Investigação da atividade tocolítica do óleo essencial de Lippia microphylla Cham. (Verbenaceae) e dos seus constituintes majoritários, carvacrol e timol, em útero de rata.

Abstract

ABSTRACT From leaves of Lippia microphylla Cham. (Verbenaceae) was extracted the essential oil (LM - OE), which has carvacrol and thymol as major constituents . The aim of this work was to investigate and to characterize the tocolytic effect of LM - OE on rat uterus, as well as to verify if this effect is du e its isolated major constituents, carvacrol and thymol, or themself mixture. For this, w ere performed measures of isotonic and isometric contractions on isolated rat uterus. LM - OE inhibited both phasic contractions induced by carbachol (CCh) 10 - 5 M and by oxytocin 10 - 2 UI/mL (IC 50 = 7.8 ± 1.3 and 3 5.1 ± 4.9 μg/mL, respectively). While the carvacrol, thymol and thymol - carvacrol mixture (1.46:1) antagonized the phasic contractions induced by CCh ( E max = 41.4 ± 10.3; 35.4 ± 8.3 and 56.5 ± 9 . 2% , respectively) with low efficacy . But when the contractions were induced by oxytocin, only thymol and thymol - carvacrol mixture, showed inhibitory effect ( E max = 38.8 ± 4.8 and 69.8 ± 2.4% , respectively). Similarly , LM - OE relaxed in an equipotent manner the uterus pre - contracted with 60 mM KCl (EC 50 = 5.0 ± 0.8 μg/mL ) and oxytocin 10 - 2 UI/mL ( EC 50 = 2.7 ± 0.8 μg/mL) . As the common step in the signaling pathway of these contractile agents is voltage - dependent calcium channels (Ca V ), we hypothesized that somehow LM - OE would preventing Ca 2+ influx by these channels. T he LM - OE antagonized cumulative concentration - response curves to CaCl 2 in Ca 2+ - free depolarizing medium suggesting blocking calcium influx through Ca V . This hypothesis was discarded when the LM - OE relaxed uterus pre contracted with 3 x 10 - 7 M of S ( ) Bay K8644 , CA V 1 agonist , but with a very low efficacy ( E max = 17.4 ± 5.0% ) and without dependence of concentration , confirming that the LM - OE directly does not block the calcium influx through these channels. Since K + channels can negatively modulate the Ca V , we decided to investigate the role of these channels in the tocolytic effect of LM - OE . To assess this hypothesis has been tested its effect in the presence of CsCl 5 mM, a non - selective potassiu m channels blocker . The results showed that LM - OE (EC 50 = 30 . 3 ± 2 .2 μg/mL) appears to activate/upregulate positively these channels, however other experiments sho uld be conducted to confirm which potassium channels subtypes are involved in this tocolytic effect . Thus, the tocolytic effect of LM - OE does not directly involves blocking of calcium influx through Ca V , however involves the participation of K + channel s , while their major isolated constituents and the mixture of these have low efficacy in isolated rat uterus.