Methods for studying protein synthesis and degradation in liver and skeletal muscle

Different methods used for measuring protein turnover in liver and skeletal muscle are described, with special emphasis on technical and practical aspects and the advantages and limitations of different techniques. In the first part of the review, the concept of precursor specific radioactivity and its importance for accurate determination of protein synthesis rate is discussed. In the second part, different in vivo techniques for protein turnover measurements are reviewed, including continuous administration of tracer amino acid, flooding dose technique, indirect measurement of protein synthesis, and estimation of protein degradation in vivo. In the third part of the report, in vitro techniques are described, including measurement of protein turnover in incubated liver slices, perfused liver, isolated hepatocytes, incubated isolated muscles or muscle biopsies, and perfused rat hemicorpus. In vivo techniques are preferred when accurate absolute values of protein turnover rates are desired. In vitro techniques offer the advantage of standardized conditions, maintaining strict control of substrate and hormone concentrations, and eliminating complicating interactions with other tissues. For several in vitro techniques, a good correlation has been demonstrated between relative changes in protein turnover in vitro and in vivo in different conditions.

Skeletal-muscle glycogen synthesis during the starved-to-fed transition in the rat

The pattern of glycogen deposition in skeletal muscles of varying fibre composition was examined in rats during the starved-to-fed transition. In all the muscles studied, glycogen concentrations steadily increased during the first 8 h after chow re-feeding, and the fed value was exceeded. Rates of glycogen deposition varied, not with muscle fibre composition, but with the extent of glycogen depletion during starvation. There was no evidence for skeletal-muscle glycogen breakdown during the period of hepatic glycogenesis, making it unlikely that recycling of carbon from muscle glycogen to lactate is quantitatively important for the provision of glycogenic precursors to the liver, but moderate glycogen loss was observed from 8 to 24 h after re-feeding, when the liver is in the lipogenic mode. The factors influencing glucose disposal by skeletal muscle after re-feeding are discussed.

Magnesium and methionine deprivation affect the response of rats to boron deprivation

A series of nine experiments were done to obtain further evidence that boron might be involved in major mineral metabolism (Ca, P, and Mg), thus indicating that boron is an essential nutrient for animals. Eight factorially arranged experiments of 6-10 wk durations were done with weanling Sprague-Dawley male rats. One factorially arranged experiment was done with weanling spontaneously hypertensive rats. The variables in each experiment were dietary boron supplements of 0 and 3 micrograms g, and dietary magnesium supplements of either 200 (Experiments 1-3) or 100 (Experiments 4-9) and 400 micrograms/g. In Experiments 7 and 9, a third variable was dietary manganese supplements of 25 and 50 micrograms/g. Methionine status was varied throughout the series of experiments by supplementing the casein-based diet with methionine and arginine. Findings were obtained indicating that the severity of magnesium deprivation and the methionine status of the rat strongly influence the extent and nature of the interaction between magnesium and boron, and the response to boron deprivation. When magnesium deprivation was severe enough to cause typical signs of deficiency, a significant interaction between boron and magnesium was found. Generally, the interaction was characterized by the deprivation of one of the elements making the deficiency signs of the other more marked. The interaction was most evident when the diet was not supplemented with methionine and especially when the diet contained luxuriant arginine. Signs of boron deprivation were also more marked and consistent when the diet contained marginal methionine and luxuriant arginine. Among the signs of boron deprivation exhibited by rats fed marginal methionine were depressed growth and bone magnesium concentration, and elevated spleen wt/body wt and kidney wt/body wt ratios. Because the boron supplement of 3 micrograms/g did not make the dietary intake of this element unusual, it seems likely that the response of the rats to dietary boron in the present study were manifestations of physiological, not pharmacological, actions, and support the hypothesis that boron is an essential nutrient for the rat.

Transport of ferrous iron and lactate production in Bifidobacterium bifidum var. pennsylvanicus

Initial rates of ferrous iron transport into Bifidobacterium bifidum var. pennsylvanicus were measured at low and high iron concentrations. The low affinity system (LAFIUS) had an apparent Km of 167 microM, the high affinity system (HAFIUS) had a Km of 50 microM. Iron removal from preloaded bifidobacteria revealed the existence of a labile and an inert iron pool in the bacterial cells. Iron uptake by the bifidobacteria was associated with lactate production, though lactate production could continue without iron uptake. Cessation of iron uptake and lactate production was not because of an exhaustion of any nutrient nor the accumulation of fermentation end products in the medium. It was apparently the result of an inactivation of the cellular enzyme machinery without replacing it through normal biosynthetic processes.

Hypocarotenemia in patients fed enterally with commercial liquid diets

We have found that 12 patients requiring permanent enteral feeding secondary to cerebrovascular accident with adequate Vitamin A nutritional status had serum concentrations of various carotenoids which were only 8-17% of sex- and age-matched healthy controls. Their serum retinol levels were normal, but only 61% of their controls despite receiving two to three times the recommended daily allowance (RDA) in retinol equivalents. Commercial enteral formulas were found to contain only negligible quantities of the carotenoids and were the cause of the hypocarotenemia. To assess the ability of these patients to absorb beta-carotene, nine tube-fed patients were given 15 mg of beta-carotene (2.5 times the RDA) in a single dose. Serum concentration time curves showed that only four patients absorbed significant quantities of the beta-carotene and absorption was delayed compared to previously studied subjects taking enteral formulas as meals. These studies suggest that the efficiency of absorption of the fat soluble vitamins may be lower in tube-fed patients and that patients receiving long-term tube feeding are denied the possible protective effects of the carotenoids normally contained in the American diet.

