Thymol and Carvacrol as Potential Tocolytic and Anti-inflammatory Agents in Pregnant Rat Uterus

This work aimed to evaluate the anti-inflammatory and myorelaxant effect of thymol (TM) and carvacrol (CAR) in the pregnant rat uterus. Both compounds exhibit considerable antimicrobial, antispasmodic, and anti-inflammatory effects and due to these properties, they were studied in this in vitro model of premature birth induced by infection.

All uterine tissues were studied in uterine contraction tests to determine the inhibitory effect of TM, CAR (10, 56, 100, 150, and 230 μM), and nifedipine (a calcium channel antagonist) on phasic and tonic contraction induced by electro- and pharmacomechanical stimuli. The quantitative determination of cyclic adenosine monophosphate (cAMP) induced by TM and CAR in the uterine lysate was carried out by ELISA. For the determination of the anti-inflammatory effect of TM, the pro-inflammatory cytokine, interleukin (IL)-1β, in uterine samples stimulated with lipopolysaccharide (LPS) was measured. Forskolin (FSK) was used as a positive control to evaluate the cAMP and cytokine levels. TM, CAR, and nifedipine inhibited the uterine contractions at the highest concentration level, however, nifedipine was the most equipotent (p<0.05). In addition, TM and CAR did not increase the intracellular cAMP production in comparison with FSK (p<0.05). However, both compounds were able to decrease the LPS-induced production in a concentration-dependent manner that was considered statistically significant (p>0.05).

Finally, both the anti-inflammatory and uterine relaxing effects induced by TM and CAR were neither associated with the increase in cAMP levels nor with the production of IL-1β in pregnant rat uterine samples. Therefore, TM and CAR can be considered as alternative adjuvants for the treatment of infection-induced preterm labor. Before the in vitro experiments, an in-silico analysis was conducted using the Expaisy online server to evaluate the biological effects of thymol on uterine contraction.

It is crucial to know the interaction and identification of genes encoding the Voltage-dependent L-type calcium channel subunit alpha-1C proteins, because of the functional relationship it may have in the inhibition of the uterine contraction. These properties place TM as a potentially safe and effective adjuvant agent in cases of preterm birth, an area of pharmacological treatment that requires urgent improvement.