Albumin synthesis by liver parenchymal cells isolated from young, adult and old rats

Comparison of α2-macroglobulin synthesis by juvenile vs. mature rats after identical inflammatory stimulation

Synthesis of α2-macoglobulin (α2M) by 3-week-old juvenile rats was compared to that of mature 7- and 11-week-old rats. Serum concentrations of α2M, interleukin (IL)-6- and cytokine-induced neutrophil chemoattractant (CINC)-1 were measured by enzyme-linked immunosorbent assay. The area under the concentration vs. time curve (AUC) for α2M was significantly different among the three groups. The synthesis of α2M increased in an age-dependent manner. No significant difference was observed for the AUC of IL-6, but that of CINC-1 in 3-week-old rats was significantly lower than that in 7- or 11-week-old rats. These results suggest that synthesis of α2M was increased in mature compared to juvenile rats, possibly due to differences in liver function. The maximum concentration of CINC-1 in 3-week-old rats was observed 6 h after turpentine oil injection. The serum concentrations of IL-6 and CINC-1 increased more quickly in juvenile rats than in mature rats after inflammatory stimulation.

The role of albumin in human physiology and pathophysiology, Part III: Albumin and disease states

The serum albumin level is one of several clinical parameters of the status of general health. There is a marked correlation between low albumin levels and the incidence of morbidity and mortality in hospitalized patients. Therefore, it is not surprising to find that hypoalbuminemia is a common finding among hospitalized patients. This results from alterations in the catabolic or anabolic rates, losses of albumin, or redistribution between the various fluid compartments of the body. Somewhat less well defined than the role of albumin as a prognostic indicator is its role in compounding pathophysiology. Hypoalbuminemia is known to be associated with delayed wound healing. The hypoalbuminemic state interferes with the normal functioning of the gastrointestinal tract. Qualitative changes in the albumin molecule which occur in renal disease may damage the nephron. Low serum albumin levels may adversely affect the coagulation system. Further investigation into the role of albumin in pathophysiology is warranted.

Hepatocyte fine structure during maturation and senescence

Aging is accompanied by a myriad of changes in cell structure, function, and composition. The fact that much of the information concerning age-related alterations in cellular morphology is qualitative precludes meaningful correlations with biochemical changes in order to enhance data interpretation. The mammalian liver has been subjected to both qualitative and quantitative evaluations of hepatocyte structure as a function of aging, i.e., development, maturation, and senescence. Although these data are characterized by considerable variability and, in some instances, blatant contradictions, there exists sufficient agreement in several parameters to permit a consensus in the inbred rat model. Certainly the volume of individual hepatocytes increases with age, and many of the organelle compartments reflect this change. While old rats exhibit a high incidence of polyploidy, there is no definitive evidence to demonstrate a concomitant increase in the binuclear hepatocyte index. Several specific hepatocellular organelles undergo changes in their relative volume or surface area that appear to correlate with functional alterations. The volume density of the lysosomal compartment enlarges significantly during senescence and is accompanied by increased activities of several constituent hydrolases. The hepatic concentration of smooth-surfaced endoplasmic reticulum declines markedly with aging, as does the yield of liver microsomes and the activities of several microsomal enzymes, e.g., mono-oxygenases and glucose-6-phosphatase. However, the responses of the majority of hepatocyte organelles to aging is varied and inconsistent based on the limited data currently available.

