Age-related changes in the hepatic endoplasmic reticulum: a quantitative analysis

The effects of aging on hepatic microsomal scaling factor and hepatocellularity number in the horse

1. Scaling factor values for the in vitro-in vivo extrapolation of hepatic metabolic clearance for xenobiotics have not yet been determined in horses. Scaling factors were determined by comparing the total protein and or cytochrome (CYP) P450 content in microsomes and cryopreserved hepatocytes against the content in the liver. 2. Microsomal protein per gram of liver (MPPGL) and hepatocellularity number per gram of liver (HPGL) using CYP P450 content method ranged 41-73 mg/gram of liver (mean= 57 mg/gram of liver, n = 39) and 146-320 × 10⁶ cells/g of liver (mean = 227× 10⁶ cells/g of liver, n = 18), respectively and 156-352 × 10⁶ cells/g of liver (mean = 232× 10⁶ cells/g of liver) using total protein method. 3. A non-monotonic and inverse relationship between age and MPPGL and HPGL, respectively, was observed. Between one and 20 y of age, the liver cell size decreases as age increases. Subsequently, the cell size increases until the hepatocytes of the oldest horses approached the size found in the youngest horses. Hepatocyte density was inversely related to the size of the hepatocytes. 4. This study provides the first extensive and comprehensive data demonstrating the relationship between the size of hepatocytes and HPGL in any species.

Ginger and alpha lipoic acid ameliorate age-related ultrastructural changes in rat liver

Because of the important role that oxidative stress is thought to play in the aging process, antioxidants could be candidates for preventing its related pathologies. We investigated the ameliorative effects of two antioxidant supplements, ginger and alpha lipoic acid (ALA), on hepatic ultrastructural alterations in old rats. Livers of young (4 months) and old (24 months) Wistar rats were studied using transmission electron microscopy. Livers of old rats showed sinusoidal collapse and congestion, endothelial thickening and defenestration, and inconsistent perisinusoidal extracellular matrix deposition. Aged hepatocytes were characterized by hypertrophy, cytoplasmic vacuolization and a significant increase in the volume densities of the nuclei, mitochondria and dense bodies. Lipofuscin accumulation and decreased microvilli in bile canaliculi and space of Disse also were observed. The adverse alterations were ameliorated significantly by both ginger and ALA supplementation; ALA was more effective than ginger. Ginger and ALA appear to be promising anti-aging agents based on their amelioration of ultrastructural alterations in livers of old rats.

ER stress and hormetic regulation of the aging process

An ability to mount a stress resistance under pressure is a major host defence mechanism and has been a fundamental force during evolution. However, the adaptation capacity clearly declines during aging and this loss of stress resistance accelerates the aging process exposing the organism to degenerative diseases. The effect of stress on organisms seems to be a dose-dependent response, i.e. mild stress induces a stress tolerance and extends the lifespan whereas excessive stress accentuates the aging process. This paradox is known as hormesis in aging research. It is essential to distinguish the intensity of cellular stress and thus mount an appropriate host defence. The endoplasmic reticulum (ER) contains three branches of stress transducers, i.e. IRE1, PERK, and ATF6 pathways, all of which recognize stress-related disturbances in the function of ER. These transducers trigger a complex signaling network which activates an unfolded protein response (UPR). Interestingly, ER stress transducers can distinguish the intensity of ER stress and induce a dose-dependent UPR, either adaptive response to stress or apoptotic cell death. The efficiency of the stress recognition system and UPR signaling declines during aging. We will discuss the role of ER stress in hormetic regulation of aging process and longevity.

Age-related changes in liver structure and function: Implications for disease ?

The geriatric populations of many countries are growing rapidly and they present major problems to healthcare infrastructures from both medical and economic perspectives. The elderly are predisposed to a variety of diseases, which contribute to a marked increase in morbidity in this subpopulation. The incidence of liver disease increases in the elderly, but the cellular and subcellular perturbations that underlie this suspected predisposition to pathology remain unresolved. Several age-related changes have been documented, including (a) a decline in liver volume, (b) an increase in the hepatic dense body compartment (lipofuscin), (c) moderate declines in the Phase I metabolism of certain drugs, (d) shifts in the expression of a variety of proteins and (e) diminished hepatobiliary functions. Other more subtle changes (e.g., muted responses to oxidative stress, reduced expression of growth regulatory genes, diminished rates of DNA repair, telomere shortening) may contribute to reduced hepatic regenerative capacity, shorter post-liver transplant survival and increased susceptibility to certain liver diseases in the elderly.

