Binding of steroids to the progestin and glucocorticoid receptors analyzed by correspondence analysis

The relative binding affinities of over 30 steroids have been measured for the cytosol glucocorticoid receptor (GR) of thymus, liver, and hepatoma tissue culture cells and for progestin, androgen, and mineralocorticoid receptors. The data have been analyzed by correspondence analysis to reveal the singularities among the receptors of different hormonal classes, the similarities in GR of different origins, and the different specificities of the ligands. Additional data on new steroids have been injected into the system as well as results on a further parameter, namely the induction of tyrosine aminotransferase (TAT) activity, to illustrate the power and flexibility of the methodology. The analysis has confirmed previous correlations between GR binding and TAT response but also highlighted the antiglucocorticoid activity of progestins. This method should prove to be a substantial aid to the interpretation of increasingly complex data, in particular with regard to the action of existing and newly synthesized steroids on glucocorticoid systems of differential sensitivity.     

Third-generation model for corticosteroid pharmacodynamics: Roles of glucocorticoid receptor mRNA and tyrosine aminotransferase mRNA in rat liver

A third-generation pharmacokinetic/pharmacodynamic model was proposed for receptor/genemediated corticosteroid effects. The roles of the messenger RNA (mRNA) for the glucocorticoid receptor (GR) in hepatic GR down-regulation and the mRNA for hepatic tyrosine aminotransferase (TAT) induction by methylprednisolone (MPL) were examined. Male adrenalectomized Wistar rats received 50 mg/kg MPL iv. Blood and liver samples were collected at various time points for a period of 18 hr. Plasma concentrations of MPL, free hepatic cytosolic GR densities, GR mRNA, TAT mRNA, and TAT activities in liver were determined. Plasma MPL profile was biexponential with a terminal t_1/2 of 0.57 hr. Free hepatic GR density rapidly disappeared from cytoplasm after the MPL dose and then slowly returned to about 60% of starting level after 16 hr. Meanwhile, GR mRNA level fell to 45% of baseline within 2 hr postdosing, and remained at that level for at least 18 hr. The GR down-regulation of GR mRNA and protein turnover rate were modeled. The TAT mRNA began to increase at about 2 hr, reached a maximum at about 5 hr, and declined to baseline by 14 hr. TAT induction followed a similar pattern, except the induction was delayed about 0.5 hr. Pharmacodynamic parameters were obtained by fitting seven differential equations in a piecewise fashion. The cascade of corticosteroid steps were modeled by a series of inductions for steroid-receptor-DNA complex, two intermediate transit compartments, TAT mRNA, and TAT activity. Results indicate that GR mRNA and TAT mRNA are major controlling factors for the receptor/gene-mediated effects of corticosteroids. This work was supported by Grant GM 24211 from the National Institute of General Medical Sciences, NIH.     

Changes in liver tyrosine aminotransferase after acute and chronic administration of morphine in the rat.

Acute administration of Morphine (20 mg/kg/s.c.) in the rat results in a rise of liver tyrosine aminotransferase (TAT) expressed as mumoles of p-hydroxyphenylpyruvate/100 mg/h. With chronic administration, a tolerance develops to this enzymatic effect. TAT induction is not evident in pregnant rats, given the narcotic, in which enzyme levels are already initially high. After delivery TAT returns to normal levels and it is possible to show both induction and tolerance developing to morphine. Enzyme activity in fetal livers is much lower than that of adult animals: after maternal administration of morphine only a modest TAT increase is seen which is not, however, statistically significant. TAT activity is fully evident in livers of offspring, with much higher mean levels in newborn rats from morphine-treated animals, as a possible consequence of morphine deprivation. In this latter group of newborn rats narcotic administration causes TAT activity to return to levels as high as those of naive animals. On the other hand, morphine administration to the prole of naive rats results in an induction of liver TAT.     

Cadmium induction of renal and hepatic ornithine decarboxylase activity in the rat. Effects of sex hormones and involvement of the renin-angiotensin system.

We investigated the effect of sex hormones on the sex-dependent response of rat kidney ornithine decarboxylase (ODC) activity to cadmium (Cd) administration and the involvement of the renin-angiotensin system in mediating stimulation of the liver enzyme by the metal. The response of renal ODC to Cd, which occurs in intact adult males but not in females, is also detectable in prepubertal and castrated males. Upon treatment with 17 beta-estradiol, the basal levels of enzyme activity in intact or castrated adult males were enhanced and Cd administration failed to increase them further. In adult females the kidney enzyme became responsive after ovariectomy. Also, in prepubertal females renal ODC was induced by Cd, and this was prevented by treatment with 17 beta-estradiol. Under the same conditions, changes in the levels of Cd accumulation within the kidney, that might account for variations in the response of ODC activity, did not occur. Cd caused an increase in renin activity starting minutes after its injection. Captopril, which specifically inhibits the conversion of angiotensin I to angiotensin II, prevented completely the induction of liver ODC by this metal; stimulation of the enzyme by Co was not affected by the drug. A similar inhibitory effect was exerted by propranolol. Adrenalectomy had no influence on the response of hepatic ODC to Cd; the decarboxylase was unaffected by aldosterone administration. It is suggested that Cd may induce liver ODC through the increase in angiotensin II following stimulation of renin by the metal.     

