Reduced tuberoinfundibular dopaminergic neuronal function in rats after long-term withdrawal of estrogen treatment

Summary Hypothalamic fragments from female rats treated repeatedly with estradiol valerate (EV) and bearing prolactin (PRL)-secreting tumors contained, seven months after the last EV injection, lower concentrations of dopamine (DA) than age-matched controls. Depolarizing concentrations of K⁺ (35 mM) and amphetamine (50 M) evoked in PRL-secreting tumor bearing rats an endogenous DA release significantly lower than in controls.     

Effect of various doses of catecholestrogens on uterine eosinophilia in the immature rat

This paper describes the induction of uterine eosinophilia as well as of deep endometrial edema and increase of uterine wet weight in the immature rat by the catecholestrogens 2-OH-estradiol and 4-OH-estradiol. These effects are thought to be mediated by eosinophils via a specific eosinophil receptor system. 4-OH-estradiol was equipotent with estradiol, whereas the effect of 2-OH-estradiol was significantly weaker.     

Demonstration of a receptor for 5 alpha-androstane-3 beta, 17 beta-diol in the cytosol of the anterior pituitary of prepubertal male rats]

The presence of a specific receptor for 5alpha-androstan-3beta, 17beta-diol (3beta-diol) in the pituitary cytosol from prepubertal male rats was demonstrated. Its characteristics were: Ka = 5.2.10(7) M-1 KD = 1.9 X 10(-8) M, number of specific binding = 8.7 10(-14) moles per mg of proteins. Its sedimentation constant was 3 S. Competition assays showed that only 3beta-diol itself and estrogens were able to compete for the binding sites for 3beta-diol. Androgens, including 3alpha-diol, were inefficient. This receptor was found only in pituitary cytosol, it was missing from hypothalamic or cortical cytosols. This special localization seemed to foreshadow a specific role for 3beta-diol in the anterior hypophysis.     

Peptide-stimulated release of prolactin from the fowl anterior pituitary gland

Summary Anterior pituitary glands from broiler fowl were preincubated for 24 h in either medium 199 only or medium containing estradiol 17, following which they were incubated in medium containing thyrotrophin releasing hormone (TRH), vasoactive intestinal polypeptide (VIP) or substance P (SP), alone or with the dopamine agonist, apomorphine. Estradiol priming stimulated release of prolactin and enhanced apomorphine-inhibition of prolactin release. TRH stimulated prolactin release, an effect reversed by apomorphine, and priming with estradiol potentiated both effects. VIP stimulated prolactin to a lesser degree and again this was inhibited by apomorphine and potentiated by estradiol. SP had little effect on the nonsteroid-primed pituitary, but stimulated release of prolactin after estradiol treatment, though less effectively than TRH or VIP.     

Effect of various doses of catecholestrogens on uterine eosinophilia in the immature rat

Summary This paper describes the induction of uterine eosinophilia as well as of deep endometrial edema and increase of uterine wet weight in the immature rat by the catecholestrogens 2-OH-estradiol and 4-OH-estradiol. These effects are thought to be mediated by eosinophils via a specific eosinophil receptor system. 4-OH-estradiol was equipotent with estradiol, whereas the effect of 2-OH-estradiol was significantly weaker.Acknowledgments. This work was supported by Grant B-1493-8435 from the University of Chile. We are indebted to Prof. R. Knuppen, Lübeck, for providing the CE.     

