Inhibitory Effect Of Cortisol Research Articles

RU486 Reversal of Cortisol Repression of 1,25-Dihydroxyvitamin D<sub>3</sub> Induction of the Human Osteocalcin Promoter

In conditions of corticosteroid excess, such as Cushing’s syndrome, a reduction in serum osteocalcin is observed and bone loss occurs. The human osteocalcin gene is induced by 1,25-dihydroxyvitamin D3 derivatives and repressed by glucocorticoids. In this paper we show that cortisol, a natural glucocorticoid, represses both basal and vitamin D induced activity of the human osteocalcin promoter. Furthermore, we address the specific question as to whether the anti-progestin anti-glucocorticoid RU486 is able to antagonize the inhibitory effect of cortisol on osteocalcin gene expression. We show that RU486 has agonist activity alone, in that it is able to repress the basal promoter activity of the osteocalcin gene and antagonist activity, reversing incompletely the cortisol mediated repression of 1,25-dihydroxyvitamin D3 induction.

Exogenous glucocorticoids decrease subgenual cingulate activity evoked by sadness.

The glucocorticoid hormone cortisol is known to have wide-ranging effects on a variety of physiological systems, including the morphology and physiology of the amygdala and hippocampus. Disruptions of cortisol regulation and signaling are also linked with psychiatric disorders involving emotional disturbances. Although there is much evidence to suggest a relationship between cortisol signaling and the brain physiology underlying emotion, few studies have attempted to test for direct effects of cortisol on the neurophysiology of emotion. We administered exogenous synthetic cortisol (hydrocortisone, HCT) using two different dosing regimens (25 mg/day over 4 days, 100 mg single dose), in a double-blind placebo-controlled functional magnetic resonance imaging (fMRI) study. During fMRI scanning, healthy subjects viewed images designed to induce happy, sad, and neutral emotional states. Subjective emotional reactions were collected for each experimental stimulus after fMRI scanning. Mood ratings were also collected throughout the 4 days of the study. Both dose regimens of HCT resulted in decreased subgenual cingulate activation during sadness conditions. The 25 mg/day regimen also resulted in higher arousal ratings of sad stimuli. No effects of HCT were observed on any mood ratings. Few reliable effects of HCT were observed on brain activity patterns or subjective emotional responses to stimuli that were not sad. The inhibitory effects of cortisol on sadness-induced subgenual cingulate activity may have critical relevance to the pathophysiology of major depression, as both subgenual hyperactivity and decreased sensitivity to cortisol signaling have been documented in patients with depression.

The differential effect of Eriobotrya japonica hydrophilic leaf extract on cytokines production and modulation

Stimulating or modulating the release of cytokines by immunomodulators or immunostimulating agents is an attractive mode for treating several diseases such as viral infections. For instance, patients with viral infections may be in need of increasing or inducing T helper 1 (Th1) or proinflammatory cytokines, which ultimately activate T cytotoxic and Natural killer lymphocytes to kill virally infected cells. Of these agents, we found that Eriobotrya japonica hydrophilic leaf extract (EJHE) can induce and modulate cytokines in dose-dependent manner. Twenty-four hour exposure of increasing concentrations of EJHE increased significantly ( p < 0.001) the production of IFN-γ and TNF-α, from PHA+LPS-stimulated whole blood. However, the production of IFN-γ and TNF-α plateaued at high EJHE concentrations (10–100 μg/ml). No significant changes in the production of IL-10 were seen. In addition, EJHE at 1 and 10 μg/ml reversed significantly ( p < 0.01) the inhibitory effect of hydrocortisone on the IL-12 p70, IFN-γ and TNF-α production from PHAS+LPS stimulated whole blood. Without PHA and LPS, EJHE was found to induce significantly ( p < 0.001) IFN-γ, IL-12 p70, TNF-α, and IL-10 from whole blood culture in concentration dependent manner. The maximum induction of IFN-γ, IL-12 p70, and TNF-α by EJHE was at 1 and 10 μg/ml. On the other hand, IL-10 induction kept increasing even at the highest concentration used (100 μg/ml) of EJHE. Furthermore, intra-peritoneal injection of EJHE into mice increased significantly serum cytokines level mainly at 10 and 100 μg/ml. Two-hour post i.p. injection, EJHE increased serum IFN-γ, TNF-α, and IL-10 to ∼750, 1000, and 250 pg/ml, respectively. However, 24 h post i.p. injection, the levels of TNF-α, and IL-10 were similar to basal levels but IFN-γ levels were 200 pg/ml. These results indicate that EJHE induces proinflammatory and Th1 cytokines in concentration dependent manner and the effect of this induction should be studied further in viral models to check the efficacy of such cytokine induction.

