Serum binding and biliary excretion of bilirubin after bilirubin loading in Nagase analbuminemic rats and heterozygous (Jj) Gunn rats

To elucidate the effects of albumin on the handling of serum bilirubin, hepatic metabolism and biliary excretion of bilirubin were examined during intravenous bilirubin infusion in Sprague-Dawley (SD) rats, Gunn (heterozygous, Jj) rats, and Nagase analbuminemic rats (NARs). Serum bilirubin was primarily bound to a protein fraction with a molecular weight of about 600 x 10(3) or more in NARs. About 39.2% +/- 12.5% of the serum bilirubin during infusion of bilirubin was bound to the same fraction in Gunn rats. Bilirubin was substantially taken up into the liver and excreted into the bile in NARs, suggesting the role of a high molecular protein, probably a lipoprotein, in its blood transport and the hepatic uptake process. In NARs, biliary bilirubin secretion reached the peak between 20 and 40 minutes after the initiation of bilirubin loading and decreased thereafter, whereas it continued to increase in SD rats and in NARs to which albumin was administered 20 minutes after the start of bilirubin loading. Biliary bilirubin fractions before bilirubin loading were similar in SD rats and NARs, whereas an increase in bilirubin monoglucuronide (BMG) and a decrease in bilirubin diglucuronide (BDG) were observed in Gunn rats. After the initiation of bilirubin loading, a decrease in biliary BDG and an increase in BMG and unconjugated bilirubin were observed in all groups of rats.

Serum bilirubin fractions in analbuminemic rats after bile duct ligation. Albumin requirement in the formation of covalently protein-bound bilirubin

To clarify the role of albumin in the production of covalently protein-bound bilirubin (delta bilirubin, B delta) in the blood and the pathophysiological relevance of B delta, changes in the serum bilirubin level and histological findings in the liver, kidneys and myocardium were studied in Sprague-Dawley (SD) rats and Nagase analbuminemic rats (NAR) after bile duct ligation (BDL). In SD rats, the serum bilirubin level increased until 3 days after BDL, and was followed by the appearance of B delta. The increase in serum bilirubin was smaller in NAR, and no serum B delta was noted. Albumin administration to NAR 1 day after BDL increased serum bilirubin with the appearance of B delta. Serum bilirubin decreased in both SD rats and NAR 7 days after BDL. Marked deposition of bile pigments was noted in NAR in the renal tubular epithelium. The renal bilirubin content was decreased after albumin administration. From these results it is concluded that albumin is necessary for the production of B delta, and that renal deposition of bile pigments progresses in the absence of albumin.

High susceptibility of an analbuminemic congenic strain of rats with an F344 genetic background to induced bladder cancer and its possible mechanism

The susceptibility of an analbuminemic congenic strain of rats (F344-alb) originating from the F344 strain to N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) was examined. F344-alb rats were found to be highly susceptible to induction of urinary bladder cancers. The incidences of bladder cancers in F344-alb and F344 rats were 94% (15/16) and 31% (5/16) in males and 100% (16/16) and 19% (3/16) in females. The bladder weights of these rats, including tumors, were 307 +/- 294 mg, 123 +/- 26 mg, 183 +/- 80 mg and 93 +/- 11 mg, respectively. Administration of 0.05%, 0.1% and 0.3% BBN in the drinking water for 2 weeks resulted in greater increases in the bladder content of N-butyl-N-(3-carboxypropyl)nitrosamine in F344-alb rats than in F344 rats. This increase was prevented by the presence of rat albumin.

Albumin-negative hepatocytes in Sprague-Dawley x analbuminemic F1 rats treated with hepatic carcinogens

Analbuminemic rats (NAR) are a mutant breed with an inherent inability to synthesize albumin. However, heterozygous rats born of a pair of NAR and Sprague-Dawley (SD) rats can synthesize albumin. Immunohistochemical staining for albumin shows that, although the majority of hepatocytes of SD x NAR F1 (female SD x male NAR) rats are positive for albumin, a small number of hepatocytes are negative. These albumin-negative hepatocytes are frequently found in the form of clusters which appear cytologically normal. When the rats were given a dietary regimen of 2-acetyl-aminofluorene (2-AAF), there was a significant increase in the number of albumin-negative hepatocytes. On the other hand, diethylnitrosamine (DEN) or 5-azacytidine did not increase the number of albumin-negative hepatocytes. 2-AAF and DEN also induced enzyme-altered hepatocytes but the albumin-negative hepatocytes were of a completely different class from the enzyme-altered hepatocytes. The results of this study indicate that some kind(s) of carcinogens induce mutated hepatocytes which are probably not involved in carcinogenesis.

