Effect of fasting on skeletal muscle triglyceride content

Summary The effect of prolonged food deprivation on the triglyceride level in different types of skeletal muscle was studied in the rat. It has been found that fasting gradually reduces the triglyceride content in each muscle type. It is concluded that i.m. triglycerides play an important role as energy fuel during fasting.     

Heterogeneous bioenergetic behaviour of subsarcolemmal and intermyofibrillar mitochondria in fed and fasted rats

This study was designed to examine energetic behaviour of skeletal muscle subsarcolemmal and intermyofibrillar mitochondrial populations. The data show that subsarcolemmal mitochondria exhibited a lower degree of coupling and efficiency than intermyofibrillar ones, and can therefore be considered less efficient at producing ATP. In addition, subsarcolemmal mitochondria showed an increased sensitivity to palmitate-induced uncoupling, in line with high adenine nucleotide translocator content and decreased oxidative damage. We then determined the effect of 24 h fasting on energetic characteristics of skeletal muscle mitochondrial populations. We found that fasting enhanced proton leak and decreased the degree of coupling and efficiency, both in the absence and in the presence of palmitate only in subsarcolemmal mitochondria. Moreover, this mitochondrial population showed lower oxidative damage, probably due to a counter-regulatory mechanism mediated by uncoupling protein 3. Subsarcolemmal and intermyofibrillar mitochondria appear to exhibit different energetic characteristics and can be differently affected by physiological stimuli. Received 28 September 2005; received after revision 9 November 2005; accepted 28 November 2005     

Relationship of phosphatidylcholine to hydrophobic surfactant on rat intestinal chylomicron secretion

Hydrophobic surfactants such as Poloxalene inhibit triglyceride secretion into lymph by enterocytes. The inhibitory effect of these agents on triglyceride secretion is reversed when lipid presented for absorption is exclusively in the form of phosphatidylcholine (PC) and not triglyceride. The present investigation performed in conscious mesenteric lymph fistula rats was designed to determine whether various mixtures of triglyceride and PC given intraduodenally with Poloxalene would also reverse the inhibitory effect of Poloxalene on triglyceride secretion into lymph. A 50–50 mixture of triolein (TO) and PC resulted in normal triglyceride secretion into lymph. However, when the mixture of lipids was 75-25, TO to PC, results for triglyceride recovery in lymph were considerably reduced. The transport rate for triglyceride into lymph was not as depressed, however, as observed for Poloxalene treated rats given lipid for absorption basically in the triglyceride form. Substitution of phosphatidylethanolamine for PC had no beneficial effect on triglyceride secretion in Poloxalene treated rats. It is concluded that PC can reverse the inhibitory effect of Poloxalene on triglyceride secretion into lymph even when considerable amounts of triglyceride along with PC are presented for absorption.     

VLDL substrate properties and efficiency of their metabolic transformation by LPL

Summary A study was made of the regulation of the triglyceride hydrolysis catalysed by LPL from bovine milk, by the apoproteins from human plasma VLDL. Both isolated apolipoproteins, and those found on the surface of plasma VLDL particles, were investigated. A concentration-dependent activating action of apo C-II on the hydrolysis of emulsified triolein, and uncompetitive inhibition of VLDL triglyceride hydrolysis by apo C-III were found. It is suggested that VLDL lipolysis might be controlled in vivo trough the variation of the relative surface content of these enzymatic activity modulators.     

VLDL substrate properties and efficiency of their metabolic transformation by LPL

A study was made of the regulation of the triglyceride hydrolysis catalysed by LPL from bovine milk, by the apoproteins from human plasma VLDL. Both isolated apolipoproteins, and those found on the surface of plasma VLDL particles, were investigated. A concentration-dependent activating action of apo C-II on the hydrolysis of emulsified triolein, and uncompetitive inhibition of VLDL triglyceride hydrolysis by apo C-III were found. It is suggested that VLDL lipolysis might be controlled in vivo through the variation of the relative surface content of these enzymatic activity modulators.     

The biochemistry of natural fasting at its limits.

There are several groups of animals that are adapted for extremely long duration fasting as part of their reproductive cycle. Penguins, bears and seals routinely fast without food or water for months at time. However, they do not 'starve', as the biochemical implications of starving are very different from those of successful fasting. There are distinct biochemical adaptations in lipid, carbohydrate and especially protein metabolism that allow these animals to survive. It appears, at least for penguins and seals, that the duration of the fast may be limited by changes that occur in biochemical regulation near the ned of the fast. In all of these species, the biochemistry of fasting and the ecological and behavioral demands of their breeding cycles are closely interrelated.     