Sex Difference in the Suppressive Effect of Cortisol on Pulsatile Secretion of Luteinizing Hormone in Sheep

We tested the hypothesis that there are sex differences in the inhibitory effect of cortisol on pulsatile LH secretion and pituitary responsiveness to GnRH in gonadectomized sheep. In experiment 1, pulsatile LH secretion was examined in gonadectomized ewes and rams infused with either saline, a low (250 microg/kg.h) or a high (500 microg/kg.h) dose of cortisol for 30 h. In experiment 2, direct pituitary actions of cortisol were assessed by monitoring LH pulse amplitude in response to exogenous GnRH in hypothalamo-pituitary disconnected ewes and rams infused with the low dose of cortisol. In experiment 1, the mean (+/-sem) plasma LH concentration was (P<0.05) reduced significantly during cortisol infusion in both sexes, but the effect was greater in rams. In ewes, LH pulse amplitude and frequency were reduced (P<0.05) at the high, but not the low, cortisol dose, whereas total LH output (LH pulse amplitude multiplied by frequency) was reduced (P<0.05) at both doses. In rams, LH pulse frequency and amplitude and total LH output were (P<0.05) reduced significantly at both cortisol doses. In experiment 2, plasma LH concentration and pulse amplitude in response to exogenous GnRH were not affected by infusion of cortisol in either sex. We conclude that gonadectomized rams are more sensitive than gonadectomized ewes to the effects of cortisol to inhibit LH secretion and that sex differences exist in the specific actions of cortisol on LH pulses. The results of experiment 2 suggest that intact hypothalamic input to the pituitary is necessary for cortisol to inhibit pituitary responsiveness to GnRH.

Inhibitory Effect of Cortisol on the Defense Activities of Tilapia Neutrophils in Vitro.

On the premise that fish neutrophil activities are depressed under stressed conditions, this study investigated the direct effect of cortisol on the in vitro activity of neutrophiles collected from tilapia Oreochromis niloticus. Neutrophils were obtained from swim bladders and exposed to different levels of cortisol (0-1000 ng/mL), and their chemotactic, phagocytic and respiratory burst activities were assessed. This treatment suppressed neutrophil activities as seen in the reduction of chemotactic, phagocytic and respiratory burst activities. Neutrophil activities appeared to be suppressed in a dose-dependent manner leading to a considerable reduction in neutrophil activities with high concentrations of cortisol. Nevertheless, we showed that the respiratory burst activity was able to recover from the observed effect after cortisol was removed. The results in this study strongly suggest that cortisol has a directly adverse effect on fish neutrophil defense activities, but that the effect is reversible.

Inhibitory Effect of Cortisol on the Degranulation of Eosinophilic Granular Cells in Tilapia.

We examined the effect of cortisol on the degranulation and number of eosinophilic granular cells (EGCs) in tilapia, Oreochromis niloticus. One hour after injection of stimulants (killed Escherichia coli or substance P, a neurotransmitter) into the swim bladder, the percent of the degranulated EGCs in the swim bladder membrane was determined. Peritoneal implantation of coconut oil containing cortisol (50 mg/kg body weight) 24 h before injection of stimulants significantly reduced the percent of the degranulated EGCs, compared with the control fish administered with coconut oil without Cortisol. Cortisol also suppressed the in vitro degranulation of EGCs stimulated with substance P or with tilapia normal sera containing zymosan. To investigate the effect of cortisol on the abundance of EGCs, the number of EGCs in the swim bladder membrane was counted. Density of EGCs was decreased after implantation of cortisol, compared with that of the control group. These results suggest that cortisol suppresses the degranulating activity of EGCs and decreases the density of EGCs in the tissue.