Analysis of effect of age on synthesis of specific proteins by hepatocytes

The effect of age on the synthesis of specific proteins by hepatocytes was studied in Fischer F344 rats using two-dimensional polyacrylamide gel electrophoresis. Almost all proteins synthesized by hepatocytes from young rats were synthesized by hepatocytes isolated from old rats. Of over 500 proteins visually compared by two-dimensional polyacrylamide gel electrophoresis, only 11 proteins were observed to disappear and/or appear consistently with increasing age. The rates of synthesis of 36 randomly chosen proteins were quantified. Interestingly, the synthesis of 35 of the 36 proteins decreased between 5 and 30 months of age. The decrease in protein synthesis varied (15% to 70%) from one protein to another; i.e., a heterogeneity was observed in the age-related decrease in the synthesis of proteins. The age-related decrease in protein synthesis was statistically significant for 53% of the proteins studied. The total decrease in the rate of synthesis of all 36 proteins studied was 40% between 5 and 30 months of age, which is essentially the same as the decrease in total protein synthesis by suspension of hepatocytes isolated from 5- and 30-month-old rats. The results of this study demonstrate that the mechanism underlaying aging is different from development, which is characterized by a major change in the species of proteins synthesized by a cell.

Doxorubicin toxicity and pharmacokinetics in old and young rats

Doxorubicin (Dx) toxicity was compared in old (24 months) and young (6 weeks) Crl:CD(SD) BR male rats, and a clear age-related increase was found. The mortality of all animals receiving a single i.v. Dx dose was followed for 270 days. Old rats died after doses of 2.5 mg/kg, while young animals died after doses two times higher, 5 mg/kg. In old rats body weight loss started 10 to 15 days after Dx, compared to 50 to 80 days for young animals. In young and old rats pharmacokinetic and metabolic studies of Dx were conducted in vivo and in the liver perfusion model. Peak levels of Dx and areas under the time/concentration curves (AUC) in serum and in several tissues of old rats were 1.5 to 2 times higher than in young rats. Concentrations of Dx metabolites in serum and tissues (doxorubicinol, Dxol, and doxorubicinone, Dxone) in young and old rats were not noteworthy. However, higher percentages of Dxone than Dxol were found in both groups in vivo and in vitro. Old livers appeared to produce more Dxone as a percentage, particularly in the bile, which was higher. Urinary elimination of Dx markedly slowed with age; only small amounts of the metabolites were eliminated in urine. In vivo and in vitro availability of Dx and its metabolites is discussed in view of their possible role in the greater toxicity observed in 24-month-old rats.

Albumin elimination in female WAG/Rij rats with age: a longitudinal study

A longitudinal study was performed to examine total albumin elimination and urinary albumin excretion in the female WAG/Rij rat. Complete necropsies were performed following the spontaneous death of the animals. The survival characteristics of this group was similar to that of survival cohorts. An increase in total albumin elimination, urinary protein excretion and urinary albumin excretion was observed with age. A proportional increase in the contribution of albumin to the urinary protein excretion was also observed. However, the observed increase in urinary albumin excretion could not totally account for the increase in total albumin elimination. The predominant kidney lesion was chronic progressive nephrosis. The histological severity of the renal lesions were closely correlated with the increase in urinary albumin and total protein loss. It is concluded that the increase in total albumin elimination in rats in this study was due to age-related changes and not to cohort effects.

Serum albumin

The liver manufactures albumin at a massive rate and decreases production in times of environmental, nutritional, toxic and trauma stress. Osmotic pressure is a basic evolutionary regulatory factor, and hormonal control over albumin production has been demonstrated. Where and why new or old albumin is degraded are questions which have not been clarified, although the vascular endothelium may well be the degradative site. Albumin is important as a transport protein, as a measure of evolution and as a model to study secretion following synthesis without the intervening steps of glycosylation. Investigations as to how this protein enters the endoplasmic membrane may well answer some of the questions concerning signal peptide insertion (288). The role of the urea cycle intermediate ornithine and its participation in polyamine synthesis, which has a positive effect on albumin synthesis, is under study. Likewise, the inverse relation between acute-phase protein synthesis and albumin synthesis regulated by interleukin 1 and other cytokines will merit further study. These are a few of the concepts which will be tested in the future.