Heterogeneity in the rate of benzo[a]pyrene metabolism in single cells: quantitation using flow cytometry

We describe a method for quantitating heterogeneity in the rate of benzo[a]pyrene metabolism in single cells by using flow cytometry. We have used the technique to study the response of Hepa-1c1c7 mouse hepatoma cells to the microsomal enzyme inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin. Cells responded in a relatively homogeneous fashion at different times of induction with a maximally inducing concentration of the inducer. However, the induction response could be heterogeneous at a submaximal inducer concentration. We found even higher heterogeneity of enzyme activity among low-activity variants derived from the Hepa-1c1c7 cell line. When cells of either high or low activity were isolated from such a clonal population, propagated, and reanalyzed, they displayed average enzyme activity and heterogeneity identical to the parental cells; therefore, the heterogeneity represents transient, nonheritable differences between cells within the population.

Heterogeneity in the rate of benzo[a]pyrene metabolism in single cells: quantitation using flow cytometry

We describe a method for quantitating heterogeneity in the rate of benzo[a]pyrene metabolism in single cells by using flow cytometry. We have used the technique to study the response of Hepa-1c1c7 mouse hepatoma cells to the microsomal enzyme inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin. Cells responded in a relatively homogeneous fashion at different times of induction with a maximally inducing concentration of the inducer. However, the induction response could be heterogeneous at a submaximal inducer concentration. We found even higher heterogeneity of enzyme activity among low-activity variants derived from the Hepa-1c1c7 cell line. When cells of either high or low activity were isolated from such a clonal population, propagated, and reanalyzed, they displayed average enzyme activity and heterogeneity identical to the parental cells; therefore, the heterogeneity represents transient, nonheritable differences between cells within the population.

Liver function and phase I drug metabolism in the elderly: a paradox

Aging is accompanied by marked changes in the physiology of many organs, as well as in their constituent cells. These nonpathological alterations in structure and/or function may affect normal physiological processes in the elderly (individuals > 65 years), for example drug disposition. The liver plays a major role in drug clearance and aging has been reported to diminish this hepatic capacity, particularly the clearance of drugs that undergo mandatory oxidation by the microsomal cytochrome P450-dependent mono-oxygenase systems. Liver volume and blood flow decline with age in humans and, no doubt, this contributes to the diminished clearance of drugs that exhibit first-pass kinetic profiles. Changes in liver morphology with aging that have been described in rodents are limited to the hepatocytes, for example accumulation of dense bodies and loss of smooth surfaced endoplasmic reticulum. There is no evidence that the increase in intracellular lipofuscin adversely affects hepatocyte functions. A number of studies have documented significant age-related declines in the amounts, specific activities and rates of induction of liver microsomal mono-oxygenases in inbred male rats. On the basis of a variety of clinical tests, most liver functions in humans appear to be well preserved. The most remarkable characteristic of liver function in the elderly is the increase in interindividual variability, a feature that may obscure age-related differences. Most in vitro studies using nonhuman primate or human liver tissue did not detect age-related deficiencies in cytochrome P450-dependent microsomal mono-oxygenases. On the other hand, there have been recent reports of age-related, but not gender-related, declines in the in vitro activities of several human liver mono-oxygenases, for example the cytochrome P450 isoform CYP3A. Nevertheless, reduced liver volume and blood flow in the elderly permit the reconciliation of: the in vivo clinical pharmacokinetic data indicative of reduced hepatic drug clearance; and the absence of significant age-related declines in the amounts or in vitro activities of liver microsomal mono-oxygenases.

