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

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Abstract
The vascular response to norepinephrine is expressed in terms of a resistance ratio, 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 .mu.g/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 [standard error of the mean]; N = 7). Pretreatment with 20 .mu.g of prostaglandin E2/min 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. Indomethacin potentiated this response.