Age-related changes in plasma proteins of analbuminemic rats

A mutant strain, Nagase analbuminemia rats (NAR), was established from Sprague-Dawley rats. Age-related changes in plasma proteins of NAR were investigated to obtain information of their abnormalities of protein metabolism. The total protein concentration in the serum of NAR of various ages was almost the same as that of normal rats of the same age. The albumin level of NAR was less than 0.05 mg/ml at all ages examined. The concentrations of serum alpha 1-antitrypsin, alpha-X protein, alpha 2-macroglobulin, transferrin, ceruloplasmin, IgG, IgA and IgM were higher in NAR than in normal rats except for the perinatal stage, but alpha 1-acid glycoprotein level in NAR was normal. The serum transferrin and ceruloplasmin levels were especially high in female adult NAR. The plasma fibrinogen concentration was also increased in NAR. These findings indicate that the normal total serum protein level of NAR was maintained by increase in the globulin concentration.     

Characterization of serum, liver, and intestinal sialyltransferases from rats treated with colchicine

A modified high pressure liquid chromatographic method using lactose (Gal beta 1----4Glc) as an exogenous acceptor has been used to characterize the sialyltransferases known to increase in the serum of colchicine-treated rats. The results show a 10-fold increase of Gal beta 1----4GlcNAc alpha 2----6 sialyltransferase (alpha 2----6 ST), whereas the Gal beta 1----3GlcNAc alpha 2----3 sialyltransferase showed only 1.6-fold increase in the serum after 17 h of colchicine treatment. The sialyltransferase activity in serum using exogenous desialylated, alpha 1-acid glycoprotein as acceptor also showed an eightfold increase. In liver homogenate and Golgi membrane, the sialyltransferase activity when assayed with desialylated alpha 1-acid glycoprotein as acceptor showed a slight decrease after 4 h, but returned to normal level after 17 h. A similar trend was seen when the two transferases were assayed with lactose as acceptor. The antiserum to rat alpha 2----6 ST inhibited the sialyltransferase activity in serum, liver, and jejunal incubation medium. Jejunal sections from rats treated with colchicine for 4 h in presence of heated serum showed a decrease of sialyltransferase, with consequent increase of the alpha 2----6 ST enzyme activity in the medium. This result suggests that intestinal tissue could be a source of increased serum enzyme activity in colchicine treatment.     

Interaction between calcofluor white and carbohydrates of alpha 1-acid glycoprotein.

Interactions between the fluorescent probe, calcofluor white, and human serum albumin (HSA) and alpha 1-acid glycoprotein (orosomucoid) are compared. The two proteins have comparable isoelectric points, but alpha 1-acid glycoprotein is highly glycosylated (40% of glycans by weight), while the serum albumin is not. Binding of calcofluor to the proteins induces an increase in both the fluorescence anisotropy and the fluorescence intensity of the fluorophore. Also, we found that the calcofluor exhibits a fluorescence emission with a maximum located at 432, 415 or 445 nm, respectively, in the absence of proteins, in the presence of HSA, and in the presence of alpha 1-acid glycoprotein. The stoichiometries of the calcofluor-serum albumin and calcofluor-alpha 1-acid glycoprotein complexes are 2:1 and 1:1, respectively. The association constants are 0.04 and 0.15 microM-1, respectively. The calcofluor does not interact with Lens culinaris agglutinin (LCA), although the protein has a hydrophobic site. Nevertheless, one cannot exclude that the binding of the fluorophore to the HSA is nonspecific. Our results, when compared with those obtained with calcofluor dissolved in the hydrophobic solvent isobutanol, and with the fluorescent probe, potassium 6-(p-toluidino)-2-naphthalenesulfonate (TNS), bound to alpha 1-acid glycoprotein, indicate that the emission of calcofluor bound to HSA occurs from a hydrophobic state, while that of calcofluor bound to alpha 1-acid glycoprotein occurs from a hydrophilic state. The fluorescence intensity of calcofluor decreases in the presence of carbohydrates isolated from alpha 1-acid glycoprotein, while it increases in the presence of alpha 1-cellulose. Thus, calcofluor interacts mainly with the glycan moiety of alpha 1-acid glycoprotein, and its fluorescence is sensitive to the secondary structure of the glycans.     

Interaction between calcofluor white and carbohydrates of alpha 1-acid glycoprotein.

