Dexamethasone attenuates the estradiol-induced increase of IGF-I mRNA in the rat uterus

In recent years growth factors, e.g. insulin-like growth factor-I (IGF-I), transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF), have been considered as mediators of estradiol-stimulated growth in the uterus. In the liver, dexamethasone (Dex) has been shown to inhibit the IGF-I mRNA increase induced by growth hormone (GH). In the present study the influence of Dex on estradiol-stimulated induction of uterine IGF-I mRNA was examined. The concentration of IGF-I mRNA in the uterus and liver was monitored, as well as the levels of ER mRNA and estrogen receptor (ER). Since it has been previously shown that the maximal induction of uterine IGF-I mRNA after estradiol (E2) stimulation occurs after 21-24 h, Dex was administered to ovariectomized (ovx) rats 3 h before an E2 injection and 24 h before sacrifice. There was a significant decrease in IGF-I mRNA in the Dex+E2 treated rats compared to the rats given E2 only. In both groups an increase was seen compared to the level in the ovx control group. The uterine ER mRNA levels in E2 and Dex+E2 treated animals were significantly elevated compared to the ovx control. There were no significant changes in uterine ER content after hormone treatment compared to the level in ovx control rats. In the liver no effects on IGF-I mRNA were detected. Hepatic ER mRNA was significantly increased in the E2 treated group, compared to both the ovx control group and the animals that received Dex+E2. The hepatic ER level was also increased in the E2 treated group compared to the ovx control and the group which received Dex+E2. In conclusion, Dex does attenuate the estrogen-induced uterine IGF-I mRNA increase in ovx rats. In addition to this, Dex was found to inhibit the estrogen-induced increase in ER and ER mRNA in the liver of ovx rats.

Androgen regulation of the insulin-like growth factor-I and the estrogen receptor in rat uterus and liver

For the first time testosterone is shown to be an important regulator of the insulin-like growth factor-I (IGF-I) in the rat uterus under in vivo conditions. In this study the regulation of IGF-I and the estrogen receptor (ER) by gonadal steroids in the uterus and liver of female rats was monitored. The ER level was assayed by hormone binding after treatment with testosterone, 5 alpha-dihydrotestosterone or estradiol and specific mRNA species were analyzed by a solution hybridization/RNase protection assay using 35S-labeled RNA probes. Ovariectomized rats restored uterine weight after treatment with testosterone. Uterine IGF-I mRNA was more than 20-fold higher in testosterone treated rats compared to untreated ovariectomized controls after 48 h treatment. The effects of testosterone on ovariectomized animals was followed in a timecourse study. Testosterone administration increased uterine IGF-I mRNA expression during the first 48 h and the maximally induced level was maintained throughout the duration of the experiment (168 h). Since induction of IGF-I mRNA by estrogen is transient, these data indicate that androgen and estrogen increase IGF-I mRNA by different mechanisms. Regulation of IGF-I mRNA by gonadal steroids was also studied in hypophysectomized animals. The rats were given either testosterone, 5 alpha-dihydrotestosterone or estradiol, and uterine IGF-I mRNA was measured after 1 week of treatment. At this timepoint estrogen treated rats showed levels of IGF-I mRNA not significantly different from those of hypophysectomized controls. In contrast testosterone and 5 alpha-dihydrotestosterone increased the IGF-I mRNA level 30 and 40 times, respectively, relative to hypophysectomized control animals. Since 5 alpha-dihydrotestosterone is not convertable to estrogen, the induction by testosterone was considered to be a true androgenic phenomenon.

The hormonal regulation of the oestrogen receptor in rat liver: an interplay involving growth hormone, thyroid hormones and glucocorticoids

The regulation of the formation of the hepatic oestrogen receptor (ER) in adult female rats was studied by assaying steady state levels of ER and ER messenger RNA under different endocrine conditions. Hypophysectomy (HX) drastically reduced ER levels from 67.5 +/- 7.9 to 8.4 +/- 0.5 (means +/- S.E.M.) fmol/mg cytosolic protein. Continuous infusion of growth hormone (GH) to HX animals tripled ER and doubled ER mRNA levels. Treatment with triiodothyronine (T3) in a high dose (10 micrograms/day) doubled ER mRNA levels. The effects of T3 were dose-dependent, since a lower dose (1 microgram/day) increased neither ER nor ER mRNA levels. ER mRNA concentrations were increased by GH to 481 +/- 44% and by T3 to 372 +/- 35% of HX control levels 4 h after single injections of the hormones in HX animals. The glucocorticoid dexamethasone (DEX) alone increased neither ER nor ER mRNA levels in HX animals. DEX and GH in combination increased ER 5-fold and ER mRNA 2-fold compared with control levels in HX animals, whereas DEX and T3 in combination increased neither ER nor ER mRNA levels. Treatment with prolactin affected neither ER nor ER mRNA levels in HX rats. Insulin-like growth factor I (IGF-I) mRNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA levels were measured. GAPDH mRNA levels were increased 2.5-fold in HX rats by DEX and T3 in combination and almost 2-fold by DEX and GH in combination. IGF-I mRNA levels in HX rats were increased 4.5-fold by continuous infusion of GH alone, 6-fold by GH and T3 in combination, and 2.5-fold by GH and DEX in combination. These data indicate that both GH and T3 act directly on the liver to increase ER mRNA levels. GH, the most important of these hormones, also acts at the translational and/or post-translational level to increase ER protein levels. DEX treatment suppresses the stimulatory effects of T3, but not of GH.

