Acetylcholine (ACh)

Bose, Saifi and Sharma, Archives Internationales de Pharmacodynamie et de Therapie (1963),30 found that PHT lowered acetylcholine levels in rat heart by 9.6% at 4 mg/kg PHT and by 18.9% at 8 mg/kg.

30. Bose, B. C., Saifi, A. Q., and, Sharma, S. K., Studies on anticonvulsant and antifibrillatory drugs, Arch. Int. Pharmacodyn., 146: 106-113, 1963.

Agarwal and Bhargava, Indian Journal of Medical Research (1964),1 determined brain acetylcholine (ACh) levels in rat using a frog rectus abdominis muscle bioassay. PHT (100 mg/kg) intraperitoneally, lowered brain ACh levels 38%; methedrine lowered brain ACh by 42%; and pentamethylene tetrazol lowered brain ACh by 47%. In contrast, phenobarbital, pentobarbital, morphine, meprobamate and reserpine increased brain ACh, and chlorpromazine produced no change.

1. Agarwal, S. L. and Bhargava, V., Effect of drugs on brain acetylcholine levels in rats, Indian J. Med. Res., 52: 1179-1182, 1964.

Baker, Okamoto and Riker, The Pharmacologist (1971),789 found that in a cat soleus nerve-muscle preparation, pretreatment with PHT counteracts the additional excitation produced by injecting acetylcholine. The authors note that PHT selectively suppresses the post-tetanic potentiation of motor nerve terminals without impairing single impulse transmission.

789. Baker, T., Okamoto, M., and Riker, W. F., Diphenylhydantoin (DPH) suppression of motor nerve terminal (MNT) excitation by acetylcholine (ACh), Pharmacologist, 13: 265, 1971.

Woodbury and Kemp, Psychiatria, Neurologia, Neurochirurgia (1971),1696 discuss the work of Van Rees, Woodbury and Noach at their laboratory in which small amounts of PHT (0.3-3 µg/ml) were found to increase the release of acetylcholine from parasympathetic nerve endings in the wall of the ileum and also from the intramural ganglia and thus have a stimulating effect on the contraction of the ileum. However, when the contraction of the ileum was made excessive by the addition of acetylcholine, PHT inhibited the contractions. Thus, a biphasic effect of PHT in this circumstance was referred to by the authors.

1696. Woodbury, D. M. and Kemp, J. W., Pharmacology and mechanisms of action of diphenylhydantoin, Psychiat. Neurol. Neurochir., 74: 91-115, 1971.

Gilbert and Wylie, Advances in Epileptology (1978),2536 studied the effects of PHT and other drugs on magnesium-ATPase located in synaptic vesicles and on acetylcholine and norepinephrine release. They found that PHT (200 µM) can inhibit magnesium- and sodium-potassium-ATPase in the nerve terminal. PHT did not alter basal acetylcholine release, but increased basal norepinephrine release. PHT abolished the electrically-evoked release of acetylcholine and reduced the evoked release of norepinephrine.

2536. Gilbert, J. C., Wyllie, M. G., Effects of anticonvulsants at the nerve terminal, Advances in Epileptology, Meinardi, H., Rowan, A. J., Swets & Zeitlinger, Amsterdam, 172-75, 1978.

Vizi and Pasztor, Experimental Neurology (1981),3050 reported that PHT (1 µM) significantly reduced the ouabain-induced release of acetylcholine, without affecting resting release, in isolated human cortical brain slices. The authors suggest that PHT's ability to reduce repetitive firing and ACh release contributes to its therapeutic effects.

3050. Vizi, E. S., Pasztor, E., Release of acetylcholine from isolated human cortical slices: inhibitory effect of norepinephrine and phenytoin, Exp. Neurol., 73: 114-53, 1981.

Aly and Abdel-Latif, Neurochemical Research (1982),2285 reported on the effects of PHT, carbamazepine, phenobarbital and valproate on acetylcholine-stimulated 32P incorporation into phospholipids in rat brain synaptosomes. Of the four drugs studied, only PHT (10-100 µM) blocked the ACh-stimulated labeling of phosphatidylinositol and phosphatidic acid and break-down of polyphosphoinositides. In the absence of acetylcholine, PHT had no effect on the 32P labeling of phospholipids or ATP. The authors suggest that PHT's regulation of sodium and calcium membrane permeability is important to its actions on ACh-stimulated phospholipid metabolism and, thus, synaptic function.

2285. Aly, M. I., Abdel-Latif, A. A., Studies on the effects of acetylcholine and antiepileptic drugs on 32Pi, incorporation into phospholipids of rat brain synaptosomes, Neurochem. Res., 7(2): 159-69, 1982.