Effect of a steroid contraceptive, "Enidrel" on the pre- and postnatal development of rats

To determine the long-term effects of prolonged and intensive treatment with an anticonceptive steroid, 60 female Wistar rats were given 1 mg/kg/day Enidrel (norethynodrel plus ethinyl estradiol 3-methyl-ether) by gastric sound for 60 days. The animals were divided into 2 groups and were placed with males for 10 days. Group 1 continued to recieve Enidrel through mating to the 15th day of gestation; Group 2 received no further treatment. General behavior and weight of the animals was unchanged when compared with controls. There were profound disturbances in the estrous cycle, but couplings and number of impregnations were normal in both groups. Most of the females in Group 1 aborted normal fetuses between Gestation Days 8 and 15; those in Groups 2 continued to term. Group 1 animals were remated and siblings of the 1st generation were crossed. The animals were fertile and the ne onates developed normally. It is concluded that Enidrel had no effect on morphogenesis and no masculinization effect on the hypophyso-hypothalamic system, as evidenced by the normal sexual behavior and fertility of the females.     

Cell proliferation in the rat pituitary gland: a mechanism of control in prolactin cells.

We investigated the relationship between prolactin content and DNA replication in the anterior pituitary gland. Thymidine incorporation in pregnant rats is significantly lower than in virgin controls. This is accompanied by a decreased activity of DNA polymerase. Sulpiride administration to pregnant rats enhances thymidine incorporation to levels similar to virgin controls. The results indicate a negative feedback between prolactin content and DNA synthesis in the rat anterior pituitary gland.     

Cell proliferation in the rat pituitary gland: A mechanism of control in prolactin cells

Summary We investigated the relationship between prolactin content and DNA replication in the anterior pituitary gland. Thymidine incorporation in pregnant rats is significantly lower than in virgin controls. This is accompanied by a decreased activity of DNA polymerase. Sulpiride administration to pregnant rats enhances thymidine incorporation to levels similar to virgin controls. The results indicate a negative feedback between prolactin content and DNA synthesis in the rat anterior pituitary gland.We are grateful to Prof. Carlos J. Gómez for the opportunity to perform this work. These studies were supported by PLA-MIRH 99.178.1.78, by the Consejo Nacional de Investigaciones Científicas y Técnicas and by the Comisión Nacional de Energía Atómica (Argentina).     

Binding of estradiol to synaptosomal mitochondria: physiological significance

The subsynaptosomal distribution and specific binding of 17beta-estradiol in vitro to mitochondria isolated from presynaptic nerve endings of female rat brain were examined. 17Beta-estradiol is (i) distributed unequally in synaptosomes and mitochondria posses the highest capacity to bind estradiol with respect to the available amount of the hormone. (ii) Estradiol binds specifically to isolated synaptosomal mitochondria. A Michaelis-Menten plot of specific binding was sigmoidal within a concentration range of 0.1-5 nM of added estradiol, with a saturation plateau at 3 nM. Binding of higher estradiol concentrations demonstrated an exponential Michaelis-Menten plot, indicating non-specific binding to mitochondria. Vmax and Km for the sigmoidal-shape range were estimated as 46 +/- 6 fmol of estradiol/mg of mitochondrial proteins and 0.46 +/- 0.07 nM free estradiol respectively. (iii) Estradiol binding is not affected by the removal of ovaries. The results show that inhibition of Na-dependent Ca2+ efflux from mitochondria by estradiol occurs according to an affinity change of the translocator for Na+, at the same estradiol concentrations that show specific binding to mitochondrial membranes. These data imply that physiological concentrations of estradiol, acting on mitochondrial membrane properties, extragenomically modulate the mitochondrial, and consequently the synaptosomal content of Ca2+, and in that way exert a significant change in nerve cell homeostasis.     

Hyperprolactinemia and estrogen-induced rhythms in LH and prolactin release in the ovariectomized rat

Short-term (9 days) hyperprolactinemia induced by pituitary grafts reduced basal plasma LH levels in ovariectomized rats whereas long-term (31 days) grafts increased basal LH levels. Although long-term grafts inhibited estradiol-induced prolactin surges, hyperprolactinemia had no effect on the LH surge. It is concluded that the estrogen-treated ovariectomized rat is not suitable for studying the effects of hyperprolactinemia on LH release.     

