Variation of tyrosine aminotransferase expression during the day in rats of different ages.

The activity of the enzyme tyrosine aminotransferase and the synthesis of its specific mRNA were evaluated at different hours of the day in the liver of 3-, 12- and 24-month old BN rats. The enzyme activity has a circadian rhythm with a peak at midnight in 3- and 12-month old, which shifts to 03.00 hrs in 24-month old animals, in agreement with previous results. The expression of TATmRNA also changes during the day indicating circadian fluctuations which change with age. In 3-month old rats the TATmRNA peak is at 19.00 hrs, preceding that of the enzyme activity. In 12-month old rats the TATmRNA synthesis reaches a maximum at midnight and in 24-month old rats at 03.00 hrs. The results show that the circadian rhythm of tyrosine aminotransferase activity is due to a different gene expression throughout the day, which is influenced by age.     

Role of the glycerophosphate shunt in regulating oxidation of cytoplasmic NADH and ATP synthesis by liver mitochondria during rat ontogeny

The activity of alpha-glycerophosphate dehydrogenase rate of alpha-glycerophosphate oxidation and ATP synthesis were determined in the liver mitochondria of 1, 3, 12 and 24-month old rats in norm and two days after thyroxin daily administration in a dose of 0.25 mg per 100 g of body mass. The value of the studied parameters decreases with the age, most considerably--from one to three months and then--from 3 to 24-month age. This evidence for the fact that the role of glycerophosphate shuttle in the energy supply of cells falls with ageing; thyroxin administration evoked almost a two-fold increase of the mentioned parameters in one-month rats and more than three-fold in 12 and 24-month animals. A decrease in the alpha-glycerophosphate dehydrogenase activity with ageing is supposed to be connected with the thyroid gland function.     

Effect of graded doses of tri-iodothyronine on ventricular myosin ATPase activity and isomyosin profile in young and old rats.

Ventricular myosin ATPase activity, V1 isomyosin content and serum T3 (tri-iodothyronine) values decrease with age in male Fischer 344 rats. To determine if the age decrement in ATPase activity and V1 isomyosin content are caused by decreased T3 levels or an age-related decrease in V1 isomyosin induction by T3, 3-, 12- and 24-month-old male Fischer 344 rats were given constant T3 infusions by osmotic minipump. Rats at all ages were given 0.75, 5 and 15 micrograms(/100 g per 24 h) doses of T3, whereas 12- and 24-month-old rats were given an additional 0.4 microgram dose. In control rats, T3 levels decreased from 97 +/- 2.7 at 3 months to 75 +/- 4.7 ng/100 ml at 24 months. Likewise, Ca2+-activated myosin ATPase activity decreased from 1.04 +/- 0.05 to 0.68 +/- 0.05 mumol of Pi/min per mg of protein, and the relative proportion of V1 of isomyosin decreased from 90 +/- 4.0 to 26 +/- 2.0%. The lowest (0.4 microgram) T3 dose, which was sufficient to restore T3 levels in 24-month-old animals to 3-month control values, abolished the age decrement in myosin ATPase activity and markedly increased the proportion of V1 isomyosin present in the ventricle. These findings indicate that the senescent ventricle responds readily to small doses of T3 and strongly suggest that the age decrement in serum T3 levels is sufficient to contribute to the age-related decrease in myosin ATPase activity and V1 isomyosin content. Since these parameters correlate with ventricular contractility, the age decrement in T3 levels may also contribute to the decreased ventricular contractility and cardiac output observed in senescent rats.     

Peculiarities of urea distribution in tissues of rats of different age

The content of urea was studied in protein-free filtrates of the liver kidneys, skeletal muscles, myocardium, spleen, brain tissues and blood serum as well as in urine of 1, 3, 6, 12 and 24-month rats. It is shown that at the age of 6 months the content of urine in most tissues under study is significantly decreased (by 42-73%), at the age of 12 months in the spleen and at the age of 24 months in the brain tissues as compared to the one-month animals. The level of urine decrease in the liver and brain tissues of 24-month animals is less pronounced than in other tissues, that corresponds to age peculiarities of their protein metabolism. A decrease of blood consumption per weight unit and a relative increase in the amount of nitrogen excreted with urine are observed with ageing. The arginase activity in the liver decreases essentially only in 3-month animals. A conclusion is drawn that peculiarities of food consumption and the character of changes in the urea content in tissues and urine are adaptation manifestation of an age decrease in the intensity of nitrogen metabolism and protein demand of the organism.     