Molecular aspects of age-related changes in albumin synthesis in female WAG/Rij rats

The rate of albumin gene transcription and the level of albumin RNA sequences in liver nuclei of rats of various ages were determined to investigate the regulation of age-related changes in levels of cytoplasmic albumin mRNA in rat liver. No change was observed with age in both the rate of albumin gene transcription and the amount of nuclear albumin RNA sequences, which suggests that the increase in cytoplasmic albumin mRNA content in the rat liver with age is caused by a decreased turnover of this messenger. The length of poly(A)-tails of rat liver cytoplasmic RNA with age was also examined. Although no change with age was observed in the poly(A)-tail length sedimenting at the peak fraction, a shift towards shorter poly(A)-tails was found with age in the overall poly(A)-tail length distribution.

Aging in the AXC/SSh rat: characterization of moderately abundant ventral prostate proteins showing age-dependent diminution and one protein exhibiting age-invariant content

To determine whether prior demonstrations of age-related decrements in prostate content of minor, androgen regulated proteins represent a generalized phenomenon, we validated a denaturing polyacrylamide gel electrophoretic protocol for separation and quantification of moderately abundant ventral prostate cytoplasmic proteins. We established age-related, progressive 3- to 3.5-fold decreases in prostate content of proteins of 90, 79, 63, and 58 kDa and found that content of a 46 kDa protein was age-invariant. The amount of 90 and 46 kDa proteins was not significantly altered, whereas the level of 79, 63 and 58 kDa proteins decreased during 72 h post-orchiectomy of 3-month-old rats. Testosterone injection of intact 26-month-old rats caused an average 2-fold increase in 90, 79, 63, and 58 kDa protein content and did not affect 46 kDa protein level. Because we demonstrated the 46 kDa protein is not a secretory protein, absence of an affect of aging or testosterone on prostate content is not due to secretion mediated inaccessibility to intracellular processing. The apparent relation between age and prostate content of these proteins is not a consequence of potential age-related changes in ventral prostate cell content or distribution because biochemical and histologic analyses show this does not significantly occur. Our studies establish age-related decreases in ventral prostate content of moderately abundant, androgen responsive proteins and show that content of at least one protein is age- and androgen-independent. It remains to be determined whether these findings reflect direct effects of gene regulation.

Degradation of immunoreactive albumin in young and old conscious female rats

The kinetics of inactivation of plasma albumin was studied in young (3-4 months) and old (25-28 months) Sprague-Dawley female rats. Conscious, free-moving animals carrying indwelling atrial and carotid cannulas received a single injection of [125I]-albumin (rat) via the carotid cannula. Sequential blood samples were removed at intervals during the following 120 min, and total (TR) and immunoprecipitable radioactivity (IPR) were determined in the corresponding plasmas. TR disappearance curves for young and old animals were almost identical but IPR disappearance curves showed a significantly faster decline in the young rats. The absolute plasma volumes for young and old rats were (mean +/- S.E.M.), 10.8 +/- 1.1 and 14.4 +/- 1.5 ml, respectively (P less than 0.05). The IPR/TR ratio, an estimate of albumin inactivation within the plasma space, showed a monoexponential decrease in vivo with a t 1/2 of 11.4 +/- 5.1 and 39.3 +/- 10.8 h (P less than 0.05) for young and old rats, respectively. The in vitro t 1/2s for albumin were 5.25 +/- 1.02 and 3.42 +/- 0.91 days (NS) for young and old rats, respectively. It is concluded that: the rate of albumin catabolism declines with age in the female rat; albumin is mainly inactivated in the extravascular space; and total plasma volume increases significantly with age in this species.

Changes in fluid-phase endocytosis in the rat with age and their relation to total albumin elimination

Rates of fluid-phase endocytosis were determined in several organs and tissues of female WAG/Rij rats of several ages by using 125I-labelled polyvinylpyrrolidone ([125I]-PVP) as a marker. Liver, muscle and skin accounted for a high level of [125I]PVP uptake 28 h after injection. When PVP uptake was expressed per gram of organ/tissue, the liver and spleen were found to be the most active. An age-related increase in [125I]PVP uptake was seen at between 12 and 36 months of age in liver, kidneys and heart. Except for the kidneys this increase is caused by an increase in wet weight of these organs and not by an increase in the specific endocytic rate. These data, together with reported findings on the major sites of albumin catabolism, in liver, kidney, spleen and intestine, indicate that fluid-phase endocytosis is a main mechanism for the observed age-related increase in albumin elimination in these rats.

