Comparative induction of unscheduled DNA synthesis by physical and chemical agents in non-proliferating primary cultures of rat hepatocytes

The incorporation of [3H]thymidine into DNA due to unscheduled DNA synthesis (UDS) induced by N-OH-2-acetylaminofluorene (N-OH-AAF), aflatoxin B1 (AFB1), ethyl methanesulfonate (EMS) and ultra-violet light was quantitated by autoradiography and by scintillation spectrometry on acid precipitable macromolecules or DNA insolated by isopycnic banding in cesium chloride (CsCl). Dose-dependent increases in UDS due to N-OH-AAF and AFB1 treatment were found. Only 2-fold increases at the highest dose levels were found, however, when incorporated [3H]thymidine was quantitated by scintillation spectrometry. Seven, 11, and 25-fold increases in UDS induced by AFB1, N-OH-AAF and ultra-violet light, respectively, were found when incorporated [3H]thymidine was quantitated by autoradiography, indicating a high sensitivity for detecting 'long patch' repair by this technique. Scintillation spectrometry was completely ineffective in detecting EMS-induced UDS, whereas autoradiography demonstrated a small, but significant induction in [3H]thymidine incorporation at high dose levels. The non-proliferative nature of the primary hepatocyte prohibits the uniform radioactive prelabeling of DNA, necessary in other techniques, for the detection of 'short patch' repair induced by compounds such as EMS. Therefore, the sensitivity of the primary cultured rat hepatocyte in conjunction with UDS for detecting DNA damage caused by mutagens and carcinogens which induce 'short patch' repair may be limited to the autoradiographic analysis of the unscheduled incorporation of [3H]thymidine.

[New information on the biotransport of the x-ray contrast substance, bilignost, in the hepatocyte]

Electron microscopic studies on rats have shown that promptly (30 sec--5 min) after administration to the portal vein, bilignost progresses diffusely, through the cell membrane, from Disse's space and intercellular slits to the hepatocytic cytoplasm. It is accumulated by the cytoplasm and subcellular organellas and then is rapidly eliminated from the cells to bile capillaries.

Effects of supplementation and depletion of a single essential amino acid on hepatic polyribosome profile in rats

The effects of supplementation and depletion of one essential amino acid on hepatic polysome profile of rats were investigated in the meal-feeding condition. Only methionine supplementation to a protein-free diet reduced the population of monosomes and disomes per total profile. The single supplementation of other essential amino acids did not change the polysome profile as compared with the protein-free diet group. The results suggested that, when rats were fed a protein-free diet, methionine is the first limiting amino acid for liver protein synthesis. In the case of depletion of one essential amino acid (tryptophan, methionine-cystine, threonine, phenylalanine-tyrosine, leucine, isoleucine, valine, lysine), the values of monosomes and disomes per total ribosomes of rats were significantly higher than that of rats fed a complete amino acid mixture diet. In rats tube-fed the threonone-deficient diet three times a day for 3 or 5 days, the polysomes in liver were aggregated heavier than those of rats that received a complete diet. These results indicated that, under meal-feeding condition which may be considered more a physiological condition than force-feeding, the deficiency of single essential amino acid generally causes the disaggregation of hepatic polysomes leading the decreased synthesis of hepatic proteins.

Polypeptide-synthesizing activity of eukaryotic chromatin. Properties, dependence on poly(ADP-ribose) and connection with the cell cycle

Isolated nuclei incubated with [14C]protein hydrolysate are shown to incorporate labelled amino acids into the acid-insoluble fraction. Purified chromatin and the complex of DNA with firmly bound proteins possess similar ability. The optimum pH of the reaction is 6.5-7.0, 2 mM MgCl2 stimulates incorporation, the temperature optimum is 37-40 degrees C. Chloramphenicol depresses incorporation by 70%, puromycin by 40%, cycloheximide does not affect the chromatin activity. Incorporation does not depend on the presence of ATP or GTP, and is substantially inhibited by deoxyribonuclease but not by ribonuclease treatment of chromatin or of the nuclei. Specific activity of firmly bound chromatin non-histone proteins is higher than that of labile bound ones; histones are not labelled. After pronase treatment of proteins radioactivity changes to an acid-soluble state. The molecular weight of isolated labelled polypeptides is about 6000 as shown by gel filtration and the analysis of NH2-terminal amino acids. Labelled polypeptides firmly bound to DNA consist of 7-10 amino acids. Specific activity of proteins firmly bound to DNA increases linearly with the time of incubation of chromatin with [14C]protein hydrolysate, the activity curve of labile bound non-histone proteins has a distinct sygmoid character. The polypeptide-synthesizing activity of rat liver chromatin increases between 9 h and 21 h after partial hepatectomy. Irradiation with 800 rads 30 min before the operation prevents activation of amino acid incorporation. From nine amino acids studied alanine, methionine, lysine, tyrosine and arginine are not incorporated in the system described. Glutamic acid is polymerized most effectively. Glutamine, asparagine and glycine are incorporated 7-8 times less. The data are given indicating that the incorporation is not random when an amino acid mixture is present. Preincubation of chromatin with NAD+ but not with its analogues increases the polypeptide-synthesizing activity of chromatin. The activation is prevented by thymidine and nicotinamide. Storage (18 h at 2-4 degrees C) brings about a complete loss of the polypeptide-synthesizing activity of chromatin. The ability of 'old' chromatin to incorporate amino acids can be restored by preincubating it with NAD+. Storage of chromatin in the presence of 5 mM adenosine 3',5'-monophosphate (cAMP) does not result in decrease of the polypeptide-synthesizing activity. It is assumed that poly-(ADP-ribose) is the energy source for amino acid activation in the system described.

