The neuromuscular blockade produced by pure alkaloid, mitragynine and methanol extract of kratom leaves (Mitragyna speciosa Korth.).
OBJECTIVE
The effects of pure alkaloid, mitragynine and a methanolic extract of kratom leaves were investigated on neuromuscular junction and compound nerve action potential.


METHODS
Wistar rats were killed by cervical dislocation and decapitated. The phrenic nerve-hemidiaphragms, hemidiaphragms and sciatic nerve were isolated.


RESULTS
Kratom methanolic extract present at 0.1-1 mg/mL and mitragynine (0.0156 mg/mL) decreased the muscle twitch on the isolated phrenic nerve-hemidiaphragm and hemidiaphragm preparation. Muscle relaxation caused by kratom extract (1 mg/mL) was greater than the effect of mitragynine. Pancuronium and succinylcholine potentiated the effect of kratom extract. It also had a direct relaxation effect on the hemidiaphragm muscle. The muscle relaxation caused by kratom extract was not antagonized by neostigmine, tetraethylammonium and calcium chloride. High concentrations of kratom extract (10-40 mg/mL) and mitragynine (2 mg/mL) blocked the nerve conduction, amplitude and duration of compound nerve action potential.


CONCLUSIONS
The mechanism of action of kratom extract might not act as a competitive antagonist of acetylcholine yet its dominant effect was at the neuromuscular junction and not at the skeletal muscle or somatic nerve.
Chittrakarn
Somsmorn
S
Department of Pharmacology, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla, Thailand. somsmorn.c@psu.ac.th
Keawpradub
Niwat
N
Sawangjaroen
Kitja
K
Kansenalak
Supaporn
S
Janchawee
Benjamas
B
D000818:Animals; D003964:Diaphragm / Q000187:drug effects; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D032065:Mitragyna / Q000737:chemistry*; D009126:Muscle Relaxation / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation; D019148:Neuromuscular Blockade / Q000379:methods*; D009469:Neuromuscular Junction / Q000187:drug effects*; D010791:Phrenic Nerve / Q000187:drug effects; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000187:drug effects; D046948:Secologanin Tryptamine Alkaloids / Q000302:isolation & purification / Q000494:pharmacology*
D010936:Plant Extracts; D046948:Secologanin Tryptamine Alkaloids; C001801:mitragynine