Direct effect of insulin on albumin gene expression in primary cultures of rat hepatocytes

The purpose of this study was to identify a cell culture system in which the role of insulin in regulating albumin gene expression could be investigated. The system selected was rat hepatocytes maintained in primary culture in a chemically defined, serum-free medium. Under control conditions albumin secretion was nearly the same as the rate recorded in vivo and in perfused liver and was reasonably well maintained during 8 days of culture. Deletion of insulin from the culture medium for 3-6 days resulted in 40-60% reductions in albumin secretion. Furthermore, albumin secretion relative to the rate of total protein synthesis was reduced by approximately 50% as a result of insulin deficiency. Readdition of the hormone to insulin-deficient cultures restored secretion to the control rate. A maximal effect of insulin was observed within 3 days after readdition of the hormone, and a half-maximal response was obtained with a hormone concentration of approximately 3.0 nM. The relative abundance of albumin mRNA, as measured by solution hybridization using a complementary DNA probe, responded in a parallel fashion to the changes in albumin secretion. Thus rat hepatocytes maintained under appropriate culture conditions reflect the effects of diabetes and insulin treatment on albumin gene expression observed in vivo and provide an excellent model system in which to study the mechanism(s) of insulin action.

A comparison of DNA repair synthesis in primary hepatocytes from young and old rats

DNA repair synthesis has been compared in primary hepatocyte cultures obtained from 3-month-old and 16-20-month-old rats. Several morphological and metabolic characteristics were determined to assure cultures of comparable quality. DNA damage was induced by the addition of bleomycin or the exposure of the culture to UV irradiation. DNA repair (unscheduled DNA synthesis) was determined by measuring [3H]thymidine incorporation. After UV irradiation, there was almost twice as much [3H]thymidine incorporation in cells obtained from young rats as in those obtained from old rats. Equal amounts of bleomycin resulted in substantially greater damage to DNA in cells from old rats than from young rats. For equal amounts of DNA damage there was again diminished [3H]thymidine incorporation in cells obtained from old rats. Finally equal amounts of bleomycin resulted in equal damage to DNA when the bleomycin was added to isolated rat liver nuclei from young or old rats. Bleomycin treated nuclei from young rats incorporated substantially more [3H]thymidine triphosphate (TTP) than bleomycin treated nuclei from old rats. The results indicate that hepatocytes from old rats are much more susceptible to bleomycin than hepatocytes from young rats and that the capacity for DNA repair synthesis is impaired in hepatocytes from old rats.

Changes in the sequence content of albumin mRNA and in its translational activity in the rat liver with age

To investigate the regulation of age-related changes in albumin synthesis in the rat liver, total postnuclear RNA and polyribosomes, both membrane-bound and free, were prepared from livers of rats of different ages. By the use of a specific complementary DNA probe, the albumin mRNA sequence content was quantitated in these RNA fractions. These studies showed a specific increase in albumin mRNA sequence content in total postnuclear RNA and membrane-bound polyribosomes at between 12 and 24 months of age. Between 24 and 36 months of age, the increase in the amount of albumin mRNA in these two fractions was due only to an increase in liver weight. The increase in albumin mRNA sequence content was not found in the poly(A)+ fraction but in the RNA extracted from the void of oligo(dT)-cellulose column chromatography. The isolated polyribosomes were translated in a cell-free system to assess age-related changes in total protein and albumin synthesis due to translational control. No changes with age were found in the translational capacity of membrane-bound and free polyribosomes per RNA unit. Immunoprecipitation of the synthesized albumin in the translation products revealed that albumin synthesis in the cell-free system is not increased proportionally with the elevated albumin mRNA level between 12 and 24 months of age. This indicates that albumin mRNAs present in the livers of old rats are biologically less active than those found in younger animals.