The effect of age on inducibility of various types of rat liver cytochrome P-450

1. The content and specific activities of inducible cytochrome P-450 enzymes were determined in liver microsomes of rats of various ages after maximal induction with phenobarbital, isosafrole of 3-methylcholanthrene, and in untreated animals. 2. With age an increase in liver weight was observed both in untreated rats and in maximally induced ones; the microsomal protein content/g of liver decreased with age in untreated animals but not in induced ones. Total cytochrome P-450 content/mg microsomal protein remained unchanged with age in all experimental groups. 3. Immunologically detectable levels of cytochrome P4501A1/1A2 and 2B1/2B2 remain unchanged with age both in untreated animals and in maximally induced ones. 4. Several cytochrome P-450 activities showed an age-related decrease in untreated animals, but no change with age was observed in the activities of cytochrome P4501A1, 2A2 and 2B1/2B2 in rat liver microsomes. This indicates that ageing affects only the activity of some constitutive forms of cytochrome P-450 in male rats, but not the activity of inducible types of P-450. 5. Although previous results indicated decreased inducibility of the cytochrome P-450 mRNA levels with age, the present study clearly demonstrates that this is not reflected in decreased enzyme levels or activities after maximal induction. From this it is concluded that the decreased mRNA levels might rather be reflected in a decreased rate at which maximal induction can be achieved.

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.

A biochemical and stereological study of neonatal rat hepatocyte subpopulations. Effect of pre- and postnatal exposure to ethanol

Hepatocytes from 12-day-old rats, pre- and post-natally exposed to alcohol, together with those from pair-fed controls, were isolated and subfractionated in six cell subpopulations on Percoll density gradients. These cells were characterized using a combination of biochemical and stereological methods. The low density cells (F2) mainly showed biochemical and stereological features of perivenous hepatocytes, whereas the heavier cells (F6) were primarily periportal hepatocytes. The alcohol-metabolizing enzymes, alcohol dehydrogenase and aldehyde dehydrogenase (high and low Km) showed more activity in the F2 fraction. Alcohol-altered mitochondria and Golgi apparatus occurred mainly in F2 cells, whereas the endoplasmic reticulum and lysosomes appeared to be more altered in the F6 hepatocytes. Alcohol also induced the appearance of some small hepatocytes, with a well-developed rough endoplasmic reticulum and an increased number of mitochondria. Biochemical data indicated that glutamate dehydrogenase and alanine aminotransferase were more affected in F2 cells from alcohol-treated rats, and that the activity of the ethanol-metabolizing enzymes was alos reduced in these hepatocytes. Our results indicate that alcohol exposure during zonal development in the liver could have a selective effect on specific cell components depending on the acinar zone, and that the perivenous hepatocytes appear to be more damaged under these conditions.

Isoflurane as an anesthetic for experimental animal surgery

Isoflurane is an inhalational anesthetic agent associated with no known hepatic toxicity. Despite this fact, isoflurane has not been widely utilized as an anesthetic agent in studies of liver structure and function in experimental animals. For this reason, livers from rats treated with pentobarbital or diethylether were compared to those from rats treated with isoflurane to determine differences in biochemical and morphologic parameters. Liver from pentobarbital-treated rats showed a significant decline in glutathione-S-transferase activity compared to liver from isoflurane/O2 or ether-treated rats. Liver microsomes from isoflurane/O2-treated rats retained more cytochrome-C(P450)-reductase activity than did those from pentobarbital-treated, ether-treated, or decapitated rats. Despite these biochemical alterations, morphometric analysis of liver from isoflurane/O2 and pentobarbital-treated rats showed no quantitative or qualitative differences in liver structure or organelle volume densities. Neither were differences detected in uptake and distribution of 125I-epidermal growth factor when analyzed by electron microscopic autoradiography. These data show that isoflurane with supplemental O2 has no effects on hepatic structure and fewer effects on hepatic function than other anesthetics and may be a better experimental anesthetic than any currently in use.

Changes in ascorbate-induced lipid peroxidation of hepatic rough and smooth microsomes during postnatal development and ageing of rats

In female Wistar rats, sensitivity to ascorbate-induced lipid peroxidation in rough and smooth microsomes increases with age, reaching a maximum in 1-year-old rats and decreases during ageing. Time course of lipid peroxidation, and lipid peroxidation with optimum concentrations of ascorbic acid, Fe2+ and protein in rough microsomes show that 1-year-old rats are the most susceptible followed by 75-day-old, 15-day-old, 2-year-old and 1-day-old rats. However, smooth microsomes show a slightly different trend with maximum sensitivity in 1-year-old rats followed by 15-day-old, 75-day-old, 2-year-old and 1-day-old rats. Smooth microsomes are more susceptible to lipid peroxidation than the rough in all age groups except 75-day-old rats. Smooth microsomes are also more sensitive to inhibitors of lipid peroxidation. Microsomal content of phospholipid increases during postnatal development and decreases during ageing, whereas that of ascorbic acid and alpha-tocopherol do not show any particular trend.

