Progesterone-regulated changes in transcriptional events in rabbit uterus

Deficient brain RNA polymerase and altered nucleolar structure persists until day 8 after perinatal asphyxia of the rat

RNA polymerases (POL) are integral constituents of the protein synthesis machinery, with POL I and POL III coding for ribosomal RNA and POL II coding for protein. POL I is located in the nucleolus and transcribes class I genes, those that code for large ribosomal RNA. It has been reported that the POL system is seriously affected in perinatal asphyxia (PA) immediately after birth. Because POL I is necessary for protein synthesis and brain protein synthesis was shown to be deranged after hypoxic-ischemic conditions, we aimed to study whether POL derangement persists in a simple, well-documented animal model of graded global PA at the activity, mRNA, protein, and morphologic level until 8 d after the asphyctic insult. Nuclear POL I activity was determined according to a radiochemical method; mRNA steady state and protein levels of RPA4O-an essential subunit of POL I and III-were evaluated by blotting methods; and the POL I subunit polymerase activating factor-53 was evaluated using immunohistochemistry. Silver staining and transmission electron microscopy were used to examine the nucleolus. At the eighth day after PA, nuclear POL I decreased with the length of the asphyctic period, whereas mRNA and protein levels for RPA4O were unchanged. The subunit polymerase activating factor-53, however, was unambiguously reduced in several brain regions. Dramatic changes of nucleolar morphology were observed, the main finding being nucleolar disintegration at the electron microscopy level. We suggest that severe acidosis and/or deficient protein kinase C in the brain during the asphyctic period may be responsible for disintegration of the nucleolus as well as for decreased POL activity persisting until the eighth day after PA. The biologic effect may be that PA causes impaired RNA and protein synthesis, which has been already observed in hypoxic-ischemic states.

Brain RNA polymerase and nucleolar structure in perinatal asphyxia of the rat

Ribosomes are integral constitutens of the protein synthesis machinery. Polymerase I (POL I) is located in the nucleolus and transcribes the large ribosomal genes. POL I activity is decreased in ischemia but nothing is known so far on POL I in perinatal asphyxia. We investigated the involvement of POL I in a well-documented model of graded systemic asphyxia at the level of activity, mRNA, protein, and morphology. Caeserean section was performed at the 21st day of gestation. Rat pups still in the uterus horns were immerged in a water bath for asphyctic periods from 5-20 min. Brain was taken for measurement of pH, nuclear POL I activity, and mRNA steady state, and protein levels of RPA40, an essential subunit of POL I and III. Silver staining and transmission electron microscopy with morphometry when appropriate were used to examine the nucleolus. Brain pH and nuclear POL I activity decreased with the length of the asphyctic period while POL-I mRNA and protein levels were unchanged. Accompanying the decrease in brain pH we found significant changes of nucleolar structure in the course of perinatal asphyxia at the light and electron microscopic level. As early as ten min following the asphyctic insult, morphological disintegration of the nucleolus was observed. The changes became more dramatic with longer duration of perinatal asphyxia. We conclude that severe acidosis may be responsible for decreased POL activity and for disintegration of nucleoli in neurons. This condition may lower the ribosome content in neonatal neurons and impair protein synthesis.

Triiodothyronine effects on RNA polymerase activities in isolated neuronal and glial nuclei of the mature rat brain cortex

Our previous study demonstrated that a high level of nuclear triiodothyronine receptors (NT3R), which are identical to the hepatic NT3R, exists in neuronal nuclei of the cerebral cortex from an adult rat brain. To investigate whether thyroid hormone acts through binding to nuclear receptors, we measured RNA polymerase activities in isolated neuronal and glial nuclei of cerebral cortices prepared from three groups of rats with different T3 levels: T3 (20 micrograms/100 g BW/d, for three days)-injected hyperthyroid rats, control normal rats, and thyroidectomized rats. The enzyme activities in both nuclear fractions were assayed under the condition of dose-response linearity. When RNA polymerase I activity in neuronal nuclei from control rats was expressed as 100%, the activities from T3-injected and hypothyroid rats were 112.3 +/- 3.4% (n = 5, P less than .05) and 86.9 +/- 3.5% (n = 5, P less than .05), respectively. The increase in the enzyme activities were parallel to the increase in T3 content in neuronal nuclei among the groups. Glial nuclear RNA polymerase I showed the same tendency in response to T3, although the enzyme activity was smaller than from neuronal nuclei. RNA polymerase II, however, showed no significant change in response to altered T3 levels. The existence of numerous receptors and an induction of increased RNA polymerase I activity by T3 in neuronal nuclei raise the possibility that thyroid hormone through a NT3R pathway in the cerebral cortex of even the mature rat brain.