Distribution and repair of O6-methylguanine in different fractions of rat liver DNA after dimethylnitrosamine administration

The removal of the promutagenic DNA alkylation product O6-methylguanine from different fractions of rat liver DNA has been examined using the technique of DNA-DNA reassociation. Male Wistar rats were given a low non-toxic dose of N,N-dimethylnitrosamine (DMN) (2 mg/kg) and killed 3 or 18 h later (a period corresponding to the removal of 50% of the O6-methylguanine from 'total' liver (DNA). DNA was extracted from liver, denatured in alkali and incubated at 60 degrees C for periods corresponding to the reassociation of highly repetitive (polycopy), middle repetitive and 'unique' sequences i.e. different 'kinetic' classes of DNA. Reassociated and single-stranded DNA were separated by hydroxyapatite chromatography and analyse for O6-methylguanine content. Three hours after administration of DMN the levels of O6-methylguanine in the reassociated and single-stranded DNA were the same after each period of reassociation indicating that O6-methylguanine was randomly distributed among the DNA classes. At 18 h the levels of O6-methylguanine were again the same in the reassociated and single-stranded DNA but approx. 50% lower than in the 3 h DNA samples. The rate of loss of O6-methylguanine from the three DNA classes was thus the same and there was therefore no indication of preferential removal of this base from any one kinetic class of DNA under the conditions used.

[Effect of antihepatocytotoxic serum on processes of cellular and intracellular regeneration of pathologically altered liver]

The parameters of the liver regeneration: mitotic index, DNA synthesis, nucleolar size of hepatocytes and histological structure, were studied in adult female rats with CCl4-affected liver during administration of the gamma-globulin fraction of antihepatocytotoxic serum (gamma-AHCS). It was shown that in various periods after exposure to CCl4 either the cellular processes of regeneration are predominant or the intracellular ones. gamma-AHCS (0.06 microgram protein per 100g body weight/one injection) intensifies and makes longer both the processes.

Receptor binding of B-norsteroids

The binding of B-nor-analogues of glucocorticoids, estrogens and of an androgen to specific cytosol receptors was compared with that of parent compounds of the normal series. In the study of binding of B-norcortisol and related compounds rat liver cytosol was used, while in a case of B-norestrogens rat uterus cytosol and for 17 alpha-methyl-B-nortestosterone rat prostate cytosol was used. The displacement of the appropriate radioligands by B-norsteroids was remarkably lower than that caused by correspondinga steroids with normal B-ring with the exception of 17 alpha-methyl-B-nortestosterone.

Effects of phentolamine on hepatic PO2 in endotoxemia

The effect of phentolamine, an alpha-adrenergic blocker, on hepatic oxygen supply, plasma glucose, and lactate, and survival in fasted male rats administered Echerichia coli endotoxin (25 mg/kg, ip) has been studied. Survival at 24 h was 8% in untreated endotoxic rats, 83% in rats receiving phentolamine (5 mg/kg, ip) and endotoxin, and 100% in phentolamine controls. Measurements during the initial 8 h postendotoxin recorded transiently lower systemic arterial pressure in the phentolamine-endotoxic rats. Arterial PO2 and increases of pH and heart rate were similar in both endotoxic groups. Lactacidemia, present by 4 h in untreated endotoxic rats, did not develop in the phentolamine group and plasma glucose was significantly higher at 8 h (98 +/- 2.5 vs. 77 +/- 5.6 mg%, mean +/- SE). Mean hepatic PO2 at 6 h in phentolamine-endotoxic rats was 9.6 mmHg with 28% of the values below 5 mmHg. By contrast, the mean in untreated endotoxic rats was 1.9 mmHg with 88% of values below 5 mmHg. Phentolamine controls were stable over 8 h; mean hepatic PO2 was 17.7 mmHg. The differences in plasma glucose and lactate suggest protection of hepatic metabolism in phentolamine-treated endotoxic rats by prevention of excessive hepatic hypoxia.