基质金属蛋白酶-2、-9及其组织抑制剂-1在大鼠肺组织中的增龄变化

目的研究基质金属蛋白酶（MMPs）-2、-9及组织型基质金属蛋白酶抑制剂（TIMPs）-1在大鼠肺组织中的增龄性变化规律。方法不同月龄（1月龄、3月龄、12月龄、18月龄、24月龄）雄性清洁级（SD）大鼠47只分为5组,按月龄取实验大鼠的右下叶肺组织,用流式细胞术检测MMP-2、MMP-9及TIMP-1的表达水平,进行定量分析。结果 MMP-2、MMP-9和TIMP-1均随着月龄的增长呈先降后升波谷型曲线变化;3月龄、12月龄和18月龄MMP-2、MMP-9和TIMP-1均较1月龄明显下降,且以12月龄为最低值;24月龄MMP-2、MMP-9和TIMP-1均较1月龄上升。MMP-2/TIMP-1比值和MMP-9/TIMP-1比值均随着月龄的增长呈先升后降波峰型曲线变化;12月龄和18月龄均较1月龄明显升高,且以18月龄为最高点;3月龄的MMP-2/TIMP-1较1月龄有所上升,3月龄的MMP-9/TIMP-1与1月龄持平;24月龄的MMP-2/TIMP-1和MMP-9/TIMP-1较1月龄也有不同程度上升。结论大鼠肺组织中MMPs及其抑制剂TIMPs随月龄的增长,呈特征性变化规律。     

Endocrine and behavioral modifications in aging male rats

Endocrine and behavioral effects of age and aging have been studied in 4 groups of Sprague-Dawley male rats (2, 6, 12, 24 months old). Plasma testosterone decreases after 6 months of age, plasma estradiol decreases from 2 to 6 months, then it increases with age and decreases again with aging (from 12 to 24 months). Aromatization of testosterone in brain tissue is similar in 2-, 12- and 24-month-old rats, but at 6 months a significant increase is observed. Testosterone biosynthesized in the gonad from dehydroepiandrosterone increases from 2 to 6 months, then it decreases, while the other metabolites of dehydroepiandrosterone show an increment with age. Corticosterone and 17 alpha-hydroxyprogesterone biosynthesized in the adrenal decrease with aging. Explorative and locomotor activity decreases with age and aging, while emotionality decreases from 2 to 12 months, but it increases with aging. These results indicate that endocrine equilibrium is remarkably altered by aging process showing a decrease of plasma sexual hormones and of gonadal activity. The decrement of aromatization of testosterone in the brain, which occurs between 6 and 12 months, is correlated with the decrement of plasma testosterone. It could be hypothesized that the hormones of the brain-pituitary-gonad axis are involved in the control of explorative behavior or that both hormonal and behavioral parameters are controlled by a common factor.     

Hepatic and renal conjugation (Phase II) enzyme activities in young adult, middle-aged, and senescent male Sprague-Dawley rats

Acetaminophen (APAP)-induced nephrotoxicity is age dependent in male Sprague-Dawley rats: nephrotoxicity occurs at lower dosages of APAP in 12- to 14-month olds compared with 2- to 3-month olds. The mechanisms responsible for enhanced nephrotoxicity in 12-month-old Sprague-Dawley rats are not entirely clear, but may be related to age-dependent differences in APAP metabolism in liver and/or kidney. Major pathways of hepatic APAP metabolism include sulfation and glucuronidation; glutathione conjugation represents a pathway for detoxification of reactive oxidative APAP metabolites. The present studies were designed to quantify in vitro activity of three Phase II enzyme activities: glutathione S-transferase using 1-chloro-2,4-dinitrobenzene as substrate, UDP-glucuronyl transferase using APAP as substrate, and sulfotransferase using APAP as substrate, in subcellular fractions of liver and kidney of 3-, 12-, 18-, and 30-month-old naive male Sprague-Dawley rats. In liver, glutathione S-transferase, UDP glucuronyl transferase, and sulfotransferase activities were not significantly different in rats from 3 through 30 months of age. Renal UDP glucuronyl transferase and sulfotransferase activities were similar in rats from 3 through 30 months of age. In contrast, renal glutathione S-transferase activity was characterized by a lower Km in 12- and 30-month olds when compared with 3-month olds. These data suggest that the reduced total systemic clearance of APAP in 12-month-old male Sprague-Dawley rats previously observed cannot be attributed to age-dependent differences in hepatic APAP metabolism. In addition, it is unlikely that differences in renal APAP metabolism contribute to age-dependent APAP nephrotoxicity.     