Interactions between the fluorescent probe, calcofluor white, and human serum albumin (HSA) and alpha 1-acid glycoprotein (orosomucoid) are compared. The two proteins have comparable isoelectric points, but alpha 1-acid glycoprotein is highly glycosylated (40% of glycans by weight), while the serum albumin is not. Binding of calcofluor to the proteins induces an increase in both the fluorescence anisotropy and the fluorescence intensity of the fluorophore. Also, we found that the calcofluor exhibits a fluorescence emission with a maximum located at 432, 415 or 445 nm, respectively, in the absence of proteins, in the presence of HSA, and in the presence of alpha 1-acid glycoprotein. The stoichiometries of the calcofluor-serum albumin and calcofluor-alpha 1-acid glycoprotein complexes are 2:1 and 1:1, respectively. The association constants are 0.04 and 0.15 microM-1, respectively. The calcofluor does not interact with Lens culinaris agglutinin (LCA), although the protein has a hydrophobic site. Nevertheless, one cannot exclude that the binding of the fluorophore to the HSA is nonspecific. Our results, when compared with those obtained with calcofluor dissolved in the hydrophobic solvent isobutanol, and with the fluorescent probe, potassium 6-(p-toluidino)-2-naphthalenesulfonate (TNS), bound to alpha 1-acid glycoprotein, indicate that the emission of calcofluor bound to HSA occurs from a hydrophobic state, while that of calcofluor bound to alpha 1-acid glycoprotein occurs from a hydrophilic state. The fluorescence intensity of calcofluor decreases in the presence of carbohydrates isolated from alpha 1-acid glycoprotein, while it increases in the presence of alpha 1-cellulose. Thus, calcofluor interacts mainly with the glycan moiety of alpha 1-acid glycoprotein, and its fluorescence is sensitive to the secondary structure of the glycans.     

The effects of 17 alpha-ethynyloestradiol and of acute inflammation on the plasma concentration of rat alpha 1-acid glycoprotein and on the induction of its hepatic mRNA.

We measured the serum concentration of alpha 1-acid glycoprotein (alpha 1-AGP) and we evaluated the content of its hepatic mRNA in rats after 17 alpha-ethynyloestradiol treatment or after turpentine-induced acute inflammation, or after both treatments performed simultaneously. We have also studied the affinity of serum alpha 1-AGP for concanavalin A under these conditions. Both types of stimuli induce a marked retention of the glycoprotein on free concanavalin A. The serum concentration of alpha 1-AGP is increased about 14-fold compared with that in control rats when a single pharmacological dose (50 micrograms) or multiple injections of 17 alpha-ethynyloestradiol are administered. This increase is greater in turpentine-oil-injected rats (about 21-fold) and reaches a maximum (about 32-fold) in rats injected with 17 alpha-ethynyloestradiol plus turpentine oil; this increase in alpha 1-AGP corresponds to the addition of the effects of the two inducing agents. Similar changes are also observed either in the alpha 1-AGP mRNA content as estimated by using an alpha 1-AGP-specific cDNA probe, or in the amount of translatable alpha 1-AGP mRNA. The results indicate that: after a high dose of 17 alpha-ethynyloestradiol and after acute inflammation, the increase of the alpha 1-AGP serum concentration is due to an accumulation of the alpha 1-AGP mRNA; different mechanisms and/or pathways are probably involved in regulating the synthesis of alpha 1-AGP under various stimuli; 17 alpha-ethynyloestradiol as well as acute inflammation seem to control the glycosylation process of alpha 1-AGP in an identical manner.     

Protein glycosylation regulates the externalization of two distinct classes of glucocorticoid-induced glycoproteins in rat hepatoma cells

The relationship of protein glycosylation to the externalization of glucocorticoid inducible alpha1-acid glycoprotein and mouse mammary tumor virus glycoproteins was examined in M1.54, a clonal population of mouse mammary tumor virus-infected rat hepatoma cells. Multiple freeze-thaw of isolated microsomes revealed that while alpha 1-acid glycoprotein is carried through the cell as a soluble component of vesicles, extracellular viral glycoproteins are initially membrane-associated. At concentrations of tunicamycin that specifically inhibited N-linked protein glycosylation, alpha 1-acid glycoprotein fractionated between the cellular and extracellular compartments. Thus, approximately one half of the newly synthesized, nonglycosylated (22,000 Mr) alpha 1-acid glycoprotein was rapidly secreted with kinetics similar to its glycosylated counterpart (release half-time of 60 min), while the remaining species first localized in an undefined intracellular compartment prior to its slow secretion (release half-time of 24 h). The same distribution of nonglycosylated alpha 1-acid glycoprotein was observed at various absolute levels of polypeptide, suggesting that this was not due simply to the saturation of an efficient secretory pathway at high polypeptide levels. In contrast to alpha 1-acid glycoprotein, no labeled viral antigens were released by tunicamycin-treated M1.54, while a nonglycosylated viral precursor glycopolyprotein was expressed intracellularly. Taken together, these results suggest that carbohydrate attachment strongly regulates the externalization of both alpha 1-acid glycoprotein and mouse mammary tumor virus species, which represent two distinct classes of extracellular glycoproteins.     