Regulation of uteroglobin synthesis and conservation of progesterone and estrogen receptors in immature rabbit uterus during prolonged progesterone treatment

Daily progesterone administration (1.33 mg/kg body weight) to immature rabbits brought about an initial increase in the uterine content of uteroglobin which, however, subsided when progesterone treatment was continued for 10 days. During this treatment period progesterone did not lose its own uterine receptors nor did it lose its inhibitory effect on the accumulation of occupied nuclear estrogen receptors. Since immature rabbits were used, the decrease of uteroglobin concentration cannot be explained by inhibitory effects of endogenous estrogens. The results suggest that termination of uteroglobin secretion may be a selective and inherent effect of progesterone itself.

Nuclear androgen receptors in the epithelium and stroma of human benign prostatic hypertrophic glands

Androgen receptors have been characterized and quantified in nuclear extracts of separated epithelium and stroma from human benign prostatic hypertrophic (BPH) glands. Tritiated dihydrotestosterone was used as the ligand and incubation was carried out at 15 degrees C for 18-20 hr before separation of bound and free ligand using dextran-coated charcoal. The results were analysed by Scatchard-type analysis. The concentration of receptor was found to be significantly (p = 0.022) greater in stromal than in epithelial nuclei: 1765 +/- 152 vs 1030 +/- 227 fmol/mg DNA (SEM, n = 6). Fourteen competitors were tested and the results indicated the presence of specific androgen receptors rather than contaminating sex-hormone-binding globulin. This was also borne out by the results of agar gel electrophoresis and sucrose gradient ultracentrifugation studies. The results are in line with current opinion that prostatic stroma is an important androgen-sensitive tissue, particularly in human BPH.

Cytosol and nuclear estrogen and progesterone receptors in the rabbit endocervix

This report describes the measurement of estrogen and progesterone receptors in cytosols and nuclear fractions from endocervical tissue components. Unoccupied cytosol estrogen receptor levels as determined by Scatchard analysis of [3H]-estradiol binding data indicated a single class of high affinity binding sites for the epithelial-stromal complex (KD = 0.74 x 10(-9) M). Binding was specific for estrogen (estradiol greater than estriol greater than estrone) and unaffected by desoxycorticosterone, dihydrotestosterone and progesterone. Assays for total estrogen receptor verified that 71.6 +/- 5.3% of this 8S estrogen receptor is in the epithelial-stromal complex while the remaining approximately 28% is localized in the stroma and fibromuscular wall, with the cells of the complex containing the highest receptor concentration. In 5-day pseudopregnant and ovariectomized rabbits compared to estrous rabbits there was a 50% decrease in the cytosol estrogen receptor in the epithelial-stromal complex and a 30% decrease in the concentration of nuclear receptor. Cytosol and nuclear progesterone receptors were measured as an indicator of estrogen action in the rabbit endocervix. Cytosol progesterone receptor concentrations (fmol/mg DNA) in 5-day pseudopregnant and ovariectomized animals were reduced to approximately 35% of the concentration in estrous animals. Nuclear progesterone receptor concentrations decreased 65% in 5-day pseudopregnant and 90% in ovariectomized animals suggesting decreased receptor synthesis. Collectively these data support the concept that the rabbit endocervix may be directly regulated by estrogens.

The effect of progesterone on RNA polymerases in the rat uterus

The effect of progesterone on transcription was investigated in the uterus of the ovariectomized rat. Progesterone rapidly depressed both RNA polymerase A and B activities for up to 6 h after steroid administration. Both enzyme activities returned to control values 24 h after steroid treatment. In contrast, in the estrogen-primed rat uterus, progesterone was capable of stimulating RNA polymerase B activity 30 min after hormone treatment. The cellular entities or mechanisms which progesterone uses to alter transcription in cell nucleus remain to be determined.

