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J Tepperman

Publications and source records attributed to J Tepperman.

At least 37 records · Page 2Linked to original sources
PubMed1980

Dietary effects on the formation of dolichyl monophosphate mannose by microsomal preparations of rat adiopose tissue.

Microsomal preparations from rat adipose tissue catalyse the transfer of [(14)C]mannose from GDP-[(14)C]mannose to an endogenous acceptor forming a [(14)C]mannosyl lipid. The mannosyl lipid co-chromatographs with hen oviduct dolichyl monophosphate beta-mannose on three solvent systems. It is stable to mild alkaline hydrolysis, but strong alkaline treatment yields a compound that co-migrates with mannose 1-phosphate. The mannosyl lipid is labile to mild acid hydrolysis, yielding [(14)C]mannose. Formation of the compound is reversible by GDP, but not GMP, and is stimulated by exogenous dolichyl phosphate. The kinetics of transfer of [(14)C]mannose from GDP-[(14)C]mannose to form dolichyl monophosphate mannose were studied by using preparations derived from rats fed on one of four diets: G (high glucose), L (high lard), F (fructose) or GC (high glucose, 0.9% cholesterol). The K(m) and V(max.) values for transfer from GDP-mannose were virtually indistinguishable in the four preparations.In the absence of exogenous dolichyl phosphate, the largest amount of transfer of [(14)C]mannose into the mannosyl lipid was observed with preparations from fructose-fed animals. Preparations from glucose-fed animals showed about 60% as much transfer, whereas membranes from rats fed the other diets showed intermediate values between the fructose- and glucose-fed animals. The inclusion of cholesterol in the glucose diet elicited an increase in transfer of mannose. Under conditions of saturating exogenous dolichyl phosphate, preparations from lard-fed animals have 1.5 times as much enzyme activity as do preparations from animals fed the other three diets.

Adipose Tissue↗
PubMed1980

Control of endogenous triglyceride breakdown in the mouse diaphragm.

The control of endogenous triglyceride breakdown was studied in vitro, in the incubated intact mouse diaphragm. Isoproterenol (2 microgram/ml) produced parallel increases in glycerol and free fatty acid release, and in tissue cyclic AMP levels, suggesting that cyclic AMP mediates the action of the catecholamine on triglyceride mobilization. In addition to cyclic AMP, calcium seems to be involved in the action of isoproterenol because preincubation of hemidiaphragms in the presence of the calcium ionophore A23187 decreased the lipolytic effect of the drug. Insulin (12.5 mU/ml) antagonized the action of isoproterenol on triglyceride breakdown (it decreased glycerol and free fatty acid release) without altering its stimulatory effect on cyclic AMP levels. On the other hand, no detectable effect on lipolysis was observed with carbachol in control and denervated hemidiaphragms, although the latter possess acetylcholine receptors over the entire surface area of the muscle. It was concluded that catecholamines control triglyceride breakdown in muscle while the cholinergic system does not seem to be involved. Cyclic AMP, calcium, and insulin all affect lipolysis in muscle and the interrelationships remain to be elucidated.

Animals↗
PubMed1980

Lipolysis and cyclic AMP response to isoproterenol in diaphragms from control and dystrophic mice.

A comparison was made of the sensitivity of lipolysis (glycerol and free fatty acid release) and of cyclic AMP production to the action of isoproterenol in diaphragms from control and dystrophic Bar Harbor mice at 7 weeks of age. An increased lipolytic response was observed in diaphragms from dystrophic mice that was more apparent in the males, and was demonstrable when cyclic AMP was used instead of isoproterenol. The increased glycerol and free fatty acid release in response to isoproterenol and cyclic AMP cannot be explained by a higher triglyceride content of diaphragms from dystrophic mice, because it was found to be similar to that of controls when it was estimated by biochemical and light microscopic techniques. The increased lipolytic response was not paralleled by changes in cyclic AMP levels, which were found to be similar in diaphragms from control and dystrophic mice, whether in the basal or the stimulated state. It was concluded that the lipolytic apparatus in muscles from dystrophic mice shows an increased sensitivity to isoproterenol that seems to be related to events more intracellular than the cAMP production step.

Animals↗
PubMed1979

Lipid composition of liver plasma membranes isolated from rats fed a high glucose or a high fat diet.

