In vitro effects of cytosolic inhibitor and opiates on the binding of [3H]oestradiol to nuclear type II binding sites of rat uterus and hypothalamus

Antiestrogenic effect of opioid peptides in rat uterus

The effects of a single injection or continuous infusion of opioid peptide, [D-Met(2),pro(5)]enkephalinamide (ENK) on the hormone binding and transcriptional properties of estrogen receptors were investigated in estradiol (E(2)) treated rat uterus. The level of estrogen- (ER) and progesterone receptor (PR) proteins, the hormone binding of E(2) receptors and the effects of single injection of ENK with or without naltrexone (NAL) on the E(2)-induced changes in the level of Fos and Jun proteins and the binding of AP-1 proteins to DNA were studied. The receptor proteins levels were determined by Western blots and the binding of AP-1 to DNA by electrophoretic mobility shift assay. Both the ER and PR protein concentrations and the [3H]Estradiol binding to the high affinity nuclear receptors decreased after ENK treatment during the first two days. At 72 h the PR concentration decreased further, while no significant changes were found in the level of ER, however, at this time the former competitive E(2) binding turned into positive cooperativity. The E(2)-induced increase in the level of Fos proteins and the binding of AP-1 proteins to DNA was inhibited by a single injection of ENK. We conclude that the endogenous opioid peptides may interact with E(2) in the gene regulation of rat uterus.

Epidermal growth factor influenced by opioid peptides in immature rat uterus

The aim of the present experiment was to investigate the effect of [D-Met2,Pro5] enkephalinamide (ENK) implantation on the development of the uterus during 8-33 days of age and the involvement of epidermal growth factor (EGF) in the effect. Administration of ENK was attained by osmotic minipumps (5 microg/h) implanted intraperitoneally. ENK resulted in a decrease in the EGF content of the uterus, which was already significant after 48 h of the implantation. The DNA content 24 and 48 h after the treatment decreased, no change at 72 h was found, however the protein/DNA ratio on the effect of ENK treatment was significantly decreased at this time in all examined age groups. High affinity and lower capacity competitive naloxone binding sites were demonstrated in the membrane fraction of the uteri. Seventy-two h after ENK treatment the binding capacity of these sites significantly dropped. The present results suggest a novel multiple interaction between estrogen and two probably paracrine hormones, EGF and opioid peptide, in the regulation of growth and development of the uterus.

Opioid peptides inhibit the estradiol-induced proliferation of cultured rat uterine cells

The effect of opioid peptides on estradiol-induced cell proliferation in adult rat uterine primary cell cultures was studied. Estradiol increased cell density by 40%. This estradiol-induced stimulation of cell proliferation was decreased to control values by [D-Met2,Pro5]enkephalinamide. The opioid-induced inhibition of uterine cell proliferation was blocked completely by the specific opiate antagonist naloxone, while naloxone did not have any effect on its own. The inhibition of cell proliferation by enkephalinamide was apparent at each stimulatory estradiol concentration examined. This opioid effect was mediated mainly by the mu opiate receptor. The observed effects occurred within the physiological nanomolar concentration range. Enkephalinamide did not have any effect on the basal proliferation rate of adult rat uterine cells. However, enkephalinamide inhibited the basal rate of cell proliferation in cell cultures prepared from 7-day-old immature rats. In summary, here we present evidence of novel physiological direct cross-talk between the opioid and estrogenic signaling systems in the regulation of normal uterine growth.

Opioids regulate cell proliferation in the developing rat uterus: effects during the period of sexual maturation

The present studies demonstrate, for the first time, that the rate of DNA synthesis in rat uterus of 21-32 days of age is inhibited by opioid peptides [D-Met2, Pro5]enkephalinamide. At around the time of vaginal opening (approximately 33 days) the opioids failed to act. High-affinity nuclear [3H]naloxone binding sites with linear Scatchard plots were detected in the uteri during the opioid-sensitive periods of DNA synthesis. Characteristics of these binding sites and the opioid sensitivity of uterine DNA synthesis are dependent on the age of the animals, the level of circulatory oestradiol and/or the maturity of the nuclear oestrogen receptor system.