Protection of rat myocardial phospholipid against peroxidative injury through superoxide-(xanthine oxidase)-dependent, iron-promoted Fenton chemistry by the male contraceptive gossypol

Metal-promoted oxygen free-radical chemistry is a cause of tissue damage in many disease states, such as myocardial ischemia. The effect of gossypol, a polyphenolic plant pigment and male contraceptive, on the peroxidation of myocardial membrane phospholipid was studied and quantitatively characterized. As a result of exposure to xanthine oxidase (superoxide)-dependent, iron-promoted Fenton chemistry, cardiac phospholipid was readily peroxidized with defined kinetics. The peroxidation could be blocked by substances which interdict at specific points in the Fenton chemistry: superoxide dismutase, alpha-tocopherol, the iron chelator desferrioxamine, and the xanthine oxidase substrate-analogs allopurinol and oxypurinol. The oxidative-injury system displayed a characteristic antiperoxidant response to each type of inhibitor. Gossypol, at low micromolar concentrations, profoundly altered the rate and extent of myocardial phospholipid peroxidation. Gossypol was ineffective as a xanthine oxidase inhibitor and as a superoxide scavenger at concentrations that abolished myocardial lipid peroxidation. Since metal chelation was an effective means of preventing lipid peroxidation in this system only when the iron therein was completely chelated, the low anti-peroxidant IC50 for gossypol, 1.1. microM, relative to the concentration of iron (100 microM) did not support a functionally significant antiperoxidant role for gossypol as an iron chelator. Rather, it appears that, at low micromolar gossypol concentrations which approximate the peak plasma concentrations in humans, the antiperoxidant effects of gossypol against superoxide-mediated, iron-promoted lipid damage rest with the ability of gossypol to intercept lipid radical intermediates as a "chain-breaking" aromatic phenol.

Bone cell biology: the regulation of development, structure, and function in the skeleton

Bone cells compose a population of cells of heterogeneous origin but restricted function with respect to matrix formation, mineralization, and resorption. The local, mesenchymal origin of the cells which form the skeleton contrasts with their extraskeletal, hemopoietic relatives under which bone resorption takes place. However, the functions of these two diverse populations are remarkably related and interdependent. Bone cell regulation, presently in its infancy, is a complicated cascade involving a plethora of local and systemic factors, including some components of the skeletal matrices and other organ systems. Thus, any understanding of bone cell regulation is a key ingredient in understanding not only the development, maintenance, and repair of the skeleton but also the prevention and treatment of skeletal disorders.

Maple syrup urine disease: a possible biochemical basis for the clinical heterogeneity

Nine patients with maple syrup urine disease (MSUD), of whom eight were detected by mass-screening of neonates for inherited metabolic disease, were studied to determine possible relationships between clinical features and properties of the branched-chain alpha-keto acid dehydrogenase complex (BCKDH) in cultured lymphoblastoid cells. Based on their tolerance for leucine and on the clinical manifestations observed after 2 years of age, most could be classified into three types; classical (tolerate less than 600 mg of leucine per day, N = 2), intermediate (N = 3) and intermittent (N = 3) types. In the other patient two of these three phenotypes were present. The BCKDH activities measured at a lower alpha-ketoisovaleric acid concentration (0.054 mM) were 0.026 +/- 0.015 in classical, 0.118 +/- 0.016 in intermediate and 0.625 +/- 0.139 in intermittent types and 7.052 +/- 0.779 (nmol/h per milligram of protein) in two controls, respectively; the differences being statistically significant (P less than 0.01, classical vs intermediate types; P less than 0.01, intermediate vs intermittent types; P less than 0.01, intermittent vs control). Kinetic and immunochemical analyses of the BCKDH revealed that, although there are a few exceptions, classical, intermediate and intermittent types correspond to the enzyme properties of sigmoidal kinetics with E1 beta subunit deficiency, near-sigmoidal kinetics with E1 beta subunit deficiency and hyperbolic kinetics with E2 subunit deficiency of the BCKDH, respectively.

Effects of corticotropin-releasing factor on food intake and brown adipose tissue thermogenesis in rats

Corticotropin-releasing factor (CRF) has been administered into the third ventricle of rats in acute and chronic experiments. Following a single 5-micrograms injection of CRF, there was an acute reduction in food intake at 30 and 60 min that was no longer significant at 3 h. Guanosine 5'-diphosphate (GDP) binding to mitochondria from interscapular brown adipose tissue (IBAT) of 21-h deprived rats was significantly increased 30 min after the acute infusion of 5 micrograms of CRF. Serum corticosterone was elevated in both groups but was significantly higher in the group treated with CRF. Serum glucose was unchanged. During a 7-day infusion of CRF (4.8 micrograms/day) into the third ventricle, the treated animals showed a slight, but significant, decrease in food intake but a progressive decline in body weight of 53 g over 7 days. Mitochondrial GDP binding was increased in the ad libitum-fed rats chronically treated with CRF. Serum corticosterone levels, although significantly higher than controls, were lower than following acute administration of CRF. These data show that CRF can acutely reduce food intake and increase sympathetic activity and that chronically it reduces body weight and may increase sympathetic activity without any consistent decrease in food intake.

