Differential expression of myometrial oxytocin receptor and prostaglandin H synthase 2, but not estrogen receptor alpha and heat shock protein 90 messenger ribonucleic acid in the gravid horn and nongravid horn in sheep during betamethasone-induced labor

In the present study, we characterized four myometrial contraction-associat ed proteins (mCAPs): oxytocin receptor (OTR), prostaglandin H synthase 2 (P GHS2) estrogen receptor alpha (ER alpha), and heat shock protein 90 (Hsp90) messenger RNA (mRNA) expression in the nongravid horn of pregnant sheep an d compared them with their expression in the gravid horn that is exposed to a greater degree of stretch. We also examined the regulatory effects of es trogen and progesterone on OTR mRNA expression in ovariectomized nonpregnan t sheep. In addition, we determined the ontogeny of mCAP expression in the gravid horn throughout late pregnancy and during spontaneous term labor. Gr avid horn and nongravid horn myometria were removed under general anesthesi a from control ewes not in labor at 130-140 days gestational age (dGA; n = 3) and during betamethasone-induced labor (n = 6) at the same gestational a ge. Gravid horn myometrium was also collected from ewes not in labor at 95 dGA (n = 3), 101-110 dGA (n = 3), 111-120 dGA (n = 3), 121-130 dGA(n = 3), 131-140 dGA (n = 3), and 141-145 dGA (n = 4) and hom ewes in spontaneous te rm labor (n = 4). All ewes mere carrying single fetuses. Myometrium was als o collected from ovariectomized nonpregnant ewes treated with saline (n = 5 ), estradiol (50 mu g/day; n = 5), progesterone (0.3 g, intravaginally; n = 5), and estradiol plus progesterone (n = 5). Myometrial RNA was extracted and analyzed by Northern blot for OTR, PGHS2, ER alpha, and Hsp90 mRNA, nor malized for 188 ribosomal RNA or beta-actin. ER alpha, Hsp90, OTR, and PGHS 2 mRNA were all significantly up-regulated during betamethasone-induced lab or (P < 0.01) in gravid and nongravid horn myometrium. The level of gravidh orn OTR mRNA during labor was 3 times the level of nongravid horn OTR mRNA (P < 0.0001). Gravid horn PGHS2 mRNA was also higher than nongravid horn PG HS2 (P < 0.02). In contrast, in spontaneous term labor nongravid horn, ER a lpha and Hsp90 mRNA were similar to gravid horn. Myometrial ER alpha and Hs p90 mRNA remained unchanged throughout late pregnancy and increased at spon taneous term labor (P < 0.05). In contrast, myometrial OTR increased around 130 dGA (P < 0.01) and further increased at spontaneous term labor (P < 0. 02). Progesterone significantly inhibited myometrial OTR mRNA expression in nonpregnant sheep and estradiol antagonized progesterone's inhibitory effe ct. Mechanical stretch differentially regulated mCAP mRNA expression in the ovine gravid horn and nongravid horn. Mechanical stretch appears largely r esponsible for increased OTR mRNA and to a lesser degree PGHS2 mRNA. In add ition, endocrine factors may be required for full activation of OTR and PGH S2 mRNA associated with labor. ER alpha and Hsp90 mRNA are not under the co ntrol of uterine stretch in keeping with our previous results, indicating t hat systemic hormones such as estradiol, are prime regulators for these two mCAP mRNA expression during labor.