RESUMO
Ginger [Zingiber officinale] is universally known food plant reputed for its medicinal use in gastrointestinal disorders as a prokinetic and laxative. We recently showed that 70% aqueous-methanolic extract of ginger [Zo.Cr] exhibits prokinetic activity in rats via activation of post-synaptic muscarinic M[3] receptor in rat stomach fundus. In view of the physiological significance of pre-synaptic muscarinic M[1] and M[2] autoreceptors, this study was undertaken to further look into the possible mode of action of the prokinetic effect of ginger through inhibition of pre-synaptic muscarinic receptors. Isolated tissue bath experiments were performed with Sprague-Dawley rat stomach fundus strip preparations immersed in Kreb's solution at 37 degree C. Carbachol [CCh] maximum responses [1 microM] were obtained in rat stomach fundus. Zo.Cr, given in multiple increasing bolus concentrations [0.01-0.1 mg/ml] 10 min prior to administration of CCh, potentiated the CCh peak responses showing that it is possibly inhibiting the pre-synaptic muscarinic receptors. Like wise, increasing bolus concentrations of pirenzepine [0.03-0.3 micro M] and himbacine [0.01-0.03 micro M], standard muscarinic M[1] and M[2] antagonists respectively, also potentiated the CCh responses. These results show that ginger, in addition to having a direct cholinergic effect on the post-synaptic M[3] receptors, also has a possible inhibitory effect on pre-synaptic muscarinic autoreceptors, similar to standard muscarinic antagonists, thus reiterating the gastric stimulant effect of this age-old plant