Guanylate cyclase activity in rat liver and other tissues with starvation and streptozotocin-induced diabetes mellitus.

Guanylate cyclase activities in supernatant and particulate fractions of homogenates from various rat tissues were examined in fed and fasted normal animals and in those with diabetes mellitus induced with streptozotocin. With fasting guanylate cyclase activity in supernatant fractions increased in liver and epididymal fat, decreased in kidney and lung, and was unchanged in cerebral cortex and skeletal muscle. Lung particulate activity also decreased with fasting while particulate activities in other tissues were unchanged. In diabetic animals soluble but not particulate activity was less in several tissues and the effect of fasting on soluble liver guanylate cyclase was absent. The effect of fasting on soluble liver guanylate cyclase reversed with refeeding animals and was associated with a decrease in the apparent K_m for GTP as well as an increase in V. An inhibitory material was found in livers from fed but not fasted animals. The inhibitory material had properties of a nucleotide and inhibited guanylate cyclase in a competitive manner. Thus, soluble and particulate guanylate cyclase activities can be influenced independently of one another in the same and different tissues with fasting, refeeding, and diabetes mellitus. Some of these effects may be attributable to altered levels of small heat-stable inhibitory materials such as nucleotides.     

The characteristics of hGH binding to the liver macrophages

Macrophages isolated from female rat liver as well as hepatocytes bind 125I-hGH. This study compares the effect of sex of the rat, hypophysectomy (hypox) and preincubation of the cells with oPrl on the binding of 125I-hGH to the cells. The percent of 125I-hGH to the hepatocytes was decreased in cells from hypox female and male rats, and hepatocytes preincubated with oPrl to 0.43, 0.21 and 0.39, respectively, of that observed in hepatocytes from normal female rats. In the hepatocytes from normal female, hypox female, and male rats, hGH was the most effective competitor for 125I-hGH binding with an ID50 of 0.73-0.99 nM. The concentration of oPrl, bGH and rGH that produced half-maximal inhibition (ID50) of 125I-hGH binding to hepatocytes from female rat liver was 6.3, 100, and 420 nM respectively. In hepatocytes from male and hypox female rats, and hepatocytes preincubated with oPrl, the ID50 for bGH and rGH varied from 2.1 to 15.9 nM. The percent of 125I-hGH bound by the macrophages from hypox female and male rats, and macrophages preincubated with oPrl was 0.06, 0.15 and 0.18, respectively, of that bound by macrophages from normal female rat liver. In contrast to hGH binding to the hepatocytes, the ID50 for hGH was 6 to 180-fold greater in macrophages from hypox female and male rats, and macrophages preincubated with oPrl compared to that observed in macrophages from normal female rats, Rat GH was the most effective competitor for 125I-hGH binding in the macrophages from the hypox female and male rat liver with ID50 of 5.5 and 85 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects on extrahepatic UDP-glucuronosyltransferases in hypophysectomized rat

The effects of hypophysectomy on hepatic and extrahepatic UDP-glucuronosyltransferase activities in adult male rats were observed. UDP-glucuronosyltransferase activities toward 1-naphthol decreased to 20-30% of control in the liver, kidney, lung, and testis. The mRNA of UGT1A6, which is an isoform contributing to the glucuronidation of various phenolic xenobiotics such as 1-naphthol, were decreased drastically in the liver, kidney, and testis by hypophysectomy. However, while bilirubin UDP-glucuronosyltransferase activity in the liver intensified, there was only a slight increase in the activity in the kidney and no alteration in the lung. The mRNA of UGT1A1, which is an isoform contributing to the glucuronidation of bilirubin, increased significantly in the liver and slightly in the kidney after hypophysectomy. These inductions and reductions in enzymatic activities and mRNA levels in each tissue were restored to control levels by intermittent injections of rat growth hormone. Interestingly, while hepatic UGT activity toward bisphenol A remained constant in hypophysectomized rats, the testicular UGT activity declined to 10-15% of control but returned to normal levels following growth hormone treatment, suggesting that an unknown UGT isoform (s) mediates bisphenol A glucuronidation in the testis. These results indicate that the expression of extrahepatic UGT is isoform-specific and regulated differentially in tissues by the pituitary gland.     

