Barakol suppresses norepinephrine-induced inhibition of spontaneous longitudinal smooth muscle contractions in isolated rat small intestine.
The present study aimed to investigate the purgative effects of barakol, the purified extract of Cassia siamea Lam., on the longitudinal smooth muscle contractions of the rat ileum. The extract increased the force of spontaneous muscle contractions in a concentration-dependent manner (EC50=0.3 mM). Saxitoxin (0.3 microM) abolished the stimulatory effects of barakol, a result indicating a neural mechanism of action. In addition, atropine (10 microM) but not propanolol (10 microM) or phentolamine (10 microM), partially inhibited barakol-induced smooth muscle contractions suggesting that cholinergic nerves were involved. The motor effects of barakol were further examined in muscle strips treated with catecholamines to suppress spontaneous contractile activity and decrease muscle tone. Norepinephrine or dopamine (10 microM) decreased the amplitude of spontaneous contractions by 72% and 18%, respectively. Pretreatment of the tissues with barakol (1 mM) significantly decreased the inhibitory effect of norepinephrine by 60%, but not that of dopamine. Its ability to potentiate atropine- and saxitoxin-sensitive contractions and inhibit the antimotility actions of norepinephrine suggests that barakol may increase longitudinal smooth muscle contractions by decreasing the inhibitory effect of norepinephrine on excitatory cholinergic motor neurons. Barakol may produce a purgative action in small intestine which may be clinically important in patients with intestinal hypomotility disorders.
Deachapunya
Chatsri
C
Department of Physiology, Faculty of Medicine, Srinakharinwirot University, Sukhumvit 23, Wattana, Bangkok 10110, Thailand. chatsri@swu.ac.th
Thongsaard
Watchareewan
W
Poonyachoti
Sutthasinee
S
D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology*; D004298:Dopamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007082:Ileum / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology*; D043803:Phenalenes / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D001578:Benzopyrans; D043803:Phenalenes; C107911:barakol; D004298:Dopamine; D009638:Norepinephrine