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The aim of this study was to determine whether expression of prostanoid receptor genes varied with gestational age or labour in the decidua and chorion of baboons. Tissues were obtained at the time of Caesarean hysterectomy in 15 baboons, 10 prior to the onset of labour in the last third of pregnancy and 5 in spontaneous labour at term. Expression of prostanoid receptor genes was determined using Northern blot analysis and the level of expression was related to each of three housekeeping genes. Expression of the genes encoding the EP(1) and FP receptor in decidua and the EP(4) receptor in chorion was lower with advancing gestational age. Expression of the EP(2) receptor gene was lower in labour in decidua, whereas expression of the IP receptor gene was higher in labour in both decidua (twofold) and chorion (fourfold). It is concluded that there is a complex pattern of change in expression of prostanoid receptor genes in chorion and decidua with advancing gestational age and in association with labour. It seems likely that direct effects of prostaglandins on the choriodecidua may have an important role in parturition in the primate.

The present study was designed to determine the effect of the spatial gradient from the cervix to the uterine fundus on the control of local prostaglandin H synthase (PGHS) 2 mRNA expression. We performed total cesarean hysterectomies during the last trimester in 12 pregnant baboons, 7 not in labor and 5 in labor, and examined PGHS2 mRNA expression throughout the uterus. PGHS2 mRNA abundance was quantified by in situ hybridization and northern blot analysis in the uterine fundus, lower uterine segment and the different segments of the cervix. Quantitative northern blot and in situ analysis demonstrated a gradient of PGHS2 mRNA expression, with the highest levels at the level of the lower portion of the cervix and decreased expression through the mid- and upper portion of the cervix and lower uterine segment; the lowest levels of expression were seen in the uterine fundus. Moreover, cellular localization of PGHS2 mRNA and protein demonstrated high levels of expression in the cervical glandular epithelial cells with only occasional staining of smooth muscle cells in pregnant baboons. Decreased PGHS2 mRNA concentration gradient from the cervical external os to the fundus suggests that prostaglandin (PG) production in the uterus and cervix strongly depends on anatomical relations. This increased local PG production activity may be critical to pregnancy-associated lower uterine segment elongation, cervical softening and effacement in primate labor. These data provide a compelling biological basis for the use of PGHS2 inhibitors in the prophylaxis of preterm birth and cervical incompetence.