Methionine synthesis, aminoimidazole carboxamide excretion and folate levels in pregnant rats

The capacity for tetrahydrofolate regeneration through folate-linked methionine synthesis and for purine-ring closure through formylation of aminoimidazole carboxamide ribotide was studied in pregnant female rats fed diets containing either methionine or homocystine with or without folic acid. Plasma and liver folates, serine transhydroxymethylase, 5,10-methylene tetrahydrofolate dehydrogenase and glutamate formiminotransferase activities were also assayed. Pregnancy proceeded normally in all groups. Hypotrophic fetuses were observed only with the diet containing homocystine and no folic acid. Plasma folates were severely depleted at the end of pregnancy even when folic acid was present in the diet. Hepatic stores of folate were twice as high in the methionine as in the homocystine-fed pregnant females supplemented with folic acid. This favorable effect of methionine was not observed in folic acid-deficient females. No change in levels of serine transhydroxymethylase, 5,10-methylenetetrahydrofolate dehydrogenase, glutamate formimino-transferase activities was observed. Pregnancy did not stimulate methionine synthetase activity, the level of which was primarily affected by the nutritional conditions. Because of its low output and narrow range of adaptativity, methionine synthetase cannot be the sole regulatory factor of THF regeneration. Urinary excretion of aminoimidazole carboxamide was enhanced in folic acid-deficient pregnant females and was not prevented by supplying methionine.

[Specific glucocorticoid receptor in human liver cytosol]

Specific cytoplasmic glucocorticoid receptors were isolated from biopsy material of liver tissue, obtained after operation of the patients with chronic impairment of bili ferous tract or from the patients with ulcerous disease of stomach within the stage of remission. The receptors isolated were saturated with dexamethasone; the dissociation constant value (Kdiss) of the complex was 1.37 10(-8) M and the amount of binding sites (n) was 1.96 10(-14) mol/mg of protein as calculated from a Scatchards' plot. Dexamethasone, corticosterol, hydrocortisone and deoxycorticosterol exhibited the highest competition for the binding sites of the receptor. The receptor of human liver studied was similar in its main properties to the dexamethasone-binding receptor from liver tissue of experimental animals.

Copper- and zinc-binding proteins in sheep liver and intestine: effects of dietary levels of the metals

Liver cytosol from sheep fed diets containing 2.2, 11.3 or 47 microgram Cu/g diet with or without supplemental zinc (543 or 46 microgram Zn/g diet), fractionated on Sephadex G-100, yielded three main copper- and zinc-containing proteins with approximate molecular weights of greater than 150,000, 27,000 and 10,000. Amino acid analysis of the 10,000-molecular-weight proteins were of the metallothionein type. Copper-chelatin was not present in sheep liver cytosol. Copper concentration of the metallothionein fraction increased (P less than 0.01) as dietary copper increased from 2.2 to 11.3 microgram Cu/g, but did not increase further when dietary copper increased to 47 microgram Cu/g in unsupplemented sheep. A low-molecular-weight (approximately 3,500) copper-, but not zinc-containing fraction appeared at this highest level of copper. Zinc supplementation of the diet increased not only the zinc content of the metallothionein fraction but also its copper content, most dramatically in sheep fed the highest copper level. In intestinal mucosal cytosol, no copper and little zinc was associated with the metallothionetin fraction which was not affected by dietary treatment. Evidence from this study suggests that sheep have limited capacity to synthesize metallothionein in response to increased dietary copper.

Evidence for and characterization of a liver cell proliferation factor from blood plasma of partially hepatectomized rats

A boiled extract acidified to pH 5.5 from the blood plasma of partially hepatectomized rats was treated with neuraminidase and injected i.p. into untreated rats. The DNA-synthesis of the liver cells showed a four-fold increase in comparison with controls. Extracts from the plasma of partially hepatectomized rats without neuraminidase treatment showed no increase in DNA-synthesis. Injections of boiled acid extracts from plasma of normal rats, however, showed no comparable differences before and after neuraminidase treatment. The activity of neuraminidase treated boiled, plasma extract is lost after treatment both with trypsin-chymotrypsin and with beta-galactosidase. Gel chrmoatography of the factor gave a molecular weight of about 38,000 D. The specific activity of the active extract after chromatography was raised by a factor of 300. According to affinity chromatography the factor was shown to be a glycoprotein containing N-Ac-glucosamine. The factor is inert with respect to the proliferation of spleen and kidney, i.e. it is organ specific. According to these results a regulatory system of hepatopoiesis is proposed.

