To determine whether neonatal age and estrogen exposure affect uterine growth, morphogenesis, and protein synthesis, crossbred gilts were randomly assigned at birth (Day 0) to receive either corn oil vehicle (CO) or estradiol-17 beta valerate (EV; 50 micrograms/kg BW/day). Gilts were treated for 7 days, chosen to coincide with specific periods of uterine development, prior to hysterectomy on Day 7, 14, or 49. Uteri were weighed, and tissues were fixed for histology or explanted with L-4,5-[3H]leucine (3H-leu) for 24 h. Endometrial and myometrial thicknesses were measured in uterine wall cross sections. Radiolabeled proteins produced by uterine wall tissues from 3H-leu and released into explant medium were identified by fluorography of two-dimensional SDS-PAGE gels. Proteins for which fluorographic spot intensities were consistently affected by age and/or treatment were excised from gels, and associated radioactivity was quantified. Normal growth and histogenesis were observed in uteri from CO-treated gilts. Exposure to EV increased (p < 0.01) uterine wet weight on all days examined, although effects were most pronounced on Day 49 (day x treatment, p < 0.01). Histologically, uteri of EV-treated gilts exhibited precocious or altered patterns of development of endometrial glands and folds. Endometrial thickness was greater (p < 0.01) in EV-treated gilts, and response was most pronounced on Day 49 (day x treatment, p < 0.01). Treatment with EV increased (p < 0.01) myometrial thickness on Day 49 only. Twenty-five uterine proteins were identified to be affected consistently by neonatal age, EV, or both. Production of four of these proteins was affected by age alone, while six were affected exclusively by treatment with EV alone, and 15 were affected differentially by both age and EV. Treatment with EV affected production of three of these 25 proteins on Day 7, 8 of 25 on Day 14, and 14 of 25 on Day 49. Results indicate that uterine growth and development of the porcine uterine wall during early neonatal life are accompanied by predictable alterations in patterns of uterine protein synthesis. Data also demonstrate that the neonatal porcine uterus is estrogen-sensitive and that both physical and biochemical responses of uterine tissues to estrogen vary with period of exposure. It is suggested that EV may be useful as a tool with which to induce developmental lesions in neonatal porcine uterine tissues.(ABSTRACT TRUNCATED AT 400 WORDS)