Lignocaine augments the in-vitro uterine contractions involving NO-guanylyl cyclase dependent mechanisms.

AIMS: Lignocaine is used during intrapartum and postpartum period but there are conflicting reports regarding the effect of lignocaine on uterine contractility. Therefore, this study was undertaken to delineate the effect of lignocaine on uterine contractility and the underlying mechanisms.

MAIN METHODS: The in vitro contractions were recorded from the uterine segments obtained from adult rats (in estrous phase) and also from human myometrial tissue. Effect of lignocaine on spontaneous uterine contractions was recorded in the absence or presence of antagonists. Effect of sodium nitroprusside (SNP, NO donor) on uterine contractility was assessed. The NO2(-) was assayed (indicator of NO activity) from the supernatant after exposing the myometrial tissue to lignocaine in the absence or the presence of L-NAME or hemoglobin.

KEY FINDINGS: Lignocaine (100μM) increased the amplitude of uterine contractions by 75% with no alterations in frequency. Similar magnitude of increase was seen with human myometrial tissue also. The spontaneous activities were absent in Ca(2+)-free or in nifedipine (10μM) containing medium. Heparin (IP3 blocker, 10IU/ml), but not the indomethacin (10μM) blocked the lignocaine-induced augmentation. L-NAME (NOS inhibitor, 10μM) or methylene blue (guanylyl cyclase inhibitor, 100μM) partially blocked the lignocaine-induced augmentation. SNP (30μM) increased the amplitude of spontaneous uterine contractions. Lignocaine increased the NO2(-) content (indicator of NO activity) of uterine tissue and the increase was blocked by L-NAME or hemoglobin.

SIGNIFICANCE: Present observations indicate that lignocaine augments the amplitude of uterine contractions via Ca(2+)-dependent mechanisms involving NO-G cyclase-dependent mechanisms.