Activities of some free-radical scavenging enzymes and glutathione concentrations in human and rat liver and their relationship to the pathogenesis of tissue damage in iron overload

The activities and subcellular distribution of enzymes implicated in the protection of cells from free-radical mediated damage were determined in liver biopsy specimens from control and iron-overloaded patients. 2. There was a small but insignificant decrease in the activity of glutathione reductase in patients with secondary iron overload due to multiple transfusion therapy for thalassaemia major. 3. The activities of superoxide dismutase, catalase and glutathione peroxidase were similar in both patient groups. 4. Subcellular fractionation studies indicated a major cytosolic localization of these enzymes with a minor mitochondrial component. The relative proportions of the enzymes in the two locations was similar in both control and iron-overloaded patients. 5. Approximately 80% of the hepatic glutathione was present in the reduced form in both patient groups and it is concluded that although free-radical mediated damage might be implicated in the pathogenesis of tissue damage due to iron overload no significant defect in these protective mechanisms can be demonstrated.

Maturation and nucleo-cytoplasmic transport of rat-liver ribosomal RNA upon D-galactosamine inhibition of transcription

D-Galactosamine (250 mg/kg body weight) causes 90--95% inhibition of [14C]orotate or inorganic [32P]phosphate incorporation in vivo into rat liver nuclear RNA within 30 min. The transcription of both nucleolar and nucleoplasmic genes is inhibited to the same extent. Under these conditions, prelabbeled 45-S pre-rRNA is processed quantitatively to nuclear 28-S and 18-S rRNA. The nucleocytoplasmic transport of both 28-S and 18-S rRNA remains unaltered for about 60 min after blockage of transcription. At this stage the nucleo-cytoplasmic transport of 18-S rRNA is almost completed. It is concluded that formation and nucleo-cytoplasmic transport of ribosomes is independent of concurrent transcription of rRNA or nucleoplasmic genes. At later stages, the nucleocytoplasmic transport of 28-S rRNA is delayed and its partial degaradation in the nucleus may take place. This effect is correlated with a decreased (up to 40% of controls) labelling of nuclear proteins. However, the labelling of total cellular or microsomal proteins remains unchanged up to 3 h after D-galactosamine administration. It is suggested that the last nuclear steps of ribosome formation are dependent on the continuous supply of rapidly-labelled nuclear proteins.

Effects of manipulating dietary protein and energy intake on energy balance and thermogenesis in the pig

Weight maintenance was achieved by feeding either restricted amounts of a high-protein diet (HP) or ad libitum amounts of low-protein diet (LP) to 6 and 20 kp pigs for up to 42 days. In all cases, LP animals consumed approximately three times as much energy as the HP animals but in the 20-kp pigs, almost all (70%) of this excess was deposited in the carcass as fat. In 6-kg pigs fed the LP diet, changes in body energy content accounted for only a small fraction (27%) of the total energy intake; a large difference in energy expenditure was seen between these animals and the HP group, which was attributed to differences in dietary-induced thermogenesis. Six-kilogram LP pigs showed elevated plasma triiodothyronine levels and hepatic mitochondrial alpha-glycerophosphate dehydrogenase activity and an enhanced sensitivity to the in vitro lipolytic effects of norephinephrine (NE) on adipose tissue. These changes are similar to those observed in rats exhibiting dietary-induced thermogenesis and the relevance of these findings to the increased heat production of LP pigs is discussed.

Effect of androgen mediated by the estrogen receptor of fish liver: vitellogenin accumulation

We have investigated the action of high doses of androgens in Gobius niger L., a marine teleostean fish, by characterizing specific steroid receptors in liver and by assaying the plasma vitellogenin concentration under different hormonal treatments. Estrogen and androgen receptors were characterized in the liver nuclear extracts according to their binding specificity. The maximum binding capacity was 25 fmoles/mg protein for the estrogen and androgen receptors. In vivo, high doses of DHT()increased the concentration of plasmatic vitellogenin as assayed by immunodiffusion while low doses were inefficient. In spite of a similar number of estrogen and androgen nuclear receptor sites (25 fmoles/mg protein), DHT was at least 70 fold less active than E2 on yolk protein and vitellogenin induction both in male and female Gobius niger. In addition, the antiestrogen tamoxifen, which was inactive by itself, inhibited the E2 and the DHT induced accumulation of vitellogenin. Progesterone (2 mg/fish) was also totally inactive in inducing vitellogenin. We conclude that the induction of vitellogenin by DHT is mediated by the estrogen receptor rather than by the androgen receptor. In addition to the estradiol induced protein in rat uterus and to other estrogenic responses obtained by androgens in mammary cancer, fish vitellogenin is another estrogen regulated protein which can be induced by high doses of androgens.

