Specificity and inhibition of glucocorticoid-induced macrocortin secretion from rat peritoneal macrophages

Regulation of colony stimulating factor-1 (CSF-1) in endometrial cells: glucocorticoids and oxidative stress regulate the expression of CSF-1 and its receptor c-fms in endometrial cells

OBJECTIVE

To evaluate the regulation and expression of CSF-1 and its receptor c-fms in endometrial cells.

DESIGN

In vitro study.

SETTING

Research and teaching institution.

PATIENT(S)

None.

INTERVENTION(S)

In vitro experimental study.

MAIN OUTCOME MEASURE(S)

The effect of glucocorticoid and oxidative stress on the expression of CSF-1 and c-fms in endometrial cells.

RESULT(S)

Cultured nonmalignant EM42 cells not only express CSF-1 and c-fms but are also capable of responding to exogenous CSF-1. We have also seen that glucocorticoids can regulate the expression of CSF-1/c-fms in endometrial cells. Furthermore, this study shows that oxidative stress plays a significant role in the induction of CSF-1 and its receptor c-fms.

CONCLUSION(S)

The results suggest that CSF-1 may promote the growth of nonmalignant endometrial cells in both an autocrine and paracrine manner and that endometrial cells under oxidative stress induce CSF-1 and c-fms.

A novel approach to the discovery of non-systemic anti-inflammatory steroids; antedrug

Therapeutic use of anti-inflammatory steroids is limited due primarily to their systemic suppressive effects on pituitary function and the immune system. To overcome the clinical limitation, a new approach toward the discovery of non-systemic anti-inflammatory steroids is based upon the antedrug concept introduced by this laboratory. The new concept describes locally active agents which are designed to undergo a predictable biotransformation to inactive metabolites upon entry into systemic circulation from the applied site. Thus, true antedrugs are devoid of systemic adverse effects. In a continuing effort, 16alpha-carboxylate and isoxazoline derivatives of prednisolone have been synthesized and screened. In the croton oil-induced ear edema bioassay, the following relative potencies were obtained setting hydrocortisone=1.0; 3a, 1.5; 3b, 3.1; 4a, 4.0; 4b, 12.2; 5b, 8.2; 6b, 11.2; 7a, 1.9; 7b, 4.1; 8a, 3.3; 8b, 6.8; 9a, 0.7; 9b, 8.6; 10a, 2.6; 10b, 7.4. Results of the five-day bioassay indicated that, in contrast to the parent compound, the novel steroidal antedrugs did not significantly alter body weight gain, thymus weights, adrenal weights or plasma corticosterone levels. Taken together, the antedrug concept appears to be a fundamentally sound strategy for the separation of local anti-inflammatory activity from systemic adverse effects.

Regulation of monocyte to macrophage differentiation by antiglucocorticoids and antioxidants

OBJECTIVE

Our purpose was to examine RU 486 and related compounds on monocyte to macrophage differentiation through scavenger receptors and cellular adhesion.

STUDY DESIGN

Human monocytes were isolated, cultured, and treated with dexamethasone, levonorgestrel, RU 486, and other structurally related compounds alone or in combination. Macrophage scavenger receptor activity, inhibited by glucocorticoids and associated in the current literature with macrophage cellular adhesion, was determined in this study by counting the number of adherent cells after treatment. In addition, fluorescent-labeled acetyl-low-density lipoprotein uptake was determined as a function of scavenger receptor biologic activity.