Age-related changes in albumin elimination in female WAG/Rij rats

Albumin elimination rates were determined in 3-, 12-, 24- and 36-month-old female WAG/Rij rats. No change in elimination half-life was found with age. However, as there was an increase in the whole-body albumin pool, a concomitant increase in albumin clearance was observed at between 12 and 36 months of age. It was concluded that the increase in clearance between 12 and 24 months of age was only due to a change in the animal's physiology, whereas between 24 and 36 months of age it was also due to changes in the albumin molecule. The age-related changes in albumin clearance were thought not to be caused by changes in the albumin excretion via the urine or via the gastrointestinal tract.

The effect of age on serum proteins in mice

The relation of serum protein levels to age was investigated in the Swiss mouse. The present study demonstrates for the first time a dynamic age-dependent relationship between the various serum proteins. Total serum protein displayed a nonlinear change, decreasing from 10 to 136 days of age and thereafter increasing with advancing age with a peak at 465 days of age. Globulin concentration increased throughout the life span while albumin decreased for the first 136 days, after which it rose and peaked at 465 days of age. The relative percentage of each serum protein undergoes a significant non-constant, non-linear and non-quadratic change with increasing age. The patterns displayed by the various globulin fractions are strikingly similar to each other and tend to be inversely related to the pattern displayed by albumin. The relative percentage of each globulin fraction displayed a biphasic change with a peak at 200 days and a trough at 500 days of age.

The relationship between cell volume, ploidy. and functional activity in differentiating hepatocytes

Liver cells were isolated by collagenase perfusion from rats of 1 day, and 1, 3, 5, and 12 weeks of age, fractionated by velocity sedimentation at 1 g (STAPUT), and the major cell types were identified in terms of specific functions. Alphafetoprotein and albumin were used as markers of differentiating hepatocytes and these functional activities were evaluated in a quantitative manner using a radioimmunoassay. The capacity of this cell type to store 35S-BSP, an indicator of bile formation, was also evaluated. Sinusoidal cells and hematopoietic cells were identified on the basis of their ability to take up 99mTC-colloid sulfur and to incorporate 59Fe, respectively. The fractionation procedure allowed a good separation of sinusoidal cells from hepatocytes at all postnatal ages and also of erythroid cells still present during the first week after birth. With increasing age, alphafetoprotein-producing hepatocytes exhibited changes in sedimentation velocities that parallelled those of albumin-producers. In turn, the latter hepatocyte subpopulation underwent gradual shifts in modal peak velocities similar to those of bile-forming hepatocytes. The fractionated hepatocytes obtained at different ages were further analyzed in terms of cell volume and nuclear ploidy using a Coulter counter system. This quantitative analysis obtained at the cellular level demonstrated that during the age-related differentiation of hepatocytes, which occurs during the postnatal period and results in the gradual appearance of cells of higher ploidy levels, the extent of albumin production and bile formation can be correlated with the hepatocyte volume.

Sex and strain dependency of age-related changes in protein synthesis of isolated rat hepatocytes

In previous studies, a decrease in protein synthesis by hepatocytes isolated from female WAG/Rij rats was observed in the first year of life, while an increase was seen in advanced age. In the present study, no change in protein synthesis in early age was found for hepatocytes isolated from male WAG/Rij and female BN/Bi rats, suggesting that the decline in protein synthesis is sex and strain dependent. In contrast, the increase in protein synthesis in advanced age could be demonstrated with hepatocytes from male WAG/Rij and female BN/Bi rats and therefore seems to be independent of strain and sex. The increase in protein synthesis in advanced age could be attributed to increased excretion of protein in the urine.

Role of microtubuli in the lysosomal degradation of endogenous and exogenous protein in isolated rat hepatocytes

Colchicine and vinblastine, two well known inhibitors of microtubular function, inhibited endogenous protein degradation as well as protein secretion and the degradation of an exogenous, internalized protein (asialo fetuin), in isolated rat hepatocytes. The inhibitors appeared to selectively affect the lysosomal pathway of degradation, since their effects were not additive to that of ammonia, a lysosomotropic degradation inhibitor.