Uptake of choline by rat mammary-gland epithelial cells

The neonatal mammal requires especially large amounts of choline to sustain growth. Much of this choline is derived from the newborn's only source of food, milk. The concentration of choline in rat milk [182 +/- 24 microM (S.E.M.)] was much higher than that in maternal serum (11.6 +/- 0.9 microM), suggesting that a mechanism capable of concentrating choline into milk must exist. We characterized choline uptake by mammary epithelial cells (the site of milk production) of the lactating rat. We observed two uptake processes, one saturable and obeying Michaelis-Menten kinetics, and the other non-saturable and linear. At physiological blood choline concentrations, the saturable component of choline uptake predominated. The saturable component had Kapp. = 35 +/- 16 microM, and Vmax. = 1.24 +/- 0.19 nmol/h per mg of protein. Saturable uptake of choline was inhibited by hemicholinium-3. Ca2+ was required for uptake, but Mg2+ was not. Replacement Na+ with K+, Li+ or sucrose inhibited transport. Ouabain did not inhibit choline uptake. Choline concentration in epithelial cells was 67.7 +/- 1.9 nmol/g wet wt. at the start of incubation at 37 degrees C and rose to 80.9 +/- 6.5 nmol/g wet wt. over 30 min. Much of the choline accumulated by the mammary gland (in the presence of endogenous concentrations of choline) remained in the form of choline (50 +/- 1.2%), phosphatidylcholine (12 +/- 2.3%), lysophosphatidylcholine (0.1 +/- 0.03%), betaine (7 +/- 0.3% and phosphocholine (6 +/- 0.5%). In addition, we isolated 25 +/- 1.2% of choline-derived radiolabel in an unidentified compound.

Relationship between mitochondrial lipid peroxidation and alpha-tocopherol levels in the guinea-pig adrenal cortex

Lipid peroxidation in mitochondria from the functionally distinct inner (zona reticularis) and outer (zona fasciculata + zona glomerulosa) zones of the guinea-pig adrenal cortex was investigated. Ferrous ion (Fe2+)-induced lipid peroxidation was far greater in inner than outer zone mitochondria. Ascorbic acid similarly initiated lipid peroxidation to a greater extent in inner zone mitochondrial preparations. Differences in the unsaturated fatty acid content of inner and outer zone mitochondria could not account for the regional differences in lipid peroxidation. Total fatty acid concentrations were greater in the outer than in the inner zone, and the relative amounts of each fatty acid were similar in the two zones. However, mitochondrial concentrations of alpha-tocopherol, an antioxidant known to inhibit lipid peroxidation, were approx. 5-times greater in the outer than inner zone. The results demonstrate that there are regional differences in mitochondrial lipid peroxidation in the adrenal cortex which may be attributable to differences in alpha-tocopherol content. Thus, alpha-tocopherol may serve to protect outer zone mitochondrial enzymes from the consequences of lipid peroxidation and thereby contribute to some of the functional differences between the zones of the adrenal cortex.

Serum apolipoprotein A-IV and lipoprotein cholesterol in patients undergoing total parenteral nutrition

The distinctive biological properties of apolipoprotein (apo) A-IV suggest that serum levels of this apoprotein should be profoundly and selectively depressed by nutritional modalities that totally bypass the intestine. To test this hypothesis we have measured serum lipid and apoprotein levels in 18 fasting patients receiving total parenteral nutrition and in a group of 31 normal controls. Measurement of total serum lipids revealed that the patients had significantly higher serum triglyceride levels and lower total serum cholesterol levels than the controls. The lower total serum cholesterol levels were a consequence of decreases in both low-density lipoprotein and high-density lipoprotein cholesterol. The mean serum level of apo A-IV in the patients was 15 +/- 13 AU/dl, compared with 93 +/- 29 AU/dl in the controls. This difference was almost threefold greater than the differences between levels of apo A-I, apo B, or lipoprotein subfractions. Moreover, apo A-IV was undetectable in 4 patients who had undergone significant small intestinal resection. A trend toward lower apo A-IV levels was seen in the resected patients as compared with those with intact small intestine. Linear regression analysis showed that levels of apo A-IV were not correlated with any apoprotein or lipoprotein parameter in either the patient or control group, with the exception of a positive correlation between serum apo A-IV levels and total serum cholesterol in the controls only, suggesting that apo A-IV synthesis is regulated independently of the synthesis of the major classes of plasma lipoproteins. We conclude that serum apo A-IV levels are especially sensitive to the interruption of enteral feeding and rapidly fall to very low values during prolonged fasting.