RESULTS

Dexamethasone, levonorgestrel (antiglucocorticoid only) and RU 486 (antiglucocorticoid and antioxidant) all significantly decreased adherent macrophages (4%, 52%, and 74% of control). Levonorgestrel, however, demonstrated a marked uptake of fluorescent-labeled scavenger receptor ligand. RU 486 and dexamethasone were antagonistic when combined (P < .001); levonorgestrel was less antagonistic but, however, still significant (P < .05). Reduced RU 486 (antioxidant but loses antiglucocortioid activity) decreased cellular adhesion, yet scavenger receptor function was enhanced. Both probucol (extracellular mechanism of action) and probucol analog (intracellular action) markedly up-regulated scavenger function, but once again a separation of adhesion from scavenger activity was noted. Vitamin E (antioxidant) and onapristone (antioxidant and antiglucocorticoid) had virtually little to no effect on adhesion and scavenger receptor activity. Finally, pyrrolidine dithiocarbamate, a potent oxygen-free radical quencher, was toxic to all cells examined.

CONCLUSIONS

RU 486 is a known antiglucocorticoid with novel antioxidant properties first demonstrated by our laboratories. Levonorgestrel has antiglucocorticoid but no antioxidant activity. RU 486 antagonized the inhibitory effect of dexamethasone on scavenger receptor development, whereas levonorgestrel was stimulatory. A separation of scavenger receptor-induced cellular adhesion and scavenger receptor internalized ligand was demonstrated by (1) reduced RU 486, which loses its antiglucocorticoid activity but retains its antioxidant activity, and (2) probucol analog, which is chemically altered to allow intracellular entry. Glucocorticoids decrease the development of scavenger receptors, whereas antioxidants regulate inflammatory cytokines by intracellular mechanisms. It is therapeutically important to up-regulate scavenger receptor activity by antiglucocorticoids in the peritoneal cavity of women with endometriosis. However, because these mechanisms also induce inflammatory cytokines, a balance of antioxidants and antiglucocorticoids such as those demonstrated in the above study may prove beneficial.

Blockade of the classical pathway of protein secretion does not affect the cellular exportation of lipocortin 1

The mechanism by which lipocortin 1 (LC1) is extruded from cells in the brain and periphery in response to a glucocorticoid challenge is unknown. This study examined the influence of three inhibitors of the classical endoplasmic reticulum-Golgi pathway of protein secretion on the dexamethasone-induced (0.1 microM, 2-3 h) cellular exportation of LC1 in vitro in brain (cortex, hippocampus, hypothalamus), anterior pituitary tissue and peritoneal macrophages. In all instances, the steroid-induced exportation of LC1 was unaffected by brefeldin A (1.4 microM), monensin (10 microM) and nocodazole (3.3 microM); however, these drugs readily blocked the release of corticotrophin from pituitary tissue. These data suggest that LC1 is exported by a mechanism distinct from the classical pathway of protein secretion.

Glucocorticoids modulate the cellular disposition of lipocortin 1 in the rat brain in vivo and in vitro

The role of glucocorticoids in the regulation of lipocortin 1 (LC1) mRNA/protein expression in the brain is uncertain. This study has examined the influence of dexamethasone on the disposition of LC1 protein in various central and peripheral tissues in the rat. LC1 was readily detectable in all tissues studied by Western blot analysis. Exposure to dexamethasone in vitro (0.1 microM, 3 h) or in vivo (20 micrograms/100 g i.p., 24 h before autopsy) had no discernible effects on intracellular LC1 levels but increased the amount of LC1 attached to the outer surface of cells (pericellular LC1) in cortex, hippocampus, hypothalamus, pituitary gland and peritoneal macrophages (in vitro only). The results suggest that in central tissues, as in the periphery, glucocorticoids promote the translocation of LC1 from intracellular to pericellular sites.

