Cytoplasmic and nuclear estrogen receptors and leucine incorporation in endometrium of cyclic and pregnant pigs to day 19 postestrus.

Endometrium was recovered from a total of 37 pigs sacrificed on d 4, 10, 12, 16 and 19 of the estrous cycle and on d 10, 12, 16 and 19 of gestation to determine whether the concentrations of cytoplasmic and nuclear estrogen receptors were altered during pregnancy. In addition, [3H]-leucine incorporation into endometrium was studied in vitro to determine whether any estrogen action mediated through a receptor might involve increased protein synthesis. Cytoplasmic estrogen receptor decreased from d 10 through d 16 in both pregnant and cyclic pigs. The concentration of the cytoplasmic estrogen receptor was less from d 10 through d 16 in pregnant pigs than in cyclic pigs; however, the reduced concentrations did not appear to result from translocation of filled sites to the nucleus, because estrogen and estrogen receptor concentrations in the nucleus were similar in pregnant and cyclic pigs through d 16. The amount of [3H]-leucine incorporated into endometrium did not differ between pregnant and cyclic pigs through d 16 nor did the RNA:DNA ratio. Therefore, no evidence of pregnancy-specific increases in total RNA synthesis mediated by estrogen receptors was found in pregnant pigs through d 16. These observations do not preclude actions of steroids through receptors to induce the synthesis of RNA that codes for specific proteins but that constitutes only a small portion of the total RNA. From d 16 to 19, both [3H]-leucine incorporation and RNA:DNA ratio increased in cyclic pigs (both P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)