Several plasma membrane associated functions have been shown to differ in rats fed a high lard, carbohydrate free diet (L rats) from those observed in preparations from rats fed a high glucose, fat free diet (G rats). To explore the possibility that differences in the lipid components of the plasma membranes might contribute to these functional changes, groups of rats were fed each diet for 5 days and the lipids of their plasma membranes were separated and analyzed. The major differences found were a greater cholesterol content in the plasma membranes from L rats compared to those of G rats (12.2 +/- 2.20 versus 7.8 +/- 1.40 mg/100 mg membrane protein) and more than twice as much phosphatidyl serine and phosphadidyl inositol in the plasma membranes of the former group. Of several variations in fatty acid distribution found in the phospholipid and neutral lipid fractions, the most notable quantitatively were an increase in phospholipid oleic acid (18:1) and a decrease in phospholipid stearic acid (18:0) in L rat plasma membranes. Whether these changes are related to altered membrane function is not known.

Animals↗
PubMed1979

Effects of high-glucose and high-fat diets on concanavalin A binding to rat liver plasma membranes and on the amount and pattern of their glycoprotein carbohydrates.

Purified liver plasma membranes were prepared from rats fed a high-fat, carbohydrate-free diet or a high-glucose, fat-free diet. Membranes from rats fed the high-fat diet bound significantly less 125I-labeled concanavalin A (Con A) than did those from rats fed the fat-free diets. The magnitude of the binding difference increased with increasing concentrations of Con A. Neither association nor dissociation rates of the lectin-receptor complex was affected by diet. The extent of degradation of Con A by liver plasma membrane preparations from rats fed either diet was the same. Chemical analysis of delipidated liver plasma membrane showed that membranes prepared from high-fat diet-adapted rats had significantly lower values for all carbohydrate components measured with the exception of galactose. The results indicate that, in liver cells, a change in plasma membrane glycoproteins is part of the complex adaptation to altered diet composition.

Animals↗
PubMed1979

Studies on the utilization and mobilization of lipid in skeletal muscles from streptozotocin-diabetic and control rats.

Several aspects of lipid metabolism in the soleus and diaphragm muscles of streptozotocin-diabetic and control rats were investigated. The triglyceride content of both muscles was elevated in the diabetic state and the presence of increased intracellular lipid was confirmed by electron microscopy. In vitro glucose and palmitate oxidation studies showed that both types of muscle from the diabetic animals metabolized more fat than did the soleus and diaphragm from control rats. While isoproterenol alone produced a significant lipolytic response in both the soleus and diaphragm from control and diabetic animals, there was no difference in the percent increase in fatty acids released from muscles of diabetic rats compared to controls. However, the absolute difference was greater when the diaphragms were compared. Muscles from experimental and control animals showed a marked reduction in the amount of free fatty acids released in response to insulin. In addition, in the presence of the hormone, both the absolute and percent isoproterenol-stimulated increases in fatty acids were significantly greater for both diaphragm and soleus muscles from diabetic rats. The effects of insulin, isoproterenol, and the combination of these two hormones on the amount of glycerol released into the incubation medium were similar to those found on free fatty acid release. The results of these experiments show that there is an apparent increase in fat utilization in skeletal muscle of diabetic rats. Furthermore, measurements of triglyceride concentration and the enhanced response to isoproterenol stimulation in the muscles from these animals suggests that they may have an increased capacity for mobilization of intracellular lipids. Finally, in the diabetic state, both the soleus and diaphragm appear to demonstrate an increased response to the antilipolytic effect of insulin as measured by the decreased amount of fatty acid released into the incubation medium, the percent change also being significant for the soleus muscle.-Stearns, S. B., H. M. Tepperman, and J. Tepperman. Studies on the utilization and mobilization of lipid in skeletal muscles from streptozotocin-diabetic and control rats.

Animals↗
PubMed1978

The concentration of cyclic AMP and the activity of cyclic AMP dependent protein kinase and an inhibitor in the adipose tissue of rats fed lard or glucose diets.

Measurements of tissue cyclic AMP (cAMP) concentration, the activity of cAMP-dependent protein kinase and the level of the enzyme's thermostable, macromolecular inhibitor were made on preparations of rat epididymal fat pad from animals fed high fat or high carbohydrate diets. The cAMP concentration from rats adapted to a high lard diet for 14-15 days was 153 +/- 17.8 pmoles/mg protein as opposed to 76 +/- 6.0 found with high glucose diet. No significant difference in total cAMP-dependent protein kinase activity was observed among rats fed high glucose, high lard or laboratory chow, although the enzyme's activity ratio (-cAMP)(+cAMP) was significantly elevated with lard feeding (0.49 +/- 0.02) as opposed to glucose feeding (0.43 +/- 0.01). Crude preparations from lard and glucose fed animals were equivalent in inhibitory activity when tested with enzyme from chow fed animals. Agarose column chromatography separated holoenzyme and C subunit forms of the protein kinase when 500 mM NaCl was present in the elution buffer. Absence of the salt allowed subunit reassociation to occur. Direct addition of NaCl greater than or equal to 75 mM significantly inhibited protein kinase activity. The results indicate that the adipose tissue of rats fed a high lard diet has a higher concentration of cAMP and an increased protein kinase activity ratio than tissue from rats fed a fat free, high glucose diet. Total cAMP-dependent protein kinase activity and the level of a thermostable macromolecular inhibitor remained unchanged.