Human placental Fc gamma-binding proteins in the maternofetal transfer of IgG

Annexin II, a member of the annexin family of Ca2+ and phospholipid binding proteins, is present in human placenta. Placental annexin II has low affinity FcR activity, and is present as a heterotetramere on syncytiotrophoblast apical cell membrane extracellular surface. In addition to annexin II, transmembraneous leukocyte FcRIII is present on syncytiotrophoblast apical membrane. Either one, or both molecules may mediate the binding of IgG and thereby facilitate its transport through the syncytiotrophoblast layer. However, the presence of other maternal plasma proteins in syncytiotrophoblasts that are not transported to the human fetus is suggestive of nonspecific fluid phase endocytosis. The MHC class I like FcR, similar to the receptor found in neonatal rodent intestine, FcRn, is present intracellularly in human syncytiotrophoblasts, as is its light chain beta 2-microglobulin. The hFcRn is not detected on the apical plasma membrane. The placental hFcRn co-localizes with IgG in syncytiotrophoblast granules. It is likely that hFcRn binds and transcytoses IgG through the syncytiotrophoblast. Protected transfer of IgG may occur within syncytiotrophoblast endocytotic vesicles prior to release in the villous stroma and subsequent translocation into the lumen of fetal stem vessels by uptake and transport in endothelial caveolae.

The effect of RU 486 and related compounds on cultured macrophage differentiation and function

OBJECTIVE

Our purpose was to examine RU 486 and related compounds on macrophage scavenger receptors and cellular adhesion.

STUDY DESIGN

THP-1 cells were activated with phorbol myristate acetate and treated with dexamethasone, levonorgestrel, and RU 486 alone or in combination. Scavenger receptor activity was determined by counting adhered cells. In addition, fluorescently labeled acetyl low density lipoprotein uptake was determined.

RESULTS

Both dexamethasone and RU 486 significantly decreased activated macrophages (81% and 26% of control). Levonorgestrel stimulated adherent cells in activated monocytes (130% of control). RU 486 and dexamethasone were antagonistic when combined (p < 0.001). In contrast, dexamethasone could not overcome the stimulatory effect of levonorgestrel (p < 0.001). Fluorescent studies yielded similar results.

CONCLUSIONS

RU 486 is a known antiglucocorticoid with novel antioxidant properties. Levonorgestrel has antiglucocorticoid but no antioxidant activity. Glucocorticoids decrease scavenger receptors and antioxidants regulate inflammatory cytokines. RU 486 antagonized the inhibitory effect of dexamethasone on scavenger receptors, whereas levonorgestrel was stimulatory. It is therapeutically important to up-regulate scavenger receptor activity by antiglucocorticoids in the peritoneal cavity of women with endometriosis. However, because these mechanisms also induce inflammatory cytokines, a balance of antioxidants and antiglucocorticoids may prove beneficial.

Translocation of lipocortin (annexin) 1 to the membrane of U937 cells induced by phorbol ester, but not by dexamethasone

1. Induction of lipocortin 1 secretion by dexamethasone has been demonstrated, although the secretory mechanism is still unknown. We have studied the effects of 12-tetradecanoyl phorbol 13-acetate (TPA) and/or dexamethasone on the expression, translocation, and secretion of lipocortin 1 in U937 cells. 2. The expression of lipocortin 1 and its mRNA increased during TPA-induced differentiation of U937 cells to a maximum of 1.9 fold and 8.2 fold, respectively, after 48 h. Both the protein and the mRNA levels decreased after 48 h. 3. TPA caused the translocation of lipocortin 1 from the cytosol to the membrane of U937 cells in a time-dependent manner, as determined by Western blot analysis. The translocation was concurrent with the differentiation of the cells. After 48 h of TPA treatment, 82.6 +/- 6.5% of lipocortin 1 was present in the membrane fraction compared to 41.6 +/- 1.7% in untreated cells. 4. The amount of lipocortin 1 that was externally bound (associated) with the membrane increased to 3.2 fold as the cytosol to membrane translocation of lipocortin 1 increased. 5. Dexamethasone decreased the externally bound lipocortin 1, but had no effect on the cytosol to membrane translocation. 6. This offers a model system with which the function and the secretion mechanism of lipocortin 1 can be studied. Our data is consistent with the hypothesis that the secretory mechanism is through an unknown pathway, involving the translocation of lipocortin 1 from the cytosol to the internal membranes, and then, its secretion to the external membrane.