The effect of osmotic pressure on oligomycin-sensitive ATPase activity and the liberation of Mg2+ from liver mitochondria of rats of various ages]

The influence of osmotic pressure of the incubating medium (25-500 mM sucrose) on oligomycin--sensitive, 2,4-dinitrophenyl-stimulated ATP-ase-activity, Mg2+ release and swelling of the liver mitochondria in 1-, 3-, 12-, 24-months Wistar rats is, investigated to determine age changes of structurally functional state of mitochondria. An increase in the sucrose concentration in the medium from 150 to 500 mM causes almost equal and practically absolute inhibition of ATP-ase-activity in different-age groups of rats, regardless of the presence or absence of Mg2+ ions in the medium A fall of the sucrose concentration to 150-25 mM induces a decrease in mitochondria ATP-ase-activity in Mg2+ free medium in 12- and 24-months rats (to 30 and 22%, respectively). No changes are observed in 1- and 3-months animals. Differences in rates of exogenous NADH oxidation by mitochondria of 1- and 12-months rats as a reflection of inner membrane damage degree are not observed under these conditions. Relative changes in ATP-ase-activity in a Mg2+ free medium with sucrose concentration of 25 mM (compared with 150 mM) correlate (r = 0.82) with those of optical density of mitochondria, measured at light wave length of 520 nm. It is obvious that the liver mitochondria of young and old rats sufficiently differ in spontaneous swelling rate in the media with different osmotic pressure: mitochondria of 1-month rats swell much faster than those of old rats. Considerable age differences of osmotic dependence of Mg2+ output from mitochondria are observed. They depend also on peculiarities of spontaneous organelle swelling dynamics.(ABSTRACT TRUNCATED AT 250 WORDS)     

Involvement of cAMP but not PKA in the increase of corticosterone secretion in rat zona fasciculata-reticularis cells by aging

The effects and mechanisms of aging on corticosterone secretion in zona fasciculata-reticularis (ZFR) cells of ovariectomized (Ovx) rats were studied. Young (3-month) and old (24-month) female rats were Ovx for 4 days before decapitation. ZFR cells were isolated and incubated with different hormones or reagents at 37 degrees C for 30 min. Aging increased the basal secretion of corticosterone both in vivo and in vitro. The adrenocorticotropin (ACTH)-, forskolin-, 3-isobutyl-l-methylxanthine (IBMX)-, 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP)-, and ovine prolactin (oPRL)-stimulated release of corticosterone by ZFR cells was greater in old than in young Ovx rats. H89, an inhibitor of protein kinase A (PKA), decreased the production of corticosterone in ZFR cells from young but not old Ovx rats. Forskolin-, or IBMX-induced production of cAMP was greater in old than in young Ovx animals, which correlated with the increase of corticosterone production by aging. The activity of 11 beta-hydroxylase that converts deoxycorticosterone (DOC, 10(-9) or 10(-8) M) to corticosterone in rat ZFR cells was decreased by age. However, the corticosterone production in response to high dose of DOC (10(-7) M) was indifferent between young and old groups. These results suggest that aging increases corticosterone production in Ovx rats via a mechanism in part associated with an increase of adenylyl cyclase activity and a decrease of phosphodiesterase activity, and then an increase of the generation of cAMP, but not related to either PKA activity or 11 beta-hydroxylase.     

Influence of age on the production of rat spermatozoa, on their concentration in the cauda epididymidis, and on FSH, LH and testosterone plasma levels

Testis samples were taken from young (3 months), middle-aged (12 months) and aged (24 months) male rats, processed, stained and examined via a light microscope. There were no prominent abnormal germinal epithelium and interstitial tissue. However, the aging process promoted a significant decrease in the mean amount of spermatids 19 per cross tubular section, and in the amount of Sertoli cells per cross tubular section in 24-month-old rats. The concentration of spermatozoa in the cauda epididymidis showed a gradual decrease from 3 to 12 and 24 months. After hCG injection all groups of animals exhibited an increase in plasma testosterone level, although the response was smaller in 12- and 24-month animals compared to the young mature (3 months) ones.     