Effect of thyroid hormones on oxidative and nonoxidative glucose metabolism in humans

The glucoregulatory function of thyroid hormones was investigated in six healthy subjects before and after 14 day 3,5,3',5'-tetraiodothyronine (T4) treatment (300 micrograms/day) using a sequential clamp protocol for 5 h at euglycemia (0-2 h) and hyperglycemia (165 mg/dl, 2-5 h) and different insulin infusion rates (1.0 for 0-3.5 h and 6.5 mU.kg-1.min-1, for 3.5-5 h). T4 treatment increased basal energy expenditure (+8%), glucose disposal (+31%), and oxidation (+87%) but decreased nonoxidative glucose metabolism (-30%) and was without effect on lipid oxidation. During the euglycemic clamp, T4 treatment enhanced insulin-induced glucose disposal (+16%), glucose oxidation (+34%), and inhibition of lipid oxidation (-66 vs. -40%); nonoxidative glucose metabolism was stimulated to a similar extent before and after T4. During hyperglycemia, 3,5,3'-triiodothyronine (T3) did not affect glucose disposal but increased carbohydrate-induced lipogenesis at both insulin infusion rates. We conclude that T4 treatment promotes glucose disposal and oxidation, T3 decreases noninsulin-mediated glucose storage but does not antagonize insulin action.

The effect of maternal smoking on the relationship between maternal and fetal zinc status and infant birth weight

We have previously reported a trapping of zinc in the placenta directly related to circulating cadmium that comes from cigarette smoke. The purpose of this study was to examine in detail the effect of smoking on (a) the relationship between maternal and fetal zinc status and (b) the relationship between zinc status and birth weight. One hundred and eighteen smokers and 172 nonsmokers without any medical complications during pregnancy were studied. Atomic absorption spectroscopy was used to assess zinc status in maternal and cord vein plasma and red blood cells. Plasma alkaline phosphatase was also determined as an index of zinc status. Thiocyanate was used as an index of smoking status. The data were analyzed using univariate correlations and repeated measures analysis of variance. Infants of smokers had a statistically significant decrease in plasma zinc (5%), alkaline phosphatase (13%), and in cord vein RBC zinc (12%). Furthermore, the results showed an altered relationship between maternal and fetal indices of zinc status and zinc status and birth weight due to maternal smoking. The infant of the nonsmoking mother appears to be able to maintain adequate zinc status due to depletion of maternal zinc. However, it appears that the infant of the smoking mother may be marginally zinc deficient. These findings support studies of zinc supplementation in the pregnancy complicated by smoking.

Determinants of urinary nitrogen excretion in burned patients

A retrospective study of urinary urea excretion has been performed in 91 burned patients. Maximum mean excretion occurred between days 5 and 8 after injury. The rate of excretion during this peak period correlated significantly with the sex and age of the patient as well as the burn size. It is suggested that peak nitrogen excretion may be more accurately predicted if all three variables are considered. However, the wide variation seen in patient response and differences in clinical management mean that regular measurement of urinary urea excretion still provides the most reliable guide to dietary protein requirements after a burn.

The hypothyroid (hyt/hyt) mouse: a model system for studying the effects of thyroid hormone on developmental changes in gene expression

Thyroid hormone has been implicated as an important factor in rodent development. We have used a strain of mice with a recessive mutation producing congenital primary hypothyroidism (C.RF/J-hyt/+) to study the effects of thyroid hormone on developmental changes in the expression of genes encoding a number of proteins involved in lipid metabolism and transport. Total cellular RNA was prepared from the small intestine and liver of hyt/hyt mice and their unaffected littermates (+/?) at various times during postnatal development. RNA blots were probed with apolipoprotein A-I, A-II, A-IV, B, and E cDNAs plus cDNAs encoding the low density lipoprotein receptor, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and three cytoplasmic hydrophobic ligand-binding proteins (two fatty acid-binding proteins and a protein that binds all-trans-retinol). Hypothyroidism results in small changes (1.5- to 5-fold) in the concentration of many of these mRNAs in liver and small intestine between postnatal days 15 and 50. A much greater tissue-specific effect was noted on apolipoprotein B (apoB) gene expression. In euthyroid +/? animals, apoB mRNA levels fall by a factor of 30 in liver between days 20 and 35 without a comparable decrease in the small intestine. This liver-specific decrease does not occur in hyt/hyt animals. The normal decrease in hepatic apoB mRNA levels is accompanied by a decrease in plasma apoB-100 but not apoB-48. No reduction in either form of plasma apoB was noted in hyt/hyt animals. Mutant hyt/hyt mice given thyroxine from birth to 35 days had liver apoB mRNA levels comparable to those in +/? littermates. In contrast, hepatic apoB mRNA concentrations did not fall to normal levels in hyt/hyt mice given thyroxine from postnatal days 15 to 35. All treatment groups have comparable levels of plasma corticosteroids. These data suggest that (i) there is a critical period or a required response time during postnatal development for thyroid hormone action on apoB gene expression, (ii) thyroid hormone's effect on apoB is tissue specific, and (iii) the hyt/hyt mouse represents a useful system to evaluate the developmental effects of thyroid hormone on specific gene expression.