EFFECTS OF 1α,25-DIHYDROXYCHOLECALCIFEROL AND CORTISOL ON THE GROWTH AND DIFFERENTIATION OF PRIMARY CULTURES OF MOUSE MAMMARY EPITHELIAL CELLS IN COLLAGEN GEL

We examined the effects of 1α,25-dihydroxycholecalciferol (1,25-DHCC) and the glucocorticoid, cortisol, on primary mouse mammary epithelial cells in collagen gel cell culture systems. Physiological low concentrations (10−11–10−9m) of 1,25-DHCC stimulated growth of the cells in a collagen gel matrix culture in serum-free DMEM+Ham's F12 (1:1) medium containing BSA, EGF and cholera toxin, and the cell number reached 1.8-fold the control after 6d in culture. In contrast, supraphysiological concentrations (10−8–10−7m) of 1,25-DHCC suppressed cell growth. Cortisol produced similar, but smaller, dose-dependent effects. The addition of serum to the culture medium masked the stimulatory effect of 1,25-DHCC and both the stimulatory and inhibitory effects of cortisol. 1,25-DHCC also affected casein synthesis by cells cultured in a serum-free floating collagen gel culture containing prolactin, insulin and cortisol, enhancing synthesis at low concentrations (10−11–10−9m) and inhibiting it above 10−8m. In the absence of cortisol, no detectable change in casein synthesis was induced by 1,25-DHCC. These results suggest a physiological role for 1,25-DHCC in stimulating both growth and differentiation of mouse mammary epithelial cells, though 1,25-DHCC does not substitute for glucocorticoids in the differentiation of the cells.

Endogenous tumor necrosis factor-alpha production by a pancreatic beta-cell line: inhibitory effects of hydrocortisone and nicotinamide.

The purpose of this study was to examine regulation of interleukin-1(IL-1)-induced tumor necrosis factor-alpha (TNF-alpha) production by a mouse beta-cell line (beta TC1). Three-hour incubation of beta TC1 cells with 5 U/ml of IL-1 beta results in the expression of TNF-alpha mRNA and intracellular accumulation of TNF-alpha. It has been shown that glucocorticoids and immunosuppressive agents such as cyclosporin and FK-506 inhibit TNF-alpha generation by T-lymphocytes and monocytes. Hydrocortisone of 1 and 10 mumol/l suppressed TNF-alpha mRNA levels and the TNF-alpha content of beta TC1 cells exposed to IL-1 beta, whereas neither cyclosporin nor FK-506 altered the TNF-alpha content. Nicotinamide of 5-10 mmol/l also reduced TNF-alpha mRNA and TNF-alpha protein levels in beta TC1 cells. Addition of exogenous TNF-alpha did not inhibit IL-1-induced transcription of TNF-alpha gene. These observations support the potential therapeutic role of glucocorticoids and nicotinamide in protecting beta-cells against cytokine-mediated damage, although glucocorticoid agonists have hyperglycemic metabolic effects.

Glucocorticoids and interferon-alpha in the acquired immunodeficiency syndrome.

