Transplacental passage and hemodynamic effects of esmolol in the gravid ewe.

Using a chronic maternal-fetal sheep preparation, the authors determined the transplacental passage and the hemodynamic changes consequent to maternal administration of esmolol. Fifteen experiments were performed in six chronically instrumented pregnant ewes near term. Each animal received esmolol iv, 500 micrograms.kg-1.min-1, for 4 min and then 300 micrograms.kg-1.min-1 for 6 min. Maternal and fetal blood esmolol concentrations (mean +/- SEM) were 1.2 +/- 0.28 and 0.1 +/- 0.03 micrograms/ml, respectively, at the completion of the infusion, and 0.03 +/- 0.01 microgram/ml in the mother and not detectable in the fetus 10 min after stopping the infusion. Despite the relatively low blood esmolol concentration in the fetus compared to the mother, the hemodynamic effects in the fetus were similar to those in the mother. The maximal decrease of maternal mean arterial pressure (MAP) and heart rate (HR) were 7 +/- 2 and 14 +/- 3% (mean +/- SEM), respectively (P less than .05). The maximal decrease of fetal MAP and HR were 7 +/- 2 and 12 +/- 3%, respectively (P less than .05). No changes were seen in maternal or fetal acid-base variables, and intra-amniotic pressure was not affected. The authors conclude that esmolol has a rapid but relatively small transplacental passage, and it is eliminated rapidly from both maternal and fetal plasma.

The effect of vasopressor agents upon uterine artery blood flow velocity in the gravid guinea pig subjected to ritodrine infusion.

The purpose of the present study was to assess the effects of intravenously administered vasopressors upon uterine artery blood flow velocity (UBFV) in the gravid guinea pig subjected to ritodrine infusion. Fourteen experiments were performed in 14 chronically instrumented pregnant guinea pigs near term. Immediately following a 1-h intravenous infusion of ritodrine (0.05-0.20 mg.kg.min-1), each animal received an intravenous bolus of vasopressor solution: 1) epinephrine, 0.001 mg/kg; 2) phenylephrine, 0.01 mg/kg; 3) mephentermine, 1.0 mg/kg; 4) ephedrine, 1.0 mg/kg; or 5) placebo. The experimental sequence was performed five times, so that each animal received all five solutions. The vasopressor sequence was randomly altered between animals. Infusion of ritodrine increased maternal heart rate 18 +/- 1% (P less than .0001), decreased maternal mean arterial pressure (MMAP) 4 +/- 1% (P less than .01), and decreased UBFV 5 +/- 1% (P less than .001). The four active vasopressor solutions resulted in similar, though not equivalent, increases in MMAP. Further, the MMAP response to each active vasopressor differed from the response to placebo (P less than .0001). Epinephrine and phenylephrine each significantly decreased UBFV (P less than .002). Ephedrine clearly preserved UBFV, whereas mephentermine appeared to result in an intermediate response.