Effect of Nicardipine on Contraction Inhibition, β-Adrenergic Receptor Cascade, and Oxytocin Receptors

Abstract

We evaluated in pregnant sheep the effectiveness of nicardipine, a calcium channel blocker, in inhibiting and maintaining inhibition of oxytocin-induced myometrial contractility over a 24-hr period. We also evaluated the effect of this agent on the myometrial β-adrenergic receptor cascade and oxytocin receptors. We placed catheters into the maternal aorta, inferior vena cava and amnionic cavity and obtained a myometrial biopsy from 5 near term pregnant sheep. After 1–4 days of recovery, we infused nicardipine intravenously at a rate of 4 μg/kg/min for 24 hrs. Animals received the same bolus injection of oxytocin into the aorta prior to and after 4 and 24 hr of nicardipine infusion. We quantified the uterine response to oxytocin by measuring the area under the uterine pressure-time curve with planimetry. After 24 hr infusion of nicardipine, the animals were sacrificed and another myometrial biopsy was obtained. Nicardipine concentrations neared steady state concentration by 4 hr averaging 61 ± 23 ng/ml. Ox...