Inhibitor Report for: Amitriptyline

1. The effect of amitriptyline on human serum butyrylcholinesterase (acylcholine acylhydrolase E.C.3.1.1.8) has been investigated. From the Lineweaver-Burk plot and the plot of v versus amitriptyline concentration, it was concluded that amitriptyline inhibition is partially competitive, and the kinetic parameters have been calculated as Ks = 0.11 mM, alpha = 1425 and Ki = 0.01 mM. 2. Because amitriptyline is a partial competitive inhibitor of butyrylcholinesterase, acquired deficiency may be seen in patients treated with amitriptyline and may cause complications in operations.

The effects of two cognition enhancers on avoidance impairment induced by the tricyclic antidepressant amitriptyline were assessed during shuttle-box avoidance acquisition and in previously trained mice of the DBA/2 strain. The nootropic agent piracetam (50, 100 or 200 mg/kg, i.p.) had slight or no effect in mice receiving amitriptyline (5 or 10 mg/kg, i.p.). Conversely, the acetylcholinesterase inhibitor tacrine (0.5, 1, 2 or 3 mg/kg, i.p.) prevented the avoidance impairment induced by 5 mg/kg amitriptyline on shuttle-box avoidance acquisition as well as on a previously learned avoidance response. The avoidance disrupting action produced by 10 mg/kg of the antidepressant drug was not affected by the anticholinesterase drug. The preventing action of tacrine seems specifically related to the avoidance impairment induced by amitriptyline, since the acetylcholinesterase inhibitor did not reduce, but enhanced the avoidance impairing action of the neuroleptic chlorpromazine. Taken together, the results indicate that amitriptyline-induced avoidance impairment, and the related preventing action of tacrine, may be ascribed to drug effects on the performance of the avoidance response, rather than to interferences with learning processes.

The response of central cholinergic neurotransmission to the chronic administration of some psychotropic drugs to rats was investigated using brain acetylcholinesterase activity as a neurochemical marker for cholinergic neurons. Rats were divided into four groups. Three experimental groups were given chlorpromazine, amitriptyline, or diazepam respectively, for a period of 30 days; and the control group received physiological saline only. Long-term treatment of chlorpromazine and amitriptyline resulted in significant increases in rat brain cortex enzyme activity, whereas only a slight increase was observed in the diazepam-treated group. These results indicate that the chronic treatment with some psychotropic drugs causes changes in central cholinergic transmission.

1. The effect of several central nervous system active drugs was studied in vitro on ATPase-ADPase activity and acetylcholinesterase (AChE) activity from the cerebral cortex of adult rats. 2. Lithium (1.0-10.0 mM) had no effect on either ATPase-ADPase or acetylcholinesterase activity. 3. Imipramine (0.5-5.0 mM), desipramine (0.5-5.0 mM), amitriptyline (0.1-1.0 mM) and diazepam (0.5-2.0 mM) inhibited ATP and ADP hydrolysis at all concentrations tested. 4. AChE activity was altered by imipramine (1.0-2.0 mM) and by diazepam (0.5-2.0 mM). 5. The possible participation of ATP diphosphohydrolase and AChE in the action of these drugs cannot be ruled out. The probable reduction of ATP, ADP and acetylcholine hydrolysis by the inhibitory effect of these drugs is discussed.

1. The effect of amitriptyline on human serum butyrylcholinesterase (acylcholine acylhydrolase E.C.3.1.1.8) has been investigated. From the Lineweaver-Burk plot and the plot of v versus amitriptyline concentration, it was concluded that amitriptyline inhibition is partially competitive, and the kinetic parameters have been calculated as Ks = 0.11 mM, alpha = 1425 and Ki = 0.01 mM. 2. Because amitriptyline is a partial competitive inhibitor of butyrylcholinesterase, acquired deficiency may be seen in patients treated with amitriptyline and may cause complications in operations.

