Effects of ephedrine and phenylephrine on maternal and fetal atrial natriuretic peptide levels during elective cesarean section.

The effects of ephedrine and phenylephrine on fetal and maternal plasma atrial natriuretic peptide (ANP) concentrations were studied during 30 elective cesarean sections. After induction of spinal anesthesia, reductions from baseline maternal blood pressure were corrected with one of these pressor agents administered in a double-blinded, randomized manner. Immediately following delivery, umbilical artery (UA) ANP concentrations were significantly higher than umbilical vein (UV) concentrations (pg/ml) for both groups (ephedrine, 120.8 +/- 64.0 vs. 86.8 +/- 40.8, phenylephrine, 125.0 +/- 54.2 vs. 72.4 +/- 31.7), but there were no differences between groups for UA and UV ANP levels. Postpartum maternal ANP concentrations were significantly higher than baseline values in both groups, but again there were no differences between groups. Correlations between total doses of ephedrine or phenylephrine and UA or UV ANP levels did not reach significance. Postpartum maternal (MV2), UA, and UV blood gas variables (pH, PCO2, and PO2) were also not different between groups. These data suggest that effects of pressor doses of ephedrine (beta and alpha agonist) and phenylephrine (alpha agonist) on maternal and fetal ANP levels are not different. Therefore, 1) assuming these pressor drugs stimulate ANP release, this stimulation is not solely mediated by beta receptors and 2) to the extent that fetal ANP influences feto-placental circulatory homeostasis, the effects of ephedrine and phenylephrine on this regulatory mechanism do not appear to be different.