Mechanisms for glucocorticoid inhibition of immediate hypersensitivity reactions in rats.

The inhibitory mechanisms of immediate hypersensitivity reactions by glucocorticoid (GC) were studied in rats. Homologous passive cutaneous anaphylaxis (PCA) mediated by IgE antibodies and cutaneous reactions caused by histamine, serotonin and leukotriene C4 were elicited at the same time in the same rats. Three kinds of GC, hydrocortisone, prednisolone and dexamethasone, inhibited all these reactions significantly. Although mediator-induced cutaneous reactions were inhibited transiently around 2 hours after GC administration, inhibition of PCA was more potent and lasted longer. A time lag seemed to be essential for both inhibitions. IgE antibody-mediated histamine release in vivo in the rat peritoneal cavity was also inhibited by GC administration significantly, and the inhibition was long lasting when compared to those of the mediator-induced cutaneous reactions. Tyrosine amino-transferase (TAT) activity in the rat liver increased significantly by GC administration, and the increased TAT activity was completely abrogated by simultaneous administration of 5 mg/kg of cycloheximide (CH). In the same experimental condition, although inhibition of histamine-induced cutaneous reaction by GC was completely abrogated, the inhibition of PCA elicited at the same time in the same rats was only partially attenuated. Furthermore, the same dose of CH little affected the dexamethasone inhibition of histamine release in the rat peritoneal cavity, although the increase of TAT activity in the liver of the same rats was completely abrogated. These results demonstrate that PCA is inhibited by GC through at least 2 mechanisms, inhibition of mediator release from mast cells and non-specific inhibition of vascular permeability increase caused by released mediators. Although the latter action of GC is dependent upon protein synthesis, the former seems to be mediated by a unique mechanism independent of protein synthesis.     

Glucocorticoid receptor regulation in the rat embryo: a potential site for developmental toxicity?

Glucocorticoids play a key role in controlling numerous cellular processes during embryogenesis and fetal development. Excess glucocorticoids during development have been linked to dysmorphogenesis and/or intrauterine growth impairment in rodents. The actions of glucocorticoids are mediated by interaction with their receptors. Negative feedback regulation of glucocorticoid receptor (GR) is important for limiting cellular sensitivity to the hormones. Hence, acute exposure of the adult rat to the synthetic glucocorticoid dexamethasone (DEX) reduced both GR mRNA and protein in a variety of tissues that include hippocampus and liver, in a dose- and time-dependent fashion. Reduction in GR mRNA and protein were observable when DEX was given repeatedly at doses as low as 0. 05 mg/kg. In the control whole rat embryo, GR mRNA was low but measurable at as early as gestational day (GD) 10, but underwent rapid ontogenetic increase in the ensuring days. In contrast to the adult, neither GR mRNA nor protein in the whole rat embryo was affected by acute or repeated DEX administration to pregnant rats on GD10-13, even at doses as high as 0.8 mg/kg. Similar results were obtained in embryonic palate and liver, tissues known to be glucocorticoid targets. These data suggest that GR autoregulation does not occur during organogenesis in the rat. Accordingly, hormonal elevations from stress or chemical insults can be transduced unrestrictedly, ultimately leading to aberrant cell function and development. The unique mode of GR regulation seen in the embryonic cells may provide a potential common mechanism for developmental perturbation and toxicity for a variety of insults.     

Alterations in the hepatic glucocorticoid response to mirex treatment

Corticosterone has been shown to be involved in the regulation of mirex-induced adaptive liver growth. To further investigate the role of corticosterone in this response, plasma corticosterone, hepatic tyrosine aminotransferase (TAT) activity, and hepatic cytosolic binding of glucocorticoids were determined in male Sprague-Dawley rats following a single oral dose of mirex (100 mg/kg body wt). Mirex stimulated a significant elevation in plasma corticosterone levels 12 and 24 hr after dosing; however, hepatic tyrosine aminotransferase activity was not induced above control levels 6, 12, or 24 hr after mirex dosing. Mirex does not appear to directly inhibit the enzyme because tyrosine aminotransferase activity was increased in a dose-dependent manner in both intact and adrenalectomized rats when corticosterone supplements (1-50 mg/kg body wt) were given after mirex dosing. In an effort to explain the lack of hepatic TAT induction, the concentration of cytosolic binding sites for [3H]dexamethasone in intact, adrenalectomized, and adrenalectomized corticosterone-supplemented rats was measured 12, 24, and 48 hr after mirex dosing. There was a significant decrease in the total concentration of cytosolic binding sites for [3H]dexamethasone 12 and 48 hr after mirex dosing in intact rats, 12 and 48 hr after mirex dosing in adrenalectomized rats, and 12 and 24 hr after mirex dosing in adrenalectomized corticosterone-supplemented rats. There was a significant increase in the apparent dissociation constant (Kd) in intact rats dosed with mirex as compared to the oil controls, but there was no difference in Kd after mirex dosing in the adrenalectomized (ADX) rats when compared to the Kd for the oil-dosed control rats. The maximal binding capacity (Bmax) was not significantly different from oil controls after mirex dosing in either intact or ADX rats. The lack of hepatic TAT induction in the presence of increased plasma levels of corticosterone appears to be related to glucocorticoid receptor alterations in the liver of intact rats.     