Protein-mediated hepatic uptake of rose bengal in analbuminemic mutant rats (NAR). Albumin is not indispensable to the protein-mediated transport of rose bengal

Recent kinetic studies using in situ perfused rat liver suggested that the hepatic uptake of extensively albumin-bound ligands is mediated primarily by direct interaction of the albumin-ligand complex with the hepatocyte surface rather than by the small unbound fraction of ligand, as has been generally believed [Ockner et al., Am. J. Physiol. 245, G13 (1983)]. In order to investigate this mechanism in vivo, rose bengal (RB) was injected iv to the normal and Nagase analbuminemic mutant rats (NAR) and both the pharmacokinetic parameters and the serum protein binding parameters for the two groups were compared. The serum disappearance curves of RB in normal rats and NAR were almost superimposed, and no significant difference in various pharmacokinetic parameters including the hepatic uptake clearance (k12V1) was observed between the two groups. Nevertheless, the unbound fractions of RB in serum were approximately 4-fold (equilibrium dialysis method) and 10-fold (spectrophotometric method) higher than those in normal rats. However, in both groups of rats RB is extensively bound to plasma proteins and more than 99.8% of RB in the plasma exists as the protein-bound form. The intrinsic ability of the two groups of rats to take up unbound RB was compared using isolated liver cells. No significant difference between the two groups was observed in the initial velocity of uptake. From these findings, we concluded that the hepatic uptake of RB is primarily driven by the serum protein-bound form and not by the unbound form and that the serum protein-mediated uptake mechanism of RB was not specific only for serum albumin but also for other serum proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Strain differences in N-butyl-N-(4-hydroxybutyl)nitrosamine bladder carcinogenesis in rats

Differences in susceptibility of the urinary bladder epithelium to N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) in various strains were examined. In experiment 1, 5 strains of male rats were given 0.025% BBN in the drinking water for 8 weeks followed by drinking water without BBN for 32 weeks. Analbuminemic rats (NAR) and ACI rats had high incidences of urinary bladder lesions (papillary or nodular hyperplasia, papilloma and carcinoma), F344 and Wistar rats had low incidences, and Sprague-Dawley (SD) rats showed an intermediate incidence. Carcinoma area was largest in NAR rats followed in decreasing order by SD, ACI and F344 rats. The extent of tumor invasion was higher in NAR and ACI rats than in SD rats. In experiment 2, the 5 strains of male rats were administered 0.025% BBN in the drinking water. Some rats from each group were killed after each of weeks 4 and 8. The urinary bladder of ACI and NAR rats given BBN had the most marked lesions observed by scanning electron microscopy, with less marked changes in SD rats. F344 and Wistar rats showed the weakest response. Cytochrome P-450 content of the liver in ACI rats treated with BBN for 4 weeks was significantly higher than those of controls. Cytochrome P-450 and cytochrome b5 contents of the control and BBN-treated rats were significantly higher in ACI and SD rats than in Wistar, F344 or NAR rats. These results indicate that there are strain differences in the urinary bladder response to BBN.

Lack of albumin as genotypic marker of preneoplastic analbuminemic rat hepatocytes transplanted within albumin-positive liver

In analbuminemic rats, preneoplastic hepatocytes lack the capability to produce albumin. On the other hand, the hepatocytes of F1 hybrids born from parents of analbuminemic rats and normal rats retain their capability to produce albumin, since the analbuminemia is inherited as a recessive trait in rats. We isolated hyperplastic nodule cells from Nagase's analbuminemic rats and transplanted them into the livers of F1 hybrid rats by infusion into the mesenteric vein. The host rats were subjected to a short term dietary 2-acetylaminofluorene and underwent a two-thirds partial hepatectomy to promote the growth of preneoplastic hepatocytes. Within 10 to 13 days after transplantation, may albumin-negative hepatocytic nodules were formed in the albumin-positive host livers. Almost all the albumin-negative nodules expressed conventional biochemical markers for preneoplastic hepatocytes. Eight to 9 weeks after the transplantation, almost the same number of albumin-negative nodules were observed as on days 10-13. However, roughly a half of the albumin-negative nodules showed no biochemical markers. The results indicate that the majority of early preneoplastic lesions revert to become phenotypically normal after removal of the promoting stimuli.

Alterations in the glomerulus in aminonucleoside nephrosis in analbuminemic rats

Whether obliteration of glomerular epithelial foot processes and increases in urinary N-acetyl-beta-D-glucosaminidase (NAG) activity are the consequence or the cause of proteinuria after administrations of the aminonucleoside of puromycin was examined using Nagase analbuminemic rats. The administration of puromycin aminonucleoside to Nagase analbuminemic rats did not induce proteinuria. However, the increase in urinary NAG activity and the degree of abnormality of foot processes in the glomerular cells were similar to those in control Sprague-Dawley rats. These findings suggest that NAG excretion and the morphological alterations of epithelial cells in nephrosis are not the consequence of massive proteinuria.