[Biomembrane permeability and lipid peroxidation upon exposure of the body to a shearing force]

Transversal overloading /3.5 and 6 un/ distinctly altered penetration of 14C-nicotinate and 35S-lipoate into cells and mitochondria. Increased secretion of proteins from cells, mitochondria and lysosomes was observed under these experimental conditions, especially in presence of Triton X-100 and in hypotonic media. Within the first 30 sec of overloading an increase in lipid peroxidation was found. Pretreatment with vitamin E decreased the effect of overloading on lipid peroxidation and on the membrane permeability.

Epinephrine-induced insulin resistance in man

Endogenous release of epinephrine after stress as well as exogenous epinephrine infusion are known to result in impaired glucose tolerance. Previous studies of man and animals have demonstrated that this effect of epinephrine results from inhibition of insulin secretion and augmentation of hepatic glucose production. However, the effect of epinephrine on tissue sensitivity to insulin, and the relative contributions of peripheral vs. hepatic resistance to impaired insulin action, have not been defined. Nine young normal-weight subjects were studied with the insulin clamp technique. Plasma insulin was raised by approximately 100 muU/ml while plasma glucose concentration was maintained at basal levels by a variable glucose infusion. Under these conditions of euglycemia, the amount of glucose metabolized equals the glucose infusion rate and is a measure of tissue sensitivity to insulin. Subjects received four studies: (a) insulin (42.6 mU/m(2).min), (b) insulin plus epinephrine (0.05 mug/kg.min), (c) insulin plus epinephrine plus propranolol (1.43 mug/kg.min), and (d) insulin plus propranolol. During insulin administration alone, glucose metabolism averaged 5.49+/-0.58 mg/kg.min. When epinephrine was infused with insulin, glucose metabolism fell by 41% to 3.26 mg/kg.min (P < 0.001). After insulin alone, hepatic glucose production declined by 92% to 0.16+/-0.08 mg/kg.min. Addition of epinephrine was associated with a delayed and incomplete suppression of glucose production (P < 0.01) despite plasma insulin levels >100 muU/ml. When propranolol was administered with epinephrine, total glucose metabolism was restored to control values and hepatic glucose production suppressed normally. Propranolol alone had no effect on insulin-mediated glucose metabolism. These results indicate that epinephrine, acting primarily through a beta-adrenergic receptor, markedly impairs tissue sensitivity to an increase in plasma insulin levels, and that this effect results from both peripheral and hepatic resistance to the action of insulin.

[Physical exercise in the diabetic. The importance of understanding endocrine and metabolic responses (author's transl)]

During physical activity in normals, metabolic control is well regulated despite major changes in metabolic fuels, glucose and non esterified fatty acids (NEFA). Release of NEFA from adipose tissue is stimulated by a decrease of insulin and blood glucose as well as by an increase of growth hormone, catecholamines and adrenergic stimulation. The increase in glucose utilisation by muscle during physical activity is balanced by an increase in glucose production by the liver. This hepatic glucose production is due to glycogenolysis (beginning of exercise) and by gluconeogenesis (later in time). The metabolic pathways are favoured by decreased insulin and blood glucose levels induced by physical activity and by increased levels of epinephrine, cortisol and glucagon. On the other hand in insulin-dependent diabetics, these compensatory mechanisms might be seriously unbalanced because of non physiologic insulin levels. In well controlled diabetics, moderate physical activity induces the same changes in energetic fuels as in normal controls. When a diabetic exercises after insulin injection, the levels of circulating insulin are always higher than in non-diabetics where blood insulin levels decrease. In diabetics on insulin this supra-normal level of insulin during physical activity decreases hepatic glucose production and increases peripheral glucose uptake with a resultant tendency to hypoglycemia. On the other hand, in poorly controlled diabetics, physical activity can induce a rise in blood glucose. Increased hepatic glucose output, decreased peripheral utilisation of glucose and increased growth hormone, glucagon, epinephrine and cortisol levels might even lead to development of ketosis. Physical activity can disturb the stability of diabetes when insulin levels are either too low or too high leading to high and low blood glucose responses respectively. The benefit of physical activity in the diabetic will therefore depend upon the degree of diabetes control; ideal control is not always easy to obtain or to maintain. Thus, to derive maximum benefit to health both the diabetic and the physician should clearly understand how to adapt treatment to physical activity (prevention of hypoglycemia, change in insulin doses, etc.).

