Effect of fetal and maternal intravascular antipyrine infusion on maternal plasma prostaglandin concentrations in the pregnant sheep at 104 to 127 days' gestation

Antipyrine is commonly used to measure umbilical and uterine blood flow in the pregnant sheep. In the present experiment we investigated the effect of antipyrine on prostaglandin metabolism. Four pregnant ewes at 104 to 127 days' gestation were infused with either 1, 4, or 15 mg of antipyrine per minute via the fetal jugular vein. The 15 mg · min^-1 dose was also infused into the maternal jugular vein in a fourth experiment. Prostaglandins in the uterine vein draining the pregnant horn were measured by radioimmunoassay and antipyrine by high-performance liquid chromatography. No change in the concentrations of either 13,14-dihydro-15-keto-prostaglandin F_2α or 6-keto-prostaglandin F_1α was observed with infusion of antipyrine at 1 mg · min^-1. The 4 and 15 mg · min^-1 infusion rates into the fetal jugular vein induced a significant decrease (p < 0.05) in maternal uterine vein 13,14-dihydro-15-keto-prostaglandin F_2α plasma concentrations. These concentrations decreased from 669.3± 161.3 pg · ml^-1 (mean ± SD) before infusion to 306.5 ± 104.0 pg · ml^-1 after 3 hours of infusion at 4 mg · min^-1 and from 744.2 ± 256.8 to 105.0 ± 24.2 pg · ml^-1 at 15 mg · min^-1. Significant changes in maternal uterine vein plasma 6-keto-prostaglandin F_1α and the 6-keto-prostaglandin F_1α/13,14-dihydro-15-keto-prostaglandin F_2α ratio occurred only at the 15 mg · min^-1 infusion of antipyrine into the fetal jugular vein (p < 0.05). Maternal uterine vein 6-keto-prostaglandin F_1α fell from 86.0 ± 31.6 to 37.0 ± 11.5 pg · ml^-1 and the 6-keto-prostaglandin F_1α/13,14-dihydro-15-keto-prostaglandin F_2α ratio rose from 0.14 ± 0.10 to 0.35 ± 0.10. We conclude that: (1) antipyrine at doses currently used to measure uterine and umbilical blood flows inhibits 13,14-dihydro-15-keto-prostaglandin F_2α production and (2) infusion rates of antipyrine less than 1 mg · min^-1 probably do not affect maternal prostaglandin metabolism. We therefore recommend that if this method is to be used for measuring blood flow, antipyrine infusion rates should be less than 1 mg · min^-1.