Regulation of the Uterine Expression of Messenger Ribonucleic Acids Encoding the Oestrogen Receptor and IGF–I Peptides in the Pig Uterus

Abstract

The acute effects of oestradiol-17 p on the expression of the oestrogen receptor (ER) and insulinlike growth factor I (IGF-I) in the endometrium of ovariectomized pigs were examined. The steroid receptor level was assayed by hormone binding techniques and specific mRNAs analyzed by solution hybridization using %-labelled RNA probes complementary to the ligand-binding domain of the ER receptor gene and a 160 bp PanI-Pvul fragment of the IGF-I gene. One hour after a single injection of oestradiol (1 pg/kg BW), the nuclear oestrogen receptor (ER,) mean level was increased 3-fold whereas the ER mRNA content had not changed significantly. After 3 hours the ER, mean concentration was still high; the mean ER mRNA level had decreased by 15 % and the mean IGF-I mRNA had increased 3-fold above that in the samples collected prior to treatment from these ovariectomized animals. Six hours after the injection the ER, content had returned to the basal level and stayed there during the following six hours. The ER mRNA concentration continued to decline, reached its lowest value after six hours and had increased slightly by twelve hours. The IGF-I mRNA level increased steadily during the course of the experiment. At twelve hours after the injection it had increased 3-fold. From these data we conclude that in the pig uterus oestradiol down-regulates its own receptor and acts as a potent stimulator of endometrial growth by inducing IGF-I expression.

Expression of mRNAs for the Estrogen and Progesterone Receptors, Insulin-like Growth Factor-I and Thioredoxin in the Porcine Cervix.

“…The effects of gonadal steroids are mediated via their respective receptors, which function as intracellular transcription factors (for a review, see [24]) and the local regulation of their effects was investigated with regards to tissue levels of estrogen and progesterone receptors and their mRNAs. The mRNA levels of both IGF-I and thioredoxin have been shown to be increased by estrogen [11,12,17,19] and therefore included in this investigation.…”

“…During the estrous cycle, the follicular phase (d.19-2) is compared to the luteal phase (d. [4][5][6][7][8][9][10][11][12][13][14][15][16], and during pregnancy the midperiod (d.51-84) is compared to term (d.110-5 h post partum), the results being presented as mean ± S.E.M. Results were evaluated with Mann-Whitney U-test and p<0.05 was considered significant.…”

“…In the pig, however, estrogen alone does not promote cervical softening [8]. The effect of estrogen is indirectly mediated by way of polypeptide growth factors to which insulin-like growth factor-I belongs [9][10][11]. Both estrogen and progesterone has been shown to stimulate uterine IGF-I secretion in pigs [12].…”

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

“…The effects on growth and differentiation in the uterus is now believed to be indirect with estrogen inducing growth factors and/or their receptors [28]. One of these is IGF-I [16,17,29,30]. The IGF family is involved in the growth and differentiation of tissues and organs in many vertebrate species [31].…”

“…Furthermore, it has been shown that estradiol upregulates IGF-I mRNA in the uterus [16,17] and increases plasma levels of IGF-I [18] in a dose dependent manner. Both porcine blastocysts and uterine tissue possess specific receptors for IGF-I [19,20] implicating a role for IGF-I in embryonic and uterine development [21].…”