Effect of beta-adrenergic blockade on intramuscular triglyceride mobilization during exercise

Summary It was shown in the rat that mobilization of intramuscular triglyceride during exercise is controlled by the adrenergic system.Acknowledgments. The work was supported by the Polish Academy of Sciences, grant No. 10.4.2.01.3.2.     

The biochemistry of natural fasting at its limits

There are several groups of animals that are adapted for extremely long duration fasting as part of their reproductive cycle. Penguins, bears and seals routinely fast without food or water for months at time. However, they do not starve, as the biochemical implications of starving are very different from those of successful fasting. There are distinct biochemical adaptations in lipid, carbohydrate and especially protein metabolism that allow these animals to survive. It appears, at least for penguins and seals, that the duration of the fast may be limited by changes that occur in biochemical regulation near the end of the fast. In all of these species, the biochemistry of fasting and the ecological and behavioral demands of their breeding cycles are closely interrelated.     

Satellite cells in denervated muscles.

It is known that, in a denervated striated muscle, the satellite cells multiply by mitotic division. A liaison between these satellite cells and the Schwann cell in front of the post-synaptic membrane in denervated frog muscle has been observed. It is probable that such cell connections help in the subsistence of the Schwann cell in a denervated muscle.     

Satellite cells in denervated muscles

Summary It is known that, in a denervated striated muscle, the satellite cells multiply by mitotic division. A liaison between these satellite cells and the Schwann cell in front of the post-synaptic membrane in denervated frog muscle has been observed. It is probable that such cell connections help in the subsistence of the Schwann cell in a denervated muscle.     

Influence of corpora allata and brain extract on the lipid release from the fat body of termite queen Odontotermes assmuthi

Summary Short term in vitro experiments on the influence of the extracts of corpora allata and brain from the termite queenOdontotermes assmuthi on the lipid release from the fat body into the haemolymph indicated that the extract of corpora allata does not influence the lipid mobilization, whereas the brain extract increases the free fatty acid level in the haemolymph. It is believed that the brain extract stimulates triglyceride hydrolysis in the fat body.     

Production of butyrylcholinesterase by Caco-2 cells: lack of relationship with triglyceride production

Elevated levels of butyrylcholinesterase activity occur under a number of hypertriglyceridemic conditions, including diabetes and obesity. This study examines whether butyrylcholinesterase activity has a direct effect on triglyceride production, using Caco-2 cells, a human intestinal adenocarcinoma cell line. Caco-2 cells were incubated with 500 μM oleate to stimulate triglyceride production, and butyrylcholinesterase activity was measured in the cellular homogenate. Butyrylcholinesterase activity was approximately 3 × 10^-3 mmol/min per milligram protein. Although triglyceride production increased by almost five-fold after 18 h of stimulation with oleate, butyrylcholinesterase activity was not increased. Furthermore, inhibition of butyrylcholinesterase activity using 1 mM tetraisopropylpyrophosphoramide did not significantly affect triglyceride production or secretion. Human insulin (100 μU/ml) increased the production of butyrylcholinesterase without increasing triglyceride production. This demonstrates that stimulation of fatty acid production and butyrylcholinesterase activity occur by independent mechanisms and suggests that their correlation in hyperlipidemic conditions is not due to a direct relationship in production in situ. Received 23 April 2001; received after revision 25 May 2001; accepted 20 June 2001     

Human muscle structure after exposure to extreme altitude

Muscle structural changes during typical mountaineering expeditions to the Himalayas were assessed on muscle biopsies. A significant reduction in muscle fiber size (-20%) and a loss of muscle oxidative capacity (-25%) were observed. The capillary network was not affected by catabolism. It is concluded that the oxygen supply to muscle mitochondria after high altitude exposure is thus improved.     

Structure and function of a calmodulin-dependent smooth muscle myosin light chain kinase

In smooth muscle the Mr 20,000 light chain of myosin is phosphorylated by a calmodulin-dependent protein kinase. It consists of 2 subunits: calmodulin, an acidic protein of Mr 17,000 that binds 4 moles of Ca2+; and a larger protein of Mr circa 130,000. Activation of the kinase is dependent upon their association in the presence of Ca2+. Cyclic AMP-dependent protein kinase phosphorylation of the myosin light chain kinase occurs at 2 sites. It decreases the affinity of the kinase for calmodulin and a reduction in the rate of light chain phosphorylation occurs. The kinase has an overall asymmetric shape composed of a globular head and tail region for the skeletal muscle enzyme. Trypsin digestion of this kinase releases a fragment of Mr 36,000 from the globular region that contains the catalytic and calmodulin binding sites. Chymotrypsin digestion of the kinase from smooth muscle generates a fragment of Mr 80,000 that does not contain the calmodulin binding or cyclic AMP-dependent protein kinase phosphorylation sites. It is a Ca2+-independent form of the kinase that phosphorylates the light chain of myosin. These structural features indicate a regulatory role for the kinase in smooth muscle phosphorylation and contraction.     