Metabolism and biliary excretion of benzo[a]pyrene 4,5-oxide in the rat

The excretion and biliary metabolites of intravenously administered benzo[a]pyrene 4,5-oxide were studied in the rat at two dose levels. After administration of 4.5 or 0.47 mumol, half of the dose was excreted in the bile in 60 min. Biliary metabolites were separated by reverse-phase high-pressure liquid chromatography and identified by cochromatography with biosynthetic standards, beta-glucuronidase hydrolysis, ultraviolet spectrophotometry and, in the case of the thioether conjugates, identification of the constituent amino acids. The major biliary metabolite was a mixture of isomeric glutathione conjugates. Some cysteine conjugate was also present, but no cysteinylglycine conjugate was detected. Hydration to transbenzo[a]pyrene-4,5-dihydrodiol followed by glucuronidation was also a quantitatively important metabolic pathway. Although benzo[a]pyrene-4,5-dihydrodiol glucuronide was more readily excreted by the liver than was benzo[a]pyrene 4,5-oxide:glutathione conjugate, the rate of glucuronidation of the dihydrodiol was low, resulting in its accumulation in the liver and possible release into the circulation. Therefore, the glutathione S-transferases may provide a more efficient mechanism for the removal of benzo[a]pyrene 4,5-oxide from the body than is provided by expoxide hydrolase.

Influence of nephrectomy on the glucoregulatory response to insulin administration in the rat

Insulin sensitivity and resistance were examined in vivo in uremic rats by using tracer methods which permit the assessment of "non-steady-state" glucose kinetics. By relating the changes in the rates of glucose output by the liver (Ra), uptake by tissues (Rd), and metabolic clearance (MCR) to immunoreactive glucagon and insulin, it was possible to assess the tissue sensitivity to physiologic and supraphysiologic levels of these two hormones and the site of insulin resistance. The effect of an intravenous injection of insulin (100 mU) on glucose turnover was studied in acutely uremic rats 15 h after bilateral nephrectomy and in sham-operated controls, in the postabsorptive state. Glucose output by the liver and uptake by tissues were determined by the primed constant infusion technique using [3H]glucose. Under basal conditions, no significant difference in Ra and Rd between the two groups were observed, while a significant hyperglycemia and a reduced glucose metabolic clearance rate in the face of hyperglucagonemia and normal plasma insulin levels were observed in nephrectomized rats. After insulin injection, the glycemic curves were similar in the two groups, while Ra, Rd, and MCR displayed significantly lower values in nephrectomized rats in the face of higher plasma concentrations of insulin and glucagon. It was concluded that acute uremia in the rat is characterized by a loss of the normal ability of insulin to promote peripheral glucose uptake with retention of hepatic sensitivity to insulin.

Decreased insulin binding and degradation associated with depressed intracellular ATP content

The effect of metabolic inhibitors, 2,4-dinitrophenol (DNP) and NaF, on insulin binding and degradation has been studied in cultured Buffalo rat liver (BRL) cells. In control studies, 1.8 fmol of 125I-insulin binds to 1.2 x 10(6) cells, possessing approximately 40,000 receptor sites per cell with binding affinity of 5.52 x 10(-8) M. When the cells were preincubated with increasing concentrations of either DNP or NaF, a dose- and time-dependent decrease in both insulin binding and degradation was observed. The total amount of 125I-insulin bound to BRL cells preincubated with metabolic inhibitors was reduced to 1.2 fmol per 1.2 x 10(6) cells. The point of 1/2 B max was achieved in the presence of 50 ng/ml of native insulin, 1.7 times that of the control level. The number of receptor sites was unaffected by either DNP or NaF, but an average affinity profile revealed a decrease in the affinity of the ATP-depleted cells for insulin (KD: 7.31 x 10(-8) M and 7.06 x 10(-8) M in DNP- and NaF-treated cells, respectively). The decrease in insulin binding and degradation following the exposure of the BRL cells to the metabolic inhibitors was associated with a 20% reduction in intracellular ATP and adenylate energy charge. DNP and NaF did not affect the equilibrium constant for the myokinase catalyzed reaction and the intracellular concentration of hypoxanthine was stable, confirming the integrity of the cells during the experiments. It is suggested that ATP levels must remain intact to maintain normal insulin receptor affinity. Furthermore, the rate of insulin degradation by ATP-depleted cells is slower than that of intact cells. It is conceivable that the depression of insulin degradation by partially ATP-depleted cells results from either diminished binding or decreased endocytosis and lysosomal activity, all of which appear to be energy dependent.