A new radioimmunoassay of free thyroxine using 125I-labelled thyroxine-protein complex uninfluenced by albumin and thyroxine-binding globulin

We describe a double-antibody solid phase radioimmunoassay for free thyroxine (FT4) in serum with use of 125I-labelled thyroxine-human chorionic gonadotropin conjugate. Since the labelled conjugate does not bind to thyroxine binding globulin (TBG) and albumin because of its large molecular weight, the method is uninfluenced by TBG or albumin. The measurable range of FT4 in serum was 2.0 to 128 ng/l. The mean coefficients of variation within and between assays were 4.6-8.6% and 6.3-11.6%, respectively. The FT4 values determined by the proposed method correlated well with those determined by commercial radioimmunoassay in subjects with normal albumin concentration (r = 0.98). The FT4 concentrations in serum as determined by this method were 9 to 17 ng/l for healthy adult subjects; high for patients with hyperthyroidism; low for patients with hypothyroidism; and within normal limits for pregnant women, and patients with high or low concentrations of thyroxine-binding globulin.

A high level of transferrin mRNA in the liver of analbuminemic rats

By means of immunological screening, a cDNA clone bearing the mRNA sequence for rat transferrin was isolated from a cDNA library of rat liver mRNA. The amounts of transferrin mRNA in livers of analbuminemic rats (NAR, Nagase analbuminemia rats) and normal rats were determined by RNA blot hybridization using a cloned transferrin cDNA probe. The level of transferrin mRNA in the NAR liver was about 1.7 times that in the normal rat liver. These findings suggest that the enhanced synthesis of transferrin in the NAR liver resulted from an increase in the transferrin mRNA level.

Establishment and characteristics of five analbuminemic inbred strains of rats

Five analbuminemic inbred strains of rats (AD/1, AD/2, AD/3, AD/4, AD/5) were established from Nagase analbuminemic rats (NAR). They showed no genetic differences in coat color, biochemical marker gene loci and skin grafting test. Their serum levels of total cholesterol, phospholipids, triglycerides, and beta-lipoproteins were compared with normal inbred strains (L) derived from Sprague-Dawley rats. Their plasma apoproteins were also examined. All inbred strains of analbuminemic rats showed hyperlipidemia progressing with age although there were slight variations in their lipid and apoprotein levels. These analbuminemic inbred strains of rats may be multigenic models of lipid metabolism abnormality.

Mechanism of furosemide resistance in analbuminemic rats and hypoalbuminemic patients

To elucidate the mechanism of resistance of hypoalbuminemic patients to furosemide, the effect of this diuretic on urine volume of normal and analbuminemic rats (NAR) and of hypoalbuminemic patients was studied. Intravenous administration of furosemide rapidly enhanced sodium diuresis in normal rats but not in NAR. Total plasma clearance and distribution volume of furosemide were much larger in NAR than in normal rats, while no significant difference in these pharmacokinetic parameters was observed for the unbound fraction of the diuretic between the two animal groups. In contrast, urinary secretion of furosemide was significantly lower in NAR than in normal rats. Injected furosemide bound to albumin markedly promoted diuresis in NAR, while the same dose of albumin alone had no effect, indicating that binding to albumin is essential for the delivery of furosemide to the kidney, the site for its action. Injection of the complex rapidly increased the urine volume of hypoalbuminemic patients who showed a marked resistance to this diuretic. Thus, the resistance to furosemide in both NAR and hypoalbuminemic patients may be explained on the same basis.

Inter-organ metabolism and transport of a cysteine-S-conjugate of xenobiotics in normal and mutant analbuminemic rats