The effects of two cognition enhancers on avoidance impairment induced by the tricyclic antidepressant amitriptyline were assessed during shuttle-box avoidance acquisition and in previously trained mice of the DBA/2 strain. The nootropic agent piracetam (50, 100 or 200 mg/kg, i.p.) had slight or no effect in mice receiving amitriptyline (5 or 10 mg/kg, i.p.). Conversely, the acetylcholinesterase inhibitor tacrine (0.5, 1, 2 or 3 mg/kg, i.p.) prevented the avoidance impairment induced by 5 mg/kg amitriptyline on shuttle-box avoidance acquisition as well as on a previously learned avoidance response. The avoidance disrupting action produced by 10 mg/kg of the antidepressant drug was not affected by the anticholinesterase drug. The preventing action of tacrine seems specifically related to the avoidance impairment induced by amitriptyline, since the acetylcholinesterase inhibitor did not reduce, but enhanced the avoidance impairing action of the neuroleptic chlorpromazine. Taken together, the results indicate that amitriptyline-induced avoidance impairment, and the related preventing action of tacrine, may be ascribed to drug effects on the performance of the avoidance response, rather than to interferences with learning processes.

This investigation has been carried out on albino mice. In the first series of experiments, we determined the dependence of LD50 of aminostigmine on different doses of 10 cholinolytics, and conversely, the dependence of LD50 of cholinolytics on aminostigmine administration. The initial slopes of the dose-effect curves were calculated. This data form the basis for evaluation of the character and degree of interactions. We established that benactyzine, spasmolytin, ftoracizin, arpenal, atropine, ganglerone, and methacin at low doses exhibit antagonism (with decreasing activity), whereas at high doses they exhibit synergism to the toxic effect of aminostigmine. In the interaction with aminostigmine, pirenzepine and amitriptyline (M1--cholinolytics) reveal a slightly pronounced antagonism, whereas aetyrophene, a selective central N-cholinolytic, displays mutual synergism. In the second series of experiments we showed that a combination of M1-, M2-cholinolytic atropine with M1- cholinolytics does not change the efficacy of the prophylaxis of aminostigmine and physostigmine poisoning, whereas a combination with N-cholinolytic increases it.

We compared the effects of YM796 [(-)-S-2,8-dimethyl-3-methylene-1-oxa-8- azaspiro[4,5]-decane L-tartrate monohydrate], a novel muscarinic agonist, on passive avoidance response with those of the cholinomimetics AF102B [(+/-)-cis-2-methylspiro-(1,3-oxathiolane-5,3')-quinuclidine hydrochloride] and NIK247 [9-amino-2,3,5,6,7,8-hexahydro1H-cyclopenta(b)- quinoline monohydrate hydrochloride] in senescence-accelerated mice. SAMP8@YAN (SAM-P/8, senescence-accelerated-prone substrain) showed an age-dependent shortening in the latency of step-through when compared with SAMR1/YAN (SAM-R/1, senescence-accelerated-resistant substrain). The shortened latency of step-through in SAMP8@YAN was prolonged by administration of YM796 (0.3 and 1 mg/kg, PO), AF102B (3 and 10 mg/kg PO), and NIK247 (30 mg/kg, PO) in a bell-shaped manner. In contrast, amitriptyline (10, 30, and 50 mg/kg, PO), with cholinolytic properties, had no effect on this shortened latency of step-through. These results suggest that YM796, AF102B, and NIK247 ameliorated the disturbance of learning behavior, presumably due to facilitation of the central cholinergic system in SAMP8@YAN mice and that SAMP8@YAN may be an appropriate age-dependent model of amnesia for evaluating pharmacological actions of drugs.

The response of central cholinergic neurotransmission to the chronic administration of some psychotropic drugs to rats was investigated using brain acetylcholinesterase activity as a neurochemical marker for cholinergic neurons. Rats were divided into four groups. Three experimental groups were given chlorpromazine, amitriptyline, or diazepam respectively, for a period of 30 days; and the control group received physiological saline only. Long-term treatment of chlorpromazine and amitriptyline resulted in significant increases in rat brain cortex enzyme activity, whereas only a slight increase was observed in the diazepam-treated group. These results indicate that the chronic treatment with some psychotropic drugs causes changes in central cholinergic transmission.