Xylitol chewing gum in caries prevention: a field study in children

As the prevalence of dental caries decreases in industrialized nations like the United States, it simultaneously increases in developing nations and Third World countries. The decrease in the West is attributed to increased use of fluorides, but the increase in developing countries has been explained by an increase in the consumption of sugar. As this information continues to propel researchers to find sucrose substitutes, xylitol has been singled out as a proposed sucrose replacement. The question tackled by this study was: Can the daily use of chewing gum containing xylitol increase the efficacy of the existing caries-preventive measures now regularly used for 11- to 15-year-old children in most industrialized western countries?

Low serum levels of carotenoids in sickle cell anemia

Serum carotenoids, tocopherols and retinol were analyzed in patients with sickle cell anemia (SCA) and in control subjects. The data show the following: the serum levels of the major carotenoids, alpha and beta carotene, cryptoxanthin, lycopene lutein, alpha tocopherol and retinol were significantly lower in SCA patients. These findings reflect an additional abnormality of the antioxidant system in SCA patients. Gamma tocopherol, on the other hand, was significantly elevated, consistent with the previously reported reciprocal relationship between serum alpha and gamma tocopherols. Thus, these data taken together with the earlier findings on the lower levels of plasma alpha tocopherol and ascorbic acid suggest that the entire antioxidant system may be compromised in SCA patients. This may contribute in part to the phenotypic expression of the condition.

Selenium-containing proteins of rat kidney

Rat kidney selenium (Se)-containing proteins were studied by isotopic labeling with [75Se]selenite or [75Se]selenomethionine via three routes: oral, intraperitoneal injection, and incubation of kidney slices with the isotope. The two major Se-containing proteins in kidney were fractionated and partially characterized. 75Se elution profiles from Sephadex G-150 chromatography were similar for each labeling protocol, except for the profile obtained following incubation of slices with [75Se]selenomethionine. Of the two major 75Se-containing proteins, the one eluting at the void volume during Sephadex G-150 fractionation had a subunit of 23,000 Mr. The 75Se-labeled tryptic peptide from this protein and a 75Se-containing tryptic peptide from glutathione peroxidase had the same elution time from an HPLC column. A 75,000 Mr 75Se-containing protein had a 65,000 Mr subunit, and the 75Se-labeled tryptic peptide from this protein eluted from the HPLC column before that of glutathione peroxidase. Glutathione peroxidase is the most abundant kidney selenoprotein. Injection of animals with 75Se is the method of choice for isotopic labeling of rat kidney Se-containing proteins. Appropriate methods were developed that can be used in future studies of kidney Se-containing proteins.

The establishment of essential and metabolically derived amino acid profiles in developing chick embryo organs

The accumulation of certain essential and metabolically derived amino acids in the free amino acid pools of three excitable tissues has been studied in the chick embryo. Valine together with leucine are at the onset present in the yolk at higher concentrations than any of the other essential amino acids. By 15 days all the amino acids studied have accumulated in the embryonic pools at a higher rate than valine, although certain amino acids, such as phenylalanine or methionine, always remain at lower relative concentrations than valine. This reflects their low supply in the yolk, rather than a more rapid rate of disappearance (utilization). During early embryogenesis (E2-E4), tissues preferentially concentrate glutamic acid, besides taurine and phosphoethanolamine (6). The next distinct stage of development (E4-E7) is marked in the brain by a gradual rise in glutamic acid, glutamine and aspartic acid; the same three amino acids do not demonstrate a further increase in the pool of the heart, while in the whole eye the amino acid profile begins to resemble the blood. Leucine in all three tissues declines rapidly, to reach isoleucine levels by day 7 of development; tyrosine increases slowly in apparent reciprocity to an equally gradual phenylalanine decrease. Into the second week of embryo growth (E7-E15), GABA appears in the mesencephalon (E7) and the eye (E9-E10). In the mesencephalon, the free amino acid pool composition exhibits a rather sudden increase of most metabolically derived amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Carcinogenesis as the result of the deficiency of some essential trace elements

"Energetic" biological trace elements [gallium (III), germanium (IV), silicon (silica), arsenic (V) and selenium (IV)] occurring in DNA of eukaryotic cells may improve the semiconductor properties of DNA and may influence the mechanisms that control genetic expression at the electronic level. Their roles are postulated as follows: (i) to maintain the level and direction of free sliding electrons in DNA, (ii) to modulate the electron conductivity and hole conductivity of DNA. This specific electronic nature of DNA take the form of magnetic pigeonholes in which an electric pulse is (0), or is not (1) stored as an area of local magnetisation. These types of conductivity occurring in different parts of DNA of different cells could participate in the switch on and switch off of genetic information in gene expression. This model may help to elucidate the mechanism of action of these naturally occurring antitumor agents and may help in understanding the role of trace elements in charge transport of DNA and in carcinogenesis.