Some patients with acquired immunodeficiency syndrome (AIDS) develop glucocorticoid resistance characterized by low receptor affinity (Kd) for glucocorticoids in mononuclear, cells and high values of ACTH and cortisol. As glucocorticoids regulate interferon-alpha (IFN alpha) production, we hypothesized that IFN alpha, a cytokine produced predominantly by monocytes in AIDS, should be increased in cortisol-resistant AIDS, attributing the lack of cortisol inhibition to IFN alpha production. Therefore, we examined glucocorticoid receptor characteristics on monocytes by [3H]dexamethasone binding and measured IFN alpha, cortisol, and ACTH in AIDS patients with (AIDS-GR) or without glucocorticoid resistance (AIDS-C) and controls (C). Monocytes of AIDS-GR patients had a receptor Kd of 10.5 +/- 4.2 nmol/L that was higher than that in the AIDS-C group (2.9 +/- 0.8 nmol/L) and normal subjects (2.0 +/- 0.8 nmol/L; P < 0.01). IFN alpha levels were increased in the AIDS-GR group (17 +/- 6 vs. 4 +/- 1 U/mL in the AIDS-C group and 2 +/- 0.5 U/mL in the C group; P < 0.01). Correlations were found between plasma IFN alpha and receptor Kd on monocytes of AIDS-GR (r = 0.77) and between IFN alpha and plasma cortisol in the same group (r = 0.74). The poly(I)-poly(C)-induced IFN alpha production by monocytes was inhibited by glucocorticoids in the C and AIDS-C groups (approximately 80% inhibition in both groups); the effect was reversed by the receptor antagonist RU-38486. By contrast, glucocorticoids failed to inhibit IFNalpha production from AIDS-GR monocytes (approximately 20% inhibition). In conclusion, elevated IFN alpha levels in AIDS-GR may be due to the lack of inhibitory effect of cortisol on IFN alpha production due to cortisol resistance in monocytes.

Effects of mixed leukocyte reaction, hydrocortisone and cyclosporine on expression of leukocyte adhesion molecules by endothelial and mesangial cells.

We investigated the effects of mixed leukocyte reaction (MLR), hydrocortisone (HC) and cyclosporine A (CsA) on the expression of leukocyte adhesion molecules on the mesangial (MC) and endothelial cells (EnC). Cell surface enzyme immunoassay showed that INFnu, IL-1beta, or TNF alpha stimulated expression of ICAM-1, or VCAM-1 on MC after 24 hours. Flow cytometric analysis demonstrated that MLR supernatant induced a marked increase in mean fluorescence of or % of cells highly expressing intercellular adhesion molecule(ICAM)-1 or vascular cell adhesion molecule (VCAM)-1 on both cells after 24 hours (p<0.001). HC treatment(300 ng/ml) during MLR effectively inhibited MLR-induced upregulation of ICAM-1 and VCAM-1 on both cells (p<0.005). When MLR supernatant with HC was added to adhesion molecule assay, there was no inhibitory effect of HC on VCAM-1. CsA treatment (500 ng/ml) during MLR caused a modest decrease in upregulation of VCAM-1 on EnC (p<0.05), but had no effects on ICAM-1 on both cells. CsA directly decreased expression of VCAM-1 on MC. In conclusion, alloreactive lymphocytes and monocytes upregulate the expression of VCAM-1 and ICAM-1 on target cells probably by the mediation of cytokines. HC effectively prevents MLR-induced upregulation of VCAM-1 and ICAM-1. CsA does not increase the expression of VCAM-1 and ICAM-1.

Hexarelin, a novel GHRP-6 analog, counteracts the inhibitory effect of hydrocortisone on growth hormone secretion in acromegaly.

Hexarelin (His-D-2-Methyl-Trp-Ala-Trp-D-Phe-Lys-NH2) is a GHRP-6 analog with the substitution of D-tryptophan with its 2-methyl derivative. The aim of our study was to ascertain whether hexarelin was able to counteract the glucocorticoid-mediated increase in hypothalamic somatostatin tone and consequent inhibition on serum GH levels in acromegalic patients. Ten patients (5 males, 5 females; age range 27-71 years; BMI range 23.3-35 kg/m2) with active acromegaly underwent: 1) hydrocortisone alone: a bolus iv injection of 100 mg hydrocortisone succinate in 2 mL saline, at time -60 followed by a 120 min iv infusion of 250 mg hydrocortisone succinate in 250 mL saline, from -60 to 60 min; 2) hexarelin+hydrocortisone: a bolus iv injection of hexarelin 100 micrograms, 60 min after initiation of a 2-hour hydrocortisone infusion; 3) hexarelin alone: a bolus iv injection of hexarelin at time 0, 60 min after initiation of a 2-hour saline infusion. The mean GH peak, expressed as percent change with respect to baseline level (mean of -75 and -60 minute samples), after hexarelin (1750 +/- 1157%) did not differ significantly with respect to that observed after hexarelin+hydrocortisone (1120 +/- 770%). After hydrocortisone alone the patients showed a mean decrease in GH levels as compared to baseline levels, of 47 +/- 7%. Our data show that the GH response to hexarelin in acromegaly is resistant to the inhibitor action of an acute and sustained elevation of serum cortisol levels. That hexarelin counteracts the glucocorticoid-mediated inhibition of GH secretion supports the hypothesis of an hexarelin-induced decrease in endogenous somatostatin tone.