Age-related changes in photosensitive melanopsin-expressing retinal ganglion cells correlate with circadian rhythm impairments in sighted and blind rats

The melanopsin system consists of intrinsically photosensitive retinal ganglion cells containing the photopigment melanopsin (mRGCs). These mRGCs mediate several non-image-forming visual functions, including light entrainment of circadian rhythms. Here we evaluate age-related alterations of the melanopsin system and circadian rhythms in P23H line 1 (P23H-1) rats, a rodent model of retinitis pigmentosa (RP). In homozygous P23H-1 rats and wild-type control rats from the same genetic background (Sprague–Dawley), body temperature and locomotor activity were continuously monitored at 10-min intervals for 7 days, once every 4–5 weeks, between 2 and 24 months of age, using a telemetry transmitter. The distribution and number of mRGCs were assessed in control rats at 12, 18, and 24 months of age and in P23H-1 rats aged 12, 18, 24, and 30 months by immunostaining whole-mount retinas with antibodies against melanopsin. The mean density of mRGCs in control rats showed no significant variations when evaluated at 12 and 18 months of age, and fell by approximately 56% between 18 and 24 months of age. Meanwhile, a significant decrease in the mean number of mRGCs was found in 18-month-old P23H-1 rats as compared to 18-month-old control rats (81% decrease). Parametric and non-parametric analyses of the records showed a gradual age-dependent weakening of body temperature and locomotor activity circadian rhythms robustness in both control and P23H-1 rats from 2 to 24 months of age. However, body temperature and locomotor activity circadian patterns were less robust throughout the experiment in P23H-1 as compared to control rats, with lower amplitude, weaker coupling strength to environmental zeitgebers and higher fragmentation of the rhythms. The present study shows that the degeneration of photoreceptors and inner retinal neurons, characteristic of RP, has age-related degenerative effects on the melanopsin system and is associated with weaker circadian patterns.     

Age-related changes in rat hepatic acetyl-coenzyme A carboxylase

Acetyl-CoA carboxylase (ACC) catalyzes the rate-limiting step in the synthesis of long-chain fatty acids. Since aging influences adiposity, we studied the activity of ACC and its mRNA content in livers of 4-, 12-, and 24-month-old male Fischer 344 rats. The mean (+/- SEM) activity of ACC (mU/mg protein) in liver homogenates from 4-month-old rats was 1.01 +/- 0.14. There was an 80% increase in activity (1.83 +/- 0.27) in 12-month-old rats (P < 0.01). However, there was significantly less activity (0.46 +/- 0.06) in livers of 24-month-old rats (P < 0.001). The total activity of ACC (per g liver) followed the same trend. The enzyme from all age groups was purified by avidin-affinity chromatography. The purified preparation migrated as a major protein band (M(r) 262,000) on sodium dodecyl sulfate (SDS)-polyacrylamide gels. The specific activity of the purified preparation was 1.5, 1.8, and 1.8 U/mg for 4-, 12-, and 24-month-old rats, respectively. The alkali-labile phosphate content was 5.66 +/- 0.17, 5.64 +/- 0.21, and 6.21 +/- 0.35 mols P(i)/mole subunit for 4-, 12-, and 24-month-old rats, respectively. These age-related differences were not significant. The hepatic ACC mRNA measured by ribonuclease protection assay when corrected for G3PDH mRNA was significantly reduced in 24-month-old rats (0.24 +/- 0.03) compared with 12-month-old (0.58 +/- 0.04) or 4-month-old rats (0.43 +/- 0.007) P < 0.01. In summary: (i) Aging in rats is associated with significant changes in ACC activity; (ii) the purified ACC preparations from the three age groups had similar specific activity and similar phosphate content; and (iii) the changes in ACC mRNA content of the liver paralleled the changes in total enzyme activity when 12-month-old rats were compared with 24-month-old rats whereas the increase in ACC activity in 12-month-old rats compared with 4-month-old rats could not be ascribed to changes in hepatic mRNA levels. These results indicate that the age-related changes in hepatic ACC occur at a post-translational level during early years of aging and at a pretranslational level at late states of senescence. These changes may contribute to the age-related alterations in body adiposity.     

Effect of hypophysectomy on liver nuclear ribonucleic acid synthesis in aging rats.

