Mechanisms involved in the relaxant action of the ethanolic extract of propolis in the guinea-pig trachea in-vitro.
This study examines the mechanisms by which the standardised ethanolic extract of propolis induces relaxation of the guinea-pig trachea in-vitro. In guinea-pig trachea with or without epithelium and contracted by histamine, the propolis extract caused reproducible and graded relaxation, with a mean EC50 value of 3.8 or 10.5 microg mL(-1) and Emax of 100%, respectively. The propolis extract-induced relaxation was markedly reduced (26+/-9 and 96+/-3%) when guinea-pig tracheas were exposed to Krebs solution containing elevated K+ in the medium (40 or 80 mM). Pre-incubation of guinea-pig tracheas with tetraethylamonium (100 mM) or with 4-aminopyridine (10mM) reduced the propolis extract-induced relaxation by 31+/-10% and 28+/-2%. Likewise, apamin (0.1 microM), charybdotoxin (0.1 microM) or iberiotoxin (0.1 microM) caused marked inhibition of propolis extract-mediated relaxation in guinea-pig trachea (percentage of inhibition: 65+/-3%, 60+/-5% and 65+/-9%, respectively). Also, glibenclamide (1 microM) inhibited the relaxant response caused by the propolis extract by 57+/-4%. Omega-conotoxin GIVA (0.1 microM) or capsaicin (1 microM) produced small but significant inhibition (30+/-5% or 47+/-7%, respectively) of the propolis extract-induced relaxation. The vasoactive intestinal peptide (VIP) antagonist D-p-Cl-Phe6,Leu17[VIP] porcine (0.1 microM) inhibited relaxation by 55+/-5%, while propranolol (1 microM) induced a parallel rightward displacement (about 20 fold) of the propolis extract concentration-response curve. Finally, the propolis extract-induced relaxation was inhibited by the nitric oxide synthase inhibitor L-N(G)-nitroarginine (L-NOArg, 100 microM) (48+/-6%), and by the soluble guanylatecyclase inhibitormethylene blue (10 microM) (37+/-6%), whilethe moreselectivesoluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolol[4,3-alquinoxalin-1-one (ODQ, 1 microM) produced only a parallel (about 3 fold) rightward displacement of the propolis extract concentration-response curve. Collectively, these results support the notion that the propolis extract-mediated relaxation in the guinea-pig trachea involves the release of nitric oxide, probably from sensory neurons, besides the activation of soluble guanylate cyclase and activation of Ca2+- and ATP-sensitive K+ channels. Furthermore, the stimulation of beta2-adrenergic and VIP receptors also seems to account for its relaxant action.
Paulino
Niraldo
N
Grupo de Pesquisa e Desenvolvimento de Biofármacos, Universidade do Sul de Santa Catarina, Tubarão, Brasil. niraldo@unisul.br
Scremin
Fernando M
FM
Raichaski
Lisiane B
LB
Marcucci
Maria Cristina
MC
Scremin
Amarilis
A
Calixto
João B
JB
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001938:Brazil; D002851:Chromatography, High Pressure Liquid; D000431:Ethanol; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000037:antagonists & inhibitors; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D011429:Propolis / Q000737:chemistry / Q000494:pharmacology*; D018343:Receptors, Adrenergic, beta-2 / Q000187:drug effects; D018005:Receptors, Vasoactive Intestinal Peptide / Q000037:antagonists & inhibitors; D012997:Solvents; D014132:Trachea / Q000187:drug effects* / Q000502:physiology
D000319:Adrenergic beta-Antagonists; D007473:Ion Channels; D018343:Receptors, Adrenergic, beta-2; D018005:Receptors, Vasoactive Intestinal Peptide; D012997:Solvents; D000431:Ethanol; D011429:Propolis