Effect of rat age on serum levels of growth hormone and somatomedins

The somatomedins are a family of hormones which appear to mediate many of the anabolic actions of growth hormone; these processes often exhibit an age-associated deterioration in intact animals. We have demonstrated the validity of a radioreceptor assay for the determination of somatomedin levels in rat serum. In this assay, we measure displacement of 125I-labeled Multiplication Stimulating Activity (MSA) from receptors prepared from human placental membranes. Results with this procedure confirm and extend a previous report from this laboratory indicating a significant decrease in somatomedin levels during the latter part of the lifespan. Data are presented to eliminate possible artifactual explanations for the observed age-related changes. Furthermore, we find that the decrease in somatomedin levels can not be a simple result of an age-related decrease in basal levels of growth hormone in serum. We conclude that the decrease with age in circulating levels of the somatomedins is most probably attributable to a decrease in the activity of responsiveness of the tissues (most probably liver) which secrete somatomedins in response to stimulation by growth hormone.

Albumin synthesis in young and elderly subjects using a new stable isotope methodology: response to level of protein intake

Albumin synthesis was evaluated in 5 young adult males (19-25 yr) and 6 elderly males (64-78 yr) by a procedure involving oral administration of 15N-glycine every 3 hr over a 60-hr period. From about 40 hr onwards, urinary urea achieved a plateau of 15N-enrichment, which was estimated from the average of the last five (low protein) or seven (adequate protein) consecutive three-hourly urinary samples of the 60-hr period. This enrichment plateau was used as an index of the 15N-enrichment of the guanidine N of hepatic free arginine. The 15N-enrichment of the guanidine N of arginine in serum albumin was determined and albumin synthesis was estimated by comparing this value with the estimated enrichment of precursor hepatic arginine. Using this methodology, serum albumin concentration, synthesis, rate and plasma volume were measured when the young and elderly subjects had received an adequate protein intake (1.5 g x kg-1 for 7 days) or a low protein intake (0.4 g x kg-1 for 14 days). Serum albumin concentration was lower in the elderly at both levels of protein intake; protein intake did not affect this parameter in either age-group. Plasma volume (per kg body weight) did not differ between young and old, but increased in both groups when they were given the low-protein diet, so that the total intravascular albumin mass increased in both age groups significantly in the case of the young, and was probably due to net transfer of albumin from the extravascular pool. The fractional synthesis rate of the whole body albumin pool with adequate intake of protein was 4.0%/day in the young and 3.4%/day in the elderly. This fractional rate was reduced significantly by giving the low-protein diet to the young subjects, but was not reduced in the elderly. Absolute synthesis rates, calculated per kg body weight and per kg body cell mass, led to a similar conclusion. Whole body protein synthesis was also estimated from urinary 15N-urea enrichment using the Picou and Taylor-Roberts model. Albumin synthesis as a percentage of whole body protein synthesis (5%-6%) was reduced in the young adults by giving the low-protein diet, but was unchanged in the elderly. In conclusion, the rate of albumin synthesis in the young, but not in the elderly, is sensitive to changes in protein intake. It is suggested that albumin synthesis in the elderly is controlled at a lower set point, which prevents its response to higher protein intakes.

RNA and protein synthesis in cultured human fibroblasts derived from donors of various ages

RNA synthesis in human fibroblasts from donors of various ages was studied in fibroblasts made permeable to nucleoside triphosphates with the nonionic detergent Nonidet P40. Cells from donors of 11 years and older showed a 30-40% decline in total RNA synthesis. The decrease in RNA synthesis was primarily due to a lowering of RNA polymerase II activity (alpha-amanitin sensitive). Studies on the incorporation of leucine into protein also showed a 30-40% decrease in cells from older donors.