Metallothionein induction in the liver, kidney, heart and aorta of cadmium and isoproterenol treated rats

Metallothionein (MT), induced in different organs in response to heavy metals and oxidative conditions, exerts antioxidant properties and thus could be implicated in cardiovascular physiopathology. The aim of this study was to investigate the capacity of cadmium (Cd) and isoproterenol to induce in vivo MT not only in rat liver and kidneys but also in heart and aorta. Tissue MT levels, catalase (CAT) and glutathione peroxidase (GPX) activities were assayed at different times after Cd or isoproterenol injection. Cd induced a dose-dependent induction of MT with a higher response in the liver than in the kidney, aorta and heart. The hepatic increase was early (12 h) and maintained (72 h), whereas the elevation was maximal around 48 h for the other organs. Isoproterenol induced a transient (12 h) hepatic and a biphasic (12 and 36 h) renal and cardiac increase. CAT activity was decreased in the liver and increased in the heart with the higher Cd doses. Isoproterenol increased the cardiac GPX activity. In conclusion, the results demonstrate that MT can be induced in rat liver and kidneys but also in heart after a Cd or isoproterenol injection. This enhancement of cardiac and vascular MT levels could be used to study the potential protective effect of MT in cardiovascular diseases.     

Suppression by delta 9-tetrahydrocannabinol of induction of hepatic tyrosine aminotransferase and tryptophan oxygenase.

The present study characterizes the action of Δ⁹-THC on enzyme induction by studying its effects on the induction of hepatic tyrosine aminotransferase (TAT) by steroids. In none of our studies did Δ⁹-THC inhibit TAT activity in the absence of steroid. Although treatment with hydrocortisone (HC, 150 mg/kg, 2 hr prior to sacrifice) caused a 2.1-fold induction of enzyme activity, pretreatment with Δ⁹-THC (200 mg/kg, 2 hr prior to sacrifice) decreased this induction to 1.3-fold. When mice were treated with Δ⁹-THC 1 hr prior to HC induction, TAT activity was induced only 1.1-fold over control while HC alone induced TAT activity 2.5-fold. Even when steroid treatment preceded Δ⁹-THC administration by 3 hr, there was significant inhibitory activity. Enzyme activity at 0, 3, and 6 hr after steroid was 18.7, 41.4, and 55.5 μmol of PPA/g of liver/hr, respectively. When Δ⁹-THC was administered at 3 hr after steroid and mice killed 3 hr later, enzyme activity was reduced to 36.2 μmol PPA/g liver/hr. Inhibition of steroid induction was dose-related over a range of 50–400 mg/kg of Δ⁹-THC. Δ⁹-THC had little effect on induction of TAT or tryptophan oxygenase in mouse liver by tryptophan and had no effect on tryptophan induction of tryptophan oxygenase in rat liver.     

糖皮质激素对人卵巢癌细胞系3A0增殖分化及对糖皮质激素受体表达的影响(英文)

目的:观察不同浓度地塞米松(Dex)对人卵巢癌细胞系(3AO)增殖及分化的影响及其对糖皮质激素受体(GR)的调节作用.方法:以不同浓度Dex处理3AO细胞,采用活细胞计数法观察细胞增殖,用氨基安替比林法测定碱性磷酸酶(AKP)活性;用酶联免疫法测定细胞标志抗原CA125水平的变化;用放射配体结合法测定GR的表达.结果:Dex对3AO细胞的增殖有抑制作用,同时伴有细胞形态的变化及AKP活性增高和CA125的表达下降.Dex对3AO细胞AKP活性的诱导作用可被RU486所阻断.在3AO细胞中存在糖皮质激素受体(GR),Dex对GR结合活性有下调作用.结论:Dex对3AO细胞有增殖抑制和诱导分化作用,这种作用是通过GR来介导的.     

糖皮质激素对人卵巢癌细胞系3AO增殖分化及对糖皮质激素受体表达的影响

目的：观察不同浓度地塞米松（Dex)对人卵巢癌细胞系（3AO）增殖及分化的影响及其对糖皮质激素受体（GR）的调节作用。方法：以不同浓度Dex处理3AO细胞,采用活细胞计数法观察细胞增殖,用氨基安替比林法测定碱性磷酸酶（AKP）活性;用酶联免疫法测定细胞标志抗原CA125水平的变化;用放射配体结合法测定GR的表达。结果：Dex对3AO细胞的增殖有抑制作用,同时伴有细胞形态的变化及AKP活性增高和CA125的表达下降。Dex对3AO细胞AKP活性的诱导作用可被RU486所阻断。在3AO细胞中存在糖皮质激素受体（GR）,Dex对GR结合活性有下调作用。结论：Dex对3AO细胞有增殖抑制和诱导分化作用,这种作用是通过GR来介导的。