Crown ethers which influence cardiac and respiratory muscle contractility

Guinea-pig tracheal smooth muscle and heart muscle demonstrated a variety of in vitro positive and negative inotropic responses to concentrations of crown ethers in the nmole/1 to mumole/1 range. It is suggested that these ionophoretic compounds have potential as therapeutic agents.     

Role of intracellular calcium in promoting muscle damage: a strategy for controlling the dystrophic condition.

It is suggested that various muscle diseases and examples of experimentally-induced muscle damage arise because of a high calcium level in the myoplasm. When [Ca2+]i is raised experimentally in amphibian or mammaliam muscle by treatment with A23187 or caffeine, myofilament degradation follows quickly. Such a rapid action suggests the involvement of a sequence of proteolytic activity that is stimulated by a rise in [Ca2+]i. Ca2+ might either trigger protease activity directly or indirectly, or promote the release of lysosomal enzymes. A high [Ca2+]i in dystrophic muscle is believed to be the resultant of a sequence of events that is summarized in the figure. Suggestions are presented for different ways in which the steady-state position of [Ca2+]i might ultimately be controlled for the clinical amelioration of some dystrophic conditions.     

Structure and function of a calmodulin-dependent smooth muscle myosin light chain kinase

Summary In smooth muscle the M_r 20,000 light chain of myosin is phosphorylated by a calmodulin-dependent protein kinase. It consists of 2 subunits: calmodulin, an acidic protein of M_r 17,000 that binds 4 moles of Ca²⁺; and a larger protein of M_r circa 130,000. Activation of the kinase is dependent upon their association in the presence of Ca²⁺. Cyclic AMP-dependent protein kinase phosphorylation of the myosin light chain kinase occurs at 2 sites. It decreases the affinity of the kinase for calmodulin and a reduction in the rate of light chain phosphorylation occurs. The kinase has an overall asymmetric shape composed of a globular head and tail region for the skeletal muscle enzyme. Trypsin digestion of this kinase releases a fragment of M_r 36,000 from the globular region that contains the catalytic and calmodulin binding sites. Chymotrypsin digestion of the kinase from smooth muscle generates a fragment of M_r 80,000 that does not contain the calmodulin binding or cyclic AMP-dependent protein kinase phosphorylation sites. It is a Ca²⁺-independent form of the kinase that phosphorylates the light chain of myosin. These structural features indicate a regulatory role for the kinase in smooth muscle phosphorylation and contraction.     

Interaction of lipid transfer protein with plasma lipoproteins and cell membranes

Summary The hydrophobic lipid components of lipoproteins, cholesteryl ester and triglyceride, are transferred between all lipoproteins by a specific plasma glycoprotein, termed lipid transfer protein (LTP). LTP facilitates lipid transfer by an exchange process in which cholesteryl ester and triglyceride compete for transfer. Thus, LTP promotes remodeling of the lipoprotein structure, and plays an important role in the intravascular metabolism of these particles and in the lipoprotein-dependent pathways of cholesterol clearance from cells. The properties of LTP, its mechanisms of action, its roles in lipoprotein metabolism, and its modes of regulation are reviewed along with recent data that suggest a possible role for this protein in directly modifying cellular lipid composition.     

Certain biochemical effects of garlic oil on rats maintained on high fat-high cholesterol diet

The feeding of a high fat-high cholesterol (HF-HC) diet to normal rats for 1 month increased the lipid components cholesterol and triglyceride in serum, liver and kidneys and decreased the serum albumin very significantly. Administration of garlic oil (100 mg/kg b. wt/day) for 1 month together with the HF-HC diet to another group almost nullified the lipid-increasing and albumin-decreasing effects of that diet. The reduction in total lipids, cholesterol and triglycerides and the restoration to normal level of serum albumin were highly significant in the garlic oil group. Adipose tissue triglyceride lipase activity was significantly increased in both the above groups with a much greater rise in the oil group.     

Certain biochemical effects of garlic oil on rats maintained on high fat-high cholesterol diet

Summary The feeding of a high fat-high cholesterol (HF-HC) diet to normal rats for 1 month increased the lipid components cholesterol and triglyceride in serum, liver and kidneys and decreased the serum albumin very significantly. Administration of garlic oil (100 mg/kg b. wt/day) for 1 month together with the HF-HC diet to another group almost nullified the lipid-increasing and albumin-decreasing effects of that diet. The reduction in total lipids, cholesterol and triglycerides and the restoration to normal level of serum albumin were highly significant in the garlic oil group. Adipose tissue triglyceride lipase activity was significantly increased in both the above groups with a much greater rise in the oil group.