Uteroglobin mRNA and levels of nuclear progesterone receptor in endometrium

To investigate the mechanism of induction of uteroglobin by progesterone, the relationship between uteroglobin mRNA (mRNAug) activity and nuclear progesterone receptor levels has been examined in rabbit endometrium during early pregnancy. mRNAug activity was assessed by translation in vitro of poly A-rich endometrial RNA and immunoprecipitation of the synthesized peptides using anti-uteroglobin antibodies. Progesterone receptor was determined in purified endometrial nuclei by Scatchard analysis of the specific binding of 3H-R5020 under exchange conditions. mRNAug activity reached a peak on Day 4 of pregnancy and declined thereafter up to Day 8. Nuclear progesterone receptor levels showed a slight rise on Day 2, then returned to baseline levels. When mRNAug activity was high, progesterone receptor levels had declined. A cause-and-effect relationship between nuclear progesterone receptors and specific mRNA or protein synthesis remains to be established.

Early changes in nucleoplasmic poly(A) polymerase activity in immature rabbit uterus after estradiol administration

To study the role of post-transcriptional polyadenylation in the mechanism of estrogen action, we measured free nucleoplasmic poly(A) polymerase activity in intact uterine nuclei of immature rabbits at timed intervals after a single intravenous dose of estradiol (20 microgram/kg body weight). Uterine nuclear poly(A) polymerase activity was altered in a biphasic manner by estradiol treatment with maximal activities occurring at 0.5 h and 12 h of steroid administration, at which time periods they were about 2- and 3-fold higher than pretreatment levels, respectively. The later increase in the enzyme activity was totally abolished by a prior cycloheximide (0.5 mg/kg) administration, whereas the initial activation of poly(A) polymerase seemed to occur via mechanism(s) independent of protein synthesis. It thus appears that changes in uterine nuclear poly(A) polymerase closely resemble those previously reported for the activity of RNA polymerase II after estradiol treatment.

Uteroglobin mRNA activity and levels of nuclear progesterone receptor in endometrium

To investigate the mechanism of induction of uteroglobin by progesterone, the relationship between uteroglobin mRNA (mRNAUG) activity and nuclear progesterone receptor levels has been examined in rabbit endometrium during early pregnancy. mRNAUG activity was assessed by translation in vitro poly A-rich endometrial RNA and immunoprecipitation of the synthesized peptides using anti-uteroglobin antibodies. Progesterone receptor was determined in purified endometrial nuclei by Scatchard analysis of the specific binding of 3H-R5020 under exchange conditions. mRNAUG activity reached a peak on Day 4 of pregnancy and declined thereafter up to Day 8. Nuclear progesterone receptor levels were uniformly low through this period, except for a slight rise on Day 2. When mRNAUG activity was high, progesterone receptor levels were low. A cause-and-effect relationship between nuclear progesterone receptors and specific mRNA or protein synthesis remains to be established.

Regulation of cytosol and nuclear progesterone receptors in rabbit uterus by estrogen, antiestrogen and progesterone administration

A synthetic progestin, 16 alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3,20-dione (ORG 2058), was utilized to measure progesterone receptors from the rabbit uterus. This steroid has a high affinity for both cytosol and nuclear receptors, with KD values of 1.2 nM (at 0--4 degrees C) and 2.3 nM (at 15 degrees C), respectively. Administration of estradiol-17 beta or a non-steroidal antiestrogen, tamoxifen, for 5 days to estrous rabbits led to a progressive rise in the cytosol receptor levels: from 34,000 to 120,000 (estradiol-17 beta) and 80,000 (tamoxifen) receptors/cell, without any major influence on the nuclear receptor content. A single intravenous injection of progesterone (5 mg/kg) elicited a 3-fold increase in the mean nuclear receptor content at 30 min after injection (from 18,000 to 48,000 receptors/nucleus). Nuclear receptor accumulation was short-lived and returned to control levels within 4 h after treatment. A second dose of progesterone given 24 h later doubled the nuclear receptor level (from 18,000 to 35,000 receptors/nucleus). The concomitant decline in the cytosol receptor content was twice that accounted for by the nuclear receptor accumulation (70,000 vs. 30,000, and 40,000 vs. 17,000 receptors/cell, after the first and second progesterone injection, respectively). Following progesterone administration, the cytosol receptor level reached a nadir by 30 min, exhibited minimal replenishment within the ensuing 24 h, and remained at approx. 50% of the pretreatment values. After a single dose or two consecutive doses of progesterone, total uterine progesterone receptor content declined to about 60% of the level prior to each dose, a nadir being reached at 2 h after treatment.