Hypoxia and estrogen receptor profile influence the responsiveness of human breast cancer cells to estradiol and antiestrogens

Angiogenesis activation mediated by vascular endothelial growth factor (VEGF) is one of the factors that can cause antiestrogen treatment failure in estrogen receptor (ER)?positive breast cancer patients. Since VEGF synthesis is modulated not only by hypoxia but also by steroid hormones, we investigated the relationship between hypoxic and estrogenic/antiestrogenic stimuli in two human breast cancer cell lines expressing both ER6α and ERβ (MCF7) or only ERβ (MDA-MB231). In both cell lines, the VEGF level was significantly influenced by hypoxic conditions and in antiestrogen-responsive MCF7 cells, this effect was not counteracted by tamoxifen or ICI 182,780, thus providing an experimental explanation for the resistance to endocrine treatment observed in patients with ER-positive tumors. In MDA-MB231 cells, estradiol significantly reduced the VEGF level, suggesting that through the ERβ isoform it may function as a negative modulator of VEGF synthesis under hypoxia, and providing evidence for a complex interplay of the estrogen-dependent and hypoxia-dependent pathways.     

Hyperprolactinemia and estrogen-induced rhythms in LH and prolactin release in the ovariectomized rat

Summary Short-term (9 days) hyperprolactinemia induced by pituitary grafts reduced basal plasma LH levels in ovariectomized rats whereas long-term (31 days) grafts increased basal LH levels. Although long-term grafts inhibited estradiol-induced prolactin surges, hyperprolactinemia had no effect on the LH surge. It is concluded that the estrogen-treated ovariectomized rat is not suitable for studying the effects of hyperprolactinemia on LH release.     

Dynamics of estrogen binding by uterine cells in vivo

The dynamics of the in vivo binding and release of tritiated estradiol in different uterine cell types are described. The very early binding of estrogens by the cytosol-nuclear and the eosinophil receptor systems is in accordance with the hypothesis that some estrogenic effects are mediated by these receptor systems.     

Effects of thyroidectomy and thyroxine replacement on the responsiveness of the anterior pituitaries from male rats to thyrotropin-releasing hormone in vitro

Summary Thyroidectomy decreased prolactin concentrations in the anterior pituitary (AP) and serum of the male rat. The amount of basal and thyrotropin-releasing hormone (TRH)-stimulated release of prolactin by AP in vitro was lower in thyroidectomized (Tx) rats than in sham Tx rats. These results suggest that the inhibitory effects of thyroidectomy on pituitary and serum prolactin in male rats are mediated in part by the reduction of the production and spontaneous release of prolactin and the responsiveness of prolactin to TRH.     

Standardization of "exchange" techniques to measure estradiol receptors in extracts exposed to biospecific adsorbants]

The measurement of the binding of steroid hormone receptors to biospecific adsorbants requires the development of "exchange" techniques. Two types of techniques based on the principle of differential dissociation were standardized: solid phase exchange with hydroxylapatite and liquid phase exchange with adsorption of the ligand to charcoal dextran. In both cases, binding of oestradiol to its receptor was measured in calf uterine cytosol extracts. Results obtained by both techniques were comparable. The half-times of the oestradiol-receptor complex dissociation determined from exchange kinetics are on the same order as those obtained by direct methods used in previous studies.     

The involvement of the renin-angiotensin system in the regulation of cell proliferation in the rat endometrium

