Uterine Prostaglandin Concentrations in Sheep during Late Pregnancy and Adrenocorticotropin-Induced Labor*

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Abstract
Concentrations of prostaglandin E (PGE), PGF, and 6-oxo-PG1α (the hydrolysis product of PGI2) were measured by RIA in different areas of myometrium, endometrium, cotyledons, amnion, and chorioallantoic membrane taken from chronically catheterized sheep. The animals were 130 days pregnant and had been treated for 70 h with continuous intrafetal infusions of either ACTH-(1–24) or saline. Maternal and fetal plasma samples were collected at 8-h intervals beginning 48 h before the start of infusion, and maternal plasma progesterone, estrone, and estradiol and fetal plasma cortisol concentrations were estimated by RIAs. As suggested by a significant fall in maternal plasma progesterone and rises in maternal plasma estrone and fetal plasma cortisol concentrations, sheep receiving intrafetal ACTH were in early labor at the time tissue samples were taken for PG determinations. For myometrium, analysis of variance indicated a significant effect of uterine area on PG concentrations. Concentrations of 6-oxo-PG1α, were elevated toward the cervical end of the myometrium in ACTH-treated animals. PGF and PGE concentrations were higher at the tubal and cervical ends of the myometrium in both groups of animals. In the endometrium of treated animals, concentrations of PGE, but not PGF or 6-oxo-PG1α, were elevated significantly. For cotyledons and chorioallantois, concentrations of PGF and 6-oxo-PGF1α, but not PGE, were elevated significantly in ACTH-treated animals. PG concentrations were not elevated in amnion taken from ACTH-treated animals. For both groups, the areas of highest PG concentrations were cotyledons and chorioallantois, suggesting that these may be major sites of synthesis.