The distribution of cytochrome P-450-mediated drug oxidation and glutathione in periportal and perivenous rat hepatocytes after phenobarbital treatment

The effect of phenobarbital pretreatment on acinar distribution of microsomal drug metabolizing enzymes was investigated by analysis of periportal (pp) and perivenous (pv) enriched rat hepatocytes isolated by collagenase gradient perfusion. In untreated animals the activities of cytochrome P-450, NADPH-cytochrome c reductase and microsomal ethanol oxidation were significantly higher in pv cells. Phenobarbital produced a 45% increase of the yielded microsomes related to the hepatocytic protein but did not change their relative distribution. The content of reduced glutathione (GSH) was lower in hepatocytes from the pv area. The GSH content was more than 20% increased after phenobarbital treatment in both subclasses of cells, but the distribution pattern remained unchanged. The higher activity of drug metabolizing enzymes in the pv area of untreated animals may account for the higher cytotoxicity of numerous drugs to the perivenous hepatocytes. A 3-day treatment with phenobarbital equalized the pp-pv difference by producing more induction of the periportal cytochrome P-450-mediated drug and ethanol oxidation capacities in microsomes derived from periportally enriched hepatocytes.

Age-dependent alterations in the physicochemical properties of rat liver microsomes

Aging results in a significant decline in liver drug metabolism which is largely attributable to changes in the microsomal mixed function oxidase system. For example, the mixed function oxidase system in the livers of senescent rats is characterized by: (1) a reduced cytochrome P-450 content; (2) a decline in the specific activity of NADPH-cytochrome c (P-450) reductase; and (3) a slower rate of ethylmorphine N-demethylation in comparison to young adult animals. Since several factors intrinsic to the microsomes may influence the efficacy of the mixed function oxidase system, e.g. the phospholipid and cholesterol contents, the saturation index of the fatty acids and the fluidity of the membranes, we conducted a physicochemical analysis of liver microsomes isolated from young adult (3-4 months), mature (12-16 months) and senescent (25-27 months) male Fischer rats. Although the microsomal cholesterol content did not change appreciably between maturity and senescence, there was a marked decline in the total phospholipid content. This resulted in a significant increase in the cholesterol/phospholipid ratio, 0.49 to 0.65 between 16 and 27 months of age. The age-related changes in the total phospholipid content were largely reflected in each of the major fractions, i.e. phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine + phosphatidylserine. Small increases in the relative percentages of highly unsaturated fatty acid species were offset by similar decreases in the more frequent and more saturated species as a function of increased age. As a result, the net change in the fatty acid saturation index was probably minimal. However, the increase in the cholesterol/phospholipid ratio most likely contributes to the significant decline in the order parameter of microsomes isolated from old rats which, in turn, may impair the functional capacity of the hepatic mixed function oxidase system.

Age-related alterations in cultured human fibroblast membrane structure and function

Membrane enzyme activities, lipid composition, and fluorescence probe characteristics in isolated plasma membranes, microsomes and mitochondria of cultured human fibroblasts were used to determine if structural alterations occurred as a function of donor age. The cells were sex matched and allowed to undergo approximately 8 population doublings under identical culture conditions. Plasma membrane (Na+, K+)-ATPase, microsomal NADPH cytochrome c reductase, and mitochondrial succinate cytochrome c activities showed variation as a function of increasing donor age but these changes were not statistically significant. At the same time the cholesterol/phospholipid molar ratio was unaltered in plasma membranes, decreased 50% in microsomes, and unchanged in mitochondria with increasing donor age. The phosphatidylcholine/phosphatidylethanolamine ratio increased in all three membrane fractions with increasing age of the fibroblast donor. The ratio of unsaturated/saturated fatty acids decreased in the phospholipids of microsomes but not of plasma membranes or mitochondria. The structural properties of the membranes were determined with two different fluorescence probe molecules, trans-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene. These probe molecules indicated that the fluorescence lifetime and/or fluorescence polarization of the trans-parinaric acid probe decreased in microsomes, mitochondria, and in the plasma membrane, such that the limiting anisotropy, indicative of restrictions to probe motions, was significantly lower (high fluidity) with increasing subject age in plasma membranes, microsomes and mitochondria. The trans-parinaric acid fluorescence lifetime displayed two components in plasma membranes, microsomes, and mitochondria, a finding consistent with the coexistence of fluid and solid membrane lipid areas in the cultured human fibroblast subcellular membranes. The trans-parinaric acid partitioned preferentially into solid membrane areas. The limiting anisotropy of 1,6-diphenyl-1,3,5-hexatriene, a fluorescent probe that partitioned almost equally into different lipid domains, was also decreased in microsomes and mitochondria with increasing donor age. In contrast, 1,6-diphenyl-1,3,5-hexatriene indicated a small increase in limiting anisotropy (0.219 vs 0.195) in plasma membranes. Arrhenius plots of trans-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene absorbance-corrected fluorescence in plasma membranes, microsomes and mitochondria demonstrated characteristic breakpoints near 20 degrees C and 30 degrees C. These breakpoints were not altered as a function of age.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in enzymes of hepatic rough and smooth microsomes during postnatal development and ageing of rats

