The Effect of Prostaglandin E₂ and Indomethacin on the Placental Vascular Response to Norepinephrine

The vascular response to norepinephrine is expressed in terms of a resistance ratio which is defined as the ratio of the vascular resistance seen 1.5 min after norepinephrine administration to that seen before norepinephrine administration. The injection of 1 μg/kg of norepinephrine to near-term sheep significantly increased the vascular resistance of the placenta to a ratio of 2.27 ± 0.52 (mean ± SEM; N = 7). Pretreatment with 20 jug of prostaglandin E₂ per minute significantly decreased the placental response to norepinephrine to a resistance ratio of 1.47 ± 0.21 which was 65% of the untreated response (N = 7). Pretreatment with 10 mg/kg indomethacin significantly increased the placental response to norepinephrine from a resistance ratio of 2.25 ± 0.70 to 2.71 ± 0.84, which is 120% of the untreated value (N = 6). Prostaglandin E₂ attenuated the placental vascular response to norepinephrine and indomethacin potentiated this response.