Effect of a thermogenic agent, BRL 26830A, on insulin receptors in obese mice

The effect of a new type of antidiabetic agent, BRL 26830A, has been tested in obese mice. Since this drug increases thermogenesis, insulin receptor binding and kinase activity were studied in brown adipose tissue and skeletal muscle of mice made obese by gold thioglucose. At 1 mg.kg-1.day-1, a 3-wk treatment normalized the glycemia and increased the uncoupling protein content of brown adipose tissue. The insulin receptor number and its associated kinase activity increased only in brown adipose tissue. At 2 mg.kg-1.day-1, additional effects, i.e., a 20% reduction in body weight and a normalization of insulin receptor number both in brown adipose tissue and in skeletal muscle, were observed. All those results were obtained even though hyperinsulinemia was not corrected. At the higher drug dosage, insulin receptor kinase activity evolved in direct proportion to the receptor number in brown adipose tissue. By contrast, in skeletal muscle, the receptor kinase activity toward exogenous substrates increased more than the receptor number, suggesting that the alteration of insulin receptor kinase activity previously reported in skeletal muscle of obese mice was partly reversed by BRL 26830A. None of these parameters was modified by the drug in lean mice. These results show that, even without affecting obesity, BRL 26830A improves insulin resistance in obese mice, probably through its effect on insulin receptors. This action prevails in brown adipose tissue, supporting the idea that this tissue plays an important role in glucose homeostasis. Thermogenic drugs could thus be powerful agents for the treatment of noninsulin-dependent diabetics.

Demonstration of ferric L-parabactin-binding activity in the outer membrane of Paracoccus denitrificans

Under low-iron conditions, Paracoccus denitrificans excretes a catecholamine siderophore, L-parabactin, to sequester and utilize iron. In this report, we demonstrate the presence of stereospecific high-affinity ferric L-parabactin-binding activity associated with P. denitrificans membranes grown in low-iron medium. Isolated outer membrane components were shown to be three to four times higher in specific activity for ferric L-parabactin. The same amount of binding activity existed whether or not the radiolabel was present in the metal (55Fe) or the ligand (3H) portion of ferric parabactin chelate, suggesting that binding was to the intact complex. Ion-exchange chromatography of a Triton X-100-solubilized outer membrane mixture on DEAE-cellulose resulted in a 10-fold increase in binding activity relative to that present in whole membranes. Polypeptide profiles by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the products of each stage of the purification showed that binding activity copurified with one or more of the low-iron-induced outer membrane proteins in the 80-kilodalton (kDa) region. Membrane proteins and [55Fe]ferric L-parabactin electrophoresed in nondenaturing gels demonstrated the presence of membrane component(s) which stereo-specifically bound ferric L-parabactin, thus providing independent confirmation of the binding assay results. Moreover, when the band labeled by [55Fe]ferric L-parabactin was excised and profiled by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, 80-kDa polypeptides were the major components present. These results demonstrate the presence of a high-affinity ferric L-parabactin receptor in P. denitrificans membranes and suggest that one or more of the 80-kDa low-iron-induced polypeptides are components of the ferric L-parabactin receptor.

Glucocorticoids modulate beta-adrenoceptor subtypes and adenylate cyclase in brown fat

Thermogenesis in brown adipose tissue (BAT) serves as a regulator of body temperature and weight maintenance. Thermogenesis can be stimulated by catecholamine activation of adenylate cyclase through the beta-adrenergic receptor. Glucocorticoids potentiate the action of catecholamines in some tissues by increasing the expression of beta-adrenergic receptors. Paradoxically, glucocorticoids suppress and adrenalectomy enhances BAT thermogenesis. To further study the reasons for this discrepancy, we assessed the effects of methylprednisolone administration, adrenalectomy, and adrenalectomy with corticosterone replacement on adenylate cyclase activity in BAT and on beta-adrenergic receptor density in lungs and BAT of rats. In lungs, the density of the beta 2-adrenergic receptor subtype increases after methylprednisolone administration and decreases after adrenalectomy. There was no change in BAT receptor density, but isoproterenol-, NaF-, and forskolin-stimulated adenylate cyclase activity was reduced by 20-35% after methylprednisolone treatment. There was a two- to threefold increase in adenylate cyclase activity after adrenalectomy, which was reversed by corticosterone administration. These data suggest that one mechanism by which glucocorticoids regulate BAT thermogenesis is by modulating the beta-adrenergic pathway at the level of adenylate cyclase activation.

Lipid abnormalities in pancreatic tissue of streptozotocin-induced diabetic rats

Pancreatic lipid and fatty acid composition was determined in streptozotocin-induced diabetic rats and compared to control and insulin-treated diabetic rats. A pronounced decrease of total fatty acids was recorded and mainly accounted for by a drop of fatty acids in glycerides. Cholesterol, on the other hand, was significantly increased two- to three-fold, leading to an elevated cholesterol/phospholipid ratio. Morpho-cytochemical studies confirmed these findings because the multiple lipid droplets present in acinar cells of diabetic animals were found to be of cholesterol nature. The major alterations in phospholipid-fatty acid composition were characterized by an increase of linoleate coupled to a decrease of monounsaturates and arachidonate, suggesting defective metabolism of saturates and of linoleate. This was further supported by fatty acid ratios that suggested low delta 5 and delta 9 desaturation. Daily administration of insulin for 10 days restored and overcorrected the various lipid alterations. This study suggests that there are alterations in lipid composition and metabolism in the exocrine pancreas of chronic streptozotocin-induced diabetic rats. Their possible role in the mechanism regulating pancreatic function and secretion remains to be elucidated.

