[Effect of serotonin on uteroplacentofetal circulatory system in pregnant rabbit].

The effects of serotonin (5-hydroxytryptamine) on the uteroplacentofetal circulatory system were studied in pregnant rabbits. Serotonin infusion (50 micrograms/kg) induced transient, but significant fetal bradycardia (deceleration), without any significant changes in maternal blood pressure, heart rates, pO2, pCO2 and uterine activities. Pretreatment with methysergide, a serotonin antagonist, with a dose of 2.5 mg/kg blocked the inhibitory effect of serotonin on fetal heart rate. However, methysergide itself produced the uterine contraction associated with mild fetal bradycardia. Direct injection of serotonin (1,000 micrograms/kg) into fetuses did not produce any changes in fetal heart rates. These data indicated that serotonin would influence the uteroplacental vasculature, which in turn induced fetal bradycardia.