Studies on the Endocrinology of Parturition: Relative Steroidogenesis in Coexisting Genetically Dissimilar Ovine Fetuses, Concomitant with the Temporal Patterns of Maternal C₁₈ and C₁₉ Steroids and Prostaglandin F_2α Release

Abstract

Ovine embryos collected from two breeds of ewes possessing different gestational periods [Finnish Landrace (Finn), 145.5 ± 1.4 days; Rambouillet (Ra), 150.7 ± 1.3 days] were transferred to common, randomly selected recipients. Fetal plasma samples were collected from mixed-breed (MB, one Finn and one Ra; n = 6) and single-breed (SB, single Finn, n = 3; single Ra, n = 3) chronic fetal preparations during the last trimester. In the MB pregnancy, the Ra sibling had temporal patterns of androstenedione similar to those observed in the Finn co-twin; however, these particular changes were greatly accelerated in comparison to the same day of gestation in SB Ra fetuses. Similarly, temporal patterns of change in unconjugated estrone, estrone sulfate, and 17β-estradiol were accelerated by as much as 4.6 to 5 days in Ra fetuses of MB pregnancies when compared to Ra fetuses in the SB pregnancies (P<0.001), with no difference noted between Ra and Finn co-twins. Maternal progesterone concentrations changed from 8 to 2 ng/ml, androstenedione from 200 to 400 pg/ml, estrone from 65 to 250 pg/ml, and 15-keto-13,14-dihydroprostaglandin F_2α from 200 pg/ml to 6000 pg/ml over the last 4 or 5 days of gestation. Chronic fetal manipulation accelerated parturition, with mean gestational lengths in MB, SB Finn, and SB Ra pregnancies being 141.5 ± 0.7, 141.7 ± 0.7, and 149.3 ± 0.9 days, respectively. In this study fetal endocrine changes were largely controlled in the MB pregnancy by the fetal co-twin exhibiting a shorter gestational period.