Mechanisms of direct inhibitory action of propofol on uterine smooth muscle contraction in pregnant rats.

Background: Although propofol directly inhibits uterine smooth muscle contraction, the mechanisms of this effect are still unknown. The current study aimed to clarify the mechanisms of the inhibitory effect of propofol on oxytocin-induced uterine smooth muscle contraction by measuring (1) the concentration of intracellular free Ca(2+) ([Ca(2+)](i)) simultaneously with muscle tension, (2) the amount of intracellular inositol 1,4,5-triphosphate ([IP(3)](i)), and (3) voltage-dependent Ca(2+) channel (VDCC) activity.

Methods: Uterine smooth muscle tissues were obtained from pregnant rats (in late gestation). [Ca(2+)](i) with isometric tension was monitored by the 500-nm light emission ratio of preloaded Ca(2+) indicator fura-2. [IP(3)](i) and VDCC activity were measured by radioimmunoassay and patch clamp techniques, respectively. The uterine smooth muscle was stimulated by 20 nm oxytocin and exposed to propofol (10(-7) approximately 10(-4) m).

Results: Propofol had significant inhibitory effects on oxytocin-induced uterine smooth muscle contraction and increased [Ca(2+)](i) in pregnant rats in a dose-dependent manner, without affecting the agonist-receptor binding affinity. Propofol inhibited the increase in [IP(3)](i) induced by oxytocin. Propofol also inhibited VDCC activity in both activated and inactivated states. The solvent Intralipid had no effects on these parameters.

Conclusions: Propofol inhibits oxytocin-induced uterine smooth muscle contraction, at least in part, by decreasing [Ca(2+)](i) without affecting agonist-receptor binding; the inhibitory effect of propofol on [Ca(2+)](i) might be mediated both by a decrease in [IP(3)](i) and by inhibition of VDCC activity.