The effect of tumour-bearing on 2-deoxy[U-14C]glucose uptake in normal and neoplastic tissues in the rat

The extent to which normal and neoplastic tissues of the rate take up glucose was assessed by the 2-deoxy[U-14C]glucose tracer technique. Measurements of glucose uptake were made over 40 min in anaesthetized rats under conditions where the blood glucose concentration was constant. In fed tumour-bearing rats, the relative rates of glucose uptake per g wet wt. of tissue were tumour (100), small intestine (72), brain (61), heart (61), spleen (50), lung (42), adipose tissue (11) and muscle (8). Normal tissues of the fed tumour-bearing rats had decreased rates of glucose uptake as compared with the same tissues in fed non-tumour-bearing control rats. Blood glucose concentrations were similar in both groups, but insulin concentrations were decreased in tumour-bearing rats. Starvation decreased the rates of glucose uptake by normal tissues in both control and tumour-bearing rats, but the difference between the fed and starved states was greater in the control rats. Starvation did not decrease glucose uptake by the tumour. On an organ basis, the tumour (12-14% of body wt.) took up 4 times more glucose than did muscle (40% of body wt.).

Trans fatty acids. 1. Growth, fertility, organ weights and nerve histology and conduction velocity in sows and offspring

Effects of dietary trans fatty acids on the pre- and postnatal growth and development in pigs were studied with special emphasis on nervous tissue. In experiment 1, female pigs were fed partially hydrogenated fish oil (PHFO) (28% trans) or soybean oil (PHSBO) (36% trans), in comparison with lard (0% trans) from weaning (3 wk) through the first reproduction cycle (up to 2 yr). In experiment 2, female pigs were fed two fish oils (33 and 19% trans) in comparison with coconut oil (0% trans) in diets with low and high levels of linoleic acid (18:2n-6 cis, cis) from gestation until their offspring were three wk old. Compared with the trans-free fats, the trans-containing fats had no effect on growth and development, feed consumption and utilization or on the weight of the brain, heart, kidneys, liver, lungs or spleen in the adult sows and their offspring. No effects from the experimental fats were found on histology and conduction velocity of the peroneal nerve. An increased number of the sows fed PHFO had fertility problems compared with those fed lard and PHSBO in Expt. 1, but no similar effects were seen in Expt. 2. It is concluded that consumption of trans fatty acids with 18-22 carbon atoms from PHFO and with 18 carbon atoms from PHSBO at levels that were 5 to 12 times higher than those normally consumed by humans had no detrimental effects on female pigs or their offspring during pregnancy and lactation.

An evaluation of the relation between food consumption rate and equilibrium body-weight in male rats

1. Two experimental approaches were employed to assess the relation between food consumption rate and maintenance requirements in male weanling rats. The first approach involved restricting food intake in rats previously given free access to food from weaning to 59 d of age. The second approach involved restriction of food intake to various levels after weaning. Maintenance requirements (g food/d per g body-weight (W] were estimated by dividing the rate of food consumption by the resulting equilibrium W (EBW) for each animal. In addition, food consumption was partitioned into growth-independent (maintenance) and growth-dependent (gain) components by alternately setting W and specific growth rate (W') to zero in an equation relating food intake rate to W and W'. Coupling coefficients representing maintenance consumption (g food/d per g W) and gain consumption (g food/g gain) were estimated for each animal by least squares. 2. Both techniques for estimating maintenance consumption provided similar estimates within and across experiments, and regardless of when food restriction was imposed or its severity, consumption for maintenance was about 5% W/d. 3. The EBW to which animals in each treatment group aspired was directly proportional to that group's food intake rate. 4. Coventional measures of growth efficiency were also related to food intake; efficiency decreased with decreasing food intake. Partitioning food consumption into maintenance and gain components revealed that as the rate of food intake decreased, the proportion of total intake consumed for maintenance increased. The results suggest that growth efficiency declines during food intake restriction because proportionately more of total intake is used for maintenance, leaving less available for gain.

Iron absorption in man calculated from erythrocyte incorporation of the stable isotope iron-54 determined by fast atom bombardment mass spectrometry

The methodology of precise isotope abundance determinations of erythrocyte iron by fast atom bombardment mass spectrometry and signal averaging is established. For the determination of the 54Fe/56Fe ratio a relative precision of 0.5% and an absolute precision of 0.03% is achieved. After oral loading with 54Fe-enriched samples in the range between 5 and 25 mg per subject, the 14-day erythrocyte incorporation of 54Fe has been determined in five individuals, namely, two adults, two children, and one infant. In the two adults, the oral dose of 54Fe was simultaneously labeled with a trace amount of carrier-free 59Fe. In these double-isotope loading tests, a good agreement was observed between the absorption data determined on the basis of whole body retention of 59Fe and on the basis of the 54Fe erythrocyte incorporation. The stable isotope methodology applied allows measurement of the iron absorption using highly enriched 54Fe at a dose of 25 mg for an adult or at a dose of 5 mg for infants of about 1 year of age.

