Effects of lidocaine on rat myometrial sodium channels and implications for the management of preterm labor.

Abstract

We examined the effects of lidocaine on ionic channels of single uterine myocytes and on the duration of pregnancy. The electrophysiologic effects of lidocaine on the sodium, calcium, and potassium channels of freshly dissociated myocytes from rat uteri in late pregnancy were studied with the tight-seal patch-clamp method. Dose-response relations on the sodium and calcium currents and effects on the availability relation for sodium current were examined. Also studied were the effects of long-term administration of lidocaine on the duration of pregnancy. Lidocaine blocks Na+ channels selectively, with an ED50 (concentration of lidocaine capable of blocking half of the Na+ current) of 0.11 mmol/L. It shifts the availability relations for sodium ion to more negative voltages. When administered from day 20 until delivery, lidocaine prolonged term by 7%. Lidocaine can selectively block myometrial Na+ channels, thereby reducing excitability. It can prolong term in the pregnant rat. These observations suggest that lidocaine might be useful in the clinical management of preterm labor.