Oestrogens are known to enhance angiotensin biosynthesis by increasing the elaboration of its precursor, angiotensinogen. On the other hand, we found that inhibition of angiotensin-converting enzyme (ACE) suppressed the proliferative response of the rat anterior pituitary gland to oestrogens. To answer the question whether the angiotensin system is involved in the control of the cell proliferation of the uterine epithelium, the effects of an ACE inhibitor, enalapril maleate, and of angiotensins II and IV, alone or together with losartan, an antagonist of angiotensin receptor type 1 (AT1), on endometrial epithelial cell proliferation have been studied. The experiments were performed on ovariectomized female Wistar rats. In the first experiment the animals were injected with a single dose of oestradiol benzoate or received an injection of solvent only. Half of the oestrogen-treated rats were injected additionally with enalapril maleate (EN, twice daily). The incorporation of bromodeoxyuridine (BrDU) into endometrial cell nuclei was used as an index of cell proliferation. It was found that oestradiol alone dramatically increased the BrDU labelling index (LI) of endometrial cell nuclei, and this effect was partially blocked by the simultaneous treatment with EN. In the second experiment, the animals were injected intraperitoneally with angiotensin II (AII), angiotensin IV (AIV) or saline, alone or together with losartan. It was found that AIV induced an increase in the LI in uterine epithelium, and this effect was not blocked by the simultaneous treatment with losartan. The increase in LI in uterine epithelium was also observed in the rats treated with AII and with losartan. These findings suggest an involvement of angiotensin IV in the control of uterine epithelium cell proliferation. Received 12 October 1998; received after revision 6 January 1999; accepted 2 February 1999     

Role of lysosomes, microtubules and microfilaments in the mechanism of the lactogenic action of prolactin in the rabbit mammary gland]

The lysosomotropic agents, ammonium chloride and chloroquine, added to the culture medium of pseudopregnant Rabbit mammary gland, did not inhibit the initiation of casein synthesis by prolactin. By contrast, they considerably reduced the down-regulation of prolacting receptors. Converse-y, colchicine totally blocked the lactogenic action of prolactin without altering the down-regulation of the receptor. Cytochalasin B inhibited only partly the lactogenic action of prolactin while it has no effect on the down-regulation of the receptor. These data suggest that the degradation of the prolactin-receptor complex in lysosome is not a compulsory step in the mechanism of prolactin action. The integrity of microtubules but not of microfilaments is required for prolactin to initiate casein synthesis. These elements of the cytoskeleton are not strictly involved in the down-regulation of the receptor.     

Desensitization by human chorionic gonadotropin (hCG): demonstration of a negative control of gonadotropin receptors by hCG at the level of testicular Leydig cells]

A single injection of hCG (500 IU) to intact and hypophysectomized prepubertal rat increases plasma testosterone levels and decreases hCG receptors in the testicular Leydig cells for 4 to 5 days. In intact animals testosterone exhibit a rapid increase within hours and a delayed paradoxical increase between 60 and 96 hours. In hypophysectomized animals the first peak is not present. In both intact and hypophysectomized rats hCG receptors are almost undetectable between 10 and 96 hours following hCG injection. Since receptor occupancy cannot account for this phenomenon it is concluded that hCG is exerting a negative control on its own receptors.     

Effect of in vivo irradiation of the rat on the taurine concentration of the heart

Summary The taurine concentration in the heart of the rat (moles/g of tissue) was not modified during 10 days after an in vivo irradiation of 900 R.     

Action of various progestational hormones on the electric activity of the rat myometrium in pregnancy after biovariectomy

8-day-pregnant rats were ovariectomized, then injected im with progestagens and estrogens while their uterine motility and electrical activity were being recorded simultaneously with a strain gauge and 2 bipolar electrodes. The injections, known to maintain pregnancy after ovariectomy, were progesterone 50 mg/kg, progesterone with estradiol 5 mcg/kg, or medroxyprogesterone acetate 25 mg/kg. Base line recordings for 20 minutes showed the normal pregnant state of brief periods of synchromous electrical and mechanical activity. After ovariectomy, untreated controls exhibited increased duration of synchronized mechanical and electrical activity and height of contractions. When any of the 3 progestagen treatments coincided with ovariectomy, synchrony was decreased and the intervening interval lasted longer. These procedures demonstrated how quickly the hormonal deficit due to ovariectomy is compensated for when ablation is performed before placental progesterone synthesis has begun.