Immunohistochemical localization of alpha1-acid-glycoprotein in human liver parenchymal cells.

alpha1-Acid glycoprotein, a major human serum glycoprotein was detected and localized in human liver parenchymal cells of a biopsy specimen. A heavy metal salt containing fixative was required to retain sufficient antigen determinants of alpha1-acid glycoprotein in order to visualize this protein by the peroxidase-anti-peroxidase unlabeled antibody enzyme method.     

Tertiary structure of human alpha1-acid glycoprotein (orosomucoid). Straightforward fluorescence experiments revealing the presence of a binding pocket

Binding of hemin to alpha1-acid glycoprotein has been investigated. Hemin binds to the hydrophobic pocket of hemoproteins. The fluorescent probe 2-(p-toluidino)-6-naphthalenesulfonate (TNS) binds to a hydrophobic domain in alpha1-acid glycoprotein with a dissociation constant equal to 60 microM. Addition of hemin to an alpha1-acid glycoprotein-TNS complex induces the displacement of TNS from its binding site. At saturation (1 hemin for 1 protein) all the TNS has been displaced from its binding site. The dissociation constant of hemin-alpha1-acid glycoprotein was found equal to 2 microM. Thus, TNS and hemin bind to the same hydrophobic site: the pocket of alpha1-acid glycoprotein. Energy-transfer studies performed between the Trp residues of alpha1-acid glycoprotein and hemin indicated that efficiency (E) of Trp fluorescence quenching was equal to 80% and the F?rster distance, R0 at which the efficiency of energy transfer is 50% was calculated to be 26 A, revealing a very high energy transfer.     

Acute phase protein alpha 1-acid glycoprotein interacts with plasminogen activator inhibitor type 1 and stabilizes its inhibitory activity.

alpha(1)-Acid glycoprotein, one of the major acute phase proteins, was found to interact with plasminogen activator inhibitor type 1 (PAI-1) and to stabilize its inhibitory activity toward plasminogen activators. This conclusion is based on the following observations: (a) alpha(1)-acid glycoprotein was identified to bind PAI-1 by a yeast two-hybrid system. Three of 10 positive clones identified by this method to interact with PAI-1 contained almost the entire sequence of alpha(1)-acid glycoprotein; (b) this protein formed complexes with PAI-1 that could be immunoprecipitated from both the incubation mixtures and blood plasma by specific antibodies to either PAI-1 or alpha(1)-acid glycoprotein. Such complexes could be also detected by a solid phase binding assay; and (c) the real-time bimolecular interactions monitored by surface plasmon resonance indicated that the complex of alpha(1)-acid glycoprotein with PAI-1 is less stable than that formed by vitronectin with PAI-1, but in both cases, the apparent K(D) values were in the range of strong interactions (4.51 + 1.33 and 0.58 + 0.07 nm, respectively). The on rate for binding of PAI-1 to alpha(1)-glycoprotein or vitronectin differed by 2-fold, indicating much faster complex formation by vitronectin than by alpha(1)-acid glycoprotein. On the other hand, dissociation of PAI-1 bound to vitronectin was much slower than that from the alpha(1)-acid glycoprotein, as indicated by 4-fold lower k(off) values. Furthermore, the PAI-1 activity toward urokinase-type plasminogen activator and tissue-type plasminogen activator was significantly prolonged in the presence of alpha(1)-acid glycoprotein. These observations suggest that the complex of PAI-1 with alpha(1)-acid glycoprotein can play a role as an alternative reservoir of the physiologically active form of the inhibitor, particularly during inflammation or other acute phase reactions.     