Effect of RU-486 and related compounds on the proliferation of cultured macrophages

PROBLEM

Macrophages are implicated in the pathophysiology of endometriosis and are influenced by anti-inflammatory steroids as well as anti-oxidants.

METHODS

We tested the effect of RU-486, an antiprogesterone, antiglucocorticoid and an antioxidant, on the proliferation of RAW macrophages.

RESULTS

The incorporation of 3H-thymidine was significantly inhibited by both progesterone and RU-486. Progesterone and RU-486, in combination, synergistically inhibited macrophage growth. In contrast, dexamethasone-stimulated growth was antagonized by RU-486 in a dose dependent manner. ZK 112,993 which is structurally related to RU-486 but lacks antioxidant properties, also inhibited thymidine incorporation. The synergistic effect of RU-486 and ZK 112,993 with progesterone implicate a mechanism of action separate from receptor bound antagonists. A cell permeable antioxidant, pyrrolidine dithiocarbamate was very effective in inhibiting the incorporation of 3H-thymidine into cells.

CONCLUSIONS

These results suggest novel therapeutic modalities in the management of endometriosis via antiglucocorticoid as well as antioxidant mechanisms.

Modulation of complement gene expression by glucocorticoids

The addition of dexamethasone, prednisolone or cortisol (in order of efficacy) to human monocytes in culture produced dose-related increases in the synthesis rates of the complement components C1 inhibitor (C1-inh), factor B (B) and C2. In contrast, concentrations of C3 and lysozyme in the culture supernatants were decreased. Indomethacin stimulated synthesis of C1-inh, C2 and B, but had little effect on synthesis of C3 or lysozyme. The simultaneous addition of cycloheximide (2.5 micrograms/ml) abrogated the effects of dexamethasone on synthesis of C2, B and C1-inh, but the effect of indomethacin on the synthesis of these components was unchanged. These data suggest that protein synthesis is required for the effects of glucocorticoids on the synthesis of C2, B and C1-inh to occur. Dexamethasone and indomethacin increased the abundances of C1-inh mRNA, B mRNA and C2 mRNA in parallel with changes in the synthesis rates of these proteins. The changes in mRNA abundance were not transcriptional, but were shown to be due to increased mRNA stability. In contrast, dexamethasone decreased the expression of C3 and lysozyme by decreasing the rate of transcription of these genes. Indomethacin had no effect on transcription of the C3 and lysozyme genes. The half-lives of C3 mRNA, lysozyme mRNA and actin mRNA were not altered by dexamethasone or indomethacin. It is concluded that the effects of glucocorticoids on monocyte synthesis of C2, B and C1-inh are due to increased mRNA stability and may be related to inhibition of prostaglandin synthesis, as these effects are similar to those produced by indomethacin. The effects of dexamethasone on the synthesis of C3 and lysozyme differ from those on C2, B and C1-inh as they depend upon a decrease in gene transcription, which is not affected by indomethacin.

Eleventh Gaddum memorial lecture. Lipocortin and the mechanism of action of the glucocorticoids

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Receptor-mediated effects of glucocorticoids on inflammation: enhancement of the inflammatory response with a glucocorticoid antagonist

Glucocorticoids suppress the inflammatory response by altering leukocyte traffic and function, cytokine secretion and action, and phospholipid metabolism. We employed the glucocorticoid receptor antagonist RU 486, to examine whether glucocorticoids suppress the inflammatory response through a receptor-mediated mechanism and whether basal glucocorticoid secretion exerts antiinflammatory effects in the resting (non-stress) state. To test these hypotheses we evaluated the effects of increasing doses of dexamethasone, RU 486, or dexamethasone plus RU 486 on the exudate volume and concentrations of leukocytes, prostaglandin E2, (PGE2) and leukotriene B4 (LTB4) in intact rats that received subcutaneous carrageenin. Exudate volume, leukocyte concentration and LTB4 and PGE2 levels were all suppressed by dexamethasone in a dose-dependent fashion (P less than 0.005). RU 486 was able to antagonize fully the suppressive effects of dexamethasone on the inflammatory response (P less than 0.001) and to cause increases of exudate volume and leukocyte, PGE2 and LTB4 concentrations when given alone (P less than 0.05). These increases ranged between 30 and 100% above the basal inflammatory response. We conclude that glucocorticoids most likely suppress the inflammatory response by a glucocorticoid receptor-mediated mechanism and under basal conditions exert tonic antiinflammatory effects.