Changes in RNA synthesis in liver nuclei were observed at different ages and after hypophysectomy and hormone replacement in female Sprague-Dawley rats. As determined by the incorporation of [3H]UMP into an acid-insoluble product, RNA synthesis decreased by about 75% in intact rats from 6 months to 24 months of age. This decline with age was not observed in liver nuclei from 24-month-old rats that had been hypophysectomized at 12 months and maintained on a minimal hormone-replacement therapy. Thyroid hormones and somatotropin (growth hormone) had an additive effect on RNA synthesis in liver nuclei from these hypophysectomized rats. The same hormones had no significant effect on intact, age-matched rats. With advancing age, nuclei of intact rats had an increase in the pool of free RNA polymerase and an apparent decrease in the enzyme activity bound to nuclear chromatin. There was no change in total enzyme with age. In hypophysectomized, hormone-treated rats, free RNA polymerase activity decreased and chromatin-bound activity increased. There was no difference in total nuclear RNA polymerase activity between operated or intact rats. However, the ratio of the bound to the free activity was different. These results suggest that the ability of RNA polymerase to bind to chromatin may be involved in the age-related decrease in liver nuclear RNA synthesis of intact rats.     

Wistar大鼠心脏自发性病变的病理学观察

目的了解Wistar大鼠心脏自发性病变发病情况,为长期致癌性研究、老年病学研究及毒性病理学提供背景资料。方法采用160只清洁级Wistar大鼠,雌雄各半,常规饲养,分别在9月龄、12月龄、18月龄、24月龄时处死40只大鼠,HE及Masson三色法染色,观察心脏的病理改变。结果 9月龄Wistar大鼠心脏未见明显病理改变;12月龄Wistar大鼠月龄心脏病变的发病率为2.5%（1/40）,表现为少数心肌细胞变性坏死伴少量以单核细胞为主的炎细胞浸润;18月龄大鼠心脏病变的发病率为57.5%（23/40）,表现为轻至中度心肌病,雄性发病率高于雌性。24月龄大鼠100%（40/40）出现不同程度的心肌病,并有2.5%（1/40）发生心内膜下纤维组织增生。Masson染色显示9月龄大鼠心脏血管周围及心脏瓣膜环下有少量胶原纤维,随年龄增长,血管周围及心脏瓣膜环下胶原纤维逐渐增多,并延伸入心肌细胞间。结论随年龄增长,大鼠心脏自发病变比率升高,主要病变为心肌病,偶尔可发生心内膜下纤维组织增生;胶原纤维沉积首先发生于血管周围及心脏瓣膜环下,随年龄增长而增多,可能与大鼠心肌病的的发生密切相关。     

Age-related changes in antioxidant defence mechanisms and peroxidation in isolated hepatocytes from spontaneously hypertensive and normotensive rats

The effects of age and hypertension on the antioxidant defence systems and the lipid peroxidation in rat isolated hepatocytes were studied. Four different age groups (1,3,6 and 12 months) were considered in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Age-associated changes were observed on vitamin E status, glutathione (GSH) level, MDA formation and glutathione peroxidase (GSH-Px) activity in both strains. Maximal levels or activities of these parameters were found at 3 and 6 months, except for MDA which was low at 3 months. Then, a fall was observed at 12-month-old compared to 6-month values. In addition, GSH-Px activity was significantly lower in SHR than in WKY rats, except at the age of one month. The decrease of this enzyme activity could induce an increased cellular generation of radical species and lipid peroxidation, which might be link to hypertension.     

The effect of age and cholesterol on the rat lung beta-adrenergic system

To assess the influence of membrane lipid composition on beta-adrenergic receptor number and adenylate cyclase activity in aging, we investigated the effect of cholesteryl hemisuccinate on these parameters in lung membranes of 3-, 12-, and 24-month-old CDF (F-344) rats. When cholesteryl hemisuccinate (0.5 mg/ml) was incubated with lung membranes, beta-adrenergic receptor density was increased by 70%. This effect was the same for each age group studied and indicated that the density of both basal and CHS-sensitive receptors is unaltered in rat lung with age. Forskolin, NaF, p[NH]ppG, and isoproteronol-stimulated adenylate cyclase activity is 30% lower in lung membranes from aged rats. Since enzyme activity is affected by the lipid environment and membrane composition often changes with age, we assessed adenylate cyclase activity following cholesteryl hemisuccinate incorporation. There was up to a 75% decrease in adenylate cyclase activity following cholesteryl hemisuccinate incorporation in lung membranes in each of the three age groups. In untreated membranes, there was no significant difference in cholesterol or lipid phosphate content with age. These data suggest that cholesterol content does not account for alterations in senescent rat lung adenylate cyclase activity.     

