repeated oral administration of OT-7100 (10 and 30 mg/kg) was effective in normalizing the mechanical nociceptive threshold in the injured paw without affecting the nociceptive threshold in the uninjured paw in the Bennett model. Indomethacin had no effect in this model. While amitriptyline (10 and 30 mg/kg) and clonazepam (3 and 10 mg/kg) significantly normalized the nociceptive threshold in the injured paw, they also increased the nociceptive threshold in the uninjured paw. These results suggest that OT-7100 is a new type of analgesic with the effect of normalizing the nociceptive threshold in peripheral neuropathic hyperalgesia. (+info)
Amitriptyline and procainamide inhibition of cocaine and cocaethylene degradation in human serum in vitro.
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Amitriptyline (AMI) and procainamide (PA) have been reported to inhibit the activity of human plasma butyrylcholinesterase, an enzyme important in the metabolic degradation of cocaine (COC) and its ethyl analogue cocaethylene (CE). Because both AMI and PA may be used in the treatment of COC intoxication and abuse, the effect of high pharmacological concentrations of these compounds on the degradation of COC and CE in pooled human serum was studied. AMI (1.8 micromol/L) modestly inhibited the degradation of COC by 4.2% and of CE by 4.0%. PA (42.5 micromol/L) profoundly inhibited degradation of COC by 42.7% and of CE by 47.2%. In contrast, lithium carbonate (1 mmol/L, control) showed no inhibition of degradation of either COC or CE. These results suggest that AMI and PA may prolong the half-life of COC and CE in human serum. (+info)
Determination of amitriptyline and nortriptyline in human liver microsomes with reversed-phase HPLC in vitro.
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AIM: To develop a method for simultaneous determinations of amitriptyline (Ami) and its metabolite nortriptyline (Nor) in human liver microsomes. METHODS: An incubation buffer containing microsomes, NADPH-generating system, and Ami, after termination of enzyme reaction and desipramine (Des) as internal standard (IS), was extracted with diethy ether and separated on a reversed-phase ODS column. Detection was achieved at 242 nm by ultraviolet detector. RESULTS: No potential interfering peaks were found. Ami and Nor gave rapid elution and baseline resolution. The linear curves of both analyses ranged 0.02-10 nmol and the limit of detection was 0.01 nmol. The recovery (94%-101%) had good precision with relative s of < 8.3%. CONCLUSION: This method is rapid, sensitive, and simple for studying the metabolism of Ami and Nor. (+info)
Pharmacokinetic and pharmacodynamic characterization of OROS and immediate-release amitriptyline.
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AIMS: To characterize the pharmacokinetics of amitriptyline and its metabolite nortriptyline following OROS and IR treatments, and to correlate them with anticholinergic side-effects. METHODS: The pharmacokinetics and safety of amitriptyline following administration of an osmotic controlled release tablet (OROS and an immediate release (IR) tablet were evaluated in 14 healthy subjects. In this randomized, open label, three-way crossover feasibility study, the subjects received a single 75 mg OROS tablet, three 25 mg IR tablets administered every 8 h, or 3x25 mg IR tablets administered at nighttime. In each treatment arm serial blood samples were collected for a period of 84 h after dosing. The plasma samples were analysed by gas chromatography for amitriptyline and its metabolite nortriptyline. Anticholinergic effects such as saliva output, visual acuity, and subject-rated drowsiness and dry mouth were measured on a continuous scale during each treatment period. RESULTS: Following dosing with OROS (amitriptyline hydrochloride), the mean maximal plasma amitriptyline concentration Cmax (15.3 ng ml-1 ) was lower and the mean tmax (25.7 h) was longer than that associated with the equivalent IR dose administered at nighttime (26.8 ng ml-1 and 6.3 h, respectively). The bioavailability of amitriptyline following OROS dosing was 95% relative to IR every 8 h dosing, and 89% relative to IR nighttime dosing. The metabolite-to-drug ratios after the three treatment periods were similar, suggesting no change in metabolism between treatments. The relationships between plasma amitriptyline concentration and anticholinergic effects (e.g. reduced saliva weight, dry mouth, and drowsiness) were similar with all three treatments. Of the anticholinergic effects, only decreased saliva weight and dry mouth correlated well with plasma amitriptyline concentrations; drowsiness did not. There was no apparent correlation between anticholinergic effects and the plasma nortriptyline concentration. CONCLUSIONS: The bioavailability of OROS (amitriptyline hydrochloride) was similar to that of the IR treatments and the pharmacokinetics of amitriptyline after OROS dosing may decrease the incidence of anticholinergic effects compared with that seen with nighttime dosing of the IR formulation. Therefore, this controlled-release formulation of amitriptyline may be appropriate for single daily administration. (+info)
Relaxant effects of antidepressants on human isolated mesenteric arteries.