Regional differences in ribonuclease content of rat and mouse kidney

Kidney cortex, red medulla and white medulla were separated into nuclei, mitochondria, microsomal and 105000g supernatant fractions. Assay of RNAase (ribonuclease) activity at pH7.8 revealed that, for each subcellular fraction, activity was much greater in cortex than in red or white medulla; this was true for both free RNAase and total (free plus latent) RNAase. For example, the free RNAase activity in the 105000g supernatant of cortex was 5 and 8 times higher than in red and white medulla respectively. No latent RNAase activity was found in any particulate fraction. Latent supernatant RNAase activities (suggesting presence of bound RNAase inhibitor) were similar in cortex and medulla. The cortex supernatant contained minimal free RNAase inhibitor, whereas that of the red and white medulla showed about one-third and one-tenth respectively of the inhibitor activity measured in liver. Adrenalectomy did not change RNAase activity in any fraction nor the content of free RNAase inhibitor in the kidney supernatant, but did decrease the liver RNAase inhibitor content by 40%. In supernatants from mouse kidney, both free and total RNAase activities of both cortex and red medulla were similar to those of rat red medulla. Mouse cortex contained appreciably higher amounts of free RNAase inhibitor than rat cortex. The difference between the rat and mouse cortical RNAase activity and inhibitor content may help explain the relative ease with which satisfactory renal polyribosome profiles were obtained from mouse kidneys. Our results, as well as those of Kline & Liberti [(1973) Biochem. Biophys. Res. Commun. 52, 1271–1277], showing that renal red and white medulla are more active than cortex in protein synthesis, are consistent with the hypothesis that the RNAase–RNAase-inhibitor system may participate in the regulation of protein synthesis.     

Induction of specific human growth hormone binding sites in rat liver by human growth hormone.

125I-Labeled hGH was bound to liver plasma membranes which were obtained from female rats. The binding was displaced by hGH, hPRL, bPRL, rPRL and bGH but not by rGH. This result indicated that hGH was bound to lactogenic binding sites in rat livers. After hypophysectomy, the binding was markedly decreased. Treatment of hypophysectomized rats with hGH (80 micrograms/day) for 10 days increased the binding sites for hGH. These binding sites were different from those found in normal female rat livers because of their high affinity and specificity for hGH. These results indicate that hGH induces specific binding sites for hGH in rat livers.     

Heterogeneous cellular expression of creatine kinase isoenzyme during normal rat heart development

The degree to which developmentally related alterations in cardiac creatine kinase (CK) activity reflect modification of CK isoenzyme gene expression remains uncertain. The present studies addressed this question by assessing multiple aspects of CK in rat heart during the perinatal to adult transition. In addition to whole tissue, isolated and purified muscle and nonmuscle cells were studied, as well as myofibrillar, mitochondrial, and cytosolic subcellular fractions. Whole homogenate CK enzyme specific activity nearly doubled during the weanling to adult developmental period. Muscle cell CK activity increased by a similar magnitude. Nonmuscle cell activity decreased. In the adult heart, both myofibrillar and mitochondrial CK activities were augmented versus the weanling heart. The cytoplasmic fraction activity held constant during development. Electrophoretic isoenzyme analyses of both weanling and adult cardiac muscle cells indicated the presence of mitochondrial CK and MM-CK isoforms. Weanling heart nonmuscle cells contained mitochondrial, MM, MB, and BB isoforms; however, BB isoform was not detected in the adult heart nonmuscle cells. Arrhenius plots provided information regarding heart muscle and nonmuscle cell alterations during development. CK activation energies were also determined for whole tissue, muscle/nonmuscle cells, myofibrils, mitochondria, and cytosol. Results demonstrate that heterogeneous muscle/nonmuscle cellular composition and differential myofibrillar/mitochondrial subcellular composition account for normal, developmentally related changes in heart CK enzyme activity. CK isoenzyme gene expression changes were not detected in cardiac muscle cells, and transition of CK-B to CK-M gene expression is limited to nonmuscle cells during normal, weanling to adult development in the rat heart.     