Studies on incorporation of mannose into rat alpha 1-acid glycoprotein: evidence for precursor forms in rough membranes

Rats were given pulse injections of D-[14C]mannose and were killed at various times up to 60 min after injection. Rough, smooth, and Golgi fractions were prepared from liver, and alpha 1-acid glycoprotein was isolated from Lubrol extracts of the fractions. The kinetics of incorporation of D-[14C]mannose into total protein, Lubrol protein, and alpha 1-acid glycoprotein showed that proteins associated with rough fractions had particularly high specific radioactivities at early times of incorporation. One explanation for the kinetic data is that glycoproteins contain a high mannose content at early times of assembly of oligosaccharide chains. This idea was confirmed in the case of alpha 1-acid glycoprotein by isolation of a high mannose containing precursor species of alpha 1-acid glycoprotein from rough fractions of liver. This species contained 56 residues of hexose (mainly mannose) compared with 35 residues of hexose (roughly equal amounts of mannose and galactose) which are found in the native protein. It is proposed that the high mannose precursor is a form of alpha 1-acid glycoprotein that exists at an early stage in assembly of the glycoprotein and which contains largely unprocessed carbohydrate chains. In addition, evidence is presented from amino acid analyses and gel electrophoresis of the high mannose precursor and another fraction from which it is formed by limited tryptic treatment, that pro-forms of alpha 1-acid glycoprotein with extensions of the polypeptide chain may also exist.     

alpha3-galactosylated glycoproteins can bind to the hepatic asialoglycoprotein receptor.

In mammals, clearance of desialylated serum glycoproteins to the liver is mediated by a galactose-specific hepatic lectin, the 'asialoglycoprotein receptor'. In humans, serum glycoprotein glycans are usually capped with sialic acid, which protects these proteins against hepatic uptake. However, in most other species, an additional noncharged terminal element with the structure Galalpha1-->3Galbeta1-->4R is present on glycoprotein glycans. To investigate if alpha3-galactosylated glycoproteins, just like desialylated glycoproteins, could be cleared by the hepatic lectin, the affinities of alpha3-galactosylated compounds towards this lectin were determined using an in vitro inhibition assay, and were compared with those of the parent compounds terminating in Galbeta1-->4R. Diantennary, triantennary and tetraantennary oligosaccharides that form part of N-glycans were alpha3-galactosylated to completion by use of recombinant bovine alpha3-galactosyltransferase. Similarly, desialylated alpha1-acid glycoprotein (orosomucoid) was alpha3-galactosylated in vitro. The alpha3-galactosylation of a branched, Galbeta1-->4-terminated oligosaccharide lowered its affinity for the membrane-bound lectin on whole rat hepatocytes 50-250-fold, and for the detergent-solubilized hepatic lectin 7-50-fold. In contrast, alpha3-galactosylation of asialo-alpha1-acid glycoprotein caused only a minor decrease in affinity, increasing the IC50 from 5 to 15 nM. Fully alpha3-galactosylated alpha1-acid glycoprotein, intravenously injected into the mouse, was rapidly cleared from the circulation, with a clearance rate close to that of asialo-alpha1-acid glycoprotein (t1/2 of 0.42 min vs. 0.95 min). Its uptake was efficiently inhibited by pre-injection of an excess asialo-fetuin. Organ distribution analysis showed that the injected alpha1-acid glycoprotein accumulated predominantly in the liver. Taken together, these observations suggest that serum glycoproteins that are heavily alpha3-galactosylated will be rapidly cleared from the bloodstream via the hepatic lectin. It is suggested that glycosyltransferase expression in murine hepatocytes is tightly regulated in order to prevent undesired uptake of hepatocyte-derived, circulating glycoproteins.     

Concentrations of major plasma proteins in serum and whole-tissue extracts of porcine fetuses during development.

In extracts from fetuses up to 32 days of gestation, the major serum proteins were fetuin, alpha-fetoprotein and alpha 1-antitrypsin, but albumin was not detected. The concentration of all proteins rose with age until 40-50 days of gestation; and then the serum concentration of alpha-fetoprotein (2.9 mg ml-1), alpha 1-antitrypsin (4.4 mg ml-1) and transferrin (2.6 mg ml-1) fell progressively to about 1 mg ml-1 at birth, whereas those of fetuin, albumin and alpha 1-acid glycoprotein increased. The patterns of serum proteins in fetuses at about the middle of gestation were similar in extracts and sera. At birth, the major proteins were alpha 1-acid glycoprotein and fetuin, which accounted for 45 and 18% of serum proteins, respectively. Albumin represented only 7% of serum proteins at this age. For most of the second gestational period, the six quantified proteins accounted for about 85% of total serum proteins. In early gestation, a significant proportion of serum proteins was intracellular.     