Effects of nutrients, endogenous secretions, and fasting on in vitro glucose uptake

The effect of luminal nutrients, endogenous secretions, and metabolic balance on the initial velocity of glucose uptake was measured in everted rings of rat intestine. Animals were fed either by total parenteral nutrition (TPN), or into the midjejunum for 7 days, or fasted for 72 h. Luminal feeding resulted in higher midjejunal glucose uptake per milligram of protein, DNA, and centimeter gut length, when compared to fasting or TPN. Kinetic analysis revealed a higher "apparent" Vmax in the luminally fed group, whereas the "apparent" Km was similar in all groups. Diversion of the pancreaticobility secretions did not affect glucose uptake in luminally fed or TPN-fed animals. TPN-fed and fasted animals had similar glucose uptake. Luminal feeding did not have a remote effect on glucose uptake in intestine isolated from the nutrient stream. The results indicate that luminal nutrients maintain carrier-mediated glucose transport after direct contact with the mucosa. Overall metabolic balance and pancreaticobiliary secretions do not affect carrier-mediated glucose transport. The nutrient effect appears to involve an increased number of glucose carriers per cell without a change in carrier affinity for glucose.

[Hepatitis A: antibody conversion under gamma globulin (author's transl)]

55 soldiers of the Austrian UNO contingent to the Near East, stationed on the Golan Heights for 6 months were examined before and after their period of duty for hepatitis A antibodies and the liver specific enzymes GOT, GTP and gamma-GT were determined. All received prophylactic gamma globulin to prevent infectious hepatitis at a dosage of 0.05 ml/kg body weight before flying out and after three months. No cases of hepatitis occurred, but 4 sero-negative subjects displayed antibody conversion. No concomitant changes in the liver enzyme values were recorded, however. These findings are discussed.

[Characteristics of synthesized RNA in the isolated and perfused rat liver]

The incorporation of 3H-orotic acid into nuclear and microsomal RNA from isolated perfused rat liver has been studied. The specific radioactivity of nuclear RNA indicates that the efficiency for RNA synthesis in the perfused liver is similar to that of the liver 'in vivo'. In contrast, the microsomal RNA specific radioactivity is well below that observed 'in vivo'. This may indicate a slower transport of the labelled RNA from the nucleus to the cytoplasm. Labelling pattern of total nuclear RNA, nuclear poly(A) containing RNA and microsomal RNA appear to be in line with these assumptions.

Effect of bilayer membrane curvature on activity of phosphatidylcholine exchange protein

Effect of bilayer membrane curvature of substrate phosphatidylcholine and inhibitor phosphatidylserine on the activity of phosphatidylcholine exchange protein has been studied by measuring transfer of spin-labeled phosphatidylcholine between vesicles, vesicles and liposomes, and between liposomes. The transfer rate between vesicles was more than 100 times larger than that between vesicles and liposomes. The transfer rate between liposomes was still smaller than that between vesicles and liposomes and nearly the same as that in the absence of exchange protein. The markedly enhanced exchange with vesicles was ascribed to the asymmetric packing of phospholipid molecules in the outer layer of the highly curved bilayer membrane. The inhibitory effect of phosphatidylserine was also greatly dependent on the membrane curvature. The vesicles with diameter of 17 nm showed more than 20 times larger inhibitory activity than those with diameter of 22 nm. The inhibitory effect of liposomes was very small. The size dependence was ascribed to stronger binding of the exchange protein to membranes with higher curvatures. The protein-mediated transfer from vesicles to spiculated erythrocyte ghosts was about four times faster than that to cup-shaped ghosts. This was ascribed to enhanced transfer to the highly curved spiculated membrane sites rather than greater mobility of phosphatidylcholine in the spiculated ghost membrane.

Antagonistic effect of insulin on glucagon-evoked hyperpolarization. A correlation between changes in membrane potential and gluconeogenesis

In the perfused rat liver, administration of glucagon causes a hyperpolarization of the liver cell membrane and increases gluconeogenesis. Insulin, a hormone which is known to antagonize the effect of glucagon on gluconeogenesis also blocks the hyperpolarizing effect of glucagon. Because of this inhibitory effect of insulin of the glucagon-evoked hyperpolarization, a systematic study of possible correlation between changes in membrane potential and gluconeogenesis was undertaken. The membrane potential was changed by valinomycin, tetracaine, or by varying the ionic composition of the perfusate. A highly significant correlation between changes in membrane potential and the rate of gluconeogenesis was noticed. The possibility was raised that changes in membrane potential might exert an influence on metabolic process by a yet unknown mechanism.