Production of apolipoproteins E and A-I by rat hepatocytes in primary culture

Hepatocytes were isolated from normal adult rat livers and cultured in a modified HI-WO/BA medium. A nearly confluent monolayer was established at the plating concentration employed. The hepatocytes synthesized ansd secreted albumin at rates similar to those observed in vivo. The cells secreted triacylglycerol in the absence of fatty acid substrate. Under these conditions the most abundant triacylglycerol molecular species contained 53 carbons. Incubation with oleic acid markedly increased triacylglycerol secretion predominantly in the form containing a total carbon number of 57. Approx. 80% of the secreted cholesterol was in the free form and this was unaffected by oleic acid. Employing monospecific antibodies constant rates of synthesis and secretion of apolipoproteins E and A-I were demonstrated by quantitative electroimmunoassay of the cell culture media. The rates of albumin, apolipoprotein E, and apolipoprotein A-I production were 1480, 170 and 60 microgram/h per g cell protein, respectively.

Effects of the type of dietary fat at two levels of vitamin E in Wistar male rats during development and aging. I. Life span, serum biochemical parameters and pathological changes

This experiment was designed to study in rats the implications of the dietary type of fat at two levels of vitamin E on the life span as well as on several biochemical and anatomopathological age-related changes. For this purpose, six different isoenergetic diets containing 15% coconut oil (SFD), safflower oil (UFD) or a combination of both (CFD) with 2 or 200 mg% of dl-alpha-tocopherol were offered ad libitum to outbred Wistar male rats from weaning to senescence. The results indicated that up to 9--12 months the body weights of rats consuming the CFD or the UFD increased generally faster than those fed the SFD, and that all rats developed moderate degrees of obesity. Age-dependent changes in organ weights (kidneys, testes, spleen, brain, liver and heart) were unaffected by diet. Serum levels of vitamin E generally reflected the corresponding dietary levels, but were also influenced by the type of dietary fat. Serum cholesterol levels were not significantly affected by the type of diet or by age. Only transient hypotriglyceridemic and hypophospholipidemic effects of the UFD were observed and, while the levels of triglycerides decreased with age up to the 18th month followed by an increase at 24 months, the levels of serum phospholipids remained unchanged. Neither diet nor age modified the serum albumin/globulin ratios. While no differences in maximum life span were found between dietary groups, the 50% survival time of rats fed the UFD at high level of vitamin E was significantly longer than in all the other groups. This beneficial effect was related to postponement of the onset and reduction of incidence of malignant neoplasms, but was apparently not related to any particular influence on the incidence or severity of chronic nephropathy which practically developed in all rats. Various neoplastic, degenerative and inflammatory diseases encountered in rats dying during the course of the experiment were tabulated and compared with similar findings reported by others in different strains of rats. Pituitary and adrenocortical adenomas as well as adrenocortical and renal carcinomas were the most frequent tumors found in this study. All the pathological changes provided useful baseline information for the evaluation of data presented in this and subsequent communications of this series of studies.

A comparison of protein synthesis by liver parenchymal cells isolated from Fischer F344 rats of various ages

Rates of protein synthesis by intact liver parenchymal cells isolated from male Fischer F344 rats ranging in age from 2.5 to 30 months were determined by measuring the incorporation of [3H] valine into acid-insoluble material and the specific activity of the extracellular valine. The rate of protein synthesis decreased 44% from 2.5 to 18 months and then increased slightly (18%) from 18 to 30 months. There was no dramatic change in the types of proteins synthesized by isolated liver parenchymal cells isolated from 2- or 18-month-old rats as determined by SDS-polyacrylamide gel electrophoresis. The ribosomal-transit time by liver parenchymal cells isolated from 18-month-old rats was 60% higher than the ribosomal-transit time of liver parenchymal cells isolated from 4-month-old rats. The fidelity of protein synthesis by parenchymal cells isolated from 4- and 18-month old rats was compared by measuring the incorporation of p-fluorophenyl alanine (an analogue of phenylalanine) into acid-insoluble material. Although protein synthesis decreased significantly from 4 to 18 months, the fidelity of protein synthesis remained constant.