Abnormal temporal patterns of glucose tolerance in obesity: relationship to sleep-related growth hormone secretion and circadian cortisol rhythmicity.

To define the chronobiology of glucose tolerance and insulin secretion in obesity, nine obese men and nine lean men were studied during constant glucose infusion for 53 h, including 8 h of nocturnal sleep, 28 h of continuous wakefulness, and 8 h of daytime sleep. Blood samples were collected at 20-min intervals to assay glucose, insulin, C-peptide, cortisol, and GH. Sleep was polygraphically monitored. Abnormal temporal profiles of glucose regulation were observed during wakefulness and sleep in obese subjects. During daytime hours, the normal profile of glucose tolerance was reversed, as an improvement, rather than a deterioration, was observed from morning to late evening. This reversal of the daytime pattern appeared to be caused by a dual defect in glucose regulation during the previous night. Indeed, during early sleep, GH secretion was markedly reduced, and the nocturnal rises of glucose and insulin secretion were dampened. During late sleep, obese subjects failed to suppress insulin secretion and plasma glucose, resulting in high morning levels. Comparisons of metabolic and hormonal patterns during nocturnal and daytime sleep suggest that the failure to suppress insulin secretion in late sleep may reflect a relative insensitivity of the beta-cell to acute inhibitory effects of cortisol in addition to insulin resistance.

Hydrocortisone Regulation of Interleukin-6 Protein Production by a Purified Population of Human Peripheral Blood Monocytes

The direct effect of the endogenous glucocorticoid (GC) hydrocortisone (HC) on interleukin-6 (IL-6) production was examined using purified populations of human peripheral blood monocytes (Mo). Lipopolysaccharide (LPS) induced IL-6 production by Mo in a dose-dependent fashion. IL-6 was detected in Mo supernatants as early as 2 hr after stimulation, with peak IL-6 production observed by 16 hr. Simultaneous addition of HC and LPS resulted in a significant decrease of IL-6 production 4 hr after LPS treatment, with maximum inhibition observed at 16-24 hr. An attenuation of the inhibitory effect of HC occurred with greater concentrations of LPS and with the delay of HC addition until after LPS. However, there was no correlation between the quantity of IL-6 produced by Mo and the level of HC inhibition. The inhibitory effect of HC was greater if LPS, rather than IL-1β, were used as a stimulus to induce IL-6 production. The EC 50 of LPS-induced IL-6 production by HC was 2.0 × 10 -7 M. The inhibitory effect of HC on LPS-stimulated IL-6 production was GC specific and receptor mediated because: (i) equivalent inhibition was not observed with other endogenous steroids and (ii) equimolar amounts of the GC antagonist RU 486 blocked the GC-mediated effect.

Perturbation of the Immunosuppressive Action of Glucocorticoids in Rat Thymocytes by Liposoluble Extracts of Serum from AIDS Patients

Liposoluble extracts of serum from healthy men and AIDS patients (stages IVC1 and IVD by CDC criteria) inhibited the incorporation of [3H]thymidine into isolated rat thymocytes, but AIDS extracts were less inhibitory, requiring 1.8 times more cortisol in the AIDS extracts than in the healthy extracts to inhibit [3H]thymidine incorporation by 50%. Although the total serum extracts from AIDS patients contained 1.7 times more cortisol than the extracts from healthy controls, the AIDS extracts decreased the binding affinity (Ka) of [3H]dexamethasone to rat thymus glucocorticoid receptors by 50% less than the healthy control extracts. The present study seems to indicate that a substance(s) can be extracted from the serum of AIDS patients that attenuates the inhibitory effect of cortisol on thymocyte proliferation and interferes with the binding of cortisol to the glucocorticoid receptor.