The nucleotide sequence of a major species of leucine tRNA from bovine liver

Through the use of a variety of post-labeling techniques, the nucleotide sequence of a major species of leucine tRNA from bovine liver was determined to be pG-G-U-A-G-C-G-U-G-m-G-C-ac-C-G-A-G-C-G-G-D-C-psi-A-A-G-G-C-m-G-C-U-G-G-A-psim- U-I-A-G-m-G-C-psi-C-C-A-G-U-C-psi-C-psi-U-C-G-G-G-G-G-m-C-G-U-G-G-G-T-psi-C-G-m -A-A-U-C-C-C-A-C-C-G-C-U-G-C-C-A-C-C-AOH. A comparison of known sequences of leucine tRNAs shows a consistent set of features which clearly distinguish prokaryotic and eukaryotic leucine tRNAs from each other.

The subunit structure of the high affinity insulin receptor. Evidence for a disulfide-linked receptor complex in fat cell and liver plasma membranes

125I-Insulin equilibrated with high affinity fat cell and liver plasma membrane receptors was cross-linked to the membrane by addition of disuccinimidyl suberate. Autoradiographic analysis of the 125I-insulin-linked membranes subsequent to dodecyl sulfate electrophoresis in the absence of reductant revealed the presence of one labeled species which migrated with an apparent molecular weight of 300,000. Electrophoresis of these membranes in the presence of dithiothreitol resulted in the appearance of one major labeled band of about Mr = 125,000 concomitant with the loss of label in the Mr = 300,000 region. Another radioactive species which migrated in the Mr = 225,000 region on the reduced gels contained a much smaller amount of label. The degree to which the Mr = 125,000 membrane component was cross-linked to 125I-insulin in these experiments paralleled the extent of occupancy of high affinity membrane receptors by the 125I-insulin. 125I-Insulin-linked plasma membranes derived from adipocytes alkylated with N-ethylmaleimide prior to homogenization to prevent spontaneous sulfhydryl oxidation also exhibited the Mr = 300,000 and 125,000 labeled bands upon electrophoresis in the absence and presence of reductant, respectively. These same radioactive species were observed when 125I-insulin was covalently corss-linked to intact adipocytes. These data indicate that the labeled monomer with an apparent molecular weight of 125,00 represents a high affinity insulin receptor subunit which exists in the native adipocyte plasma membrane in a disulfide-linked complex. The amount of cross-linked label present in the reduced form of the receptor (Mr = 125,000) was only 20 to 30% of that present in the oxidized species (Mr = 300,000). Since the 125I-insulin used in these studies is labeled predominantly on the A chain, this large loss of label upon reduction indicates that it is predominantly the B chain of insulin that is covalently linked to the receptor protein by disuccinimidyl suberate. 125I-Proinsulin which lacks an A chain NH2 terminus could also be cross-linked to the receptor, indicating that the A1 glycine is not critical to the cross-linking reaction. 125I-Insulins modified either at lysine B29 with an acetyl group or at phenylalanine B1 with a phenylthiocarbamoyl group were both readily cross-linked to the receptor with roughly equal efficiency. It is concluded that the B1 terminal amino and B29 lysine amino groups are both accessible for cross-linking of insulin to the receptor by disuccinimidyl suberate.

Determination of the mitochondrial protonmotive force in isolated hepatocytes

The intracellular distribution of lipophilic ions and weak acids and bases was studied in intact hepatocytes as indicators of gradients of pH and membrane potential. Mitochondrial and plasma membrane potentials of 161 and 32.8 mV (negative inside), respectively, were calculated from the intracellular accumulation of triphenylmethylphosphonium (TPMP+) and thiocyanate in the intact hepatocyte, assuming a two-compartment model. The predominantly mitochondrial localization of TPMP+ was confirmed using disruption procedures that selectively break the plasma membrane but not the mitochondrial membrane. The intracellular distribution of 5,5-dimethyloxazolidine-2,4-dione and methylamine was studied with similar techniques. A cytosolic pH of 6.95 to 7.00 and a mitochondrial delta pH of 0.97 units was observed. From these results, a total mitochondrial protonmotive force in the intact cell in excess of -200 mV was obtained.