Regulation of hepatic malic enzyme by perfluorodecanoic acid

Perfluorodecanoic acid (PFDA) administration to adult male rats increased both the activity of hepatic malic enzyme and liver weight in a dose-dependent manner. Hepatomegaly and augmented activity of malic enzyme in liver were apparent within one day following PFDA administration and reached a plateau by three days posttreatment. Malic enzyme quantity per liver in PFDA-treated rats was elevated within one day following dosing and increased continually throughout five days posttreatment. Administration of PFDA to rats in the fed state also led to an increase in the specific activity of hepatic malic enzyme that peaked at three days following dosing. When compared to the fed condition, rats fasted for 48 hours had a decrease in both relative liver weight and the quantity of supernatant protein per liver. The total activity (U/liver) and specific activity of malic enzyme in the liver were also reduced in the fasted state. During the 24 hours after treatment in rats fasted for 48 hours, the body weight as well as the absolute and relative liver weight of animals receiving vehicle declined continuously in the absence of feed. Following the administration of PFDA to fasted rats, body weight was maintained until eight hours posttreatment but then declined at a rate similar to that found with the vehicle-treated group. Absolute and relative liver weight in PFDA-treated rats were increased significantly at eight hours posttreatment when compared to those receiving vehicle, and this increment was maintained throughout the rest of the 24 hours following dosing. While the activity and enzyme content of hepatic malic enzyme decreased in the vehicle-treated group, administration of PFDA to rats fasted for 48 hours prevented their decline. The specific activity of hepatic malic enzyme in 48 hours fasted rats receiving PFDA was also elevated significantly at 16 hours posttreatment. Thus, the administration of PFDA to the adult male rat in both the fed and fasted nutritional states was found to regulate hepatic malic enzyme by not only increasing enzyme quantity but also by augmenting the specific activity, (ie, catalytic state) of the enzyme.     

Different tissue distribution and hormonal regulation of messenger RNAs encoding rat insulin-like growth factor-binding proteins-1 and -2.

The insulin-like growth factor-binding proteins IGFBP-1 and IGFBP-2 are low mol wt IGFBPs that are similar in structure. They are not glycosylated and have a homologous amino acid sequence, including the number and position of 18 cysteine residues and a carboxyl-terminal Arg-Gly-Asp sequence that can be recognized by cell adhesion receptors. The present study demonstrates that expression of mRNAs encoding the two BPs differs in some fetal rat tissues and in the livers of adult rats after hypophysectomy, fasting, or streptozotocin-induced diabetes. As determined by Northern blot hybridization using cDNA probes for rat IGFBP-2 or human IGFBP-1, both mRNAs are expressed at high levels in liver of 21-day gestation and 1-day-old rats and at lower levels in 21- and 65-day-old rat liver. Levels of both mRNAs are higher in liver than in other fetal rat tissues. The relative abundance of the two mRNAs in most fetal tissues is similar to that in liver, except that kidney and brain have 8-fold and more than 25-fold higher relative levels of IGFBP-2 mRNA, respectively. IGFBP-2 mRNA is about 10- to 20-fold increased after hypophysectomy or fasting, whereas IGFBP-1 mRNA is relatively unchanged. IGFBP-2 mRNA levels are decreased completely by refeeding fasted rats for 3 days, but only partially decreased by treatment of hypophysectomized rats with GH, cortisone acetate, T4, and testosterone for 4 days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in distribution of ribonuclease isoenzymes in cytosol and granules in normal human granulocytes and in granulocytes of patients with chronic granulocytic leukemia (CGL)

Distribution of ribonuclease (RNAase), acid phosphatase (acid Ph-ase) and beta glucuronidase (BGU) between the granule, cytosol-soluble and post-granule fractions in normal human granulocytes and in granulocytes of chronic granulocytic leukemia (CGL) was studied. CGL granulocytes were found to display relative RNAase activity 1.2 times higher, relative acid Ph-ase activity 2.5 times higher than normal granulocytes. The granule fraction of CGL granulocytes showed 1.4 times higher relative RNAase activity but 0.87 times lower acid Ph-ase activity and the same BGU activity as normal granulocytes. On the other hand, the supernatant soluble fraction of CGL granulocytes showed 4.4 times higher relative RNAase activity, 1.2 times higher relative acid Ph-ase activity and BGU 2.2 times higher than in cytosol soluble fraction of normal granulocytes. Thus, cytosol soluble fraction of CGL granulocytes show a relative activity of the lysosomal enzymes studied which is remarkably higher than in normal granulocytes. The percentage distribution of RNAase, acid Ph-ase and BGU showed that CGL granulocytes contain only 36% of total RNAase activity versus 46% of that in normal ones. On the other hand, CGL granulocytes in cytosol soluble fraction will contain 48% of total RNAase versus 29% of total RNAase in cytosol of normal granulocytes. The isoenzyme profiles of RNAase of granule fractions were similar in normal and CGL granulocytes, while the RNAase isoenzyme profiles of cytosol fractions were different for normal and CGL granulocytes, indicating that some essential part of CGL granulocyte cytosol RNAase differs from RNAase contained in granules and in cytosol of normal granulocytes.     