Adipose Tissue↗
PubMed1978

Studies on serum lipids, insulin, and glucagon and on muscle triglyceride in rats adapted to high-fat and high-carbohydrate diets.

A comparisonwas made of lipid circulation, storage, and mobilization in rats adapted to lard or glucose diets. In the morning, lard-fed rats had higher blood triglyceride (TG) and free fatty acid (FFA) levels. In the evening TG was higher, but FFA was significantly lower in the lard vs. the glucose group. Fasting did not produce the characteristic increase in blood FFA in the lard-fed rats but was associated with a severe drop in their serum TG. Circulating glucose and insulin were not affected, while glucagon levels were increased by lard feeding. Nicotinic acid decreased fasting FFA levels to a greater extent in the glucose-fed rats. It was concluded that lard feeding depresses mobilization of fat from adipose tissue; on the other hand, it was found to increase storage and utilization of muscle TG. Fat feeding increased diaphragm TG concentrations threefold, as well as the number and size of intracellular fat droplets at the light and electron microscopic levels. Fasting decreased diaphragm TG in both groups, but the amount lost was greater in the fat-fed rats. Also, in vitro basal isoproterenol-stimulated (1 microgram/ml) FFA release by the incubated diaphragm was higher in the lard-fed group.

Animals↗
PubMed1977

The effect of diet fat on rat adipocyte glucose transport.

Rats were fed either a high fat diet (67% of calories as lard) or high glucose diet (67% of calories as glucose) for 7-8 days. Basal and insulin stimulated net uptake of D glucose (D-L) and 2 deoxy D glucose uptake by free fat cells of fat rats were depressed. Net transport of D glucose (D-L) by purified adipocyte plasma membranes of fat red rats was also diminished. Incubation of fat cells from glucose fed rats with insulin before homogenization for membrane preparation increased net D glucose transport by subsequently purified membranes in two experiments to a greater extent than in similar preparations from rat fed rats. These experiments suggest that fat feeding modifies the plasma membranes of fat cells so that both glucose transport and the stimulatory effect of insulin on the process are decreased.

Adipose Tissue↗
PubMed1977

Effect of adaptation to meal-feeding on insulin, glucagon and the cyclic nucleotide-protein kinase system in rats.

Diurnal changes in insulin, glucagon and the cyclic nucleotide-protein kinase system were examined in rats trained to eat a 2-hour daily meal and in control rats fed ad libitum. Sharp increases in both insulin and glucagon were observed in response to feeding in trained rats. However, throughout most of the rest of the day, the plasma concentrations of both hormones were lower in meal-fed than in control rats. In adipose tissue, diurnal changes in cyclic AMP concentration were inversely correlated with changes in plasma insulin concentration. In general, cyclic AMP concentrations were depressed and cyclic GMP elevated in adipose tissue of meal-fed rats compared with those fed ad libitum. Diurnal changes in cyclic GMP concentration tended to parallel those of cyclic AMP. Cyclic AMP-activated protein kinase was elevated in adipose tissue of meal-fed rats. However, with the exception of fasting rats, the percentage of the enzyme in the active form was decreased. In liver, there was no clear relation significant differenced were observed with the protein kinase. It can be concluded that the magnitude of the adaptive response of the cyclic nucleotide-protein kinase system to meal-feeding in rats is greater in adipose tissue than in liver.

Adaptation, Physiological↗
PubMed1977

A comparison of insulin binding by liver plasma membranes of rats fed a high glucose diet or a high fat diet.