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AIMS: The therapeutic action of tricyclic agents may be accompanied by unwanted effects on the cardiovascular system. The evidence for the effects on vascular and nonvascular smooth muscle comes from animal studies. Whether these studies can be extrapolated to human vessels remains to be determined. Therefore, the present study was designed to investigate the influence of amitriptyline, nortriptyline and sertraline on the contractile responses of human isolated mesenteric arteries to electrical field stimulation, noradrenaline and potassium chloride. METHODS: Arterial segments (lumen diameter 0.8-1.2 mm) were obtained from portions of the human omentum during the course of 41 abdominal operations (22 men and 19 women), and rings 3 mm long were mounted in organ baths for isometric recording of tension. In some artery rings the endothelium was removed mechanically. RESULTS: In precontracted artery rings amitriptyline, nortriptyline and sertraline (3x10(-7)-10(-4) m ) produced concentration-dependent relaxation that was independent of the presence or absence of vascular endothelium. Incubation with indomethacin (3x10(-6) m ) reduced the pD2 values thus indicating the participation of dilating prostanoid substances in this response. Amitriptyline and nortriptyline inhibited both the neurogenic-and noradrenaline-induced contractions. In contrast, only the highest concentration of sertraline reduced the adrenergic responses. Amitriptyline, nortriptyline and sertraline inhibited contractions elicited by KCl and produced rightward shifts of the concentration-response curve to CaCl2 following incubation in calcium-free solution. CONCLUSIONS: These results indicate that amitriptyline and nortriptyline could act as adrenoceptor antagonists and direct inhibitors of smooth muscle contraction of human mesenteric arteries, whereas sertraline might principally exert its action only as direct inhibitor of smooth muscle contraction. This relaxant mechanism involves an interference with the entry of calcium. (+info)
Inhibition of the high affinity myo-inositol transport system: a common mechanism of action of antibipolar drugs?
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The mechanism of action of antibipolar drugs like lithium, carbamazepine, and valproate that are used in the treatment of manic-depressive illness, is unknown. Lithium is believed to act through uncompetitive inhibition of inositolmonophosphatase, which results in a depletion of neural cells of inositol and a concomitant modulation of phosphoinositol signaling. Here, we show that lithium ions, carbamazepine, and valproate, but not the tricyclic antidepressant amitriptyline, inhibit at therapeutically relevant concentrations and with a time course similar to their clinical actions the high affinity myo-inositol transport in astrocyte-like cells and downregulate the level of the respective mRNA. Inhibition of inositol uptake could thus represent an additional pathway for inositol depletion, which might be relevant in the mechanism of action of all three antibipolar drugs. (+info)
Inhibition of the current of heterologously expressed HERG potassium channels by imipramine and amitriptyline.
