The relaxant effect of nicardipine on the isolated uterine smooth muscle of the pregnant rat

BACKGROUND: Nicardipine, a calcium channel blocker, is used to treat hypertension in pregnancy or preterm labor. The current study was conducted to investigate the relaxant effects of nicardipine on the isolated uterine smooth muscle of the pregnant rat. METHODS: We obtained uterine smooth muscle strips from pregnant female SD rats. After uterine contraction with oxytocin 10 mU/ml, we added nicardipine (10(−12) to 10(−8) M) accumulatively every 20 min. We recorded active tension and frequency of contraction, and calculated EC(5) (effective concentration of 5% reduction), EC(25), EC(50), EC(75), and EC(95) of active tension and frequency of contraction using a probit model. RESULTS: Nicardipine (10(−12) to 10(−8) M) decreased active tension and frequency of contraction in a concentration-dependent manner. The EC(50) and EC(95) of nicardipine in the inhibition of active tension of the uterine smooth muscle were 2.41 × 10(−10) M and 3.06 × 10(−7) M, respectively. The EC(50) and EC(95) of nicardipine in the inhibition of frequency of contraction of the uterine smooth muscle were 9.04 × 10(−11) and 4.18 × 10(−7) M, respectively. CONCLUSIONS: Nicardipine relaxed and decreased the frequency of contraction of the uterine smooth muscle in a concentration-dependent pattern. It might be possible to adjust the clinical dosage of nicardipine in the obstetric field based on our results, but further clinical studies are needed to confirm them.