Biosynthesis of N-acetylcysteine S-conjugates of toxic electrophiles, mercapturic acids, occurs via inter-organ metabolism and transport in which liver, small intestine and kidney play an important role. Since a mercapturic acid is a hydrophobic organic anion and strongly binds to plasma albumin in vitro, the ligand-albumin interaction may affect the metabolic fate of this final metabolite in vivo. To investigate the role of the circulating albumin in detoxication and elimination of a toxic electrophile, urinary occurrence of the final metabolite was determined in normal and mutant Nagase analbuminemic rats (NAR) after administration of S-benzylcysteine, a model compound of cysteine conjugates. S-Benzylcysteine intravenously administered was excreted rapidly into urine as its N-acetyl derivative in both animal groups. However, the urinary recovery of this mercapturic acid was significantly lower in NAR than in normal animals. The lower urinary recovery in NAR was due to a rapid and random distribution of the unbound metabolite in the circulation to extrarenal tissues. In contrast, no significant difference in the urinary recovery of the final metabolite was observed between the two animal groups if S-benzylcysteine was given orally. Kinetic analysis revealed that the major part of the orally administered S-benzylcysteine was transferred to the liver and acetylated predominantly in this organ in both animal groups; the mercapturic acid which was synthesized in the liver can be transferred to the kidney and excreted into urine even in the absence of the circulating albumin. These results indicate that albumin is important for a final elimination of a mercapturic acid when animals were extraorally challenged with a large dose of toxic electrophiles by which the rate of biosynthesis and the plasma level of the amphipathic metabolites were increased.

Conversion of androstenedione to 3 beta-hydroxy-5-androsten-17-one and 3 beta-hydroxy-4-androsten-17-one by the testicular microsomal fraction of Sprague-Dawley rats

When androstenedione was incubated with testicular microsomes of Sprague-Dawley rats in the presence of reduced nicotinamide-adenine dinucleotide (NADH), unknown metabolites were produced, in addition to testosterone and 7 alpha-hydroxyandrostenedione. The metabolites were identified as 3 beta-hydroxy-4-androsten-17-one and 3 beta-hydroxy-5-androsten-17-one (3:1) by biochemical and radiochemical methods. These results confirmed the occurrence of the reverse reactions from androstenedione to 3 beta-hydroxy-4-androsten-17-one and 3 beta-hydroxy-5-androsten-17-one catalyzed by the 3 beta-hydroxysteroid dehydrogenase and 5-ene-4-ene isomerase in the microsomal fraction of Sprague-Dawley rat testes.

A long-term cortical blindness after head trauma

Here is a case of long-term cortical blindness after a head trauma. Its etiology is ascribed to the cerebral vascular occlusion caused by the head trauma. From the findings of both a computerized tomography (CT) and magnetic resonance image (MRI), the lesions of our case are assumed to be in the bilateral areas 17 (Brodmann), some part of the bilateral areas 18, 19 (Brodmann) and bilateral optic radiations. On determination of the areas of these lesions, the location of the lesion in the bilateral areas 17 has been especially done by using the MRI. The MRI findings in our case have a full significance on this point.

[Research related to hormones in Nagase analbuminemic rats]

The levels of hormones in the anterior pituitary gland and serum in Nagase analbuminemic rats (NAR) were examined. For the anterior pituitary gland, the contents of prolactin, TSH, GH, LH and FSH in male NAR were lower than those of normal rats. In female NAR, prolactin and TSH levels were also lower than those in normal rats, whereas LH, FSH and GH were unchanged. In serum, the concentrations of TSH, T3, T4, estradiol, testosterone and prolactin (female only) were examined. The serum prolactin level in female NAR was lower than that of normal rats, whereas a higher level of serum TSH was seen in NAR. Male NAR had a higher T3 level and a lower T4 level. Although the estradiol concentration in male NAR was normal, the serum testosterone level was only a quarter of that in normal rats. We investigated the reason for the low level of serum testosterone in male NAR through biochemical studies on steroid metabolism. The results indicated that the low serum concentration of testosterone in NAR was mainly attributable to decreased biosynthesis of testosterone in the testes. Prolactin is the primary hormone for experimental mammary tumorigenesis. In association with the lower prolactin level in female NAR, induction of tumors by 7, 12-dimethylbenz (a) anthracene (DMBA) was studied. NAR showed a significantly lower mammary tumor response to DMBA. The incidences of spontaneous mammary tumor in NAR and normal rats after 2 years were also compared. The incidence was much lower in NAR than in the controls. Thus the lower mammary tumor induction in NAR could mostly be ascribed to the lower level of circulating prolactin.

Transplantation of putative preneoplastic hepatocytes of analbuminemic rats in the livers of Sprague-Dawley x analbuminemic hybrid rats

As the analbuminemia of analbuminemic rats (NAR) is inherited as a recessive trait, the livers of F1 hybrids of Sprague-Dawley X NAR (SD X NAR) retain the capability to produce albumin. We induced albumin-negative hyperplastic nodules in the livers of NAR, isolated the nodule cells and transplanted them in the livers of SD X NAR by infusion into the mesenteric vein. When the hosts were treated with dietary 2-acetylaminofluorene plus a partial hepatectomy, numerous albumin(-) nodules of donor origin were formed within the albumin(+) livers of the hosts. This system should be useful to analyze sequential events during hepatocarcinogenesis by using a genotypic marker.