Significant changes are observed in wet weight, microsomal protein content and enzymes of purified rough and smooth microsomes of liver during postnatal development and ageing of female Wistar rats. Protein content of total microsomes increases up to 15 days of age and remains steady during subsequent development, unlike that of rough and smooth microsomes which shows changes throughout the same period. Activities of cytochrome P-450, cytochrome b5 and NADPH-cytochrome c reductase increase during the period of maturation and decline during senescence. The decrease during senescence is at different rates in the two microsomal fractions. Microsomal glucose-6-phosphatase, but not adenosine triphosphatase, shows a similar increase during development and decrease during senescence.

Age-dependent changes in rat liver microsomal NADPH cytochrome C (P-450) reductase: a kinetic analysis

Rat liver microsomal NADPH cytochrome c (P-450) reductase (EC 1.6.2.4) exhibits several marked age-dependent changes, including a decline in specific activity, reduced inducibility and enhanced thermostability, which are indicative of an alteration in the quality of this enzyme. The present study examined the kinetic profile of the microsomal-bound enzyme in an effort to further define the effects of aging on the hepatic mixed function oxidase system. Intact microsomes isolated from young adult (3 months), mature (16 months) and senescent (27 months) rats were subjected to an extensive double reciprocal kinetic analysis employing NADPH and cytochrome c as substrates. The Km values obtained with the initial substrate (NADPH) remained unchanged with animal age, whereas there was a decline in this parameter for the artificial acceptor substrate, cytochrome c. The Vmax values for both substrates were reduced as a function of increasing age, perhaps reflecting a concomitant decline in the relative amount(s) of efficient reductase in the microsomes.

Development of ultrastructural heterogeneity among hepatocytes in the mouse

Ultrastructural stereological analyses of periportal and centrilobular hepatocytes of newborn, 5- and 10-day-old, and adult male ddY mice were carried out to study the postnatal development of the morphologic heterogeneity among hepatocytes. In newborn animals, the periportal and centrilobular cells did not differ in the volume densities of the smooth and rough endoplasmic reticulum; in the volume and numerical densities of the mitochondria, lysosomes, peroxisomes, and lipid droplets; or in the shape (the axial ratio) of the mitochondria. In 5-day-old animals, the volume densities of the mitochondria and rough endoplasmic reticulum were greater in periportal cells than centrilobular cells, and the volume density of the smooth endoplasmic reticulum was greater in centrilobular cells than periportal cells. In 10-day-old animals, a further difference was seen in the numerical density of the mitochondria, which was greater in centrilobular cells than periportal cells. Adult hepatocytes showed also a difference in the axial ratio of the mitochondria, which was greater in centrilobular than periportal cells; there was no difference in the volume density of the rough endoplasmic reticulum. When the data were expressed as volume and number per hepatocyte, the patterns of sublobular distributions of these organelles differed from the patterns seen in the volume and numerical density data, mainly in adult animals. This difference was caused by the marked increase in hepatocyte volume between 10 days of age and adulthood, especially in centrilobular cells. The results show that, in general, the ultrastructural heterogeneity among hepatocytes, evident in adult animals, is not present in newborn animals but arises during postnatal development, and suggest the occurrence of a lobular gradient in postnatal development of hepatocyte functions.