Interaction between cortisol and arachidonic acid on the secretion of LH from ovine pituitary tissue

In several species, glucocorticoids act directly on the pituitary gonadotroph to suppress the gonadotrophin-releasing hormone (GnRH)-induced secretion of the gonadotrophins, especially LH. A mechanism for this action of these adrenal steroids has not been established, but it appears that the glucocorticoids influence LH release by acting on one or more post-receptor sites. This study investigated whether glucocorticoids disrupt GnRH-induced LH release by altering the liberation of arachidonic acid from plasma membrane phospholipids, a component of GnRH-induced LH release. Using perifused ovine pituitary tissue, it was established that exposure of gonadotrophs to 1-1000 nmol cortisol/l for 4 h or longer significantly reduced GnRH-stimulated LH release with the maximal inhibitory effect being observed after 6 h of exposure to cortisol. This suppressive effect of cortisol could be reversed by administration of arachidonic acid, which in its own right could stimulate LH release from ovine pituitary tissue. Furthermore, the inhibitory effect of cortisol on GnRH-stimulated LH release could be directly correlated with decreased pituitary responsiveness to GnRH-stimulated arachidonic acid liberation, consistent with our hypothesis that glucocorticoids can suppress GnRH-induced secretion of LH by reducing the amount of arachidonic acid available for the exocytotic response of GnRH.

The role of DNA synthesis in the responses of fetal rat calvariae to cortisol

To determine the extent to which the effects of cortisol on collagen synthesis in 21 day fetal rat calvariae are linked to its effects on cell replication, calvariae were cultured for 24-72 h with 0.1 and 1 microM cortisol in the presence or absence of 1 mM hydroxyurea (HU) or 30 microM aphidicolin (APC), inhibitors of DNA synthesis. The incorporation of [3H]proline into collagenase-digestible protein (CDP) and [3H]thymidine into DNA were measured during the last 2 h of culture. At 24 h HU and APC decreased thymidine incorporation by greater than 90%, and this remained low for the duration of culture. In contrast, cortisol reduced thymidine incorporation by only 44% at 72 h. Although cortisol caused a 24 h stimulatory effect and a 48 and 72 h inhibitory effect on CDP labeling and the percentage of collagen being synthesized (PCS), HU, and APC had no effect on basal CDP labeling or PCS over the 72 h culture period. Cortisol caused parallel alterations in the steady-state levels of alpha-1(I) procollagen mRNA, suggesting that its effects occur at the pretranslational level. At 24 h HU and APC did not prevent the stimulatory effect of cortisol on CDP labeling and PCS. At 48 h the inhibitory effects of cortisol on CDP labeling and PCS were observed in the presence of APC but not in the presence of HU. At 72 h the inhibitory effects of cortisol on CDP labeling and PCS were still observed in the presence of HU and APC.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoids inhibit the induction of nitric oxide synthase in macrophages

The effect of glucocorticoids on the production of NO 2 − and NO by the macrophage cell line J774 was investigated. Stimulation of the cells with lipopolysaccharide (LPS) resulted in a time-dependent accumulation of NO 2 − in the medium, reaching a plateau after 48h. Concomitant incubation of the cells for 24h with dexamethasone (0.001–1.0 μM) or hydrocortisone (0.01–10.0 μM) caused a concentration-dependent inhibition of NO 2 − formation. The cytosol of J774 cells stimulated with LPS and IFN-γ produced a time-dependent increase in the release of NO. This was blocked in a concentration-dependent manner by dexamethasone and hydrocortisone, but not progesterone, administered concomitantly with the immunological stimulus. None of these compounds had any effect on the release of NO once the enzyme had been induced. The inhibitory effect of hydrocortisone on NO formation was blocked by cortexolone. These data suggest that part of the anti-inflammatory and immunosuppressive actions of glucocorticoids is due to their inhibition of the induction of the NO synthase.