Metabolic utilization of linoleic acid from fat emulsion in infants during total parenteral nutrition

The metabolic utilization of linoleic acid (C18:2w6) from intravenous (iv) soybean oil emulsion via its conversion to higher homologues and prostaglandin biosynthesis was studied in 21 infants. The infants were of normal birth weight, in good clinical and metabolic condition, and aged from 1-4 months. They all received total parenteral nutrition after birth for more than 1 month; the only lipid was provided by iv Intralipid 20%, at levels approximating 350 mg/kg/24 h of linoleic acid (2.5% of the infants' total daily energy intake). Study of the fatty acids of plasma and erythrocyte phospholipids in these infants, compared to healthy controls of the same age (N = 26), showed that 350 mg/kg/24 hr of C18:2w6 supply resulted in normalization of erythrocyte phospholipid fatty acid distribution. This was particularly true of the higher homologues of C18:2w6 (C18:3w6, C20:3w6, and C20:4w6). This suggested that delta 6 and delta 5 desaturation activities are normal in these conditions with this C18:2w6 supply. These results were confirmed by the study of 24-hr urinary excretion of prostaglandins PGE1 and PGE2. With 350 mg/kg/24 hr of C18:2w6 supply their urinary levels were not significantly different from those observed in normal children of the same age receiving an equivalent oral C18:2w6 intake.

Release of fatty acid-binding protein from isolated rat heart subjected to ischemia and reperfusion or to the calcium paradox

The release of cardiac fatty acid-binding protein (cFABP) and of fatty acids from isolated rat hearts was measured during both reperfusion following 60 min of ischemia and the calcium paradox (readmission of Ca2+ after a period of Ca2+-free perfusion). Total cFABP release was much more pronounced after Ca2+ readmission (over 50% of tissue content) than during post-ischemic reperfusion (on average, 3% of tissue content), but in both cases, it closely paralleled the release of lactate dehydrogenase. Only minor amounts of long-chain fatty acids, if any, were released from the heart. These observations are challenging the idea that cFABP plays a fatty acid-buffering role under the pathophysiological conditions studied.

Normal and warfarin-resistant rat hepatocyte metabolism of vitamin K 2,3-epoxide: evidence for multiple pathways of hydroxyvitamin K formation

Vitamin K and 3- (and/or 2)-hydroxy-2,3-dihydro-2-methyl-3-phytyl-1,4-naphthoquinone (hydroxyvitamin K) have been identified as metabolites of vitamin K 2,3-epoxide incubated with hepatocytes isolated from normal and warfarin-resistant rats. Dithiothreitol added to the extracellular medium differentially enhanced the formation of both metabolites: hydroxyvitamin K formation, almost undetectable in the absence of dithiothreitol, was particularly affected. Addition of the vitamin K 2,3-epoxide reductase inhibitors warfarin (5 to 100 microM) and brodifacoum (1 to 5 microM) to normal rat hepatocyte cultures produced a slight increase in hydroxyvitamin K formation and a marked inhibition of vitamin K formation. Brodifacoum was a weak inhibitor of hydroxyvitamin K formation at higher concentrations. Hepatocytes from warfarin-resistant rats catalyzed hydroxyvitamin K formation 1.5 to 2 times faster and vitamin K formation 1.5 to 2 times slower than did normal rat hepatocytes. The addition of warfarin to these cultures had no effect on epoxide metabolism to hydroxyvitamin K and only partially diminished metabolism to vitamin K. In contrast, brodifacoum (1 microM) addition produced 50% inhibition of hydroxyvitamin K formation and almost complete inhibition of vitamin K formation. These data suggest that in resistant, but not in normal rat hepatocytes, the vitamin K 2,3-epoxide reductase makes a significant contribution to hydroxyvitamin K formation. A second sulfhydryl-dependent pathway, present in both strains, is also involved in the formation of this metabolite. They also suggest that in resistant rats, warfarin inhibition of the vitamin K 2,3-epoxide reductase, and presumably the sulfhydryl-dependent vitamin K reductase, is incomplete and independent of concentration.

Hepatic autophagy and intracellular ATP. A morphometric study

In order to estimate the sensitivity of macroautophagy in liver toward changes in ATP we have analyzed the volume density of the autophagic/lysosomal system in isolated rat hepatocytes, incubated under conditions where intracellular ATP was partially depleted. (a) It appeared that reduction of the intracellular ATP concentration by 30-50% decreased the volume density of autophagic vacuoles by 70%. (b) Partial ATP depletion did not involve significant changes in the volume density of dense bodies. Together with studies showing that the rate of overall proteolysis via macroautophagy decreases with decreasing ATP concentration (P.J.A.M. Plomp, E.J. Wolvetang, A.K. Groen, A.J. Meijer, P.B. Gordon, and P.O. Seglen (1987) Eur. J. Biochem. 164, 197-203) our data indicate that changes in intracellular ATP primarily affect early steps in the autophagic/proteolytic pathway.