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1 Tricyclic antidepressants (TCAs) are associated with cardiovascular side effects including prolongation of the QT interval of the ECG. In this report we studied the effects of two TCAs (imipramine and amitriptyline) on ionic current mediated by cloned HERG potassium channels. 2 Voltage clamp measurements of HERG currents were made from CHO cells transiently transfected with HERG cDNA. HERG-encoded potassium channels were inhibited in a reversible manner by both imipramine and amitriptyline. HERG tail currents (IHERG) following test pulses to +20 mV were inhibited by imipramine with an IC50 of 3.4+/-0.4 microM (mean+/-s.e.mean) and a Hill coefficient of 1.17+/-0.03 (n = 5). 3 microM amitriptyline inhibited IHERG by 34+/-6% (n = 3). The inhibition showed only weak voltage dependence. 3 Using an 'envelope of tails' comprised of pulses to +20 mV of varying durations, the tau of activation was found to be 155+/-30 ms for control and 132+/-26 ms for 3 microM imipramine (n = 5). Once maximal channel activation was achieved after 320 ms (as demonstrated by maximal tail currents), further prolongation of depolarization did not increase imipramine-mediated HERG channel inhibition. 4 Taking current measurements every second during a 10 s depolarizing pulse from -80 mV to 0 mV, block was observed during the first pulse in the presence of imipramine and the level of IHERG block was similar throughout the pulse (n=5). 5 A three pulse protocol (two depolarizing pulses to +20 mV separated by 20 ms at -80 mV) revealed that imipramine did not significantly alter the kinetics of IHERG inactivation. The tau of inactivation was 8+/-2 ms and 5.6+/-0.4 ms (n = 5) in the absence and presence of 3 microM imipramine, respectively, and currents inactivated to a similar extent. 6 Our data are consistent with TCAs causing components of block of the HERG channel in both the closed and open states. Any component of open channel block occurs rapidly upon depolarization. Inhibition of IHERG by the prototype TCAs imipramine and amitriptyline may suggest a mechanism for QT prolongation associated with risks of arrhythmia and sudden death that accompany high concentrations of TCAs following overdose. (+info)
Fluoxetine and amitriptyline inhibit nitric oxide, prostaglandin E2, and hyaluronic acid production in human synovial cells and synovial tissue cultures.
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OBJECTIVE: To evaluate the effects of fluoxetine and amitriptyline on nitric oxide (NO), prostaglandin E2 (PGE2), and hyaluronic acid (HA) production in human synovial cells and synovial tissue cultures. METHODS: Human synovial cells, synovial tissue, and cartilage were cultured in the presence or absence of cytokines, lipopolysaccharides (LPS), fluoxetine, or amitriptyline. Production of NO, PGE2, and HA was determined in culture media. Sulfated glycosaminoglycan (S-GAG) synthesis was evaluated in cartilage by 35S incorporation. RESULTS: Fluoxetine (0.3 microg/ml, 1 microg/ml, and 3 microg/ml) inhibited NO release by 56%, 62%, and 71%, respectively, in the media of synovial cells stimulated by interleukin-1alpha (IL-1alpha; 1 ng/ml) plus tumor necrosis factor alpha (TNFalpha; 30 ng/ml). Amitriptyline (0.3 microg/ml, 1 microg/ml, and 3 microg/ml) caused a 16%, 27.3%, and 51.4% inhibition of NO release. Fluoxetine and amitriptyline (0.3 microg/ml, 1 microg/ml, and 3 microg/ml) significantly (P<0.05) inhibited PGE2 release in the media of human synovial cells in the presence of IL-1alpha plus TNFalpha, in a dose-dependent manner (up to 88% inhibition). Fluoxetine (0.3 microg/ml, 1 microg/ml, and 3 microg/ml) and amitriptyline (1 microg/ml and 3 microg/ml) significantly (P<0.05) inhibited PGE2 release in the media of human synovial tissue in the presence of LPS. Fluoxetine and amitriptyline (0.3 microg/ml, 1 microg/ml, and 3 microg/ml) also significantly (P<0.05) inhibited HA production by human synovial cells in the presence of IL-1beta plus TNFalpha. Fluoxetine and amitriptyline (1 microg/ml) partially reversed IL-1beta-induced inhibition of 35S-GAG synthesis by human cartilage cultures (P<0.05). Neither fluoxetine nor amitriptyline had a toxic effect on cells in the concentrations used. CONCLUSION: Inhibition of NO and PGE2 production by connective tissue cells is a mechanism by which some antidepressant medications may affect pain, articular inflammation, and joint damage. (+info)