Characterisation of the anti-inflammatory and antinociceptive activities and the mechanism of the action of Lippia gracilis essential oil

Aim of the study

Lubricating gut pill (LGP), a traditional Chinese formula, had been conformed to improve the loperamide-induced rat constipation by stimulation of Cl⁻ secretion, but its mechanism has not been fully explored. Thus, the purpose of this study was to identify the action sites of LGP-stimulated Cl⁻ secretion across rat distal colonic mucosa.

Materials and methods

Rat distal colonic mucosa was mounted in Ussing chambers and short circuit current (I_SC), apical Cl⁻ current and basolateral K⁺ current were recorded. Intracellular cyclic adenosine monophosphate (cAMP) content and protein kinase A (PKA) activity were determined with ELISA kit and the non-radioactive PepTag test, respectively.

Results

LGP at 800 μg/ml elicited a sustained increase in Cl⁻ secretory response, which was inhibited by CFTR_inh172, a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor. Permeabilizing apical membrane with nystatin revealed that LGP-stimulated basolateral K⁺ current was significantly inhibited by KCNQ1 K⁺ channel inhibitor chromanol 293B. LGP-stimulated I_SC was markedly reduced by pretreatment with cis-N-2-phenylcyclopentyl]-azacyclotridec-1-en-2amine (MDL-12,330A) and N-2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not with inhibitors of Ca²⁺-dependent signaling pathway. Treatment of tissue with LGP resulted in an increase in intracellular cAMP level and the activation in protein kinase A. The E-prostanoid₄ (EP)₄ receptor antagonist L-161,982 completely eliminated LGP-induced response.

Conclusions

The results showed that LGP enhances Cl⁻ and fluid secretion via prostanoid receptor signaling and also cAMP and protein kinase A pathway, subsequently triggering the activation of apical Cl⁻ channels mostly CFTR and basolateral cAMP-dependent K⁺ channel.