Effect of vasoconstrictor and vasodilator on isolated human umbilical vein

The mechanical properties of the longitudinal and circular muscle tissues of the human umbilical vein and the effects of nicardipine were investigated. Spontaneous contractions were observed in the isometric condition. When high concentrations of potassium (118mM-K+), oxytocin and serotonin were applied, these substances evoked contractions. Oxytocin (10(-4)-10(-2) U/ml) enhanced the spontaneous contractions. Serotonin produced contractions at 10(-9)-10(-4) M in both the longitudinal and circular muscle strips. When nicardipine (10(-5) M) was applied, contractions induced by 118mM-K+ were completely inhibited, but contractions induced by serotonin could not be completely abolished, i.e., tonic contractions ceased but small phasic contractions continued. Nicardipine (10(-8) M) did not inhibit the amplitude and frequency of spontaneous contractions, but decreased the basal tonus. These results suggested that nicardipine might improve feto-placental blood flow while decreasing the spontaneous basal tonus.