Developmental Changes in Rat Liver Xanthine Oxidase(s) and Its Intracellular Distribution

Developmental change and subcellular distribution of xanthine oxidase in the rat liver were examined.

The specific activity of the fetal liver xanthine oxidase increased sharply to the levels of the adult liver on the day of the birth. After birth, the activity dropped rapidly and on the 14th day after birth it was about 1/4 of adult level. Then the activity was regained and around 28th day after birth it was about the same as in adult level.

In the livers from 80 days old rats, about 60% of total xanthine oxidase activity was found in soluble fraction and the rest was distributed among particulate fractions including microsomal, lysosomal, mitochondrial and nuclear fractions.

In contrast to the adult livers 80% of total xanthine oxidase activity in fetal liver was found to be in particulate fractions.

From kinetic studies of xanthine oxidases in particulate and soluble fractions it was suggested that xanthine oxidase in soluble fraction and xanthine oxidase in particulate fraction might be different in their natures of protein molecule.     

Changes of gamma-glutamyltranspeptidase activity in the rat during development and comparison of the fetal liver, placental and adult liver enzymes

Changes in the activity of gamma-glutamyltranspeptidase (GGT, EC 2.3.2.2) during development in rats were investigated. The activity of GGT in fetal liver increased rapidly immediately before birth, reached a maximum at birth and then decreased rapidly within a week after birth to nearly the level in adult rat liver. In contrast, placental GGT showed higher activity at an early stage (from day 13 to day 15) of the gestation period, but the activity decreased in the last part of fetal life. The activity in the amniotic fluid increased significantly just before birth, in parallel with the increase of activity in the fetal liver. No change of activity in the uterine wall was observed throughout gestation. The kinetic and immunological properties of partially purified GGTs from fetal liver and placenta were almost identical with those of adult liver GGT. However, the activity of soluble GGT in fetal liver was less effectively inhibited by antibody against adult kidney GGT. Thus, it is likely that at least one isozyme of GGT is present in the soluble fraction of fetal liver.     

Isolation of ribonuclease-free intact polyribosomes from rat kidney.

High levels of RNAase present in rat kidney have prevented isolation of intact polyribosomes from this tissue. This problem has been circumvented by a thorough in situ arterial perfusion of rat kidney, coupled with homogenization of the perfused rat kidney in heparin and detergents-fortified high-speed supernatant prepared from rat liver. This procedure reduced RNAase activity in the homogenate by as much as 70%. Sedimentation of the polyribosomes from this homogenate through a layer of 2.0 M sucrose resulted in a 78--80% yield of polyribosomes from the rat kidney. The resulting polyribosomal pellet contained less than 8% of the RNAase activity present in polyribosomes from non-perfused rat kidney. The remaining RNAase activity was separated from the larger polyribomes by sucrose density gradient centrifugation. The majority of the polyribosomes were larger than tetramers. This procedure also incrased both the yield and size of polyribosomes from rat and mouse liver.     

Changes in the activity of trout lysosomal enzymes during fasting

Activity of lysosome enzymes (acidic phosphatase, beta-glucosidase, DNAase, RNAase and cathepsin D) is determined for its variation in different organs of rainbow trout during complete fasting. It is shown that the activity of most enzymes of concern almost in all organs except skeletal muscles is on the higher level in trouts fasted for 30 days than in the control ones. With an increase of the fasting term to 60 days the acid phosphatase, DNAase, RNAase activity decreases while the glucosidase and cathepsin D activity in some organs increases. Variations detected in the enzyme profile of the trout lysosomes under fasting are of adaptive character.     

Protein degradation in rat liver during post-natal development.