Estrogen regulation of the estrogen receptor and insulinlike growth factor-I in the rat uterus: a potential coupling between effects of estrogen and IGF-I

The interrelationship between estrogen and insulin-like growth factor-I (IGF-I) in the regulation of uterine growth was studied in the rat. The levels of the estrogen receptor (ER), ER mRNA, and IGF-I mRNA in rat uterus and liver were monitored. Uterine ER in normal cycling rats was highest in proestrus and diestrus, as was IGF-I mRNA. ER mRNA and plasma estradiol peaked in proestrus. Hepatic ER mRNA and IGF-I mRNA were highest in diestrus, whereas ER was not significantly changed during the estrous cycle. The temporal effects of multiple injections or continuous infusion of 17 beta-estradiol in ovariectomized rats were examined. In the uterus of animals subjected to multiple injections, a 10-fold increase in IGF-I mRNA was seen 24 h after the start of the treatment, whereas rats given continuous infusion of estradiol showed a more than 16-fold increase. In both groups, the increase of IGF-I mRNA was transient although estrogen treatment was continued. To study local hormonal effects, ovariectomized rats were given estradiol in vaginal implants. The uterine IGF-I mRNA level increased two-fold in 3 days. The ER mRNA level increased 1.5-fold and the uterine weights were doubled. The plasma estradiol concentration did not change during the treatment. A separate experiment was carried out to establish whether IGF-I itself exercises estrogen-like effects. Ovariectomized rats were given hrIGF-I in osmotic minipumps for 3 days. The uteri of the treated animals weighted significantly more than did the controls. Quantitation of the level of uterine estrogen receptors revealed a significant decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of the estrogen receptor by growth hormone and glucocorticoid substitution in primary cultures of rat hepatocytes

Hepatic estrogen receptors (ER) mediate estrogenic effects on mammalian liver metabolism and are thereby involved in the regulation of important physiological/pathological processes, such as coagulation, atherosclerosis, and hypertension. The regulation of the formation of the ER in primary cultures of rat hepatocytes was studied by assaying ER and ER mRNA under different endocrine conditions. The ER concentration was measured using two different methods, a ligand-binding technique and an ER enzyme immunoassay. The results obtained by the two methods showed good correlation, and linear regression analysis gave a correlation coefficient of 0.95. ER concentrations fell to low steady state levels within 16 h after establishing the cell culture and remained low in the absence of hormonal substitution. Upon medium supplementation with pituitary GH and the glucocorticoid dexamethasone (DEX) in combination, the ER concentration increased 6-fold from 4.2 +/- 1.0 to 25.8 +/- 7.0 fmol/mg cytosolic protein. ER mRNA was measured by solution hybridization. Substitution with GH and DEX in combination increased ER mRNA to 210 +/- 14% of control levels. No effect on ER mRNA stability was seen after hormone treatment. It is concluded that the regulatory effects of GH and DEX on the hepatic ER in this in vitro system are very similar to the effects of these hormones under in vivo conditions. The inducible expression of the ER has never before, to our knowledge, been demonstrated in any mammalian liver cell culture system.

Regulatory effects of growth hormone, glucocorticoids, and thyroid hormone on the estrogen receptor level in the rat liver

The multihormonal regulation of the estrogen receptor in the liver of female rats was studied under in vivo conditions. The steroid receptor level was assayed by hormone binding and specific mRNA analyzed by solution hybridization using a 35S-labeled RNA probe complementary to the ligand-binding domain of the estrogen receptor gene. Serum growth hormone levels were measured and correlated to the effects of glucocorticoid and thyroid hormone administration on the estrogen receptor expression. In animals subjected to adrenalectomy plus thyroidectomy, the estrogen receptor concentration was reduced from 59 fmol/mg cytosol protein to 10 fmol/mg protein (i.e., with 87% relative to control animals). Adrenalectomy or thyroidectomy alone caused a decrease with 14% and 66%, respectively. Substitution with 10 micrograms betamethasone and 1 microgram triiodothyronine daily for 9 days completely restored the receptor content to control levels. Substitution with either hormone alone increased, but only partially restored receptor levels. The effect of betamethasone alone was dose dependent from 10 micrograms/d to 100 micrograms/d. This dose dependence was not seen when the animal simultaneously received 1 microgram of triiodothyronine. Superphysiologic doses of triiodothyronine did not raise estrogen receptor levels above those seen in animals treated with physiologic doses. High doses of triiodothyronine (greater than 20 micrograms/d) decreased serum growth hormone levels. The estrogen receptor mRNA levels in livers from hypophysectomized animals were increased after treatment with growth hormone (2.5-fold), thyroid hormone (two-fold), and glucocorticoids (1.5-fold). The results obtained indicate a very complex regulation of liver estrogen receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the uterine expression of messenger ribonucleic acids encoding the oestrogen receptor and IGF-I peptides in the pig uterus

The acute effects of oestradiol-17 beta on the expression of the oestrogen receptor (ER) and insulin-like 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 35S-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 micrograms/kg BW), the nuclear oestrogen receptor (ERn) mean level was increased 3-fold whereas the ER mRNA content had not changed significantly. After 3 hours the ERn 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 ERn 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.