The synthesis of glycosaminoglycans in aging rat liver. A brief note

The synthesis of glycosaminoglycans (GAG) was studied in liver slices from postnatal (9 days), young (140 days), adult (490 days) and senescent (940 days) rats. It was found that the rate of synthesis was highest in postnatal rat liver and decreased to about half in young rats with no further reduction in adult and senescent age groups. The specific radioactivity of the precursors of GAG synthesis did not change with age. The synthesis pattern of specific types of GAG in postnatal liver was characterized by a significant higher percentage of chondroitin sulfate and hyaluronic acid. In the following age classes the profile of specific GAG synthesis did not change significantly (heparin sulfate: chondroitin sulfate" hyaluronic acid: "keratin sulfate" = 84%:8.3%:1.5%:1.6%).

Rates of protein synthesis by hepatocytes isolated from rats of various ages

The rate of total protein synthesis in isolated hepatocytes was determined. The incorporation of L-[3H]valine into protein is linear for at least two hours of incubation and is affected by the concentration of amino acids in the medium. Uptake of valine by hepatocytes from 1.5- and 18-month-old rats was identical and appears to occur by simple passive diffusion. Within five minutes, the specific activities of the intracellular and extracellular valine pools are equivalent. The specific activities of these pools are saturated by 1.6mM valine and remain constant for 60 minutes of incubation. The rates of protein synthesis by hepatocytes from 1- to 2-month-old rats is 96.8 pmoles of valine per minute per milligram protein. This is comparable to rates of protein synthesis reported for perfused liver and liver in vivo and is approximately 64% higher than the rate of protein synthesis by hepatocytes from 18-month-old rats.

The effect of D-galactosamine on LCAT secretion and ultrastructure of isolated rat hepatocytes

The effect of D-galactosamine on secretory activity and morphology of isolated rat hepatocytes was investigated: Galactosamine was found to reduce the secretion of lipoproteins (as indicated by the release of free cholesterol and triacylglycerol) as well as the secretion of lecithin: cholesterol acyltransferase (LCAT) and [14C]-labelled proteins from the isolated cells. The secretion of LCAT was inhibited much more than that of the other secretory products studied. Transmission electron microscopy revealed that galactosamine induced morphological changes in RER, mitochondria and nucleoli. The most striking feature of galactosamine-treated hepatocytes, however, was the appearance of swollen lysosomes. Some of these organelles measured up to 3 mumicrometer in diameter. Uridine did not abolish the effect of galactoosamine upon the secretory activity of hepatocytes. The most conspicuous ultrastructural feature in cells that had been incubated with both uridine and galactosamine was the appearance of large amounts of glycogen. The possibility that galactosamine inhibits glycogenolysis is discussed. The rather selective effect of galactosamine on LCAT secretion suggests the use of this compound for the study of the interrelationship between LCAT and lipoprotein secretion.

The effect of age on protein synthesis by isolated liver parenchymal cells

The protein synthesizing capacity of liver parenchymal cells isolated from 3-, 12-, 24-, 31- and 36-month-old rats was determined by the incorporation of 14C-leucine. Conditions for optimum protein synthesis included the use of an enriched medium (modified Waymouth's MB 752/1) and cell suspension concentrations ranging from 0.25 to 4 X 10(6) cells/ml medium. The cells were incubated with a dose of 6 micronmol leucine/ml medium for 2 h at 37 degrees C under an atmosphere of 95% O2 and 5% CO2. With parenchymal cells isolated from 3-month-old rats, a leucine incorporation rate of 14.4 nmol leucine/h/10(6) cells was found. The capacity of the parenchymal cells to synthesize protein decreased between 3 and 12 months, remained constant between 12 and 24 months and increased between 24 and 26 months. Degradation of newly synthesized proteins or reutilization of 14C-leucine did not occur during the incubation period. The ratio between albumin and total protein synthesis as a function of age was determined. This ratio did not change between 3 and 24 months but there was a significant increase between 24 and 36 months. The increase in total protein synthesis in late age may be due to a compensation by the liver for a more pronounced proteinuria, increased proteolysis or an accumulation of "altered" proteins.