Protein degradation rates for liver subcellular and submitochondrial fractions from neonatal (8-day), weanling (25-day) and adult rats were estimated by the double-isotope method with NaH14CO3 and [3H] arginine as the radiolabelled precursors [Dice, Walker, Byrne & Cardiel (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 2093-2097]. Decreased protein degradation rates were found during post-natal development for homogenate, nuclear, mitochondrial, lysosomal and microsomal proteins. A decrease in degradation rates for the immunoisolated subunits of monoamine oxidase and pyruvate dehydrogenase was also observed in neonatal and weanling rats respectively. The results suggest coordinate degradation of the subunits of the multi-subunit enzyme pyruvate dehydrogenase. Pyruvate dehydrogenase has a faster rate of degradation in adult rat liver than does cytochrome oxidase. Data analysis suggests heterogeneity of protein degradation rates in the mitochondrial outer membrane and intermembrane space fractions at each developmental stage but not in the mitochondrial inner membrane or matrix fractions. Results obtained for protein degradation rates in adult rat liver by the method of Burgess, Walker & Mayer [(1978) Biochem. J. 176, 919-926] in general confirmed the results obtained for the adult rat liver by the above method. No evidence of a subunit-size relationship for protein degradation was found for proteins in any subcellular or submitochondrial fraction.     

INCORPORATION IN VIVO OF RADIOACTIVE LEUCINE INTO NEURONAL AND GOAL NUCLEAR PROTEINS OF RAT BRAIN

Purified neuronal and glial nuclei were separated from rat brain cells. The fraction rich in neuronal nuclei contained 68 ± 9 per cent neuronal nuclei and the fraction rich in glial nuclei contained 89 ± 6 per cent glial nuclei. The fraction rich in neuronal nuclei isolated from cells of adult rat brain incorporated l -[4,5-³H]leucine into TCA-insoluble material at a rate comparable to those of the microsomal and the soluble fractions of the brain, and at a much higher rate than the fraction rich in glial nuclei. The proteins soluble in buffered-saline, the acid-soluble deoxyribonucleoproteins, and the residual proteins of the neuronal nuclei are apparently the proteins which account for the higher specific activity of neuronal proteins compared with glial nuclear proteins. In liver and kidney, the incorporation of [³H]leucine into nuclear proteins was lower than into other subcellular fractions from the same organs.     

Changes in Creatine and Urea Formation in Rats Fasted and Fed Low Protein Diets

Changes in the time course of the urinary excretion of creatinine, creatine and urea, and the activities of kidney transamidinase and liver urea-cycle enzymes were investigated in rats fasted and fed on a 10% casein diet and 10% casein diets supplemented with 10% glycine and/or 1.4% arginine.

The urinary total-creatinine of the fasted rats increased extremely during fasting for 7 days, while that of the animals given the 10% casein diet supplemented with glycine and arginine rose exceedingly on the 3rd day and thereafter no significant change was observed. Most of the increase of total-creatinine could be accounted for by the increase of creatine. The activity of kidney transamidinase in the fasted rats decreased in the 3rd day and thereafter kept nearly constant. The transamidinase activity of rats fed on the 10% casein diet after giving a protein-free diet for 5 days increased in the 3rd day. An inverse relation was observed between the urinary creatine and the transamidinase activity. The urinary urea increased in the rats fasted or fed on the 10% casein diets with the supplement of glycine and/or arginine. In fasting, the activities of liver urea-cycle enzymes, except arginase, had a tendency of increasing with the lapse of time. The arginase activity remained more or less constant. The reason of the extreme increase of urinary creatine during starvation was discussed.     

Alkaline ribonuclease and ribonuclease inhibitor in mammary gland during the lactation cycle and in the R3230AC mammary tumour.

Alkaline RNAase (ribonuclease) and RNAase inhibitor were assayed to determine the potential role of the degradative process in regulating the amount of RNA in the mammary gland and mammary tumour. Very little free alkaline RNAase activity was found in the cytosol fraction of the mammary gland of virgin, pregnant, lactating or involuting Fischer rats. However, addition of p-chloromercuribenzoate to the assay medium revealed latent RNAase which, when expressed on a DNA basis, decreased during pregnancy and lactation. The cytosol latent RNAase is stable in 0.125 M-H2SO4. The non-cytosol RNAase activity also decreased during pregnancy and lactation. Addition of Triton X-100 produced slightly higher activity at all stages tested. The inhibitor activity in rat mammary gland was very low before pregnancy, increased gradually during pregnancy and more dramatically at parturition, continued to increase throughout lactation and returned to resting-gland values by the sixth day of involution. The increase during pregnancy may be due to the increased cellularity of the gland, whereas the gain during lactation was more than could be accounted for by increases in cell number. The R3230AC transplantable mammary tumour resembles the normal gland in early lactation with respect to both its cytosol and non-cytosol alkaline RNAase activities and its moderately high content of RNAase inhibitor. The relatively high inhibitor and low RNAase activities in both the gland of the lactating rat and in the tumour are of potential significance in maintaining high amounts of RNA and increased rates of protein synthesis in these tissues.     