Identification of a breast tumor-associated orosomucoid by concanavalin A affinity chromatography.

Con A-Sepharose affinity chromatography was utilized to examine the glycoproteins in phosphosaline extracts of normal and breast tumor tissues and breast patient sera. In extracts of normal breast tissue, normal sera and patient sera, all glycoproteins were eluted from the Con A-Sepharose with a linear gradient of 0.0-0.5 M alpha-methylmannose. Using breast tumor extracts, a glycoprotein peak which could not be eluted as with normal tissue extracts was observed. This tightly-binding peak could be eluted from the Con A-Sepharose with acetate buffer containing 1.0 M KCl. Polyacrylamide electrophoresis of this tightly-binding glycoprotein peak revealed one major glycoprotein and four minor glycoproteins. The major glycoprotein obtained from electrophoresis represented about 60% of the Con A-Sepharose tightly-binding protein and reacted with antiserum to human orosomucoid (alpha 1-acid glycoprotein). All glycoproteins isolated from tumor tissue extracts appeared to represent normal serum constituents as they were retained on an immunoadsorbent containing antibodies to normal serum proteins. The possible significance of the isolated tumor-associated orosomucoid is discussed.     

Induction of alpha 1-acid glycoprotein by recombinant human interleukin-1 in rat hepatoma cells

The induction of alpha 1-acid glycoprotein mRNA by recombinant murine interleukin-1, recombinant human interleukin-1 alpha, and recombinant human interleukin-1 beta has been studied in the rat hepatoma cell line Fao. Whereas the stimulatory capacities of recombinant human interleukin-1 alpha and recombinant murine interleukin-1 were almost identical, the concentrations of recombinant human interleukin-1 beta needed for half-maximal induction of alpha 1-acid glycoprotein mRNA were lower by three orders of magnitude. A 60-fold increase in alpha 1-acid glycoprotein mRNA levels was observed 18 h after the addition of recombinant interleukin-1 beta. In parallel albumin mRNA levels decreased to about 30%. The alpha 1-acid glycoprotein mRNA induction was strictly dependent on the presence of dexamethasone. For a full stimulation dexamethasone concentrations of greater than 10(-7) M were needed, whereas concentrations of less than 10(-12) M were ineffective. The increase in alpha 1-acid glycoprotein mRNA after recombinant human interleukin-1 beta was followed by a 36-fold stimulation in alpha 1-acid glycoprotein synthesis and secretion. When protein synthesis was blocked by either cycloheximide, puromycin, or emetine, the induction of alpha 1-acid glycoprotein mRNA by recombinant human interleukin-1 beta was impaired suggesting the involvement of a short-lived protein in the induction of alpha 1-acid glycoprotein mRNA.     

Binding of norgestrel to human plasma proteins.

Binding of [14, 15-3H](+/-)-norgestrel to human plasma proteins has been investigated. Norgestrel showed greater affinity to plasma than to human serum albumin indicating specific norgestrel binding protein(s) in the plasma. alpha1-acid glycoprotein showed high affinity for norgestrel when compared with human serum albumin. The binding protein was eluted at pH 5.8 by step by step elution on a DEAE-cellulose column. Norgestrel binding to plasma proteins was not affected at 60 degrees C. The optimal binding occurred between pH 7 and 8. Ligand specificity of the binding protein revealed that progesterone was able to compete for the norgestrel binding sites, whereas corticosterone, testosterone, oestradiol, and norethindrone acetate did not show much competition. The molecular weight of the binding protein was found to be approximately 43 000. Sucrose density gradient analysis indicated that norgestrel bound to a macromolecular component of sedimentation coefficient 2.9 S. The association constant (Kass) and dissociation constant (Kdiss) of norgestrel-binding plasma protein was found to be 1.4-10(6) M-1 and 0.7-10(-6) M respectively. The number of binding sites was 0.5-10(-9) mol/mg protein. Norgestrel-binding protein in the plasma appeared to be a protein different from human serum albumin, corticosteroid-binding globulin and sex-steroid-binding protein. This binding protein showed some similarities to alpha1-acid glycoprotein.     