Clinical pharmacology and pharmacokinetic properties of topically applied corticosteroids. A review

The development of topical corticosteroids since the 1950s has opened new doors for dermatologists previously faced with treating intractable dermatoses, so that the pharmacology of topically applied corticosteroids is now reasonably well described. Manipulation of the steroid molecule has produced compounds with greater lipophilicity, fewer mineralocorticoid properties and high potency. Potency is determined through various techniques, notably the vasoconstrictor assay as well as the mitotic index suppression method and atrophogenic potential assay. The mechanism of activity of corticosteroids is thought to result, at least in part, from binding of the drug to steroid receptors, with resultant effects on the synthesis of proteins responsible for specific effects. Corticosteroids are proposed to alter the inflammatory response, and thus provide therapeutic benefits, via actions on mediator release and function, inflammatory cell function and release of lysosomal enzymes. Disadvantages of corticosteroid activity include the possibility of adrenal suppression, epidermal and dermal thinning, and local effects such as purpura, striae, and steroid-induced rosacea and perioral dermatitis. The cutaneous pharmacokinetics, particularly of absorption of topical corticosteroids, must be examined in parallel with their pharmacodynamic effects to gain a more complete understanding of activity. Many factors can affect percutaneous steroid absorption: drug lipophilicity and solubility, drug concentration, anatomical site, age of the patient, presence of skin disease and use of occlusive dressings will each influence the degree to which topically applied corticosteroids achieve their intended therapeutic results. Cutaneous metabolism is a poorly understood process at present, but one which is acknowledged to have some impact on the biotransformation of corticosteroids applied topically. Thus, although some gaps still persist in present knowledge of the pharmacology and pharmacokinetics of this important class of drugs, there can be no denying the contribution of topical corticosteroids to the therapy of dermatoses.

Suppression of yeast ingestion by dexamethasone in macrophage cultures: evidence for a steroid-induced phagocytosis inhibitory protein

The mechanism by which glucocorticoid steroids suppress yeast phagocytosis in cultures of resident and thioglycollate-elicited murine peritoneal macrophages was examined. Time course and dose-response studies demonstrated that the phagocytic capacity of resident macrophages was suppressed by dexamethasone to the same extent in both newly established cultures and cultures that were incubated for several days. In contrast, relative to newly established cultures of elicited cells that were treated with the drug, elicited macrophages that were incubated for at least 1 day prior to exposure to dexamethasone, exhibited enhanced sensitivity to the action of the steroid. Steroid-induced phagocytic inhibitory responses were blocked by the metabolic inhibitors cycloheximide and actinomycin D. The suppression of phagocytosis by dexamethasone was mediated by a factor, present in the cellular homogenates of steroid-treated macrophages, that was partially purified by Sephadex G-25 chromatography. Since the phagocytic inhibitory activity in these homogenates was destroyed following exposure to heat and trypsin, the factor has been named phagocytosis inhibitory protein (PIP). The antiphagocytic activity of PIP was neutralized by treatment with RM23, a monoclonal antibody directed against lipocortin. The results support the hypothesis that the suppression of yeast ingestion is mediated by the action of PIP, which is induced in dexamethasone-treated macrophage cultures. Moreover, PIP appears to belong to the lipocortin family of phospholipase inhibitory proteins.

