Ovine Maternal and Fetal Circulatory Responses to an Endoperoxide Analog

There are extensive data on the circulatory responses to prostaglandins during pregnancy, but little is known about the precursor endoperoxides. The endoperoxide analog (15S)-hydroxy-9α, 11α-(epoxymethano)prosta-5Z, 13E-dienoic acid (EPA₁) was used to evaluate the circulatory effects of endoperoxides in pregnant sheep. Ten near-term ewes and their fetuses were chronically catheterized to permit the measurement of regional blood flows by the radioactive microsphere method. In five sheep a fetal IV bolus injection of 12.5 μg/kg EPA₁ produced a significant increase in fetal blood pressure from 43 to 51 mm Hg, vascular resistance of the cotyledons from 0.06 to 0.09 PRU·kg⁻¹, membranes from 0.84 to 3.15 PRU·kg⁻¹, and kidneys from 1.18 to 1.94 PRU·kg⁻¹. In five sheep a 10-min maternal infusion of 0.5 μg/kg/min EPA₁ produced a significant increase in blood pressure from 89.0 to 115.0 mm Hg, resistance of the uterus from 0.49 to 1.10 PRU, and kidneys from 0.13 to 0.20 PRU. There was no significant change in maternal cotyledonary resistance. It is evident from these results that EPA₁ causes widespread vasoconstriction. In the placenta, however, there is vasoconstriction on the fetal side but the resistance of the maternal vascular bed is unaltered.