Prostanoid Concentrations in Maternal/Fetal Plasma and Amniotic Fluid and Intrauterine Tissue Prostanoid Output in Relation to Myometrial Contractility during the Onset of Adrenocorticotropin-Induced Preterm Labor in Sheep*

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Abstract
Prostanoid [prostaglandin (PG)] concentrations were measured in ovine maternal and fetal plasma and amniotic fluid during the onset of preterm labor induced by the administration of a pulsatile infusion of ACTH-(1-24) (P-ACTH; 66.7 ng/min for 15 min every 2 h) to the fetus and in saline-infused controls. P-ACTH administration stimulated a change in intrauterine pressure from type A activity, characterized by sustained increases of low amplitude, to type B labor-like activity of short duration, high amplitude (.gtoreq. 10 mm Hg) increases which occurred between 12 and 8 h before the onset of labor. PGF2.alpha. and/or PGFM (13,14-dihydro-15-keto PGF2.alpha.) concentrations increased consistently in all fluids 16 h or earlier before labor. All PGs increased in fetal carotid arterial plasma (PGE2 > PGF2.alpha.) and emniotic fluid, and the relative increases in each PG were similar. PGF2.alpha. and PGFM selectively increased in maternal vena caval and aortic plasma, whereas smaller or negligible increases in the prostacyclin hydrolysis metabolite 6-keto PGF1.alpha. (6KF) and PGE2 were noted. The output of PGs E2 and F2.alpha. (pg per 105 cells/8 h) increased 1.6- and 1.7-fold, respectively, by cells dispersed from the chorioallantois of P-ACTH-treated animals compared to that in control animals infused with saline for 100 h. From fetal cotyledons, these increases were 2.4-fold (P < 0.05) and 3.6-fold, respectively. No significant changes occurred in 6-keto PGF1.alpha. output from any tissue or PGE2 or PGF1.alpha. output from amnion or maternal cotyledons. PGs increase in all fluids before the increase in uterine mechanical activity during induced preterm labor, implying that PGs mediate this event and are not a result thereof. Syntheses of PGs E2 and F2.alpha. increase similarly in intrauterine tissues with the onset of labor. A selective increase in PGF2.alpha. a myometrial stimulatory PG, occurs exclusively in maternal plasma, suggesting that endoperoxide conversion to PGF2.alpha., is specifically enhanced during parturition or suggesting the existence of an intrauterine tissue source of 9-keto PG reductase.