Control of prostanoid synthesis: role of reincorporation of released precursor fatty acids

Prostanoid synthesis is limited by the availability of free arachidonic acid. This polyunsaturated fatty acid is liberated by phospholipases and usually is an intermediate of the deacylation-reacylation cycle of membrane phospholipids. In rat peritoneal macrophages, ethylmercurisalicylate (merthiolate) or N-ethylmaleimide (NEM) dose dependently inhibited the incorporation of arachidonic acid into cellular phospholipids, at lower concentrations specifically into phosphatidylcholine. Furthermore, merthiolate could be shown to be a rather selective inhibitor of lysophosphatidylcholine acyltransferase. In contrast, phospholipase A2 activity was not affected over a wide dose range. Consequently, macrophages showed a large increase in prostanoid synthesis (prostaglandin E, prostacyclin and thromboxane) in the presence of both lysophosphatide acyltransferase inhibiting agents. Similar results were obtained with human platelets, in which merthiolate increased the release of thromboxane. Addition of free arachidonic acid also enhanced prostanoid synthesis in macrophages. At optimal concentrations, merthiolate had no further augmenting effect. It is concluded that the rate of prostanoid synthesis is not only controlled by phospholipase A2 activity, but rather by the activity of the reacylating enzymes, mainly lysophosphatide acyltransferase.

A rapid assay for activity of phospholipase A2 using radioactive substrate

A rapid method for the assay of phospholipase A2 has been developed using a radioactive substrate, L-alpha-dipalmitoyl-(2-[9,10(N)-3H]palmitoyl)-phosphatidylcholine. The substrate diluted with cold carrier (1 mM) is dissolved in 80% ethanol containing 25 mM sodium deoxycholate. The enzymatic reaction is performed in 1.0 ml 0.1 M glycine-NaOH buffer, pH 9.0, containing 2 mumol CaCl2, 10 micrograms bovine serum albumin, 2.5 mumol sodium deoxycholate, 0.01 unit (or less) phospholipase A2, and 40-100 nmol substrate. The enzymatic reaction is terminated by adding 0.2 ml 5% Triton X-100 solution containing 40 mumol EDTA. The product of the enzymatic reaction, radioactive palmitic acid, is extracted by 10 ml hexane containing 0.1% acetic acid in the presence of anhydrous sodium sulfate (0.5 g/ml). Activity of phospholipase A2 is directly determined from the radioactivity in the hexane extract. The present method achieves a quick separation of the radioactive product, [3H]palmitic acid, from the radioactive substrate, L-alpha-dipalmitoyl-(2-[3H]palmitoyl)-phosphatidylcholine, without the need of separation by TLC.

Glucocorticoid receptor IB: mediator of anti-inflammatory and teratogenic functions of both glucocorticoids and phenytoin

We studied the glucocorticoid receptor complexes of pulmonary and thymic cytosols of female A/J and CD-1 mice and of hepatoma G2 cells by two column-chromatographic systems, using both [3H]dexamethasone (DEX) and [3H]phenytoin (DPH) as ligands. Three DNA-cellulose adsorbable [3H]DEX-receptor complexes were separated in each system. Molecular sieving gave a 7-, a 5.4-, and a 3.5-nm complex (Stokes radii), and DEAE-Sephadex A-50 chromatography gave a complex eluting in the wash, one at 0.14 M KCl, and one at 0.20 M KCl by a KCl gradient. DPH blocked the binding of the 7- and 3.5-nm, wash, and 0.14 M KCl [3H]DEX complexes. Only two DNA-cellulose adsorbable [3H]DPH complexes, each blocked by DEX, were obtained in each system: a 7- and a 3.5-nm, a wash, and a 0.14 M KCl complex. Thus, there is a common receptor for both DPH and DEX. This receptor has two properties which distinguish it from the 5.4-nm DEX-specific receptor: (i) it binds with a variety of steroids other than glucocorticoids and DPH, and (ii) it rebinds new [3H]DEX or [3H]DPH after loss of ligand during chromatographic separation. These results indicate that DPH binds to receptor IB and not to receptor II of Litwack. [G. Litwack, 1976, in Glutathion: Metabolism and Function (Arias, I.M., and Jakoby, W.B., eds.), pp. 285-299, Raven Press, New York]. We have also found that hepatoma G2 cells have only receptor II. DPH affects neither the induction of tyrosine aminotransferase by DEX nor the basal level of this enzyme in these cells. Moreover, neither DEX nor DPH inhibits the release of [3H]arachidonic acid prelabeled in these cells, as they do in thymocytes which have the common receptor. Thus, it appears that glucocorticoid receptor IB binds DEX and DPH as glucocorticoid agonists mediating the anti-inflammatory and teratogenic action of these drugs, while receptor II apparently is responsible for the induction of tyrosine aminotransferase by DEX.

