Abstract: 184

NEONATAL ESTRADIOL EXPOSURE ALTERS SUBSEQUENT PORCINE UTERINE RESPONSES TO STEROIDS.

Becky J. Tarleton^{1 *}, Anne A. Wiley^{1 *}, Frank F. Bartol^{1 *}
Department of Animal and Dairy Sciences, Auburn University, Auburn, AL ¹

Porcine endometrial maturation involves activation of a uterine estrogen receptor- (ER) system that develops shortly after birth (postnatal day = PND 0) in stroma and glandular epithelium (GE) [Tarleton et al. Biol Reprod 1998; 58:1009]. Exposure of gilts to estradiol valerate (EV) from PND 0 altered endometrial development and reduced litter size [Bartol et al. J Reprod Fert 1993; Suppl 48:99]. Objectives here were to determine effects of transient neonatal EV exposure on subsequent responses to EV and progesterone (P) in prepubertal gilts as reflected by uterine progesterone receptor (PR) and ER mRNA levels. Crossbred gilts received EV (50µg/kg bw/day, im; n=10) or corn oil (CO; 65µl/kg bw/day, im; n=10) from PND 0 through PND 20. On PND 70, all gilts received EV for two days (EV2; 100µg/day, sc; n=10). Five gilts from each group (CO+EV2 and EV+EV2) were hysterectomized on PND 72. Remaining gilts received P (2.2 mg/day, sc; CO+EV2+P, n=5 and EV+EV2+P, n=5) from PND 72 through PND 86 and uteri were obtained on PND 87. Uterine mRNA levels were determined for ER by ribonuclease protection and for PR by slot blot assay using cRNA probes, quantified by phosphorimaging, and expressed in relative units. Signal for ER mRNA was evaluated by in situ hybridization. Neonatal EV did not affect uterine ER mRNA levels but increased (p<.002) PR mRNA levels by 20% on PND 72 after EV2. On PND 87, EV2+P increased (p<.0001) uterine ER mRNA levels 3.7-fold relative to PND 72, and increased ER signal markedly in GE. This response was reduced (p<.03) by 26% in neonatally EV-exposed gilts. Altered prepubertal uterine responses to EV and P in neonatally EV-treated gilts indicate that disruption of estrogen-sensitive developmental events could affect endometrial integration of endocrine and conceptus signals. (USDA-NRI 95-37203-1995 and 98-35203-6198)

    This abstract is being presented on Sunday, August 1 at 2:45 PM at Todd 216.