Prasad and Kumari, Indian Journal of Pharmacology (1982),2879 reported the effects of PHT on acetylcholine content of different areas of the dog brain and on the release of ACh from dog cerebral cortex. They found that intravenous PHT (30 mg/ kg) increased ACh in the frontal cortex, hippocampus, corpus callosum and midbrain, but decreased it in the hypothalamus. PHT significantly reduced release of ACh from the cerebral cortex.

2879. Prasad, S., Kumari, P., Effect of diphenylhydantoin (DPH) sodium on some neurotransmitters of central nervous system, Indian J. Pharmacol., 14: 25, 1982.

Quest, Breed and Gillis, Journal of Cardiovascular Pharmacology (1982),2887 found that PHT significantly reduced cardiac slowing produced by both vagus stimulation and injected acetylcholine in cats with cervical vagotomy and spinal cord transection. PHT's blockade of the ACh response suggested that it acts on the postsynaptic membrane.

2887. Quest, J. A., Breed, C. R., Gillis, R. A., Effect of phenytoin on cardiac slowing induced by cholinergic stimulation, J. Cardiovasc. Pharmacol., 4: 629-34, 1982.

Diamond, Gordon, Davis and Milfay, Advances in Neurology (1983),2451 studied the effects of PHT on the phosphorylation of acetylcholine receptors (AChR) in the electric organ of the eel. They found that the membrane-bound AChR is reversibly phosphorylated by endogenous protein kinase and that PHT markedly inhibits this phosphorylation. Half-maximal inhibition occurred at 50 µM. The authors suggest that PHT achieves this inhibition by its direct effects on the availability of postsynaptic protein substrates for the phosphorylation reaction and that PHT may modulate receptor sensitivity by this mechanism.

2451. Diamond, I., Gordon, A. S., Davis, C. G., Milfay, D., Phenytoin and phosphorylation of nicotinic receptors, Advances in Neurology. Status Epilepticus, Delgado-Escueta, A. V., et al., Eds., Raven Press, New York, 339-44, 1983.

Pincus and Weinfeld, Brain Research (1984),2870 studied the effect of PHT on acetylcholine release from rat brain synaptosomes. PHT (200 µM) reduced the depolarization-dependent release of ACh in media containing 1.0 mM calcium and 56 mM potassium-chloride. PHT increased ACh release in non-depolarized synaptosomes, irrespective of calcium concentration. PHT did not affect release of ACh from depolarized synaptosomes in calcium-free media. The authors note that PHT has two effects. By limiting sodium-calcium exchange, it increases calcium concentration intracellularly, leading to an increase in spontaneous ACh release. By interfering with calcium uptake at the synaptosomal membrane during depolarization, PHT decreases depolarization-linked ACh release.

2870. Pincus, J. H., Weinfeld, H. M., Acetylcholine release from synaptosomes and phenytoin action, Brain Res., 296: 313-17, 1984.

Miller and Richter, British Journal of Pharmacology (1985),2795 reported that PHT, administered intraperitoneally prior to preparation of synaptosomes, increased high-affinity choline uptake (20-48%) in mouse hippocampal synaptosomes. This was in contrast to barbiturates, which inhibited choline uptake, and to carbamazepine, which had no effect.

2795. Miller, J. A., Richter, J. A., Effects of anticonvulsants in vivo on high affinity choline uptake in vitro in mouse hippocampal synaptosomes, Br. J. Pharmacol., 84(l): 19-25, 1985.

Pincus and Kiss, Brain Research (1986),3495 reported that phenytoin (10 M) inhibited the potassium-evoked release of acetylcholine from rat brain synaptosomes, a process which is biphasic. Phenytoin acted only on the early phase of release. Replacement of external sodium with lithium did not modify phenytoin's effect. Phenytoin augmented the spontaneous release of acetylcholine from resting synaptosomes, but this effect was eliminated in lithium-containing media. The authors suggest that PHT reduces potassium-evoked calcium uptake and sodium/calcium exchange by separate mechanisms.

3495. Pincus, J.H. and Kiss, A., Phenytoin reduces early acetylcholine release after depolarization, Brain Res., 397: 103-7, 1986.

Pincus and Kiss, Experimental Neurology (1986),3496 assayed the effect of phenytoin (100 to 200 M) and/or tetrodotoxin (1 M) on acetylcholine release in rat brain synaptosomes depolarized with either KCl (56 mM) or veratridine (10 M). Phenytoin reduced release in both depolarizing solutions. In KCl the effect of phenytoin was greater at 200 M than 100 M, but with veratridine, phenytoin (200 M) was not more effective than 100 M. Tetrodotoxin failed to affect release induced by KCl, but the effect of tetrodotoxin and phenytoin on veratridine-stimulated release was much greater than that with phenytoin alone (100 M). The authors conclude that the inhibition of acetylcholine release by phenytoin must be independent of any effect of the drug on Na conductance.

3496. Pincus, J.H. and Kiss, A., Phenytoin, tetrodotoxin, and acetylcholine release, Exp. Neurol., 94: 777-81, 1986

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