Steroid-protein interactions. XXXIV. Chemical modification of alpha1-acid glycoprotein for characterization of the progesterone binding site.

The nature of the steroid binding site in alpha1-acid glycoprotein (orosomucoid) was investigated by chemical modification of individual amino acids and subsequent examination of the binding affinity for progesterone. Equilibrium dialyses were performed under conditions that excluded contact with human skin. Reaction of the lysyl residues with trinitrobenzenesulfonic acid or arylisocyanates resulted in a reduction of active sites. In an alternate approach, one lysyl residue of alpha1-acid glycoprotein was protected from modification by trinitrobenzenesulfonic acid when progesterone was present to form the complex with alpha1-acid glycoprotein. We conclude that a lysyl residue is located in the binding site. Reaction of tetranitromethane with the tyrosine groups in alpha1-acid glycoprotein also reduced the number of active binding sites for progesterone. Again, a partial protection of this modification was seen in the presence of progesterone and other delta4-3-ketosteroids. The progesterone binding activity observed in the tyrosine-modified alpha1-acid glycoprotein by equilibrium dialysis and by fluorescence quenching titration can be interpreted best by the presence of one tyrosyl residue in the binding site, and involvement of a second tyrosine nearby. Modification of tryptophan in alpha1-acid glycoprotein by mild acid hydrolysis, N-bromosuccinimide, hydroxynitrobenzylbromide, and formic acid resulted in a decreased steroid binding; the formylation reaction was fully reversible. The approximate distance between progesterone and the tryptophan involved in the binding was calculated to be between 9.1 A and 14.1 A. When alpah1-acid glycoprotein was cleaved by the cyanogen bromide procedure according to Ikenaka et al. (1972, Biochemistry 11, 3817-3829), both the amino and the carboxyl fragment had a weak progesterone binding affinity which could be measured in 4 M NaCl. This result thus failed to specify the location of the steroid binding site in alpha1-acid glycoprotein. However, the closeness of tryptophan, lysine and tyrosine in the primary and presumably the tertiary structure of alpha1-acid glycoprotein is in agreement with the properties of the binding site suggested by our studies.     

Hepatocyte specific long lasting inhibition of protein N-glycosylation by D-galactosamine

The effect of D-galactosamine on protein N-glycosylation was studied in rat hepatocyte primary cultures for alpha 1-antitrypsin (three complex type oligosaccharide chains) and alpha 1-acid glycoprotein (six complex type oligosaccharide chains). D-Galactosamine at a concentration of 4 mM inhibited partially de novo N-glycosylation leading to the formation of alpha 1-antitrypsin lacking one to two and of alpha 1-acid glycoprotein lacking one to five of its carbohydrate side chains. In addition D-galactosamine interfered with oligosaccharide processing, leading to the formation of some carbohydrate side chains remaining in an endoglucosaminidase H sensitive, i.e., not completely processed, form. D-Galactosamine impaired the secretion of alpha 1-antitrypsin and of alpha 1-acid glycoprotein but did not inhibit the secretion of the unglycosylated albumin. The inhibitory effect of D-galactosamine on de novo glycosylation as well as on oligosaccharide processing lasted for at least 24 h after it had been removed from the cells. D-Galactosamine impaired the glycosylation of alpha 1-antitrypsin only in hepatocytes, but not in human monocytes. Furthermore, D-galactosamine did not impair the N- and O-glycosylation of interleukin-6 in human monocytes and in MRC 5 fibroblasts. The results indicate that the effect of D-galactosamine on protein glycosylation is restricted to D-galactosamine metabolizing hepatocytes and is not exerted by the drug itself but by its metabolites.     

Partial hepatectomy and mediators of inflammation decrease the expression of liver alpha 2-HS glycoprotein gene in rats

Liver mRNA levels of two acute phase reactant (APR) proteins, alpha 2-HS glycoprotein (a major negative APR) and alpha 1-acid glycoprotein (a major positive APR) were measured in male rats at different times after the administration of turpentine, of tumor necrosis factor, or following partial hepatectomy. In every case, a marked decrease in mRNA levels of alpha 2-HS glycoprotein was observed which reached a maximum at 24 h. A concomitant increase of alpha 1-acid glycoprotein mRNA levels was observed under the same conditions. These results indicate that the decreased levels of alpha 2-HS glycoprotein induced by the acute-phase response following inflammatory mediators and partial hepatectomy are due to a down-regulation of the gene expression of this protein in rat liver.