Organ scaling in mammals: the liver

1. Values for liver weight, in growing and adult male and female mammals, both terrestrial and aquatic, as well as values for hepatic blood flow, blood volume and oxygen consumption are submitted to linear (log-log) regression analysis. 2. The slope of the regression line for liver weight on adult body weight in adult mammals was found to be 0.886. No statistically significant difference was found between male and female, nor between terrestrial and aquatic mammals (at the 1% confidence level). 3. Over about four orders of magnitude there is (on present evidence) a tendency for the mammalian liver to grow as about the 0.94 power of body weight (pre- and post-natal). 4. The slopes of the regression lines for hepatic blood flow, blood volume and oxygen consumption were found to be 0.91, 0.86 and 0.69, respectively. 5. The mean hepatocyte size in fixed tissue of rats was found to be 7400 micrometers 3. 6. It is argued that the slope of the regression line for hepatic oxygen consumption in mammals generally is likely to fall in the range of 0.67-0.77.

Effects of the type of dietary fat at two levels of vitamin E in Wistar male rats during development and aging. III. Biochemical and morphometric parameters of the liver

The purpose of this study was to explore in rats the possible influence of the type of dietary fat at two extreme levels of vitamin E on several biochemically determined hepatic changes and on a number of quantitatively analyzed structural and ultrastructural variations with age in hepatic cells. Six groups of weanling Wistar male rats were fed ad libitum isoenergetic diets containing similar amounts (15 g per 100 g diet) of saturated fat (coconut oil), unsaturated fat (safflower oil) or a combination of both at two levels of dl-alpha-tocopherol (2 or 200 mg per 100 g of diet). Determinations were performed in rats killed at 3, 6, 12, 18 and 24 months. Although in relation to age and irrespective of the type of diet, several of the biochemical parameters fluctuated with time, comparisons of the results between the youngest and oldest rats showed no changes in the levels of hepatic RNA, phospholipids, cholesterol, total tocopherols and total collagens, significant increases in DNA and triglycerides and a significant decrease in total protein. While the type of diet did not have in general significant influences on the levels of DNA, RNA, total protein and collagens, either the type of dietary fat and/or the levels of vitamin E had some definite effects on the levels of triglycerides, cholesterol, phospholipids and total tocopherols, as well as on the in vitro formation of malonaldehyde and on the eventual occurrence of in vivo lipoperoxidation (diene conjugation). These effects, however, varied in relation to the duration of the diverse dietary treatments. The morphologic studies indicated that all the livers had variable but generally moderate degrees of fatty changes (mainly due to triglyceride accumulation) which were attributed to the moderate obesity found in the rats. The mean nuclear and cell dimensions of hepatocytes, the number of binucleated hepatocytes, surface density of rough endoplasmic reticulum, numerical density of mitochondria and the fractional cytoplasmic volume occupied by lipofuscin pigment in hepatocytes were not significantly affected by the type of diet, by age or by the eventual occurrence of in vivo hepatic lipoperoxidation, whereas the numerical density of hepatocytes (mono- and binucleated) and "litoral cells" (endothelial, Kupffer and Ito cells), although unaffected by diet, significantly increased with age. On the other hand, the fractional volume of mitochondria and peroxisomes, as well as the numerical density of peroxisomes, were significantly influenced by the type of dietary fat and to lesser extent by the dietary levels of vitamin E.

Effects of aging and phenobarbital on the rat liver microsomal drug-metabolizing system

Significant declines in the non-induced activities of liver microsomal drug-metabolizing enzymes and in the amount of cytochrome P-450 occur between maturity (16 months) and senescence (27 months) in male Fischer 344 rats, whereas there are essentially no differences between very young (1 month) and mature animals. Several hepatic responses to chronic phenobarbital administration also demonstrate marked age-dependent changes. The livers of young and mature animals exhibit: (1) greater hepatomegaly; (2) faster rates of induction and post-induction recovery of microsomal mixed function oxidase enzyme activities and hemoprotein concentration; and (3) higher maximally induced levels of these components in comparison to senescent rats. When considered with information from previous studies, the present data suggest that the age-related decline in liver drug metabolism may be due to qualitative and/or quantitative changes in the structural and/or functional components of the hepatic microsomal mixed function oxidase system.