Metabolic and mitochondrial disturbances in streptozotocin-treated Sprague-Dawley and Sherman rats

This study provides explanation for conflicting evidence in the literature relating to changes in mitochondrial function and metabolic parameters during chemically induced diabetes. Diabetes of 3 days' duration (early ketosis) did not alter heart, kidney, or liver mitochondrial respiratory rates with glutamate or succinate even though serum glucose and triglycerides were elevated. Diabetes of 5 weeks' duration did not alter kidney or liver mitochondrial function in the fed adult rat although weight gain was depressed. The amount of kidney mitochondrial protein isolated per gram of tissue was increased by 30% in the diabetic. This increase was reversed by insulin treatment as were the other biochemical modalities measured. Superimposition of a 24-hr fast resulted in enhanced gluconeogenesis as measured by an animal weight loss of 17% within 24 hr (liver weight loss, 21%) and an elevation of serum urea nitrogen by 180% compared to fasted control. Respiratory rates of diabetic kidney mitochondria with glutamate were unaffected in the fasted animal whereas diabetic liver mitochondrial respiratory rates during succinate oxidation were reduced by 43%. Respiratory control was unchanged in the fasted diabetic rat. All the observed changes were reversed by insulin. Variation in the serum and liver metabolic indices (urea nitrogen, creatinine, glycerol, free fatty acids, free amino acids, triglycerides, and glucose) and liver mitochondrial responses to 7 weeks of chemically induced diabetes was affected by the rat strain, Sprague-Dawley versus Sherman, and rat weight, 72 g versus 222 g. Liver mitochondrial respirations in fed Sherman rats were not depressed by diabetes. Both rat strains had elevated liver free fatty acids and glutamate dehydrogenase activity in the diabetic state. Serum leucine, isoleucine, and valine were more elevated and serum lysine and arginine were more depressed in the diabetic Sprague-Dawley rat than in the Sherman rat. Conjectures on these results are presented in the text.     

On lysosomal fragility and induction of liver hexose-monophosphate dehydrogenases in the fasted-refed rat.

Young adult male rats were fasted for 3 days, then fed a glucose-rich diet, ad libitum. At the end of the fasting period, the specific activity of liver glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase was decreased to 60% of control (nonfasted) levels. After 24 to 72 h of refeeding, the specific activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase increased seven- and twofold, respectively. During the fasting period, the liver lysosome fragility increased, as judged by increased release of bound acid phosphatase and β-N-acetylglucosammidase activity during standard homogenization. Three hours after feeding a carbohydrate-rich diet, a further increase in liver lysosomal fragility was observed that returned to control values prior to the induction of the dehydrogenases. Similarly, the susceptibility of liver lysosomes from fasted rats to increased fragility by the intraperitoneal injection of glucose or galactose was also observed. Prior starvation was not a requisite for labilization of lysosomal membranes by injected glucose, but induction of the pentose phosphate shunt dehydrogenase was not observed.In a group of 6-week old male rats fed a commercial pellet diet throughout, the injection of insulin caused no change in liver lysosomal fragility, though hypoglycemia resulted. Similar animals made diabetic by treatment with Streptozotocin and diabetic rats given insulin, showed no change in liver lysosmal fragility based on the percentage of free to total activities of β-N-acetylglucosaminidase, β-glucuronidase, β-galactosidase, and Cathespin D. However, when adult female rats were fasted for 24 h, then injected with sufficient insulin to produce hypoglycemia, liver lysosomal fragility, based on the release of β-N-acetylglucosaminidase during homogenization, increased nearly threefold. These studies demonstrate that stimulated lysosomal fragility can be initiated by refeeding fasted animals a carbohydrate-rich diet, by intraperitoneal injections of fasted rats with glucose or galactose, or by administering insulin alone to fasted rats. However, hyperglycemia induced by diabetogenic doses of Streptozotocin, or hypoglycemia induced in well-fed animals by insulin injection failed to elicit an enhanced liver lysosomal fragility. Whether induction of the enzymes of lipogenesis by rat liver is dependent upon a prior lysosomal membrane labilization remains to be determined.