Effects of d- and l-limonene on the pregnant rat myometrium in vitro

AIM: To study the effects of d- and l-limonene on pregnant rat myometrial contractility in vitro, and investigate how these effects are modified by other agents. D- and l-limonene (10(−13)-10(−8) M) caused myometrial contraction in a dose-dependent manner. METHODS: Contractions of uterine rings from 22-day-pregnant rats were measured in an organ bath in the presence of d- or l-limonene (10(−13)-10(−8) M) and nifedipine (10(−8) M), tetraethyl-ammonium (10(−3) M), theophylline (10(−5) M), or paxilline (10(−5) M). Uterine cyclic adenosine monophosphate (cAMP) level was detected by enzyme immunoassay. Oxidative damage was induced by methylglyoxal (3 × 10(−2) M) and the alteration was measured via noradrenaline (1 × 10(−9) to 3 × 10(−5) M) -induced contractions. RESULTS: Pre-treatment with nifedipine (10(−8) M), tetraethylammonium (10(−3) M), and theophylline (10(−5) M) attenuated the contracting effect of d- and l-limonene, while in the presence of paxilline (10(−5) M) d- and l-limonene were ineffective. The two enantiomers decreased the myometrial cAMP level, but after paxilline pretreatment the cAMP level was not altered compared with the control value. Additionally, l-limonene (10(−6) M) diminished consequences of oxidative damage caused by methylglyoxal (3 × 10(−2) M) on contractility, whereas d-limonene was ineffective. CONCLUSION: Our findings suggest that l-limonene has an antioxidant effect and that both d-and l-limonene cause myometrial contraction through activation of the A(2A) receptor and opening of the voltage-gated Ca(2+) channel. It is possible that limonene-containing products increase the pregnant uterus contractility and their use should be avoided during pregnancy.