Electron-microscopic morphometric analysis of mouse liver. II. Effect of ageing and thymus transplantation in old animals

The influence of age and thymus on liver cells has been investigated by performing a complete morphometric analysis. The age-dependence was tested in three groups of mice aged 2, 12, and 24 months, while the action of the thymus was studied on 24-month-old mice grafted with neonatal thymus 30 days before the analysis was performed. Among the investigated parameters, the most considerable changes were found in the mean nuclear volume, which displayed a significant increase during ageing. The thymus was capable of reversing such an age-dependent increase when grafted into old animals. The volume of single hepatocytes also displayed an age-dependent increase which was not corrected by thymus grafting. The data presented suggest that the thymus influences the mitotic activity of the hepatocytes and further support the hypothesis that the thymus also plays an important role in non-immunological processes of ageing.

The influence of age on the hypothalamo-neurohypophyseal system of the mouse: a quantitative ultrastructural analysis of the supraoptic nucleus

A quantitative study of various morphological parameters in endocrine cells of the neuroendocrine region of the laboratory mouse was carried out. The supraoptic nucleus of the hypothalamo-neurohypophyseal system synthesises the hormones vasopressin and, to a lesser extent, oxytocin, and transports them to the posterior pituitary. Female C57BL/Icrfat mice at 8 and 26 months of age, free of macroscopic pathology, were sampled when in a physiologically defined resting state. No significant differences in the volume fractions of most cell and subcellular components could be detected at the two ages studied; however, significant increases in the volume fractions of hormone-containing granules and lipofuscin (aging pigment) were demonstrated in older animals. These observations are similar to those made on rat endocrine pancreas also in the resting state. The notion that these hormone-secreting cells are "protected" to some extent from the aging process, and may have some of the qualities of "pace-maker" cells, is discussed.

Aging in the rat olfactory bulb: quantitative changes in mitral cell organelles and somato-dendritic synapses

Quantitative measurements of the major organelles in the mitral cell perikaryon as well as numbers of mitral somato-dendritic synapses, have been made on electron micrographs from rats aged 3 to 30 months. The volume fraction of the cisternae of rough endoplasmic reticulum (RER) is constant throughout the period studied. Hence the amount of RER per cell reflects changes in perikaryal size. Thus there is a 3-fold increase of volume of cisternae of RER per mitral cell from 3 to 27 months and a halving from 27 to 30 months. A similar pattern is seen for the volume of mitochondria per cell. The volumes of dense bodies and cisternae of the Golgi complex per cell show a different pattern, that of a linear increase throughout the period, with no suggestion of a decrease from 27 to 30 months. An interesting finding is that the volume fraction of ground substance (perikaryal cytoplasm exclusive of the measured organelles) shows a remarkably constant value from 3 to 27 months and then a highly significant decrease from 27 to 30 months. This decrease, restricted to the period from 27 to 30 months, suggests a fundamental breakdown in cellular homeostasis in the oldest animals. Numbers of somato-dendritic, mitral-to-granule synaptic junctions per mitral cell and per olfactory bulb show a significant increase from 3 to 24 and 27 months, respectively, and then a suggestive decrease from 24 and 27 to 30 months. This finding indicates that new synapse formation is possible in normal adult rats, perhaps even in quite old rats.

Ultrastructure of neurons in the auditory cortex of ageing rats: a morphometric study

The cell bodies of pyramidal cells in layers II and V of rat auditory cortex were quantitatively examined in groups of rats 3, 6, 15, 23, 27 and 34-36 months of age. The mean diameters of cell bodies of both layer II and layer V neurons, as measured in 1 micron plastic sections, increased between 3 and 15 months of age, then decreased to a diameter that was less in the 36-month-old than in the 3-month-old rats. Morphometry of the nuclei of the cells was done by measuring nuclear area and nuclear envelope length directly on electron micrographs. In the layer II cells, neither parameter changed with advancing age. In the layer V cells, the mean nuclear area decreased significantly in the old animals and the mean envelope length increased. Point-counting techniques were applied to electron micrographs of cell bodies to determine the relative volume of selected organelles, inclusions and ground substance in the perikaryal cytoplasm. In this part of the study the chronological pattern of change in layer II and layer V pyramidal cells was similar. The relative volume of dense bodies increased linearly with advancing age, with a slightly more accelerated rate in layer II cells. The relative volume of ground substance remained essentially constant through 27 months, and then at 34-36 months decreased to 83% and 89% of the three-month level in layer V and layer II, respectively. The relative volume of the rough endoplasmic reticulum (RER) did not change significantly until after 15 months, at which time it began to occupy increasingly a larger fraction of the perikaryal cytoplasm. Finally, the relative volumes of mitochondria, multivesicular bodies and Golgi apparatus did not show clear trends of change during the 33-month period.