The interaction of (125)I-labeled insulin with purified liver plasma membrane from rats fed a high fat (L) diet or a high glucose (G) diet was studied with respect to specific binding, insulin degradation, binding site degradation, and rate of hormone association and dissociation. Scatchard analysis suggested the presence of high and low affinity binding sites for membranes of both G and L diet-adapted rats. However, liver plasma membrane from rats fed the high glucose diet bound 50% more insulin than did membrane from rats fed the high fat diet. Diet did not change insulin binding site degradation. The results suggested that an apparently reduced number of insulin binding sites (G = 10.2 +/- 2.45 x 10(-12) mol/mg membrane protein, L = 4.5 +/- 1.73 x 10(-12) mol/mg membrane protein) associated with fat feeding as compared to glucose feeding was responsible for the reduced insulin binding by membrane from rats fed the high fat diet. The effects of concanavalin A (Con A) on insulin binding to liver plasma membranes were also investigated. Con A enhanced the specific binding of insulin to liver plasma membranes from rats fed either diet at concentrations lower than 50 micro g/ml, whereas at concentrations higher than 50 micro g/ml Con A inhibited insulin binding to these membranes. The stimulatory effect of Con A on insulin binding at low concentrations was greater and inhibition of binding at high concentration was less in the case of membrane prepared from L diet-adapted animals. These results suggested that diet can modify the plasma membrane glycoproteins.

Animals↗
PubMed1976

Effect of p-chlorophenoxyisobutyrate on the antilipolytic action of insulin and insulin binding in isolated adipocytes.

The present study was undertaken to investigate the potentiation by p-chlorophenoxyisobutyrate (CPIB) of the antilipolytic effect of insulin in isolated adipocytes from rats fed a (1) sucrose diet, (2) glycerol-lard diet, or (3) chow diet. CPIB supplementation in the diet consistently resulted in decreased serum triglyceride levels in rats from the three dietary groups. The catecholamine-stimulated glycerol release was significantly depressed to a greater extent by insulin when the fat cells were obtained from rats given CPIB compared to those without drug treatment. The enhanced insulin sensitivity was, however, not accompanied by any changes in insulin binding to adipocytes. These two observations were found in cell preparations from rats fed any one of the diets, although differences among dietary groups could be detected. In an in vitro experiment, epinephrine-stimulated glycerol release was progressively inhibited by increasing concentrations of CPIB in the incubation medium. However, the antilipolytic response to an optimal concentration of insulin (100 muU/ml) was augmented in the presence of CPIB. Thus, it seems that CPIB can potentiate the action of insulin in inhibiting mobilization of free fatty acid from the adipose tissue, and the coordinated effect of both antilipolytic agents is important in lowering serum triglyceride concentration. The mechanism by which CPIB facilitates the effect of insulin is discussed.

Adipose Tissue↗
PubMed1976

Insulin binding and insulin response of adipocytes from rats adapted to fat feeding.

The effect of fat feeding on adipocyte insulin binding was examined to expand a study of adaptive changes in plasma membrane functions. Cells from rats fed a high fat (L) diet for five to seven days bound less insulin and showed a decreased response to insulin (glucose oxidation) compared to those from rats fed a high glucose (G) diet. Both high and low affinity sites were influenced; the extent of the binding difference increased as increasing concentrations of insulin were present in the assay medium. Diet did not change hormone degradation on the capacity of phospholipase C to increase binding. Concanavalin A effects on fat cells were also decreased by L diet both in inhibition of insulin binding and its insulin-like effect on glucose oxidation. Spermine, which had no effect on insulin binding, also had a smaller insulin-like effect on glucose oxidation by L cells than by G cells. Serum insulin was significantly lower (30 +/- 3.7 muU/ml) in L than in G (43 +/- 3.1 muU/ml) groups. Dietary fat produces alterations in fat cells that decrease insulin binding as a part of a complex overall adaptation to the diet.

Adipose Tissue↗
PubMed1975

Nicotinamide adenine dinucleotide phosphate-malic enzyme of rat liver. Purification, properties, and immunochemical studies.

Rat liver malic enzyme (EC 1.1.1.40) was purified from livers of rats fasted and refed a high sucrose diet containing 1% desiccated thyroid powder. The purification was accomplished by a six-step procedure. The specific activity of the purified enzyme was increased 181-fold above that of the initial high speed supernatant of liver extracts. Slight additional purification of malic enzyme was achieved with preparative disc electrophoresis. The specific activities of the purified rat liver malic enzyme from the least two steps were between 28.0 and 30.5 units per mg of protein. Homogeneity of the purified enzyme was determined by disc and starch gel electrophoresis as well as sedimentation velocity and sedimentation equilibrium studies. The molecular weight and S20, w values of rat liver malic enzyme are 268,000 and 10.2, respectively. Amino acid analysis based on milligram of protein hydrolyzed yielded higher amounts of leucine and glutamic acid but lower quantities of alanine and voline per subunit than the corresponding Escherichia coli enzyme...

Amino Acids↗