Cortisol Inhibits the Synthesis of Insulin-Like Growth Factor-I in Skeletal Cells*

Supraphysiological levels of cortisol inhibit bone cell replication and matrix synthesis, but its mechanism of action is unknown and could be secondary to an inhibition of local growth factor synthesis. These inhibitory effects of cortisol are the converse of the observed anabolic influences of the endogenously produced insulin-like growth factor-I (IGF-I); therefore, cortisol was examined for its effect on the production of IGF-I in osteoblast (Ob)- and fibroblast/preosteoblast-enriched cell cultures prepared from fetal rat parietal bone. Synthesis of IGF-I was monitored by Northern blot analysis to determine steady state IGF-I mRNA levels and by an IGF-I-specific RIA to quantitate polypeptide levels in acidified and fractionated culture medium. Cortisol at 100 nM decreased IGF-I transcript levels by 60% or more in Ob cultures within 6 h of treatment, and the concentration of immunoreactive IGF-I by 50% after 24 h; these effects were observed in the absence of a change in cellular DNA content. In Ob cultures, PTH at 10 nM increased IGF-I transcripts at 6 h and polypeptide levels at 24 h by 2.5- and 4.1-fold, respectively, and cortisol opposed this effect. The inhibitory effect of cortisol was not specific for the Ob cell population, since at 100 nM it also decreased IGF-I transcript and immunoreactive IGF-I levels in fibroblast/preosteoblast cultures and opposed the stimulation of IGF-I synthesis after treatment with 100 ng/ml GH. In conclusion, high levels of cortisol decrease skeletal IGF-I synthesis by reducing IGF-I transcript levels, and this effect probably contributes to the inhibitory influence of cortisol on bone formation.

The inhibitory effect of hydrocortisone on interferon production by rat spleen cells.

The effect of hydrocortisone on interferon r(IFN-r) production by rat spleen cells and its mechanism were studied. The results showed that hydrocortisone inhibited IFN-r production at concentrations as low as 5.52 x 10(-10) M, with complete suppression at 5.52 x 10(-8) M, and the total number and survival rate of the cultured spleen cells were not apparently affected by 5.52 x 10(-8) M hydrocortisone. The inhibitory effect was dose-dependent when the concentration was from 5.52 x 10(-10) M to 5.52 x 10(-8) M and could be blocked by RU38486, a competitive antagonist of glucocorticoid. Our results suggested that glucocorticoid may inhibit IFN-r production through a receptor-mediated mechanism.

Defective distal regulatory element at the 5′ upstream of rat prolactin gene of steroid-nonresponsive GH-subclone

The prolactin-nonproducing (PRL −) GH cell strains (rat pituitary tumor cells in culture). GH 12C 1 and F 1BGH 12C 1, do not respond to steroid hormones estradiol or hydrocortisone (HC). However, the stimulatory effect of estradiol and the inhibitory effect of hydrocortisone on prolactin synthesis can be demonstrated in the prolactin-producing GH cell strain, GH 4C 1. In this investigation we have examined the 5′ end flanking region of rat prolactin (rat PRL) gene of steroid-responsive, GH 4C 1 cells to identify the positive and negative regulatory elements and to verify the status of these elements in steroid-nonresponsive F 1BGH 12C 1 cells. Results presented in this report demonstrate that the basel level expression of the co-transferred Neo gene (neomycin phosphoribosyl transferase) is modulated by the distal upstream regulatory elements of rat PRL gene in response to steroid hormones. The expression of adjacent Neo gene is inhibited by dexamethasone and is stimulated by estradiol in transfectants carrying distal regulatory elements (SRE) of steroid-responsive cells. These responses are not observed in transfectants with the rat PRL upstream sequences derived from steroid-nonresponsive cells. The basal level expression of the host cell α-2 tubulin gene is not affected by dexamethasone. We report here the identification of the distal steroid regulatory element (SRE) located between 3.8 and 7.8 kb upstream of the transcription initiation site of rat PRL gene. Both the positive and the negative effects of steroid hormones can be identified within this upstream sequence. This distal SRE appears to be nonfunctional in steroid-nonresponsive cells. Though the proximal SRE is functional, the defect in the distal SRE makes the GH substrain nonresponsive to steroid hormones. These results suggest that both the proximal and the distal SREs are essential for the mediation of action of steroid hormones in GH cells.