A quantitative analysis of hepatic ultrastructure in rats during enhanced bile secretion

The ultrastructural changes in hepatocytes of rats subjected to selective biliary obstruction (SBO), wherein the biliary system draining approximately two-thirds of the liver is obstructed, were evaluated by quantitative electron microscopy or stereology. The remaining unobstructed portion of the organ compensates for this loss of bile secretion by functioning in a hypersecretory mode. This animal model permits the comparison of hepatocellular fine structure associated with the conditions of nonsecretion and hypersecretion of bile with that found in normal secreting sham-operated rats. Since recent evidence suggests the presence of lobular gradients in hepatic structure and function, both centrolobular and periportal hepatocytes were examined. The low incidence of Golgi membrane profiles in high magnification electron micrographs results in a low confidence level of sampling and, thus, necessitates the application of a novel parameter for estimating the amount of Golgi complex, i.e., the Golgi-rich area. For the most part, the lobular variation in hepatic fine structure in the sham-operated animals was similar to that described by Loud ('68). However, the periportal parenchyma contained approximately twice the volume of Golgi-rich area as the centrolobular tissue. The amount of cytoplasmic lipid increased significantly in the SBO unobstructed lobes, although there were few or no changes in the other intracellular organelles or inclusions except those related to the Golgi complex. The volume of Golgi-rich area increased significantly in the centrolobular tissue of the SBO unobstructed (hypersecretory) lobes to the extent that both intralobular zones contained similar amounts of this component. These data suggest that the Golgi complex is a dynamic unit which responds to changes in hepatocellular activity and may be involved in bile secretion.

Stereological analysis of hepatic fine structure in the Fischer 344 rat. Influence of sublobular location and animal age

Stereological analysis of hepatic fine structure in Fischer 344 male rats at 1, 6, 10, 16, 20, 25, and 30 mo of age revealed differences in the amounts and distributions of hepatocellular organelles as a function of sublobular location or animal age. Between 1 and 16 mo of age, both the centrolobular and periportal hepatocytes increased in volume by 65 and 35%, respectively. Subsequently, the cell volumes declined until the hepatocytes of 30-mo-old rats approached the size of those found in the youngest animals. Regardless of animal age, the centrolobular cells were consistently larger than the corresponding periportal hepatocytes. The cytoplasmic and ground substance compartments reflected similar changes in their volumes, although there was no significant alteration in the nuclear volume. The volumes of the mitochondrial and microbody compartments increased and decreased concomitant with the changes in average hepatocyte size. Both lobular zones in the 30-mo-old rats contained significantly smaller relative volumes of mitochondria than similar parenchyma in 16-mo-old animals. The volume density of the dense bodies (lysosomes) increased markedly in both lobular zones between 1 and 30 mo of age, confirming reports of an age-dependent increase in this organelle. The surface area of the endoplasmic reticulum in the centrolobular and periportal hepatocytes reached its maximum level in the 10-mo-old rats and subsequently declined to amounts which approximated those measured in the 1-mo-old animals. This age-related loss of intracellular membrane is attributable to a significant reduction in the surface area of the smooth-surfaced endoplasmic reticulum (SER) in animals beyond 16 mo of age. The amount of rough-surfaced endoplasmic reticulum (RER) in the periportal parenchymal cells was unaffected by aging, but the centrolobular hepatocytes of 30-mo-old animals contained 90% more RER than similar cells in the youngest rats. The centrolobular parenchyma contained more SER and the portal zones more RER throughout the age span studied. These quantitative data suggest that (a) certain hepatic fine structural parameters undergo marked changes as a function of animal age, (b) there exists a gradient in hepatocellular fine structure across the entire liver lobule, and (c) there are remarkable similarities in hepatocyte ultrastructure between very young and senescent animals, including cell size and the amount of SER.