Role of opioid peptides in the regulation of DNA synthesis in immature rat uterus

The effects of a single dose of naloxone and of [D-Met2,Pro5]enkephalinamide on the DNA synthesis in the uterus of 7, 14 and 21-day-old rat were studied. After [D-Met2,Pro5]enkephalinamide treatment, an age-dependent decrease in in vitro [3H]thymidine incorporation into DNA was observed in all studied age groups. In the 21-day-old age group a reduced rate of DNA synthesis was detected for 12 h after [D-Met2,Pro5]enkephalinamide treatment followed by the return to control values at 24 h. The rate of inhibition was more marked in the younger age groups. The effect was also more pronounced in younger animals. Specific [3H]naloxone binding was detected both in membrane and nuclear fractions of uterine homogenates. While no age-related changes in binding affinities were found, the number of binding sites varied characteristically during development. Our data suggest the novel involvement of opioid peptides and their receptors in the regulation of uterine development.

Changes of [3H]naloxone binding in oestrogen stimulated rat uterus

Effects of a single dose of oestradiol (Oe) on [3H]naloxone (Nal) binding in ovariectomized rat uterus were studied. Specific [3H]Nal binding was assessed by saturation analysis in 800 g supernatants and pellets of uterine homogenates. Two binding sites with higher (Kd approximately 1 nM) and lower affinity (Kd approximately 15 nM) for Nal were observed, their binding capacities and affinities have changed after Oe treatment in a time-dependent manner. The high affinity binding sites, detected only in the cytoplasmic fraction, disappeared after 1 h and only became detectable again at 24 h after hormone treatment, the lower affinity binding sites, after an initial drop, slowly increased, peaking at the 9th hour of hormone injection. The competition experiments indicate the involvement of different opiate receptor subpopulations in Oe induced changes. In the nuclear fraction, the Bmax values started to increase at 15 h, reaching the highest level at 18 h. The Kd values of lower affinity sites, in both studied compartments, were increased, i.e. the affinity decreased in the second half of the examined period.

Inhibition of oestradiol-induced DNA synthesis by opioid peptides in the rat uterus

Opioid drugs and peptides were investigated for their effect on uterine DNA synthesis induced by a single injection of 17 beta-oestradiol given to ovariectomized rats 24 h prior to decapitation. [D-Met2,Pro5]-enkephalinamide administered 12, 2 or 1 h before killing resulted in a significant (approximately 50%) inhibition of in vitro [3H]-thymidine incorporation into DNA, while injections given 24 or 6 h before decapitation were ineffective. Non-linear regression of the dose-effect curves resulted in an ED50 of approximately 0.26 and approximately 0.45 microgram/100 g b.wt. for the opioid treatments given 12 or 2 h before killing, respectively. These effects could be completely reversed by the opioid antagonist naloxone injected 30 min prior to the agonist treatment, while naloxone itself had no effect. Morphine and [D-Ala2,D-Leu5]-enkephalin administered 12 h, as well as dynorphin A fragment 1-13 given 2 h before decapitation also inhibited oestradiol-induced uterine DNA synthesis. In ovariectomized animals without 17 beta-oestradiol priming no significant effect of [D-Met2,Pro5]-enkephalinamide or naloxone on [3H]TdR incorporation was found.

Low dose RU486 prevents progesterone antagonism on uterine growth and concomitant type II oestradiol binding induction by oestradiol in rats

The effect of RU486, a synthetic antisteroid, on the antagonism of progesterone (Pg) and dexamethasone (Dex) against oestradiol (Oe) induced uterine growth, and on uterine oestradiol binding (type I and type II sites) was studied in ovariectomized CFY rats. Changes of hypothalamic low affinity [3H]Oe binding have also been evaluated. Inhibitory effects of Pg but not of Dex on uterine growth and type II Oe binding site induction were prevented by RU486. Antiprogestin effect of RU486 could also be demonstrated on low affinity [3H]Oe binding in hypothalami. The inhibitory effect of dexamethasone on type II Oe binding was not opposed by antisteroid, on the contrary, RU486 seemed to potentiate this effect of Dex. Evaluation of type I binding was complicated by the distorting effect of type II binding at the saturation curve. Changes of type I binding seemed to parallel those of type II binding except after Oe+Dex treatment where an increased level of uterine cytoplasmic type I sites and a simultaneous decrease of type II sites were found. Blockage of [3H]Oe binding at high RU486 concentrations was found in vitro in the uterine cytoplasmic fraction. A less pronounced effect was observed in the nuclear fraction. Possible mechanisms of the RU486 effect on type II Oe binding are discussed.