RESUMEN
We investigated the in vitro effect of the essential oil of Croton nepetifolius Baill., Euphorbiaceae (EOCN), on spontaneous or induced contractions of circular and longitudinal muscles from the ovine cervix during the luteal phase of the estrous cycle. The relaxant effect of EOCN was expressed as a percentage of the contraction recorded before the addition of the oil and calculated relative to the preparations exposed only to the vehicle. The IC50 (concentration of oil required to produce a 50% maximal reduction in muscle contraction) for relaxation of spontaneous contractions in circular and longitudinal muscles was significantly lower than the IC50 for blockade of K+-induced contraction (27.19 µg mL-1 versus 262.72 µg mL-1 and 40.92 µg mL-1 versus 222.47 µg mL-1, respectively). Interestingly, there was a high degree of selectivity in the action of EOCN on cervix layers concerning the inhibition of acetylcholine-induced contraction in circular (IC50 277.10 µg mL-1) and longitudinal (IC50 52.56 µg mL-1) muscles. In conclusion, EOCN is able to relax ovine cervix during the luteal phase. This work opens the perspective of applying EOCN in ovine embryo transfer.