Mechanism of cyclosporin A-induced inhibition of prostacyclin synthesis by macrophages

In vitro studies of PG production over a 24 h period by adherent rat peritoneal macrophages activated by serum-opsonized zymosan revealed that CSA (0.3-10 micrograms/ml) caused a dose-related inhibition of PGI2 (assayed as 6-oxo-PGF1 alpha) formation. Indomethacin (IND, 0.01-10 micrograms/ml) and dexamethasone (DEX, 0.01-10 micrograms/ml) also inhibited the PG production in a dose-related manner. When arachidonic acid (10 micrograms/ml) was added together with the inhibitors, there was no change in the level of PGI2 produced by IND-treated cells whilst the PGI2 levels of DEX- and CSA-treated cells were elevated to the control level. Therefore CSA like DEX does not inhibit cyclo-oxygenase activity. However unlike DEX, CSA (1-30 micrograms/ml) caused inhibition of phospholipase A2 (PLA2) activity when assayed on the hydrolysis of a synthetic substrate by pancreatic PLA2 in a cell-free system. The direct inhibition of PLA2 might well be a manifestation of the fundamental activity of CSA on immunocompetent cells.

45Calcium uptake during the transition from reversible to irreversible liver injury induced by D-galactosamine in vivo

The hepatic uptake of 45calcium (45Ca) was studied in rats after administration of D-galactosamine (3 mmoles per kg, i.v.). In contrast to measurements of the hepatic calcium content, 45Ca uptake served as a dynamic rather than a static indicator of calcium homeostasis during the transition from reversible to irreversible liver injury which occurs between 3 and 4 hr after injection of the hepatotoxin. 45Ca uptake during a 1 hr-labeling period increased from 25 to 100% above control between 3 and 4 hr and subsequently remained at this level. The rise in 45Ca uptake and in hepatic calcium content occurred 2 to 3 hr after the D-galactosamine-induced depletion of UTP, UDP-galactose, UDP-glucose and UDP-glucuronate. The level of UDP-glucuronate was the earliest to recover. The enhanced 45Ca uptake was associated with hepatic glycogen breakdown and with an increased SGPT activity in plasma. Inhibition of RNA polymerase II by alpha-amanitin (0.5 mg per kg, i.p.) and of dolichol-dependent protein glycosylation as well as ganglioside synthesis by tunicamycin (2 mg per kg, i.p.) were used to imitate two of the early actions of D-galactosamine and indicated that an interference with either process can lead to an enhanced uptake of 45Ca into the liver in vivo. Uridine, at a dose replenishing uracil nucleotide pools after their depletion by D-galactosamine, prevented or reversed the rise in 45Ca uptake. The antiinflammatory steroid dexamethasone, injected prior to or simultaneously with D-galactosamine also protected against the loss of calcium homeostasis and the development of liver injury.(ABSTRACT TRUNCATED AT 250 WORDS)