Estrogen and Antiestrogen Effects on Neonatal Ovine Uterine Development1

Abstract

Postnatal development of the ovine uterus between birth and Postnatal Day (PND) 56 involves differentiation of the endometrial glandular epithelium from the luminal epithelium followed by tubulogenesis and branching morphogenesis. These critical events coincide with expression of estrogen receptor alpha (ERalpha) by nascent endometrial glands and stroma. To test the working hypothesis that estrogen and uterine ERalpha regulate uterine growth and endometrial gland morphogenesis in the neonatal ewe, ewes were treated daily from birth (PND 0) to PND 55 with 1) saline and corn oil as a vehicle control (CX), 2) estradiol-17 beta (E2) valerate (EV), an ERalpha agonist, 3) EM-800, an ERalpha antagonist, or 4) CGS 20267, a nonsteroidal aromatase inhibitor. On PND 14, ewes were hemihysterectomized, and the ipsilateral oviduct and ovary were removed. The remaining uterine horn, oviduct, and ovary were removed on PND 56. Treatment with CGS 20267 decreased plasma E2 levels, whereas EM-800 had no effect compared with CX ewes. Uterine horn weight and length were not affected by EM-800 or CGS 20267 but were decreased in EV ewes on PND 56. On PND 14 and PND 56, treatment with EV decreased endometrial thickness but increased myometrial thickness. The numbers of ductal gland invaginations and endometrial glands were not affected by CGS but were lower in EM-800 ewes on PND 56. Exposure to EV completely inhibited endometrial gland development and induced luminal epithelial hypertrophy but did not alter uterine cell proliferation. Exposure to EV substantially decreased expression of ERalpha, insulin-like growth factor (IGF) I, and IGF-II in the endometrium. Results indicate that circulating E2 does not regulate endometrial gland differentiation or development. Although ERalpha does not regulate initial differentiation of the endometrial glandular epithelium, results indicate that ERalpha does regulate, in part, coiling and branching morphogenesis of endometrial glands in the neonatal ewe. Ablation of endometrial gland genesis by EV indicates that postnatal uterine development is extremely sensitive to the detrimental effects of inappropriate steroid exposure.

The IGF system in the neonatal ovine uterus

“…Although immunoreactive IGF-1R protein was observed in all uterine cell types, the most abundant expression was detected on the apical surfaces of endometrial LE and GE during postnatal development. Collectively, available results strongly support the idea that local IGF-I and IGF-II of stromal origin act on IGF-1R in the epithelium and stroma to regulate uterine growth and endometrial adenogenesis in the neonatal ewe (Taylor et al 2001, Carpenter et al 2003a, Hayashi et al 2004. Although IGF-II plays a fundamental role in embryonic and fetal development, its role during the postnatal period is generally thought to be less important since it is substituted by IGF-I (DeChiara et al 1990).…”

“…In the neonatal ewe, circulating levels of estradiol-17b are below detectable limits after birth to at least PND 56 (Carpenter et al 2003a,c), suggesting that circulating IGF-I and IGF-II are not regulated by ovarian steroids in the neonatal ewe. Previous studies found that IGF-I and IGF-II mRNAs were expressed in the endometrial stroma of the neonatal ovine uterus surrounding the developing glands (Taylor et al 2001, Carpenter et al 2003a. IGF-1R mRNA was expressed by all uterine cell types, but was particularly abundant in the endometrial epithelia.…”

“…Interestingly, IGF-I and IGF-II mRNAs were most abundant in the stroma surrounding the developing glands in the intercaruncular areas of the endometrium (Taylor et al 2001). Recently, estrogen disruption of uterine growth and endometrial adenogenesis was correlated with alterations in normal patterns of IGF-I, IGF-II and IGF-1R expression in the neonatal ewe (Carpenter et al 2003a, Hayashi et al 2004, supporting the idea that this intrinsic growth factor system regulates uterine development after birth. The IGF system is also implicated in postnatal rodent uterine development (Adesanya et al 1999, Gu et al 1999, and adult IGF-I null female mice have severe reductions in uterine weight and size (Baker et al 1996).…”

“…Ewes included in the following experiment were born between October 2003 and January 2004, and lambs were suckling their dams throughout the experiment. As described previously (Carpenter et al 2003a), ewes (n ¼ 14) were assigned randomly at birth (PND 0) to receive daily i.m. injections from PND 0 to PND 55 of: (1) corn oil vehicle as a control (CX) or (2) estradiol-17b valerate (EV; Sigma) in corn oil at a dose of 50 mg per kg body weight.…”

Neonatal exposure to xenoestrogens impairs the ovarian response to gonadotropin treatment in lambs

“…Serum was then collected and stored at K20 8C for hormone analysis. Serum E 2 levels were determined by a double-antibody RIA procedure (DSL-4800; Beckman Coulter Ultra-Sensitive Estradiol RIA, Inc., Webster, TX, USA) (Taylor et al 2000, Carpenter et al 2003, validated for use with ovine samples. The RIA used rabbit anti-E 2 (polyclonal) serum and iodinated estradiol.…”