Phospholipid hydroperoxide glutathione peroxidase activity and vitamin E level in the liver microsomal membrane: effects of age and dietary alpha-linolenic acid deficiency

Age and diet-induced variations of phospholipid hydroperoxide glutathione peroxidase (PHGPx) activity and alpha-tocopherol concentration in the liver microsomal membrane were studied in male Wistar rats fed a semipurified diet either balanced in n-6 and n-3 polyunsaturated fatty acids (PUFA) (Control) or deprived of alpha-linolenic acid, i.e. n-3 PUFA (Deficient) over two generations. The animals were studied at the age of 6 months (adult) or 24 months (old). Both PHGPx activity and vitamin E level were significantly higher in 24-month old rats as compared to 6-month old rats. By contrast, the thiobarbituric acid reactive substances (TBARS) following stimulated in vitro peroxidation of membrane lipids were markedly lower (P < 0.01) with aging. The fatty acid composition of microsomal membrane phospholipids (PL) was also considerably modified by age. In particular, the levels of arachidonic acid and total n-6 PUFA were lower (P < 0.001) whereas n-3 PUFA levels were higher (P < 0.001) in most PL main classes. The alpha-linolenic acid deficiency markedly influenced these age-related changes. The higher PHGPx activity in the old rats as compared to the adult rats was only significant in those fed the control diet. In the 6-month old rats (but not in the 24-month old rats), the deficient diet led to a higher membrane vitamin E level and to lower TBARS production than the control diet. The results suggest that the nature of dietary PUFA may influence the age-related variations in this pair of membrane antioxidants and also in the fatty acid composition of microsomes.     

Changes in membrane-bound leucine aminopeptidase activity during maturation and ageing of brain.

Aminopeptidases are believed to be enzymes that regulate the activity of various neuropeptides. However, their physiological role, as well as their mechanisms of regulation, are not well understood. To analyze a part of the regulatory mechanisms that control the activity of these enzymes, the subcellular distribution of membrane-bound leucyl aminopeptidase activity was studied in rat brain during development and ageing. Except in fetuses, the enzymic activity was greatest in the microsomal fraction in all ages tested. Except in microsomal and myelin fractions, compared with fetuses, leucyl aminopeptidase activity showed a decrease in 1-week-old rats and a subsequent increase to adult levels in 1-month-old rats. This profile differed in the microsomal fraction, where the activity increased steadily up to 1-month-old rats. After this age, the activity decreased progressively in 5-month and 24-month-old rats. These results may reflect changes in the functional status of the susceptible substrates during development and ageing.     

Age variations in ethylmorphine demethylase and benzopyrene hydroxylase activities in rat liver microsomes

The ethylmorphine demethylase activity of the rat liver microsomes was higher in three-month animals (as compared to one-month), remained at a high level in the 12-month and decreased in old rats. The benzopyrene hydrolase activity increased in three-month animals, decreased in 12-month rats and remained the same with subsequent ageing of the organism. Asynchronicity of variations in the oxidation rate of different xenobiotics with ageing is considered as a result of changes in substrate specificity of the monooxygenase system due to metabolic peculiarities which reflect the age development of the organism and extinction of the reproduction function.     

Effects of brief starvation on brain protease activity

Changes in the activity of proteases (cathepsin D and calpains) caused by 48-h food withdrawal were studied in the brain, liver, kidney, spleen, and heart of 3-, 12-, and 24-month-old Fischer rats. Cathepsin D activity was similar in brain, liver, and heart of control animals; in kidney it was 5-fold higher and in spleen about 10-fold higher. With age, activity increased in all organs tested except spleen. Brief starvation caused no change of cathepsin D activity in brain, but caused an increase in liver and a decrease in spleen. Neutral proteolytic activity in control was highest in the pons-medulla-cerebellum fraction of brain, and activity in liver and heart was below that in brain. Activity increased with age in brain and decreased in other organs. Brief starvation in young animals caused an increase in activity in brain, and a decrease in liver and spleen. Isolated calpain II activity was high in control brain. It increased with age in the cerebrum. Brief starvation resulted in a decrease in the brain. The results indicate that the protease content of the brain is altered with age and in malnutrition, with changes not being the same for all proteases, and changes in brain being different from those in other organs.Special issue dedicated to Dr. Louis Sokoloff.