Expression of the Estrogen and Progesterone Receptors and Insulin-like Growth Factor-I Genes in the Porcine Myometrium during Early Pregnancy.

Abstract

After conception and during early pregnancy in pigs, uterine motility plays a keyrole in sperm transport and embryo spacing prior to placentation. This process is modulated by gonadal steroids. Early pig embryos secrete estradiol with a peak d. 12-13 and estradiol elicits part of its influence on target cells in the genital tract via the insulin-like growth factor-I (IGF-I). Therefore, in the present study, the levels of the estrogen receptor (ER) and progesterone receptor (PR), as well as their mRNAs and the IGF-I mRNA, were measured in the myometrium of early pregnant pigs (days 8-30 after onset of estrus) by EIA and solution hybridization, in order to establish relationships among the expressions of IGF-I, ER and PR during early pregnancy. The ER level was low on days 8-10 and decreased even further to very low levels on days 25-30 while the level of ER mRNA was unchanged during the same period. The PR level was decreasing during the days monitored, although PR mRNA showed a tendency to increase from days 12-13 to days 25-30. The level of myometrial IGF-I mRNA was higher on days 25-30 as compared to days 8-18 indicating that myometrial IGF-I mRNA expression is not affected by the production of conceptus estradiol on days 12-13. Significant correlations were found between the expressions of IGF-I mRNA and PR mRNA and between the levels of ER and PR. The results suggest that in the porcine myometrium the expressions of IGF-I and PR genes, respectively ER and PR, may have common regulating factors.